EP1563333A1 - Miroir de balayage a frequence naturelle accordable - Google Patents

Miroir de balayage a frequence naturelle accordable

Info

Publication number
EP1563333A1
EP1563333A1 EP03786631A EP03786631A EP1563333A1 EP 1563333 A1 EP1563333 A1 EP 1563333A1 EP 03786631 A EP03786631 A EP 03786631A EP 03786631 A EP03786631 A EP 03786631A EP 1563333 A1 EP1563333 A1 EP 1563333A1
Authority
EP
European Patent Office
Prior art keywords
electrode
teeth
voltage
voltage difference
scanning
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP03786631A
Other languages
German (de)
English (en)
Inventor
Yee-Chung Fu
Ting-Tung Kuo
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Advanced Nano Systems Inc
Original Assignee
Advanced Nano Systems Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US10/302,413 external-priority patent/US7034370B2/en
Priority claimed from US10/302,387 external-priority patent/US6769616B2/en
Application filed by Advanced Nano Systems Inc filed Critical Advanced Nano Systems Inc
Publication of EP1563333A1 publication Critical patent/EP1563333A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/0816—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements
    • G02B26/0833—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD
    • G02B26/0841—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD the reflecting element being moved or deformed by electrostatic means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
    • B81B7/00—Microstructural systems; Auxiliary parts of microstructural devices or systems
    • B81B7/02—Microstructural systems; Auxiliary parts of microstructural devices or systems containing distinct electrical or optical devices of particular relevance for their function, e.g. microelectro-mechanical systems [MEMS]
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/10—Scanning systems
    • G02B26/101—Scanning systems with both horizontal and vertical deflecting means, e.g. raster or XY scanners
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/35—Optical coupling means having switching means
    • G02B6/351—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements
    • G02B6/3512—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements the optical element being reflective, e.g. mirror
    • G02B6/3518—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements the optical element being reflective, e.g. mirror the reflective optical element being an intrinsic part of a MEMS device, i.e. fabricated together with the MEMS device
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/35—Optical coupling means having switching means
    • G02B6/3564—Mechanical details of the actuation mechanism associated with the moving element or mounting mechanism details
    • G02B6/3568—Mechanical details of the actuation mechanism associated with the moving element or mounting mechanism details characterised by the actuating force
    • G02B6/357—Electrostatic force

Definitions

  • This invention relates to micro-electro-mechanical systems (MEMS), and more particularly to MEMS scanning mirrors.
  • MEMS micro-electro-mechanical systems
  • MEMS scanning mirrors have been proposed. Their applications include barcode readers, laser printers, confocal microscopes, f ⁇ ber- optical network components, projection displays for projectors, rear projection TVs, wearable displays, and military laser tracking and guidance systems.
  • a MEMS scanning mirror is driven at its main resonance to achieve a high scan angle.
  • the manufacturing processes produce MEMS scanning mirrors with dimensional inconsistencies that vary the natural frequencies of the individual devices. If the main natural frequency of a minority of the MEMS scanning mirrors is too low or too high, the minority devices will not produce the proper scan speed and the proper scan angle under an alternating current (AC) drive voltage selected for a majority of the MEMS scanning mirrors.
  • AC alternating current
  • 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 (e.g., an electrical ground).
  • 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.
  • the mobile element is a mirror.
  • FIGS. 1 A and IB respectively illustrate assembled and exploded views of a MEMS structure 100 in one embodiment.
  • FIGS. 1C, ID, and IE illustrate top views of the layers in MEMS structure 100 in one embodiment.
  • FIG. IF illustrates a method for configuring and operating MEMS structure 100 in one embodiment of the invention.
  • FIGS. IG, 1H, II, and 1J illustrate top views of the various layers in MEMS structure 100 in different embodiments.
  • FIGS. 2 A and 2B respectively illustrate assembled and exploded views of a MEMS structure 200 in one embodiment.
  • FIGS. 2C and 2D illustrate top views of the layers in MEMS structure 200 in one embodiment.
  • FIGS. 3 A and 3B respectively illustrate assembled and exploded views of a MEMS structure 300 in one embodiment.
  • FIGS. 3C, 3D, 3E, 3F, and 3G illustrate top views of the layers in MEMS structure 300 in one embodiment.
  • FIG. 4 illustrates a MEMS system in one embodiment of the invention.
  • FIG. 5 illustrates DC and AC voltages used to oscillate a MEMS structure in one embodiment of the invention.
  • FIG. 4 illustrates a MEMS system 400 in one embodiment of the invention.
  • MEMS system 400 includes a MEMS structure (e.g., MEMS structure 100, 200, or 300) with a mobile element that is electrostatically moved under voltages supplied by a voltage source 402.
  • Voltage source 402 provides a voltage difference between a stationary electrode and a moving electrode of the mobile element to adjust the natural frequency of MEMS structure 100 to a desired scanning frequency.
  • Voltage source 402 also provides an AC voltage difference between another stationary electrode and the moving electrode of the mobile element at the desired scanning frequency to oscillate the mobile element with a desired scanning angle.
  • the movement of the mobile element (e.g., the scanning frequency and the scanning angle) is measured by a sensor 404 and fed back to a controller 406.
  • Controller 406 compares the measured movement to a desired movement of the mobile element and then instructs voltage source 402 to provide the appropriate voltages to achieve the desired movement.
  • MEMS structure 100, voltage source 402, sensor 404, and controller 406 can be build on the same chip or on different chips.
  • FIGS. 1A and IB respectively illustrate assembled and exploded views of a MEMS structure 100 in one embodiment.
  • MEMS structure 100 can be used in any application that requires a single axis of motion (e.g., a unidirectional scanning mirror).
  • MEMS structure 100 includes a conductive layer 105, an insulating layer 107, and a conductive layer 109.
  • 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 components on conductive layers 105 and 109. Insulating layer 107 is also used to physically bond conductive layers 105 and 109.
  • FIG. 1C illustrates a top view of one embodiment of conductive layer 105.
  • Conductive layer 105 includes a scanning mirror 101 and a bias pad 112.
  • Scanning mirror 101 includes a reflective area 124 that is connected by torsion hinges 102 A and 102B to anchors 108 A and 108B, respectively.
  • Mirror 101 rotates about an axis 122.
  • torsion hinges 102 A and 102B include internal holes 114 to lower the rotational modal frequency of structure 100.
  • the rotational modal frequency is the lowest of the modal frequencies to ensure scanning mirror 101 rotates about the axis 122 without coupling with other unwanted rotational and translational structural vibrations.
  • Mirror 101 includes moving teeth 104A and 104B (collectively “moving teeth 104") on different sides of rotational axis 122.
  • Moving teeth 104A and 104B extend from bars 106A and 106B, respectively.
  • Bars 106A and 106B are connected to reflective area 124 and run parallel to torsion hinges 102A and 102B.
  • Bias pad 112 includes stationary teeth 103 A and 103B (collectively “stationary teeth 103”) on the different sides of rotational axis 122.
  • Stationary teeth 103A and 103B are respectively interdigitated with moving teeth 104A and 104B when bias pad 112 and mirror 101 are in the same plane (e.g., when mirror 101 is not rotated).
  • anchor 108 A is coupled to ground 116 and bias pad 112 is . coupled 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 creates a steady voltage difference between stationary teeth 103 and moving teeth 104.
  • the steady voltage difference between stationary teeth 103 and moving teeth 104 creates an electrostatic torque that rotates mirror 101 until the electrostatic torque is equal to the restoring torque in an equilibrium position.
  • the steady voltage difference between stationary teeth 103 and moving teeth 104 creates a nonlinear electrostatic system that changes the natural frequency of MEMS structure 100. Accordingly, the natural frequency of MEMS structure 100 can be adjusted (e.g., tuned) by increasing or decreasing the steady voltage difference between stationary teeth 103 and moving teeth 104.
  • DC voltage source 118 is built on the same chip as structure 100. Alternatively, DC voltage source 118 is built on a chip separate from structure 100. In one embodiment, DC voltage source 118 is servo-controlled during operation to generate a DC bias voltage value that produces the desired natural frequency of structure 100.
  • FIG. ID illustrates a top view of one embodiment of intermediate layer 107.
  • Insulating layer 107 has the same shape as conductive layer 105 but for mirror 101 in order to electrically insulate the components on layer 101.
  • Insulating layer 107 defines a cross-shaped opening 121 for the scanning motion of mirror 101.
  • FIG. IE illustrates a top view of one embodiment of conductive layer 109.
  • Conductive layer 109 includes a drive pad 126 that defines a cross-shaped opening 11 1.
  • Drive pad 126 includes stationary teeth 110A and HOB (collectively "stationary teeth 110") on the different sides of rotational axis 122.
  • opening 111 is a free space reserved for the scanning motion of mirror 101.
  • Stationary teeth 110A are interdigitated with moving teeth 104A when mirror 101 is rotated in a first direction (e.g., clockwise), and stationary teeth HOB are interdigitated with moving teeth 104B when mirror 101 is rotated in a second direction (e.g., counterclockwise).
  • Teeth 110A and HOB are electrically connected.
  • stationary teeth 110 and moving teeth 104 form an electrostatic actuator (e.g., a vertical comb drive actuator) that oscillates scanning mirror 101.
  • drive pad 126 is coupled to an AC voltage source 120 and anchor 108 A is coupled to ground 116.
  • AC voltage source 120 provides an AC drive voltage to drive pad 126 that creates an oscillating voltage difference between stationary teeth 110 and moving teeth 104.
  • AC drive voltage has a frequency equal to the natural frequency of structure 100 to achieve the maximum scan angle.
  • the oscillating voltage difference between teeth 110 and 104 causes electrostatic torques that create the scanning motion of mirror 101.
  • AC voltage source 120 is built on the same chip as structure 100. Alternatively, AC voltage source 120 is built on a chip separate from structure 100. In one embodiment, AC voltage source 120 is servo-controlled during operation to generate an AC drive voltage that produces the desired scanning speed and scanning angle.
  • FIG. IF illustrates a method 150 for configuring and operating a MEMS structure 100 in one embodiment.
  • Structure 100 is generally a device from a batch of mass produced structures 100. Described below, actions 151 and 152 occur during the manufacturing of structure 100, and actions 153, 154, 156, and 160 occur during the use of structure 100.
  • a designer determines the scanning frequency and the scanning angle of an application (e.g., 1 kHz and 5 - 10 degrees for a barcode reader) and modifies the basic design of structure 100 to achieve a specific natural frequency equal to the scanning frequency.
  • the designer modifies the design by changing the stiffness of the hinges (e.g., the geometry of the hinges) or changing the inertia of the structure (e.g., the geometry of the mirror).
  • Action 152 is followed by action 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 (Fig. 5) to tune the natural frequency of this structure 100 to the scanning frequency of the application.
  • the designer presets the amplitude and the frequency of the AC drive voltage (Fig. 5) to achieve the desired scan angle for this structure 100.
  • the designer can also preset the vertical offset of the AC drive voltage (Fig. 5) to achieve the desired neutral scanning position about which the oscillation occurs.
  • an end user may store different characteristics for the DC bias voltage and the AC drive voltage in controller 406. The end user may wish to do so to change the desired scanning frequency, the desired scanning angle, and the desired neutral scanning position.
  • controller 406 instructs voltage source 402 to apply the DC bias voltage and the AC drive voltage.
  • Voltage source 402 represents the various DC and AC voltage sources (e.g., DC voltage source 118 and AC voltage source 120).
  • the DC bias voltage is initiated with the default values stored in controller 406 and then servo-controlled to ensure the rotational natural frequency is the scanning frequency. Servo-control of the DC bias voltage is necessary in the operational stage because the natural frequency of structure 100 may drift away from the desired value due to temperature changes, material aging, or any other reasons.
  • the AC drive voltage is initiated with the default values stored in controller 406 and then servo-controlled to ensure the desired scanning frequency and the scanning angle are achieved. Servo-control of the AC drive voltage is necessary in the operational stage because the scanning frequency, the scanning angle, and the neutral scanning position may drift away from the desired values due to temperature changes, material aging, or any other reasons.
  • Action 154 is followed by action 158:
  • sensor 404 is used to monitor the motion of the scanning mirror (e.g., the scanning frequency, the scanning angle, and the scanning neutral position) and the measured information is outputted to controller 406. Action 158 is followed by action 160.
  • the scanning mirror e.g., the scanning frequency, the scanning angle, and the scanning neutral position
  • controller 406 receives the motion information from sensor 404. Controller 406 computes and provides the needed DC bias voltage and the needed AC drive voltage to voltage source 402. The servo-control of the DC bias voltage is accomplished by perturbing the amplitude of the DC bias voltage and sensing the change in the scanning angle. If the DC bias voltage is increased and the scanning angle is also increased at the same time, then the natural frequency is approaching the scanning frequency, and vice versa. It is generally more effective to maintain the scanning amplitude by controlling the natural frequency with DC bias voltage change if the Bode plot shows a high Q factor of the main natural frequency.
  • the servo-control of the AC drive voltage is accomplished by perturbing the amplitude, the frequency, and the vertical offset of the AC drive voltage and sensing the change in the scanning angle, the scanning frequency, and the scanning neutral position.
  • the amplitude of the AC drive voltage is increased to increase the angle of rotation, and vice versa.
  • the frequency of the AC drive voltage is increased to increase the scanning frequency, and vice versa.
  • the vertical offset of the AC drive voltage is changed to optimize the scanning neutral position.
  • Action 160 is followed by action 154 and the method continues in a feedback loop.
  • FIG. IG illustrates a top view of another embodiment of conductive layer 105 of structure 100. Same or similar parts between FIGS. 1C and IG are indicated by the same reference numerals.
  • reflective area 124 is connected to bars 128 A and 128B.
  • Moving teeth 104A and 104B extend from opposite edges of bars 128A and 128B.
  • the ends of bars 128A and 128B are connected by torsion hinges 130A and 130B to anchors 108 A and 108B, respectively.
  • Each of torsion hinges 130A and 130B has a serpentine shape that increases translational stiffness but maintains the torsional flexibility of hinges 102 A and 102B.
  • DC voltage source 118 is coupled to bias pad 112 and ground 116 is coupled to anchor 108 A.
  • Method 150 described above can be used to configure and operate a structure 100 with conductive layer 105 of FIG. IG.
  • FIG. 1H illustrates a top view of another embodiment of conductive layer 109. Same or similar parts between FIGS. IE and 1H are indicated by the same reference numerals.
  • drive pad 126 only includes stationary teeth 110B. This configuration provides a large initial torque to excite the mirror rotational oscillation.
  • the oscillating voltage difference between stationary teeth HOB and moving teeth 104B alone creates the scanning motion of mirror 101. However, the oscillating voltage difference may be increased to match the response amplitude of the above embodiment in FIG. IE because layer 109 in this embodiment exerts a force with stationary teeth 110 on only one of the opposing sides.
  • Method 150 described above can be used to configure and operate a structure 100 with conductive layer 109 of FIG. 1H.
  • FIG. II illustrates a top view of another embodiment of conductive layer 109. Same or similar parts between FIGS. IE and II are indicated by the same reference numerals.
  • conductive layer 109 is divided into two drive pads 132A and 132B (collectively "drive pads 132") that together define opening 121.
  • Stationary teeth 110A and 110B extend from opposing edges of drive pads 132 A and 132B, respectively.
  • Drive pad 132 A is coupled to an AC voltage source 134A while drive pad 132B is coupled to another AC voltage source 134B.
  • AC voltage sources 134A and 134B have the same frequency but a phase difference of 180 degrees to provide the highest torsional actuation force and initial excitation torque.
  • the oscillating voltage difference between stationary teeth 110 and moving teeth 104 creates the scanning motion of mirror 101.
  • Method 150 described above can be used to configure and operate a structure 100 with conductive layer 109 of FIG. II.
  • FIG. 1J illustrates a top view of an additional layer 136 below conductive layer 109 that electrically insulate drive pads 132 A and 132B.
  • insulating layer 136 is made of intrinsic silicon. Insulating layer 136 may include a free space reserved for the scanning motion of mirror 101.
  • FIGS. 2A and 2B respectively illustrate assembled and exploded views of a MEMS structure 200 in one embodiment.
  • MEMS structure 200 can be used in any application that requires a single axis scanning mirror.
  • MEMS structure 200 includes a conductive layer 205, an isolative and bonding layer 207, and a structure anchoring layer 209.
  • conductive layer 205 is made of doped silicon while isolative layer 207 is made of SiO 2 to electrically insulate elements of conductive layer 205.
  • Layer 209 provides a support structure for the two upper layers. If layer 209 is made of non-conductive intrinsic silicon, layer 207 will only be used as a bonding layer and may be optional for this configuration.
  • FIG. 2C illustrates a top view of one embodiment of conductive layer 205.
  • Conductive layer 205 includes a scanning mirror 201, bias pad 212, and drive pads 232A and 232B. Similar to mirror 101, mirror 201 includes a reflective area 224 that is connected by torsion hinges 202 A and 202B to anchors 208A and 208B, respectively. Mirror 201 rotates about an axis 222.
  • torsion hinges 202A and 202B include internal holes 214 to lower the rotational modal frequency.
  • Mirror 201 also includes a set of moving teeth 204A and 204B (collectively "moving teeth 204"). Moving teeth 204A and 204B extend from bars 206A and 206B, which are on different sides of axis 222. Bars 206A and 206B are connected to reflective area 224 and run parallel to torsion hinges 202A and 202B.
  • Inner moving teeth 204B are closer to reflective area 224 and are interdigitated with stationary teeth 210A and 210B (described later). Outer moving teeth 204A are farther from reflective area 224 and are interdigitated with stationary teeth 203A and 203B (described later).
  • mirror 201 is asymmetric because it generally has a square shape with one or more corners removed. Thus, the center of gravity of mirror 201 is shifted to one side of the axis 222. Such a design may be preferred when an application requires mirror 201 to start at some initial rotational position or to reach some initial rotational position quickly.
  • Bias pad 212 includes stationary teeth 203 A and 203B (collectively “stationary teeth 203") on the different sides of axis 222.
  • Stationary teeth 203A and 203B are respectively interdigitated with outer moving teeth 204A when bias pad 212 and mirror 201 are in the same plane (e.g., when mirror 201 is not rotated).
  • Drive pads 232A and 232B respectively include stationary teeth 210A and 210B (collectively “stationary teeth 210"). Stationary teeth 210A and 210B are interdigitated with inner moving teeth 204B when drive pads 232 and mirror 201 are in the same plane.
  • anchor 208 A is coupled to ground 216 and bias pad 212 is coupled to a DC voltage source 218.
  • DC voltage source 218 provides a DC bias voltage to bias pad 212 that creates a steady voltage difference between stationary teeth 203 and outer moving teeth 204A.
  • the steady voltage difference between stationary teeth 203 and moving teeth 204A creates an electrostatic force that changes the natural frequency of structure 200. Accordingly, the natural frequency of MEMS structure 200 can be tuned by changing the steady voltage difference between stationary teeth 203 and moving teeth 204A.
  • stationary teeth 210 and moving teeth 204B form an electrostatic actuator (e.g., a comb drive actuator) that oscillates scanning mirror 201.
  • drive pads 232 are coupled to an AC voltage source 220. When activated, AC voltage source 220 provides an AC drive voltage to drive pads 232 that creates an oscillating voltage difference between stationary teeth 210 and inner moving teeth 204B. The oscillating voltage difference between stationary teeth 210 and inner moving teeth 204B causes electrostatic torque that creates the scanning motion of mirror 201.
  • DC voltage source 218 and AC voltage source 220 are built on the same chip as structure 200.
  • voltage sources 218 and 220 are built on one or more chips separate from structure 200. These one or more chips are then coupled to bias pad 212 and drive pads 232 via wires.
  • DC voltage source 218 is servo-controlled during operation to generate a DC bias voltage value that produces the desired natural frequency of structure 100
  • AC voltage source 220 is servo-controlled during operation to generate an AC drive voltage that produces the desired scanning speed and scanning angle.
  • FIG. 2D illustrates a top view of one embodiment of isolative layer 207.
  • Isolative layer 207 defines a cross-shaped opening 221. Similar to opening 121, opening 221 is a free space reserved for the scanning motion of mirror 201.
  • Method 150 (FIG. IF) described above can be applied to operate structure 200.
  • FIGS. 3A to 3B respectively illustrate assembled and exploded views of a MEMS structure 300 in one embodiment.
  • MEMS structure 300 can be used in any application that requires rotational motion with respect to two rotational axes (e.g., a bidirectional scanning mirror).
  • MEMS structure 300 includes a structure anchoring layer 301, an insulating layer 304, a conductive layer 302, an insulating layer 305, and a conductive layer 303.
  • layer 301 is made of intrinsic silicon or doped silicon
  • conductive layers 302 and 303 are made of doped silicon
  • insulating layers 304 and 305 are made of silicon dioxide (SiO 2 ). Insulating layers 304 and 305 electrically insulate components on layers 301, 302, and 303.
  • Insulating layer 304 is also used to physically bond layers 301 and 302.
  • insulating layer 305 is also used to physically bond conductive layers 302 and 303.
  • FIG. 3C illustrates a top view of one embodiment of conductive layer 303.
  • Conductive layer 303 includes a scanning mirror 316, drive pads 306 and 309, ground pad 307, and bias pad 308.
  • Scanning mirror 316 includes a reflective area 352 that is connected by serpentine torsion hinges 315A and 315B to anchors 328 and 329, respectively.
  • Mirror 316 rotates about the Y-axis via hinges 315 A and 315B.
  • Hinges 315A and 315B determine the mirror scanning frequency/speed in the Y-axis.
  • Mirror 316 includes moving teeth 314A and 314B (collectively "moving teeth 314") on different sides of the Y-axis.
  • Drive pad 306 is connected by a serpentine torsion hinge 324 to a comb 388.
  • Comb 388 has stationary teeth 313 that are interdigitated with some of moving teeth 314A when comb 388 and mirror 316 are in the same plane (e.g., when mirror 316 is not rotated about the Y-axis).
  • drive pad 309 is connected by a serpentine torsion hinge 326 to a comb 390.
  • Comb 390 has stationary teeth 311 that are interdigitated with some of moving teeth 314B when mirror 316 is not rotated about the Y- axis.
  • Bias pad 308 is connected by a serpentine torsion hinge 325 to a comb 323B.
  • Comb 323B is connected by a bar 330A to a comb 323A.
  • Combs 323A and 323B respectively have stationary teeth 310A and 310B (collectively "stationary teeth 310").
  • Stationary teeth 310A and 310B are respectively interdigitated with some of moving teeth 314A and 314B when mirror 316 is not rotated about the Y-axis.
  • Ground pad 307 is connected by a serpentine torsion hinge 327 to an L-shaped bar
  • ground pad 307 is coupled to ground 354 and bias pad 308 is coupled to a DC voltage source 356.
  • DC voltage source 356 provides a DC bias voltage to bias pad 308.
  • the DC bias voltage creates a steady voltage difference between stationary teeth 310 and moving teeth 314.
  • the steady voltage difference between stationary teeth 310 and moving teeth 314 creates a nonlinear electrostatic system that changes the natural frequency of MEMS structure 300 about the Y-axis. Accordingly, the natural frequency of MEMS structure 300 about the Y-axis can be changed (e.g., tuned) by changing the steady voltage difference between stationary teeth 310 and moving teeth 314.
  • DC voltage source 356 can be built on the same chip as structure 300. Alternatively, DC voltage source 356 can be built on a chip separate from structure 300. In one embodiment, DC voltage source 356 is servo-controlled during operation to generate a DC bias voltage value that produces the desired natural frequency of structure 300 about the Y-axis.
  • (1) stationary teeth 311 and moving teeth 314B and (2) stationary teeth 313 and moving teeth 314A form two electrostatic actuators (e.g., comb drive actuators) that oscillate scanning mirror 316 about the Y-axis.
  • drive pads 306 and 309 are coupled to an AC voltage source 360, and ground pad 307 is coupled to ground 354.
  • AC voltage source 360 creates an oscillating voltage difference (1) between stationary teeth 311 and moving teeth 314B, and (2) between stationary teeth 313 and moving teeth 314A.
  • AC drive voltage has a frequency equal to the natural frequency of structure 300 to achieve the maximum scan angle.
  • the oscillating voltage difference between the teeth causes electrostatic torques that create the scanning motion of mirror 316 about the Y-axis.
  • AC voltage source 360 is built on the same chip as structure 300.
  • AC voltage source 360 is built a chip separate from structure 300.
  • AC voltage source360 is servo-controlled during operation to generate an AC drive voltage that produces the desired scanning speed and scanning angle about the Y-axis.
  • conductive layer 303 further includes drive pads/combs 317A and 317B located on different sides of the X-axis.
  • Combs 317A and 317B include stationary teeth 318 A and 318B, respectively.
  • Stationary teeth 318A and 318B are used to rotate mirror 316 about the X-axis (described later in reference to layer 302).
  • Combs 317A and 317B are coupled to an AC voltage source 374 (described later).
  • FIG. 3D illustrates a top view of one embodiment of insulating layer 305.
  • Insulating layer 305 has the same shape as conductive layer 303 but for mirror 316 in order to electrically insulate the components on layer 303.
  • Insulating layer 305 defines an opening 358 reserved for the scanning motion of mirror 316.
  • FIG. 3E illustrates a top view of one embodiment of conductive layer 302.
  • Conductive layer 302 includes rotational frame 364 and bias pads/combs 319A and 319B.
  • Rotational frame 364 defines an opening 358 for the scanning motion of mirror 316.
  • Rotational frame 364 includes combs 322A and 322B on different sides of the X-axis.
  • Rotational frame 364 is connected by serpentine torsion hinges 332A and 332B to grounding pads/anchors 331A and 331B, respectively.
  • Rotational frame 364 can rotate about the X-axis via hinges 332A and 332B.
  • Mirror 316 is mounted atop rotational frame 364.
  • anchors 328 and 329 of mirror 316 are respectively mounted atop of anchor mounts 366 and 367 of rotational frame 364. This allows mirror 316 to rotate about the Y-axis using hinges 315A and 315B, and about the X-axis using hinges 332A and 332B.
  • Combs 322 A and 322B respectively include moving teeth 321 A and 32 IB (collectively “moving teeth 321").
  • Combs 319A and 319B respectively include stationary teeth 320A and 320B (collectively “stationary teeth 320").
  • 320B are respectively interdigitated with moving teeth 321A and 321B when combs 322A, combs 322B, and rotational frame 364 are in the same plane (e.g., when rotational frame 364 is not rotated about the X-axis).
  • anchor 331A is coupled to ground 368
  • combs 319A and 319B are coupled to a DC voltage source 370.
  • DC voltage source 370 provides DC bias voltages to comb 319A and 319B.
  • the DC bias voltages create a steady voltage difference between stationary teeth 320 and moving teeth 321.
  • the steady voltage difference between stationary teeth 320 and moving teeth 321 creates a nonlinear electrostatic system that changes the natural frequency of MEMS structure 300 about the X-axis. Accordingly, the natural frequency of MEMS structure
  • DC voltage source 370 is built on the same chip as structure 300.
  • DC voltage source 370 is built on a chip separate from structure 300.
  • DC voltage source 370 is servo-controlled during operation to generate a DC bias voltage value that produces the desired natural frequency of structure 300 about the X-axis.
  • comb 317A and 317B respectively have stationary teeth 318A and 318B (Fig. 3C).
  • Moving teeth 321A (Fig. 3E) of rotational frame 364 (Fig. 3E) are interdigitated with stationary teeth 318A when minor 316 (Fig. 3C) is rotated in a first direction
  • moving teeth 32 IB (Fig. 3E) of rotational frame 364 are interdigitated with stationary teeth 318B when mirror 316 is rotated in the opposite direction.
  • (1) stationary teeth 318A and moving teeth 321 A and (2) stationary teeth 318B and moving teeth 32 IB form two electrostatic actuators (e.g., a comb drive actuators) that oscillate scanning minor 316 about the X-axis.
  • combs 317A and 317B are coupled to an AC voltage source 374 (Fig. 3C) and ground pad 331 A (Fig. 3E) is coupled to ground 368 (Fig. 3E).
  • AC voltage source 374 creates an oscillating voltage difference between stationary teeth 318A and moving teeth 321A, and between stationary teeth 318B and moving teeth 321B.
  • the AC drive voltage has a frequency equal to the natural frequency of structure 300 to achieve the maximum scan angle.
  • the oscillating voltage difference between the teeth causes electrostatic torques that create the scanning motion of minor 316 about the X-axis.
  • AC voltage source 374 is built on the same chip as structure 300.
  • AC voltage source 374 is built on a chip separate from structure 300.
  • AC voltage source 374 is servo-controlled during operation to generate an AC drive voltage that produces the desired scanning speed and scanning angle about the X-axis.
  • FIG. 3F illustrates a top view of one embodiment of insulating layer 304.
  • Insulating layer 304 has the same shape as conductive layer 302, but for rotational frame 364, in order to electrically insulate the components on layer 302. Insulating layer 304 defines opening 358 reserved for the scanning motion of mirror 316 and rotational frame
  • FIG. 3G illustrates a top view of one embodiment of structure anchoring layer 301.
  • Layer 301 includes a frame 378 that defines opening 358 for the scanning motion of mirror 316 and rotational frame 364.
  • Rotational frame 364 is mounted atop frame 378.
  • anchors 331 A and 33 IB of rotational frame 364 are respectively mounted atop of anchor mounts 380 and 382 of frame 378.
  • Combs 319A and 319B of conductive layer 302 are respectively mounted atop of comb mounts 384 and 386.
  • Method 150 (FIG. IF) described above can be modified to configure and operate a MEMS structure 300 in one embodiment.
  • Structure 300 is generally a device from a batch of mass produced structures 300.
  • action 151 a designer determines the scanning frequencies and the scanning angles for both axes of rotation of an application and modifies the basic design of structure 300 to achieve specific natural frequencies equal to the scanning frequencies.
  • the designer modifies the design by changing the stiffness of the hinges (e.g., the geometry of the hinges) or changing the inertia of the structure (e.g., the geometry of the minor).
  • Action 152 is followed by action 152.
  • action 152 the designer presets the characteristics of the DC voltage differences for both axes of rotation to tune the natural frequencies of this structure 300 to the scanning frequencies.
  • the designer also presets the characteristics of the AC voltage differences for both axes of rotation to achieve the desired scan angles and the desired neutral scanning positions about which the oscillation occurs. These characteristics are then stored into controller 406 for this structure 300 as the initial/default characteristics for the DC bias voltages and the AC drive voltages.
  • an end user may store different characteristics for the DC bias voltages and the AC drive voltages in controller 406. The end user may wish to do so to change the desired scanning frequencies, the desired scanning angles, and the desired neutral scanning positions.
  • controller 406 instructs voltage source 402 to apply the DC bias voltage and the AC drive voltage.
  • Voltage source 402 represents the various DC and AC voltage sources (e.g., DC voltage sources 356 and 370, and AC voltage sources 360 and 374).
  • the DC bias voltages are initiated with the default values stored in controller 406 and then servo-controlled to ensure the rotational natural frequencies are the scanning frequencies.
  • the AC drive voltages are initiated with the default values stored in controller 406 and then servo-controlled to ensure the desired scanning frequencies, the desired scanning angles, and the desired scanning neutral positions are achieved.
  • Action 154 is followed by action 158.
  • action 158 sensor 404 is used to monitor the motion of the scanning minor and the measured information is outputted to controller 406. Action 158 is followed by action 160.
  • controller 406 receives the scanning frequencies and angles information from sensor 404. Controller 406 computes and provides the needed DC bias voltages and the needed AC drive voltages to voltage source 402. Action 160 is followed by action 154 and the method continues in a feedback loop.

Abstract

L'invention concerne, dans un mode de réalisation, une structure de systèmes mécaniques microélectriques (MEMS) comprenant une première électrode, une deuxième électrode et un élément mobile. La première électrode est couplée à une première source de tension. La deuxième électrode est couplée à une deuxième source de tension. L'élément mobile comprend une troisième électrode couplée à une troisième source de tension. Une différence de tension constante entre la première et la troisième électrode est utilisée pour accorder la fréquence naturelle de la structure avec une fréquence d'exploration d'une application. Une différence de fréquence d'oscillation entre la deuxième électrode et la troisième électrode, à la fréquence d'exploration de l'application est utilisée pour faire osciller l'élément mobile. Dans un mode de réalisation, l'unité mobile est un miroir.
EP03786631A 2002-11-22 2003-11-10 Miroir de balayage a frequence naturelle accordable Withdrawn EP1563333A1 (fr)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
US10/302,413 US7034370B2 (en) 2002-11-22 2002-11-22 MEMS scanning mirror with tunable natural frequency
US302413 2002-11-22
US10/302,387 US6769616B2 (en) 2002-11-22 2002-11-22 Bidirectional MEMS scanning mirror with tunable natural frequency
US302387 2002-11-22
PCT/US2003/035776 WO2004049034A1 (fr) 2002-11-22 2003-11-10 Miroir de balayage a frequence naturelle accordable

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EP1563333A1 true EP1563333A1 (fr) 2005-08-17

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EP (1) EP1563333A1 (fr)
JP (1) JP2004177957A (fr)
KR (1) KR20060026001A (fr)
AU (1) AU2003295445A1 (fr)
TW (1) TWI238143B (fr)
WO (1) WO2004049034A1 (fr)

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TWI238143B (en) 2005-08-21
AU2003295445A1 (en) 2004-06-18
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KR20060026001A (ko) 2006-03-22
TW200416194A (en) 2004-09-01
JP2004177957A (ja) 2004-06-24

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