Two-dimensional MEMS micromirror based on nonlinear internal resonance phenomenon and driving method thereof

Abstract

The application discloses a two-dimensional MEMS micro-mirror based on a nonlinear internal resonance phenomenon and a driving method thereof, which comprises a reflecting mirror, a movable frame, a driving beam, an external torsional spring for deflecting the reflecting mirror and the movable frame around a horizontal axis in a first rotational resonance mode, an internal torsional spring for deflecting the reflecting mirror around a vertical axis in a second rotational resonance mode, and a control circuit, the first rotational resonance mode is a torsional movement of the reflecting mirror and the movable frame around the external torsional spring, the second rotational resonance mode is a torsional movement of the reflecting mirror around the internal torsional spring, and a ratio of inherent frequencies of the first rotational resonance mode and the second rotational resonance mode is 1:N or N:1, wherein N is a positive integer, and the nonlinear internal resonance phenomenon of the first rotational resonance mode and the second rotational resonance mode is ensured. The application realizes the vibration of the first and second rotational modes of the two-dimensional micro-mirror by the nonlinear internal resonance driving, simplifies the structure design of the two-dimensional micro-mirror and the complexity of a control loop, and simultaneously controls the first and second rotational modes of the two-dimensional micro-mirror by a single driving signal.

Description

Technical Field

[0001] This invention relates to the field of microelectromechanical systems (MEMS) technology, and in particular to a two-dimensional MEMS micromirror based on nonlinear internal resonance phenomenon and its driving method. Background Technology

[0002] MEMS (Micro Electro Mechanical System) micromirrors are optical MEMS devices used for beam steering. They can scan one-dimensional or two-dimensional laser beams and have advantages such as high scanning frequency, low power consumption, low cost, and small device size. They have been widely used in laser display, biomedical imaging, optical detection and ranging and other fields.

[0003] Traditional two-dimensional MEMS micromirrors can twist their mirrors in both the horizontal (X-axis) and vertical (Y-axis) directions. By designing corresponding drive beams in the mutually perpendicular X and Y axes, simultaneous X-axis and Y-axis mode actuation and two-dimensional object scanning can be achieved.

[0004] Patent document CN112817141A describes a two-dimensional MEMS micromirror and its driving method, which applies a first driving signal V with a frequency of ω1 through an external piezoelectric transducer. A (Piezoelectric signal) and second drive signal V B Due to the first driving signal V A Second drive signal V B The phases are opposite, and the bending deformation of the piezoelectric drive beam is opposite to that of the piezoelectric drive beam. The external torsion spring is subjected to the torsional torque of the piezoelectric drive beam, which causes the movable support, the internal piezoelectric transducer, the internal torsion spring, and the reflector to deflect about the X-axis, i.e., the first rotational resonance mode; a third driving signal V with a frequency of ω2 is applied to the internal transducer. C (Piezoelectric signal) and fourth drive signal V D Due to the third driving signal V C and the fourth driving signal V D The phase of the two-dimensional MEMS micromirror is opposite to that of the piezoelectric drive beam 5a-1, and the bending deformation of the other piezoelectric drive beam is opposite to that of the piezoelectric drive beam 5a-1. The internal torsion spring is subjected to the torsional torque of the piezoelectric drive beam 5a-1, which causes the mirror to deflect about the Y-axis, i.e., the second rotational resonant mode. From the perspective of energy flow, external energy is input into the first and second rotational resonant modes of the two-dimensional MEMS micromirror through the external piezoelectric transducer and the internal transducer, respectively. The two modes are independent of each other, without interaction or energy exchange. The two-dimensional scanning motion of the mirror is achieved by controlling the internal and external drive beams respectively.

[0005] It is evident that to drive a mirror in two-dimensional resonance, transducers (drivers and sensors) need to be set in the horizontal direction (X-axis) and the vertical direction (Y-axis) respectively. However, the internal transducers are often designed to deflect around the Y-axis along with the mirror, which results in complex structural design and manufacturing process, complex control circuit, high cost, and small mirror area. Summary of the Invention

[0006] The purpose of this invention is to provide a two-dimensional MEMS micromirror and its driving method to solve the technical difficulties of existing two-dimensional micromirror driving structures, small mirror area, complex control loops, and the need to improve stability.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a two-dimensional MEMS micromirror based on nonlinear internal resonance, comprising a mirror, a movable support, a drive beam, an external torsion spring for deflecting the mirror and the movable frame about a horizontal axis (X-axis) in a first rotational resonance mode, an internal torsion spring for deflecting the mirror about a vertical axis (Y-axis) in a second rotational resonance mode, and a control circuit. The horizontal axis (X-axis) is perpendicular to the vertical axis (Y-axis). The first rotational resonance mode is the torsional motion of the mirror and the movable support about the X-axis, and the second rotational resonance mode is the torsional motion of the mirror about the Y-axis. By adjusting the moment of inertia and torsional stiffness of the two-dimensional MEMS micromirror in different rotational resonance modes, the ratio of the natural frequencies of the first rotational resonance mode to the second rotational resonance mode is designed to be 1:N or N:1 (where N is a positive integer).

[0009] Furthermore, the drive beam can be designed as a piezoelectric transducer, electrostatic transducer, electromagnetic transducer, or electrothermal transducer. One end of the internal torsion spring is connected to the reflector and the other end is connected to the movable frame. One end of the external torsion spring is connected to the movable frame and the other end is connected to the drive beam. The control circuit can achieve closed-loop control of the two vertical scanning modes by applying a drive signal to the drive beam.

[0010] On the other hand, this invention provides a nonlinear internal resonance driving method for a two-dimensional MEMS micromirror. In a two-dimensional MEMS micromirror where the natural frequency ratio of the first rotational resonance mode to the second rotational resonance mode is 1:N or N:1 (where N is a positive integer), the first and second rotational resonance modes will exhibit nonlinear internal resonance under nonlinear vibration conditions, meaning that vibrational energy can be transferred between the two rotational resonance modes. By directly exciting the first rotational resonance mode to the nonlinear vibration range through a driving beam, the second rotational resonance mode can be indirectly excited, thus achieving two-dimensional resonance scanning.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0012] 1) Two-dimensional MEMS micromirror scanning is achieved through a pair of external driving beams, which reduces the number of driving beam structures for two-dimensional MEMS micromirrors, simplifies the design of the driving structure of two-dimensional MEMS micromirrors, increases the area of ​​the reflector, and reduces the requirements for high-focusing laser sources.

[0013] 2) By using a nonlinear internal resonance driving method, a single driving signal can be used to simultaneously control the first and second rotational modes of vibration of a two-dimensional micromirror, simplifying the complexity of the two-dimensional micromirror control loop.

[0014] 3) By using the nonlinear internal resonance driving method, the vibration stability of the two-dimensional micromirror can be improved and the scanning error of the micromirror can be reduced. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of an existing two-dimensional MEMS micromirror.

[0016] Figure 2 This is a schematic diagram of existing driving methods for two-dimensional MEMS micromirrors.

[0017] Figure 3 This is a schematic diagram of the structure of a two-dimensional MEMS micromirror provided in an embodiment of the present invention.

[0018] Figure 4 This is a schematic diagram of the nonlinear internal resonance driving method for a two-dimensional MEMS micromirror provided in an embodiment of the present invention.

[0019] Figure 5 This is a cross-sectional view of the two-dimensional MEMS micromirror provided in the embodiment of the present invention. Detailed Implementation

[0020] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0021] One embodiment of the present invention provides a two-dimensional MEMS micromirror, such as Figure 3As shown, the device includes a reflector 1; a movable support 2 surrounding the reflector 1 to support it via a pair of internal torsion springs 3a and 3b; and a piezoelectric transducer including symmetrically arranged piezoelectric transducers 5a and 5b. Opposite piezoelectric transducers 5a include a piezoelectric actuator 6a and a piezoelectric sensor 7a. The piezoelectric actuator 6a includes piezoelectric drive beams 6a-1 and 6a-2, and the piezoelectric sensor 7a includes piezoelectric sensing beams 7a-1 and 7a-2. Opposite piezoelectric transducers 5b include a piezoelectric actuator 6b and a piezoelectric sensor 7a. b. The piezoelectric actuator 6b includes piezoelectric drive beams 6b-1 and 6b-2, and the piezoelectric sensor 7b includes piezoelectric sensing beams 7b-1 and 7b-2. Opposed piezoelectric transducers 5a and 5b are connected at one end to the movable support 2 via external torsion springs 4a and 4b, respectively, and at the other end to the fixed support 8. They can act as drive beams to drive the reflector 1 to deflect about the horizontal axis (X-axis) via the movable support 2, and simultaneously act as sensors to sense the deflection of the reflector 1 about the horizontal axis (X-axis). Furthermore, utilizing the nonlinear internal resonance effect, the X-axis rotational vibration mode can transfer vibration energy to the Y-axis rotational vibration mode, which has a harmonic relationship, through nonlinear coupling force, thereby realizing two-dimensional vibration scanning of the reflector 1.

[0022] The first rotational resonance mode of the two-dimensional MEMS micromirror is the deflection of the reflector 1, movable support 2, and internal torsion springs 3a and 3b around the X-axis via external torsion springs 4a and 4b, with a natural frequency of ω1. The second rotational resonance mode of the two-dimensional MEMS micromirror is the deflection of the reflector 1 around the Y-axis via internal torsion springs 3a and 3b, with a natural frequency of ω2. When the ratio of ω1 to ω2 is approximately equal to 1:N or N:1 (where N is a positive integer), the two-dimensional MEMS micromirror will experience internal resonance under nonlinear vibration. This phenomenon refers to the nonlinear energy exchange between two or more resonance modes, which induces nonlinear forces within the mechanical system through nonlinear vibration, thereby generating harmonic vibration signals to achieve nonlinear coupling between modes with integer multiple frequency ratios. This enables nonlinear coupling between the first and second rotational modes and improves the vibration stability of the micromirror. The two-dimensional MEMS micromirror provided in this embodiment applies a driving signal with a frequency of ω1 to the opposing piezoelectric transducers 5a and 5b, directly exciting the first rotational resonant mode of the MEMS micromirror, causing the reflector 1 to deflect and vibrate around the X-axis. Simultaneously, it indirectly excites the second rotational resonant mode of the MEMS micromirror using an internal resonance phenomenon. Through nonlinear internal resonance, the vibrational energy of the first rotational mode is transferred to the second rotational resonant mode, achieving biaxial vibration of the reflector. This embodiment can achieve biaxial rotational mode excitation through a pair of external driving beams, reducing the number of driving beams in the two-dimensional MEMS micromirror, simplifying the driving structure and control system of the MEMS micromirror. Furthermore, eliminating the internal driving beams significantly increases the area of ​​the reflector 1.

[0023] The natural frequency ω1 of the first rotational resonant mode of the two-dimensional MEMS micromirror satisfies the formula ω1=(k1 / J1). 1 / 2 Where k1 is the torsional stiffness of the external torsion springs 4a and 4b about the X-axis, and J1 is the rotational inertia of the mirror 1, the movable support 2, and the internal torsion springs 3a and 3b about the X-axis; the natural frequency ω2 of the second rotational resonance mode of the two-dimensional MEMS micromirror satisfies the formula ω2=(k2 / J2). 1 / 2 Where k2 is the torsional stiffness of the internal torsion springs 3a and 3b about the Y-axis, and J2 is the moment of inertia of the reflector 1 about the Y-axis. By optimizing the internal and external torsional stiffness and the internal and external moments of inertia respectively, the ratio of the natural frequencies of the first and second rotational resonance modes of the two-dimensional MEMS micromirror is ω1∶ω2≈1∶2. Therefore, the modal frequency ratio of the two-dimensional MEMS micromirror meets the harmonic requirements of nonlinear internal resonance.

[0024] The nonlinear internal resonance driving method is described below. In the two-dimensional MEMS micromirror provided in this embodiment, the ratio of the natural frequencies of the first rotational resonance mode and the second rotational resonance mode is designed to be an integer ratio of 1:2. This design allows the first and second rotational resonance modes of the two-dimensional MEMS micromirror to undergo nonlinear internal resonance coupling under nonlinear vibration conditions, that is, energy can be transferred between modes with an integer frequency ratio. The nonlinear internal resonance driving method is as follows: Figure 4 As shown, a first drive signal V with a frequency of ω1 is applied to the opposing piezoelectric transducers 5a and 5b. A (Piezoelectric signal) and second drive signal V B Due to the first driving signal V A Second drive signal V BThe phases are opposite, and the bending deformations of piezoelectric drive beams 5a-1 and 5b-1 are opposite to those of piezoelectric drive beams 5a-2 and 5b-2. External torsion springs 4a and 4b are subjected to torsional moments from piezoelectric drive beams 9a-1, 9b-1, 9a-2, and 9b-2, causing the movable support 2, internal torsion springs 3a and 3b, and reflector 1 to deflect about the X-axis, i.e., the first rotational resonance mode. When the energy input from piezoelectric transducers 5a and 5b to the two-dimensional MEMS micromirror is sufficiently large, the first rotational resonance mode can be driven into the nonlinear region and generate a high-order nonlinear force within the micromirror system, i.e., generating a harmonic signal that is an integer multiple of the first rotational resonance mode. Thus, vibrational energy can be transferred between the first (ω1) and second (2ω1) rotational resonance modes, resulting in the second rotational resonance mode being excited at a frequency of 2ω1. In other words, the vibration of reflector 1 about the Y-axis can be indirectly excited by nonlinear vibration about the X-axis. From the perspective of energy flow, external energy is directly input into the first rotational resonant mode through the piezoelectric transducer. Through the nonlinear internal resonance effect between the first and second modes, the energy is transferred from the first rotational resonant mode to the second rotational resonant mode. Therefore, using the nonlinear internal resonance driving method, the torque generated by the piezoelectric transducer can directly excite the rotational modes of the X-axis and indirectly excite the rotational modes of the Y-axis, respectively, realizing two-dimensional scanning of the reflector.

[0025] In a specific example, combining the above implementation method, in the two-dimensional MEMS micromirror of this example, P needs to be set. a1 P a2 P a3 P b1 P b2 P b3 A total of six pads are used to drive and detect the opposed piezoelectric transducer, among which, pad P a1 Upper electrode layer 208 connected to piezoelectric drive beams 6a-1 and 6b-1; pad P a2 Upper electrode layer 208 connected to piezoelectric sensing beams 7a-1 and 7b-1; pad P a3 The lower electrode layer 206 is connected to the piezoelectric drive beams 6a-1 and 6b-1 and the piezoelectric sensing beams 7a-1 and 7b-1; pad P b1 Upper electrode layer 208 connected to piezoelectric drive beams 6a-2 and 6b-2; pad P b2 Upper electrode layer 208 connected to piezoelectric sensing beams 7a-2 and 7b-2; pad P b3 The lower electrode layer 206 is connected to the piezoelectric drive beams 6a-2, 6b-2 and the piezoelectric sensing beams 7a-2 and 7b-2. The control circuit (controller) 20 is used to apply a first drive signal (voltage signal) of frequency ω1 to the pad P. a1Provide driving voltage to piezoelectric drive beams 6a-1 and 6b-1; apply a second driving signal with frequency ω1 to pad P. b1 A driving voltage is provided to the piezoelectric drive beams 6a-2 and 6b-2. The first and second driving signals have the same frequency but opposite phase, and closed-loop control of the two-dimensional micromirror can be achieved through a single phase-locked loop; by supplying driving voltage to the pad P... a3 A composite reference voltage is applied to provide a reference voltage to the piezoelectric drive beams 6a-1 and 6b-1 and the piezoelectric sensing beams 7a-1 and 7b-1; this is achieved by applying a reference voltage to the pad P. b3 A composite reference voltage is applied to provide a reference voltage to the piezoelectric drive beams 6a-2 and 6b-2 and the piezoelectric sensing beams 7a-2 and 7b-2; this is achieved through pad P. a2 The first sensing signal (voltage signal) of piezoelectric sensing beams 7a-1 and 7b-1 is detected; via pad P b3 The second sensing signals of piezoelectric sensing beams 7a-2 and 7b-2 are detected; the first sensing signal and the second sensing signal are processed using a differential detection method, and the first driving signal and the second driving signal are controlled in a closed loop based on the detection results.

[0026] The structure of each component in this example 2D MEMS micromirror will be further explained below, such as... Figure 5 As shown, a single-crystal silicon support layer 202, an intermediate silicon oxide layer 203, and a single-crystal silicon active layer 204 are formed on a silicon-on-insulator (SOI) substrate. Reference numerals 205 denote a silicon dioxide layer, 206 a lower electrode layer made of MO or the like, 207 an aluminum scandium nitride (AlScN) layer, 208 an upper electrode layer made of Cr, Au, or the like, 209 a metal reflective layer made of Cr, Au, or the like, and 201 a hard mask layer made of silicon dioxide or the like. The mirror 1 is made of the single-crystal silicon support layer 202, which serves as a vibrating plate, and the metal reflective layer 209, which serves as a reflector. The movable frame 2 and the torsion springs 3a, 3b, 4a, and 4b are composed of the single-crystal silicon active layer 204 and the silicon dioxide layer 205. The piezoelectric drive beams 6a-1, 6a-2, 6b-1, 6b-2 and the piezoelectric sensing beams 7a-1, 7a-2, 7b-1, 7b-2 are composed of a monocrystalline silicon active layer 204, a silicon dioxide layer 205, a lower electrode layer 206, a piezoelectric (AlScN) layer 207 and an upper electrode layer 208. The fixed support 8 is composed of a hard mask layer 201, a monocrystalline silicon support layer 202, an intermediate silicon oxide layer 203, a monocrystalline silicon active layer 204, and a silicon dioxide layer 205.

Claims

1. A two-dimensional MEMS micromirror based on nonlinear internal resonance, comprising a mirror, a movable frame, a drive beam, an external torsion spring for deflecting the mirror and the movable frame about a horizontal axis in a first rotational resonance mode, an internal torsion spring for deflecting the mirror about a vertical axis in a second rotational resonance mode, and a control circuit, characterized in that, The first rotational resonance mode is the rotational vibration of the reflector and the movable frame around the external torsion spring, and the second rotational resonance mode is the rotational vibration of the reflector around the internal torsion spring. The ratio of the natural frequencies of the first rotational resonance mode and the second rotational resonance mode is 1:N or N:1, where N is a positive integer, to ensure that the first rotational resonance mode and the second rotational resonance mode exhibit nonlinear internal resonance. The first rotational resonance mode is directly excited to the nonlinear vibration range by the drive beam, thereby indirectly exciting the second rotational resonance mode, so that vibration energy can be transferred between the two rotational resonance modes, realizing two-dimensional scanning vibration controlled by a single drive signal.

2. The two-dimensional MEMS micromirror according to claim 1, characterized in that, Energy transfer includes the conversion of electrical signal energy into mechanical energy of the driving beam through an external exciter. The mechanical energy of the driving beam directly excites the first rotational resonance mode, and the vibration energy of the first rotational resonance mode is transferred to the second rotational resonance mode through a nonlinear internal resonance phenomenon.

3. The two-dimensional MEMS micromirror according to claim 1, characterized in that, N≤6。 4. The two-dimensional MEMS micromirror according to claim 1, characterized in that, The drive beam can achieve rotational mode driving and induction through piezoelectric transducers, electrostatic transducers, electromagnetic transducers or electrothermal transducers.

5. The two-dimensional MEMS micromirror according to claim 1, characterized in that, One end of the internal torsion spring is connected to the reflector and the other end is connected to the movable frame. One end of the external torsion spring is connected to the movable frame and the other end is connected to the drive beam.

6. The two-dimensional MEMS micromirror according to claim 1, characterized in that, By applying a drive signal to the drive beam and collecting the induced signal generated by the deformation of the drive beam or the deflection light signal generated by the rotation of the reflector, the frequency of the drive signal is adjusted to achieve closed-loop control of the two vertical scanning modes.

7. A driving method for a two-dimensional MEMS micromirror as described in any one of claims 1-6, characterized in that, By applying two driving signals with opposite phases, the mirror and the movable frame are deflected about the horizontal axis, i.e., the first rotational resonance mode. When the energy input to the two-dimensional MEMS micromirror is large enough, the first rotational resonance mode can be driven into the nonlinear region and generate a high-order nonlinear force in the micromirror system, i.e., generate a frequency harmonic signal that is an integer multiple of the first rotational resonance mode. Thus, the vibration energy is transferred between the first and second rotational resonance modes, so that the vibration of the mirror about the vertical axis can be indirectly excited by the nonlinear vibration of the horizontal axis. That is, the torque generated by the drive beam transducer can directly excite the first rotational mode and indirectly excite the second rotational mode, respectively, to realize the two-dimensional scanning vibration of the mirror.

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