US 2014/0338452 A1Published application

Tri-axial mems accelerometer

AssigneeChinese Academy of Sciences Institute of Geology and Geophysics

InventorsChen Sun, Lian Zhong Yu

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Abstract

A tri-axial MEMS accelerometer includes a top cap silicon wafer and a bottom cap silicon wafer coupled with a measurement mass. The measurement mass has a two level structure, each level having an inner frame coupled to an outer frame by a plurality of first elastic beams, a mass coupled to the inner frame by a plurality of second elastic beams, and a comb coupling structure between the mass and the inner frame. The comb coupling structures are arranged in an orthogonal orientation. The top level and bottom level measurement masses measure acceleration in perpendicular directions. The top level and bottom level measurement masses and the inner frame form an integral unit which moves along a third direction. Acceleration in the third direction is measured from the change in capacitance between the integral unit and the top cap silicon wafer and bottom cap silicon wafer.

Claims22

Dependent claims

A tri-axial MEMS accelerometer, comprising:

a top level measurement structure and a bottom level measurement structure, each measurement structure including:
an outer frame;
an inner frame located within the outer frame;
a mass coupled with the inner frame;
and
a comb coupling the mass and the inner frame,
wherein, on a projection plane, the orientation of the comb on the top level measurement structure is orthogonal to the orientation of the corresponding comb on the bottom level measurement structure;
wherein the inner frame is coupled with the outer frame by a plurality of first elastic beams, and the inner frame is coupled to the mass by a plurality of second elastic beams;
a top cap silicon wafer coupled with the top level measurement structure;
and
a bottom cap silicon wafer coupled with the bottom level measurement structure;
wherein, the top level measurement structure and the bottom level measurement structure allow measurement of acceleration in respective perpendicular directions as a change in capacitance between the mass and the inner frame for each level;
and
wherein the top level measurement mass, the bottom level measurement mass, and the respective inner frames move together along a third direction, wherein the acceleration in the third direction can be determined by measuring the change in capacitance between the top and bottom level measurement masses and respective inner frames as a unit, and the top and bottom cap silicon wafers.

11 more elements

A fabrication technique for a tri-axial MEMS accelerometer, the accelerometer including a top level measurement structure having a top cap silicon wafer and a bottom level measurement structure having a bottom cap silicon wafer, each measurement structure including an outer frame, an inner frame located within the outer frame, a mass coupled with the inner frame;

and a comb coupling the mass and the inner frame, wherein the comb on the top level measurement structure is oriented orthogonally to the corresponding comb on the bottom level measurement structure, and wherein the inner frame is coupled with the outer frame by a plurality of first elastic beams, and the inner frame is coupled to the mass by a plurality of second elastic beams, comprising the following steps:
(i) growing an epilayer on a top silicon layer of a silicon on insulator (SOI) silicon wafer;
(ii) growing, by use of thermal oxidation or chemical deposition, a silicon dioxide layer on the surfaces of the top silicon layer and a bottom silicon layer;
(iii) removing, by use of photolithography and etching, a portion of the silicon dioxide layer, which is on the surface of the bottom silicon layer, and exposing a portion of the bottom silicon layer;
(iv) forming, by depositing silicon nitride on the surface of the silicon dioxide layer, a silicon nitride layer;
(v) removing, by use of photolithography and etching, an outer portion of the silicon nitride layer and the silicon dioxide layer, which are on the surface of the bottom silicon layer, and exposing a portion of the bottom silicon layer;
(vi) removing, by use of photolithography and etching, an inner portion of the silicon nitride layer, which is on the surface of the bottom silicon layer, and exposing the silicon dioxide layer;
(vii) etching the exposed outer portion of the bottom silicon layer to a certain depth to form a portion of an outer frame;
(viii) removing, by use of etching, the exposed inner portion of the silicon dioxide layer, and exposing the bottom silicon layer;
(ix) further etching the exposed portion of the bottom silicon layer until exposing the buried oxide layer at the outer portion of the bottom silicon layer, thus forming the outer frame and the inner frame;
(x) removing, by use of etching, the buried oxide layer at the outer portion of the bottom silicon layer;
and further etching the exposed portion of the bottom silicon layer, until exposing the buried oxide layer at the inner portion of the bottom silicon layer, thus forming a plurality of second elastic beams;
(xi) removing the silicon nitride layer on the surface of the bottom silicon layer, and etching the outer portion of the bottom silicon layer to the epilayer, thus forming a plurality of first elastic beams, while at the same time etching a center portion of the bottom silicon layer, where the mass of the bottom level measurement structure is located, to a certain thickness, thus forming a gap space between the mass of the top level measurement structure and the mass of the bottom level measurement structure;
(xii) removing the silicon dioxide layer on the surface of the bottom silicon layer, and bonding together, by a back-to-back silicon bonding, two etched silicon on insulator silicon wafers;
(xiii) forming, by use of photolithography and deep etching, a plurality of holes, with depth from silicon nitride layer to the epilayer, on the surface of top silicon layer;
(xiv) forming, by performing deep etching to the holes, a plurality of through holes, thus forming the freely moveable first and second elastic beams;
(xv) removing the silicon nitride layer and the silicon dioxide layer on the surfaces of the bonded wafer structure thereby forming a top level measurement structure and a bottom level measurement structure;
and
(xvi) bonding the top cap silicon wafer to the top level measurement structure and bonding the bottom cap silicon wafer to the bottom level measurement structure.

16 more elements

A method for fabricating a tri-axial MEMS accelerometer, the accelerometer including a top level measurement structure having a top cap silicon wafer and a bottom level measurement structure having a bottom cap silicon wafer, each measurement structure including an outer frame, an inner frame located within the outer frame, a mass coupled with the inner frame;

and a comb coupling the mass and the inner frame, wherein the comb on the top level measurement structure is oriented orthogonally to the corresponding comb on the bottom level measurement structure, and wherein the inner frame is coupled with the outer frame by a plurality of first elastic beams, and the inner frame is coupled to the mass by a plurality of second elastic beams, comprising:
(i) growing an epilayer on the top silicon layer of a silicon on insulator (SOI) silicon wafer;
(ii) growing a silicon dioxide layer on the surfaces of the top silicon layer and a bottom silicon layer;
(iii) removing a portion of the silicon dioxide layer, which is on the surface of the bottom silicon layer, and exposing a portion of the bottom silicon layer;
(iv) forming a silicon nitride layer on the surface of the silicon dioxide layer;
(v) removing an outer portion of the silicon nitride layer and the silicon dioxide layer, which are on the surface of the bottom silicon layer, and exposing a portion of the bottom silicon layer;
(vi) removing an inner portion of the silicon nitride layer, which is on the surface of the bottom silicon layer, and exposing the silicon dioxide layer;
(vii) etching the exposed outer portion of the bottom silicon layer to a certain depth to form an outer frame;
(viii) removing the exposed inner portion of the silicon dioxide layer, and exposing the bottom silicon layer;
(ix) further etching the exposed portion of the bottom silicon layer until exposing the buried oxide layer at the outer portion of the bottom silicon layer, thus forming the outer frame and the inner frame;
(x) removing the buried oxide layer at the outer portion of the bottom silicon layer;
and
further etching the exposed portion of the bottom silicon layer, until exposing the buried oxide layer at the inner portion of the bottom silicon layer, thus forming the second elastic beams, while at the same time, etching a center portion of the bottom silicon layer, where the mass is located, to a certain thickness, thus forming the gap space between the mass of the top level measurement structure and the mass of the bottom level measurement structure;
(xi) removing the silicon dioxide layer on the surface of the bottom silicon layer, and bonding two etched silicon on insulator silicon wafers;
(xii) forming a plurality of holes, with depth from silicon nitride layer to the epilayer, on the surface of top silicon layer;
(xiii) forming a plurality of through holes in the holes, thus forming the freely moveable first and second elastic beams;
(xiv) removing the silicon nitride layer and the silicon dioxide layer on the surfaces of the bonded wafer structure, and thereby forming a top level measurement structure and a bottom level measurement structure;
and
(xv) bonding the top cap silicon wafer to the top level measurement structure and bonding the bottom cap silicon wafer to the bottom level measurement structure.

16 more elements

Dependencies are inferred from the claim text.