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US 12,753,070 B2Granted
MEMS resonator
AssigneeSiTime Corporation
InventorsCharles I. Grosjean, Nicholas Miller, Paul M. Hagelin, Ginel C. Hill, Joseph C. Doll
Life of this patent
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Abstract
Multiple degenerately-doped silicon layers are implemented within resonant structures to control multiple orders of temperature coefficients of frequency.
Claims23
A method of fabricating a microelectromechanical systems (MEMS) device having a body that is adapted to move or deflect during operation of the MEMS device, the method comprising:
- forming the body so as to have a plurality of layers supported by a substrate, the plurality of layers including at least one silicon layer and a layer of piezoelectric material;
- wherein forming comprises providing, as part of the body, one or more electrodes operable to induce the body to move or deflect at a resonance frequency and to sense the resonance frequency, wherein the resonance frequency is characterized as having a temperature-dependent variation;
- wherein forming comprises structuring a given layer of the at least one silicon layer such that:
- the given layer comprises crystal silicon;
- the crystal silicon of the given layer defines a predominant lattice configuration of the layer, the predominant lattice configuration having an associated lattice crystallographic axis;
- (i) an angular relationship between the lattice crystallographic axis and an axis of the body, (ii) a type of dopant present in the given layer, (iii) a concentration of the dopant present in the given layer, and (iv) a thickness of the given layer, are such that a contribution of the given layer to at least one of a second-or-higher-order component of the temperature-dependent variation, is inverse in sign to, and at least partially offsets, a second-or-higher-order component of a contribution of the layer of piezoelectric material to the temperature dependent variation, over a predetermined temperature range;
- and
- an absolute value of variation in the resonance frequency as a function of temperature is no more than a predetermined value over the predetermined temperature range;
- and
- covering or encapsulating the body, so as to be hermetically-sealed within a cavity.
7 more elements
A method of fabricating a die having a microelectromechanical systems (MEMS) resonator with a body that is adapted to move or deflect during operation of the MEMS resonator, and having an electrical contact operable to carry an electrical signal dependent a resonance frequency of the body, the method comprising:
- forming the body so as to have a plurality of layers, including two silicon layers and a layer of piezoelectric material in between the two silicon layers;
- wherein forming comprises providing, as part of the body, one or more electrodes operable to induce the body to move or deflect at a resonance frequency and to sense the resonance frequency, wherein the resonance frequency is characterized as having a temperature-dependent variation;
- wherein at least one of the silicon layers is degenerately-doped and also is one of the one or more electrodes;
- wherein forming comprises structuring a given one of the two silicon layers such that:
- the given one comprises crystal silicon;
- the crystal silicon of the given one defines a predominant lattice configuration of the layer, the predominant lattice configuration having an associated lattice crystallographic axis;
- (i) an angular relationship between the lattice crystallographic axis and an axis of the body, (ii) a type of dopant present in the given one, (iii) a concentration of the dopant present in the given one, and (iv) a thickness of the given one, are such that a contribution of the given one to at least one of a second-or-higher-order component of the temperature-dependent variation, is inverse in sign to, and at least partially offsets, a second-or-higher-order component of a contribution of the layer of piezoelectric material to the temperature dependent variation, over a predetermined temperature range;
- and
- an absolute value of variation in the resonance frequency as a function of temperature is no more than a predetermined value over the predetermined temperature range;
- covering or encapsulating the body, so as to be hermetically-sealed within a cavity, the electrical contact being outside of the cavity;
- and
- forming an electrical communication path which passes through the substrate, a cover or an encapsulant, so as to place one of the electrodes in electrical communication with the electrical contact.
9 more elements
A method of fabricating a microelectromechanical systems (MEMS) device having a body that is adapted to move or deflect during operation of the MEMS device, the method comprising:
- forming the body so as to have a plurality of layers supported by a substrate, the plurality of layers including at two degenerately-doped silicon layers and a layer of piezoelectric material, the layer of piezoelectric material lying in between the two degenerately-doped silicon layers;
- wherein forming comprises providing, as part of the body, one or more electrodes operable to induce the body to move or deflect at a resonance frequency and to sense the resonance frequency, wherein the resonance frequency is characterized as having a temperature-dependent variation, and wherein at least one of the two degenerately-doped silicon layers is to act as an electrode of the one or more electrodes;
- wherein forming comprises structuring a given one of the two silicon layers such that:
- the given one comprises crystal silicon;
- the crystal silicon of the given one defines a predominant lattice configuration of the layer, the predominant lattice configuration having an associated lattice crystallographic axis;
- (i) an angular relationship between the lattice crystallographic axis and an axis of the body, (ii) a type of dopant present in the given one, (iii) a concentration of the dopant present in the given one, and (iv) a thickness of the given one, are such that a contribution of the given one to at least one of a second-or-higher-order component of the temperature-dependent variation, is inverse in sign to, and at least partially offsets, a second-or-higher-order component of a contribution of the layer of piezoelectric material to the temperature dependent variation, over a predetermined temperature range;
- and
- an absolute value of variation in the resonance frequency as a function of temperature is no more than a predetermined value over the predetermined temperature range;
- and
- covering or encapsulating the body, so as to be hermetically-sealed within a cavity.
7 more elements
Dependencies are inferred from the claim text.