Semiconductor device and method of forming a semiconductor device
A power semiconductor device has an active region that includes a drift region. At least a portion of the drift region is provided in a membrane which has opposed top and bottom surfaces. In one embodiment, the top surface of the membrane has electrical terminals connected directly or indirectly thereto to allow a voltage to be applied laterally across the drift region. In another embodiment, at least one electrical terminal is connected directly or indirectly to the top surface and at least one electrical terminal is connected directly or indirectly to the bottom surface to allow a voltage to be applied vertically across the drift region. In each of these embodiments, the bottom surface of the membrane does not have a semiconductor substrate positioned adjacent thereto.
1. A lateral power semiconductor device having an active region that includes a drift region, at least a portion of the drift region being provided in a membrane having opposed top and bottom surfaces, the top surface of the membrane having electrical terminals connected directly or indirectly thereto to allow a voltage to be applied laterally across the drift region, the lateral power semiconductor device being constructed and arranged such that, when the lateral power semiconductor device is an off-state and operating in a voltage-blocking mode, the equi-potential lines within said at least a portion of the drift region are all substantially perpendicular to the top and bottom surfaces of the membrane and are substantially uniformly distributed across said at least a portion of the drift region so that the electric field across said at least a portion of the drift region is substantially uniform.
2. A lateral power semiconductor device according to claim 1 , wherein only part of the drift region is provided in the membrane.
3. A lateral power semiconductor device according to claim 1 , wherein the whole of the drift region is provided in the membrane.
4. A lateral power semiconductor device according to claim 1 , comprising at least one isolation layer surrounding the drift region.
5. A lateral power semiconductor device according to claim 1 , comprising at least one isolation layer surrounding the drift region and provided outside the membrane.
6. A lateral power semiconductor device according to claim 1 , and further comprising at least one additional power device having a drift region at least a portion of which is provided on said membrane or on a separate membrane.
7. A power integrated circuit, comprising:
a lateral power semiconductor device having an active region that includes a drift region, at least a portion of the drift region being provided in a membrane having opposed top and bottom surfaces, the top surface of the membrane having electrical terminals connected directly or indirectly thereto to allow a voltage to be applied laterally across the drift region, the lateral power semiconductor device being constructed and arranged such that, when the lateral power semiconductor device is an off-state and operating in a voltage-blocking mode, the equi-potential lines within said at least a portion of the drift region are all substantially perpendicular to the top and bottom surfaces of the membrane and are substantially uniformly distributed across said at least a portion of the drift region so that the electric field across said at least a portion of the drift region is substantially uniform; and
at least one low voltage device.
8. A lateral power semiconductor device according to claim 1 , wherein the membrane comprises a semiconductor layer provided on an electrically insulating layer.
9. A lateral power semiconductor device according to claim 1 , comprising a mechanically strong and electrically insulating layer provided under the membrane.
10. A lateral power semiconductor device according to claim 1 , wherein the drift region has a non-uniform doping profile.
11. A lateral power semiconductor device according to claim 10 , wherein the doping concentration of the drift region at a high voltage terminal side of the lateral power semiconductor device is relatively high and the doping concentration of the drift region at a low voltage terminal side of the lateral power semiconductor device is relatively low.
12. A lateral power semiconductor device according to claim 10 , wherein the doping concentration of the drift region varies linearly from one side of the drift region to the other.
13. A lateral power semiconductor device according to claim 1 , wherein the drift region comprises at least two semiconductor layers of alternating conductivity type arranged one above the other and in contact with each other.
14. A lateral power semiconductor device according to claim 1 , wherein the drift region comprises a plurality of laterally adjacent semiconductor regions of alternating conductivity type.
15. A lateral power semiconductor device according to claim 1 , comprising a termination region adjacent to and in contact with the drift region, said termination region being provided to reduce the effect of premature breakdown at the edge of the drift region.
16. A lateral power semiconductor device according to claim 15 , wherein at least a portion of the said termination region is placed inside the membrane.
17. A lateral power semiconductor device according to claim 15 , wherein at least a portion of the said termination region is placed outside the membrane.