Miniature silicon accelerometer and method
AssigneeNorthrop Corporation
InventorsBenedict B. O'Brien, Brent E. Burns, John A. Geen
Life of this patent
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Abstract
A miniature accelerometer is fabricated using integrated circuit manufacturing and silicon micromachining techniques to form a closed loop, force balance sensor utilizing a silicon proofmass formed from and connected to a layer of silicon by a split flexure etched therein. The sensor circuitry detects AC signals coupled from the proofmass to a pair of electrodes formed on glass surfaces anodically bonded to the silicon layer. A DC restorative force is applied to the electrodes in response to the detected AC signals to balance acceleration forces applied to the proofmass. The sensor design is highly symmetrical.
Claims22
A miniature accelerometer, comprising:
- a pair of spaced insulating layers;
- a pair of electrodes disposed on said insulating layers;
- a silicon proofmass assembly including a proofmass and a mounting;
- means for suspending said proofmass from the mounting between said electrodes with a gap between each electrode and said proofmass;
- means for applying an AC excitation signal directly to said proofmass;
- means for detecting AC signals coupled to said electrodes therefrom;
- and
- means responsive to the AC signals detected for applying acceleration opposing forces to said proofmass.
A miniature accelerometer, comprising:
- a pair of spaced electrodes deposited on a pair of spaced insulating layers made of material having thermal expansion coefficient closely matched to silicon;
- a silicon proofmass;
- means for suspending said proofmass between said electrodes;
- bias linear means including an amplifier responsive to differential capacitive coupling between the electrodes and the proofmass for generating an electrical signal for opposing acceleration forces applied thereto;
- means for measuring a change in the value of said signal as a measure of said acceleration;
- said electrodes including forcer electrode means for applying electrostatic forces to the proofmass in response to and for opposing acceleration forces applied thereto;
- and
- guard electrode means for preventing contact between the forcer electrode means and the proofmass.
A miniature accelerometer, comprising:
- a pair of spaced electrodes deposited on a pair of spaced insulating layers made of material having thermal expansion coefficient closely matched to silicon;
- a silicon proofmass;
- means for suspending said proofmass between said electrodes;
- bias linear means including an amplifier responsive to differential capacitive coupling between the electrodes and the proofmass for generating an electrical signal for opposing acceleration forces applied thereto;
- means for measuring a change in the value of said signal as a measure of said acceleration;
- a forcer electrode metalization for applying an electrostatic force to the proofmass;
- and
- a guard electrode metalization, substantially thicker than the forcer electrode metalization, for preventing contact between the forcer electrode metalization and the proofmass.
A method of sensing acceleration using a proofmass and electrodes disposed on spaced insulating layers to form an accelerometer,
- suspending the proofmass in a balanced position between the electrodes to define equal coupling capacitances between the electrodes and the proofmass,
- electronically sensing differential capacitive coupling between the electrodes and the proofmass whenever the proofmass is moved away from a balanced position due to acceleration,
- electronically generating an electrical signal which, when applied to the electrodes, generates an electrostatic force on the proofmass which will tend to move the proofmass toward said balanced position,
- applying said electrical signal to said electrodes to create acceleration opposing forces to be applied to the proofmass, and
- applying an electrostatic force from a forcer electrode to the proofmass;
- preventing contact between the forcer electrode and the proofmass with a guard electrode, and
- measuring the magnitude and sign of said electrical signal required to restore said balance as a measure of the acceleration experienced by the proofmass.
A miniature accelerometer, comprising:
- a pair of insulating layers having metalized electrodes thereon;
- a silicon proofmass suspended between the layers;
- means for applying an A.C. signal directly to the proofmass;
- means responsive to the induced signal in the electrodes for detecting AC signals coupled to the electrodes therefrom;
- and
- means responsive to the AC signals detected for applying differential electrostatic forces between the electrodes and the proofmass linearly proportional to the detected AC signals.
A miniature accelerometer, comprising:
- a pair of electrode layers;
- a silicon proofmass suspended therebetween;
- guard electrode means for preventing contact between the proofmass and the electrode layers;
- and
- means responsive to differential capacitive coupling between the electrode layers and the proofmass for opposing acceleration forces applied thereto.
Dependencies are inferred from the claim text.