Semiconductor device having transistor with high electro-static discharge capability and high noise capability

A semiconductor device, comprising:

• a semiconductor layer having a first conductivity type:
• a transistor formed in a transistor well in the semiconductor layer, the transistor having a second conductivity type;
• an input terminal;
• an output terminal;
• a voltage source terminal;
• and
• a surge absorption element that protects the transistor and that is formed in a surge absorption well in a semiconductor layer at a position spaced apart from the transistor well, the surge absorption well having the second conductivity type, the surge absorption element being provided in a circuit location between the input terminal and voltage source terminal, a circuit location between the output terminal and voltage source terminal, or a circuit location between the voltage source terminal and ground;
• wherein the surge absorption element and the transistor satisfy all of the following relationships:
• the surge absorption element has a resistance during breakdown operation of the surge absorption element that is smaller than a resistance of the transistor during breakdown operation of the transistor,
• a secondary breakdown current of the surge absorption element is larger than a secondary breakdown current of the transistor,
• the secondary breakdown voltage of the surge absorption element is smaller than the secondary breakdown voltage of the transistor,
• the breakdown voltage of the surge absorption element is smaller than the breakdown voltage of the transistor, and
• the secondary breakdown current of the surge absorption element is larger than a surge current flowing to the surge absorption element.