Analog Devices,inc.

Robert W Tsang

Theresa A Core

A Paul Brokaw

Steven J Sherman

Richard S Payne

Jeffrey A Farash

A monolithic capacitance-type microstructure includes a semiconductor substrate, a plurality of posts extending from the surface of the substrate, a bridge suspended from the posts, and an electrically-conductive, substantially stationary element anchored to the substrate. The bridge includes an element that is laterally movable with respect to the surface of the substrate. The substantially stationary element is positioned relative to the laterally movable element such that the laterally movable element and the substantially stationary element form a capacitor. Circuitry may be disposed on the substrate and operationally coupled to the movable element and the substantially stationary element for processing a signal based on a relative positioning of the movable element and the substantially stationary element. A method for fabricating the microstructure and the circuitry is disclosed.

Monolithic micromechanical apparatus with suspended microstructure

Methods for fabricating monolithic device containing circuitry and

A method for providing a conductive ground plane beneath a suspended microstructure. A conductive region is diffused into a substrate. Two dielectric layers are added: first a thermal silicon dioxide layer and then a silicon nitride layer. A first mask is used to etch a ring partially through the silicon nitride layer. Then, a second mask is used to etch a hole through both dielectric layers in a region having a perimeter that extends between the inner and outer edges of the ring. This leaves the conductive region exposed in an area surrounded by a ring that has the silicon dioxide layer and a narrow silicon nitride layer. The ring is surrounded by an area in which the silicon dioxide and silicon nitride layers have not been reduced. A spacer silicon dioxide layer is deposited over the dielectric and then a polysilicon layer is deposited and formed into the shape of a the suspended microstructure. When the spacer layer is etched away, the silicon dioxide under the narrow silicon nitride layer is removed, along with the narrow silicon nitride layer, leaving an exposed ground plane surrounded by a dielectric with minimal undercutting.

Method of forming a microstructure with bare silicon ground plane

An accelerometer comprising a microfabricated acceleration sensor and monolithically fabricated signal conditioning circuitry. The sensor comprises a differential capacitor arrangement formed by a pair of capacitors. Each capacitor has two electrodes, one of which it shares electrically in common with the other capacitor. One of the electrodes (e.g., the common electrode) is movable and one of the electrodes is stationary in response to applied acceleration. The electrodes are all formed of polysilicon members suspended above a silicon substrate. Each of the capacitors is formed of a plurality of pairs of electrode segments electrically connected in parallel and, in the case of the movable electrodes, mechanically connected to move in unison. When the substrate is accelerated, the movable electrodes move such that the capacitance of one of the capacitors increases, while that of the other capacitor decreases. The two capacitors are connected to signal conditioning circuitry which converts this differential capacitance into a corresponding voltage. Both open loop and force-balance operation are shown.

Monolithic accelerometer

The invention is a monolithic sensor comprising a silicon substrate, a suspended polysilicon microstructure for sensing a condition disposed above and suspended from the substrate, and circuitry for resolving a signal based on said sensed condition, the circuitry including bipolar circuit elements and MOS circuit elements. One disclosed embodiment is particularly adapted for sensing acceleration by means of a differential capacitor arrangement in which one capacitor plate in the arrangement is moveable responsive to an acceleration.

Monolithic chip containing integrated circuitry and suspended

The invention comprises a method for fabricating a monolithic chip containing integrated circuitry as well as a suspended polysilicon microstructure. The inventive method comprises 67 processes which are further broken down into approximately 330 steps. The processes and their arrangement allow for compatible fabrication of transistor circuitry and the suspended polysilicon microstructure on the same chip.

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Bedford, MA, United States of America

Robert W Tsang