Method for making an all-silicon capacitive pressure sensor
First Claim
1. A method for forming a capacitive pressure sensor, the method comprising the steps of:
- providing a first semiconductor wafer having at least a portion thereof characterized by a first electrical conductivity;
forming a cavity in the first semiconductor wafer so as to expose a region of the semiconductor wafer that yields a fixed capacitor plate of the capacitive pressure sensor;
bonding a semiconductor diaphragm of the first electrical conductivity type to the semiconductor wafer such that the diaphragm overlies the fixed capacitor plate, is electrically insulated from the fixed capacitor plates, and forms a hermetic seal around the fixed capacitor plate, the diaphragm being a flexible capacitor plate of the capacitive pressure sensor;
wherein the flexible capacitor plate forms a gap with the fixed capacitor plate of up to about ten micrometers, such that a capacitive output signal of the capacitive pressure sensor is produced by changes in contact area between the diaphragm and the semiconductor wafer in response to pressure applied to the diaphragm.
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Accused Products
Abstract
An all-silicon monolithic capacitive absolute pressure-sensing device and method for making the same. The device employs a single-crystal silicon diaphragm that serves at a flexible capacitor plate of a variable capacitor. The diaphragm is bonded to a single-crystal silicon wafer to overlie a cavity etched into the wafer. A fixed capacitor plate of the variable capacitor is formed by a heavily-doped region at the bottom of the cavity. A thin dielectric layer is grown on the fixed capacitor plate to complete the capacitor. The cavity has a minimal depth such that the fixed capacitor plate provides overpressure protection for the diaphragm. At least a portion of the operating range of the pressure sensor occurs while the diaphragm is contacting the doped region. As a result, the capacitive output signal of the pressure sensor is produced by changes in contact area between the diaphragm and a thin dielectric situated on the doped region in response to pressure applied to the diaphragm.
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Citations
12 Claims
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1. A method for forming a capacitive pressure sensor, the method comprising the steps of:
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providing a first semiconductor wafer having at least a portion thereof characterized by a first electrical conductivity; forming a cavity in the first semiconductor wafer so as to expose a region of the semiconductor wafer that yields a fixed capacitor plate of the capacitive pressure sensor; bonding a semiconductor diaphragm of the first electrical conductivity type to the semiconductor wafer such that the diaphragm overlies the fixed capacitor plate, is electrically insulated from the fixed capacitor plates, and forms a hermetic seal around the fixed capacitor plate, the diaphragm being a flexible capacitor plate of the capacitive pressure sensor; wherein the flexible capacitor plate forms a gap with the fixed capacitor plate of up to about ten micrometers, such that a capacitive output signal of the capacitive pressure sensor is produced by changes in contact area between the diaphragm and the semiconductor wafer in response to pressure applied to the diaphragm. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method for forming a capacitive pressure sensor, the method comprising the steps of:
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providing a first semiconductor wafer characterized by a first electrical conductivity type; forming a cavity in a surface of the first semiconductor wafer; forming a doped region of the first electrical conductivity type in the cavity to yield a fixed capacitor plate of the capacitive pressure sensor; forming a dielectric layer over the doped region; forming a second semiconductor wafer comprising a substrate and an epitaxial layer doped to be of the first electrical conductivity type; bonding the second semiconductor wafer to the first semiconductor wafer such that the epitaxial layer contacts the first semiconductor wafer and overlies the doped region; etching the second semiconductor wafer to remove the substrate; removing a portion of the epitaxial layer to expose a surface portion of the first semiconductor wafer so as to form a diaphragm that is electrically insulated from the fixed capacitor plates and forms a hermetic seal around the fixed capacitor plate, the diaphragm being a flexible capacitor plate of the capacitive pressure sensor; wherein the flexible capacitor plate forms a gap with the fixed capacitor plate of about two to about seven micrometers, such that a capacitive output signal of the capacitive pressure sensor is produced by changes in contact area between the diaphragm and the semiconductor wafer in response to pressure applied to the diaphragm.
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Specification