Frequency tunable resonant scanner and method of making

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.

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:

• 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.

A method of controlling a scanning motion of 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 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.

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.