CN1483660A - A Micro Piezoelectric Actuator for MEMS - Google Patents

Abstract

The invention discloses a micro piezoelectric driver for MEMS which can produce large deflection angle and vertical displacement and belongs to the field of micro-electronic machinery. The driver structure is a suspended folded piezoelectric composite multilayer film elastic driving arm, which has at least two or more parallel piezoelectric driving arms, and the driving arms on both sides of the suspended structure are connected to the substrate. Each segment of the piezoelectric composite multilayer elastic driving arm contains the elastic layer and the piezoelectric composite film on it. When the opposite polarity driving voltage is applied to the upper and lower electrodes of the piezoelectric film on the adjacent parallel different driving arms, Adjacent sections of piezoelectric driving arms that are paralleled bend in opposite directions. Due to the connection mode of the folded structure, the driving arm located in the middle of the suspension structure has the largest vertical displacement or deflection angle. The invention can reduce the length of the driving structure in the micro-electric mechanical system, and has greater driving force. It has the advantages of simple structure, high device reliability, simple process, easy processing, high manufacturing yield, and is suitable for mass production. It is of great value in various microelectromechanical devices and systems.

Description

A Micro Piezoelectric Actuator for MEMS

technical field

The invention belongs to the field of micro-electronic machinery, in particular to a micro piezoelectric driver for MEMS.

Background technique

Micro Electro Mechanical System (MicroElectroMachanical System), referred to as MEMS. It is the cutting-edge science in high-tech fields such as miniaturization, integration, intelligence, informatization, and advanced manufacturing. MEMS is based on advanced semiconductor technology and integrated circuit manufacturing technology, which broadens the method of manufacturing complex electromechanical systems on microchips. These methods combine the large-scale integrated circuit manufacturing technology and the unique special process of micromachining technology, and integrate micromechanical structures, microactuators, microelectronic devices and circuit systems to form a so-called system on chip (SOC). The entire MEMS involves many disciplines from design to manufacture, as well as computer technology, communication technology, microelectronics technology, automatic control technology, mechanical design and manufacturing and other technical disciplines. It can be said to be a multidisciplinary comprehensive technology. The products involved mainly include complex microsystems such as microsensors, microactuators, microoptical systems, RF radio frequency systems, microbial chips, microfluidic devices, and three-dimensional integrated circuits. Quite a number of MEMS commercial products have appeared. Widely used in industry, military, biology, medicine and other industries.

At present, MEMS devices are driven by electrostatic, electromagnetic, thermal, piezoelectric and other principles. Most of the existing micro-execution structures using these principles have a large driver size and occupy a large chip area, but the realized driving displacement and deflection are limited, the manufacturing process is complicated, the reliability is not high, the power consumption is large, and the life is short . Most of the MEMS piezoelectric film drive methods that have been widely studied use a cantilever beam structure. Due to the limited elongation of the piezoelectric film, the maximum deflection displacement on the cantilever beam structure is very limited. This characteristic limits the piezoelectric drive method. The wide application in the field of MEMS has resulted in the emergence of very few mature MEMS commercial devices driven by piezoelectric thin films. To achieve large vertical displacement or deflection of this kind of cantilever driving structure, it is required to lengthen the length of the beam and increase the driving voltage, which increases the static deflection of the cantilever beam caused by gravity on the one hand, so that when no voltage is applied, the cantilever will have The large deflection displacement seriously limits its application range. On the other hand, this long straight cantilever beam drive structure significantly reduces the mechanical strength of the drive, which is prone to vibration during work and is extremely vulnerable to impact and breakage. In addition, this long single cantilever drive structure increases the inertial influence of the cantilever itself, which reduces the operating frequency of the drive and is not suitable for many applications with high operating frequency. At the same time, a large driving voltage can easily cause breakdown of the piezoelectric film, which puts higher requirements on the quality of the piezoelectric film and increases the difficulty of the piezoelectric film deposition process. This brings many additional effects to the piezoelectric film and increases the complexity of the corresponding electronic circuit. And in terms of manufacturing, the complexity of manufacturing is significantly increased, the yield of micromachining is reduced, and the length of the driver is too long, which also makes it difficult to adapt to the application in some microstructure devices or device arrays. These severely limit the application of cantilever piezoelectric actuators in microelectromechanical devices and systems.

Contents of the invention

The object of the present invention is to provide a micro piezoelectric actuator for MEMS, which is characterized in that: the micro piezoelectric actuator adopts a folded multi-stage piezoelectric composite multilayer elastic suspension film structure, that is, it is formed by an elastic structure layer. The folded side-by-side arms of each folded arm are covered from bottom to top with a buffer layer, a lower film electrode layer that is not connected to each other, a piezoelectric film layer with a certain shape, and an upper film electrode layer. , a layer of insulating dielectric layer can also be covered on the surface of the upper electrode film layer; a driving arm using piezoelectric effect is formed on each folded arm, and one or both sides of the driving arm are connected to the substrate as a fixed end; and Driving voltages of opposite polarities are applied to the upper and lower electrodes of the piezoelectric films on different adjacent parallel driving arms, which are used to make the adjacent driving arms elongate due to the transverse elongation effect of the piezoelectric film, but the whole is composed of piezoelectric composite multiple The driving arm made of a layer of thin film material can only bend along with the elongation of the piezoelectric film, resulting in the bending of each driving arm. Since the voltage applied to the adjacent driving arms is opposite, the adjacent driving arms deflect in the opposite direction. . The maximum vertical displacement is generated at the end of each driving arm, and the vertical driving displacement and deflection angle are superimposed step by step in the direction away from the fixed end, so that a larger vertical displacement can be obtained at a lower applied voltage; when the applied voltage is removed Finally, due to the elastic material contained in the folded suspension driving arm, the driving arm returns to its original shape under the action of elastic force.

The folded piezoelectric composite multilayer film elastic suspension drive arm is divided into a form with two fixed ends and a form with only one fixed end, and can form an axisymmetric structure or a central symmetric structure.

The number of parallel driving arms may be an integer equal to or greater than two.

The piezoelectric film is a piezoelectric material in PZT, PLZT, ZnO, AlN, PVDF, or a multilayer piezoelectric film composed of more than one piezoelectric material, or a piezoelectric film and a pre-deposited piezoelectric film. Composite membrane with electron seed layer.

The folded elastic film is monocrystalline silicon, polycrystalline silicon, silicon dioxide, amorphous silicon, silicon nitride, or a composite film of more than one elastic material.

The beneficial effect of the invention is that a large vertical displacement or deflection drive is realized by adopting a folded piezoelectric composite multi-layer elastic suspension drive arm. The length of the driver is shortened, so that it can greatly save the device area in some applications; the driving voltage is reduced; the operating frequency of the driver is increased, and it has good device driving performance. At the same time, it has simple structure, high device reliability, simple process, easy processing, high manufacturing yield, and is suitable for mass production.

Description of drawings:

Figure 1 is a cross-sectional view of a suspended folded piezoelectric composite multilayer elastic driving arm.

Fig. 2 is a schematic diagram of an axisymmetric driving structure of three driving arms.

Fig. 3 is a schematic diagram of an axisymmetric driving structure of four driving arms.

Fig. 4 is a schematic diagram of an axisymmetric driving structure with five driving arms.

Fig. 5 is a schematic diagram of a centrosymmetric driving structure with two driving arms.

Fig. 6 is a schematic diagram of an asymmetric driving structure with two driving arms.

Detailed ways

The invention is a micro piezoelectric driver for MEMS. The micro-piezoelectric driver adopts a folded multi-stage piezoelectric composite multi-layer elastic suspended film structure, that is, a continuous folded parallel arm 9 is formed on the substrate silicon chip 1, and each arm 9 is formed from the elastic silicon substrate layer 1. Covered with a buffer layer 4 from bottom to top, a lower film electrode layer 5 that is not connected to each other, a piezoelectric film 6 with a certain shape, and an upper film electrode layer 7 are compositely stacked, and an insulating dielectric layer 8 can also be covered on the upper electrode film. 7 surfaces; the lower thin-film electrode layer 5 is connected to the lower electrode lead 2, and the upper thin-film electrode layer 7 is connected to the upper electrode lead 3 (as shown in Figure 1); on each section of the folded arm, a driving force utilizing the piezoelectric effect is formed. One side or both sides of the driving structure is connected to the substrate as a fixed end; and the opposite polarity driving voltage is applied to the upper and lower electrodes of the piezoelectric film on different adjacent parallel driving arms, so that the adjacent driving arms are due to The transverse elongation effect of the piezoelectric film elongates, but the entire driving arm composed of piezoelectric composite multi-layer film material can only bend along with the elongation of the piezoelectric film, resulting in the bending of each driving arm, Since the voltages applied to the adjacent driving arms are opposite, the adjacent driving arms deflect in opposite directions. The maximum vertical displacement is generated at the end of each driving arm, and the vertical driving displacement and deflection angle are superimposed step by step in the direction away from the fixed end, so that a larger vertical displacement can be obtained at a lower applied voltage. When the applied voltage is removed, since the folded suspension driving arm contains elastic material, the driving arm returns to its original shape under the action of elastic force.

The above-mentioned folded piezoelectric composite multi-layer elastic suspension drive arm is divided into a form with two fixed ends and a form with only one fixed end, and can form an axisymmetric structure or a centrosymmetric structure. The number of parallel driving arms may be equal to or greater than two (as shown in FIG. 2 , FIG. 3 , FIG. 4 , FIG. 5 , and FIG. 6 ).

The piezoelectric film is a piezoelectric material in PZT, PLZT, ZnO, AlN, PVDF, or a multilayer piezoelectric film composed of more than one piezoelectric material, or a piezoelectric film and a pre-deposited piezoelectric film. Composite membrane with electron seed layer.

The folded elastic film is monocrystalline silicon, polycrystalline silicon, silicon dioxide, amorphous silicon, silicon nitride, or a composite film of more than one elastic material.

There are many techniques for realizing the miniature piezoelectric driving structure of this patent. The following describes only one of the method flow for illustration: first use double-sided polishing substrate silicon wafer 1, deposit silicon nitride after double-sided thermal oxidation, and photolithographic structure window on the back, etch away silicon nitride, and float away the exposed Thermal oxide layer, use anisotropic etching solution such as KOH or TMAH to etch the bulk silicon to form a silicon film, then remove the silicon nitride and thermal oxide layers on both sides, and re-grow a thermal oxide film of appropriate thickness as a buffer layer 4, on the front Carry out the manufacturing process of PZT (lead zirconate titanate) composite multilayer film, deposit the lower electrode layer 5, the piezoelectric film 6, and the upper electrode layer 7 sequentially on the front, and use physical or chemical etching technology to etch the upper electrode layer in sequence. The electrode 3, the lower electrode 2 and the buffer layer 4 are finally deposited with an insulating dielectric film 8, and then the lead holes of the upper and lower electrodes are etched by a physical or chemical etching process, metal is deposited and the wiring is etched. Then photolithography and anisotropic etching process are used to etch the silicon film to release the suspended structure and form the driving structure. In this method example, the lower electrode is composed of a titanium/platinum composite layer, the piezoelectric film is composed of a piezoelectric seed layer PbTiO ₃ and a PZT composite layer, and the upper electrode is composed of titanium/platinum or platinum.

In other implementation examples of this structure, the piezoelectric film can also be made of other materials, such as various piezoelectric materials such as PLZT, ZnO, AlN, PVDF, etc., or composite multilayer piezoelectric films composed of multiple piezoelectric materials and deposited Piezoelectric materials or pre-deposited related piezoelectric seed layers to improve the performance of piezoelectric materials. The folded elastic film material may also be various other elastic materials, such as monocrystalline silicon, polycrystalline silicon, silicon dioxide, amorphous silicon, silicon nitride, or composite multilayer films of various elastic materials. This structure can be realized by combining MEMS surface micromachining technology and MEMS body processing technology.

Claims (5)

1. miniature piezoelectric driver that is used for MEMS, it is characterized in that: described miniature piezoelectric driver adopts folding shape multi-stage rotary piezoelectricity composite multi-layer elasticity suspending film structure, promptly be to form continuous folding shape arm arranged side by side by the elastic construction substrate layer, be coated with resilient coating, mutual unconnected following mea layers, piezoelectric thin film layer and upper film electrode layer complex superposition on the elastic film substrate layer of each arm from bottom to up and form, can also cover one deck insulating medium layer at the upper electrode film laminar surface with definite shape; Formed the actuating arm that utilizes piezoelectric effect on every section folding arm, the one or both sides and the substrate of whole Drive Structure are connected to stiff end; And the upper and lower electrode of the piezoelectric membrane on contiguous parallel different driving arm applies the opposite polarity driving voltage; Be used to make contiguous actuating arm owing to the transverse extension effect of piezoelectric membrane is extended, but the whole actuating arm that is made of piezoelectricity composite multi-layer thin-film material can only be accompanied by the elongation of piezoelectric membrane and bend, thereby cause the bending of each actuating arm, because adjacent driven arm institute making alive is opposite, therefore adjacent driven arm deflection round about, end at each actuating arm produces the maximum perpendicular displacement, and vertical drive displacement and deflection angle superpose step by step to the direction away from stiff end, thereby can obtain bigger vertical displacement under lower applied voltage; Behind the making alive, because folding shape suspension Drive Structure contains elastomeric material, Drive Structure restores to the original state again under resilient force when removing.

2. according to the described miniature piezoelectric driver that is used for MEMS of claim 1, it is characterized in that: described folding shape piezoelectricity composite multilayer membrane flexible drive arm is divided into a kind ofly has two stiff ends and the another kind of form of having only a stiff end, and can form axially symmetric structure or form centrosymmetric structure.

3. according to the described miniature piezoelectric driver that is used for MEMS of claim 1, it is characterized in that: the number of described actuating arm arranged side by side can be for being equal to or greater than two integer.

4. according to the described miniature piezoelectric driver that is used for MEMS of claim 1, it is characterized in that: the piezoelectric membrane of stating is a kind of piezoelectric among PZT, PLZT, ZnO, AlN, the PVDF or the composite membrane that is combined into the piezoelectricity Seed Layer of multi-layer piezoelectric film or piezoelectric membrane and deposit in advance by more than one piezoelectric.

5. according to the described miniature piezoelectric driver that is used for MEMS of claim 1, it is characterized in that: described folding shape elastic film is the compound tunic of monocrystalline silicon, polysilicon, silicon dioxide, amorphous silicon, silicon nitride or more than one elastomeric materials.

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