Frequency tunable resonant scanner and method of making
First Claim
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.
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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.
82 Citations
30 Claims
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1. A resonant microelectromechanical scanner, comprising:
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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. - View Dependent Claims (2, 3, 4, 5)
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6. A microelectromechanical device having a desired resonant frequency, comprising:
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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. - View Dependent Claims (7, 8, 9, 10)
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11. An apparatus for producing a plurality of resonant optical MEMs scanner from a single wafer, each MEMs scanner having a movable body that moves at a desired resonant frequency and carries one or more removable masses, comprising:
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a first electrical signal source configured for coupling to each respective MEMs scanner while the MEMs scanner is an integral part of the wafer, the first signal source being operative to produce a first input signal for activating the respective optical scanner;
a position sensor coupled to the movable body of the respective MEMs scanner and operative to produce an electrical signal indicative of movement of the movable body while the MEMs scanner is an integral part of the wafer;
a reference signal source operative to produce a reference signal at the desired resonant frequency;
an electronic controller coupled electrically to the position sensor and the reference signal source, the controller being operative to produce an error signal indicative of a difference between a frequency of movement of the movable body and the desired resonant frequency; and
a mass removal apparatus responsive to the electronic controller to remove selected portions of the removable masses while the respective MEMs scanner is an integral part of the wafer. - View Dependent Claims (12, 13, 14)
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15. A method of controlling a scanning motion of a MEMs device formed in a semiconductor wafer, comprising the steps of:
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while the MEMs device is an integral part of the wafer, activating the MEMs device for periodic motion of a portion of the MEMs device relative to a reference point, the portion having an inertial mass offset from the reference point by a selected distance;
monitoring the periodic motion of the MEMs device;
responsive to the monitored periodic motion of the MEMs device, identifying a deviation of the periodic 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, removing a portion of the inertial mass. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22)
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23. A method of controlling a MEMs device formed in a semiconductor wafer, comprising the steps of:
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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. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30)
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Specification