Capacitive microaccelerometers and fabrication methods
First Claim
1. A method of fabricating a moveable microstructure, comprising:
- providing a substrate having upper and lower layers;
etching trenches in the upper layer to define bonding pads, sense electrodes and a proof mass having capacitive gaps formed therebetween, and a plurality of tethers that allow the proof mass to move;
depositing a conformal conductive layer on the substrate to reduce sizes of the capacitive gaps;
etching the conformal conductive layer to remove conformal conductive material at the bottom of the trenches and provide isolation between the bonding pads and the sense electrodes; and
etching the lower layer of the substrate to form a region of extra proof mass that is coupled to the proof mass formed in the upper layer.
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Abstract
Disclosed are moveable microstructures comprising in-plane capacitive microaccelerometers, with submicro-gravity resolution (<200 ng/√Hz) and very high sensitivity (>17 pF/g). The microstructures are fabricated in thick (>100 μm) silicon-on-insulator (SOI) substrates or silicon substrates using a two-mask fully-dry release process that provides large seismic mass (>10 milli-g), reduced capacitive gaps, and reduced in-plane stiffness. Fabricated devices may be interfaced to a high resolution switched-capacitor CMOS IC that eliminates the need for area-consuming reference capacitors. The measured sensitivity is 83 mV/mg (17 pF/g) and the output noise floor is −91 dBm/Hz at 10 Hz (corresponding to an acceleration resolution of 170 ng/√Hz). The IC consumes 6 mW power and measures 0.65 mm2 core area.
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Citations
9 Claims
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1. A method of fabricating a moveable microstructure, comprising:
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providing a substrate having upper and lower layers; etching trenches in the upper layer to define bonding pads, sense electrodes and a proof mass having capacitive gaps formed therebetween, and a plurality of tethers that allow the proof mass to move; depositing a conformal conductive layer on the substrate to reduce sizes of the capacitive gaps; etching the conformal conductive layer to remove conformal conductive material at the bottom of the trenches and provide isolation between the bonding pads and the sense electrodes; and etching the lower layer of the substrate to form a region of extra proof mass that is coupled to the proof mass formed in the upper layer. - View Dependent Claims (2, 3, 4, 5)
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6. A method of fabricating a moveable microstructure, comprising:
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providing a low resistivity silicon-on-insulator substrate; etching wenches on the front side of the substrate to define bonding pads, sense electrodes and a proof mass having capacitive gaps formed therebetween; depositing a conformal conductive layer on the substrate to reduce capacitive gap sizes; doping the conformal conductive layer; etching the conformal conductive layer to remove material at the bottom of the trenches; and etching the back side of the substrate to form a region of additional proof mass and to release the microstructure. - View Dependent Claims (7)
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8. A method of fabricating a moveable microstructure, comprising:
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providing a silicon substrate; etching trenches on the front side of the substrate to define pads, sense electrodes and a proof mass having capacitive gaps formed therebetween; depositing a conformal conductive layer on the substrate to reduce capacitive gap sizes; bonding a handle substrate to the top side of the silicon substrate; etching the back side of the substrate to form a region of additional proof mass and to release the microstructure by etching the conformal conductive layer to remove material at the bottom of the trenches; and forming electrical connections through via holes in the handle substrate to the conformal conductive layer adjacent to pads defined in the silicon substrate. - View Dependent Claims (9)
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Specification