Polysilicon resonating beam transducers and method of producing the same
First Claim
1. A method of making a resonant beam force transducer comprising the steps of:
- (a) forming a beam of polysilicon mounted at its ends above a substrate;
(b) annealing the polysilicon beam so it has zero or low built-in tensile strain;
(c) encapsulating the beam in a polysilicon shell which forms with the substrate a cavity which surrounds the beam, and channels formed in the shell leading from the cavity;
(d) sealing the interior of the cavity from the external atmosphere with a gas which reacts to deposit solid material in the channels to close them and to evacuate the cavity.
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Abstract
Force transducers are formed of a beam of polysilicon which is mounted at its ends to a silicon substrate and is encapsulated within a polysilicon shell which defines, with the substrate, a cavity around the resonating beam. The cavity is sealed off from the atmosphere and evacuated to maximize the Q of the resonating beam. The beam is produced by deposition of polysilicon in such a way that, combined with subsequent annealing steps, the beam is in zero or low tensile strain. Resonant excitation of the beam may be accomplished in various ways, including capacitive excitation, and the vibratory motion of the beam may be detected utilizing an implanted resistor which is piezoresistive. Formation of the beam is carried out by depositing the beam on a sacrificial layer and surrounding it in a second sacrificial layer before the encapsulating polysilicon shell is formed. The sacrificial layers are etched out with liquid etchant which passes through channels in the periphery of the shell. Following etching, the interior of the cavity surrounding the beam is maintained in a wash liquid so that the beam is not deflected toward any of the adjacent surfaces, and the wash liquid is removed by freezing and su
This invention was made with United States government support awarded by the National Science Foundation (NSF), Grant # EET-88-15285. The United States Government has certain rights in this invention.
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Citations
6 Claims
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1. A method of making a resonant beam force transducer comprising the steps of:
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(a) forming a beam of polysilicon mounted at its ends above a substrate; (b) annealing the polysilicon beam so it has zero or low built-in tensile strain; (c) encapsulating the beam in a polysilicon shell which forms with the substrate a cavity which surrounds the beam, and channels formed in the shell leading from the cavity; (d) sealing the interior of the cavity from the external atmosphere with a gas which reacts to deposit solid material in the channels to close them and to evacuate the cavity. - View Dependent Claims (2, 3, 4, 5, 6)
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Specification