CN113281898B

CN113281898B - MEMS micro-mirror unit and MEMS micro-mirror array

Info

Publication number: CN113281898B
Application number: CN202110571642.7A
Authority: CN
Inventors: 武震宇; 汪洋; 张�浩; 王栎皓; 姜新泉
Original assignee: Shanghai Institute of Microsystem and Information Technology of CAS
Current assignee: Shanghai Institute of Microsystem and Information Technology of CAS
Priority date: 2021-05-25
Filing date: 2021-05-25
Publication date: 2022-08-05
Anticipated expiration: 2041-05-25
Also published as: CN113281898A

Abstract

The present invention provides a MEMS micro-mirror unit, comprising: the mirror layer comprises a mirror and a plurality of flexible mechanical structures arranged on the back of the mirror; an actuator layer comprising three actuators arranged in a cross, each actuator being arranged in pair with each flexible mechanical structure of the mirror layer and being coupled to the respective flexible mechanical structure by a coupling post, the actuators being for powering the mirror layer by the coupling posts and the flexible mechanical structures; and a lead layer. The invention also provides a MEMS micro-mirror array, which comprises a plurality of MEMS micro-mirror units arranged in a close-packed mode. The MEMS micro-mirror unit provided by the invention can realize accurate adjustment of three degrees of freedom, and the control mode is flexible; the micro mirror array comprising the MEMS micro mirror unit has high duty ratio and high-consistency mirror surface performance.

Description

MEMS micro-mirror unit and MEMS micro-mirror array

Technical Field

The invention relates to an MEMS micro-mirror unit and an MEMS micro-mirror array comprising the same; and more particularly, to a piezoelectric driven MEMS micro-mirror array for fast laser scanning.

Background

The MEMS micro-mirror is a chip-scale optical device manufactured based on a micro-machining process, and is widely used in various fields such as a confocal laser scanning microscope, a laser radar, a laser projection, a laser process, an MEMS optical switch, a spatial light modulator, etc., as one of key elements for fast laser scanning and phase modulation.

The MEMS micromirror array can be divided into a two-dimensional array, a one-dimensional array, and a zero-dimensional unit according to the dimension of the array, wherein a micromirror formed by tiling a multi-element micromirror array on a two-dimensional plane is called a two-dimensional array, a micromirror formed by tiling a micromirror array on a one-dimensional straight line is called a one-dimensional array, and a zero-dimensional unit is a micromirror including only a single micromirror unit. The MEMS micro-mirror array can be generally classified into four types, i.e., electrostatic driving, electromagnetic driving, electrothermal driving, and piezoelectric driving, according to the operating principle of the actuator. The electrostatic driving mode generally adopts voltage applied between parallel plate electrodes or comb teeth electrodes to generate electrostatic driving force, the electromagnetic driving mode generally utilizes the Lorentz force borne by a current coil in a magnetic field as driving force, the electrothermal driving mode generally adopts a local heating mode to cause the expansion or contraction of materials to drive a micromirror to move, and the piezoelectric driving mode utilizes piezoelectric materials with inverse piezoelectric effect, and the driving voltage is applied on two sides of the piezoelectric materials to cause the material strain, so that the driving force is generated.

The micromirrors can be classified into digital micromirrors, analog micromirrors, and resonant micromirrors according to their control modes. The digital micromirror generally has only two states of on and off, the analog micromirror can perform continuous and quasi-static motion control, the resonant micromirror works near the resonance point of the mechanical structure, the frequency of the resonant micromirror depends on the structure of the micromirror, and the resonant micromirror has a high resonance factor.

Conventionally, MEMS micromirrors control the deflection of the reflected beam by micro-scale mirror twisting, which typically involves three degrees of freedom, lateral tilting, longitudinal tilting, up-down translation, or one or two of them. Furthermore, the mirror may also include other degrees of freedom, such as torsional degrees of freedom, which are not generally referred to in the MEMS art, nor are they within the scope of the present patent discussion.

The MEMS micro-mirror for rapid laser scanning has the advantages of high scanning speed, compact structure, suitability for mass manufacturing and the like, and has urgent requirements on large-aperture laser beam control in applications such as a laser confocal scanning microscope, a laser radar, laser projection and the like.

Disclosure of Invention

In view of the above disadvantages of the prior art, an object of the present invention is to provide a MEMS micro-mirror unit and a micro-mirror array including the same, which are used to solve the problems of low operating frequency and small deflection angle of the single-mirror MEMS micro-mirror in the prior art due to the excessive mass and rotational inertia; and the problems of low duty ratio, poor consistency, complex control and the like in the existing micro-mirror array.

To achieve the above and other related objects, the present invention provides a MEMS micro-mirror unit, comprising: the mirror layer comprises a mirror and a plurality of flexible mechanical structures arranged on the back of the mirror; an actuator layer comprising three actuators arranged in a cross, each actuator being arranged in pair with each flexible mechanical structure of the mirror layer and being coupled to the respective flexible mechanical structure by a coupling post, the actuators being for powering the mirror layer by the coupling posts and the flexible mechanical structures; and the lead layers are fixedly coupled with each actuator in the actuator layers respectively so as to play a role in mechanical support and electrical connection for the actuator layers.

Preferably, the backside of the mirror layer comprises three flexible mechanical structures, which are coupled to three cross-distributed actuators via coupling posts, respectively.

Preferably, the mirror layer is axially rotatable about an X-axis or a Y-axis.

Preferably, the mirror layer is translatable up and down along the Z-axis, the resulting displacement allowing phase modulation of the beam in a particular area.

Preferably, adjacent actuators in the actuator layer have a phase difference of 120 ° between them, the actuator layer providing a tangential driving force to cause a circular motion of the mirror about its central axis.

Preferably, each actuator comprises a movable part and a fixed part.

Preferably, the movable part is connected to the flexible mechanical structure of the mirror layer by at least one coupling post, and the fixed part is connected to the lead layer.

Preferably, a piezoelectric thin film material is disposed on a surface of the actuator, and the piezoelectric thin film material deforms when a voltage is applied to provide the driving force.

Preferably, the piezoelectric thin film material comprises one of PZT, AlN and AlScN, and the thickness of the piezoelectric thin film material is 0.5 to 5 micrometers.

Preferably, the fixed portion of the actuator and the lead layer are bonded through a bonding layer.

Preferably, the lead layer includes a Through Silicon Via (TSV) structure for providing electrical connections to the actuator layer.

Preferably, the lead layer further includes a wiring layer for rewiring the electrode lead-out portion.

Preferably, the flexible mechanical structure comprises a fixing part, and two sides of the fixing part are respectively connected with the mirror layer through elastic parts.

Preferably, the back of the mirror layer has a groove portion, and the flexible mechanical structure is disposed in the groove portion.

Preferably, the elastic piece is fixedly connected with the side wall of the groove part; the side wall of the groove part is provided with a connecting part which protrudes outwards, and the elastic part is fixedly connected with the connecting part.

In another aspect, the present invention provides a MEMS micro-mirror array, which comprises a plurality of the MEMS micro-mirror units arranged in a close-packed manner.

Preferably, the MEMS micro-mirror array comprises a plurality of hexagonal mirror layers extending in a close-packed manner along the XY plane.

As described above, the MEMS micro-mirror unit of the present invention has the following advantageous effects:

the invention can realize the rotation of the mirror surface in two directions and the up-and-down translation of the mirror surface by controlling the electric signals of the actuator, thereby realizing the accurate adjustment of three degrees of freedom and flexible control mode.

The MEMS micro-mirror array comprises a plurality of MEMS micro-mirror units which are arranged in a close-packed mode, wherein a plurality of hexagonal mirror layers are expanded along an XY plane in the close-packed mode, so that the MEMS micro-mirror array has the characteristics of compact structure and high duty ratio; the MEMS micro-nano processing technology can be used for preparing a device with high consistency, and the mirror surface performance with high consistency can be obtained, so that the expansion of the optical aperture can be realized under the condition of not influencing the parameters such as vibration frequency, deflection angle and the like, and the rapid control of a large-aperture laser beam can be realized.

Drawings

Fig. 1 is a schematic diagram showing the overall structure of a single MEMS micro-mirror unit according to an embodiment of the present invention.

Fig. 2 is a schematic diagram of the backside of the mirror layer of a single MEMS micro-mirror unit according to an embodiment of the invention.

Fig. 3 is a schematic diagram illustrating a partial structure of a single MEMS micro-mirror unit according to an embodiment of the present invention.

FIG. 4 is a schematic plan view of a MEMS micro mirror array according to an embodiment of the invention.

Description of the element reference numerals

100 mirror layer

101 mirror surface reinforced structure

102 space of activity

103A first flexible mechanical structure

103B second flexible mechanical structure

103C third flexible mechanical structure

200 actuator layer

201A first coupling column

201B second coupling column

201C third coupling column

202A first actuator

202B second actuator

202C third actuator

300 lead layer

301 actuating cavity

302 bonding layer

303 silicon through hole structure

304 routing layer

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.

It should be understood that the structures, ratios, sizes, etc. shown in the drawings and attached to the description are only for understanding and reading the disclosure of the present invention, and are not intended to limit the practical conditions of the present invention, so that the present invention has no technical significance, and any modifications of the structures, changes of the ratio relationships, or adjustments of the sizes, should still fall within the scope of the technical contents of the present invention without affecting the efficacy and the achievable purpose of the present invention. In addition, the terms "upper", "lower", "left", "right", "middle" and "one" used in the present specification are for clarity of description, and are not intended to limit the scope of the present invention, and the relative relationship between the terms and the terms is not to be construed as a scope of the present invention.

In order to reduce diffraction effect in the light beam reflection process or improve the optical aperture, the MEMS micro-mirror needs a large mirror size, but the large mirror size limits the operating frequency and deflection angle of the micro-mirror, and the micro-mirror with an oversized mirror is also difficult to process in batch by the MEMS process. Generally, the size of a single mirror is better in millimeter level, and for the mirror over centimeter level, the problems of low working frequency and small deflection angle exist because the mass and the moment of inertia of the mirror are too large. To address this problem, it is an ideal way to use a single-mirror MEMS micromirror instead of a micromirror array, however, the two-dimensional or one-dimensional MEMS micromirror array is adopted, and the following problems of low duty cycle, poor consistency, and complicated control are challenges faced by the existing micromirror array.

To solve the problems of the prior art, the present invention provides a high duty cycle piezo-actuated micromirror array that can operate in an analog mode or a resonant mode, having a number of technical advantages.

Specifically, the technical scheme adopted by the invention is as follows: the MEMS micro-mirror array is adopted to realize the control of the high-speed deflection of the light beam, the MEMS micro-mirror array comprises at least one micro-mirror unit, the micro-mirror unit adopts a hexagonal mirror surface structure in the plane direction, the hexagonal mirror surface structure is densely stacked and expanded in a two-dimensional space, and the MEMS micro-mirror array with high duty ratio can be obtained. According to the invention, the high-frequency high-duty-ratio MEMS micro-mirror array sequentially comprises a mirror layer, an actuator layer and a lead layer from top to bottom along the direction vertical to the mirror surface, the actuator layer is coupled with the mirror layer by adopting a flexible mechanical structure, and the flexible mechanical structure can reduce stress while the mirror surface generates larger torsional displacement; each mirror surface is controlled by three independent hidden actuators, the actuators realize electrode leading-out through a lead layer with a TSV structure, and meanwhile, the lead layer plays a role in mechanical support of the actuator layer. By the mode, the problems of small mirror surface size and low scanning frequency of the MEMS micro-mirror can be solved, the MEMS micro-mirror array with high frequency and high duty ratio in an optical system is obtained, and meanwhile, the rapid control of large-aperture laser beams is realized.

Referring to fig. 1 to 3, the present invention provides a MEMS micro-mirror unit, which is particularly suitable for fast three-dimensional scanning imaging of a confocal laser scanning microscope.

Referring to fig. 1, an overall structure of a single MEMS micro-mirror unit according to an embodiment of the present invention is shown. The present invention provides a MEMS micro-mirror unit, which comprises a mirror layer 100, an actuator layer 200, and a wiring layer 300 in order from top to bottom in a vertical direction of a mirror surface. In an embodiment, the front side of the mirror layer 100 is coated with a reflective coating to achieve deflection of the laser beam by specular reflection. The back of the mirror layer 100 may have a flexible mechanical structure, in this embodiment, the flexible mechanical structure includes a first flexible mechanical structure 103A, a second flexible mechanical structure 103B, and a third flexible mechanical structure 103C, and the mirror layer 100 and the driver layer 200 are coupled by using the flexible mechanical structure, so that the stress borne by the mirror layer 100 when the mirror layer is driven to generate a large-angle torsion is reduced. The backside of the mirror layer 100 further comprises a recessed portion in which the first flexible mechanical structure 103A, the second flexible mechanical structure 103B and the third flexible mechanical structure 103C are disposed, as shown in fig. 2. The recessed portion defines an active space 102 that provides space for movement of the first flexible mechanical structure 103A, the second flexible mechanical structure 103B, and the third flexible mechanical structure 103C.

In one embodiment, each of the first flexible mechanical structure 103A, the second flexible mechanical structure 103B, and the third flexible mechanical structure 103C includes an elastic member, which may be directly connected to a sidewall of the recessed portion for fixation in one embodiment; in another embodiment, the elastic member may also be fixedly connected to the side wall of the recessed portion through a connecting portion protruding outward, and the position of the flexible mechanical structure may be flexibly adjusted by adjusting the shape and size of the connecting portion to meet different application requirements. Each of the first flexible mechanical structure 103A, the second flexible mechanical structure 103B, and the third flexible mechanical structure 103C may further include a fixing portion. The mirror layer 100 further comprises a mirror reinforcing structure 101 provided on the back.

In the present embodiment, a piezoelectric thin film material is deposited on the surface of the actuator layer 200, and preferably, the piezoelectric thin film material may be a commonly used piezoelectric material known to those skilled in the art, which includes but is not limited to: PZT, AlN, or AlScN. In some embodiments, the piezoelectric thin film material has a thickness of 0.5 to 5 microns. The piezoelectric film material can provide driving force by deformation generated by applying voltage to electrodes on two sides of the film. In addition, the actuator layer 200 includes a first actuator 202A, a second actuator 202B, and a third actuator 202C, which are arranged periodically, for example, in a cross arrangement. The actuator layer 200 includes a first coupling pillar 201A, a second coupling pillar 201B, and a third coupling pillar 201C, and the first actuator 202A, the second actuator 202B, and the third actuator 202C are respectively connected to the flexible mechanical structure of the mirror layer 100 through the first coupling pillar 201A, the second coupling pillar 201B, and the third coupling pillar 201C, for example, the first actuator 202A, the second actuator 202B, and the third actuator 202C may be respectively connected to the fixing portion of the flexible mechanical structure through the first coupling pillar 201A, the second coupling pillar 201B, and the third coupling pillar 201C, and the connection manner of the first coupling pillar 201A, the second coupling pillar 201B, and the third coupling pillar 201C and the fixing portion may be, for example, a snap-fit, so that the power provided by the driver is transmitted to the mirror layer 100 through the coupling pillars and the flexible mechanical structure, resulting in the rotation of the mirror layer 100. Wherein, below the mirror layer 100, a first actuator 202A is arranged in pairs with the first flexible mechanical structure 103A, a second actuator 202B is arranged in pairs with the second flexible mechanical structure 103B, and a third actuator 202C is arranged in pairs with the third flexible mechanical structure 103C. Fig. 3 is a schematic diagram of a partial structure of a single MEMS micro-mirror unit after removing the mirror layer, and the first actuator 202A, the second actuator 202B and the third actuator 202C may be three diamond-shaped actuators, each of which may be hidden under the mirror layer 100 and includes a movable part and a fixed part. The movable part may be coupled to the mirror layer 100 by a fixed part of the flexible mechanical structure. The mechanical force due to the application of a voltage to the piezoelectric film material of the actuator layer 200 may provide an actuation torque to the movable portion of the first actuator 202A, thereby rotating the actuator 202A about the R direction; while no electrical stimulus is applied to the second actuator 202B and the third actuator 202C, causing the mirror layer 100 to deflect about R1.

In one embodiment, voltages can be applied to the first actuator 202A, the second actuator 202B and the third actuator 202C, respectively, and since each unit is controlled by three independent actuators, precise adjustability in three degrees of freedom, i.e., flipping along the x-axis, flipping along the y-axis, translational movement along the z-axis, can be achieved, such that the beam can scan a specific area in rows and columns. In some embodiments, the mirror layer is a regular hexagonal mirror structure, and adjacent actuators in the actuator layer 200 have a phase difference of 120 ° between them, which can provide a tangential driving force to cause circular motion of the mirror about its central axis.

In one embodiment, the lead layer 300 is coupled to a fixed portion of the actuator layer 200. Specifically, the lead layer 300 is bonded to the first actuator 202A via the bonding layer 302 to provide mechanical fixation and mechanical support for the actuator layer 200. The lead layer 300 further includes a Through Silicon Via (TSV) structure 303, with the TSV structure 303 forming an electrical connection for providing an electrical interface to the actuator layer.

In one embodiment, wiring level 300 may further include a wiring level 304, which enables the transfer of the top surface electrical structure to wiring level 304. The upper surface of the lead layer 300 may be provided with an actuation cavity 301 for providing an actuation space for the first actuator 202A, the second actuator 202B, and the third actuator 202C.

In another embodiment, the invention provides a high-frequency high-duty-cycle MEMS micro-mirror array, which is particularly suitable for fast three-dimensional scanning imaging of a laser confocal scanning microscope.

Referring to fig. 4, which is a schematic plan view of a MEMS micro-mirror array according to an embodiment of the present invention, a mirror layer 100 is formed by two or more hexagonal mirror plates, 7 micro-mirror units are shown, but the number of micro-mirror units is not limited thereto. As shown in FIG. 4, the mirrors 49-55 of the MEMS micro-mirror array are formed as a single periodic mirror structure with mirror structures arranged in a hexagonal pattern in a two-dimensional plane to form a high duty cycle micro-mirror array. The specific structure of each mirror 49-55 in the micro mirror unit can be the structure of the mirror layer 100 described with reference to FIG. 2.

In this embodiment, the actuator layer includes 3N diamond-shaped actuators, where three diamond-shaped actuators are arranged in a group across, and N is the number of corresponding micromirror units. The movable portion of each diamond-shaped structure may be connected to the flexible mechanical structure of the mirror back via a coupling post. By applying electrical signals synchronously to each actuator group in the plurality of micromirror units, consistent control of the rotation of the mirror in both directions (as shown, deflection around R1, R2) and also translational control of the mirror up and down can be achieved. Therefore, the MEMS micro-mirror array based on the semiconductor micro-mechanical process can realize the piezoelectric driving micro-mirror array with high duty ratio and ensure the consistency of the performance of each mirror surface.

In conclusion, the MEMS micro-mirror array with high mirror surface performance consistency is prepared by adopting the MEMS micro-nano processing technology, and the number of units contained in the micro-mirror array has the extensibility in a two-dimensional space, so that the micro-mirror array has high duty ratio; the mirror structure is formed by splicing two or more hexagonal mirrors, so that the optical aperture can be expanded under the condition of not influencing parameters such as vibration frequency, deflection angle and the like, and the control of a large-aperture laser beam can be realized. Meanwhile, each micro-mirror unit is controlled by three independent actuators, so that the three-degree-of-freedom precise adjustment can be realized, the control mode is flexible, and the micro-mirror unit is particularly suitable for various application scenes such as a laser confocal scanning microscope, a laser radar, laser projection, laser processing, an MEMS optical switch, a spatial light modulator and the like. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Claims

1. A MEMS micro-mirror cell, comprising: the micromirror unit includes:

the flexible mechanical structure comprises a fixed part, and two sides of the fixed part are respectively fixedly connected with the side walls of the groove part through elastic parts;

an actuator layer comprising three actuators arranged in a cross, each actuator being arranged in pair with each flexible mechanical structure of the mirror layer and coupled to the corresponding flexible mechanical structure by a coupling post, a piezoelectric thin film material being arranged on a surface of the actuator, the piezoelectric thin film material being deformed when a voltage is applied, and power being supplied to the mirror layer through the coupling post and the flexible mechanical structure; and

a lead layer fixedly coupled to each actuator in the actuator layer to mechanically support and electrically connect the actuator layers, respectively.

2. The MEMS micro-mirror cell of claim 1, wherein: the mirror layer can axially rotate around an X axis or a Y axis.

3. The MEMS micro-mirror cell of claim 1, wherein: the mirror layer can be translated up and down along the Z axis, and the generated displacement can perform phase modulation on the light beam of a specific area.

4. The MEMS micro-mirror cell of claim 1, wherein: adjacent ones of the actuator layers have a 120 phase difference therebetween, and the actuator layers provide a tangential driving force to cause circular motion of the mirror about its central axis.

5. The MEMS micro-mirror cell of claim 1, wherein: each actuator includes a movable portion and a fixed portion.

6. The MEMS micro-mirror cell of claim 5, wherein: the movable part is connected with the flexible mechanical structure of the mirror layer through at least one coupling column, and the fixed part is connected with the lead layer.

7. The MEMS micro-mirror cell of claim 1, wherein: the piezoelectric thin film material comprises one of PZT, AlN and AlScN, and the thickness of the piezoelectric thin film material is 0.5-5 microns.

8. The MEMS micro-mirror cell of claim 1, wherein: the fixed portion of the actuator is bonded to the lead layer through a bonding layer.

9. The MEMS micro-mirror cell of claim 1, wherein: the lead layer includes a silicon via structure for providing electrical connections to the actuator layer.

10. The MEMS micro-mirror cell of claim 9, wherein: the lead layer further includes a wiring layer for rewiring the electrode lead-out portion.

11. The MEMS micro-mirror cell of claim 1, wherein: the side wall of the groove part is provided with a connecting part which protrudes outwards, and the elastic part is fixedly connected with the connecting part.

12. A MEMS micro-mirror array comprising a plurality of MEMS micro-mirror units according to any one of claims 1 to 11 arranged in a close-packed manner.

13. The MEMS micro-mirror array of claim 12, wherein: the MEMS micro-mirror array includes a plurality of hexagonal mirror layers that extend in a close-packed manner along the XY plane.