Piezoresistive transducer with low drift output voltage
First Claim
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1. A piezoresistive transducer having an output voltage that has low drift comprises:
- a lightly doped silicon substrate of a first conductivity type having a flexible silicon diaphragm on a first surface of the substrate;
a four terminal piezoresistive element of a second conductivity type, the element having two sections which are formed on a second surface of the substrate;
a first straight section of the piezoresistive element having a contact at each distal end;
a second straight section of the piezoresistive element having a contact at each distal end wherein the second section is shorter than the first section and has a midpoint that crosses perpendicularly to a midpoint of the first section;
contact material of the second conductivity type that couples the contacts to metal conductors;
an irregular periphery formed by the piezoresistive element, the contact material, and the contacts;
a leakage buffer formed from a continuous strip of highly doped material of the first conductivity type that surrounds the irregular periphery and has material of the first conductivity type projecting from the continuous strip toward the perpendicular crossing;
a dielectric that covers the second surface of the substrate; and
a fluorosilicone material that covers the dielectric.
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Abstract
Leakage current is reduced in a piezoresistive transducer by forming a leakage barrier around a piezoresistive element of a piezoresistive transducer. The leakage barrier prevents the formation of a parasitic leakage path in the substrate thereby reducing the leakage current flowing through sections of the piezoresistive element, and stabilizing the resistance value and the output voltage of the piezoresistive transducer.
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Citations
18 Claims
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1. A piezoresistive transducer having an output voltage that has low drift comprises:
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a lightly doped silicon substrate of a first conductivity type having a flexible silicon diaphragm on a first surface of the substrate; a four terminal piezoresistive element of a second conductivity type, the element having two sections which are formed on a second surface of the substrate; a first straight section of the piezoresistive element having a contact at each distal end; a second straight section of the piezoresistive element having a contact at each distal end wherein the second section is shorter than the first section and has a midpoint that crosses perpendicularly to a midpoint of the first section; contact material of the second conductivity type that couples the contacts to metal conductors; an irregular periphery formed by the piezoresistive element, the contact material, and the contacts; a leakage buffer formed from a continuous strip of highly doped material of the first conductivity type that surrounds the irregular periphery and has material of the first conductivity type projecting from the continuous strip toward the perpendicular crossing; a dielectric that covers the second surface of the substrate; and a fluorosilicone material that covers the dielectric. - View Dependent Claims (2, 3, 4, 5)
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6. A method of reducing drift in piezoresistive transducers which comprises:
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providing a silicon substrate of a first conductivity type having a thin silicon diaphragm on a first surface of the substrate; providing a four terminal piezoresistive element of a second conductivity type on a second surface of the substrate wherein the piezoresistive element has two straight sections intersecting at right angles; reducing leakage current that flows in a parasitic conduction channel in the substrate by using a leakage buffer that is formed by positioning areas of highly doped material of the first conductivity type at least adjacent to each right angle of the intersection; covering the second surface of the substrate with a dielectric; and covering the dielectric with a protective coating. - View Dependent Claims (7, 8, 9)
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10. A low drift piezoresistive transducer which comprises:
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a semiconductor substrate of a first conductivity type having a thin silicon diaphragm on a first surface of the substrate; a piezoresistive element of a second conductivity type formed on a second surface of the substrate; means for connecting the piezoresistive element to bonding pads; a leakage buffer formed of highly doped material of the first conductivity type that surrounds a peripheral boundary formed by the piezoresistive element and the means for connecting; a dielectric that covers at least the piezoresistive element; and a silicone gel that covers the dielectric. - View Dependent Claims (11, 12, 13, 14)
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15. A piezoresistive transducer having an output voltage with low drift which comprises:
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a piezoresistive element having a first straight section and a second straight section intersecting at right angles; and leakage barriers that are highly doped regions of a material that is of opposite conductivity to the piezoresistive element wherein the leakage barriers are positioned inside each right angle formed by the intersection and in a proximity of each right angle. - View Dependent Claims (16, 17)
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18. A piezoresistive transducer having an output voltage with low drift which comprises:
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at least first and second resistive areas wherein the areas are interconnected to form a piezoresistive element; and a leakage barrier that is a semiconductor material which is positioned between the at least first resistive area and the at least second resistive area to prevent leakage current from flowing between the resistive areas.
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Specification