Bipolar high voltage/power semiconductor device having first and second insulated gated and method of operation

A method of operating a bipolar high voltage/power semiconductor device, the device comprising:

• a drift region of a first conductivity type and having first and second ends;
• the first end of the drift region having adjacent thereto a region of a second conductivity type which is adjacent a region of the first conductivity type, at least said region of the first conductivity type being in electrical contact with a low voltage terminal such that charge carriers of the first conductivity type are injected into the drift region from said region of the first conductivity type when the device is in the on-state and providing current conduction in a first direction;
• the second end of the drift region having adjacent thereto a region of the first conductivity type which is adjacent a region of the second conductivity type, at least said region of the second conductivity type being in electrical contact with a high voltage terminal such that charge carriers of the second conductivity type are injected into the drift region from said region of the second conductivity type when the device is in the on-state and providing current conduction in said first direction;
• a first insulated gate terminal at or towards the first end of the drift region and positioned at least partly over the region of the second conductivity type at the first end of the drift region;
• and, a second insulated gate terminal at or towards the second end of the drift region and positioned at least partly over the region of the first conductivity type at the second end of the drift region, the method comprising:
• selectively applying:
• (i) a voltage of a first polarity to the second insulated gate with respect to the voltage applied to the high voltage terminal to form an inversion layer in at least said part of the region of the first conductivity type and the drift region that are under the second insulated gate and to allow current conduction in said first direction, and
• (ii) a voltage of a second, opposite polarity to the second insulated gate with respect to the voltage applied to the high voltage terminal to form an accumulation layer in at least said part of the region of the first conductivity type and the drift region that are under the second insulated gate and to allow current conduction in a second direction.

A method of operating a semiconductor device, the device having a drift region of a first conductivity type, a first buffer/well region of a second conductivity type at one end of the drift region, a first relatively highly doped region of the first conductivity type adjacent the first buffer/well region, a first terminal in electrical contact with the first buffer/well region and the first relatively highly doped region of the first conductivity type adjacent the first buffer/well region, a first insulated gate over at least the first buffer/well region and the adjacent end of the drift region, such that charge carriers of the first conductivity type are injected into the drift region from said relatively highly doped region of the first conductivity type when the device is in the on-state and providing current conduction in a first direction, and a second buffer/well region of the first conductivity type at the other end of the drift region, a second relatively highly doped region of the second conductivity type adjacent the second buffer/well region, a second terminal in electrical contact with the second buffer/well region and the second relatively highly doped region of the second conductivity type adjacent the second buffer/well region, and a second insulated gate over at least the second buffer/well region and the adjacent end of the drift region, such that charge carriers of the second conductivity type are injected into the drift region from said relatively highly doped region of the second conductivity type when the device is in the on-state and providing current conduction in said first direction, the method comprising:

• varying relative voltages applied to the first terminal, the second terminal, the first insulated gate and the second insulated gate so as to switch the device between
• (i) blocking current conduction in both of said directions,
• (ii) providing an insulated-gate bipolar transistor (IGBT) mode of conduction in said first direction and
• (iii) providing an anti-parallel diode mode of conduction in a second direction.