US 5,507,911 A · Monolithic micromechanical vibrating string accelerometer with trimmable resonant frequency

Abstract

A monolithic, micromechanical vibrating string accelerometer with a trimmable resonant frequency is fabricated from a silicon substrate which has been selectively etched to provide a resonant structure suspended over an etched pit. The resonant structure comprises an acceleration sensitive mass and at least two flexible elements having resonant frequencies. Each of the flexible elements is disposed generally colinear with at least one acceleration sensitive axis of the accelerometer. One end of at least one of the flexible elements is attached to a tension relief beam for providing stress relief of tensile forces created during the fabrication process. Mass support, beams having a high aspect ratio support the mass over the etched pit while allowing the mass to move freely in the direction colinear with the flexible elements. Also disclosed is a method for fabricating such an accelerometer with high aspect ratio tension relief and mass support beams.

Claims12

Dependent claims

A method for fabricating a monolithic micromechanical vibrating accelerometer with a trimmable resonant frequency, comprising the steps of:

providing a single silicon substrate having an oxidized layer generally covering said substrate;
removing selected regions of said oxidized layer;
etching said silicon substrate with an anisotropic etchant, said etching forming a pit having sidewalls and a bottom;
selectively doping the sidewalls and bottom of said pit in said silicon substrate through the regions of selectively removed oxidized layer, to form etch resistant regions in said silicon substrate;
and
etching said silicon substrate with an anisotropic etchant, said etching forming at least one non-etched silicon resonant structure selected from the group consisting of:
an acceleration sensitive mass having a center of gravity;
at least first and second flexible elements generally equally suspending said mass above an etched pit and generally co-planar with a surface of said mass;
first and second tension relief beams attached to said first and second flexible elements;
and
first and second mass support beams.

8 more elements

A method of fabricating a micromechanical vibrating string accelerometer with a trimmable resonant frequency, comprising the steps of:

providing a single crystal silicon substrate;
selectively masking and doping surface portions of said substrate in the shape of electrodes;
growing an epitaxial spacer layer over said surface portions of said substrate;
selectively masking and doping surface portions of said epitaxial layer to form structure selected from the group consisting of:
an acceleration sensitive mass;
resonant flexures;
mass support beams;
and
trimmable strain relief beams;
and
oxidizing said surface portions of said epitaxial layer to form an oxidized layer;
patterning an etch window in said oxidized layer by selectively etching portions of the oxide;
and
etching said silicon substrate inside the etch window with an anisotropic etchant to form said accelerometer suspended over a pit in said substrate and said electrodes.

11 more elements

Dependencies are inferred from the claim text.

Monolithic micromechanical vibrating string accelerometer with trimmable resonant frequency

Life of this patent

Monolithic micromechanical vibrating string accelerometer with trimmable resonant frequency

Life of this patent

Abstract

Claims12