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.

Abstract: Relative speeds of wheels are measured in different speed ranges when tires are properly inflated to learn offsets due to parameters not related to pressure. The offsets are used during leak monitoring to detect a wheel speed pattern which is abnormal due to pressure drops. During learning periods, monitoring for large pressure drops only is permitted using preliminary offset values. When learning is complete in a given speed range high sensitivity monitoring is invoked. Special sensitivity of large pressure drops shortly after vehicle start up allows a brief period of flat detection. A plurality of leak events for a given wheel are accumulated to signal a warning, with large pressure drops accumulating faster than small drops for progressive sensitivity and greater robustness.

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.