| 摘要 |
PURPOSE:To improve surge withstanding voltage by mounting a protective transistor introducing charges generated by applying surge voltage to a grounding point between a power supply terminal for a circuit constituted by an MOS transistor having LDD structure and the grounding point. CONSTITUTION:When surge voltage is applied to a high-voltage power supply terminal 19, an avalanche breakdown is generated on the interface B between the surface of a semiconductor substrate 11 and an N<-> type impurity region 13, and electron-hole pairs are produced. Electrons are absorbed to the drain D side and holes flow in the direction of the substrate, substrate currents are generated, the P type semiconductor substrate 11 in the vicinity of a sources is biassed in the forward direction, and a parasitic bipolar transistor QB using an N<+> type impurity region 122 as a collector, an N<+> type impurity region 121 as an emitter and the P type semiconductor substrate 11 as a base is brought to an ON state. The source S is grounded, and surge voltage applied to the voltage supply terminal 19 is discharged rapidly. The surge voltage of an LDD type MOS transistor is improved.
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