KR20060026001A - Mems scanning mirror with tunable natural frequency - Google Patents

Abstract

In one embodiment of the invention, a MEMS structure includes a first electrode, a second electrode, and a mobile element. The first electrode is coupled to a first voltage source. The second electrode is coupled to a second voltage source. The mobile element includes a third electrode coupled to a third voltage source. A steady voltage difference between the first electrode and the third electrode is used to tune the natural frequency of the structure to a scanning frequency of an application. An oscillating voltage difference between the second electrode and the third electrode at the scanning frequency of the application is used to oscillate the mobile element. In one embodiment, the mobile unit is a mirror.

Description

MEMS structure and MEMS structure control method {MEMS SCANNING MIRROR WITH TUNABLE NATURAL FREQUENCY}

FIELD OF THE INVENTION The present invention relates to micro-electro-mechanical systems (MEMS) and, more particularly, to MEMS scanning mirrors.

Various electrostatic designs for MEMS scanning mirrors have been proposed. Applications include bar code readers, laser printers, confocal microscopes, fiber optic network devices, projection displays for projectors, rear projection TVs, wearable displays, and military laser tracking and guidance systems. Typically, MEMS scanning mirrors are driven at their main resonance to achieve high scan angles. Invariably, the manufacturing process produces MEMS scanning mirrors with dimensional mismatches that change the natural frequencies of the individual devices. If a few major natural frequencies in the MEMS scanning mirror are too low or too high, a few devices will not produce the proper scan speed and the proper scan angle under the alternating current (AC) drive voltage selected for the minority of the MEMS scanning mirror. . Accordingly, what is needed is an apparatus and method for tuning the major natural frequencies of MEMS scanning mirrors to improve the manufacturing yield of these devices.

In one embodiment of the present invention, the MEMS structure includes a first electrode, a second electrode, and a movable element. The first electrode is connected to the first voltage source. The second electrode is connected to the second voltage source. The movable element includes a third electrode connected to a third voltage source (eg, electrical ground). The normal voltage difference between the first and third electrodes is used to tune the natural frequency of the structure to the scanning frequency of the application. The oscillation voltage difference between the second electrode and the third electrode at the scanning frequency of the application is used to oscillate the mobile device. In one embodiment, the movable element is a mirror.

1A and 1B are respectively assembled and exploded views of the MEMS structure 100 in one embodiment,

1C, 1D and 1E are top views of layers in the MEMS structure 100 in one embodiment,

1F illustrates a method of constructing and operating a MEMS structure 100 in one embodiment of the present invention;

1G, 1H, 1I and 1J are top views of the various layers in the MEMS structure 100 in different embodiments,

2A and 2B are, respectively, an assembly and exploded view of the MEMS structure 200 in one embodiment,

2C and 2D are top views of layers in the MEMS structure 200 in one embodiment,

3A and 3B illustrate an assembly and exploded view of the MEMS structure 300 in one embodiment, respectively,

3C, 3D, 3E, 3F and 3G are top views of layers in MEMS structure 300 in one embodiment,

4 illustrates a MEMS system in one embodiment of the present invention;

5 illustrates the DC and AC voltages used to oscillate a MEMS structure in one embodiment of the invention.

4 illustrates a MEMS system 400 in one embodiment of the present invention. MEMS system 400 includes a MEMS structure (eg, MEMS structure 100, 200, or 300) with a mobile element that electrostatically moves under the voltage provided by voltage source 402. The voltage source 402 provides a voltage difference between the fixed electrode and the moving electrode of the mobile device to adjust the natural frequency of the MEMS structure 100 to the desired scanning frequency. The voltage source 402 also provides an AC voltage difference between the other fixed electrode and the movable electrode of the movable element at the desired scanning frequency to oscillate the movable element at the desired scanning angle.

The mobility of the mobile device (eg, scanning frequency and scanning angle) is measured by the sensor 404 and returned to the controller 406. The controller 406 compares the measured mobility with the desired mobility of the mobile device and then instructs the voltage source 402 to provide an appropriate voltage to achieve the desired mobility. Although shown as separate components, the MEMS structure 100, voltage source 402, sensor 404, and controller 406 may be built on the same chip or on different chips.

1A and 1B each illustrate an assembly and exploded view of the MEMS structure 100 in one embodiment. The MEMS structure 100 can be used in any application that requires a single axis of movement (eg, unidirectional scanning mirror). The MEMS structure 100 includes a conductive layer 105, an insulating layer 107, and a conductive layer 109. In one embodiment, conductive layers 105 and 109 are made of doped silicon, while insulating layer 107 is made of silicon dioxide (SiO ₂ ). Insulating layer 107 electrically insulates the elements on conductive layers 105 and 109. Insulating layer 107 is also used to physically bond conductive layers 105 and 109.

1C illustrates a top view of one embodiment of a conductive layer 105. Conductive layer 105 includes a scanning mirror 101 and a bias pad 112. Scanning mirror 101 includes reflective regions 124 connected to anchors 108A, 108B, respectively, by torsional hinges 102A, 102B. The mirror 101 rotates about the axis 122.

In one embodiment, the torsion hinges 102A, 102B include an inner hole 114 to lower the rotational mode frequency of the structure 100. The rotation mode frequency is the lowest of the mode frequencies to ensure that the scanning mirror 101 rotates about the axis 122 without being connected to other undesired rotational and transforming structure vibrations.

The mirror 101 includes movable teeth 104A and 104B (collectively, "mobile teeth 104") on different sides of the rotation axis 122. The movable tooth protrusions 104A and 104B extend from the bars 106A and 106B, respectively. Bars 106A and 106B are connected to reflective area 124 and are parallel to torsion hinges 102A and 102B.

The bias pad 112 includes fixed teeth 103A, 103B (collectively, “fixed teeth 103”) on different sides of the rotation axis 122. The fixed teeth 103A and 103B are movable teeth 104A and 104B, respectively, when the bias pad 112 and the mirror 101 are in the same plane (for example, when the mirror 101 does not rotate). ) Is interlocking with each other.

 In an embodiment, anchor 108A is connected to ground 116 and bias pad 112 is connected to a direct current (DC) voltage source 118. DC voltage source 118 provides a DC bias voltage to bias pad 112. The DC bias voltage produces a normal voltage difference between the fixed tooth protrusion 103 and the movable tooth protrusion 104. The normal voltage difference between the stationary tooth protrusion 103 and the movable tooth protrusion 104 generates an electrostatic torque that rotates the mirror 101 until the electrostatic torque is equal to the restoring torque in the balanced position. In fact, the fixed voltage difference between the stationary tooth protrusion 103 and the movable tooth protrusion 104 creates a nonlinear electrostatic system that changes the natural frequency of the MEMS structure 100. Accordingly, the natural frequency of the MEMS structure 100 can be adjusted (eg, tuned) by increasing or decreasing the normal voltage difference between the stationary tooth protrusion 103 and the movable tooth protrusion 104.

In one embodiment, DC voltage source 118 is built on the same chip as structure 100. Alternatively, DC voltage source 118 is built on a chip away from structure 100. In one embodiment, the DC voltage source 118 is servo controlled during operation to produce a DC bias voltage value that produces the desired natural frequency of the structure 100.

1D illustrates a top view of one embodiment of the intermediate layer 107. The insulating layer 107 has the same shape as the conductive layer 105 except for the mirror 101 to electrically insulate the elements on the layer 101. The insulating layer 107 defines an intersecting opening 121 for the scanning movement of the mirror 101.

1E illustrates a top view of one embodiment of conductive layer 109. Conductive layer 109 includes drive pads 126 that define intersecting openings 111. The drive pad 126 includes fixed tooth protrusions 110A and 110B (collectively, “fixed tooth protrusions 110”) on different sides of the rotation shaft 122. Similar to the opening 121, the opening 111 Is the free space left for the scanning movement of the mirror 101. The fixed tooth projection 110A is a movable tooth protrusion when the mirror 101 rotates in the first direction (e.g., clockwise). Interlocking with 104A), the fixed tooth projection 110B meshes with the movable tooth protrusion 104B when the mirror 101 rotates in the second direction (eg, counterclockwise). 110B is electrically connected when an AC drive voltage is applied between the pad 112 and the pad 126, the translational resultant force first appears when the moving structure is symmetric about the axis 122. This transformation force is not useful for rotational movements. Because of the difference, it will not be fully symmetrical and will start to oscillate Once the structure begins to oscillate, the torque increases and the transformation force decreases.The potential consequence of small initial torques is that they produce forces or structures that are slightly asymmetric with respect to axis 122. For example, the lengths of the tooth protrusions 110A and 110B may be made slightly different to produce a relatively large initial torque, while the mirror shape may be made slightly asymmetric about the axis 122. Can produce the same effect.

In one embodiment, the stationary tooth protrusion 110 and the movable tooth protrusion 104 form an electrostatic actuator (eg, a vertical protrusion driving actuator) that oscillates the scanning mirror 101. In this embodiment, drive pad 126 is connected to AC voltage source 120 and anchor 108A is connected to ground 116. When activated, the AC voltage source 120 provides an AC drive voltage to the drive pad 126 to produce an oscillation voltage difference between the stationary tooth protrusion 110 and the movable tooth protrusion 104. Typically, the AC drive voltage has a frequency equal to the natural frequency of the structure 100, thus achieving a maximum scan angle. The oscillation voltage difference between the tooth protrusion 110 and the tooth protrusion 104 causes an electrostatic torque that generates the scanning movement of the mirror 101.

In one embodiment, the AC voltage source 1200 is built on the same chip as the structure 100. Alternatively, the AC voltage source 120 is built on a chip away from the structure 100. In one embodiment, the AC voltage source 120 is servo controlled during operation to generate an AC drive voltage that produces the desired scanning speed and scanning angle.

1F illustrates a method 150 of constructing and operating the MEMS structure 100 in one embodiment. Structure 100 is generally a device from a batch of mass produced structure 100. As described below, actions 151, 152 occur during the fabrication of the structure 100, and actions 153, 154, 156, 160 occur during the use of the structure 100.

At act 151, the designer determines the scanning frequency and scanning angle of the application (e.g., 1 kHz and 5-10 degrees for the barcode reader) and modifies the basic design of the structure 100 to specify a specific frequency equal to the scanning frequency. Achieve a natural frequency. The designer modifies the design by changing the stiffness of the hinge (eg the hinge geometry) or by changing the inertia of the structure (eg the mirror geometry). Action 152 follows action 151.

At act 152, the designer presets the characteristics of the DC voltage difference and the AC voltage difference for this structure 100. The designer presets the amplitude of the DC bias voltage (Figure 5) to tune the natural frequency of this structure 100 to the scanning frequency of the application. The designer presets the amplitude and frequency of the AC drive voltage (FIG. 5) to achieve the desired scan angle for this structure 100. The designer also presets the vertical offset of the AC drive voltage (FIG. 5) to achieve the desired neutral scanning position where oscillation occurs. These steps are necessary because each structure 100 is somewhat different from others due to manufacturing discrepancies. These characteristics are then stored in the controller as initial / default characteristics for the DC bias voltage and AC drive voltage for this structure 100.

At act 153, the end user may store different characteristics for the DC bias voltage and the AC drive voltage at the controller 406. The end user may wish to do so to change the desired scanning frequency, the preferred scanning angle, and the preferred neutral scanning position.

At act 154, the controller 406 instructs the voltage source 402 to apply a DC bias voltage and an AC drive voltage. Voltage source 402 represents various DC and AC voltage sources (eg, DC voltage source 118 and AC voltage source 120).

The DC bias voltage is initialized to the default value stored in the controller 406 and then servo controlled to ensure that the rotational natural frequency is the scanning frequency. Servo control of the DC bias voltage is essential in the operating phase because the natural frequency of the structure 100 may shift from the desired value due to a change in temperature, aging of the material, or any other reason.

The AC drive voltage is initialized to default values stored in controller 406 and then servo controlled to ensure that the desired scanning frequency and scanning angle are achieved. Servo control of the AC drive voltage is essential in the operating phase because the scanning frequency, scanning angle, and neutral scanning position may be moved from the desired value due to changes in temperature, aging of the material, or any other reason. Action 158 follows action 154.

In operation 158, sensor 404 is used to monitor the movement of the scanning mirror (eg, scanning frequency, scanning angle, and scanning neutral position), and the measured information is output to controller 406. Action 160 follows action 158.

At act 160, controller 406 receives movement information from sensor 404. The controller 406 provides the required DC bias voltage and the required AC drive voltage to the voltage source 402. Servo control of the DC bias voltage is achieved by perturbing the amplitude of the DC bias voltage. If the DC bias voltage increases and the scanning angle also increases simultaneously, the natural frequency approaches the scanning frequency, and vice versa. If the Bode plot shows the high Q factor of the main natural frequency, it is generally more effective to maintain the scanning amplitude by controlling the natural frequency with a DC bias voltage change.

Servo control of the AC drive voltage is achieved by perturbing the amplitude, frequency, and vertical offset of the AC drive voltage and sensing changes in scanning angle, scanning frequency, and scanning neutral position. The amplitude of the AC drive voltage increases to increase the angle of rotation, and vice versa. The frequency of the AC drive voltage increases, increasing the scanning frequency and vice versa. The vertical offset of the AC drive voltage is varied to optimize the scanning neutral position. Action 154 follows action 160, and the method continues in the feedback loop.

1G illustrates a top view of another embodiment of a conductive layer 105 of structure 100. Identical or similar parts between FIGS. 1C and 1G are denoted by the same reference numerals. In this embodiment, reflective region 124 is connected to bars 128A and 128B. The movable teeth 104A and 104B extend from opposite edges of the bars 128A and 128B, respectively. The tips of the bars 128A and 128B are connected to the anchors 108A and 108B by the torsion hinges 130A and 130B, respectively. Each of the torsion hinges 130A and 130B has a serpentine form that increases the translational stiffness but maintains the torsional flexibility of the hinges 102A and 102B. Similar to the foregoing, DC voltage source 118 is connected to bias pad 112 and ground 116 is connected to anchor 108A. The method 150 described above can be used to construct and operate the structure 100 with the conductive layer 105 of FIG. 1G.

1H illustrates a top view of another embodiment of conductive layer 109. Identical or similar parts between FIGS. 1E and 1H are denoted by the same reference numerals. In this embodiment, the drive pad 126 includes only the stationary teeth 110B. This configuration provides a large initial torque to excite the mirror rotational oscillation. The oscillation voltage difference between the fixed tooth protrusion 110B and the movable tooth protrusion 104B only generates the scanning movement of the mirror. However, the oscillation voltage difference is due to the fact that the layer 109 in this embodiment exerts a force on the stationary tooth protrusion 110 which is on only one of the opposing faces, thus reducing the response amplitude of the foregoing embodiment of FIG. It may increase to match. The method 150 described above can be used to construct and operate the structure 100 having the conductive layer 109 of FIG. 1H.

1I illustrates a top view of another embodiment of conductive layer 109. Identical or similar parts between FIGS. 1E and 1I are denoted by the same reference numerals. In this embodiment, the conductive layer 109 is separated into two drive pads 132A, 132B (collectively "drive pad 132") that together define an opening 121. Fixed teeth 110A and 110B extend from opposite edges of drive pads 132A and 132B, respectively. Drive pad 132A is connected to an AC voltage source 134A, while drive pad 132 is connected to another AC voltage source 134B. The AC voltage sources 134A, 134B have the same frequency but have a 180 degree phase difference, providing the highest torsional actuation force and initial excitation torque. Therefore, the oscillation voltage difference between the fixed tooth projection 110 and the movable tooth protrusion 104 generates a scanning movement of the mirror 101. The method 150 described above can be used to construct and operate the structure 100 having the conductive layer 109 of FIG. 1I.

1J illustrates a top view of an additional layer 136 under conductive layer 109 electrically insulating drive pads 132A, 132B. In one embodiment, insulating layer 136 is made of intrinsic silicon. The insulating layer 136 may include empty space left for the scanning movement of the mirror 101.

2A and 2B each illustrate an assembly and exploded view of the MEMS structure 200 in one embodiment. Like the MEMS structure 100, the MEMS structure 200 can be used for any application that requires a single axis scanning mirror. MEMS structure 200 includes a conductive layer 205, an insulating and bonding layer 207, and a structure fixing layer 209. In one embodiment, conductive layer 205 is made of doped silicon, while insulating layer 207 is made of SiO ₂ to electrically insulate the components of conductive layer 205. Layer 209 provides a support structure for the two top layers. If layer 209 is made of nonconductive intrinsic silicon, layer 207 will be used only as a bonding layer, and may be optional for this configuration.

2C illustrates a top view of one embodiment of conductive layer 205. Conductive layer 205 includes scanning mirror 201, bias pad 212, and drive pads 232A and 232B. Similar to mirror 101, mirror 201 includes reflective regions 224 connected to anchors 208A and 208B by torsion hinges 202A and 202B, respectively. The mirror 201 rotates about the axis 222.

In one embodiment, the torsion hinges 202A, 202B include an inner hole 214 to lower the rotation mode frequency. The mirror 201 also includes a set of movable teeth 204A and 204B (collectively, "mobile teeth 204"). The movable teeth 204A, 204B extend from the bars 206A, 206B, which are on different sides of the axis 222. Bars 206A, 206B are remote from reflective area 224 and are parallel to torsion hinges 202A, 202B.

Inwardly movable teeth 204B are closer to reflective region 224 and are engaged with fixed teeth 210A and 210B (described later). The outer movable tooth 204B is further away from the reflective region 224 and is engaged with the stationary tooth protrusions 203A and 203B (described later).

In one embodiment, the mirror 201 is generally asymmetric because it has a rectangular shape with one or more corners removed. Thus, the center of the mirror 201 is moved to one side of the axis 222. This design may be desirable when the application requires the mirror 201 to start at a certain initial rotational position or rapidly reach a predetermined initial rotational position.

Bias pad 212 includes stationary teeth 203A, 203B (collectively "" fixed teeth 203 ") on different sides of axis 222. Stationary teeth 203A, 203B When the bias pad 212 and the mirror 201 are in the same plane (eg, when the mirror 201 is not rotating), the bias pad 212 and the mirror 201 are respectively engaged with the outer movable tooth projection 204A.

Drive pads 232A and 232B (collectively, "drive pad 232") each include fixed toothed protrusions 210A and 210B (collectively, "fixed toothed protrusions 210"). The stationary tooth protrusions 210A and 210B are engaged with the inner movable tooth protrusion 204B when the drive pad 232 and the mirror 201 are in the same plane.

In one embodiment, anchor 208A is connected to ground 216 and bias pad 212 is connected to DC voltage source 218. The DC voltage source 218 provides a DC bias voltage to the bias pad 212 to produce a normal voltage difference between the fixed teeth 203 and the outer movable teeth 204A. Similar to the foregoing, the fixed voltage difference between the stationary tooth 203 and the movable tooth 204A generates an electrostatic force that changes the natural frequency of the structure 200. Accordingly, the natural frequency of the MEMS structure 200 can be tuned by changing the normal voltage difference between the stationary tooth 203 and the mobile tooth 204A.

In one embodiment, the stationary tooth protrusion 210 and the movable tooth protrusion 204B form an electrostatic actuator (eg, a protrusion drive actuator) that oscillates the scanning mirror 201. In this embodiment, the drive pad 232 is connected to an AC voltage source 229. When activated, the AC voltage source 220 provides an AC drive voltage to the drive pad 232, creating a difference in oscillation voltage between the fixed teeth 210 and the inner movable teeth 204B. The oscillation voltage difference between the fixed tooth protrusion 210 and the inner movable tooth protrusion 204B causes an electrostatic torque that generates a scanning movement of the mirror 201.

Similar to the foregoing, in one embodiment, DC voltage source 218 and AC voltage source 220 are built on the same chip as structure 200. Alternatively, voltage sources 218 and 220 are built on one or more chips away from structure 200. These one or more chips are then connected to the bias pad 212 and the drive pad 232 via wires. In one embodiment, DC voltage source 218 is servo controlled during operation to generate a DC bias voltage that generates the desired natural frequency of structure 100, while AC voltage source 220 is servo controlled during operation to provide the desired scanning speed and scanning. Generates an AC drive voltage that generates an angle.

2D illustrates a top view of one embodiment of insulating layer 207. Insulating layer 207 defines an intersecting opening 221. Similar to the opening 121, the opening 221 is an empty space left for the scanning movement of the mirror 201.

The method 150 (FIG. 1F) described above can be used to operate the structure 200.

3A-3B each illustrate an assembly and exploded view of the MEMS structure 300 in one embodiment. The MEMS structure 300 may be used in any application (eg, bidirectional scanning mirror) that requires rotational movement about two axes of rotation. MEMS structure 300 includes structure fixing layer 301, insulating layer 304, conductive layer 302, insulating layer 305, and conductive layer 303. In one embodiment, layer 301 is made of intrinsic silicon or doped silicon, conductive layers 302, 303 are made of doped silicon, and insulating layers 304, 305 are made of silicon dioxide (SiO ₂ ). Is made. Insulating layers 304, 305 electrically insulate the devices on layers 301, 302, 303. Insulating layer 304 is used to physically bond conductive layers 301 and 302. Similarly, insulating layer 305 is also used to physically bond conductive layers 302 and 303.

3C illustrates a top view of one embodiment of conductive layer 303. Conductive layer 303 includes scanning mirror 316, drive pads 306 and 309, ground pad 307, and bias pad 308. Scanning mirror 316 includes reflective regions 352 connected to anchors 328 and 329 by serpentine torsion hinges 315A and 316B, respectively. The mirror 316 rotates about the Y-axis via hinges 315A and 315B. Hinges 315A and 315B determine the mirror scanning frequency / speed in the Y-axis.

The mirror 316 includes movable teeth 314A, 314B0 (collectively, “mobile teeth 314”) on different sides of the Y-axis.The drive pad 306 is a serpentine torsion hinge 324. Is connected to the projection 388. The projection 388 may not rotate when the projection 388 and the mirror 316 are in the same plane (for example, the mirror 316 does not rotate about the Y-axis). And a stationary tooth protrusion 313 engaged with a portion of the movable tooth protrusion 314A. Similarly, the drive pad 309 is connected to the protrusion 390 by a serpentine torsion hinge 326. The protrusion 390 has a stationary tooth protrusion 311 that meshes with some of the movable tooth protrusions 314B when the mirror 316 does not rotate about the Y-axis.

The bias pad 308 is connected to the protrusion 323B by the serpentine torsion hinge 325. The projection 323B is connected to the projection 323A by the bar 330A. The protrusions 323A and 323B have fixed tooth protrusions 310A and 310B (collectively, “fixed tooth protrusions 310”), respectively. The stationary tooth protrusions 310A and 310B are engaged with some of the movable tooth protrusions 314A and 314B when the mirror 316 does not rotate about the Y-axis.

Ground pad 307 is connected to L-shaped bar 330B by serpentine torsion hinge 327. Bar 330B is connected to anchor 329. Thus, the ground pad 307 is connected to the mirror 316 and the movable tooth projection 314.

In one embodiment, ground pad 307 is connected to ground 354 and bias pad 308 is connected to DC voltage source 356. DC voltage source 356 provides a DC via voltage to bias pad 308. The DC bias voltage generates a normal voltage difference between the fixed tooth protrusion 310 and the movable tooth protrusion 314. Similar to the foregoing, the normal voltage difference between the stationary tooth protrusion 310 and the movable tooth protrusion 314 creates a nonlinear electrostatic system that changes the natural frequency of the MEMS structure 300 about the Y-axis. Accordingly, the natural frequency of the MEMS structure 300 about the Y-axis can be changed (eg, tuned) by changing the normal voltage difference between the fixed tooth protrusion 310 and the movable tooth protrusion 314. .

Similar to the foregoing, DC voltage source 356 may be built on the same chip as structure 300. Alternatively, DC voltage source 356 may be built on a chip away from structure 300. In one embodiment, the DC voltage source 356 is servo controlled during operation to generate a DC bias voltage value that generates the desired natural frequency of the structure 300 centered on the Y-axis.

In one embodiment, (1) the stationary tooth protrusion 311 and the movable tooth protrusion 314B, and (2) the stationary tooth protrusion 313 and the movable tooth protrusion 314A are scanning mirrors 316 about the Y-axis. Two electrostatic actuators (e.g., protrusion drive actuators) are formed. In this embodiment, drive pads 306 and 309 are connected to AC voltage source 360 and ground pad 307 is connected to ground 354. When activated, AC voltage source 360 is characterized by the difference in oscillation voltage between (1) fixed tooth 311 and mobile tooth 314B, and (2) between fixed tooth 313 and mobile tooth 314A. Create Typically, the AC drive voltage has a frequency equal to the natural frequency of structure 300 to achieve the maximum scan angle. The oscillation voltage difference between the tooth protrusions causes an electrostatic torque that generates a scanning movement of the mirror 316 about the Y-axis.

Similar to the foregoing, in one embodiment, the AC voltage source 360 is built on the same chip as the structure 300. Alternatively, AC voltage source 360 is built on a chip away from structure 300. In one embodiment, the Ac voltage source 360 is servo controlled during operation to generate an AC drive voltage that generates the desired scanning speed and scanning angle about the Y-axis.

In one embodiment, conductive layer 303 further includes drive pads / projections 317A, 317B located on different sides of the X-axis. The protrusions 317A and 317B include the fixed tooth protrusions 318A and 318B, respectively. Fixed teeth 318A, 318B are used to rotate mirror 316 about the X-axis (described later with reference to layer 302). The protrusions 317A, 317B are connected to an AC voltage source 374 (described later).

3D illustrates a top view of one embodiment of insulating layer 305. The insulating layer 305 has the same shape as the conductive layer 303 except for the mirror 316 to electrically insulate the elements on the layer 303. The insulating layer 305 defines an opening 358 left for the scanning movement of the mirror 316.

3E illustrates a top view of one embodiment of conductive layer 302. Conductive layer 302 includes a rotating frame 364 and bias pads / projections 319A, 319B. Rotating frame 364 defines an opening 358 for the scanning movement of mirror 316. Rotating frame 364 includes protrusions 322A, 322B on different sides of mirror 316. Rotating frame 364 is connected to ground pad / anchor 331A, 331B by serpentine torsion hinges 332A, 332B, respectively. Rotating frame 364 can rotate about the X-axis via hinges 332A and 332B. The mirror 316 is mounted above the frame 364. Specifically, the anchors 329 and 329 of the mirror 316 are mounted on top of the anchor mounts 366 and 367 of the rotary frame 364, respectively. This causes the mirror 316 to rotate about the Y-axis using hinges 315A and 315B, and to rotate about the X-axis using hinges 332A and 332B.

The protrusions 322A and 322B each include the movable tooth protrusions 321A and 321B (collectively, the "movable tooth protrusions 321"). The protrusions 319A and 319B include fixed tooth protrusions 320A and 320B (collectively, “fixed tooth protrusions 320”), respectively. The stationary tooth protrusions 320A and 320B are formed when the protrusions 322A and 322B and the rotation frame 364 are in the same plane (for example, when the rotation frame 364 does not rotate about the X-axis). Respectively engaged with the movable tooth projections 321A and 321B.

In one embodiment, anchor 331A is connected to ground 368 and projections 319A, 319B are connected to DC voltage source 370. DC voltage source 370 provides the DC bias voltage to protrusions 319A and 319B. The DC bias voltage generates a normal voltage difference between the fixed tooth protrusion 320 and the movable tooth protrusion 321. Similar to the foregoing, the normal voltage difference between the stationary tooth protrusion 320 and the movable tooth protrusion 321 creates a nonlinear electrostatic system that changes the natural frequency of the MEMS structure 300 about the X-axis. Accordingly, the natural frequency of the MEMS structure 300 about the X-axis can be varied (eg, tuned) by changing the normal voltage difference between the fixed tooth protrusion 320 and the movable tooth protrusion 321.

Similar to the foregoing, in one embodiment, the DC voltage source 370 is built on the same chip as the structure 300. Alternatively, DC voltage source 370 is built on a chip away from structure 300. In one embodiment, the DC voltage source 370 is servo controlled during operation to generate a DC bias voltage that generates the desired natural frequency of the structure 300 about the X-axis.

As described above, the projections 317A and 317B (FIG. 3C) have fixed toothed projections 318A and 318B (FIG. 3C), respectively. The movable tooth protrusion 321A (FIG. 3E) of the rotating frame 364 (FIG. 3E) is engaged with the fixed tooth protrusion 318A when the mirror 316 (FIG. 3C) rotates in the first direction, and the rotating frame ( The movable tooth projection 321B (FIG. 3E) of 364 (FIG. 3E) engages with the fixed tooth protrusion 318B when the mirror 316 (FIG. 3C) rotates in the opposite direction.

In one embodiment, (1) the fixed tooth projection 318A and the movable tooth protrusion 321A, and (2) the fixed tooth protrusion 318B and the movable tooth protrusion 321B are scanning mirrors 316 about the X-axis. Two electrostatic actuators (e.g., protrusion drive actuators) are formed. In this embodiment, the projections 317A, 317B are connected to an AC voltage source 374 (FIG. 3C) and the ground pad 331 is connected to ground 368 (FIG. 3E). When activated, the AC voltage source 374 produces a difference in oscillation voltage between the stationary teeth 318A and the mobile teeth 321A and between the stationary teeth 318B and the mobile teeth 321B. Typically the AC drive voltage has a frequency equal to the natural frequency of structure 300 to achieve a maximum scan angle. The oscillation voltage difference between the tooth protrusions causes an electrostatic torque that generates a scanning movement of the mirror 316 about the X-axis.

Similar to the foregoing, in one embodiment, the AC voltage source 374 is built on the same chip as the structure 300. Alternatively, AC voltage source 374 is built on a chip away from structure 300. In one embodiment, the AC voltage source 374 is servo controlled during operation to generate an AC drive voltage that generates the desired scanning speed and scanning angle about the X-axis.

3F illustrates a top view of one embodiment of insulating layer 304. The insulating layer 304 has the same shape as the conductive layer 302 except for the rotating frame 364 to electrically insulate the elements on the layer 302. The insulating layer 304 defines an opening 358 left for scanning movement of the mirror 316 and the rotating frame 364.

3G illustrates a top view of one embodiment of the structural fixation layer 301. Layer 301 includes a frame 378 that defines an opening 358 for the scanning movement of the mirror 316 and rotating frame 364. Rotating frame 364 is mounted on top of frame 378. Specifically, anchors 331A and 331B of rotating frame 364 are mounted on top of anchor mounts 380 and 382 of frame 378, respectively. The projections 319A and 319B of the conductive layer 302 are mounted on top of the projection mounting portions 384 and 386, respectively.

The method 150 (FIG. 1F) described above may be modified to configure and operate the MEMS structure 300 in one embodiment. Structure 300 is generally a device from a batch of mass production structure 300.

At act 151, the designer determines the scanning frequency and the scanning angle for both axes of rotation of the application and modifies the basic design of structure 300 to achieve a specific natural frequency equal to the scanning frequency. The designer modifies the design by changing the stiffness of the hinge (eg, the geometry of the hinge) or by changing the inertia of the structure (eg, the geometry of the mirror). Action 152 follows action 151.

In act 152, the designer mirrors the characteristics of the DC voltage difference for both rotational axes to tune the natural frequency of this structure 300 to the scanning frequency. The designer also presets the characteristics of the AC voltage difference for both axes of rotation to achieve the desired scan angle and preferred neutral scanning position at which oscillation occurs. These properties are then stored in the controller 406 for this structure 300 as initial / default properties for the DC bias voltage and the AC drive voltage.

At act 153, the end user may store different characteristics in the controller 406 for the DC bias voltage and the AC drive voltage. The end user may wish to do so to change the desired scanning frequency, the preferred scanning angle, and the preferred neutral scanning position.

At act 154, the controller 406 instructs the voltage source 402 to apply a DC bias voltage and an AC drive voltage. Voltage source 402 represents various DC and AC voltage sources (eg, DC voltage sources 356 and 370 and AC voltage sources 360 and 374).

The DC bias voltage is initialized to the default value stored in the controller 406 and then servo controlled to ensure that the rotational natural frequency is the scanning frequency.

The AC drive voltage is initialized to the default value stored in the controller 406 and then servo controlled to ensure that the desired scanning frequency, preferred scanning angle, and desired scanning neutral position are achieved. Action 158 follows action 154.

At act 158, sensor 404 is used to monitor the movement of the scanning mirror and the measured information is output to controller 406. Action 160 follows action 158.

At act 160, the controller 406 receives scanning frequency and angle information from the sensor 404. The controller 406 provides the required DC bias voltage and the required AC drive voltage to the voltage source 402. Action 154 follows action 160, and the method continues in the feedback loop.

Various applications and combinations of features of the described embodiments are within the scope of the present invention. Many embodiments are encompassed by the following claims.

Claims (58)

In the MEMS structure, A first electrode connected to the first voltage source, A second electrode connected to the second voltage source, A mobile device comprising a third electrode connected to a third voltage source, The normal voltage difference between the first electrode and the third electrode causes the natural frequency of the structure to change at least approximately equal to the scanning frequency of the application, and between the second electrode and the third electrode at the scanning frequency of the application. The oscillation voltage difference of the oscillating element MEMS structure. The method of claim 1, The first voltage source is a DC voltage source, the second voltage source is an AC voltage source, and the third voltage source is ground MEMS structure. The method of claim 2, The first electrode includes a plurality of first fixed tooth protrusions, the second electrode includes a plurality of second fixed tooth protrusions, and the third electrode includes a plurality of movable tooth protrusions. MEMS structure. The method of claim 2, The DC voltage source and the AC voltage source are located on the same chip as the structure. MEMS structure. The method of claim 2, At least one of (1) the DC voltage source and (2) the AC voltage source is located on a chip different from the structure MEMS structure. The method of claim 2, The movable element is a scanning mirror that rotates about an axis. MEMS structure. The method of claim 6, The scanning mirror further comprises a reflective region coupled to the torsion spring, wherein the plurality of movable teeth are extended from a bar connected to the reflective region. MEMS structure. The method of claim 7, wherein The torsion spring includes an inner hole MEMS structure. The method of claim 7, wherein The plurality of first stationary teeth are engaged with the plurality of movable teeth when the scanning mirror is in the first direction. MEMS structure. The method of claim 9, The plurality of second teeth are engaged with the plurality of movable teeth when the scanning mirror is in the second direction. MEMS structure. The method of claim 10, The first electrode and the movable element comprise a top layer and the second electrode comprises a bottom layer, wherein the top layer and the bottom layer are separated by an intermediate layer of electrically insulating material. MEMS structure. The method of claim 6, The mirror further comprises a reflective area connected to the serpentine torsion spring by a bar, wherein the plurality of movable teeth are extended from the bar. MEMS structure. The method of claim 1, And further comprising a fourth electrode connected to the fourth voltage source MEMS structure. The method of claim 13, The first voltage source is a first DC voltage source, the second voltage source is a first AC voltage source, the third voltage source is ground, and the fourth voltage source is a second AC voltage source. MEMS structure. The method of claim 14, The first AC voltage source and the second AC voltage source provide an out of phase voltage. MEMS structure. The method of claim 7, wherein The first electrode, the second electrode, and the movable element comprise one layer. MEMS structure. The method of claim 16, Wherein the plurality of first fixed teeth are interlocked with the first set of movable teeth from the plurality of mobile teeth, and the plurality of second fixed teeth are second set of movable teeth from the plurality of movable teeth. Interlocking with teeth MEMS structure. In the MEMS structure, A first layer comprising a first drive pad, the first drive pad defining a first opening, the first drive pad including a plurality of first stationary teeth, and electrically connected to an AC voltage source providing an AC voltage; A second layer overlying said first layer, said second layer defining a second opening overlapping said first opening and comprising an electrically insulating material; and A third layer overlying said second layer, The third layer, A bias pad defining a third opening overlapping said second opening, said bias pad including a plurality of second fixed tooth projections and electrically connected to a DC voltage source providing a DC bias voltage; A mirror in the third opening, The mirror is, Reflection area, A torsional hinge connected to the reflective region, An anchor connected to the torsional hinge and mounted on top of the second layer to rotate the mirror, the anchor being electrically connected to ground; A plurality of movable tooth protrusions connected to the reflective region, the plurality of movable tooth protrusions meshing with the plurality of second fixed tooth protrusions; The normal voltage difference between the plurality of mobile teeth and the plurality of second fixed teeth may change the natural frequency of the structure to the scanning frequency of the application and at the scanning frequency of the application the plurality of mobile teeth and the plurality of mobile teeth. The oscillation voltage difference between the first stationary teeth of the oscillating oscillating the scanning mirror MEMS structure. A first layer of electrically insulating material, A second layer over the first layer-the second layer, A first drive pad comprising a plurality of first stationary teeth and electrically connected to a first AC voltage source providing a first AC voltage; A second drive pad comprising a plurality of second stationary teeth, the second drive pad being electrically connected to a second AC voltage source providing a second AC voltage that is out of phase with the first AC voltage; And the second drive pad defines a first opening—and, A third layer overlying said second layer, said third layer defining a second opening overlapping said first opening and consisting of an electrically insulating material; and The fourth layer over the third layer-the fourth layer, A bias pad defining a third opening overlapping said second opening, said bias pad including a plurality of third fixed tooth projections and electrically connected to a DC voltage source providing a DC bias voltage; A mirror over the first and second openings, The mirror is, Reflection area, A torsional hinge connected to the reflective region, An anchor connected to the torsional hinge and mounted above the third layer to rotate the mirror, the anchor being electrically connected to ground; A plurality of movable tooth protrusions connected to the reflective region, the plurality of movable tooth protrusions being engaged with the plurality of third fixed tooth protrusions; The normal voltage difference between the plurality of mobile teeth and the plurality of third fixed teeth may vary the natural frequency of the structure to the scanning frequency of the application, and the plurality of mobile teeth and the plurality of mobile teeth at the scanning frequency of the application. The oscillation voltage difference between the first and second stationary teeth of the oscillation oscillates the scanning mirror. MEMS structure. A first layer defining an opening, said first layer consisting of an electrically insulating material, and Second layer-the second layer, A first drive pad comprising a plurality of first stationary teeth and electrically connected to an AC voltage source providing an AC voltage; A second drive pad comprising a plurality of second stationary teeth, the second drive pad being electrically connected to the AC voltage source; A bias pad comprising a plurality of third teeth, the bias pad being electrically connected to a DC voltage source providing a DC voltage; A mirror over the opening, The mirror is, Reflection area, A torsional hinge connected to the reflective region, An anchor connected to the torsional hinge, mounted on top of the first layer to rotate the mirror, and electrically connected to ground; A plurality of first movable tooth protrusions connected to the reflective region and engaged with the plurality of first and second fixed tooth protrusions, A plurality of second movable tooth protrusions connected to the reflective region and engaged with the plurality of third fixed tooth protrusions, The normal voltage difference between the plurality of second movable teeth and the plurality of third fixed teeth is such that the natural frequency of the structure is changed to the scanning frequency of the application and the plurality of second movable at the scanning frequency of the application. An oscillation voltage difference between the tooth protrusion and the plurality of first and second fixed tooth protrusions causes the scanning mirror to oscillate. MEMS structure. In the method of controlling a MEMS structure with a mobile device, Determining an amplitude of a DC voltage difference between the first fixed electrode and the moving electrode of the movable element, the DC voltage difference such that the natural frequency of the structure is at least approximately equal to the scanning frequency of the application; Recording the amplitude of the DC voltage difference for use in the application; Recording the scanning frequency as a frequency of an AC voltage difference between a second fixed electrode and the moving electrode of the movable element for use in the application. MEMS structure control method. The method of claim 21, The determining of the value of the DC voltage difference, Applying a DC bias voltage to the first fixed electrode; Grounding the mobile electrode connected to the mobile device; Adjusting the amplitude of the DC bias voltage until the natural frequency of the structure is at least approximately equal to the scanning frequency. MEMS structure control method. The method of claim 22, The step of recording the DC voltage difference includes programming the amplitude of the DC bias voltage to a controller to operate the MEMS structure. MEMS structure control method. The method of claim 23, Recording the scanning frequency as a frequency of an AC voltage difference includes programming the scanning frequency to the controller. MEMS structure control method. The method of claim 21, Grounding the moving electrode; Applying a DC bias voltage to the first fixed electrode to cause the DC voltage difference between the first fixed electrode and the moving electrode; Applying an AC drive voltage to the second fixed electrode, causing the AC voltage difference between the second fixed electrode and the moving electrode; MEMS structure control method. The method of claim 25, The scanning as a frequency of a second AC voltage difference between the third fixed electrode and the moving electrode of the movable element for use in the application, wherein the second AC voltage difference is out of phase with the first AC voltage difference. To record the frequency, Applying a second AC drive voltage to the third fixed electrode to cause the AC voltage difference between the second fixed electrode and the moving electrode; MEMS structure control method. In the method of controlling a MEMS structure with a mobile device, Applying a DC voltage difference between the first fixed electrode and the moving electrode of the movable element, wherein the DC voltage difference makes the natural frequency of the structure at least approximately equal to the desired scanning frequency of the application; Applying an AC voltage difference of the desired scanning frequency between the second fixed electrode and the moving electrode, the AC voltage difference causing oscillation of the mobile device. MEMS structure control method. The method of claim 27, Measuring a scanning frequency and a scanning angle of the mobile device; Comparing the measured scanning frequency and the scanning angle with the preferred scanning frequency and preferred scanning angle, Adjusting the amplitude of the DC voltage difference to change the natural frequency of the structure at least approximately equal to the desired scanning frequency of the application. MEMS structure control method. The method of claim 28, Adjusting at least one of the amplitude, frequency, and vertical offset of the AC voltage difference to change at least one of the scanning frequency, the scanning angle, and the neutral scanning position. MEMS structure control method. The method of claim 27, The step of applying a DC voltage difference, Applying a DC bias voltage to the first fixed electrode; Grounding the moving electrode; MEMS structure control method. The method of claim 30, The step of applying an AC voltage difference includes applying an AC voltage to the second fixed electrode. MEMS structure control method. A first electrode connected to the first voltage source, A second electrode connected to the second voltage source, A rotating frame comprising a third electrode connected to a third voltage source, the frame mounted on a support layer to rotate about a first axis; and A fourth electrode connected to the fourth voltage source, A fifth electrode connected to the fifth voltage source, A rotatable element comprising a sixth electrode connected to a sixth voltage source, wherein the rotatable element is mounted to the frame and rotates about a second axis; A first normal voltage difference between the first electrode and the third electrode changes the natural frequency of the structure about the first axis to be at least approximately equal to the scanning frequency of an application about the first axis, The first normal voltage difference between the fourth electrode and the sixth electrode changes the natural frequency of the structure around the second axis to be at least approximately equal to the scanning frequency of an application about the second axis. , A first oscillation voltage difference between the second electrode and the third electrode at the first scanning frequency oscillates the rotatable element about the first axis, The second oscillation voltage difference between the fifth electrode and the sixth electrode at the second scanning frequency causes the rotatable element to oscillate about the second axis. MEMS structure. The method of claim 32, The first voltage source is a first DC voltage source, the second voltage source is a first AC voltage source, and the third voltage source is ground MEMS structure. The method of claim 33, wherein The frame further includes a torsion spring mounted on the support layer, and the third electrode includes a plurality of first tooth protrusions extending from the frame. MEMS structure. The method of claim 34, wherein The first electrode includes a plurality of second tooth protrusions mounted on the support layer, and meshes with the plurality of first tooth protrusions when the frame is not rotated. MEMS structure. 36. The method of claim 35 wherein The second electrode includes a plurality of third tooth protrusions on the plurality of second tooth protrusions, the plurality of third tooth protrusions meshing with the plurality of first tooth protrusions when the frame rotates. MEMS structure. The method of claim 33, wherein The fourth voltage source is a second DC voltage source, the fifth voltage source is a second AC voltage source, and the sixth voltage source is ground MEMS structure. The method of claim 37, The rotatable element is a scanning mirror including a reflective region connected to a torsion spring mounted on the upper portion of the frame, and the sixth electrode includes a plurality of first tooth protrusions extending from the reflective region. MEMS structure. The method of claim 38, The fourth electrode includes a plurality of second tooth protrusions engaged with at least a portion of the plurality of first tooth protrusions when the frame is not rotated. MEMS structure. The method of claim 39, The fifth electrode includes a plurality of third tooth protrusions engaged with at least a portion of the plurality of first tooth protrusions when the frame is not rotated. MEMS structure. The method of claim 37, The first DC voltage source, the second DC voltage source, the first AC voltage source, and the second AC voltage source are located on the same chip as the structure. MEMS structure. The method of claim 33, wherein At least one of the first DC voltage source, the second DC voltage source, the first AC voltage source, and the second AC voltage source is located on a different chip than the structure. MEMS structure. A first layer comprising an electrically insulating material, A second layer over the first layer-the second layer, A frame comprising a plurality of first tooth protrusions extending from at least one edge, the frame being connected to a first anchor, the first anchor being electrically connected to ground, by a first torsional hinge for rotation about a first axis and, A plurality of second teeth, wherein the plurality of first and second teeth are engaged with each other when the frame is not rotating, and includes a first bias pad connected to a first DC voltage source; and A third layer overlying said second layer, said third layer comprising an electrically insulating material; and The fourth layer over the third layer-the fourth layer, A mirror connected to a second anchor, the second anchor being electrically connected to ground, by a second torsional hinge for rotation about a second axis, the plurality of third protrusions extending from at least one edge; Wow, A second bias pad comprising a plurality of fourth teeth, wherein the second bias pad is connected to a second DC voltage source, and the plurality of third and fourth teeth are engaged with each other when the mirror is not rotating; and, A first drive pad comprising a plurality of fifth teeth, the first drive pads being connected to a first AC voltage source, and the plurality of third and fourth teeth are engaged with each other when the mirror is not rotating; and, A second drive pad comprising a plurality of six teeth, wherein the second drive pad is connected to a second AC voltage source, wherein the plurality of first and six teeth are rotated about the second axis; Interlocks with-contains-, A first steady voltage difference between the plurality of first and second tooth protrusions is at least approximately equal to the first scanning frequency of an application about the first axis of the natural frequency of the structure about the first axis. To make a difference, The second normal voltage difference between the plurality of third and fourth teeth is at least approximately of the second scanning frequency of the application about the second axis of the natural frequency of the structure about the second axis. Change the same, A first oscillation voltage difference between the plurality of third and fifth tooth protrusions at the first scanning frequency oscillates the scanning mirror about the second axis; The second oscillation voltage difference between the plurality of first and sixth tooth protrusions at the second scanning frequency causes the scanning mirror to oscillate about the first axis. MEMS structure. A method of controlling a MEMS structure having a rotatable element mounted on a rotatable frame, A first DC voltage difference between a first electrode and a second electrode of the rotatable element, the first DC voltage difference being the first natural frequency of the structure about a second axis of the application about the second axis. Determining at least approximately equal to the first scanning frequency; A second DC voltage difference between a third electrode and a fourth electrode of the rotatable frame, wherein the second DC voltage difference is the application of the second natural frequency of the structure about the first axis about the first axis Determining at least approximately equal to a second scanning frequency of C; Recording the first and second DC voltage differences for use in the application; A first AC voltage difference between the fifth electrode and the second electrode of the rotatable element for use in the application, the first AC voltage difference causing oscillation of the rotatable element about the second axis Recording the first scanning frequency as a first drive frequency of; Second AC voltage difference between the sixth electrode and the fourth electrode of the rotatable element for use in the application, wherein the second AC voltage difference causes oscillation of the rotatable frame about the first axis. Recording the second scanning frequency as a second drive frequency of the; MEMS structure control method. The method of claim 44, The determining of the first DC voltage difference, Applying a first DC bias voltage to the first electrode; Grounding the second electrode of the rotatable element; Adjusting the amplitude of the first DC bias voltage until the first natural frequency is at least approximately equal to the first scanning frequency. MEMS structure control method. The method of claim 45, The determining of the second DC bias voltage difference, Applying a second DC bias voltage to the third electrode; Grounding the fourth electrode of the rotatable frame; Adjusting the amplitude of the second DC bias voltage until the second natural frequency is at least approximately equal to the second scanning frequency. MEMS structure control method. The method of claim 46, Recording the first and second DC voltage differences comprises programming the DC bias voltage and the second DC bias voltage to a controller for operating the MEMS structure. MEMS structure control method. The method of claim 47, Recording the first and second scanning frequencies includes programming the first and second scanning frequencies with the controller. MEMS structure control method. The method of claim 44, Grounding the second electrode; Applying the first DC bias voltage to the first electrode to cause the first DC voltage difference; Applying a first AC drive voltage of the first scanning frequency to the fifth electrode to cause the first AC voltage difference; Grounding the fourth electrode; Applying the second DC bias voltage to the third electrode to cause the second DC voltage difference; Applying a second AC drive voltage at the second scanning frequency to the sixth electrode to cause the second AC voltage difference. MEMS structure control method. A method of controlling a MEMS structure having a rotatable element mounted on a rotatable frame, A first DC voltage difference between a first electrode and a second electrode of the rotatable element, the first DC voltage difference being the first natural frequency of the structure about a first axis of the application about the first axis. Applying at least approximately equal to the first preferred scanning frequency; A second DC voltage difference between a third electrode and a fourth electrode of the rotatable frame, the second DC voltage difference being the second natural frequency of the structure about a second axis of the application about the second axis. Applying at least approximately equal to a second preferred scanning frequency; A first AC voltage difference between the fifth electrode and the second electrode of the rotatable element at the first preferred scanning frequency—the first AC voltage difference causes oscillation of the rotatable element about the first axis Applying- A second AC voltage difference between the sixth electrode and the fourth electrode of the rotatable frame at the second preferred scanning frequency—the second AC voltage difference causes oscillation of the rotatable element about the second axis Applying the MEMS structure control method. 51. The method of claim 50, Measuring a first scanning frequency and a first scanning angle of the rotatable element about the first axis; Comparing the measured first scanning frequency and the measured first scanning angle with the first preferred scanning frequency and the first preferred scanning angle; Adjusting the amplitude of the first DC voltage difference to change the first natural frequency at least approximately equal to the first preferred scanning frequency. MEMS structure control method. The method of claim 51, wherein Adjusting at least one of the amplitude, frequency, and vertical offset of the first AC voltage difference to change at least one of the first scanning frequency, the first scanning angle, and the first neutral scanning position of the rotatable element. Including more steps MEMS structure control method. The method of claim 51, wherein Measuring a second scanning frequency and a second scanning angle of the rotatable frame about the second axis; Comparing the measured second scanning frequency and the measured second scanning angle with the second preferred scanning frequency and the second preferred scanning angle; Adjusting the amplitude of the second DC voltage difference to change the second natural frequency at least approximately equal to the second preferred scanning frequency. MEMS structure control method. The method of claim 53 wherein Adjusting at least one of an amplitude, a frequency, and a vertical offset of the second AC voltage difference to change at least one of the second scanning frequency, the second scanning angle, and a second neutral scanning position of the rotatable element. Including more steps MEMS structure control method. 51. The method of claim 50, The step of applying the first DC voltage difference, Applying a DC bias voltage to the first electrode; Grounding the second electrode; MEMS structure control method. The method of claim 55, The step of applying the first AC voltage difference includes applying an AC voltage to the fifth electrode. MEMS structure control method. The method of claim 56, wherein The step of applying the second DC voltage difference, Applying a DC bias voltage to the third electrode; Grounding the fourth electrode; MEMS structure control method. The method of claim 57, The step of applying the second AC voltage difference includes applying an AC bias voltage to the sixth electrode. MEMS structure control method.

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