A MEMS micromirror based on radial magnetic field distribution

Abstract

The present invention discloses a MEMS micromirror based on radial magnetic field distribution, comprising a substrate, an outer frame, an inner frame, a mirror surface, a second torsion shaft and a first torsion shaft; both the outer frame and the inner frame are rings composed of two semi-circles, with a gap provided between the ends of the two semi-circles of the same frame. The mirror surface is arranged in the inner frame, and the inner frame is arranged in the outer frame; the inner frame is rotationally connected to the mirror surface through the first torsion shaft, and the outer frame is rotationally connected to the substrate through the second torsion shaft; a first magnet and a second magnet are arranged below the mirror surface, with a gap provided between the first magnet and the second magnet. The magnetic pole direction of the first magnet is axial, and the magnetic pole directions of the first magnet and the second magnet are opposite; a first coil is arranged on the surface of the inner frame facing the first magnet. The first coil is divided into two parts with the gap of the inner frame as the boundary, and each part is distributed in a serpentine folded shape around the semi-circle of the inner frame to form a loop; a second coil is arranged on the surface of the outer frame facing the first magnet, and the second coil is circular.

Description

Technical Field

[0001] The present invention belongs to the field of microelectromechanics and relates to a MEMS micromirror based on a radial magnetic field distribution. Background Art

[0002] A lidar system is a radar system that detects the position, speed and other characteristic quantities of a target by emitting laser beams, integrating a variety of advanced technologies such as laser technology, optoelectronic technology, microchip technology and optical technology. In recent years, as driverless and autonomous driving have gradually become research hotspots, lidar has been rapidly applied in the fields of driverless cars, exploration and detection of complex terrains, and three-dimensional modeling of urban buildings due to its advantages of fast scanning speed, high accuracy, small size, light weight and strong anti-interference ability compared with microwave radars.

[0003] One of the important optical devices in MEMS lidar - the MEMS micromirror, belongs to an optical MEMS actuator chip, which can deflect, modulate, turn on and off, and phase-control laser beams under the driving action.

[0004] In existing electromagnetic MEMS micromirrors, the magnetic field placement method mostly uses a 45° angle with the micromirror. The X and Y components of the magnetic field respectively provide the driving torques required for the two axes of the micromirror. In this way, the magnetic field is not fully utilized, resulting in limited driving torque and the micromirror cannot obtain a large deflection angle. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned disadvantages of the prior art and provide a MEMS micromirror based on a radial magnetic field distribution, which generates a radial magnetic field under the micromirror to realize the driving of the micromirror, effectively improving the driving torque.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A MEMS micromirror based on a radial magnetic field distribution includes a substrate, an outer frame, an inner frame, a mirror surface, a second torsion shaft and a first torsion shaft;

[0008] The outer frame, the inner frame and the mirror surface are all coplanar and are all laid flat on the substrate. The outer frame and the inner frame are both circular rings composed of two semi-circles. There is a gap between the ends of the two semi-circles of the same frame. The mirror surface is arranged in the inner frame, and the inner frame is arranged in the outer frame; the inner frame is rotationally connected to the mirror surface through the first torsion shaft, and the outer frame is rotationally connected to the substrate through the second torsion shaft;

[0009] A first magnet in the shape of a cylinder is arranged below the mirror surface. A second magnet in the shape of a toroid is arranged outside the circumferential surface of the first magnet. There is a gap between the first magnet and the second magnet. The mirror surface, the first magnet and the second magnet are concentrically arranged. The magnetic pole direction of the first magnet is axial, and the magnetic pole directions of the first magnet and the second magnet are opposite;

[0010] On one side of the inner frame facing the first magnet, a first coil is provided. The first coil is divided into two parts with the gap of the inner frame as the boundary. Each part is distributed in a serpentine folded shape around the semi-circular part of the inner frame to form a circuit. On one side of the outer frame facing the first magnet, a second coil is provided, and the second coil is circular.

[0011] Preferably, the axial directions of the first rotating shaft and the second rotating shaft are perpendicular.

[0012] Preferably, a reinforcing rib is provided between the mirror surface and the inner frame. The reinforcing rib is a ring composed of two semi-circular ribs. There is a gap between the ends of the two semi-circular ribs. The reinforcing rib is rotationally connected to the mirror surface through a first torsion shaft.

[0013] Preferably, the second torsion shaft is a serpentine folded structure.

[0014] Preferably, the first torsion shaft is a straight beam structure.

[0015] Preferably, the second coil is located at the gap between the first magnet and the second magnet.

[0016] Preferably, the mirror surface is coated with a reflective film.

[0017] Furthermore, the material of the reflective film is gold or aluminum.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] For the micromirror of the present invention, since the magnetic pole directions of the first magnet and the second magnet are opposite, the two are coupled to form a radially distributed stable magnetic field, thereby obtaining a radial magnetic field to drive the two torsion shafts. The mirror surface is rotated through the first torsion shaft and the second torsion shaft, and then the two-dimensional deflection in the orthogonal direction of the mirror surface is realized, effectively improving the driving torque. And in the micromirror structure of the present invention, there is no electroplated coil or film on the mirror surface, which belongs to a passive device and will not cause failure problems such as mirror surface deformation caused by ohmic heat generated during long-term operation or high-current driving.

[0020] Furthermore, the second torsion shaft is designed as a serpentine folded beam structure, so that under the same driving torque, a larger torsional displacement output can be realized, obtaining a larger deflection angle of the micromirror, and meeting the wide scanning field of view requirements of the MEMS lidar system.

[0021] Furthermore, the second coil is located at the gap between the first magnet and the second magnet, so that the magnetic field is coupled at the outer frame to obtain a strong radial magnetic field and the maximum Ampere force, which can avoid the excessive volume of the magnet due to the requirement of a large driving torque. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic structural diagram of the MEMS micromirror of the present invention;

[0023] Figure 2 Top view of the MEMS mirror of the present invention;

[0024] Figure 3 Schematic diagram of the second torsion axis structure of the present invention;

[0025] Figure 4 Schematic diagram of the patterned coil of the outer frame of the MEMS mirror of the present invention;

[0026] Figure 5 Schematic diagram of the patterned coil of the inner frame of the MEMS mirror of the present invention;

[0027] Figure 6 Schematic diagram of the magnet arrangement of the present invention;

[0028] Figure 7 Finite element modal simulation diagram of deflection along the outer torsion axis of the present invention;

[0029] Figure 8 Harmonic response displacement nephogram of deflection along the outer torsion axis of the present invention;

[0030] Figure 9 Finite element modal simulation diagram of deflection along the inner torsion axis of the present invention;

[0031] Figure 10 Harmonic response displacement nephogram of deflection along the inner torsion axis of the present invention.

[0032] Wherein: 1 - substrate; 2 - outer frame; 3 - inner frame; 4 - mirror surface; 5 - second torsion axis; 6 - first torsion axis; 7 - reinforcing rib; 8 - first magnet; 9 - second magnet; 10 - yoke; 11 - first coil; 12 - second coil. Detailed implementation manner

[0033] The present invention will be further described in detail below with reference to the accompanying drawings:

[0034] As Figure 1 and Figure 2 shown, the MEMS mirror based on the radial magnetic field distribution of the present invention is a two-dimensional electromagnetic MEMS mirror, with a silicon material as the basic structure, including a substrate 1, an outer frame 2, an inner frame 3, a mirror surface 4, a second torsion axis 5, a first torsion axis 6, a reinforcing rib 7, a first magnet 8 and a second magnet 9.

[0035] The outer frame 2, the inner frame 3, and the mirror surface 4 are all coplanar and are all laid flat on the substrate 1. The outer frame 2 and the inner frame 3 are both rings composed of two semi - circles, with a gap set between the ends of the two semi - circles of the same frame. The semi - circle ends of the outer frame 2 extend towards the inner frame. The mirror surface 4 is arranged in the inner frame 3, and the inner frame 3 is arranged in the outer frame 2. The axial directions of the first rotating shaft and the second rotating shaft are perpendicular; the inner frame 3 and the mirror surface 4 are rotationally connected through the first torsion shaft 6, and the outer frame 2 and the substrate 1 are rotationally connected through the second torsion shaft 5; the second torsion shaft 5 is a serpentine folding structure, and the first torsion shaft 6 is a straight beam structure. The outer frame 2 can deflect around the second torsion shaft 5, and the inner frame 3 and the circular mirror surface 4 can deflect around the first torsion shaft 6, thereby realizing the two - dimensional deflection work in the orthogonal directions of the mirror surface 4.

[0036] A reflective film is plated on the surface of the mirror surface 4, and the material of the reflective film is gold or aluminum.

[0037] Reinforcing ribs 7 are arranged between the mirror surface 4 and the inner frame 3. The reinforcing ribs 7 are rings composed of two semi - circular ribs, with a gap set between the ends of the two semi - circular ribs. The reinforcing ribs 7 and the mirror surface 4 are rotationally connected through the first torsion shaft 6.

[0038] As Figure 5 and Figure 1 shown, a first magnet 8 and a second magnet 9 are placed below the two - dimensional electromagnetic MEMS mirror body of the present invention. The second magnet 9 is arranged outside the circumferential surface of the first magnet 8, with a gap set between the first magnet 8 and the second magnet 9. A yoke 10 is arranged below the second magnet 9, and the yoke 10 connects and fixes the first magnet 8 and the second magnet 9. The mirror surface 4, the first magnet 8, and the second magnet 9 are concentrically arranged. The first magnet 8 is a cylindrical neodymium - iron - boron magnet, and the second magnet 9 is an annular neodymium - iron - boron magnet. Among them, the magnetic pole direction of the first magnet 8 is vertically upward, and the magnetic pole direction of the second magnet 9 is opposite to it, and the two are coupled to form a radially distributed stable magnetic field.

[0039] On the side of the inner frame 3 facing the first magnet 8, a first coil 11 is arranged. The first coil 11 is divided into two parts with the gap of the inner frame 3 as the boundary. Each part is distributed in a serpentine folding shape around the semi - circular parts of the inner frame 3 and the reinforcing ribs 7 to form a loop; on the side of the outer frame 2 facing the first magnet 8, a second coil 12 is arranged, and the second coil 12 is circular - ring - shaped. The first coil 11 and the second coil 12 are arranged in a single - wire single - turn manner, and the second coil 12 is located in the gap between the first magnet 8 and the second magnet 9.

[0040] When the two-dimensional electromagnetic MEMS mirror works, an external signal source supplies power to the first coil 11 and the second coil 12 through metal electrodes. When powered on, the second coil 12 placed in the radial magnetic field generates a Lorentz force, driving the outer frame 2 to deflect around the second torsion axis 5. Because of the magnet model design, the coupling strength of the radial magnetic field is the largest at the outer frame 2. When a 60 Hz square wave signal is input to the second coil 12, the outer frame 2 obtains the maximum driving torque, and is forced to passively complete a large-angle quasi-static linear deflection around the second torsion axis 5. A sine signal with the same resonance frequency as the first torsion axis 6 is input to the first coil 11, so that it works in a resonance state and resonates, actively amplifying the deflection angle of the mirror surface 4 around the first torsion axis 6. The two different drive input signals act on the patterned second coil 12 and the first coil 11 as shown in Figure 4 The graphic. This signal separation path design can reduce the crosstalk between scanning axes and improve the working stability of the mirror.

[0041] The outer torsion beam 5 of the two-dimensional electromagnetic MEMS mirror is designed as a serpentine folded beam structure. By increasing the number of folds and the beam length and reducing the beam width, the stiffness coefficient of the support beam is greatly reduced. Under the action of the same electromagnetic driving force, the serpentine folded beam structure obtains a larger displacement output than the straight beam, amplifying the deflection angle of the mirror.

[0042] The two-dimensional electromagnetic MEMS mirror is designed with a circular mirror surface 4 connected to a reinforcing rib 7 structure through the first torsion axis 6, completing part of the circuit structure of the first coil 11, making the mirror surface passive, and avoiding the influence of Joule heat generated by the coil energization on the flatness of the mirror surface; the reinforcing rib 7 structure can also effectively reduce the dynamic deformation of the mirror surface during the working deflection of the mirror, ensuring the quality of the projected scanning image.

[0043] Set the structural parameters of the two-dimensional electromagnetic MEMS mirror system: the diameter of the mirror surface is 2.6 mm, and the device thickness is 70 μm; the equivalent length of the second torsion axis is 800 μm, the width is 20 μm, and the thickness is 40 μm; the length of the first torsion axis is 300 μm, the width is 40 μm, and the thickness is 70 μm; the permanent magnet grade is N52, the diameter of the cylindrical neodymium iron boron magnet is 3.2 mm, the inner diameter of the annular neodymium iron boron magnet is 3.7 mm, and the outer diameter is 10 mm. The two are placed concentrically. In the working state, the finite element simulation angle of the mirror deflecting along the outer torsion axis is ±16°, and the simulation angle of the mirror deflecting along the inner torsion axis can reach ±25°, effectively improving the horizontal scanning field of view.

[0044] As Figure 7 shown, the first-order modal natural frequency of the finite element simulation of the mirror deflecting around the second torsion axis is 419.16 Hz, Figure 8 indicating that when the second torsion axis works in the resonance state, the serpentine folded beam structure design significantly improves the displacement deflection of the outer frame and increases the deflection angle. As Figure 9As shown, the natural frequency of the fifth-order mode of the micromirror deflecting around the first torsion axis is 3376.2 Hz, and its high resonance frequency characteristics meet the requirements of the resolution, frame rate, and robustness of the lidar. Figure 10 It shows that when the first torsion axis operates in the resonant state, the displacement output of the mirror surface in the vertical direction can reach 1.9577 mm, corresponding to a deflection angle of ±25°. The large scanning angle characteristics enable the lidar to perform 3D topography recognition and model construction within a larger field of view. The MEMS micromirror based on the radial magnetic field distribution proposed in the present invention meets the requirements of the application scenarios of hybrid solid-state lidars.

[0045] The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any modifications made on the basis of the technical solution according to the technical idea proposed in the present invention fall within the protection scope of the claims of the present invention.

Claims

1. A MEMS micromirror based on the radial magnetic field distribution, characterized in that, It includes a substrate (1), an outer frame (2), an inner frame (3), a mirror surface (4), a second torsion shaft (5) and a first torsion shaft (6); The outer frame (2), the inner frame (3) and the mirror surface (4) are coplanar and are all laid flat on the substrate (1). The outer frame (2) and the inner frame (3) are both circular rings composed of two semi - circles, and there is a gap between the ends of the two semi - circles of the same frame. The mirror surface (4) is arranged in the inner frame (3), and the inner frame (3) is arranged in the outer frame (2); The inner frame (3) is rotationally connected to the mirror surface (4) through the first torsion shaft (6), and the outer frame (2) is rotationally connected to the substrate (1) through the second torsion shaft (5); A first magnet (8) in the shape of a cylinder is arranged below the mirror surface (4). A second magnet (9) in the shape of a toroid is arranged outside the peripheral surface of the first magnet (8). There is a gap between the first magnet (8) and the second magnet (9). The mirror surface (4), the first magnet (8) and the second magnet (9) are concentrically arranged. The magnetic pole direction of the first magnet (8) is axial, and the magnetic pole directions of the first magnet (8) and the second magnet (9) are opposite; On one side of the inner frame (3) facing the first magnet (8), a first coil (11) is arranged. The first coil (11) is divided into two parts with the gap of the inner frame (3) as the boundary. Each part is distributed in a serpentine - folded shape around the semi - circle of the inner frame (3) to form a circuit; On one side of the outer frame (2) facing the first magnet (8), a second coil (12) is arranged. The second coil (12) is circular - ring - shaped; The first torsion shaft (6) is of a straight - beam structure; The second torsion shaft (5) is of a serpentine - folded structure.

2. The MEMS micromirror based on the radial magnetic field distribution according to claim 1, wherein The axes of the first shaft and the second shaft are perpendicular.

3. The MEMS micromirror based on the radial magnetic field distribution according to claim 1, wherein, Reinforcing ribs (7) are arranged between the mirror surface (4) and the inner frame (3). The reinforcing ribs (7) are circular rings composed of two semi - circular ribs, and there is a gap between the ends of the two semi - circular ribs. The reinforcing ribs (7) are rotationally connected to the mirror surface (4) through the first torsion shaft (6).

4. The MEMS micromirror based on the radial magnetic field distribution according to claim 1, wherein The second coil (12) is located in the gap between the first magnet (8) and the second magnet (9).

5. The MEMS micromirror based on the radial magnetic field distribution according to claim 1, characterized in that A reflective film is plated on the surface of the mirror surface (4).

6. The MEMS micromirror based on the radial magnetic field distribution according to claim 5, characterized in that, The material of the reflective film is gold or aluminum.

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