Trench-gate semiconductor devices
View Patent ↗A trench-gate semiconductor device, for example a MOSFET or IGBT, includes a semiconductor body ( 20 ) having a drain region ( 4 ) comprising a drain drift region ( 4 a ) and a drain contact region ( 4 b ). An insulated field plate ( 24 ) is included in the trench ( 10 ) between the gate ( 8 ) and the drain contact region ( 4 b ), wherein the field plate ( 24 ) is for connection to a bias potential greater than the gate potential and near to the bulk breakdown voltage of the drain drift region ( 4 a ). The field plate ( 24 ) causes the potential drop across the drain drift region ( 4 a ) to be spread considerably more evenly, particularly at applied voltages greater than the bulk breakdown voltage, thereby substantially increasing the breakdown voltage of the device.
1. A trench-gate semiconductor device including:
a semiconductor body ( 20 ) defining a trench ( 10 ) having an insulated gate ( 8 ) therein, the semiconductor body comprising a source region ( 2 ) and a drain region ( 4 ) of a first conductivity type which are separated by a channel-accommodating region ( 6 ) adjacent to the gate, the drain region comprising a drain drift region ( 4 a ) and a drain contact region ( 4 b ), with the drain drift region between the channel-accommodating region ( 6 ) and the drain contact region ( 4 b ), and the drain drift region ( 4 a ) doped to a lesser extent than the drain contact region ( 4 b ); and
an insulated field plate ( 24 ) in the trench ( 10 ) between the gate ( 8 ) and the drain contact region ( 4 b ), wherein the field plate ( 24 ) is connected in operation to a bias source at a bias potential greater than the gate potential and near to the bulk breakdown voltage of the drain drift region ( 4 a ).
2. A device of claim 1 wherein the trench ( 10 ) extends substantially to the junction ( 4 c ) between the drain drift region ( 4 a ) and the drain contact region ( 4 b ).
3. A device of claim 1 or 2 wherein the gate ( 8 ) is shallower than the upper boundary of the drain drift region ( 4 a ) and the drain contact region ( 4 b ).
4. A device of claim 1 or claim 2 wherein the doping level of the drain drift region ( 4 a ) increases towards the drain contact region ( 4 b ).
5. A module ( 60 ) comprising a device of claim 1 or claim 2 wherein the field plate ( 24 ) is connected to an internal voltage line of the module ( 60 ).
6. A device of claim 1 or claim 2 wherein an additional external terminal ( 54 ) is provided which is electrically connected to the field plate ( 24 ).
7. A module ( 60 ) of claim 5 wherein the bias potential is around 60 or 100% of the bulk breakdown voltage of the drain drift region ( 4 a ).
8. A module 60 of claim 7 wherein the bias potential is around 80% of the bulk breakdown voltage of the drain drift region ( 4 a ).
9. A method of operating a trench-gate semiconductor device of claim 1 or claim 2 , comprising applying to the field plate ( 24 ) of the device said bias potential greater than the gate potential and near to the bulk breakdown voltage of the drain drift region ( 4 a ).
10. A method of claim 9 wherein the bias potential is around 60 to 100% of the bulk breakdown voltage of the drain drift region ( 4 a ).
11. A method of claim 10 wherein the bias potential is around 80% of the bulk breakdown voltage of the drain drift region ( 4 a ).