Miniature silicon based thermal vacuum sensor and method of measuring vacuum pressures
First Claim
1. A gas pressure sensor for sensing gas pressures in the approximate range of 760 Torr to 1×
- 10 Torr, the pressure sensor comprising;
a single piece base having a thickness dimension of at least 100 microns and having a cavity which extends from a bottom surface of the base to a top surface of the base,an opening in a side wall of the base to the cavity,a membrane on the top surface of the base dimensioned to cover the cavity,a first resistive element on the membrane,a second resistive element on the base,a cover over the membrane, the cover having a top surface and a bottom surface, the bottom surface of the cap attached to the top surface of the base and spaced from the membrane a distance less than 10 microns,a controlled voltage source for applying voltages to the first and second resistive elements, anda measuring circuit for measuring voltage applied to the first and second resistive elements, the voltage measurements being indicative of pressure about the sensor.
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Accused Products
Abstract
A miniaturized silicon based thermally controlled vacuum sensor uses thin film resistors on a membrane in a minute measuring chamber to accurately detect vacuum pressures in the range of 760 Torr to 1×10-5 Torr. The configurations of the measuring chamber and gas diffusion port of the sensor structure insure that heat transfer from the membrane is predominately conductive over the pressure detection range to provide linear output up to 0.1 Torr. A microprocessor is used to control and measure power required to maintain a predetermined temperature differential between a sensing resistive element on the membrane and an ambient temperature sensing element of the sensor base from analog voltage and current values. Pressure detection errors introduced by ambient temperature variations are minimized by measuring power dissipated into the gas. Analog and digital converters for both current and voltage signals use a Σ-Δ conversion method to reject electrical noise by an averaging technique to produce stable signal detection of pressure down to 1×10-5 Torr. The sensor is thermally stable over an ambient temperature range of 0°-50° C. at pressures between 10-4 to 760 Torr.
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Citations
37 Claims
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1. A gas pressure sensor for sensing gas pressures in the approximate range of 760 Torr to 1×
- 10 Torr, the pressure sensor comprising;
a single piece base having a thickness dimension of at least 100 microns and having a cavity which extends from a bottom surface of the base to a top surface of the base, an opening in a side wall of the base to the cavity, a membrane on the top surface of the base dimensioned to cover the cavity, a first resistive element on the membrane, a second resistive element on the base, a cover over the membrane, the cover having a top surface and a bottom surface, the bottom surface of the cap attached to the top surface of the base and spaced from the membrane a distance less than 10 microns, a controlled voltage source for applying voltages to the first and second resistive elements, and a measuring circuit for measuring voltage applied to the first and second resistive elements, the voltage measurements being indicative of pressure about the sensor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
- 10 Torr, the pressure sensor comprising;
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20. A pressure sensing device for sensing atmospheric pressures, the pressure sensing device comprising,
a silicon chip substrate having a gas chamber formed therein, the gas chamber extending through a cross-section of the chip substrate from a bottom surface of the chip substrate to a top surface of the chip substrate, a top opening of the gas chamber covered by a membrane on a top surface of the chip, an opening in a side wall of the chip into the gas chamber, a first resistive element mounted on the membrane, a second resistive element mounted on the chip and not over the gas chamber, a cover attached to the chip and covering the membrane and first resistive element, an underside of the cover spaced from the membrane a distance not greater than 10 microns, electrical leads connected to the first and second resistive elements, a voltage source connected to a bridge containing the first and second resistive elements, and a microprocessor for receiving digitally converted analog values of voltages of the bridge applied to the first and second resistive element and for computing power values based upon voltage outputs of the bridge indicative of power required to maintain a predetermined temperature differential between the surface upon which the first resistive element is mounted and the surface upon which the second resistive element is mounted.
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33. A method of measuring vacuum pressures of a known gas in the approximate pressure range of 760 Torr to 1×
- 10-5 Tort, comprising the steps of;
providing a gas pressure sensor having a silicon chip substrate with a gas chamber which extends through a cross-section of the chip substrate from a top of the chip substrate to a bottom of the chip substrate, a top opening of the gas chamber covered by a membrane attached to a top surface of the chip substrate, a first resistive element mounted on the membrane, a second resistive element mounted on the chip substrate and not over the gas chamber, an opening through a side wall of the chip substrate to the gas chamber, and a cover attached to the chip substrate and covering the membrane and first resistive element, an underside of the cover spaced from the membrane a distance not greater than 10 microns, applying a voltage to the first resistive element, applying a voltage to the second resistive element, controlling the applied voltages to maintain a temperature differential between the membrane and the chip substrate, and measuring the voltages and currents applied to the first and second resistive elements required to maintain the temperature differential, the measurements being indicative of pressure about the membrane. - View Dependent Claims (34, 35, 36)
- 10-5 Tort, comprising the steps of;
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37. A gas pressure sensing structure for sensing vacuum pressures, the pressure sensing structure comprising:
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a base having a gas chamber cavity which extends from a top of the base to a bottom of the base, a membrane covering a top opening to the gas chamber cavity, a cover attached to the base and covering the membrane, a bottom surface of the cover spaced from a top surface of the membrane a distance not grater than 10 microns, and a first resistive element disposed at least partially on the membrane, a second resistive element disposed at least partially on the base, a voltage source connected to the first and second resistive elements, and a measuring circuit for measuring voltages and currents applied to the first and second resistive elements, the measuring circuit comprising a bridge circuit having four resistors, the bridge circuit connected to an amplifier, a capacitor and a transistor.
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Specification