Micromirror with variable scanning range based on bistable principle and lidar

Abstract

The application discloses a bistable principle variable scanning range micromirror and laser radar and belongs to the technical field of laser radar. The micromirror comprises a mirror surface, a fast axis, a fast axis driving ring, a slow axis, a slow axis driving ring, a decoupling ring, a piezoelectric film, an electrode lead, a metal electrode and a base and is integrally processed by using an SOI wafer. The mirror surface is connected with the fast axis driving ring through the fast axis and is mechanically isolated from the slow axis and the slow axis driving ring through the decoupling ring. The slow axis driving ring and the fast axis driving ring are respectively covered by the piezoelectric film. The piezoelectric film is connected with the metal electrode through the electrode lead and is used for being connected with an external driving circuit. The fast axis and the slow axis are torsional beams with rectangular sections and are located orthogonally and used for changing the deflection angles of the mirror surface in two orthogonal directions, so that the angles of reflected light rays are changed. The high and low amplitude state switching is realized through the bistable characteristic. The torsional amplitude of the micromirror can be dynamically adjusted under the same driving frequency, and the adaptability is high.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser radars, and particularly relates to a micromirror with variable scanning range based on a bistable principle and a laser radar. BACKGROUND

[0002] With the development of unmanned driving, robot technology and industrial automation, laser radars have become necessary detection and sensing components. They can precisely measure the position, shape and movement of objects by scanning laser beams and capturing reflected signals, which is crucial for robot tracking, road driving and industrial automation. In addition, laser radars can also be applied to environmental perception, safety monitoring and other scenarios, and can detect abnormalities such as fires and leaks in the surrounding environment in a timely manner.

[0003] As the core actuator of laser radars, micromirrors have the characteristics of miniaturization, low power consumption and high precision, and can be used to perceive the surrounding environment in the field of autonomous driving, achieving high-precision positioning and obstacle detection of vehicles. In addition, micromirrors are also widely used in medical imaging, laser processing and projection display. In optical imaging, they can be applied to laser scanning microscope systems to achieve high-speed and high-resolution three-dimensional image reconstruction; in laser processing systems, they can achieve high-precision positioning during the processing process by adjusting the direction of the laser beam, thereby improving the processing precision; in optical communication systems, they can control the capture of signals by adjusting the optical path.

[0004] However, traditional micromirrors mostly adopt fixed scanning angle design, and their mechanical structure parameters are fixed during the manufacturing stage. This rigid design architecture makes it difficult for the system to adapt to the adjustable requirements of beam deflection range in different application scenarios, and it can only work in a single stable state and fixed scanning range. When there is no need for centralized scanning, the background running power consumption is increased, wasting computing power; when there is a need for centralized scanning, the resolution is insufficient, resulting in large imaging errors. Although traditional micromirrors can change the scanning amplitude by adjusting the driving voltage, the hardening / softening phenomenon of the micromirror resonator makes it extremely difficult to control the amplitude, and it is difficult to achieve precise control and stable scanning, so the traditional micromirror may not perform well in some complex application scenarios with changing conditions and many disturbances. How to switch the scanning range according to the changes in the application scenario has become a key technical bottleneck restricting the cross-field application of micromirrors.

[0005] In recent years, bistable systems have become a research hotspot for improving the flexibility of devices due to their multi-stable switching characteristics in dynamic response. The bistable phenomenon is derived from the nonlinear dynamics of the system, which exhibits two stable equilibrium states at a specific frequency. By external excitation, the state can be switched, the scanning angle can be switched, and the scanning mode can be switched for different scenarios to ensure low power consumption and high-precision imaging. However, the existing technology has not effectively combined the bistable principle with the design of the micromirror structure to achieve controllable adjustment of the scanning range. SUMMARY

[0006] The application aims to solve the problems of fixed scanning range and poor adaptability of laser radar, and provides a micromirror and laser radar with variable scanning range based on bistable principle.

[0007] A micromirror and laser radar with variable scanning range based on bistable principle, from inside to outside, are mirror surface 1, fast axis 2, fast axis drive ring 3, fast axis drive ring beam 5, decoupling ring 6, slow axis 7, slow axis drive ring 8, slow axis drive ring beam 10 and base 15.

[0008] The upper and lower ends of the mirror surface 1 are connected to the fast axis 2 and the fast axis drive ring 3, and the upper and lower ends of the fast axis drive ring 3 are connected to the inner side of the decoupling ring 6 through the fast axis drive ring beam 5.

[0009] The outer side of the decoupling ring 6 is connected to the slow axis drive ring 8 through the slow axis 7 at the left and right ends, and the slow axis drive ring 8 is fixed on the base 15 through the slow axis drive ring beam 10.

[0010] Two arc-shaped fast axis piezoelectric films 4 are arranged on the two sides of the fast axis 2 on the fast axis drive ring 3.

[0011] Two arc-shaped slow axis piezoelectric films 9 are arranged on the two sides of the slow axis 7 on the slow axis drive ring 8.

[0012] Metal electrodes are arranged at the two ends of the fast axis piezoelectric film 4 and the slow axis piezoelectric film 9.

[0013] The fast axis 2 and the slow axis 7 are torsional beams with rectangular cross section.

[0014] The micromirror is prepared from single crystal silicon structural material.

[0015] Another object of the application is to provide a laser radar with variable scanning range based on bistable principle,

[0016] A laser radar with variable scanning range based on bistable principle, comprising a laser emitting unit, a beam scanning unit, an optical receiving unit, a signal processing and system control unit; the scanning unit adopts the above-mentioned micromirror with variable scanning range based on bistable principle.

[0017] Another object of the application is a micromirror scanning method based on bistable principle with variable scanning range.

[0018] A micromirror scanning method based on bistable principle with variable scanning range, the steps are as follows:

[0019] 1) Apply high-frequency alternating voltage to the fast-axis drive ring 3 through the fast-axis metal electrode 12, drive the mirror surface 1 to twist around the fast-axis 2 at high speed by using the inverse piezoelectric effect of the fast-axis piezoelectric film 4, and realize fast scanning of the light beam;

[0020] 2) Apply low-frequency alternating voltage to the slow-axis drive ring 8 through the slow-axis metal electrode 14 , wherein, U dc is the direct current bias voltage, U ac is the alternating voltage amplitude, Ω is the angular frequency, φ 0 is the initial phase; by increasing the amplitude of the alternating voltage U ac , increase the twist angle of the slow-axis 7 θ 2y , thereby amplifying the cubic nonlinearity of the slow-axis 7 K n to the mirror surface 1, so that the amplitude-frequency curve of the slow-axis 7 is bent to the left or right, and a frequency interval with high and low two stable amplitude states appears, triggering the bistable characteristics of the system;

[0021] 3) Around the natural frequency of the slow-axis 7, perform forward and reverse frequency sweeping, mark the amplitude upward jump frequency point f u and the amplitude downward jump frequency point f d , determine the frequency interval range of the bistable state f u ～f d ;

[0022] 4) Select the middle frequency value of the bistable interval as the driving frequency, change the direct current bias voltage U dc and the initial phase φ 0 , change the initial twist angle and the initial angular velocity, record the amplitude state of the twist vibration mode of the slow-axis 7 under different initial twist angles and initial angular velocities, and draw the attractor basin image;

[0023] 5) By adjusting the direct current bias voltage U dc and the initial phase φ 0 , combined with the attractor basin image, accurately select and switch the stable amplitude, so as to dynamically adjust the twist amplitude of the mirror surface 1 around the slow-axis 7, and expand or reduce the scanning range;

[0024] 6) The reflected light of the incident light under the comprehensive regulation of the torsional vibration of the fast axis 2 and the slow axis 7 will perform surface scanning on the target object; the decoupling ring 6 ensures the stability of the bistable switching by inhibiting the mechanical coupling between the fast axis 2 and the slow axis 7, and realizes high-precision dynamic regulation of the scanning range of the micro mirror.

[0025] The kinetic equations of the fast axis 2 and the slow axis 7 can be represented by the following Lagrange equations:

[0026] (1);

[0027] Wherein, t represents time, T, U represents the total kinetic energy and total potential energy of the micro mirror, θ 1x , θ 2y , θ 2x , respectively represent the torsional angle of the fast axis 2 torsional vibration mode, the slow axis 7 torsional vibration mode, and the bending vibration mode of the mirror surface 1 around the fast axis 2; , , θ 1x , θ 2y , θ 2x The first-order derivative with respect to time t, that is, the rotation angular velocity; M 1x 、M 2y 、M 2x , respectively represent the driving torque applied to the above three modes; the kinetic energy T mainly comes from the fixed-axis rotation of the mirror surface 1, the fast axis 2 and the slow axis 7, and the potential energy U is mainly stored in the form of torsional deformation in the fast axis 2 and the slow axis 7, and the expressions of T and U can be obtained through dynamic analysis:

[0028] (2);

[0029] (3);

[0030] Wherein, J 1x 、J 2y 、J 2x , respectively represent the moment of inertia of the fast axis 2 torsional vibration mode, the slow axis 7 torsional vibration mode, and the bending vibration mode of the mirror surface 1 around the fast axis 2; K 1x 、K ​2y 、K 2x linear stiffness of the fast axis 2 torsional mode, the slow axis 7 torsional mode, and the mirror 1 bending mode around the fast axis 2, respectively. Substituting equations (2) and (3) into equation (1) and adding damping terms, the three-degree-of-freedom dynamic equation of the micro-mirror is:

[0031] (4) ;

[0032] where ，C 1x 、C 2y 、C 2x linear damping of the fast axis 2 torsional mode, the slow axis 7 torsional mode, and the mirror 1 bending mode around the fast axis 2, respectively; 、 、 θ 1x , θ 2y , θ 2x The second derivative with respect to time t, i.e., the angular acceleration; the linear undamped free vibration equation of the fast axis 2 and slow axis 7 torsional modes is as follows:

[0033] (5) ;

[0034] The natural frequency of the fast axis 2 torsional mode ω 1 and the natural frequency of the slow axis 7 torsional mode ω 2 :

[0035] (6) ;

[0036] where, the moment of inertia J 1x 、J 2y is determined by the designed structural parameters, and can be expressed as:

[0037] (7) ;

[0038] (8) ;

[0039] where, m is the device layer thickness of the micro-mirror, ρ is the density of single crystal silicon, r、R 1 、R 2 ​、R 3 、R 4 、R 5 、R 6 R1, R2, R3, R4, R5, R6, R7, R8 are radius of mirror 1, inner diameter of fast axis driving ring 3, outer diameter of fast axis driving ring 3, inner diameter of decoupling ring 6, outer diameter of decoupling ring 6, inner diameter of slow axis driving ring 8, outer diameter of slow axis driving ring 8, respectively, see FIG. 1. Fig. 4 K 1x Kfast is linear stiffness of fast axis 2 torsional vibration mode and Kslow is linear stiffness of slow axis 7 torsional vibration mode. K 2y Kslow can be expressed as:

[0040] (9);

[0041] (10);

[0042] where, β 1 、β 2 Kt is torsional section coefficient related to the aspect ratio of rectangular section of fast axis 2 and slow axis 7, G G is shear modulus; b 1 、b 2 Wfast and Wslow are width of fast axis 2 and slow axis 7, respectively. L 1 、L 2 Lfast and Lslow are length of fast axis 2 and slow axis 7, respectively.

[0043] In order to make slow axis 7 torsional vibration appear bistable phenomenon, it is necessary to increase the alternating voltage applied to slow axis piezoelectric film 9, so that the torsional vibration of slow axis 7 is enhanced, and the cubic nonlinear stiffness K n causes linear stiffness softening or hardening phenomenon, resulting in the amplitude-frequency curve of slow axis 7 bending to the left or right, and appearing a bistable frequency interval with high and low two stable amplitude solutions, at this time, the nonlinear forced vibration equation of slow axis 7 can be approximately expressed as:

[0044] (11);

[0045] The fast axis frequency is 2600 Hz, and the slow axis frequency is 2150 Hz.

[0046] Another object of the present application is to provide a micromirror preparation method based on bistable principle variable scanning range. ​

[0047] A micromirror preparation method based on bistable principle variable scanning range, steps as follows:

[0048] a. Select 6 inch SOI wafer, wherein device layer 60 μm, oxide layer 2 μm, substrate layer 450 μm, and perform LPCVD / thermal oxidation top layer 200 nm SiO2;

[0049] b. Use magnetron sputtering to sequentially deposit a stack layer composed of bottom Pt, PZT and top Pt on the SOI, with thicknesses of 200 nm, 4 μm and 200 nm respectively;

[0050] c. Spin coating photoresist, dry etching ICP top Pt electrode, and stopping at PZT layer;

[0051] e. Remove photoresist, spin coating photoresist again, dry etching ICP piezoelectric layer PZT, and stopping at bottom electrode Pt layer;

[0052] f. Remove photoresist, spin coating photoresist again, using dry etching ICP bottom electrode Pt, and stopping at SiO2 layer;

[0053] g. Remove photoresist, using evaporation process to prepare top electrode insulating layer silicon oxide 500 nm;

[0054] h. Spin coating photoresist, etching insulating oxide layer, etching window size ϕ60 μm, exposing top electrode and bottom electrode;

[0055] i. Remove photoresist, spin coating photoresist again, manufacturing electrode metal pattern;

[0056] j. Magnetron sputtering Cr / Au, wherein thickness of Cr is 20 nm, thickness of Au is 200 nm;

[0057] k. Using Lift off process, preparing top and bottom metal electrodes;

[0058] l. Spin coating photoresist, dry etching HF etching oxide layer;

[0059] m. DRIE etching device layer, etching depth is 60 μm, etching through SOI device layer;

[0060] n. Remove photoresist; forward spin coating photoresist, then backward spin coating photoresist, using photoetching mask plate VII, DRIE backward etching substrate layer, etching depth is 450 μm;

[0061] o. Using photoetching mask plate VII, DRIE backward etching substrate layer, etching depth is 450 μm;

[0062] p. Dry etching HF buried oxide layer 2 μm, removing photoresist, completing release structure.

[0063] The present application has the following advantages and benefits compared with the prior art:

[0064] 1. High and low amplitude state switching is realized through bistable characteristics, the torsion amplitude of the micro mirror can be dynamically adjusted under the same driving frequency, and the adaptability of complex scenes is significantly improved;

[0065] 2. The designed decoupling ring structure can effectively suppress mechanical coupling, ensure the independence of double-axis vibration, and improve the scanning quality of the light beam;

[0066] 3. It can be processed by standard SOI-micro-nano processing technology, and the process maturity is high, which can be mass-produced and batch-produced. BRIEF DESCRIPTION OF DRAWINGS

[0067] Fig. 1 It is a schematic diagram of the overall structure of a variable scanning range micro mirror based on the bistable principle;

[0068] Fig. 2 It is a top view of a variable scanning range micro mirror based on the bistable principle;

[0069] Fig. 3 It is a partial enlarged view of a variable scanning range micro mirror based on the bistable principle;

[0070] Fig. 4 It is a labeled diagram of the overall structure of a variable scanning range micro mirror based on the bistable principle;

[0071] Fig. 5 It is a slow axis and fast axis torsional vibration modal diagram of a variable scanning range micro mirror based on the bistable principle;

[0072] Fig. 6 It is an amplitude-frequency curve diagram of the slow axis torsional vibration modal of a variable scanning range micro mirror based on the bistable principle under different driving voltages;

[0073] Fig. 7 It is an attractor basin diagram of the slow axis torsional vibration modal of a variable scanning range micro mirror based on the bistable principle;

[0074] Fig. 8 It is an optical scanning diagram of a variable scanning range micro mirror based on the bistable principle in high and low amplitude states;

[0075] Fig. 9 It is a scanning effect schematic diagram of a variable scanning range micro mirror based on the bistable principle used as a laser radar;

[0076] Fig. 10This is a process flow diagram of the fabrication process of a variable scanning range micromirror based on the bistable principle according to the present invention.

[0077] In the attached figures: 1. Mirror; 2. Fast axis; 3. Fast axis drive ring; 4. Fast axis piezoelectric film; 5. Fast axis drive ring beam; 6. Decoupling ring; 7. Slow axis; 8. Slow axis drive ring; 9. Slow axis piezoelectric film; 10. Slow axis drive ring beam; 11. Fast axis electrode lead; 12. Fast axis metal electrode; 13. Slow axis electrode lead; 14. Slow axis metal electrode; 15. Base. Detailed Implementation

[0078] Example 1

[0079] See appendix Figs. 1-4 As shown, a micromirror and lidar with variable scanning range based on the bistable principle includes: a mirror 1, a fast axis 2, a fast axis drive ring 3, a fast axis piezoelectric thin film 4, a fast axis drive ring beam 5, a decoupling ring 6, a slow axis 7, a slow axis drive ring 8, a slow axis piezoelectric thin film 9, a slow axis drive ring beam 10, a fast axis electrode lead 11, a fast axis metal electrode 12, a slow axis electrode lead 13, a slow axis metal electrode 14, and a base 15, which are fabricated using SOI wafer integrated processing;

[0080] The mirror 1 is located at the center of the entire structure, connected to the fast axis drive ring 3 via the fast axis 2, and mechanically isolated from the slow axis 7 and the slow axis drive ring 8 via the decoupling ring 6.

[0081] The mirror 1 is a large-area circular metal mirror with a smooth surface, used to reflect incident light, and its upper and lower ends are fixedly connected to the fast axis 2 respectively.

[0082] The fast shaft 2 is a torsion beam with a rectangular cross-section, comprising upper and lower parts. The inner ends of the two parts are fixedly connected to the mirror surface 1, and the outer ends are fixedly connected to the fast shaft drive ring 3. The fast shaft 2 can be twisted along its axial direction, causing the mirror surface 1 to deflect around the axis of the fast shaft 2.

[0083] The fast shaft drive ring 3 is a circular ring. The upper and lower ends of the inner part of the ring are fixedly connected to the fast shaft 2, and the upper and lower ends of the outer part of the ring are fixedly connected to the decoupling ring 6 through the fast shaft drive ring beam 5.

[0084] The fast axis drive ring 3 is covered with two fast axis piezoelectric films 4. The two fast axis piezoelectric films 4 are semi-circular rings, symmetrically arranged, and their two ends are fixedly connected to the fast axis metal electrode 12 through fast axis electrode leads 11, which are used to connect to the external drive circuit.

[0085] The fast-axis piezoelectric film 4 generates a torsional torque through the inverse piezoelectric effect, driving the fast-axis 2 to twist along its axial direction;

[0086] The fast shaft drive ring beam 5 and the fast shaft 2 are on the same axis.

[0087] The decoupling ring 6 is a single-crystal silicon structure in the shape of a circular ring, and is fixedly connected with the fast-axis driving ring beam 5 and the slow axis 7 in two orthogonal directions, respectively; the decoupling ring 6 is located between the fast-axis driving ring 3 and the slow-axis driving ring 8, and is used to reduce the coupling effect and block the energy transmission between the fast axis 2 and the slow axis 7, thereby ensuring the independence of the biaxial vibration;

[0088] The axis of the fast-axis driving ring beam 5 and the axis of the slow axis 7 are perpendicular to each other;

[0089] The slow axis 7 is a torsional beam in the shape of a rectangular section, and includes left and right two parts, the inner ends of which are fixedly connected with the decoupling ring 6, respectively, and the outer ends of which are fixedly connected with the slow-axis driving ring 8, respectively; the slow axis 7 can be twisted along the axis direction thereof, thereby driving the mirror 1 to deflect around the axis of the slow axis 7;

[0090] The axis of the slow axis 7 and the axis of the fast axis 2 are perpendicular to each other, and the spatial positions of the two are orthogonal, which is used to change the deflection angles of the mirror 1 in two orthogonal directions, thereby changing the angles of the reflected light rays;

[0091] The slow-axis driving ring 8 is in the shape of a circular ring, and the upper and lower ends inside the circular ring are fixedly connected with the slow axis 7, and the upper and lower ends outside the circular ring are fixedly connected with the base 15 through the slow-axis driving ring beam 10;

[0092] Two slow-axis piezoelectric thin films 9 are covered on the slow-axis driving ring 8, the two slow-axis piezoelectric thin films 9 are in the shape of a semicircular ring and are symmetrically arranged, and the two ends thereof are fixedly connected with the slow-axis metal electrode 14 through the slow-axis electrode lead 13, respectively, which is used to be connected with the external driving circuit;

[0093] The slow-axis piezoelectric thin film 9 generates a torsional moment through the inverse piezoelectric effect, thereby driving the slow axis 7 to be twisted along the axis direction thereof;

[0094] The slow-axis driving ring beam 10 is on the same axis as the slow axis 7.

[0095] The fast-axis metal electrode 12 and the fast-axis electrode lead 11 are used to apply an alternating voltage to drive the fast-axis piezoelectric thin film 4 to generate the inverse piezoelectric effect; the slow-axis metal electrode 14 and the slow-axis electrode lead 13 are used to apply an alternating voltage to drive the slow-axis piezoelectric thin film 9 to generate the inverse piezoelectric effect;

[0096] The two fast-axis piezoelectric thin films 4 are designed with four fast-axis metal electrodes 12 in total, and the positive and negative electrodes of the two fast-axis piezoelectric thin films 4 are connected through the four fast-axis electrode leads 11, respectively; the two slow-axis piezoelectric thin films 9 are designed with four slow-axis metal electrodes 14 in total, and the positive and negative electrodes of the two slow-axis piezoelectric thin films 9 are connected through the four slow-axis electrode leads 13, respectively;

[0097] The fast-axis electrode lead 11 is fixedly connected with the fast-axis piezoelectric film 4, the fast-axis driving ring 3, the fast-axis driving ring beam 5, the decoupling ring 6, the slow-axis 7, the slow-axis driving ring 8, the slow-axis driving ring beam 10, the fast-axis metal electrode 12 and the base 15 respectively; the slow-axis electrode lead 13 is fixedly connected with the slow-axis piezoelectric film 9, the slow-axis driving ring 8, the slow-axis driving ring beam 10, the slow-axis metal electrode 14 and the base 15 respectively.

[0098] The fast-axis metal electrode 12 and the slow-axis metal electrode 14 are fixedly connected with the base 15.

[0099] Embodiment 2: A micromirror scanning method based on a bistable principle variable scanning range

[0100] The above micromirror is used as a method for using a laser radar as follows:

[0101] 1) A high-frequency alternating voltage is applied to the fast-axis driving ring 3 through the fast-axis metal electrode 12, and the inverse piezoelectric effect of the fast-axis piezoelectric film 4 is used to drive the mirror surface 1 to twist around the fast-axis 2 at a high speed, thereby realizing fast scanning of a light beam;

[0102] 2) A low-frequency alternating voltage is applied to the slow-axis driving ring 8 through the slow-axis metal electrode 14 , wherein, U dc is a direct current bias voltage, U ac is an alternating voltage amplitude, Ω is an angular frequency, φ 0 is an initial phase. By increasing the amplitude of the alternating voltage U ac , the twist angle of the slow-axis 7 is increased θ 2y , thereby amplifying the cubic nonlinearity of the slow-axis 7 K n , which affects the mirror surface 1, so that the amplitude-frequency curve of the slow-axis 7 is bent to the left or right, and a frequency interval with high and low two stable amplitude states appears, triggering the bistable characteristics of the system.

[0103] 3) Around the natural frequency of the slow-axis 7, forward and reverse frequency sweeping is performed to mark the amplitude upward jump frequency point f u and the amplitude downward jump frequency point f d , and determine the frequency interval range of the bistable state f u ～f d ;

[0104] 4) Select the middle frequency value of the bistable interval As the driving frequency, by changing the DC bias voltage U dc and initial phase φ 0 , change the initial torsion angle and initial angular velocity, record the amplitude state of the slow axis 7 torsional vibration mode under different initial torsion angle and initial angular velocity, draw the attractor basin image, as shown in Fig. 7 .

[0105] 5) By adjusting the DC bias voltage U dc and initial phase φ 0 , combined with the attractor basin image, precise selection and switching of steady-state amplitude, so as to dynamically adjust the torsional amplitude of the mirror 1 around the slow axis 7, expand or reduce the scanning range, as shown in Fig. 8 ;

[0106] 6) Under the comprehensive control of the torsional vibration of the fast axis 2 and the slow axis 7, the reflected light of the incident light will perform surface scanning on the target object; the decoupling ring 6 can ensure the stability of the bistable switching by suppressing the mechanical coupling between the fast axis 2 and the slow axis 7, and finally realize the high-precision dynamic control of the micro-mirror scanning range.

[0107] 7) Based on the micro-mirror, develop laser radar application, as shown in Fig. 9 , through Lissajous scanning, collect two-dimensional point cloud (x, y) Combined with TPF ranging method, fuse point cloud data, form three-dimensional point cloud (x, y, z) , so as to realize high-precision three-dimensional image reconstruction of large-scale point cloud perception, and provide foundation for three-dimensional image reconstruction algorithm application of point cloud in unmanned driving, navigation map and other fields.

[0108] The natural frequency of the fast axis 2 and the slow axis 7 depends on the actual application scene demand, the natural frequency of the fast axis 2 is usually much larger than that of the slow axis 7, and the motion equation and natural frequency of the two can be derived and calculated through Lagrange energy method:

[0109] The dynamics equation of the fast axis 2 and the slow axis 7 of the whole micro-mirror can be represented by the following Lagrange equation set:

[0110] (1)

[0111] Wherein, t represents time, T, U represents the total kinetic energy and total potential energy of the micro-mirror, θ 1x , θ 2y , θ 2xφ2, φ7, and φ1, respectively, represent the torsion angles of the fast-axis 2 torsional vibration mode, the slow-axis 7 torsional vibration mode (as shown in FIG. 2), and the bending vibration mode of the mirror 1 around the fast-axis 2, respectively; Fig. 5 θ 1x , θ 2y , θ 2x The first-order derivative with respect to time t, i.e., the rotation angular velocity; M 1x 、M 2y 、M 2x The driving torques applied to the above three modes, respectively; the kinetic energy T mainly comes from the fixed-axis rotation of the mirror 1, the fast-axis 2, and the slow-axis 7, and the potential energy U is mainly stored in the fast-axis 2 and the slow-axis 7 in the form of torsional deformation, and the expressions of T and U can be obtained through dynamic analysis:

[0112] (2)

[0113] (3)

[0114] wherein, J 1x 、J 2y 、J 2x The moments of inertia of the fast-axis 2 torsional vibration mode, the slow-axis 7 torsional vibration mode, and the bending vibration mode of the mirror 1 around the fast-axis 2, respectively; K 1x 、K 2y 、K 2x The linear stiffnesses of the fast-axis 2 torsional vibration mode, the slow-axis 7 torsional vibration mode, and the bending vibration mode of the mirror 1 around the fast-axis 2, respectively. The three-degree-of-freedom dynamic equation of the micro-mirror can be obtained by substituting the formula (2) and (3) into the formula (1) and adding a damping term:

[0115] (4)

[0116] wherein, C 1x 、C 2y 、C 2x The linear dampings of the fast-axis 2 torsional vibration mode, the slow-axis 7 torsional vibration mode, and the bending vibration mode of the mirror 1 around the fast-axis 2, respectively; ​​​​、 、 For θ 1x , θ 2y , θ 2x The second derivative with respect to time t, i.e. the angular acceleration. To obtain the natural vibration angular frequency of the micromirror, the effects of damping and driving torque are eliminated, and the linear undamped free vibration equations of the fast axis 2 and slow axis 7 torsional modes are established as follows:

[0117] (5)

[0118] The natural frequency of the fast axis 2 torsional mode can be further obtained as ω 1 and the natural frequency of the slow axis 7 torsional mode as ω 2 :

[0119] (6)

[0120] where the moment of inertia J 1x 、J 2y is determined by the designed structural parameters and can be expressed as:

[0121] (7)

[0122] (8)

[0123] wherein m is the device layer thickness of the micromirror, ρ is the density of single crystal silicon, r、R 1 、R 2 、R 3 、R 4 、R 5 、R 6 are the radius of the mirror 1, the inner diameter of the fast axis drive ring 3, the outer diameter of the fast axis drive ring 3, the inner diameter of the decoupling ring 6, the outer diameter of the decoupling ring 6, the inner diameter of the slow axis drive ring 8, and the outer diameter of the slow axis drive ring 8, respectively, as shown in the accompanying drawings. Fig. 4 K 1x is the linear stiffness of the fast axis (2) torsional vibration mode and K 2y is the linear stiffness of the slow axis (7) torsional vibration mode, which can be expressed as:

[0124] ​ (9)

[0125] (10)

[0126] wherein, β 1 、β 2 is the torsional section coefficient related to the rectangular section aspect ratio of the fast axis 2 and the slow axis 7, G is the shear modulus; b 1 、b 2 are the width of the fast axis 2 and the slow axis 7, respectively, L 1 、L 2 are the length of the fast axis 2 and the slow axis 7, respectively.

[0127] In order to make the slow axis 7 torsional vibration appear bistable phenomenon, it is necessary to increase the alternating voltage applied to the slow axis piezoelectric film 9, so that the torsional vibration of the slow axis 7 is enhanced, and the cubic linear stiffness K 2x,3 The linear stiffness softening or hardening phenomenon caused by the slow axis 7, causes the slow axis 7 to bend to the left or to the right, and appears a bistable frequency interval with high and low two stable amplitude solutions, as shown in Fig. 6 The nonlinear forced vibration equation of the slow axis 7 can be approximately expressed as:

[0128] (11).

[0129] Embodiment 3: A micromirror preparation method based on the bistable principle variable scanning range

[0130] Referring to the accompanying drawings, the process flow of the micromirror of the present application is shown in Fig. 10

[0131] (a). Select a 6-inch SOI wafer, wherein the device layer is 60 μm, the oxide layer is 2 μm, the substrate layer is 450 μm, and the top layer of 200 nm SiO2 is performed by LPCVD / thermal oxidation;

[0132] (b). Using magnetron sputtering, a stack layer composed of bottom Pt, PZT and top Pt is sequentially deposited on the SOI, with thicknesses of 200 nm, 4 μm and 200 nm, respectively;

[0133] (c). Spin coating photoresist;

[0134] (d). Using a mask, the top Pt electrode of the fast axis electrode lead and the slow axis electrode lead is etched by dry etching, and stopping at the PZT layer;

[0135] (e). Remove the photoresist;​

[0136] (f). spin photoresist;

[0137] (g). dry etching the piezoelectric layer PZT of the fast axis piezoelectric film and the slow axis piezoelectric film using a mask plate and stopping at the bottom electrode Pt layer;

[0138] (h). removing the photoresist;

[0139] (i). spin photoresist;

[0140] (j). dry etching the bottom electrode Pt of the fast axis electrode lead and the slow axis electrode lead using a mask plate and stopping at the SiO2 layer;

[0141] (k). removing the photoresist;

[0142] (l) preparing a top electrode insulating layer SiO2 of the fast axis electrode lead and the slow axis electrode lead with a thickness of 500 nm using an evaporation process;

[0143] (m). spin photoresist;

[0144] (n). etching the SiO2 insulating oxide layer using a mask plate to form an etching window with a size of 60 μm, exposing the top electrode and the bottom electrode of the fast axis electrode lead and the slow axis electrode lead;

[0145] (o). removing the photoresist;

[0146] (p). spin photoresist;

[0147] (q). etching the pattern of the fast axis metal electrode and the slow axis metal electrode using a mask plate;

[0148] (r). magnetron sputtering Cr / Au, wherein the thickness of Cr is 20 nm and the thickness of Au is 200 nm;

[0149] (s). preparing the top and bottom fast axis metal electrode and slow axis metal electrode and metal mirror using a Lift off process;

[0150] (t). spin photoresist;

[0151] (u). etching the SiO2 insulating oxide layer using a mask plate;

[0152] (v). DRIE etching the device layer to a depth of 60 μm, etching through the SOI device layer to obtain a single crystal silicon body structure of the mirror, the fast axis, the fast axis drive ring, the fast axis drive ring beam, the decoupling ring, the slow axis, the slow axis drive ring, the slow axis drive ring beam, and the pedestal;

[0153] (w). removing the photoresist;

[0154] (x). Forward spin on photoresist, protect device structure;

[0155] (y). Backward spin on photoresist;

[0156] (z). DRIE etch back of substrate layer using mask, etch depth 450 μm, remove excess single crystal silicon structure;

[0157] (aa). Dry etch SiO2 insulating oxide layer 2 μm;

[0158] (bb). Remove photoresist, release structure.

Claims

1. A micromirror with variable scanning range based on bistable principle, characterized in that: The mirror surface (1), the fast axis (2), the fast axis drive ring (3), the fast axis drive ring beam (5), the decoupling ring (6), the slow axis (7), the slow axis drive ring (8), the slow axis drive ring beam (10) and the base (15) are sequentially arranged from inside to outside. The mirror surface (1) is connected with the fast axis (2) and the fast axis drive ring (3) through the fast axis (2) at the upper and lower ends of the mirror surface (1). The decoupling ring (6) is connected with the slow axis drive ring (8) through the slow axis (7) at the left and right ends of the outer side of the decoupling ring (6). The fast axis (2) is provided with two arc-shaped fast axis piezoelectric thin films (4) on the two sides of the fast axis drive ring (3). The slow axis (7) is provided with two arc-shaped slow axis piezoelectric thin films (9) on the two sides of the slow axis drive ring (8). The fast axis piezoelectric thin film (4) and the slow axis piezoelectric thin film (9) are provided with metal electrodes at the two ends thereof. The fast axis (2) and the slow axis (7) are torsional beams with a rectangular cross section.

2. A micromirror based on the principle of bistability with variable scanning range according to claim 1, characterized in that: The micromirror is prepared from a single crystal silicon structural material.

3. A laser radar with variable scanning range based on the principle of bistability, characterized in that: The laser emission unit, the light beam scanning unit, the optical receiving unit, the signal processing and system control unit are comprised; the light beam scanning unit adopts the micromirror based on the bistable principle and variable scanning range according to claim 1.

4. A scanning method of a micromirror, characterized by: The micromirror is the micromirror based on the bistable principle and variable scanning range according to claim 1, and the steps are as follows: 1) high-frequency alternating voltage is applied to the fast axis drive ring (3) through the fast axis metal electrode (12), the mirror surface (1) is driven to twist around the fast axis (2) at high speed by using the inverse piezoelectric effect of the fast axis piezoelectric thin film (4), and light beam rapid scanning is realized; 2) applying a low frequency alternating voltage to the slow axis drive ring (8) through the slow axis metal electrode (14) wherein, U dc is a DC bias voltage, U ac is an alternating voltage amplitude, Ω is an angular frequency, φ 0 is an initial phase; by increasing the amplitude U of the alternating voltage ac , the torsion angle of the slow axis (7) is increased θ 2y , thus amplifying the third order nonlinear stiffness of the slow axis (7) K n to the mirror (1), so that the amplitude-frequency curve of the slow axis (7) is bent to the left or right, and a frequency interval with high and low two steady-state amplitude states appears, triggering the bistable characteristics of the system; 3) around the intrinsic frequency of the slow axis (7), forward and reverse sweep, mark the amplitude up-jump frequency point f u and the amplitude down-jump frequency point f d , determine the bistable frequency interval range f u ～f d ; 4) selecting a middle frequency value of the bistable interval As the driving frequency, by changing the DC bias voltage U dc And the initial phase φ 0 , change the initial torsion angle and the initial angular velocity, record the amplitude state of the torsional vibration mode of the slow axis (7) under different initial torsion angles and initial angular velocities, and draw an attractor basin image; 5) by regulating the direct current bias voltage U dc and initial phase φ 0 , combined with the attraction basin image, accurate selection and switching of steady-state amplitude, thereby dynamically adjusting the torsion amplitude of the mirror (1) around the slow axis (7), expanding or reducing the scanning range; 6) under the comprehensive regulation and control of the torsional vibration of the fast axis (2) and the slow axis (7), the reflected light of the incident light will perform surface scanning on the target object; the decoupling ring (6) ensures the stability of the bistable switching by inhibiting the mechanical coupling between the fast axis (2) and the slow axis (7), and realizes high-precision dynamic regulation of the scanning range of the micromirror.

5. The scanning method of the micromirror according to claim 4, wherein: The dynamic equation of the fast axis (2) and the slow axis (7) can be represented by the following Lagrange equation set: ； where t represents time, T, U represent the total kinetic energy and total potential energy of the micromirror, θ 1x 、θ 2y 、θ 2x respectively represent the torsional angle of the fast axis (2) torsional vibration mode, the slow axis (7) torsional vibration mode, and the mirror (1) bending vibration mode around the fast axis (2); θ 1x 、θ 2y 、θ 2x the first order derivative with respect to time t, i.e. the rotation angular velocity; M 1x 、M 2y 、M 2x respectively represent the driving torque applied to the above three modes; the kinetic energy T mainly comes from the fixed axis rotation of the mirror (1), the fast axis (2) and the slow axis (7), and the potential energy U is mainly stored in the form of torsional deformation in the fast axis (2) and the slow axis (7), and the expressions of T and U can be obtained through dynamic analysis:​​​ （2）； （3）； wherein, J 1x 、J 2y 、J 2x are the moments of inertia of the twist vibration mode of the fast axis (2), the twist vibration mode of the slow axis (7), and the bending vibration mode of the mirror (1) around the fast axis (2), respectively; K 1x 、K 2y 、K 2x are the linear stiffnesses of the twist vibration mode of the fast axis (2), the twist vibration mode of the slow axis (7), and the bending vibration mode of the mirror (1) around the fast axis (2), respectively; bringing equations (2) and (3) into equation (1) and adding a damping term, the three-degree-of-freedom dynamics equation of the micro-mirror is obtained as: ； wherein C 1x 、C 2y 、C 2x respectively represent the linear damping of the fast axis (2) torsional vibration mode, the slow axis (7) torsional vibration mode, and the mirror (1) bending vibration mode around the fast axis (2); , , is θ 1x 、θ 2y 、θ 2x The second derivative with respect to time t, i.e. the angular acceleration, establishes the linear undamped free vibration equation of the fast axis (2) and slow axis (7) torsional modes as follows: （5）； Further, the natural frequency of the twist mode of the fast axis (2) can be obtained ω 1 and the natural frequency of the twist mode of the slow axis (7) ω 2 ; （6）； Wherein the moment of inertia J 1x 、 J 2y The designed structure parameters can be represented as: （7）； （8）； wherein m is the device layer thickness of the micromirror, ρ is the density of the single-crystal silicon, r、R 1 、R 2 、R 3 、R 4 、R 5 、R 6 are the radius of the mirror (1), the inner diameter of the fast-axis drive ring (3), the outer diameter of the fast-axis drive ring (3), the inner diameter of the decoupling ring (6), the outer diameter of the decoupling ring (6), the inner diameter of the slow-axis drive ring (8), the outer diameter of the slow-axis drive ring (8), respectively, K 1x are the linear stiffness of the fast-axis (2) torsional vibration mode and K 2y is the linear stiffness of the slow-axis (7) torsional vibration mode, which can be expressed as: （9）； （10）； wherein β 1 、β 2 is the twist section coefficient related to the rectangular section aspect ratio of the fast axis (2) and the slow axis (7), G G is the shear modulus; b 1 、b 2 are the width of the fast axis (2) and the slow axis (7), respectively, L 1 、L 2 are the length of the fast axis (2) and the slow axis (7), respectively, In order to make the slow axis (7) torsional vibration appear bistable phenomenon, it is necessary to increase the alternating voltage applied to the slow axis piezoelectric film (9), so that the slow axis (7) torsional vibration is enhanced, and the cubic nonlinear stiffness is shown K n The linear stiffness softening or hardening phenomenon caused by the slow axis (7) amplitude frequency curve bending to the left or right, appears the bistable frequency interval with high and low two stable amplitude solutions, at this time the nonlinear forced vibration equation of the slow axis (7) can be approximately expressed as: (11)。 6. The method of scanning a micromirror according to claim 5, wherein: The fast axis frequency is 2600 Hz, and the slow axis frequency is 2150 Hz.

7. A method of fabricating a micromirror, characterized by: The micromirror is the micromirror based on the bistable principle and variable scanning range according to claim 1, and the steps are as follows: a. 6-inch SOI wafer is selected, wherein the device layer is 60 μm, the oxide layer is 2 μm, the substrate layer is 450 μm, and the top layer of 200 nm SiO2 is subjected to LPCVD / thermal oxidation; b. a stack layer composed of bottom Pt, PZT and top Pt is deposited on the SOI in sequence by using a magnetron sputtering, and the thicknesses are 200 nm, 4 μm and 200 nm respectively; c. photoresist is spin-coated, ICP top Pt electrode is dry etched, and the process is stopped at the PZT layer; e. Remove photoresist, spin photoresist again, dry etch ICP piezoelectric layer PZT and stop at the bottom electrode Pt layer; f. Remove photoresist, spin photoresist again, dry etch ICP bottom electrode Pt and stop at the SiO2 layer; g. Remove photoresist, use evaporation process to prepare 500nm-thick top electrode insulating layer SiO2 of fast-axis electrode lead and slow-axis electrode lead; h. Spin photoresist, use mask to etch SiO2 insulating oxide layer, etch window size is ϕ60μm, expose the top and bottom electrodes of fast-axis electrode lead and slow-axis electrode lead; i. Remove photoresist, spin photoresist again, make metal electrode pattern; j. Magnetron sputter Cr / Au, thickness of Cr is 20nm, thickness of Au is 200nm; k. Use Lift off process to prepare top and bottom fast-axis metal electrode and slow-axis metal electrode and metal mirror surface; l. Spin photoresist, use mask to etch SiO2 insulating oxide layer; m. DRIE etch device layer, etch depth is 60μm, etch through SOI device layer, obtain single-crystal silicon body structure of mirror surface, fast axis, fast-axis drive ring, fast-axis drive ring beam, decoupling ring, slow axis, slow-axis drive ring, slow-axis drive ring beam and pedestal; n. Remove photoresist; Spin photoresist forwardly, spin photoresist backwardly, use photoetching mask VII, DRIE etch substrate layer backwardly, etch depth is 450μm; o. Use mask to DRIE etch substrate layer backwardly, etch depth is 450μm, remove excess single-crystal silicon structure; p. Dry etch SiO2 insulating oxide layer 2μm, remove photoresist, release structure.

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