| 摘要 |
PURPOSE:To obtain an input protecting device strong against a large current by using an insulated gate type FET in which the second gate electrode is disposed via an insulating film on the first gate electrode as a gate protection. CONSTITUTION:A polycrystalline silicon resistor 2 is formed between an input terminal 3 and a terminal 4 consecutive to an input terminal 3, and a floating electrode 9 of a protecting transistor TR is simultaneously formed. The second gate electrode 12 is disposed through the second gate oxidized film 5' for insulation on the electrode 9, and is connected to a reference potential together with a source 14. On the other hand, a drain 14' is connected via a resistor 2 to terminals 3 and 4. In this manner the withstand voltage of the drain 14' becomes considerable low value. Since the potential of the gate 9 is floated due to the capacitive coupling between the electrode 12 and the drain 14', the electrolysis in the gate oxidized film is weakened, and a breakdown in the insulation can hardly be taken plate even in large current. |
