| 摘要 |
PROBLEM TO BE SOLVED: To prevent reduction in detection sensitivity due to parasitic capacitance and to prevent the mixing-in of external noise due to electrostatic coupling in the case of a pressure sensor, etc. SOLUTION: A guard electrode 116 is provided in the main surface of a semiconductor substrate 100, and a fixed electrode 111 is formed on it via an insulating layer. A cavity is further formed on it by a diaphragm, and a movable electrode 161 is formed between the layers of the diaphragm. A substrate through hole 190 is provided from the subordinate surface of the substrate 100 to the cavity. An operational amplifier to drive so as to make the potential of the guard electrode 116 equal to the potential of the fixed electrode 111 is provided to convert changes in the capacities of the fixed electrode 111 and the movable electrode 161 into a voltage directly related to the displacement of the diaphragm. As it is possible to make the effective capacitance between the fixed elected 111 and the guard electrode 116 be of an extremely small value, it is possible to detect minute changes in capacity and to prevent reduction in sensitivity. In addition, it is possible to shield the fixed electrode 111 from electric lines of force arriving from the direction of the subordinate surface of the substrate 100. Furthermore, it is possible to arrange the circuit at the lower layer of the fixed electrode 111 and to miniaturize the device.
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