DE102023005475B4 - Microelectromechanical mirror, method for operating a microelectromechanical mirror, projection device and use of a microelectromechanical mirror - Google Patents

Abstract

Microelectromechanical mirror (1) comprising:
- a mirror element (2), and
- a torsion suspension (3) that surrounds the mirror element (2) and is connected to the mirror element (2) via two first torsion spring elements (41), wherein
- the torsion suspension (3) has an elliptical ring shape or the shape of a depressed oval ring, and
- the torsion suspension (3) does not have any piezoelectric drive elements.

Description

A microelectromechanical mirror, a method for operating a microelectromechanical mirror, and a projection device are described.

The printed matter JP 6 506 212 B2 describes an optical deflector with a mirror unit movable about two axes of rotation.

The printed matter US 10 371 940 B2 describes a device for driving a mirror and an associated operating procedure.

The printed matter JP 2008 - 020 701 A describes a two-dimensional optical scanner.

The printed matter DE 10 2021 116 165 B3 describes a Lissajous microscanner.

Microelectromechanical mirrors are used, for example, in laser projectors to selectively deflect a laser beam in order to display static or moving images. Laser projectors are used, for instance, in the automotive sector to project information onto a road surface, in HUD (head-up display) systems for matrix illumination, or for LIDAR (light detection and ranging) applications. These applications require a high depth of field, which laser projectors can provide. Furthermore, laser projectors are used, for example, as hologram projectors, in VR (virtual reality) glasses, or AR (augmented reality) glasses. Here, the deflected laser beam is coupled, for example, into a waveguide lens. The direction, and not the position, of the laser beam determines the position of the image point for the viewer, so no additional optics are required.

Laser projectors are particularly advantageous for mobile applications, such as in the automotive sector and for VR or AR glasses, as they are insensitive to vibrations and inexpensive to manufacture. A laser projector, for example, features a microelectromechanical mirror that can rotate in two directions and deflects a time-modulated laser beam to create a far-field image. In particular, the projected image is always in focus for the viewer, and the viewer's eye does not need to accommodate. JP 2008-20701 A For example, it describes a two-dimensional optical scanner.

At least one objective of certain embodiments is to provide a microelectromechanical mirror having a particularly compact design. At least one further objective of certain embodiments is to provide a method for operating such a microelectromechanical mirror. At least one further objective of certain embodiments is to provide a projection device with a microelectromechanical mirror having a particularly compact design.

These problems are solved by a microelectromechanical mirror, a method for operating a microelectromechanical mirror, and a projection device according to the independent claims. Advantageous embodiments and further developments of the microelectromechanical mirror, the method for operating a microelectromechanical mirror, and the projection device are specified in the dependent claims and are further described in the following description and drawings.

According to at least one embodiment, the microelectromechanical mirror comprises a mirror element. The mirror element, in particular, has a principal extent plane. For example, the mirror element, viewed from above, has a circular, oval, square, rectangular, or polygonal shape. The mirror element comprises, for example, a substrate with a reflective layer deposited thereon. For example, the substrate comprises or consists of silicon. Alternatively or additionally, the substrate may comprise or consist of diamond, cubic boron nitride (BN), silicon nitride (SiN), or boron. For example, the reflective layer comprises or consists of a metal.

In particular, the reflective layer is configured for the reflection and/or deflection of electromagnetic radiation in a spectral range between infrared and ultraviolet light. The reflective layer extends in a plane corresponding to the principal plane of extension of the mirror element. Here and in the following, the principal plane of extension is defined with respect to a rest position of the mirror element.

According to at least one further embodiment, the microelectromechanical mirror has a torsion suspension that surrounds the mirror element and is connected to the mirror element via two first torsion spring elements. The mirror element is bound. For example, the mirror element is arranged at the center of the torsion suspension. In particular, the torsion suspension surrounds the mirror element in its principal plane of extension when the mirror element is at rest. The torsion suspension comprises, for example, a substrate formed in a ring shape in its principal plane of extension, at the center of which the mirror element is arranged. For example, the substrate contains or consists of silicon. During operation of the microelectromechanical mirror, in which the mirror element is moved, the principal plane of extension of the mirror element can be rotated relative to the torsion suspension.

Each of the first torsion spring elements comprises, in particular, a torsion beam or consists of a torsion beam. For example, the torsion spring elements comprise a substrate that, for instance, contains or consists of silicon. The torsion spring elements each have, for example, an elongated, beam-like shape with an axis of rotation that corresponds, in particular, to a longitudinal direction of the respective torsion spring element. During operation, a torsional moment acts on the torsion spring elements with respect to the axis of rotation, causing the torsion spring elements to twist about their respective axis of rotation. In this process, a restoring torsional moment builds up, in particular, in the torsion spring elements.

The axes of rotation of the first two torsion spring elements are preferably aligned along a common first axis of rotation. In other words, the two first torsion spring elements have a common first axis of rotation about which they twist during operation. In particular, the mirror element is rotatable about the first axis of rotation relative to the torsion suspension, at least within a first angular range.

For example, the mirror element, the torsion suspension, and the first torsion spring elements share the same substrate. In other words, the aforementioned elements are formed in one piece and/or monolithically integrated.

According to at least one further embodiment, the microelectromechanical mirror has a piezoelectric drive ring that surrounds the torsion suspension and is connected to it via two secondary torsion spring elements. For example, the torsion suspension is arranged in the center of the drive ring. The drive ring is specifically designed to deflect the mirror element from its rest position during operation of the microelectromechanical mirror. In doing so, the torsion suspension and/or the mirror element are preferably rotated relative to the drive ring. For example, mechanical stresses are generated in the drive ring, which transmit a bending moment and/or a torque to the torsion suspension via the secondary torsion spring elements.

The drive ring comprises, for example, a substrate containing or consisting of silicon, on which at least partially a piezoelectric layer is applied. The piezoelectric layer is, in particular, arranged parallel to the main plane of extension of the mirror element.

The piezoelectric layer is positioned, for example, between a first electrode and a second electrode. The piezoelectric layer can consist of one or more piezoelectric materials. For example, the piezoelectric layer may contain or be composed of a piezoelectric material such as lead zirconate titanate (PZT), aluminum nitride (AlN), or bismuth ferrate barium titanate (BFO-BT). By applying an electrical voltage to the electrodes, the piezoelectric layer generates, in particular, the mechanical stresses in the drive ring.

Each of the second torsion spring elements comprises, in particular, a torsion beam or consists of a torsion beam. For example, the torsion spring elements comprise a substrate that, for instance, contains or consists of silicon. The torsion spring elements each have, for example, an elongated, beam-like shape with an axis of rotation that corresponds, in particular, to a longitudinal direction of the respective torsion spring element. During operation, a torsional moment acts on the torsion spring elements with respect to the axis of rotation, causing the torsion spring elements to twist about their respective axis of rotation. In this process, a restoring torsional moment builds up, in particular, in the torsion spring elements.

The axes of rotation of the two second torsion spring elements are preferably aligned along a common second axis of rotation. In other words, the two second torsion spring elements have a common second axis of rotation about which they twist during operation. In particular, the torsion suspension, and thus the mirror element, is rotatable around the second axis of rotation relative to the drive ring, at least within a second angular range. The second axis of rotation is, for example, transverse or orthogonal to the first axis of rotation.

According to at least one further embodiment of the microelectromechanical mirror The torsion suspension has an elongated shape with a long axis and a short axis perpendicular to it. The long axis and the short axis are, for example, axes of symmetry of the torsion suspension. In particular, the torsion suspension has a larger spatial extent in the direction of the long axis than in the direction of the short axis. In other words, the diameter of the torsion suspension in the direction of the long axis is larger than the diameter of the torsion suspension in the direction of the short axis. For example, the diameter of the torsion suspension in the direction of the long axis is at least 5% larger, preferably at least 20% larger, and most preferably at least 40% larger than the diameter in the direction of the short axis. The long axis and the short axis lie, for example, in the principal plane of extension of the mirror element.

The first axis of rotation coincides with the long axis, while the second axis of rotation coincides with the short axis. Therefore, in operation of the microelectromechanical mirror, the mirror element is at least partially rotatable relative to the drive ring, particularly with respect to the short and long axes.

Due to the elongated shape of the torsion suspension, at least one vibration mode of the mirror element and/or the torsion suspension exhibits, in particular, lower anharmonicity than a corresponding vibration mode of a torsion suspension that does not have an elongated shape. Here and in the following, anharmonicity describes, in particular, the dependence of a vibration mode's resonant frequency on its amplitude. In other words, the greater the shift in the resonant frequency when the vibration mode's amplitude is increased, the greater the anharmonicity.

• - das Spiegelelement,
• - die Torsionsaufhängung, die das Spiegelelement umschließt und über die zwei ersten Torsionsfederelemente mit dem Spiegelelement verbunden ist, wobei
• - die Torsionsaufhängung eine elliptische Ringform oder die Form eines eingedrückten Ovalrings aufweist, und
• - die Torsionsaufhängung keine piezoelektrischen Antriebselemente aufweist.

The microelectromechanical mirror includes:

• - the mirror element,
• - the torsion suspension that surrounds the mirror element and is connected to the mirror element via the two first torsion spring elements, wherein
• - the torsion suspension has an elliptical ring shape or the shape of a pressed-in oval ring, and
• - the torsion suspension does not contain any piezoelectric drive elements.

The microelectromechanical mirror described here is based on the fundamental idea of exciting two different vibration modes, in which the mirror element rotates about one of its two axes, using only a single drive ring. This makes the microelectromechanical mirror particularly compact. Furthermore, the elongated shape of the torsional suspension advantageously results in a particularly low anharmonicity in the vibration mode in which the mirror element rotates about its longer axis.

According to at least one further embodiment of the microelectromechanical mirror, the first torsion spring elements are arranged along the long axis. In particular, the first axis of rotation or a twisting axis of the first torsion spring elements is aligned along the long axis of the torsion suspension.

According to at least one further embodiment of the microelectromechanical mirror, the second torsion spring elements are arranged along the short axis. In particular, the second axis of rotation or a twisting axis of the second torsion spring elements is aligned along the short axis of the torsion suspension.

According to at least one further embodiment of the microelectromechanical mirror, the first two torsion spring elements are arranged on opposite sides of the mirror element. This improves, for example, the mechanical stability of the mirror element's suspension.

According to at least one further embodiment of the microelectromechanical mirror, the two second torsion spring elements are arranged on opposite sides of the torsion suspension. This improves, for example, the mechanical stability of the torsion suspension.

According to at least one further embodiment of the microelectromechanical mirror, the torsion suspension has an elliptical ring shape or the shape of an indented oval ring. For example, an outer circumference of the torsion suspension has the shape of an ellipse or an indented oval. For example, a major semi-axis of the ellipse corresponds to the long axis of the torsion suspension, while a minor semi-axis of the ellipse corresponds to the short axis of the torsion suspension. For example, the long axis and the short axis of the torsion suspension correspond to two axes of symmetry of the indented oval.

In the case of a compressed oval, for example, the distance between the circumference of the torsion suspension and the long axis exhibits a local minimum at the short axis. Specifically, this distance from the long axis corresponds to a distance in a direction perpendicular to the long axis. In other words, the circumference of the torsion suspension shows a constriction at the short axis. For example, the circumference of the torsion suspension has the shape of a Cassini curve.

According to at least one further embodiment of the microelectromechanical mirror, the mirror element and the first torsion spring elements are connected to each other via a connecting element. The connecting element is specifically designed to mechanically connect the mirror element to the first torsion spring elements. In particular, the connecting element is designed such that the principal plane of extension of the mirror element bends or deforms as little as possible when the mirror element oscillates about its two axes of rotation. This can, for example, reduce imaging errors during operation of the microelectromechanical mirror. For instance, the connecting element reduces the transmission of any twisting of the first torsion spring elements to the mirror element. The connecting element particularly comprises a substrate that, for example, contains or consists of silicon.

According to at least one further embodiment of the microelectromechanical mirror, the connecting element is annular in shape and connected to the mirror element via two suspension points. In particular, the mirror element is arranged at the center of the connecting element. The connecting element extends, for example, in the principal plane of extension of the mirror element.

According to at least one further embodiment of the microelectromechanical mirror, the two suspension points are arranged on opposite sides of the mirror element along the short axis. In particular, the suspension points are rotated by 90° relative to the first axis of rotation of the first torsion spring elements.

According to at least one further embodiment of the microelectromechanical mirror, the connecting element has two separate circular arc-shaped segments, each of which is connected to one of the two first torsion spring elements.

According to at least one further embodiment of the microelectromechanical mirror, each of the arc-shaped segments is connected to the mirror element via two suspension points. The suspension points are, for example, arranged at the respective ends of the arc-shaped segments. The first torsion spring elements are connected, for example, to the respective arc-shaped segment between the two suspension points.

According to at least one further embodiment of the microelectromechanical mirror, the drive ring is annular in shape and arranged in its rest position in the main plane of extension of the mirror element. In particular, the torsion suspension and the mirror element are arranged in the center of the drive ring.

According to at least one further embodiment of the microelectromechanical mirror, the drive ring is connected to a frame via two third torsion spring elements. For example, the frame completely encloses the drive ring in the principal plane of extension of the mirror element. The frame particularly includes a substrate that, for example, comprises or consists of silicon. The third torsion spring elements, for example, have a similar or identical structure to the second torsion spring elements, or are identical or similar in design to the second torsion spring elements.

For example, electrical contact points for external electrical contacting of the microelectromechanical mirror are arranged on the frame. These electrical contact points are connected to the piezoelectric drive ring via conductive traces. These conductive traces are located, in particular, on the third torsion spring element. Alternatively or additionally, the piezoelectric drive ring can be electrically connected to the electrical contact points via bond wires. Due to the minimal movement of the drive ring, the mechanical stress on the bond wires is particularly low.

According to at least one further embodiment of the microelectromechanical mirror, the two third torsion spring elements are arranged on opposite sides of the drive ring along the short axis. For example, both the second and third torsion spring elements are aligned along the short axis.

According to at least one further embodiment of the microelectromechanical mirror, the mirror element, the torsion suspension, the drive ring, the frame and the torsion spring are The elements are formed as a single component. In other words, the mirror element, the torsion suspension, the drive ring, the frame, and the torsion spring elements are monolithically integrated and/or formed from a common substrate. For example, the substrate is monocrystalline. Furthermore, the connecting element between the first torsion spring elements and the mirror element can also be formed as a single piece with the aforementioned elements. For example, in the manufacture of the microelectromechanical mirror, the common substrate is structured such that the aforementioned elements are formed within the common substrate.

According to at least one further embodiment of the microelectromechanical mirror, all elements of the one-piece component share a common substrate of constant thickness. Here and in the following, thickness describes the spatial extent of the substrate in a direction perpendicular to the principal plane of extension. This simplifies the manufacturing process of the microelectromechanical mirror. For example, the substrate thickness may range from 20 µm to 500 µm. Alternatively, the substrate may have regions of varying thickness. For instance, the substrate in the frame region may be thicker to improve the mechanical stability of the microelectromechanical mirror, while the substrate in the drive ring region may be thinner, thus providing greater flexibility and/or lower inertia. The substrate in the mirror element region may be thicker than that in the drive ring to, for example, reduce deformation of the mirror element during operation.

According to at least one further embodiment of the microelectromechanical mirror, a piezoelectric layer is applied to the drive ring, positioned between a first electrode and a second electrode. In particular, the piezoelectric layer is applied at least partially to a main surface of the drive ring that is parallel to the main extension plane of the mirror element. The piezoelectric layer comprises, for example, PZT, AlN, or BFO-BT, or consists of one of these materials. For example, the piezoelectric layer has a thickness between 0.5 µm and 5 µm.

The first and second electrodes are specifically designed to apply an electrical voltage to the piezoelectric layer. Applying this voltage during operation generates mechanical stresses in the drive ring. These mechanical stresses induce, for example, torsional moments and/or bending moments, which are transmitted via the second torsion spring elements to the torsion suspension and/or the mirror element.

According to at least one further embodiment of the microelectromechanical mirror, the second electrode has a plurality of control areas that are separate from one another. For example, the second electrode is segmented. In particular, the control areas can be electrically controlled independently of one another. By applying electrical voltages to different control areas, different torsional and/or bending moments can be generated in the drive ring, for example, in order to excite different vibration modes of the torsional suspension and/or the mirror element.

According to at least one further embodiment of the microelectromechanical mirror, at least one sensor element is arranged on the torsion suspension for determining a deflection and/or a frequency of an oscillation of the mirror element. In particular, the at least one sensor element can determine the orientation of the mirror element relative to the torsion suspension, the drive ring, and/or the frame during operation. The sensor element generates, for example, a time-dependent electrical signal that is proportional to an instantaneous deflection angle of the mirror element.

For example, the electrical signal from the sensor element can be used to control and/or fine-tune the vibration frequencies of the mirror element around its two axes of rotation. In other words, a control signal for the drive ring can be adjusted based on the measured values from the sensor element.

According to at least one further embodiment of the microelectromechanical mirror, the at least one sensor element comprises a piezoelectric layer arranged between two electrodes. The piezoelectric layer is, for example, applied to a surface of the torsion suspension that is arranged parallel to the principal plane of extension of the mirror element. A deflection of the mirror element, for example, generates a mechanical stress in the torsion suspension. This, in particular, deforms the piezoelectric layer and generates an electrical voltage. This electrical voltage The signal can, for example, be read out as an electrical signal from the sensor element.

According to at least one further embodiment of the microelectromechanical mirror, the torsion suspension is configured to linearize a vibration mode about the long axis. In other words, the vibration mode about the long axis exhibits lower anharmonicity due to the shape of the torsion suspension. For example, the elongated shape of the torsion suspension leads to a linearization of the vibration mode about the long axis. In particular, the vibration mode about the long axis is a combination of a torsional motion of the mirror element, in which the first torsion spring elements twist, and a bending motion of the torsion suspension.

• - ein Durchmesser des Spiegelelements bestimmt eine Apertur und somit eine beugungsbegrenzte Auflösung einzelner Bildpunkte;
• - ein maximaler Ablenkwinkel des Spiegelelements um die erste und zweite Drehachse bestimmt gemeinsam mit dem Durchmesser des Spiegelelements eine Bildauflösung, also eine Anzahl von Bildpunkten je Richtung. Beispielsweise soll der mikroelektromechanische Spiegel eine Bildauflösung von zumindest 1024 × 768 Pixel, bevorzugt von zumindest 720p erreichen;
• - Resonanzfrequenzen von Schwingungsmoden, bei denen das Spiegelelement um die erste Drehachse beziehungsweise um die zweite Drehachse schwingt, bestimmen insbesondere eine Bildwiederholrate und beeinflussen auch die Bildauflösung;
• - die Schwingungsmoden sollten das Spiegelelement während des Betriebs so wenig als möglich verbiegen, damit die reflektierenden Schicht möglichst eben bleibt, um Abbildungsfehler, eine Pixelverschmierung und/oder Specklemuster zu vermeiden;
• - das Spiegelelement sollte harmonisch um die erste und zweite Drehachse schwingen, um ein stabiles Frequenzverhältnis zwischen den Frequenzen der Schwingungen um die beiden Drehachsen zu gewährleisten;
• - die Resonanzen der Schwingungsmoden sollten eine nicht zu geringe Bandbreite aufweisen, um eine Feinjustage der Frequenzen der Schwingungen um die erste und zweite Drehachse während des Betriebs zu ermöglichen;
• - der mikroelektromechanische Spiegel sollte eine möglichst kompakte Bauform aufweisen;
• - der mikroelektromechanische Spiegel sollte möglichst resistent gegenüber Erschütterungen während des Betriebs sein; und/oder
• - der mikroelektromechanische Spiegel sollte eine möglichst geringe Leistungsaufnahme aufweisen, zum Beispiel höchstens 200 mW, bevorzugt höchstens 100 mW, und besonders bevorzugt höchstens 50 mW.

The microelectromechanical mirror described here is based on the following ideas in particular. Rotational vibrations of the mirror element around the first and second axes of rotation are excited resonantly. This results, for example, in a so-called Lissajous scanning, in which a laser beam deflected by the mirror element describes a Lissajous figure on a projection surface during operation of the microelectromechanical mirror. By temporally modulating the laser beam, a static or moving image can be generated on the projection surface. For a given refresh rate and image resolution, the following requirements arise for the microelectromechanical mirror:

• - The diameter of the mirror element determines an aperture and thus a diffraction-limited resolution of individual pixels;
• - A maximum deflection angle of the mirror element around the first and second axes of rotation, together with the diameter of the mirror element, determines the image resolution, i.e., the number of pixels per direction. For example, the microelectromechanical mirror should achieve an image resolution of at least 1024 × 768 pixels, preferably at least 720p;
• - Resonance frequencies of vibration modes, in which the mirror element oscillates around the first axis of rotation or around the second axis of rotation, determine in particular a refresh rate and also influence the image resolution;
• - the vibration modes should bend the mirror element as little as possible during operation so that the reflective layer remains as flat as possible to avoid image defects, pixel smearing and/or speckle patterns;
• - the mirror element should oscillate harmoniously around the first and second axes of rotation to ensure a stable frequency ratio between the frequencies of the oscillations around the two axes of rotation;
• - the resonances of the vibration modes should have a sufficiently wide bandwidth to allow fine-tuning of the frequencies of the vibrations around the first and second axes of rotation during operation;
• - the microelectromechanical mirror should have the most compact design possible;
• - The microelectromechanical mirror should be as resistant as possible to vibrations during operation; and/or
• - the microelectromechanical mirror should have the lowest possible power consumption, for example, at most 200 mW, preferably at most 100 mW, and most preferably at most 50 mW.

• - die Schwingung um die kurze Achse ist insbesondere eine reine Torsionsschwingungsmode, während die Schwingung um die lange Achse aufgrund der langgestreckten Form der Torsionsaufhängung beispielsweise eine modifizierte „Rocking“-Mode ist, die eine Kombination einer Torsionsbewegung des Spiegelelements und einer Verbiegungsbewegung der Torsionsaufhängung ist. Dadurch wird insbesondere die Anharmonizität der Rocking-Mode verringert;
• - alle Elemente des mikroelektromechanischen Spiegels weisen beispielsweise ein gemeinsames Substrat mit konstanter Dicke auf. In anderen Worten weisen alle Elemente des mikroelektromechanischen Spiegels ein Substrat mit der gleichen Dicke auf. Dadurch vereinfacht sich ein Herstellungsverfahren des mikroelektromechanischen Spiegels. Alternativ kann das Substrat auch mehrere Bereiche mit unterschiedlichen Dicken aufweisen;
• - die Resonanzfrequenzen der beiden Schwingungsmoden sind deutlich unterschiedlich und insbesondere außerhalb eines hörbaren Frequenzbereichs. Dadurch kann die Aufhängung des Spiegels für eine Richtung optimiert werden, wodurch beispielsweise auch die Dicke des Substrats reduziert werden kann;
• - ein gewünschter Spiegeldurchmesser, die Form der Torsionsaufhängung, die gewünschten Resonanzfrequenzen und die geforderte Ebenheit des Spiegelelements bestimmen in Kombination mit dem Material des Substrats die Dicke des Substrats;
• - eine Form und Größe der Torsionsaufhängung sowie eine Dimensionierung der ersten Torsionsfederelemente ergibt sich aus einem gewünschten Winkelbereich für die Drehung um die erste Drehachse, einer erlaubten mechanischen Spannung, einer gewünschten Resonanzfrequenz, sowie einer gewünschten Linearität bzw. Harmonizität der Schwingungsmode um die erste Drehachse;
• - die zweiten Torsionsfederelemente sind für die Drehung um die zweite Drehachse sind innerhalb des Antriebsringes angeordnet und um 90° zur langen Achse der Torsionsaufhängung gedreht. Dadurch weist der mikroelektromechanische Spiegel eine besonders kompakte Bauform auf. Eine Dimensionierung der zweiten Torsionsfederelemente ergibt sich aus einem gewünschten Winkelbereich für die Drehung um die zweite Drehachse, einer erlaubten mechanischen Spannung, sowie einer gewünschten Resonanzfrequenz der Schwingungsmode um die zweite Drehachse;
• - Leiterbahnen zur elektrischen Kontaktierung der piezoelektrischen Schicht des Antriebsringes können auf den dritten Torsionsfederelementen angeordnet werden, die sich während des Betriebs nicht oder nur kaum bewegen.

The microelectromechanical mirror described here fulfills at least one, preferably several, and particularly preferably all of the above-mentioned requirements, for example, due to at least one, preferably several, and particularly preferably all of the following features:

• - The oscillation about the short axis is, in particular, a pure torsional oscillation mode, while the oscillation about the long axis, due to the elongated shape of the torsional suspension, is, for example, a modified "rocking" mode, which is a combination of a torsional motion of the mirror element and a bending motion of the torsional suspension. This reduces, in particular, the anharmonicity of the rocking mode;
• - All elements of the microelectromechanical mirror, for example, share a common substrate of constant thickness. In other words, all elements of the microelectromechanical mirror have a substrate of the same thickness. This simplifies the manufacturing process of the microelectromechanical mirror. Alternatively, the substrate can also have several areas with different thicknesses;
• - The resonant frequencies of the two vibration modes are significantly different and, in particular, outside the audible frequency range. This allows the mirror's suspension to be optimized for one direction. which, for example, also allows the thickness of the substrate to be reduced;
• - The desired mirror diameter, the shape of the torsion suspension, the desired resonance frequencies and the required flatness of the mirror element, in combination with the material of the substrate, determine the thickness of the substrate;
• - The shape and size of the torsion suspension as well as the dimensioning of the first torsion spring elements result from a desired angular range for the rotation about the first axis of rotation, a permissible mechanical stress, a desired resonance frequency, and a desired linearity or harmonicity of the vibration mode about the first axis of rotation;
• The second torsion spring elements, responsible for rotation around the second axis, are located within the drive ring and rotated 90° relative to the long axis of the torsion suspension. This results in a particularly compact design for the microelectromechanical mirror. The dimensions of the second torsion spring elements are determined by the desired angular range for rotation around the second axis, the permissible mechanical stress, and the desired resonant frequency of the oscillation mode around the second axis.
• - Conductor tracks for electrical contacting the piezoelectric layer of the drive ring can be arranged on the third torsion spring elements, which do not move or hardly move during operation.

According to at least one embodiment, the microelectromechanical mirror is used for projecting information onto a surface, for head-up displays, for matrix illumination, for LIDAR applications, for hologram projectors, for VR glasses, or for AR glasses.

Furthermore, a method for operating a microelectromechanical mirror is disclosed. This method is particularly applicable to the operation of the microelectromechanical mirror described herein. All features of the microelectromechanical mirror are also disclosed for the method of operating a microelectromechanical mirror, and vice versa.

According to at least one embodiment of the method for operating a microelectromechanical mirror, the mirror element is set into a first vibration mode by means of a first alternating current electrical signal with a first frequency acting on first control areas of the drive ring, and the torsional suspension is set into a second vibration mode by means of a second alternating current electrical signal with a second frequency acting on second control areas of the drive ring. In particular, in the second vibration mode, the torsional suspension vibrates together with the mirror element. The first and second control areas correspond, in particular, to control areas of the second electrode, which is configured for electrical contacting the piezoelectric layer of the drive ring.

According to at least one further embodiment of the method, the first vibration mode comprises a rotation of the mirror element about the long axis.

According to at least one further embodiment of the method, the second vibration mode includes a rotation of the mirror element about the short axis. In particular, in the second vibration mode, the torsional suspension rotates together with the mirror element about the short axis.

According to at least one further embodiment of the method, the first and second vibration modes are excited resonantly. In particular, the first and second vibration modes are excited simultaneously and superimpose during operation of the microelectromechanical mirror. The first frequency corresponds, for example, to a resonance frequency of the first vibration mode, or deviates from the resonance frequency of the first vibration mode by at most a bandwidth of a resonance of the first vibration mode. The second frequency corresponds, for example, to a resonance frequency of the second vibration mode, or deviates from the resonance frequency of the second vibration mode by at most a bandwidth of a resonance of the second vibration mode.

According to at least one further embodiment of the method, the movement of the drive ring in the first and second vibration modes has an amplitude that is at most one-fifth, preferably at most one-tenth, of the amplitude of a movement of the mirror element. In other words, the drive ring hardly moves in the first and second vibration modes. For example, the movement of the drive ring is negligibly small compared to the mirror element. This reduces, for example, damping of the vibration modes due to air resistance and/or increases excitation efficiency. For example, by A mechanical reinforcement converts a small bending of the drive ring into a large deflection of the mirror element. Furthermore, the third torsion spring elements twist little or not at all in the first and second vibration modes.

Conductor tracks, such as those used for electrical contact with the electrodes of the drive ring via the third torsion spring elements, are subjected to minimal or no mechanical stress due to the low movement of the drive ring. This increases, for example, the service life of the microelectromechanical mirror. Alternatively or additionally, the electrodes of the drive ring can be electrically contacted via bond wires.

According to at least one further embodiment of the method, the resonant frequency of the first vibration mode is at least 1.3 times greater than the resonant frequency of the second vibration mode. Due to the significant difference between the two resonant frequencies, the suspension of the mirror element can be optimized independently for movement around the two axes of rotation.

According to at least one further embodiment of the method, the resonant frequency of the second vibration mode is at least 16 kHz, preferably at least 20 kHz. In particular, the resonant frequencies of the first and second vibration modes are not in the audible range, meaning that the microelectromechanical mirror does not generate any disturbing background noise during operation, for example. Furthermore, higher resonant frequencies allow, for example, an increase in image resolution for projection applications.

According to at least one further embodiment of the method, the first and second vibration modes are operated in a harmonic range. In other words, the first and second vibration modes exhibit low anharmonicity. Thus, the frequency ratio between the first and second vibration modes does not change, or changes only slightly, during operation. In other words, the frequency ratio advantageously remains stable during operation. For example, the frequency ratio between the first and second vibration modes changes by at most 5%, preferably by at most 1%, and most preferably by at most 0.1% during operation.

According to at least one further embodiment of the method, the second vibration mode is a torsional vibration of the torsion suspension with the mirror element about the short axis, while the first vibration mode is a combination of a torsional vibration of the mirror element about the long axis and a bending movement of the torsion suspension. In particular, the first vibration mode is a so-called "rocking" mode, in which, for example, one of the two second torsion spring elements is periodically moved in a direction perpendicular to the principal extension plane of the mirror element, while the other of the two second torsion spring elements is moved, for example, in the opposite phase. This, in particular, excites a vibration of the mirror element about the long axis.

Furthermore, a projection device is specified. The projection device includes, in particular, the microelectromechanical mirror described herein. All features of the microelectromechanical mirror are also disclosed for the projection device, and vice versa.

According to at least one embodiment, the projection device comprises a laser light source and a microelectromechanical mirror described herein. During operation, the microelectromechanical mirror deflects, for example, laser light emitted by the laser light source. Due to the previously described vibration modes of the mirror element, the deflected laser light can be used to scan, in particular, an image area perceptible to an observer. Specifically, the microelectromechanical mirror is configured for Lissajous scanning of the image area.

• 1 zeigt eine schematische Draufsicht auf einen mikroelektromechanischen Spiegel gemäß einem ersten Ausführungsbeispiel.
• 2 zeigt eine schematische Draufsicht auf einen mikroelektromechanischen Spiegel gemäß einem zweiten Ausführungsbeispiel.
• Die 3A bis 3J zeigen schematische Darstellungen von Schwingungsmoden eines mikroelektromechanischen Spiegels gemäß dem ersten Ausführungsbeispiel.
• Die 4A und 4B zeigen schematische Darstellungen einer zweiten Schwingungsmode eines mikroelektromechanischen Spiegels gemäß dem ersten Ausführungsbeispiel.
• Die 5A und 5B zeigen schematische Darstellungen einer ersten Schwingungsmode eines mikroelektromechanischen Spiegels gemäß dem ersten Ausführungsbeispiel.
• 6 zeigt eine schematische Darstellung einer Auslenkung eines Spiegelelements sowie einer mechanischen Verspannung eines mikroelektromechanischen Spiegels gemäß dem ersten Ausführungsbeispiel.
• 7 zeigt eine schematische Darstellung einer Auslenkung eines Spiegelelements eines mikroelektromechanischen Spiegels gemäß dem ersten Ausführungsbeispiel.
• Die 8A bis 8J zeigen schematische Darstellungen von Schwingungsmoden eines mikroelektromechanischen Spiegels gemäß dem zweiten Ausführungsbeispiel.
• Die 9A und 9B zeigen schematische Darstellungen einer zweiten Schwingungsmode eines mikroelektromechanischen Spiegels gemäß dem zweiten Ausführungsbeispiel.
• Die 10A und 10B zeigen schematische Darstellungen einer ersten Schwingungsmode eines mikroelektromechanischen Spiegels gemäß dem zweiten Ausführungsbeispiel.
• 11 zeigt eine schematische Darstellung einer Auslenkung eines Spiegelelements sowie einer mechanischen Verspannung eines mikroelektromechanischen Spiegels gemäß dem zweiten Ausführungsbeispiel.
• 12 zeigt eine schematische Darstellung einer Auslenkung eines Spiegelelements eines mikroelektromechanischen Spiegels gemäß dem zweiten Ausführungsbeispiel.
• 13 zeigt eine schematische Schnittdarstellung eines mikroelektromechanischen Spiegels gemäß dem zweiten Ausführungsbeispiel.
• 14 zeigt eine schematische Darstellung einer Projektionsvorrichtung gemäß einem Ausführungsbeispiel.

Further advantageous embodiments and developments of the microelectromechanical mirror, the method for operating a microelectromechanical mirror, and the projection device result from the exemplary embodiments described below in conjunction with the figures.

• 1 shows a schematic top view of a microelectromechanical mirror according to a first embodiment.
• 2 shows a schematic top view of a microelectromechanical mirror according to a second embodiment.
• The 3A to 3J show schematic representations of vibration modes of a microelectromechanical mirror according to the first embodiment.
• The 4A and 4B show schematic representations of a second vibration mode of a microelectromechanical mirror according to the first embodiment.
• The 5A and 5B show schematic representations of a first vibration mode of a microelectromechanical mirror according to the first embodiment.
• 6 Figure 1 shows a schematic representation of a deflection of a mirror element and a mechanical tension of a microelectromechanical mirror according to the first embodiment.
• 7 Figure 1 shows a schematic representation of a deflection of a mirror element of a microelectromechanical mirror according to the first embodiment.
• The 8A to 8J show schematic representations of vibration modes of a microelectromechanical mirror according to the second embodiment.
• The 9A and 9B show schematic representations of a second vibration mode of a microelectromechanical mirror according to the second embodiment.
• The 10A and 10B show schematic representations of a first vibration mode of a microelectromechanical mirror according to the second embodiment.
• 11 Figure 1 shows a schematic representation of a deflection of a mirror element and a mechanical tension of a microelectromechanical mirror according to the second embodiment.
• 12 Figure 1 shows a schematic representation of a deflection of a mirror element of a microelectromechanical mirror according to the second embodiment.
• 13 shows a schematic sectional view of a microelectromechanical mirror according to the second embodiment.
• 14 shows a schematic representation of a projection device according to an exemplary embodiment.

Identical, similar, or equivalent elements in the figures are marked with the same reference symbols. The figures and the relative sizes of the elements depicted within them are not to be considered to scale. Rather, individual elements may be exaggeratedly large or small for clarity and/or better understanding.

The microelectromechanical mirror 1 according to the first embodiment in 1 The device comprises a mirror element 2, a connecting element 6, a torsion suspension 3, a drive ring 5, a frame 7, and two first, second, and third torsion spring elements 41, 42, 43, respectively, which are formed in one piece from a common silicon substrate 8. In particular, it shows 1 a top view of the principal extension plane 21 of the mirror element 2.

The mirror element 2 is circular or elliptical and has, for example, a diameter between 1 mm and 2 mm. A reflective layer 22 (not shown) is applied to the main surface 21 of the mirror element 2. This layer may be a metal, a dielectric mirror, or a nanostructured surface and is designed to reflect electromagnetic radiation in a spectral range between infrared and ultraviolet light.

A connecting element 6 mechanically connects the mirror element 2 to two first torsion spring elements 41, which are arranged on opposite sides of the mirror element 2. The connecting element 6 comprises two arc-shaped segments 62, each of which is mechanically connected to the mirror element 2 via two suspension points 61 at its ends. The two first torsion spring elements 41 are each mechanically connected to one of the segments 61 at the midpoint between the two suspension points 61.

The first two torsion spring elements 41 mechanically connect the connecting element 6 to the torsion suspension 3. The torsion suspension 3 completely encloses the mirror element 2 and the connecting element 6 in the principal extension plane 21, such that the mirror element 2 is located at the center of the torsion suspension 3. The torsion suspension 3 has an elongated shape with a long axis 31 and a short axis 32, which are each axes of symmetry of the torsion suspension 3. The diameter of the torsion suspension 3 along the long axis 31 is approximately 50% larger than the diameter of the torsion suspension 3 along the short axis 32. One circumference of the torsion suspension 3 has the shape of a compressed or constricted oval. The first two torsion spring elements 41 are arranged along the long axis 31.

The two second torsion spring elements 42 mechanically connect the torsion suspension 3 to the drive ring 5. The two second torsion spring elements 42 are arranged on opposite sides of the torsion suspension 3 along the short axis 32.

The drive ring 5 is circular or elliptical and mechanically connected to the frame 7 via two third torsion spring elements 43. The torsion suspension 3 is located in the center of the The drive ring 5 is arranged within the frame 7. The frame completely encloses the drive ring 5 in the main extension plane 21. A piezoelectric layer 50 made of PZT (not shown) is applied to a main surface of the drive ring 5, which is arranged parallel to the main extension plane 21. This layer is positioned between a first electrode 51 (not shown) and a second electrode 52. The second electrode 52 has separate first control areas 521a, 521b and second control areas 522a, 522b.

By applying a time-oscillating electrical voltage between the first electrode 51 and the first control areas 521a, 521b of the second electrode 52, a first oscillation mode 11 of the microelectromechanical mirror 1 can be excited. By applying a time-oscillating electrical voltage between the first electrode 51 and the second control areas 522a, 522b of the second electrode 52, a second oscillation mode 12 of the microelectromechanical mirror 1 can be excited. The first oscillation mode 11 includes, in particular, a torsional oscillation of the mirror element 2 about the long axis 31, while the second oscillation mode 12 includes, in particular, a torsional oscillation of the mirror element 2 about the short axis 32. The electrical voltage is applied in the first control areas 521a and 521b, in particular, with opposite phase. Similarly, the electrical voltage in the second control areas 522a and 522b is applied, in particular with the opposite phase.

Sensor elements 9 are arranged on both the drive ring 5 and the frame 7 for determining the displacement and/or frequency of the vibration of the mirror element 2 during operation of the microelectromechanical mirror 1. The sensor elements 9 comprise a piezoelectric layer 90 (not shown) arranged between a first electrode 91 (not shown) and a second electrode 92. The sensor elements 9 detect, in particular, mechanical stresses of the microelectromechanical mirror 2 that occur during vibration of the mirror element 2 in operation of the microelectromechanical mirror 1.

• - Dicke der piezoelektrischen Schicht 50, 90: 1,7 µm;
• - Dicke des Si Substrats 8: 150 µm, wobei die kurze Achse 32 entlang einer Kristallrichtung <100> ausgerichtet ist und die lange Achse 31 entlang einer Kristallrichtung <010> ausgerichtet ist;
• - Abmessungen des mikroelektromechanischen Spiegels 1 in der Haupterstreckungsebene 21: 7,65 mm × 9,35 mm;
• - Resonanzfrequenz der ersten Schwingungsmode 11: 30,8 kHz;
• - Resonanzfrequenz der zweiten Schwingungsmode 12: 20,9 kHz;
• - maximaler Auslenkungswinkel des Spiegelelements 2 in der ersten Schwingungsmode 11: 16,5°;
• - maximaler Auslenkungswinkel des Spiegelelements 2 in der zweiten Schwingungsmode 12: 11°;
• - Q-Faktor der Schwingungsmoden: 10³;
• - Anharmonizität der ersten Schwingungsmode 11:
  • Frequenzverschiebung von 6 Hz bei einem Auslenkungswinkel von 1° bis 16,5°;
• - Anharmonizität der zweiten Schwingungsmode 12:
  • Frequenzverschiebung von -1,4 Hz bei einem Auslenkungswinkel von 1° bis 11°;
• - Sensitivität des Sensorelements 9 für die erste Schwingungsmode 11: 0,5 µA/° bis 15,0 µA/°;
• - Sensitivität des Sensorelements 9 für die zweite Schwingungsmode 12: 0,2 µA/° bis 1,5 µA/°;

The microelectromechanical mirror 1 of the first embodiment has in particular the following features:

• - Thickness of the piezoelectric layer 50, 90: 1.7 µm;
• - Thickness of the Si substrate 8: 150 µm, wherein the short axis 32 is aligned along a crystal direction <100> and the long axis 31 is aligned along a crystal direction <010>;
• - Dimensions of the microelectromechanical mirror 1 in the principal extension plane 21: 7.65 mm × 9.35 mm;
• - Resonance frequency of the first oscillation mode 11: 30.8 kHz;
• - Resonance frequency of the second oscillation mode 12: 20.9 kHz;
• - maximum deflection angle of the mirror element 2 in the first vibration mode 11: 16.5°;
• - maximum deflection angle of the mirror element 2 in the second vibration mode 12: 11°;
• - Q-factor of the vibration modes: 10 ³ ;
• - Anharmonicity of the first vibrational mode 11:
  • Frequency shift of 6 Hz at a deflection angle of 1° to 16.5°;
• - Anharmonicity of the second mode of vibration 12:
  • Frequency shift of -1.4 Hz at a deflection angle of 1° to 11°;
• - Sensitivity of sensor element 9 for the first vibration mode 11: 0.5 µA/° to 15.0 µA/°;
• - Sensitivity of sensor element 9 for the second vibration mode 12: 0.2 µA/° to 1.5 µA/°;

The microelectromechanical mirror 1 according to the second embodiment in 2 In contrast to the first embodiment, this embodiment comprises a torsion suspension 3 with an elliptical ring shape. Furthermore, additional sensor elements 9 are arranged on a main surface of the torsion suspension 3, which is arranged parallel to the main extension plane 21. The sensor elements 9 comprise a piezoelectric layer 90 (not shown) located between a first electrode 91 (not shown) and a second electrode 92. The second electrode 92 is segmented, so that the sensor element 9 on the torsion suspension 3 has multiple readout areas. The additional sensor elements 9 on the torsion suspension 3 can, for example, improve the measurement accuracy of the sensor elements.

Furthermore, in the second embodiment, the connecting element 6 is designed in an annular shape and has two suspension points 61 for the mirror element 2 along the short axis 32.

• - Dicke der piezoelektrischen Schicht 50, 90: 1,7 µm;
• - Dicke des Si Substrats 8: 50 µm, wobei die kurze Achse 32 entlang einer Kristallrichtung <100> ausgerichtet ist und die lange Achse 31 entlang einer Kristallrichtung <010> ausgerichtet ist;
• - Abmessungen des mikroelektromechanischen Spiegels 1 in der Haupterstreckungsebene 21: 7,65 mm × 9,35 mm;
• - Resonanzfrequenz der ersten Schwingungsmode 11: 20,3 kHz;
• - Resonanzfrequenz der zweiten Schwingungsmode 12: 9,2 kHz;
• - maximaler Auslenkungswinkel des Spiegelelements 2 in der ersten Schwingungsmode 11: 16,5°;
• - maximaler Auslenkungswinkel des Spiegelelements 2 in der zweiten Schwingungsmode 12: 11°;
• - Q-Faktor der Schwingungsmoden: 10³;
• - Anharmonizität der ersten Schwingungsmode 11:
  • Frequenzverschiebung von 184,6 Hz bei einem Auslenkungswinkel von 1° bis 16,5°;
• - Anharmonizität der zweiten Schwingungsmode 12:
  • Frequenzverschiebung von 21,2 Hz bei einem Auslenkungswinkel von 1° bis 11°;
• - Sensitivität des Sensorelements 9 für die erste Schwingungsmode 11: 0,5 µA/° bis 45,2 µA/°;
• - Sensitivität des Sensorelements 9 für die zweite Schwingungsmode 12: 0,04 µA/° bis 19,2 µA/°;

The microelectromechanical mirror 1 of the second embodiment has in particular the following features:

• - Thickness of the piezoelectric layer 50, 90: 1.7 µm;
• - Thickness of the Si substrate 8: 50 µm, wherein the short axis 32 is aligned along a crystal direction <100> and the long axis 31 is aligned along a crystal direction <010>;
• - Dimensions of the microelectromechanical mirror 1 in the principal extension plane 21: 7.65 mm × 9.35 mm;
• - Resonance frequency of the first oscillation mode 11: 20.3 kHz;
• - Resonance frequency of the second oscillation mode 12: 9.2 kHz;
• - maximum deflection angle of the mirror element 2 in the first vibration mode 11: 16.5°;
• - maximum deflection angle of the mirror element 2 in the second vibration mode 12: 11°;
• - Q-factor of the vibration modes: 10 ³ ;
• - Anharmonicity of the first vibration mode 11:
  • Frequency shift of 184.6 Hz at a deflection angle of 1° to 16.5°;
• - Anharmonicity of the second mode of vibration 12:
  • Frequency shift of 21.2 Hz at a deflection angle of 1° to 11°;
• - Sensitivity of sensor element 9 for the first vibration mode 11: 0.5 µA/° to 45.2 µA/°;
• - Sensitivity of sensor element 9 for the second vibration mode 12: 0.04 µA/° to 19.2 µA/°;

The 3A to 3J Figure 1 shows numerical simulations of various vibration modes of a microelectromechanical mirror 1 according to the first embodiment. In particular, the displacement of different elements of the microelectromechanical mirror 1 at a specific time is exaggerated for clarity. The resonance frequencies fR of the depicted vibration modes are listed in the following table:

Fig. 3A 3B 3C 3D 3E fR [kHz] 8, 66 10.74 17.22 20, 86 27.47 Fig. 3F 3G 3H 3I 3 years fR [kHz] 30.81 37.45 40, 73 47.32 49.10

The vibration mode in 3D corresponds to the second vibration mode 12 of the first embodiment, in which the mirror element 2 together with the torsional suspension 3 performs a rotational vibration about the short axis 32.

The vibration mode in 3F corresponds to the first vibration mode 11 of the first embodiment, in which the mirror element 2 performs a torsional vibration about the long axis 31, while the torsional suspension 3 in particular performs a bending movement.

The resonant frequencies of the different vibration modes exhibit a particularly large frequency difference, so that the first and second vibration modes 11 and 12 can be specifically excited without exciting further parasitic vibration modes.

The 4A Figure 1 shows a schematic representation of tensile stress in the material of a microelectromechanical mirror 1 according to the first embodiment. In particular, the tensile stress within the microelectromechanical mirror 1 is shown at a maximum deflection angle of the mirror element 2 of 11° about the short axis 32 in the second vibration mode 12. The maximum tensile stress is approximately 1.7 GPa.

The 4B Figure 1 shows a schematic representation of a deformation of the principal extension plane 21 of the mirror element 2 of a microelectromechanical mirror 1 according to the first embodiment. In particular, the deformation in a direction perpendicular to the principal extension plane 21 is shown at a maximum deflection angle of the mirror element 2 of 11° about the short axis 32 in the second vibration mode 12. The maximum deformation is approximately ±250 nm at the edge of the mirror element 2.

The 5A Figure 1 shows a schematic representation of tensile stress in the material of a microelectromechanical mirror 1 according to the first embodiment. In particular, the tensile stress is shown at a maximum deflection angle of the mirror element 2 of 16.5° about the long axis 31 in the first vibration mode 11. The maximum tensile stress is approximately 2.4 GPa.

The 5B Figure 1 shows a schematic representation of a deformation of the principal extension plane 21 of the mirror element 2 of a microelectromechanical mirror 1 according to the first embodiment. In particular, the deformation in a direction perpendicular to the principal extension plane 21 is shown at a maximum deflection angle of the mirror element 2 of 16.5° about the long axis 31 in the first vibration mode 11. The maximum deformation is approximately ±310 nm at the edge of the mirror element 2.

6 shows the deflection angles φ1, φ2 of a mirror element 2 about the long axis 31 and about the short axis 32 respectively, as well as a maximum tensile stress Z in the material of a microelectromechanical mirror 1 according to the first embodiment during an oscillation of the mirror element 2 according to the first and second oscillation modes 11, 12 as a function of time t.

7 Figure 1 shows the deflection angles φ1, φ2 of a mirror element 2 about the long axis 31 and about the short axis 32 of a microelectromechanical mirror 1 according to the first embodiment, in which the first vibration mode 11 and the second vibration mode 12 are driven simultaneously. In particular, the deflection of the mirror as a function of time is described by a Lissajous figure.

The 8A to 8J Figure 1 shows numerical simulations of various vibration modes of a microelectromechanical mirror 1 according to the second embodiment. In particular, the displacement of different elements of the microelectromechanical mirror 1 at a specific time is exaggerated for clarity. The resonance frequencies fR of the depicted vibration modes are listed in the following table: Fig. 8A 8B 8C 8D 8E fR [kHz] 3.08 3.85 7.67 9.20 12.99 Fig. 8F 8G 8H 8I 8J fR [kHz] 14.27 18.76 20.29 23.31 29.37

The vibration mode in 8D corresponds to the second vibration mode 12 of the second embodiment, in which the mirror element 2 together with the torsional suspension 3 performs a rotational vibration about the short axis 32.

The vibration mode in 8H corresponds to the first vibration mode 11 of the second embodiment, in which the mirror element 2 performs a torsional vibration about the long axis 31, while the torsional suspension 3 in particular performs a bending movement.

The 9A Figure 1 shows a schematic representation of tensile stress in the material of a microelectromechanical mirror 1 according to the second embodiment. In particular, the tensile stress is shown at a maximum deflection angle of the mirror element 2 of 11° about the short axis 32 in the second vibration mode 12. The maximum tensile stress is approximately 1.0 GPa.

The 9B Figure 1 shows a schematic representation of a deformation of the principal extension plane 21 of the mirror element 2 of a microelectromechanical mirror 1 according to the second embodiment. In particular, the deformation in a direction perpendicular to the principal extension plane 21 is shown at a maximum deflection angle of the mirror element 2 of 11° about the short axis 32 in the second vibration mode 12. The maximum deformation is approximately ±230 nm at the edge of the mirror element 2.

The 10A Figure 1 shows a schematic representation of tensile stress in the material of a microelectromechanical mirror 1 according to the second embodiment. In particular, the tensile stress is shown at a maximum deflection angle of the mirror element 2 of 16.5° about the long axis 31 in the first vibration mode 11. The maximum tensile stress is approximately 1.5 GPa.

The 10B Figure 1 shows a schematic representation of a deformation of the principal extension plane 21 of the mirror element 2 of a microelectromechanical mirror 1 according to the second embodiment. In particular, the deformation in a direction perpendicular to the principal extension plane 21 is shown at a maximum deflection angle of the mirror element 2 of 16.5° about the long axis 31 in the first vibration mode 11. The maximum deformation is approximately ±430 nm at the edge of the mirror element 2.

11 shows the deflection angles φ1, φ2 of a mirror element 2 about the long axis 31 and about the short axis 32 respectively, as well as a maximum tensile stress Z in the material of a microelectromechanical mirror 1 according to the second embodiment during an oscillation of the mirror element 2 according to the first and second oscillation modes 11, 12 as a function of time t.

12 shows the deflection angles φ1, φ2 of a mirror element 2 about the long axis 31 and about the short axis 32 of a microelectrome A mechanical mirror 1 according to the second embodiment, in which the first vibration mode 11 and the second vibration mode 12 are driven simultaneously. In particular, the deflection of the mirror as a function of time describes a Lissajous figure.

13 Figure 1 shows a schematic cross-sectional view of a microelectromechanical mirror 1 according to the second embodiment. In particular, a cross-section parallel to and offset from the short axis 32 is shown. The mirror element 2, the connecting element 6, the torsion suspension 3, the drive ring 5, and the frame 7 share a common substrate 8 and are formed in one piece. The substrate 8 has a constant thickness. A metallic reflective layer 22 is arranged on the main surface 21 of the mirror element 2.

On the drive ring 5, the piezoelectric layer 50 is arranged between a first electrode 51 and a second electrode 52. On the torsion suspension 3, a sensor element 9 is arranged, which comprises a piezoelectric layer 90 between a first electrode 91 and a second electrode 92.

In 14 Figure 1 shows a schematic representation of a projection device 1000 according to an exemplary embodiment, which has a microelectromechanical mirror 1 as described above. Furthermore, the projection device has a laser light source 200 which emits laser light 201 during operation.

For example, the laser light source 200 can be a so-called RGB light source, capable of emitting red, green, and blue laser light. For this purpose, the laser light source 200 can, for instance, have three correspondingly modulatable laser diodes or laser diode groups. The laser light beams can be superimposed, for example, in a beam combiner 202, so that a beam of combined laser light 201' can be directed onto the piezoelectric mirror element 100 and reflected by it into the desired image area. The laser light source 200 can, for example, be controlled by laser control electronics 206, for instance, to modulate the amplitude of the laser light 201, 201' over time.

The microelectromechanical mirror 1 can be controlled via mirror control electronics 203 to, for example, generate the desired Lissajous figure with which the desired image area can be scanned. Furthermore, sensor electronics 204 can be provided to detect the position and/or frequencies of the mirror element 2 of the microelectromechanical mirror 1, preferably in real time. In addition, image processing electronics 205 can be present, which, for example, controls the entire image display. This can, in particular, correspond to the conversion of image or film information into control signals for the laser light source 200 and the microelectromechanical mirror 1, including the temporal synchronization between the position of the mirror element 2 and the amplitudes of the laser light 201, 201'.

The invention is not limited to the description provided by means of the exemplary embodiments. Rather, the invention encompasses every new feature as well as every combination of features, which in particular includes every combination of features in the claims, even if that feature or combination itself is not explicitly stated in the claims or exemplary embodiments.

Reference sign

1

microelectromechanical mirror

11

first mode of vibration

12

second mode of vibration

2

Mirror element

21

Main extent plane

22

reflective layer

3

Torsion suspension

31

long axis

32

short axis

41

first torsion spring elements

42

second torsion spring elements

43

third torsion spring elements

5

drive ring

50

piezoelectric layer

51

first electrode

52

second electrode

521a, 521b

first control area

522a, 522b

second control area

6

Connecting element

61

Suspension points

62

segment

7

Frame

8

substrate

9

Sensor element

90

piezoelectric layer

91

first electrode

92

second electrode

200

Laser light source

201, 201'

laser light

202

Beam combiner

203

Mirror control electronics

204

Sensor electronics

205

Image processing electronics

206

Laser control electronics

1000

Projection device

t

Time

Z

Tensile stress

φ1

Deflection angle about the long axis

φ2

Deflection angle about the short axis

Claims (31)

Microelectromechanical mirror (1) comprising: - a mirror element (2), and - a torsion suspension (3) enclosing the mirror element (2) and connected to the mirror element (2) via two first torsion spring elements (41), wherein - the torsion suspension (3) has an elliptical ring shape or the shape of an indented oval ring, and - the torsion suspension (3) does not have any piezoelectric drive elements. Microelectromechanical mirror (1) according to the preceding claim, additionally comprising a piezoelectric drive ring (5) surrounding the torsion suspension (3) and connected to the torsion suspension (3) via two second torsion spring elements (42). Microelectromechanical mirror (1) according to one of the preceding claims, wherein the first torsion spring elements (41) are arranged along a long axis (31) of the torsion suspension (3). Microelectromechanical mirror (1) according to one of the Claims 2 or 3 , wherein the second torsion spring elements (42) are arranged along a short axis (32) of the torsion suspension (3). Microelectromechanical mirror (1) according to one of the preceding claims, wherein the two first torsion spring elements (41) are arranged on opposite sides of the mirror element (2). Microelectromechanical mirror (1) according to one of the Claims 2 until 5 , wherein the two second torsion spring elements (42) are arranged on opposite sides of the torsion suspension (3). Microelectromechanical mirror (1) according to one of the preceding claims, wherein the mirror element (2) and the first torsion spring elements (41) are connected to each other via a connecting element (6). Microelectromechanical mirror (1) according to Claim 7 , wherein the connecting element (6) is formed in an annular shape and is connected to the mirror element (2) via two suspension points (61). Microelectromechanical mirror (1) according to Claim 8 , wherein the two suspension points (61) are arranged on opposite sides of the mirror element (2) along the short axis (32) of the torsion suspension (3). Microelectromechanical mirror (1) according to Claim 7 , wherein the connecting element (6) has two separate arc-shaped segments (62) which are each connected to one of the two first torsion spring elements (41). Microelectromechanical mirror (1) according to Claim 10 , wherein each of the arc-shaped segments (62) is connected to the mirror element (2) via two suspension points (61). Microelectromechanical mirror (1) according to one of the Claims 2 until 11 , wherein the drive ring (5) is designed in an annular shape and is arranged in a rest position in a principal extension plane (21) of the mirror element (2). Microelectromechanical mirror (1) according to one of the Claims 2 until 12 , wherein the drive ring (5) is connected to a frame (7) via two third torsion spring elements (43). Microelectromechanical mirror (1) according to the previous claim, wherein the two third torsion spring elements (43) are arranged on opposite sides of the drive ring (5) along the short axis (32) of the torsion suspension (3). Microelectromechanical mirror (1) according to one of the Claims 13 or 14 , wherein the mirror element (2), the torsion suspension (3), the drive ring (5), the frame (7) and the torsion spring elements (41, 42, 43) are designed as a single-piece component. Microelectromechanical mirror (1) according to the previous claim, wherein all elements (2, 3, 41, 42, 43, 5, 7) of the one-piece component have a common substrate (8) which has a constant thickness. Microelectromechanical mirror (1) according to one of the Claims 2 until 16 , wherein a piezoelectric layer (50) is applied to the drive ring (5) and is arranged between a first electrode (51) and a second electrode (52). Microelectromechanical mirror (1) according to the preceding claim, wherein the second electrode (52) has a plurality of control areas (521a, 521b, 522a, 522b) which are separated from each other. Microelectromechanical mirror (1) according to one of the Claims 13 until 18 , wherein sensor elements (9) for determining a deflection and/or a frequency of a vibration of the mirror element (2) are arranged on the drive ring (5) and on the frame (7). Microelectromechanical mirror (1) according to one of the preceding claims, wherein at least one sensor element (9) for determining a deflection and/or a frequency of an oscillation of the mirror element (2) is arranged on the torsion suspension (3). Microelectromechanical mirror (1) according to Claim 20 , wherein the at least one sensor element (9) comprises a piezoelectric layer (90) arranged between two electrodes (91, 92). Microelectromechanical mirror (1) according to one of the Claims 1 until 21 , in which the torsional suspension (3) is configured to linearize a vibration mode about the long axis (31) of the torsional suspension (3). Method for operating a microelectromechanical mirror (1) according to one of the Claims 2 until 22 , in which the mirror element (2) is set into a first vibration mode (11) by means of a first alternating current electrical signal with a first frequency, which acts on first control areas (521a, 521b) of the drive ring (5), and the torsional suspension (3) is set into a second vibration mode (12) by means of a second alternating current electrical signal with a second frequency, which acts on second control areas (522a, 522b) of the drive ring (5). Method according to the previous claim, wherein - the first vibration mode (11) comprises a rotation of the mirror element (2) about a long axis (31) of the torsion suspension (3), and - the second vibration mode (12) comprises a rotation of the mirror element (2) about a short axis (32) of the torsion suspension (3). Procedure according to one of the Claims 23 or 24 , in which the first vibration mode (11) and the second vibration mode (12) are excited resonantly. Procedure according to one of the Claims 23 until 25 , in which a movement of the drive ring (5) in the first vibration mode (11) and in the second vibration mode (12) has an amplitude that is at most one fifth of an amplitude of a movement of the mirror element (2). Procedure according to one of the Claims 23 until 26 , in which a resonance frequency of the first mode of vibration (11) is at least a factor of 1.3 greater than a resonance frequency of the second mode of vibration (12). Procedure according to one of the Claims 23 until 27 , in which the first mode of oscillation (11) and the second mode of oscillation (12) are operated in a harmonic range. Procedure according to one of the Claims 23 until 28 , in which the second vibration mode (12) is a torsional vibration of the torsional suspension (3) with the mirror element (2) about the short axis (32) of the torsional suspension (3), while the first vibration mode (11) is a combination of a torsional vibration of the mirror element (2) about the long axis (31) of the torsional suspension (3) and a bending movement of the torsional suspension (3). Projection device (1000) comprising a laser light source (200) and a microelectromechanical mirror (1) according to one of the Claims 1 until 22 . Use of a microelectromechanical mirror (1) according to one of the Claims 1 until 22 for projecting information onto a surface, for head-up displays, for matrix illumination, for LiDAR applications, for holographic displays Grammar projectors, for VR glasses, or for AR glasses.