Frequency tunable resonant scanner and method of making

• US 6,515,278 B2
• Filed: 03/23/2001
• Issued: 02/04/2003
• Est. Priority Date: 08/05/1999
• Status: Expired due to Fees

• Current Assignee: Microvision, Inc.
• Original Assignee: Microvision, Inc.
• Inventors: Barger, Jon D., Tegreene, Clarence T., Helsel, Mark P., Wine, David W.
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US09/816,809
• Publication Number:
  US 20010034077A1
• Time in Patent Office: 683 Days
• Field of Search: 250/234, 250/235, 250/216, 250/306, 250/307, 359/213, 359/212, 359/221-226, 359/198, 359/199, 359/290, 359/872, 316/308, 316/309
• US Class Current: 250/234
• 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, symmetrically 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 resonant microelectromechanical scanner, comprising:

a substrate;

an oscillatory body of a first material carried by the substrate and coupled to the substrate for periodic movement;

an optical element carried by the oscillatory body; and

an array of removable masses carried by the oscillatory body and exposed on a surface thereof, the removable masses being of a second material different from the first material, the second material being of a type having a lower vaporization temperature than the first material, wherein the array of removable masses, together with the oscillatory body, forming an oscillatory mass, wherein the oscillatory mass defines the resonant frequency.

2. The microelectromechanical scanner of claim 1 wherein the oscillatory mass is coupled in a configuration that permits the periodic movement to occur about a pivot axis, and wherein the removable masses are grouped in pairs that are symmetrically positioned relative to the pivot axis.

3. The microelectromechanical scanner of claim 2 wherein the number of pairs is greater than one.

4. The micro-electro-mechanical scanner of claim 1 wherein the second material is a metal.

5. The micro-electro-mechanical scanner of claim 1 wherein the second material is an organic polymer.

6. A microelectromechanical device having a desired resonant frequency, comprising:

a base;

a movable body coupled to the base for resonant motion relative to the base about a pivot axis, the movable body having a selected inertia relative to the pivot axis;

a support interposed between the base and the movable body and coupled to permit oscillatory movement of the movable body relative to a reference point; and

a plurality of exposed masses carried by the movable body and symmetrically positioned relative to the reference point, each of the exposed masses being in an exposed position that provides access for removal, the exposed masses each being positioned to provide a supplemental inertia relative to the pivot axis, wherein the selected inertia and the supplemental inertia together determine a resonant frequency for the device.

7. The microelectromechanical resonant device of claim 6 further comprising:

a first electrode carried by the movable body; and

a reflective material carried by the movable body and positioned to reflect incident light through a periodic scan pattern as the movable body moves relative to reference point.

8. The microelectromechanical resonant device of claim 6 wherein the movable body and the support form an integral body.

9. The microelectromechanical resonant device of claim 6 wherein the exposed masses are formed of a material deposited on an exposed surface of the movable body.

10. The microelectromechanical resonant device of claim 6 wherein the support defines a first pivot axis of the movable body, further comprising a frame interposed between the base and the movable body, the frame being coupled to the base and configured to define a second pivot axis for the movable body substantially orthogonal to the first pivot axis.