A narrow and long piezoelectric MEMS micromirror

Abstract

The present invention discloses a narrow and long piezoelectric MEMS micromirror, belonging to the technical field of micro-electromechanical systems, comprising: a narrow and long mirror layer; a support column connected to the mirror layer; a driving layer, comprising a supporting platform and four piezoelectric driving arms symmetrically distributed on both sides thereof; the supporting platform is connected to the mirror layer through the support column; the piezoelectric driving arm comprises a spring, a piezoelectric driver and a deformation sensor; the piezoelectric driving arm is connected to the supporting platform through a spring; and the outer frame is connected to the side of each piezoelectric driving arm away from the corresponding spring. The present invention adopts a double-layer structure design in which the driving layer and the mirror layer are separated, and the length-to-width ratio of the upper mirror layer is large, which is particularly suitable for the application scenario of narrow and long light spots. By arranging the cantilever beam in the piezoelectric driver along a certain angle range with the X-axis direction, the piezoelectric driving arms on both sides of the supporting platform simultaneously obtain a large rotation ability around the X and Y axes, which can realize the multi-degree-of-freedom motion and large quasi-static rotation angle of the mirror layer.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-electromechanical systems, and more specifically, relates to a narrow and long piezoelectric MEMS micromirror. Background Art

[0002] MEMS micromirrors are optical devices that combine a reflector with a microactuator using MEMS technology. Microactuators can control the rotation of the mirror layer to manipulate the light beam. As one of the core devices in laser applications, micromirrors have been used in optics, telecommunications, biology, astronomy, additive manufacturing and other cutting-edge applications.

[0003] According to the working principle of the driver, MEMS micromirrors can generally be divided into four types: electromagnetic drive, electrostatic drive, thermoelectric drive and piezoelectric drive. Electromagnetic drive micromirrors use the effect of magnetic field on the current in the coil to drive the mirror layer to move; electrostatic drive micromirrors use the attraction between charges on parallel electrode plates to generate driving force, thereby achieving translation or twisting of the mirror layer; thermoelectric drive micromirrors use the property of thermal expansion of objects to drive the mirror layer to move; and piezoelectric drive micromirrors use the forward and reverse piezoelectric effect of piezoelectric materials to work, and apply a driving voltage at both ends of the piezoelectric material to induce material deformation, thereby driving the micromirror.

[0004] Among the structures of the currently proposed piezoelectric-driven MEMS micromirrors, there are few micromirrors specifically designed for narrow and long light spot scenarios, especially when the light spot has a large aspect ratio. Moreover, most of the currently proposed piezoelectric micromirrors with rectangular mirror layers can only achieve single-axis rotation of the mirror layer, and it is difficult to achieve multi-degree-of-freedom movement of the narrow and long mirror layer while ensuring a high quasi-static rotation angle. Summary of the invention

[0005] In view of the above defects or improvement needs of the prior art, the present invention provides a narrow and long piezoelectric MEMS micromirror, which aims to adopt a double-layer structure design with a separated driving layer and a mirror layer. The length-to-width ratio of the upper mirror layer is large, which is particularly suitable for application scenarios of narrow and long light spots. It can realize multi-degree-of-freedom movement and a large quasi-static rotation angle of the mirror layer, thereby solving the technical problem that the prior art is difficult to realize multi-degree-of-freedom movement of the narrow and long mirror layer while ensuring a higher quasi-static rotation angle.

[0006] To achieve the above object, according to one aspect of the present invention, a narrow and long piezoelectric MEMS micromirror is provided, comprising:

[0007] A long and narrow mirror layer;

[0008] A support column connected to the mirror layer;

[0009] The driving layer comprises a supporting platform and four piezoelectric driving arms symmetrically distributed on both sides thereof; the supporting platform is connected to the mirror layer through the supporting column; the piezoelectric driving arm comprises a spring, a deformation sensor and a piezoelectric driver connected in sequence; the piezoelectric driving arm is connected to the supporting platform through the spring;

[0010] An outer frame connected to a side of each of the piezoelectric drive arms away from the corresponding spring;

[0011] Among them, the horizontal central axis of the support platform is defined as the X-axis, the longitudinal central axis is defined as the Y-axis, and the direction perpendicular to the mirror layer is defined as the Z-axis; the cantilever beams in each of the piezoelectric drivers need to be arranged along a certain angle range with the X-axis direction to simultaneously obtain a larger rotation capability around the X-axis and around the Y-axis; by applying a set driving voltage to the piezoelectric driver, the mirror layer can be caused to rotate axially around the X-axis or the Y-axis, or to move vertically along the Z-axis.

[0012] In one embodiment,

[0013] The four piezoelectric drive arms are symmetrically arranged on the left and right sides of the support platform along the X-axis, and the two piezoelectric drive arms on the same side are symmetrical up and down along the X-axis;

[0014] The piezoelectric drive arm, minus the spring portion, is a folded beam comprising a plurality of cascaded and staggered long cantilever beams and short cantilever beams; the long cantilever beam and the short cantilever beam in each piezoelectric drive arm are parallel to each other.

[0015] In one embodiment,

[0016] Each of the long cantilever beam and the short cantilever beam is a layered structure including a substrate layer, a bottom electrode, a piezoelectric layer and a top electrode from bottom to top;

[0017] The driving voltage is input through the top electrode and the bottom electrode; and the driving effect is improved by applying driving voltages with opposite polarities to the long cantilever beam and the short cantilever beam.

[0018] In one embodiment, the material of the piezoelectric layer is AlN, Sc x Al 1-x One of N, PZT, ZnO and PMN.

[0019] In one of the embodiments, the deformation sensor includes a sensing portion and a corresponding shielding electrode;

[0020] The deformation sensor is arranged on the first cantilever beam connected to each of the piezoelectric drive arms and the spring; the feedback signal of the deformation sensor is output through the top electrode and the bottom electrode layer in the cantilever beam to which it is connected;

[0021] The shielding electrode is disposed between the sensing portion of the deformation sensor and the piezoelectric driver.

[0022] In one of the embodiments, the area covered by the top electrode is smaller than the area covered by the piezoelectric layer;

[0023] The boundary of the top electrode coverage area is determined by the principal stress distribution in each of the driving cantilever beams when the mirror layer is in a rotating state, so that the mirror layer reaches a maximum rotation angle.

[0024] In one of the embodiments, the cross-section of the support column is a waist-shaped circle, which can fit into the slot of the driving layer without slipping, thus facilitating assembly.

[0025] In one embodiment, the driving layer is completely placed under the mirror layer without exceeding the boundary range determined by the mirror layer.

[0026] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0027] 1. The present invention proposes a piezoelectric-driven MEMS micromirror capable of carrying a narrow and long mirror, which adopts a double-layer structure with a mirror layer and a driving layer separated, realizes a high duty cycle of the micromirror chip, and makes the driving structure completely located in the area directly below the mirror. In the case where the piezoelectric driving arm is completely distributed on the left and right sides of the mirror support platform, the present invention, through reasonable design, tilts a single cantilever beam in the piezoelectric driving arm relative to the transverse central axis of the driving layer, and arranges multiple cantilever beams in cascade, so that the piezoelectric driver is distributed in two directions relative to the component to be driven instead of four directions, but can also achieve the effect of four-way driving, thereby realizing the function of two-axis rotation of the mirror under the condition that the longitudinal size of the micromirror chip is strictly limited. This micromirror is particularly suitable for application scenarios of narrow and long light spots, and can realize multi-degree-of-freedom movement and large quasi-static rotation angles of the mirror.

[0028] 2. The present invention adopts the method of alternately applying voltages of opposite polarities to adjacent cantilever beams, thereby further improving the driving capability of the piezoelectric driver.

[0029] 3. The micromirror design of the present invention integrates a piezoelectric deformation sensor, which can measure the deformation of the cantilever beam, thereby achieving closed-loop control of the mirror surface rotation angle or translation displacement.

[0030] 4. Use AlN or Sc as the piezoelectric layer material x Al 1-x When N, the preparation process based on the SOI wafer of the present invention is compatible with the CMOS process, the yield is high, and the cost of large-scale preparation will be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of the overall structure of the narrow and long piezoelectric MEMS micromirror designed for the present invention;

[0032] Figure 2 A top view of the long and narrow piezoelectric MEMS micromirror driving layer designed for the present invention;

[0033] Figure 3 for Figure 2 A top view of a set of piezoelectric actuator arms in the drive layer;

[0034] Figure 4 A schematic diagram of the hierarchical structure of the narrow and long piezoelectric MEMS micromirror driving cantilever beam provided by the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] Figure 1 The overall structure of the long and narrow MEMS piezoelectric micromirror provided in this embodiment. In view of the application scenario of the long and narrow light spot, the present invention proposes a long and narrow piezoelectric MEMS micromirror, including: a mirror layer 1, a support column 2, a drive layer 3 and an outer frame 4. The mirror layer 1 includes a mirror body composed of Si and a metal film layer plated on the front thereof for increasing the reflectivity. The drive layer 3 includes a support platform, a spring, a piezoelectric driver and a deformation sensor; the mirror layer 1 and the support platform are connected up and down through the support column 2; the piezoelectric drive arm is divided into four groups, arranged on both sides of the support platform, and each group of piezoelectric drive arms is connected to the support platform through a group of springs; the end of each group of piezoelectric drive arms away from the support platform is connected to the outer frame 4, so that the three-layer structure of "mirror layer 1-support column 2-support platform" is suspended on the inner side of the outer frame 4 through the connection between the piezoelectric drive arm and the spring.

[0037] The driving layer 3 is completely placed under the mirror layer 1 without exceeding the boundary range determined by the mirror layer 1, and the mirror layer 1 can achieve a duty cycle of more than 80% of the entire micromirror (the duty cycle is equal to the ratio of the mirror layer area to the chip base area).

[0038] The micromirror provided by the present invention has a strict restriction on the longitudinal size of the structure. By arranging the cantilever beam in the piezoelectric driver along a certain angle range with the X-axis direction, a large rotation ability around the X-axis and around the Y-axis is obtained, so that the piezoelectric driving arm with a two-way distribution relative to the driven component can realize four-way driving of the mirror layer 1 while ensuring a large quasi-static rotation angle.

[0039] Specifically, the present invention adopts a double-layer structure design in which the mirror layer 1 and the driving layer 3 are separated, and the mirror layer 1 is connected to the driving layer 3 through a support column 2. The driving layer 3 is provided with four groups of piezoelectric driving arms, which are bidirectionally distributed relative to the support platform of the mirror layer. By tilting and staggering the cantilever beams in the piezoelectric driving arms, the piezoelectric driving arms can drive the mirror layer to move with multiple degrees of freedom, while ensuring a larger quasi-static rotation angle of the mirror layer.

[0040] Figure 2 It is a top view of the narrow and long MEMS piezoelectric micromirror driving layer 3 provided in this embodiment. The driving layer 3 includes a supporting platform 5 and four groups of piezoelectric driving arms 7A, 7B, 7C, and 7D. The supporting platform 5 is composed of a square in the center and connecting blocks on both sides, and is located in the center of the driving layer 3. There is an oblong through hole in the center of the supporting platform 5 for later assembly with the connecting beam 2. The piezoelectric driving arms 7A~7D are symmetrically arranged on the left and right sides of the supporting platform 5 along the longitudinal center axis of the supporting platform, and the piezoelectric driving arms on the same side are symmetrical up and down along the transverse center axis of the supporting platform 5. In the driving layer 3, a total of four groups of piezoelectric driving arms 7A~7D on the left and right sides are connected to the supporting platform 5 through transversely arranged springs 6, and the other ends of the piezoelectric driving arms 7A~7D are connected to the outer frame 4.

[0041] In one embodiment, the mirror layer 1 is a rectangular silicon block of 2mm×26mm in size, 10μm thick, and coated with a metal film layer on the front. The support column 2 is 500μm high, with a waist-shaped cross section and an arc radius of 80μm. The driving layer 3 occupies a rectangular area of ​​about 1.96mm×7.77mm, where the support platform 5 is composed of a square silicon block in the center and rectangular silicon blocks on both sides, the side length of the square in the center is 1mm, and the size of the rectangles on both sides is 0.65mm×0.31mm.

[0042] Figure 3 yes Figure 2 A top view of a group of piezoelectric drive arms in the drive layer 3 in FIG. Each group of piezoelectric drive arms is composed of a longer cantilever beam and a shorter cantilever beam alternately cascaded in sequence, excluding the spring portion. The long cantilever beam and the short cantilever beam are arranged parallel to each other, and the long and short cantilever beams are connected by a slender silicon block 12. The cantilever beams are arranged along a certain angle range with the transverse axis of the drive layer 3 (such as 30° to 60°). A special structure 8 is provided at one end of the folded beam close to the spring to facilitate connection with the spring 6, and the other end is connected to the outer frame 4. Each level of the cantilever beam includes a hierarchical structure of a substrate layer, a bottom electrode, a piezoelectric layer and a top electrode from bottom to top, wherein the top electrode does not cover the entire cantilever beam. Figure 3A schematic diagram of the structure of a piezoelectric drive arm is provided, wherein the deformation sensor includes a connection structure 8, a sensing part 9 and a shielding electrode 10; the piezoelectric driver is the part of the piezoelectric drive arm except the deformation sensor and the spring 6. In addition, the top electrode coverage areas are 9, 10, 11A, 11B, 11C, 11D, 13A, 13B, and 13C, respectively. In the top electrode coverage area, area 9 is used for deformation sensing, area 10 is a shielding electrode, and the rest is used for mirror layer driving. The electrical signal of the piezoelectric drive cantilever beam is input through the top electrode and the bottom electrode.

[0043] In one embodiment, a voltage of the same polarity is applied to the upper electrodes 11A to 11D of the long cantilever beam, and a voltage of opposite polarity to the upper electrodes 11A to 11D is applied to the upper electrodes 13A to 13C of the short cantilever beam, and the lower electrodes are uniformly grounded, so that the angular displacements of the ends of the cascaded piezoelectric cantilever beams can be superimposed, thereby improving the driving effect.

[0044] The deformation sensor structure used in the present invention is a "sandwich" structure of bottom electrode-piezoelectric layer-top electrode, which uses the positive piezoelectric effect for sensing. When the piezoelectric cantilever beam is pressurized to drive the mirror layer 1 to rotate, stress will be generated in the piezoelectric cantilever beam, thereby generating charges in the deformation sensing area, and the amount of charge is proportional to the stress of the piezoelectric cantilever beam, thereby reflecting the rotation angle or translational displacement information of the reflective mirror layer. By detecting the amount of charge generated, the deformation information of the cantilever beam can be obtained, and its feedback electrical signal is output through the top electrode and bottom electrode of the deformation sensor. In order to ensure the insulation effect, a shielding top electrode 10 is set to avoid crosstalk between the signals of the driving part and the sensing part, which affects the measurement of the deformation size of the cantilever beam.

[0045] In one embodiment, a piezoelectric film material is deposited in the driving layer 3. Preferably, the piezoelectric film material can be AlN, Sc x Al 1-x N, PZT, ZnO, PMN and other piezoelectric materials.

[0046] In one embodiment, the material of the top electrode and the bottom electrode in the piezoelectric driving arm is Pt or Mo.

[0047] Figure 4 1 is a schematic diagram of the hierarchical structure of the narrow MEMS piezoelectric micromirror driving cantilever beam provided in this embodiment, which includes, from bottom to top, a silicon substrate layer 14, a bottom electrode 15, a piezoelectric layer 16, and a top electrode 17. Preferably, the thickness of the silicon substrate 14 and the piezoelectric layer 16 are 10 μm and 1 μm, respectively.

[0048] The present embodiment is simulated and calculated by finite element simulation software. When the piezoelectric film material is AlN and the pressure at both ends of the piezoelectric layer is 120V, DCWhen the mirror layer is replaced by Sc, the static rotation angles of the mirror layer around the X and Y axes can be 6.72° and 5.16° respectively, and the translation displacement along the Z axis can be 111.84μm. 0.15 Al 0.85 N, the mirror layer can achieve static rotation angles of 11.13° and 8.46° around the X and Y axes respectively, and a translational displacement of 186.36μm along the Z axis.

[0049] In summary, the micromirror structure designed by the present invention has a relatively large length and width ratio and is a long and narrow rectangle, which is particularly suitable for application scenarios of long and narrow light spots. The micromirror structure of the present invention adopts a double-layer structure in which the mirror layer 1 and the drive layer 3 are separated, which can achieve a larger chip duty cycle. The support platform directly connected to the driving cantilever beam is very small compared to the mirror layer. Compared with the micromirror structure in which the mirror layer and the driver are in the same layer of material, the double-layer structure of the present invention can achieve the effect of angle magnification, and obtain a larger quasi-static rotation angle of the mirror layer when the cantilever beam produces the same displacement. Through the reasonable design of the cantilever beam structure of the driving layer 3, the piezoelectric driving arms distributed on both sides of the support platform can realize the multi-degree-of-freedom movement of the entire mirror layer, including rotation around the X and Y axes and translation along the Z axis. At the same time, the deformation sensing component is also integrated in the driving layer 3, which can realize closed-loop control of the mirror layer angle or translation displacement.

[0050] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A narrow and long piezoelectric MEMS micromirror, characterized in that: include: A long and narrow mirror layer; A support column connected to the mirror layer; A driving layer, comprising a supporting platform and four piezoelectric driving arms symmetrically distributed on both sides thereof; The support platform is connected to the mirror layer through the support column; the piezoelectric drive arm includes a spring, a deformation sensor and a piezoelectric driver connected in sequence; The piezoelectric drive arm is connected to the support platform via the spring; An outer frame connected to a side of each of the piezoelectric drive arms away from the corresponding spring; The horizontal central axis of the support platform is defined as the X-axis, the longitudinal central axis is defined as the Y-axis, and the direction perpendicular to the mirror layer is defined as the Z-axis; the cantilever beams in each of the piezoelectric drivers need to be arranged along a certain angle range with the X-axis direction to simultaneously obtain greater rotation capabilities around the X-axis and around the Y-axis; by applying a set driving voltage to at least one of the piezoelectric drivers, the mirror layer can be rotated axially around the X-axis or the Y-axis, or translated up and down along the Z-axis; The four piezoelectric drive arms are symmetrically arranged on the left and right sides of the support platform along the X-axis, and the two piezoelectric drive arms on the same side are symmetrical up and down along the X-axis; the piezoelectric driver is a folded beam, including a plurality of cascaded and staggered long cantilever beams and short cantilever beams, and the long cantilever beam and the short cantilever beam in each piezoelectric drive arm are parallel to each other; Each of the long cantilever beam and the short cantilever beam is a hierarchical structure including a substrate layer, a bottom electrode, a piezoelectric layer and a top electrode from bottom to top; the driving voltage is input through the top electrode and the bottom electrode; and the driving effect is improved by applying driving voltages of opposite polarities to the long cantilever beam and the short cantilever beam.

2. The elongated piezoelectric MEMS micromirror as claimed in claim 1, characterized in that: The material of the piezoelectric layer is AlN, Sc x Al 1-x One of N, PZT, ZnO and PMN.

3. The elongated piezoelectric MEMS micromirror according to claim 1, characterized in that: The deformation sensor comprises a sensing portion and a corresponding shielding electrode; The deformation sensor is arranged on the first cantilever beam at one end of each piezoelectric driving arm connected to the spring; the feedback signal of the deformation sensor is output through the top electrode and the bottom electrode layer in the cantilever beam to which it is connected; The shielding electrode is disposed between the sensing portion of the deformation sensor and the piezoelectric driver.

4. The elongated piezoelectric MEMS micromirror according to claim 1, characterized in that: The area covered by the top electrode is smaller than the area covered by the piezoelectric layer; The boundary of the top electrode coverage area is determined by the principal stress distribution in each of the cantilever beams when the mirror layer is in a rotating state, so that the mirror layer reaches a maximum rotation angle.

5. The elongated piezoelectric MEMS micromirror according to any one of claims 1 to 4, characterized in that: The cross-sectional shape of the support column is a waist circle, which can fit into the slot of the driving layer without slipping, thus facilitating assembly.

6. The elongated piezoelectric MEMS micromirror according to any one of claims 1 to 4, characterized in that: The driving layer is completely placed under the mirror layer without exceeding the boundary range determined by the mirror layer.

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