| 摘要 |
PROBLEM TO BE SOLVED: To obtain a variable capacitance circuit by which capacity change rate is reduced even when it is loaded on a semiconductor integrated circuit by constituting the variable capacitance circuit so that the entire or the most part of a projection surface of a third electrode exists inside a projection surface of a second electrode and the entire or the most part of the projection surface of the second electrode exists inside a projection surface of a first electrode. SOLUTION: The variable capacitance circuit 5 under control of a temperature compensated signal generating circuit 3 is connected with a crystal oscillation circuit 1. The variable capacitance circuit 5 is constituted of three elements. A MOS type capacitor with variable capacitance consisting of a low density diffusion area 15 of the first electrode, a high density diffusion area 17 of the first electrode, a gate insulation film 19 and the second electrode 21 is first formed on the surface of a semiconductor substrate 13. In addition, a capacitor with fixed capacitance consisting of an interlayer insulation film 27 and the third electrode 29 is constituted on the second electrode 21. Furthermore, an input resistor 11 consisting of a polycrystal silicon film containing moderate impurities is constituted on a field oxidized film 23.
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