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EP0451992A2 Expired / Lapsed EP ⏱️ 0.0 years remaining

Detection of vibrations of a microbeam through a shell

Assignee: Wisconsin Alumni Research Foundation
•
Filing: 1991-03-27
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Granted: —
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Expires: 2011-03-27
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Abstract

Abstract Force transducers are formed of a beam (34) of polysilicon which is mounted at its ends to a silicon substrate (31) and is encapsulated within a polysilicon shell (40) 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 (44) 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 sublimation. The interior surfaces of the cavity and the outer surfaces of the beam are passivated and the channels leading into the cavity may be sealed by oxidation in an oxidizing atmosphere, which also results in consumption of oxygen within the cavity.

Inventors

  • 👤 Henry Guckel
  • 👤 Jeffrey J. Sniegowski

Bibliographic Details

Application Number —
Jurisdiction EP
Data Source google_patents
Last Synchronized 2026-11-08 14:59
CPC Classifications
H; H03; H03H; H03H9/00; H03H9/02; H03H9/02244; H03H9/02259; G; G01; G01L; G01L1/00; G01L1/18; G01L1/183; G01L1/186; G01L9/00; G01L9/0001; G01L9/0008; G01L9/0019; G01L9/002; H03H3/00; H03H3/007; H03H3/0072; H03H2009/02488; H03H2009/02511

Claims Analysis

Total Claims: 10
Claim 1
Independent Claim 133 words
A resonant beam transducer comprising: (a) a substrate; (b) a polysilicon beam mounted to the substrate at at least one of its ends and spaced from the substrate between its ends to allow free vibration of the beam; (c) an encapsulating shell of polysilicon surrounding the beam and affixed to the substrate to define a cavity with the substrate which surrounds the beam and which is sealed off from the atmosphere, the cavity being substantially evacuated; (d) means for exciting mechanical vibration in the beam; and (e) means for projecting light through the polysilicon shell onto the beam and means for receiving the projected light reflected from the beam and for converting the received light into an electrical signal corresponding to the received light which is indicative of the vibration of the beam.
Claim 2
Dependent Claim 30 words
The transducer of Claim 1 wherein the means for projecting light includes a light source and an optical fiber to direct light from the light source to the polysilicon shell.
Claim 3
Dependent Claim 42 words
The transducer of claim 1 wherein the means for receiving the light reflected from the beam includes an optical fiber to direct light reflected from the beam to a remote position and a photodetector for detecting the light at the remote position.
Claim 4
Dependent Claim 46 words
The transducer of Claim 1 wherein the means for exciting mechancial vibration in the beam includes a conducting electrode formed on the polysilicon beam to which voltage can be provided and another closely spaced plate electrode such that there is capacitive coupling between the two electrodes.
Claim 5
Dependent Claim 77 words
The transducer of Claim 4 wherein the conductive electrode for exciting the beam is formed by implantation of a dopant in the surface of the polysilicon beam in a pattern, and further including a conductive plate formed on the polysilicon shell above the corresponding excitation electrode on the beam so that excitation of the beam can be obtained by providing an alternating current between the plate on the polysilicon shell and the underlying electrode on the beam.
Claim 6
Dependent Claim 32 words
The transducer of Claim 1 wherein the interior surfaces of the shell and substrate defining the cavity and the outer surface of the beam have a layer of silicon dioxide formed thereon.
Claim 7
Dependent Claim 22 words
The transducer of Claim 1 wherein the beam has a length of about 200 microns and a thickness of about 2 microns.
Claim 8
Dependent Claim 25 words
The transducer of Claim 1 wherein the beam is mounted at both of its ends to the substrate to suspend the beam above the substrate.
Claim 9
Dependent Claim 20 words
The transducer of Claim 1 wherein the means for projecting light includes a laser providing a substantially monochromatic light output.
Claim 10
Independent Claim 89 words
A method of detecting the vibrations of a microbeam encapsulated within a shell which will pass light of selected wavelengths, comprising the steps of: (a) directing substantially monochromatic light through the encapsulating shell onto the vibrating beam, the spacing between the shell and the beam being close to the wavelength of the light such that inteference patterns are formed as the beam vibrates; (b) detecting light reflected from the beam in the interference pattern and providing an electrical signal corresponding thereto which is indicative of vibrations of the beam.

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