Micro-machined accelerometer with composite material springs
First Claim
1. An improved spring structure in a micro-machined transducer having a support frame and a sensing mass, where said sensing mass is at least partially supported from said support frame via at least one E-shaped leaf spring structure, said spring structure defined by a base and three legs including two outer legs and an inner leg, each of said three legs being connected to said base at one end, said two legs connected to said frame at their other ends, said inner leg connected to said mass at its other end, and wherein said transducer is fabricated by etching of a semi-conductor wafer which has been doped with a dopant of one type, the improvement comprising,said base characterized by a coefficient of stiffnes substantially greater than that of said legs, andsaid base of said spring structure being fabricated of semi-conductor material and having an impurity diffused therein of an opposite type from that of which said semi-conductor wafer was doped and wherein said legs of said spring structure are each a composite structure of a base layer of semi-conducting material, a conducting layer and an insulating layer placed between said conducting layer and said semi-conducting material, said legs each characterized by a thickness which is small compared to the thickness of said base.
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Accused Products
Abstract
A transducer fabricated by micro-machining includes E-shaped leaf springs suspending a mass from a support. The transducer is formed by chemical etching through openings of opposite faces of a silicon wafer on which etch stop layer patterns are diffused. Sense and force conductive patterns are diffused onto opposite faces of the suspended mass. The legs of the E-shaped leaf springs are formed of a composite of a polysilicon base layer, a silicon dioxide insulating layer and a gold conducting layer. The thickness of such layers are selected to minimize bowing effects of the spring legs due to materials of different coefficients of thermal expansion. The spring-mass-support structure is sandwiched between opposite plates having corresponding force and conductive patterns which face such patterns on the suspended mass.
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Citations
25 Claims
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1. An improved spring structure in a micro-machined transducer having a support frame and a sensing mass, where said sensing mass is at least partially supported from said support frame via at least one E-shaped leaf spring structure, said spring structure defined by a base and three legs including two outer legs and an inner leg, each of said three legs being connected to said base at one end, said two legs connected to said frame at their other ends, said inner leg connected to said mass at its other end, and wherein said transducer is fabricated by etching of a semi-conductor wafer which has been doped with a dopant of one type, the improvement comprising,
said base characterized by a coefficient of stiffnes substantially greater than that of said legs, and said base of said spring structure being fabricated of semi-conductor material and having an impurity diffused therein of an opposite type from that of which said semi-conductor wafer was doped and wherein said legs of said spring structure are each a composite structure of a base layer of semi-conducting material, a conducting layer and an insulating layer placed between said conducting layer and said semi-conducting material, said legs each characterized by a thickness which is small compared to the thickness of said base.
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6. An improved spring structure in a micro-machined transducer having a support frame and a sensing mass, where said sensing mass is at least partially supported from said support frame via at least one E-shaped leaf spring structure, said spring structure defined by a base and three legs including two outer legs and an inner leg, each of said three legs being connected to said base at one end, said two outer legs connected to said frame at their other ends, said inner leg connected to said mass at its other end, the improvement comprising,
said legs including a base layer of semi-conductor material, a conducting layer and an insulating layer placed between said conducting layer and said semi-conductor material, and wherein said semi-conductor material is polysilicon, said conducting layer is gold, and said insulating material is silicon dioxide.
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11. A spring-mass transducer comprising
a support frame structure, a sensing mass structure, and an E-shaped leaf spring structure, said spring structure defined by a base and three legs including two outer legs and an inner leg, each of said three legs being connected to said frame structure at their other ends, said inner leg connected to said mass structure at its other end, said support frame structure and said sensing mass structure including top and bottom layers of etch stop material which sandwich single semi-conductor crystal wafer which has been undercut from said top and bottom layers and severed by semi-conductor etchant, said base of each said E-shaped spring structures having a coefficient of stiffness, substantially greater than that of said legs, and said legs of each of said E-shaped spring structure including a composite of a base layer of polysilicon, a layer of conducting material and a layer of insulating material between said base layer and said conducting material.
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16. The transducer of calim 15 wherein said etch stop layer pattern defining said support frame structure includes a hockey stick shaped area between one of said outer legs of said E-shaped spring structure and an adjacent etch time and undercut control area,
said hockey stick shaped area defines a foot and a leg, where said outer leg of said E-shaped spring structure is connected to the top of the foot of said hockey stick shaped area, and said foot of said hockey stick shaped area provides a strength region for connecting said outer leg to said support frame structure.
Specification