Temperature stable MEMS resonator
AssigneeSiTime Corporation
InventorsPaul M. Hagelin, Charles I. Grosjean
Life of this patent
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Abstract
A resonant member of a MEMS resonator oscillates in a mechanical resonance mode that produces non-uniform regional stresses such that a first level of mechanical stress in a first region of the resonant member is higher than a second level of mechanical stress in a second region of the resonant member. A plurality of openings within a surface of the resonant member are disposed more densely within the first region than the second region and at least partly filled with a compensating material that reduces temperature dependence of the resonant frequency corresponding to the mechanical resonance mode.
Claims22
A microelectromechanical systems (MEMS) resonator comprising:
- an anchor;
- a first beam and a second beam each extending in parallel along a length dimension “L,” each of the first beam and the second beam having a first end and a swinging end, each of the first beam and the second beam also having a second dimension that is perpendicular to the length dimension, the swinging end of each beam to vibrate in the second dimension during operation of the MEMS resonator and
- a base portion mechanically coupling the anchor and the first end of each of the first beam and the second beam;
- wherein each of the first beam and the second beam comprises crystal silicon;
- wherein the crystal silicon of each beam has a temperature coefficient of Young's Modulus (TCE) with a sign that is a first one of positive and negative at an operating temperature of the MEMS device and wherein each beam further comprises a compensating material, having a TCE with a sign that is a second one of positive and negative at the operating temperature of the MEMS device;
- and
- wherein the compensating material is concentrated in each of the first beam and the second beam along the length dimension L to be at a position of maximum flexural stress of the respective first beam or second beam that occurs when, during operation of the MEMS resonator, the swinging end of the respective beam vibrates in the second dimension.
A method of fabricating a microelectromechanical systems (MEMS) resonator, the method comprising:
- forming an anchor, a first beam, a second beam, and a base portion, end of each of the first beam and the second beam extending in parallel along a length dimension “L,” each of the first beam and the second beam having a first end and a swinging end, the base portion connecting the first end of each of the beams to the anchor, the anchor mechanically coupling the anchor and the first each of the first beam and the second beam, each of the first beam and the second beam also having a second dimension that is perpendicular to the length dimension, the swinging end of each beam to vibrate in the second dimension during operation of the MEMS resonator;
- and
- wherein forming comprises fabricating each of the first beam and the second beam to include crystal silicon and a compensating material, the crystal silicon of each beam having a temperature coefficient of Young's Modulus (TCE) with a sign that is a first one of positive and negative at an operating temperature of the MEMS device and the compensating material having a TCE with a sign that is a second one of positive and negative at the operating temperature of the MEMS device;
- and
- wherein forming comprises concentrating the compensating material in each of the first beam and the second beam along the length dimension L to be at a position of maximum flexural stress of the respective first beam or second beam that occurs when, during operation of the MEMS resonator, the swinging end of the respective beam vibrates in the second dimension.
Dependencies are inferred from the claim text.