Frequency tunable resonant scanner and method of making

• US 6,245,590 B1
• Filed: 08/05/1999
• Issued: 06/12/2001
• Est. Priority Date: 08/05/1999
• Status: Expired due to Term

• Current Assignee: Microvision, Inc.
• Original Assignee: Microvision, Inc.
• Inventors: Tegreene, Clarence T., Helsel, Mark P., Wine, David W., Barger, Jon D.
• Primary Examiner(s): Niebling, John F.
• Assistant Examiner(s): Simkovic, Viktor
• Application Number:
  US09/369,674
• Time in Patent Office: 677 Days
• Field of Search: 438/14, 438/52, 438/53, 359/198, 359/199, 310/312, 310/333, 735/79
• US Class Current: 438/52
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G02B 26/101 with both horizontal and vertical deflecting means, e.g. raster or XY scanners colour television using laser beams scanning a display screen H04N9/3129
• CPC Class Codes: G02B 27/017 Head mounted
• CPC Class Codes: G06K 7/10633 by oscillation
• CPC Class Codes: G09G 3/001 using specific devices not provided for in groups G09G3/02 - G09G3/36, e.g. using an intermediate record carrier such as a film slide; Projection systems; Display of non-alphanumerical information, solely or in combination with alphanumerical information, e.g. digital display on projected diapositive as background slide projectors per se G03B23/00 = 42 HP
• CPC Class Codes: G09G 3/025 with scanning or deflecting the beams in two directions or dimensions

Abstract

A MEM s scanning device has a variable resonant frequency. In one embodiment, the MEMs device includes a torsion arm that supports an oscillatory body. In one embodiment, an array of removable masses are placed on an exposed portion of the oscillatory body and selectively removed to establish the resonant frequency. The material can be removed by laser ablation, etching, or other processing approaches. In another approach, a migratory material is placed on the torsion arm and selectively stimulated to migrate into the torsion arm, thereby changing the mechanical properties of the torsion arm. The changed mechanical properties in turn changes the resonant frequency of the torsion arm. In another approach, symmetricaly distributed masses are removed or added in response to a measured resonant frequency to tune the resonant frequency to a desired resonant frequency. A display apparatus includes the scanning device and the scanning device scans about two or more axes, typically in a raster pattern. Various approaches to controlling the frequency responses of the scanning device are described, including active control of MEMs scanners and passive frequency tuning.

Claims

1. A method of controlling a MEMs device formed in a semiconductor wafer, comprising the steps of:

while the MEMs device is an integral part of the wafer, activating the MEMs device for resonant motion of a portion of the MEMs device relative to a reference point;

monitoring the resonant motion of the MEMs device;

responsive to the monitored resonant motion of the MEMs device, identifying a deviation of the resonant motion from a desired periodic motion;

generating an error signal in response to the identified deviation; and

while the MEMs device is an integral part of the wafer and responsive to the error signal, varying material properties with a region of the MEMs device in a manner that changes the frequency of the resonant motion by introducing an impurity into a portion of the semiconductor wafer.

2. The method of claim 1 wherein the MEMs device includes a torsional member that in part defines a resonant frequency of the MEMs device, and wherein varying the material properties includes introducing an impurity into a portion of the torsional member.

3. The method of claim 2 wherein the impurity is a metal.

4. The method of claim 2 wherein the impurity is a chromium.

5. The method of claim 2, wherein introducing an impurity into a portion of the torsional member includes:

placing an impurity on a surface of the torsional member; and

heating the torsional member.

6. The method of claim 1 wherein the step of monitoring the periodic motion of the MEMs device includes probing the wafer with a probe station.

7. The method of claim 1 wherein the step of monitoring the periodic motion of the MEMs device includes optically detecting movement or position of the portion.