| 摘要 |
PURPOSE:To apply an input surge voltage to a ground by uniformly distributing it by stepwisely varying a threshold voltage by stepwisely altering a polysilicon resistor and a channel length in combination with a protecting MIS transistor for varying the threshold voltage. CONSTITUTION:An input protecting circuit has an input pad 1 formed of aluminum, a polysilicon resistor 2 made of an N<+> type polysilicon layer formed on the field insulating film of a semiconductor substrate 3, and a protecting MIS transistor 4. The transistor 4 is formed by separating source and drain regions 5, 6 made of N<+> type diffused layers, a step 8 is formed on the portion of the region 5 opposed to a channel region 7, and channel length L is stepwisely varied. The channel length L of the transistor is stepwisely reduced to stepwisely decrease a threshold voltage VT. Accordingly, an input surge voltage can be dispersed by sharing in the channel length of the transistor. |
