Semiconductor device having two-way conduction characteristics, and electrostatic discharge protection circuit incorporating the same

An electrostatic discharge protection circuit for a main circuit connected electrically to an input/output pad transmitting an electrical signal to/from the main circuit and to a power source providing a predetermined supply voltage, said electrostatic discharge protection circuit comprising:

• a semiconductor device including
• a substrate,
• a first doped region formed in said substrate and adapted to be connected electrically to the input/output pad to receive an electrostatic accumulated voltage from the input/output pad,
• a second doped region formed in said substrate and connected to ground, and
• a third doped region formed in said substrate and connected to ground,
• each of said substrate and said third doped region being doped with a first type dopant, and each of said first and second doped regions being doped with a second type dopant such that said semiconductor device is configured to have a first threshold voltage for forward conduction between said first and second doped regions, and a second threshold voltage for forward conduction between said first and third doped regions;
• and
• a clamp unit adapted to be coupled between the power source and ground for prohibiting conduction between the power source and ground;
• wherein, when said first type dopant and said second type dopant are respectively a p-type dopant and an n-type dopant,
• if the electrostatic accumulated voltage is greater than the first threshold voltage, an electrostatic discharge current is drained by flowing through said first doped region, said substrate and said second doped region of said semiconductor device, and
• if the electrostatic accumulated voltage is less than the second threshold voltage, an electrostatic discharge current is drained by flowing through said third doped region, said substrate and said first doped region of said semiconductor device;
• and
• wherein, when said first type dopant and said second type dopant are respectively an n-type dopant and a p-type dopant,
• if the electrostatic accumulated voltage is less than the first threshold voltage, an electrostatic discharge current is drained by flowing through said second doped region, said substrate and said first doped region of said semiconductor device, and
• if the electrostatic accumulated voltage is greater than the second threshold voltage, an electrostatic discharge current is drained by flowing through said first doped region, said substrate and said third doped region of said semiconductor device.