CN115524845B

CN115524845B - MEMS micro-mirror scanning system with active tunable mirror surface

Info

Publication number: CN115524845B
Application number: CN202211264930.9A
Authority: CN
Inventors: 李金桦; 许斌; 吉垚
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2022-10-17
Filing date: 2022-10-17
Publication date: 2023-05-12
Anticipated expiration: 2042-10-17
Also published as: CN115524845A

Abstract

The invention discloses a MEMS micro-mirror scanning system with an active tunable mirror, which comprises the active tunable mirror and a two-dimensional MEMS actuator capable of providing double-degree-of-freedom torsion motion; the two-dimensional MEMS actuator comprises a first MEMS actuator and a second MEMS actuator, the second MEMS actuator is positioned in the first MEMS actuator, and the torsion directions of the first MEMS actuator and the second MEMS actuator are mutually orthogonal; the active tuneable mirror is supported by the second MEMS actuator. The invention can adaptively generate prestress acting on the MEMS mirror surface by coupling the mirror surface actuator on the back of the MEMS mirror surface, and can actively adjust to improve the dynamic deformation of the MEMS mirror surface and ensure the high dynamic optical flatness of the mirror surface; simultaneously, two actuators are utilized to twist around a fast axis (X) direction and a slow axis (Y) direction which are orthogonal to each other, so as to provide two-dimensional deflection for the active tunable mirror surface and ensure high integration of the system.

Description

MEMS micro-mirror scanning system with active tunable mirror surface

Technical Field

The invention relates to a MEMS micro-mirror scanning system with an active tunable mirror.

Background

With the rapid development of consumer electronics market, augmented Reality (AR) scene technology with MEMS (Micro electromechanical systems, microelectromechanical system) laser scanners as core components is favored, so that MEMS micromirrors, which are one of the MEMS laser scanner core devices, are also widely focused, which realize imaging display and 3D sensing by spatially modulating and projecting laser light, typically divided into high-frequency scanning in (fast axis) X-direction and quasi-static or linear scanning in (slow axis) Y-direction. Application in high resolution, high optical power, large field of view experience, high reliability AR display requires a core component MEMS laser scanner to achieve high resolution, large field of view angle, high system integration, and higher laser energy carrying, which requires MEMS micromirrors with high scanning frequency, large scanning angle, large reflective mirror, reliable structural breaking strength, and mirror dynamic deformation no higher than ± λ/10 to ensure high optical flatness of mirror dynamics, λ being the shortest laser wavelength used in scanning applications;

in formula (1), δ is the dynamic deformation of the mirror surface, f is the scanning frequency, θ is the scanning angle, t is the mirror thickness, L is the mirror surface size, and E is the young's modulus. The dynamic deformation of the mirror surface is inversely proportional to the 5 th power of the mirror surface size, the 2 nd power of the scanning frequency and the scanning angle, and the realization of larger mirror surface size, high scanning frequency and large scanning angle all bring larger dynamic deformation of the mirror surface, so that the key points of realizing larger mirror surface size, high scanning frequency and large scanning angle are to improve the dynamic deformation of the mirror surface;

increasing the mirror thickness can improve and reduce the dynamic deformation of the mirror, but the larger micro mirror mass and mass moment of inertia need higher torsion beam rigidity to maintain a certain resonant frequency, and meanwhile, the stress of the torsion beam is increased, so that the realization of higher scanning frequency is limited, the requirement of additional mass on driving force is increased, and the resonant frequency of a non-planar mode and the reliability of a system are reduced;

in the prior art, the thickness of the reflecting mirror surface is increased, and part of the area is removed at the back of the reflecting mirror surface to reduce the quality of the reflecting mirror surface, so that the torsional rigidity of the torsion beam is reduced, and the dynamic deformation is improved; adopting a plurality of torsion beams to improve the deformation of the mirror surface, and limiting the size and the scanning angle of the reflecting mirror surface; the structure supporting the MEMS reflector surface is improved to improve the dynamic deformation of the MEMS reflector surface, so that a more complex system structure is realized, meanwhile, the more complex structure can also lead to the increase of the load of a slow axis, and the scanning frequency and the scanning angle in the Y direction are reduced;

the X, Y-direction scanning module is designed into independent devices to be placed separately by the double-one-dimensional (1D) MEMS micro-mirror, so that the target performance can be realized, but the complexity of an optical system is improved, the integration level of the system is low, and the 2D MEMS micro-mirror is a solution which is better for the application scene requirements;

methods for achieving 2D MEMS micromirror driving include electromagnetic driving, piezoelectric driving, thermoelectric driving, and electrostatic driving. Under the condition of ensuring the flatness of the reflecting mirror surface, the electromagnetic driving has extremely large driving force, but is not suitable for high-frequency scanning while realizing large-mirror-surface and large-angle driving; the piezoelectric driving meets the requirements of high-frequency scanning and large-size mirror surfaces, and simultaneously limits the smaller driving force of the piezoelectric driving, so that the scanning angle of a slow axis cannot be further improved in a quasi-static mode; the thermoelectric drive is not suitable for application scenes such as micro display, micro scanning and the like because of the too slow response speed; because the driving force of the electrostatic driving is small, the driving of the large-size mirror surface is extremely difficult to realize;

the existing 2D MEMS scanning micro-mirror adopts the single driving mode, adopts the combination of electrostatic driving and piezoelectric driving, and adopts the combination of electromagnetic driving and electrostatic driving, but the design constraint caused by the dynamic deformation of the MEMS reflecting mirror surface is not solved, and the scanning angle, the scanning frequency and the structural reliability can not be improved simultaneously under the condition of realizing the large reflecting mirror surface size design.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide an active tunable MEMS micro-mirror scanning system which can adaptively generate prestress acting on an MEMS mirror surface by coupling an MEMS actuator on the back of the MEMS mirror surface, can actively adjust to improve the dynamic deformation of the MEMS mirror surface and ensure the high dynamic optical flatness of the mirror surface; simultaneously, two actuators are twisted around a fast axis (X) direction and a slow axis (Y) direction which are orthogonal to each other to provide two-dimensional deflection for the active tunable mirror surface, so that a high-integration system scanning architecture is ensured.

The aim of the invention is realized by the following technical scheme: a MEMS micromirror scanning system with an active tunable mirror comprises an active tunable mirror and a two-dimensional MEMS actuator capable of providing a two-degree-of-freedom torsion motion; the two-dimensional MEMS actuator includes a first MEMS actuator providing at least one directional torsional motion and a second MEMS actuator providing at least one directional torsional motion; the second MEMS actuator is positioned in the first MEMS actuator, and the torsion directions of the first MEMS actuator and the second MEMS actuator are mutually orthogonal; the active tuneable mirror is supported by the second MEMS actuator.

Further, the first MEMS actuator comprises an outer frame and two outer torsion beams which are symmetrically arranged, the second MEMS actuator comprises an inner frame and two inner torsion beams which are symmetrically arranged, the outer frame is connected with the inner frame through the outer torsion beams, and the inner frame is fixedly connected with the active tunable mirror surface through the inner torsion beams; the outer torsion beam and the inner torsion beam are mutually orthogonal, the first MEMS actuator twists around the outer torsion beam, and the second MEMS actuator drives the active tunable mirror surface to twist around the inner torsion beam through the inner torsion beam.

The first MEMS actuator comprises an outer frame, a first substrate positioned in the outer frame, and two outer torsion beams symmetrically arranged, wherein the outer frame is connected with and supports the first substrate through the outer torsion beams respectively, and a hollowed-out area is arranged in the middle of the first substrate;

the second MEMS actuator comprises an inner frame, a second substrate positioned in the inner frame and two inner torsion beams symmetrically arranged, wherein the inner frame is connected with and supports the second substrate through the inner torsion beams respectively, and the active tunable mirror surface is fixed in the second substrate; the inner frame is positioned at the edge position on the first substrate, the inner torsion beam and the outer torsion beam are mutually orthogonal, the first MEMS actuator twists around the outer torsion beam, and the second MEMS actuator drives the active tunable mirror surface to twist around the inner torsion beam through the inner torsion beam.

Further, the first MEMS actuator and the second MEMS actuator are driven by piezoelectric, electrostatic or electromagnetic.

The first MEMS actuator is driven by electromagnetism, and two permanent magnets are symmetrically arranged on the outer side of the outer frame and used for driving the first MEMS actuator; the first MEMS actuator twists around the outer torsion beam, namely a slow axis, which is marked as a Y axis;

the coil is led out through an external torsion beam, the coil is divided into a feedback coil and a driving coil, the driving coil is coupled with an external permanent magnet to generate Lorentz force to drive the first substrate, and the feedback coil utilizes an electromagnetic induction phenomenon to realize feedback of the movement frequency and the angle of the first substrate;

the pair of permanent magnets provide a constant magnetic field, a modulated alternating current signal with a specific waveform is applied through the driving coil, lorentz force acting on the first MEMS actuator is generated, so that the outer torsion beam of the first MEMS actuator twists in the Y direction and drives the outer frame of the second MEMS actuator and the active tunable mirror to realize the integral deflection in the Y direction, and the feedback and the driving control of the deflection action of the first MEMS actuator are realized through an electric signal generated by the electromagnetic induction phenomenon of the feedback coil;

the second MEMS actuator is driven by piezoelectricity and twists around the inner torsion beam, namely a fast axis, and is marked as an X axis; symmetrically arranging piezoelectric driving structures at the bottoms of the inner frames at two sides of the inner torsion beam or directly bonding and combining the second MEMS actuator and the external piezoelectric driving material;

the piezoelectric driving structure consists of an upper electrode layer, a lower electrode layer and a piezoelectric film material between the upper electrode layer and the lower electrode layer; the leads of the upper electrode and the lower electrode are led out from the edges of the inner frame; the second MEMS actuator leads out a wire through an electrode of the piezoelectric driving structure, applies a modulated voltage signal with a specific waveform, and enables the inner torsion beam to drive the active tunable mirror to deflect in the X direction under a torsion resonance mode according to the piezoelectric driving principle;

or the second MEMS actuator and the external piezoelectric driving material are bonded and combined, and a modulating voltage signal is applied through a lead led out from the piezoelectric driving material to drive the external piezoelectric driving structure to vibrate, so that the internal torsion beam drives the active tunable mirror to deflect in the X direction under the torsional resonance mode;

the feedback mechanism of the second MEMS actuator is achieved by the positive piezoelectric effect characteristic of the piezoelectric material: the piezoelectric film material deposited at the connecting part of the inner torsion beam and the inner frame picks up the electric signal change generated by the deformation of the piezoelectric material caused by the deflection of the inner torsion beam, so as to realize the feedback of the angle and the movement frequency in the X direction; or a feedback coil is manufactured on the back of the second substrate, and the feedback of the angle and the movement frequency of the inner frame in the X torsion direction is realized by utilizing the electromagnetic induction phenomenon.

Further, the active tunable mirror comprises an MEMS mirror surface and a mirror actuator at the back of the MEMS mirror surface, wherein the mirror actuator is driven by piezoelectricity;

the mirror actuator is composed of two electrode layers and a piezoelectric film material between the two electrode layers;

the mirror surface actuator can adaptively generate prestress acting on the MEMS mirror surface, actively adjust the prestress to improve the dynamic deformation of the MEMS mirror surface and ensure the dynamic high optical flatness of the mirror surface; the specific method comprises the following steps: electrode layer wires of the mirror surface actuator are led out through the inner torsion beam, an alternating current signal with specific waveform is applied to the two electrode layers through the wires by utilizing the inverse piezoelectric effect of the piezoelectric material, the piezoelectric film material can deform and apply prestress to the MEMS reflecting mirror surface, fluctuation of the micro mirror during high-speed scanning is limited, and dynamic high optical flatness of the mirror surface is ensured.

The active tunable mirror includes a MEMS mirror and a mirror actuator on a back side of the MEMS mirror; the mirror actuator is an electrothermal driving structure and consists of a heating electrode layer and a substrate film layer or two film layers made of film materials with different thermal expansion coefficients and a heating electrode layer between the two film layers; the lead of the heating electrode layer is led out through the inner torsion beam, and the characteristic that the material with high thermal expansion coefficient can deviate to the material with low thermal expansion coefficient is utilized, electric signals are applied to the lead to generate Joule heat and the Joule heat is conducted to the two film layers, the two film layers deviate and stress according to the difference of the thermal expansion coefficients, the fluctuation of the mirror surface during high-speed scanning of the micro mirror is limited, the dynamic deformation of the MEMS reflecting mirror surface is improved, and the dynamic high optical flatness of the mirror surface is ensured.

The active tunable mirror includes a MEMS mirror and a mirror actuator on a back side of the MEMS mirror; the mirror actuator is an electric driving structure and consists of two non-contact electrodes;

the leads of the two electrodes are led out through the inner torsion beam, and an electric signal is applied to the two electrodes through the leads by utilizing the action of electrostatic force between the electrodes, so that the electrostatic force can be generated between the electrodes, the fluctuation of the mirror surface during high-speed scanning of the micro mirror is limited, the dynamic deformation of the MEMS reflecting mirror surface is improved, and the dynamic high optical flatness of the mirror surface is ensured.

The piezoelectric film material adopts any one of lead zirconate titanate, zinc oxide, polyvinylidene fluoride, aluminum nitride or a composite material composed of thermoplastic polymer and inorganic piezoelectric material. The MEMS reflecting mirror surface is made of a thin film material; a reflective coating material is deposited on the MEMS mirror surface, wherein the coating material is a metal or dielectric film stack.

The beneficial effects of the invention are as follows: the invention combines the MEMS actuator into the active tunable mirror surface by coupling the MEMS actuator on the back of the MEMS mirror surface, the mirror surface actuator can adaptively generate prestress acting on the MEMS mirror surface, and can actively adjust to improve the dynamic deformation of the MEMS mirror surface, thereby ensuring the high dynamic optical flatness of the mirror surface, so that the design constraint of synchronously increasing the scanning frequency, the scanning angle and the diameter of the mirror surface is solved under the condition of reducing the load of the MEMS mirror surface as much as possible. The 2D MEMS actuator of the present invention comprises a first MEMS actuator and a second MEMS actuator supporting a central active tuneable mirror, both actuators being twisted about a fast (X) direction and a slow (Y) direction orthogonal to each other, providing a two-dimensional deflection for the active tuneable mirror, ensuring a high integration system scanning architecture.

Drawings

FIG. 1 is a schematic diagram of the MEMS micro mirror scanning system of embodiment 1;

FIG. 2 is an assembled schematic diagram of the MEMS micro mirror scanning system of embodiment 1;

FIG. 3 is an assembled schematic diagram of the MEMS micro mirror scanning system of embodiment 2;

FIG. 4 is a second schematic diagram of the MEMS scanning system of embodiment 2;

FIG. 5 is a schematic structural view of a first MEMS actuator and a second MEMS actuator;

FIG. 6 is a schematic illustration of an adhesive combination of a second MEMS actuator and an external piezoelectric driving material;

FIG. 7 is a schematic diagram of a feedback coil fabricated on the back of the inner frame;

FIG. 8 is a schematic diagram of the operation of a MEMS micromirror scanning system;

FIG. 9 is a schematic diagram of a piezoelectric driven mirror actuator;

FIG. 10 is a schematic diagram of a piezoelectric driven mirror actuator;

FIG. 11 is a schematic diagram of a piezo-driven mirror actuator;

FIG. 12 is a schematic diagram of an electro-thermally driven mirror actuator;

FIG. 13 is a schematic diagram of a second electro-thermally driven mirror actuator;

FIG. 14 is a schematic diagram III of an electro-thermally driven mirror actuator configuration;

FIG. 15 is a schematic diagram of an electro-thermally driven mirror actuator;

FIG. 16 is a schematic diagram of an electrostatically driven mirror actuator;

FIG. 17 is a schematic diagram of a second electrostatically driven mirror actuator configuration;

FIG. 18 is a schematic diagram III of an electrostatically driven mirror actuator configuration;

1-first MEMS actuator, 2-second MEMS actuator, 3-active tunable mirror, 4-MEMS mirror, 5-mirror actuator, 6-outer torsion beam, 7, 20-inner frame, 8-inner torsion beam, 9-outer frame, 10-piezoelectric driven top electrode layer, 11-piezoelectric driven bottom electrode layer, 12-piezoelectric film material, 13-drive coil, 14-second substrate, 15-permanent magnet, 16-first substrate, 17-piezoelectric drive structure, 18-feedback coil, 19-piezoelectric film material, 21-laser, 22-laser scan pattern, 23-top film layer, 24-intermediate electrode layer, 25-bottom film layer, 26-heat generating electrode layer, 27-base film layer, 28-electrostatic driven bottom electrode, 29-electrostatic driven top electrode, 30-support cavity, 31-feedback coil, 32-external piezoelectric drive material.

Detailed Description

The invention provides a MEMS micro-mirror scanning system with an active tunable mirror, which comprises an active tunable mirror; a two-dimensional (2D) MEMS actuator providing two degrees of freedom torsional motion. The active tunable mirror structure includes: the mirror surface actuator can adaptively generate prestress acting on the MEMS mirror surface, and can actively adjust to improve the dynamic deformation of the MEMS mirror surface and ensure the dynamic high optical flatness of the mirror surface; the 2D MEMS actuator includes a first MEMS actuator and a second MEMS actuator supporting a central active tuneable mirror, twisted around a fast axis (X) direction and a slow axis (Y) direction orthogonal to each other, ensuring a highly integrated system scanning architecture. The dynamic deformation of the reflecting mirror surface can be improved under the condition of reducing the load of the MEMS reflecting mirror surface as much as possible, so that the high dynamic optical flatness of the reflecting mirror surface can be ensured under the condition of maintaining smaller device volume, and the design constraint of synchronously increasing the scanning frequency, the scanning angle and the diameter of the reflecting mirror surface is solved.

The technical scheme of the invention is further described below with reference to the attached drawings and specific embodiments.

Example 1

As shown in fig. 1, a MEMS micro-mirror scanning system with an active tuneable mirror comprises an active tuneable mirror 3 and a two-dimensional MEMS actuator capable of providing a two-degree-of-freedom torsion motion; the two-dimensional MEMS actuator comprises a first MEMS actuator 1 providing at least one direction of torsion movement and a second MEMS actuator 2 providing at least one direction of torsion movement; the second MEMS actuator 2 is positioned in the first MEMS actuator 1, and the torsion directions of the first MEMS actuator 1 and the second MEMS actuator 2 are mutually orthogonal; the active tuneable mirror 3 is supported by a second MEMS actuator 2.

In this embodiment, the first MEMS actuator 1 and the second MEMS actuator 2 are coupled in a plane, and the active tunable mirror 3 is independently designed and then combined on the second MEMS actuator 2, as shown in fig. 2. The first MEMS actuator 1 comprises an outer frame 9 and two outer torsion beams 6 which are symmetrically arranged, the second MEMS actuator 2 comprises an inner frame 7 and two inner torsion beams 8 which are symmetrically arranged, the outer frame 9 is connected with the inner frame 7 through the outer torsion beams 6, and the inner frame 7 is fixedly connected with the active tunable mirror 3 through the inner torsion beams 8; the outer torsion beam 6 and the inner torsion beam 8 are mutually orthogonal, the first MEMS actuator 1 twists around the outer torsion beam 6, and the second MEMS actuator 2 drives the active tunable mirror 3 to twist around the inner torsion beam through the inner torsion beam 8.

Example 2

A MEMS micro-mirror scanning system with an active tuneable mirror comprising an active tuneable mirror 3 and a two-dimensional MEMS actuator capable of providing a two degree of freedom torsion motion; the two-dimensional MEMS actuator comprises a first MEMS actuator 1 providing at least one direction of torsion movement and a second MEMS actuator 2 providing at least one direction of torsion movement; the second MEMS actuator 2 is positioned in the first MEMS actuator 1, and the torsion directions of the first MEMS actuator 1 and the second MEMS actuator 2 are mutually orthogonal;

in this embodiment, the first MEMS actuator 1, the second MEMS actuator 2 and the active tunable mirror 3 are respectively and independently designed and then combined, as shown in fig. 3; or the first MEMS actuator 1 is independently designed, the second MEMS actuator 2 and the active tunable mirror 3 are coupled in one plane and combined on the first MEMS actuator 1, as shown in fig. 4;

the second MEMS actuator 2 is located within the first MEMS actuator 1; the active tuneable mirror 3 is located within the second MEMS actuator 2 and is supported by the second MEMS actuator 2.

As shown in fig. 5, the first MEMS actuator 1 includes an outer frame 9, a first substrate 16 located inside the outer frame 9, and two symmetrically disposed outer torsion beams 6, wherein the outer frame 9 is connected to and supports the first substrate 16 through the outer torsion beams 6, and a hollowed-out area is provided in the middle of the first substrate 16;

the second MEMS actuator 2 comprises an inner frame 20, a second substrate 14 positioned inside the inner frame 20, and two inner torsion beams 8 symmetrically arranged, wherein the inner frame 20 is respectively connected with and supports the second substrate 14 through the inner torsion beams 8, and the active tunable mirror 3 is fixed in the second substrate 14; the inner frame 20 is located at an edge position on the first substrate 16, the inner torsion beam 8 and the outer torsion beam 6 are orthogonal to each other, the first MEMS actuator 1 twists around the outer torsion beam 6, and the second MEMS actuator 2 twists around the inner torsion beam by driving the active tuneable mirror 3 through the inner torsion beam 8.

The first and

second MEMS actuators

1 and 2 are driven by piezoelectric, electrostatic or electromagnetic means.

The first MEMS actuator 1 is driven by electromagnetism, and two permanent magnets 15 are symmetrically arranged on the outer side of the outer frame and used for driving the first MEMS actuator 1; the permanent magnet 15 may be made of alnico, ferrite, samarium cobalt, neodymium iron boron, etc.; the first MEMS actuator 1 twists around the outer torsion beam, namely a slow axis, which is marked as a Y axis;

the coil is distributed in the first substrate 16, is led out through the outer torsion beam 6, is divided into a feedback coil 18 and a driving coil 13, the driving coil 13 is coupled with an external permanent magnet 15 to generate Lorentz force to drive the first substrate 16, and the feedback coil 18 utilizes electromagnetic induction to realize feedback of the movement frequency and angle of the first substrate 16;

the pair of permanent magnets 15 provides a constant magnetic field, a modulated alternating current signal with a specific waveform is applied through the driving coil 13, a lorentz force acting on the first MEMS actuator 1 is generated, so that the outer torsion beam 6 of the first MEMS actuator 1 twists in the Y direction and drives the outer frame of the second MEMS actuator 2 and the active tunable mirror 3 to realize the integral deflection in the Y direction, and the feedback and driving control of the deflection action of the first MEMS actuator 1 are realized through an electric signal generated by the electromagnetic induction phenomenon of the feedback coil 18;

the second MEMS actuator 2 is driven by piezoelectricity and twists around the inner torsion beam, namely a fast axis, which is marked as an X axis; symmetrically arranging the piezoelectric driving structures 17 at the bottoms of the inner frames at two sides of the inner torsion beam or directly bonding and combining the second MEMS actuator 2 and the external piezoelectric driving material 32;

the piezoelectric driving structure 17 is composed of an upper electrode layer, a lower electrode layer and a piezoelectric film material between the upper electrode layer and the lower electrode layer; the leads of the upper electrode and the lower electrode are led out from the edges of the inner frame; the second MEMS actuator 2 leads out wires through electrodes of the piezoelectric driving structure 17, applies a modulated voltage signal with a specific waveform, and enables the inner torsion beam 8 to drive the active tunable mirror 3 to deflect in the X direction under the torsional resonance mode according to the piezoelectric driving principle;

or the second MEMS actuator 2 and the external piezoelectric driving material 32 are adhesively combined as shown in fig. 6; the external piezoelectric driving structure 32 is driven to vibrate by applying a modulation voltage signal through a lead led out from the piezoelectric driving material 32, so that the internal torsion beam 8 drives the active tunable mirror 3 to deflect in the X direction under a torsional resonance mode; the external piezoelectric driving structure 32 may be a PZT piezoelectric ceramic block or a piezoelectric ceramic sheet.

The feedback mechanism of the second MEMS actuator 2 is realized by the positive piezoelectric effect specific to the piezoelectric material: through the piezoelectric film material 19 deposited at the connecting part of the inner torsion beam 8 and the inner frame 20, the electric signal change generated by the deformation of the piezoelectric material caused by the deflection of the inner torsion beam 8 is picked up, and the feedback of the angle and the movement frequency in the X direction is realized; or a feedback coil 31 is formed on the back surface of the second substrate 14 as shown in fig. 7; the angle and movement frequency feedback of the inner frame 20 in the X torsion direction is achieved using the electromagnetic induction phenomenon.

As shown in fig. 8, when the laser 21 emits laser light to the active tuneable mirror 3 while the first MEMS actuator 1 and the second MEMS actuator 2 are driven and closed-loop controlled in the above-described manner, a progressive laser scanning pattern 22 can be generated. Meanwhile, the generated laser scanning pattern can be sampled through the photoelectric sensor, the motion information of the substrate and the inner frame is calculated, and motion feedback of the substrate and the inner frame is achieved.

The materials of the second substrate 14, the first substrate 16, the outer frame and the inner frame are silicon, glass fiber epoxy resin FR-4, shape memory alloy SMA or amorphous alloy; the coil is made of high-conductivity metal material, including copper or aluminum.

The active tunable mirror 3 comprises an MEMS reflecting mirror 4 and a mirror actuator 5 at the back of the MEMS reflecting mirror 4, wherein the mirror actuator 5 is driven by piezoelectricity;

the mirror actuator 5 is composed of two electrode layers and a piezoelectric thin film material between the two electrode layers; as shown in fig. 9 to 11, the mirror actuator 5 is composed of a top electrode layer 10, a bottom electrode layer 11, and a piezoelectric thin film material 12 between the top electrode layer and the bottom electrode layer, the bottom electrode layer 11 is a whole or divided into N irregular sub-regions, the dimensions of the top electrode layer 10 and the bottom electrode layer 11 are smaller than or equal to the dimensions of the MEMS mirror 4, and the diameter of the MEMS mirror 4 may be greater than 2mm; the method comprises the steps of carrying out a first treatment on the surface of the In fig. 9, the bottom electrode 11 is a single body; in fig. 10, the bottom electrode layer is an irregular N number of sub-regions;

the mirror surface actuator 5 can adaptively generate prestress acting on the MEMS mirror surface, actively adjust to improve the dynamic deformation of the MEMS mirror surface 4 and ensure the dynamic high optical flatness of the mirror surface; the specific method comprises the following steps: electrode layer wires of the mirror actuator 5 are led out through the inner torsion beam 8, and alternating current signals with specific waveforms are applied to the two electrode layers through wires by utilizing the inverse piezoelectric effect of the piezoelectric materials, so that the piezoelectric film materials deform and apply prestress to the MEMS reflecting mirror 4, the fluctuation of the micro mirror during high-speed scanning is limited, and the dynamic high optical flatness of the mirror surface is ensured. The bottom electrode layer 11 is divided into N irregular sub-areas, the direction and the size of the deformation or mechanical stress of the piezoelectric material can be controlled by utilizing the irregular arrangement of the bottom electrode layer 11, and according to the deformation of the MEMS reflecting mirror surface 4 in different areas, the internal electrodes or the bottom electrodes in different areas are applied with voltage signals with different sizes to generate prestress for improving the dynamic deformation of the MEMS reflecting mirror surface 4, so that the dynamic high optical flatness of the mirror surface can be adjusted more accurately.

Example 3

A MEMS micro-mirror scanning system with an active tuneable mirror comprising an active tuneable mirror 3 and a two-dimensional MEMS actuator capable of providing a two degree of freedom torsion motion; the two-dimensional MEMS actuator structure is the same as in embodiment 1, except that the active tuneable mirror 3 comprises a MEMS mirror 4 and a mirror actuator 5 behind the MEMS mirror 4; the mirror actuator 5 is an electrothermal driving structure composed of a heat-generating electrode layer 26 and a base film layer 27, as shown in fig. 12; or two thin film layers made of thin film materials having different coefficients of thermal expansion and a heat generating electrode layer between the two thin film layers, as shown in fig. 13, 14 and 15. In this embodiment, the MEMS actuator 5 is composed of a top film layer 23 and a bottom film layer 25 made of film materials having different coefficients of thermal expansion, and a heat-generating electrode layer 24 between the top and bottom film layers, the top film layer 23, the bottom film layer 25, and the middle heat-generating electrode layer 24 being integral as shown in fig. 13; or divided into N irregular sub-areas as shown in fig. 14 and 15; the lead of the heating electrode layer is led out through the inner torsion beam 8, and the characteristic that the material with high thermal expansion coefficient can deviate to the material with low thermal expansion coefficient is utilized, electric signals are applied to the lead to generate Joule heat and the Joule heat is conducted to the two film layers, the two film layers deviate and stress according to the difference of the thermal expansion coefficients, the fluctuation of the mirror surface during high-speed scanning of the micro mirror is limited, the dynamic deformation of the MEMS reflecting mirror surface 4 is improved, and the dynamic high optical flatness of the mirror surface is ensured.

Example 4

A MEMS micro-mirror scanning system with an active tuneable mirror comprising an active tuneable mirror 3 and a two-dimensional MEMS actuator capable of providing a two degree of freedom torsion motion; the two-dimensional MEMS actuator structure is the same as in embodiment 1, except that the active tuneable mirror 3 comprises a MEMS mirror 4 and a mirror actuator 5 behind the MEMS mirror 4; the mirror actuator 5 is an electrostatic drive structure composed of a top electrode 29 and a bottom electrode 28 which are not in contact, as shown in fig. 16 to 18; in this embodiment, the top electrode 29 and the bottom electrode 28 are installed in the supporting cavity 30 and are respectively located at the top and the bottom of the supporting cavity 30, and are supported by the supporting cavity 30 to ensure that the two electrodes are not contacted (the supporting cavity 30 can also take other forms, only needs to support the two electrodes so that the two electrodes are not contacted), and the top electrode 29 is located at the back of the MEMS mirror 4;

the leads of the two electrodes are led out through the inner torsion beam 8, and an electric signal is applied to the two electrodes through the leads by utilizing the electrostatic force action between the electrodes, so that the electrostatic force can be generated between the electrodes, the fluctuation of the mirror surface during high-speed scanning of the micro mirror is limited, the dynamic deformation of the MEMS reflecting mirror surface 4 is improved, and the dynamic high optical flatness of the mirror surface is ensured.

In the above embodiments, the various electrodes are made of metal materials, such as: platinum, titanium, etc.; the piezoelectric thin film material 12 is any one of lead zirconate titanate, zinc oxide, polyvinylidene fluoride, aluminum nitride or a composite material composed of a thermoplastic polymer and an inorganic piezoelectric material.

The MEMS mirror surface 4 is made of a thin film material, such as a silicon nitride thin film, or other thin film materials such as silicon dioxide, silicon oxide, silicon, etc.; a reflective coating material is deposited on the MEMS mirror surface 4, the coating material being a metal or dielectric thin film stack.

Those of ordinary skill in the art will recognize that the embodiments described herein are for the purpose of aiding the reader in understanding the principles of the present invention and should be understood that the scope of the invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific modifications and combinations from the teachings of the present disclosure without departing from the spirit thereof, and such modifications and combinations remain within the scope of the present disclosure.

Claims

1. A MEMS micro-mirror scanning system with an active tuneable mirror, characterized by comprising an active tuneable mirror (3) and a two-dimensional MEMS actuator capable of providing a two-degree-of-freedom torsion movement; the two-dimensional MEMS actuator comprises a first MEMS actuator (1) providing at least one direction of torsional movement and a second MEMS actuator (2) providing at least one direction of torsional movement; the second MEMS actuator (2) is positioned in the first MEMS actuator (1), and the torsion directions of the first MEMS actuator (1) and the second MEMS actuator (2) are mutually orthogonal; the active tuneable mirror (3) is supported by a second MEMS actuator (2);

the first MEMS actuator (1) comprises an outer frame (9), a first substrate (16) positioned in the outer frame (9) and two outer torsion beams (6) symmetrically arranged, wherein the outer frame (9) is connected with and supports the first substrate (16) through the outer torsion beams (6) respectively, and a hollowed-out area is arranged in the middle of the first substrate (16);

the second MEMS actuator (2) comprises an inner frame (20), a second substrate (14) positioned inside the inner frame (20) and two inner torsion beams (8) symmetrically arranged, wherein the inner frame (20) is respectively connected with and supports the second substrate (14) through the inner torsion beams (8), and the active tunable mirror surface (3) is fixed in the second substrate (14); the inner frame (20) is positioned at the edge position of the first substrate (16), the inner torsion beam (8) is orthogonal to the outer torsion beam (6), the first MEMS actuator (1) twists around the outer torsion beam (6), and the second MEMS actuator (2) drives the active tunable mirror surface (3) to twist around the inner torsion beam through the inner torsion beam (8);

the first MEMS actuator (1) is driven by electromagnetism, and two permanent magnets (15) are symmetrically arranged on the outer side of the outer frame and used for driving the first MEMS actuator (1); the first MEMS actuator (1) twists around the outer torsion beam (6), namely a slow axis, which is marked as a Y axis;

the coil is distributed in the first substrate (16), the coil is led out through the outer torsion beam (6), the coil is divided into a feedback coil (18) and a driving coil (13), the driving coil (13) is coupled with an external permanent magnet (15) to generate Lorentz force to drive the first substrate (16), and the feedback coil (18) utilizes the electromagnetic induction phenomenon to realize feedback of the movement frequency and angle of the first substrate (16);

the pair of permanent magnets (15) provides a constant magnetic field, a modulated alternating current signal with a specific waveform is applied through the driving coil (13), a Lorentz force acting on the first MEMS actuator (1) is generated, the torsion beam (6) outside the first MEMS actuator (1) is twisted in the Y direction and drives the outer frame of the second MEMS actuator (2) and the active tunable mirror (3) to realize the integral deflection in the Y direction, and the feedback and the driving control of the deflection action of the first MEMS actuator (1) are realized through an electric signal generated by the electromagnetic induction phenomenon of the feedback coil (18);

the second MEMS actuator (2) is driven by piezoelectricity and twists around the inner torsion beam (8), namely a fast axis, and is marked as an X axis; symmetrically arranging piezoelectric driving structures (17) at the bottoms of the inner frames at two sides of the inner torsion beam or directly bonding and combining the second MEMS actuator (2) and an external piezoelectric driving material (32);

the piezoelectric driving structure (17) consists of an upper electrode layer, a lower electrode layer and a piezoelectric film material between the upper electrode layer and the lower electrode layer; the leads of the upper electrode and the lower electrode are led out from the edges of the inner frame; the second MEMS actuator (2) leads out a wire through an electrode of the piezoelectric driving structure (17) and applies a modulated voltage signal with a specific waveform, so that the inner torsion beam (8) drives the active tunable mirror (3) to deflect in the X direction under a torsional resonance mode according to the piezoelectric driving principle;

or the second MEMS actuator (2) is bonded with the external piezoelectric driving material (32), and a modulating voltage signal is applied through a lead led out from the piezoelectric driving material (32) to drive the external piezoelectric driving structure (32) to vibrate, so that the inner torsion beam (8) drives the active tunable mirror surface (3) to deflect in the X direction under the torsional resonance mode;

the feedback mechanism of the second MEMS actuator (2) is realized by a positive piezoelectric effect specific to the piezoelectric material: through the piezoelectric film material (19) deposited at the connecting part of the inner torsion beam (8) and the inner frame (20), the electric signal change generated by the deformation of the piezoelectric material caused by the deflection of the inner torsion beam (8) is picked up, and the feedback of the angle and the movement frequency in the X direction is realized; or a feedback coil (31) is manufactured on the back surface of the second substrate (14), and the feedback of the angle and the movement frequency of the inner frame (20) in the X torsion direction is realized by utilizing the electromagnetic induction phenomenon.

2. MEMS micro-mirror scanning system with active tuneable mirror according to claim 1, characterized in that the first MEMS actuator (1) comprises an outer frame (9) and two outer torsion beams (6) symmetrically arranged, the second MEMS actuator (2) comprises an inner frame (7) and two inner torsion beams (8) symmetrically arranged, the outer frame (9) is connected to the inner frame (7) by the outer torsion beams (6), the inner frame (7) is fixedly connected to the active tuneable mirror (3) by the inner torsion beams (8); the outer torsion beam (6) and the inner torsion beam (8) are mutually orthogonal, the first MEMS actuator (1) twists around the outer torsion beam (6), and the second MEMS actuator (2) drives the active tunable mirror surface (3) to twist around the inner torsion beam through the inner torsion beam (8).

3. MEMS micro-mirror scanning system with active tunable mirror according to claim 1, characterized in that the active tunable mirror (3) comprises a MEMS mirror (4) and a mirror actuator (5) behind the MEMS mirror (4), the mirror actuator (5) being driven with piezoelectricity;

the mirror actuator (5) is composed of two electrode layers and a piezoelectric film material between the two electrode layers;

the mirror surface actuator (5) can adaptively generate prestress acting on the MEMS mirror surface, actively adjust the prestress to improve the dynamic deformation of the MEMS mirror surface (4) and ensure the dynamic high optical flatness of the mirror surface; the specific method comprises the following steps: electrode layer wires of the mirror surface actuator (5) are led out through an inner torsion beam (8), an alternating current signal with specific waveform is applied to the two electrode layers through wires by utilizing the inverse piezoelectric effect of the piezoelectric material, the piezoelectric film material can deform and apply prestress to the MEMS reflecting mirror surface (4), the fluctuation of the mirror surface during high-speed scanning of the micro mirror is limited, and the dynamic high optical flatness of the mirror surface is ensured.

4. MEMS micro-mirror scanning system with active tunable mirror according to claim 1, characterized in that the active tunable mirror (3) comprises a MEMS mirror (4) and a mirror actuator (5) behind the MEMS mirror (4); the mirror actuator (5) is an electrothermal driving structure and consists of a heating electrode layer and a substrate film layer or two film layers made of film materials with different thermal expansion coefficients and a heating electrode layer between the two film layers; the lead of the heating electrode layer is led out through the inner torsion beam (8), electric signals are applied through the lead to generate Joule heat and the Joule heat is conducted to the two film layers, and the two film layers cause local stress due to mismatch of thermal expansion coefficients, so that fluctuation of the mirror surface during high-speed scanning of the micro mirror is limited, dynamic deformation of the MEMS reflecting mirror surface (4) is improved, and dynamic high optical flatness of the mirror surface is ensured.

5. MEMS micro-mirror scanning system with active tunable mirror according to claim 1, characterized in that the active tunable mirror (3) comprises a MEMS mirror (4) and a mirror actuator (5) behind the MEMS mirror (4); the mirror surface actuator (5) is an electrostatic driving structure and consists of a flat capacitor structure and parallel electrode plates thereof;

the leads of the two electrodes are led out through the inner torsion beam (8), and an electric signal is applied to the two electrodes through the leads by utilizing the action of electrostatic force between the electrodes, so that the electrostatic force can be generated between the electrodes, the fluctuation of the mirror surface during high-speed scanning of the micro mirror is limited, the dynamic deformation of the MEMS reflecting mirror surface (4) is improved, and the dynamic high optical flatness of the mirror surface is ensured.

6. The MEMS micro-mirror scanning system with an active tunable mirror according to claim 3, wherein the piezoelectric thin film material is any one of lead zirconate titanate, zinc oxide, polyvinylidene fluoride, aluminum nitride, or a composite material composed of a thermoplastic polymer and an inorganic piezoelectric material.

7. MEMS micro-mirror scanning system with active tunable mirror according to claim 3 or 4 or 5, characterized in that the MEMS mirror (4) is made using standard MEMS or semiconductor processes; a reflective coating material is deposited on the MEMS mirror surface (4), wherein the coating material is a metal or dielectric film lamination.