DE102023203688A1 - Micromechanical device - Google Patents

Abstract

The invention is based on a micromechanical device with a substrate (100), with an anchor (200) and with a micromechanical structure (400, 400', 400'', 400'''), wherein the anchor is arranged and fastened on the substrate, wherein the micromechanical structure is arranged above the substrate and fastened to the anchor.The core of the invention is that the anchor has a first region (210) which is connected to the substrate, has a second region (220) which is connected to the first region and to at least a part (400', 400'', 400''') of the micromechanical structure and the first region is electrically insulated from the second region.

Description

State of the art

The invention is based on a micromechanical device with a substrate, with an anchor and with a micromechanical structure, wherein the anchor is arranged and fastened on the substrate, wherein the micromechanical structure is arranged above the substrate and fastened to the anchor.

Such surface micromechanical devices are widely known in the state of the art. A problem with micromechanical devices, in particular sensors such as acceleration sensors, yaw rate sensors and inertial sensors in general, is the signal offset and offset stability. Intrinsic and externally induced mechanical stresses deform the micromechanical device and thus change the offset. In order to minimize this effect, designs with anchors for micromechanical structures that are as central and close to each other as possible are chosen. A typical design for a capacitive acceleration sensor has three anchors for the three electrically separate main parts of the sensor, namely the seismic mass, the first fixed electrode and the second fixed electrode. The three main parts are connected to different electrical potentials via conductor tracks via the respective anchor. The three anchors must therefore be designed separately. They must not touch each other, otherwise an electrical short circuit will occur. Even if the anchors are close to each other, variable offset conditions occur ( 1 AC ).

task of the invention

The object of the invention is to create a micromechanical device with stable offset properties.

Core and advantages of the invention

The core of the invention is that the anchor has a first region which is connected to the substrate, a second region which is connected to the first region and to at least part of the micromechanical structure, and the first region is electrically insulated from the second region.

An advantageous embodiment of the invention provides that the first region is separated from the second region by a trench which is filled with a dielectric material. The anchoring can advantageously be divided laterally into electrically isolated and mechanically connected regions by the filled trench.

It is particularly advantageous that the first region and the second region are made of silicon and the dielectric material is silicon-rich nitride. Dielectric SiRiN can be used to mechanically attach different areas of the anchor to one another, whereby the intrinsic mechanical stress can also be adjusted using the silicon content.

An advantageous embodiment of the invention provides that the first region is electrically connected to a first conductor track and the second region is electrically connected to a second conductor track. The regions can thus advantageously be connected to different electrical potentials.

It is particularly advantageous that a further anchor is arranged and fastened on the substrate and the further anchor is electrically connected to the second region by means of a spring. This further anchor can advantageously be used to connect the second region to an electrical potential, whereby the connection is largely mechanically decoupled and has no influence on the offset stability.

An advantageous embodiment of the invention provides that the anchor has a third region which is electrically insulated from the second region. It is particularly advantageous that the third region is separated from the second region or from the first region by a further trench which is filled with a dielectric material. This advantageously allows further laterally galvanically isolated regions of the anchor to be defined, in particular in order to create three regions with separate electrical potentials on a single anchor and thus to be able to mechanically fasten three parts of the micromechanical structure to a common anchor and to contact them with separate electrical potentials.

An advantageous embodiment of the invention provides that the spring is arranged between the substrate and the mechanical structure. This arrangement advantageously keeps the base area of the micromechanical device small.

It is particularly advantageous that a thin functional layer is arranged above the substrate and a thick functional layer is arranged above the thin functional layer, that the thin functional layer has a thickness which is less than one third of the thickness of the thick functional layer and that the spring in the thin functional layer consists of This advantageously makes the spring very flexible.

drawing

• 1 D zeigt schematisch eine erfindungsgemäße mikromechanische Vorrichtung mit stabilem Offset.
• 2 A zeigt schematisch den Anschluss verschiedener mechanisch getrennter Verankerungen einer mikromechanischen Vorrichtung an unterschiedliche elektrische Potentiale im Stand der Technik.
• 2 B zeigt schematisch den Anschluss eines ersten Bereichs und eines zweiten Bereichs einer Verankerung einer erfindungsgemäßen mikromechanischen Vorrichtung an unterschiedliche elektrische Potentiale.
• 3 zeigt schematisch eine erfindungsgemäße mikromechanische Vorrichtung mit einer mikromechanischen Struktur in einer ersten Funktionsebene und einer Feder zum elektrischen Anschluss eines zweiten Bereichs einer Verankerung in einer zweiten Funktionsebene über einem Substrat.
• 4 zeigt schematisch eine erfindungsgemäße mikromechanische Vorrichtung mit einer mikromechanischen Struktur mit einer ersten Festelektrode an einem zweiten Bereich und einer zweiten Festelektrode an einem dritten Bereich einer Verankerung.

The 1 A , B, C schematically show a micromechanical device with a substrate, with an anchor and with a micromechanical structure in the prior art with variable offset induced by deformations.

• 1 D shows schematically a micromechanical device according to the invention with stable offset.
• 2 A shows schematically the connection of different mechanically separated anchors of a micromechanical device to different electrical potentials in the state of the art.
• 2 B shows schematically the connection of a first region and a second region of an anchoring of a micromechanical device according to the invention to different electrical potentials.
• 3 shows schematically a micromechanical device according to the invention with a micromechanical structure in a first functional level and a spring for electrically connecting a second region of an anchor in a second functional level above a substrate.
• 4 shows schematically a micromechanical device according to the invention with a micromechanical structure with a first fixed electrode at a second region and a second fixed electrode at a third region of an anchor.

Description

The 1 A , B, C schematically show an acceleration sensor with a substrate, with an anchor and with a micromechanical structure in the state of the art with variable offset induced by deformations.

1 A shows a micromechanical device with a substrate 100, with a first anchor 200 and with a first part of a micromechanical structure 400, a movable seismic mass 400'. The first anchor is arranged and fastened on the substrate. The seismic mass 400' is movably arranged above the substrate and fastened to the first anchor. In addition, a second anchor 200' with a second part of the micromechanical structure, a first fixed electrode 400'', is arranged on the substrate, as well as a third anchor 200'' with a third part of the micromechanical structure, a second fixed electrode 400'''. A first bottom electrode 101 is arranged on the substrate below the first fixed electrode and a second bottom electrode 102 is arranged on the substrate below the second fixed electrode. A fixed electrode, a bottom electrode and the movable micromechanical structure 400' in between each form a differential capacitor as a measuring capacitance for the capacitive acceleration sensor shown. For this purpose, the movable structure 400' is made up of an upper thick functional layer 401 and a lower thin functional layer 402. The thick functional layer forms a large seismic mass and the thin functional layer forms a capacitor plate which is arranged between the fixed electrode and the bottom electrode. C1 and C2 symbolize different charges on the electrodes. The device shown has three anchors 200, 200', 200'' with three different electrical potentials.

1 B shows the acceleration sensor 1 A when the substrate 100 is deformed. As a result of the deformation, the three anchors 200, 200', 200'' and thus the three parts of the micromechanical structure 400', 400'', 400''' as well as the bottom electrodes 101, 102 change their position. The zero signal of the acceleration sensor, i.e. the offset, also changes as a result. The substrate assumes a state of deformation, which is indicated by the strongly curved line below. The components of the sensor move like rigid bodies. This property is special for acceleration measuring structures that are only connected to the substrate with small anchors. Since the electrode surfaces move in comparison to each other, the output capacitances change and thus cause an offset. This is caused by the 1 A changed charges C1 and C''.

1 C shows the acceleration sensor 1 B , whereby the bottom electrodes are omitted. Here, the two fixed electrodes 400'', 400''' with the movable structure 400' form a differential capacitor as a measuring capacitance. The omission of bottom electrodes excludes a source for the change in the offset, but the position of the micromechanical structures 400', 400'', 400''', i.e. the seismic mass and the fixed electrodes, still changes relative to one another because the three anchors 200, 200', 200'' are arranged spatially separated on the substrate.

1 D shows a micromechanical device according to the invention with a stable offset. The device has, in contrast to the device in 1 C shown acceleration sensor has a single anchor 200. The anchor has a first region 210 which is connected to the substrate 100 and a second region 220 which is connected to the second part of the micromechanical structure, the first fixed electrode 400'', the first region being electrically insulated from the second region. For this purpose, the first region is separated from the second region by a trench 300 which is filled with a dielectric material 310. The anchor also has a third region 230 which is connected to the third part of the micromechanical structure, the second fixed electrode 400''', and which is electrically insulated from the second region and the first region. For this purpose, the first region is separated from the third region by a further trench 300' which is filled with a dielectric material 310. The first region is also connected to the first part of the micromechanical structure, namely the seismic mass 400'. All three parts of the micromechanical structure are attached to the substrate with the same anchor. In the event of a deformation of the substrate, they move together for all possible substrate deformations. This allows the offset induced by deformation to be eliminated as best as possible.

2 A shows schematically the connection of various mechanically separated anchors of a micromechanical device to different electrical potentials in the prior art. A first anchor 200 is arranged on a substrate 100, which carries a first part of the micromechanical structure such as a seismic mass (not shown). The first anchor is electrically conductively connected to a first conductor track 510. Furthermore, a second anchor 200' is arranged on the substrate, which carries a second part of the micromechanical structure 400'', here a fixed electrode. The second anchor is electrically conductively connected to a second conductor track 520.

2 B shows schematically the connection of a first region 210 and a second region 220 of an anchor 200 of a micromechanical device according to the invention to different electrical potentials. An anchor 200 is arranged on a substrate 100, which has a first region 210 and a second region 220, the first region being connected to the substrate and the second region being connected to the first region. The first and second regions are mechanically connected to one another and electrically insulated from one another by arranging a trench 300 between them, which is filled with a dielectric material 310, here silicon-rich nitride (SiRiN). The first region is electrically connected to a first part of the micromechanical structure (not shown) and to a first conductor track 510. The second region is connected to a second part of the micromechanical structure 400'', the fixed electrode and to a second conductor track 520 via a further anchor 250 by means of a spring 600. This spring has a very low stiffness, which means that the connection is not effective for transmitting mechanical forces. Mechanical stresses from the further anchor 250 are not or not significantly transmitted to the fixed electrode 400'' because the spring absorbs essentially all deformations. In particular, the spring should be at least a factor of 3 softer and preferably softer than a factor of 15 compared to the stiffness of the mechanical connection via the dielectric material 310 between the first region 210 and the second region 220 of the anchor 200.

3 shows schematically a micromechanical device according to the invention with a micromechanical structure in a first functional level and a spring for electrically connecting a second region of an anchor in a second functional level above a substrate. An anchor 200 is arranged and fastened on the substrate 100. The anchor has a first region 210, a second region 220 and a third region 230, wherein these regions are electrically insulated from one another by a trench 300 and a further trench 300' and mechanically connected to one another by filling the trenches with a dielectric material 310, here silicon-rich nitride (SiRiN). The first fixed electrode 400'' and the second fixed electrode 400''' are thus attached to the anchor in an electrically insulated manner from one another and from the seismic mass 400'. The first part of the micromechanical structure, the seismic mass 400', is formed in an upper, thick functional layer 401 and a thin functional layer 402 arranged underneath. Likewise, the second part of the micromechanical structure, i.e. the first fixed electrode 400'', and the third part of the micromechanical structure, i.e. the second fixed electrode 400''', are formed in the upper thick functional layer 401 and the thin functional layer 402. The thick functional layer is made of epitaxial polysilicon. The thin functional layer is made of polysilicon. Two springs 600 are also formed in the thin functional layer 402, each of which is connected at one end to a part of the micromechanical structure 400'', 400''' and is attached to the substrate 100 at another end by means of a further anchor 250. Via the further anchors 250 and the springs 600, the first fixed electrode 400'' and the second fixed electrode 400''' are connected to different electrical potentials as described under 2 B described.
The springs 600 are formed in the thin functional layer 402, which is preferably at least 3 times thinner than the thick functional layer 401. This makes it possible to produce a spring that is very soft in all directions, but still has good conductivity. The stiffness of the spring in a direction z perpendicular to the main extension plane (x,y) of the layer depends on the cube of the layer thickness, while the conductivity is linear to the size of the layer thickness. It is therefore possible to produce a mechanically weak but electrically highly conductive spring by using a thin spring layer and slightly wider springs. Normally, wide and soft springs require a lot of space, but in this special case, the springs can be arranged entirely or partially below the thick functional layer 401, in particular below the micromechanical structure 400, so that an enlargement of the micromechanical chip can be avoided overall or reduced to a very small additional area. The springs 600 are thus formed in an area that lies between the substrate 100 and the micromechanical structure 400.

The embodiments described above relate to out-of-plane or z-acceleration sensors, i.e. sensors whose seismic mass can be deflected perpendicular to the main plane (x, y) of the underlying substrate. However, the invention can also be used for in-plane or x, y acceleration sensors, as described in the following example.

4 shows schematically a micromechanical device according to the invention with a micromechanical structure with a first fixed electrode on a second region and a second fixed electrode on a third region of an anchor. An anchor 200 is arranged centrally on a substrate 100.

The anchor has a first region 210 and on a first side a second region 220 and a third region 230, wherein these regions are electrically insulated from one another by a trench 300 and a further trench 300' and mechanically connected to one another by filling the trenches with a dielectric material 310, namely silicon-rich nitride (SiRiN). The anchor is attached to the substrate in the first region 210. This arrangement is also found on an opposite second side of the first region.

The first region 210 is also connected to a first part of a micromechanical structure 400, a seismic mass. However, this is not shown in the figure for reasons of clarity.

The second region 220 is connected to a first fixed electrode 400''. First electrode fingers 410 of the first fixed electrode are held by an underlying plate 700, which is formed from an intermediate layer. This plate is held by beams 710, which are connected and fixed to the second region 220 of the anchor 200. The electrical connection of the electrodes is analogous to the above for the 2 B and 3 described.

The third region 230 is connected to a second fixed electrode 400'''. It has the shape of a comb and has second electrode fingers 420.

The first fixed electrode 400'' and the second fixed electrode 400''' are attached to the anchor 200 in an electrically insulated manner from each other and from the seismic mass by the SiRiN filled trenches 300, 300'.

list of reference symbols

100

substrate

101

first ground electrode

102

second bottom electrode

200

anchoring

210

first area

220

second area

230

third area

250

further anchoring

300

Dig

300'

further trench

310

dielectric material

400

micromechanical structure

400'

moving structure, seismic mass

400''

first fixed electrode

400'''

second fixed electrode

401

thick functional layer

402

thin functional layer

410

first electrode fingers

420

second electrode finger

510

first conductor track

520

second conductor track

600

Feather

700

plate

710

beam

Claims (9)

Micromechanical device with a substrate (100), with an anchor (200) and with a micromechanical structure (400, 400', 400'', 400'''), wherein the anchor is arranged and fastened on the substrate, wherein the micromechanical structure is arranged above the substrate and fastened to the anchor, characterized in that the anchor has a first region (210) which is connected to the substrate, has a second region (220) which is connected to the first region and to at least a part (400', 400'', 400''') of the micromechanical structure and the first region is electrically insulated from the second region. Micromechanical device according to claim 1 , characterized in that the first region (210) is separated from the second region (220) by a trench (300) which is filled with a dielectric material (310). Micromechanical device according to claim 2 , characterized in that the first region (210) and the second region (220) are made of silicon and the dielectric material (310) is silicon-rich nitride. Micromechanical device according to one of the Claims 1 until 3 , characterized in that the first region (210) is electrically connected to a first conductor track (510) and the second region (220) is electrically connected to a second conductor track (520). Micromechanical device according to claim 4 , characterized in that a further anchor (250) is arranged and fastened on the substrate (100), the further anchor is electrically conductively connected to the second conductor track (520) and the further anchor is electrically conductively connected to the second region (220) by means of a spring (600). Micromechanical device according to one of the Claims 2 until 5 , characterized in that the anchor (200) has a third region (230) which is electrically insulated from the second region (220). Micromechanical device according to claim 6 , characterized in that the third region (230) is separated from the second region (220) and/or from the first region (210) by a further trench (300') which is filled with a dielectric material (310). Micromechanical device according to claim 5 , characterized in that the spring (600) is arranged between the substrate (100) and the micromechanical structure (400). Micromechanical device according to claim 8 , characterized in that a thin functional layer (402) is arranged above the substrate (100) and a thick functional layer (401) is arranged above the thin functional layer, that the thin functional layer has a thickness which is less than one third of the thickness of the thick functional layer and that the spring (600) is formed in the thin functional layer.

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