Semiconductor device and method of forming a semiconductor device
A bipolar high voltage/power semiconductor device has a low voltage terminal and a high voltage terminal. The device has a drift region of a first conductivity type and having first and second ends. In one example, a region of the second conductivity type is provided at the second end of the drift region connected directly to the high voltage terminal. In another example, a buffer region of the first conductivity type is provided at the second end of the drift region and a region of a second conductivity type is provided on the other side of the buffer region and connected to the high voltage terminal. Plural electrically floating island regions are provided within the drift region at or towards the second end of the drift region, the plural electrically floating island regions being of the first conductivity type and being more highly doped than the drift region.
1. A bipolar high voltage/power semiconductor device, the device comprising:
a low voltage terminal and a high voltage terminal;
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 the first conductivity type connected directly to the low voltage terminal or a region of a second conductivity type connected indirectly via a further region to the low voltage terminal;
a region of the second conductivity type at the second end of the drift region connected directly to the high voltage terminal; and,
plural electrically floating island regions within the drift region at or towards the second end of the drift region, the plural electrically floating island regions being of the first conductivity type and being more highly doped than the drift region.
2. A bipolar high voltage/power semiconductor device, the device comprising:
a low voltage terminal and a high voltage terminal;
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 the first conductivity type connected directly to the low voltage terminal or a region of a second conductivity type connected indirectly via a further region to the low voltage terminal;
a buffer region of the first conductivity type at the second end of the drift region;
a region of a second conductivity type on the other side of the buffer region and connected to the high voltage terminal such that the buffer region is between the second end of the drift region and said region of the second conductivity type; and,
plural electrically floating island regions provided at least partly within the buffer region or at least partly within the drift region at or towards the second end of the drift region, the plural electrically floating regions being of the first conductivity type and being more highly doped than both the drift region and the buffer region.
3. A device according to claim 2 , wherein at least one of the electrically floating island regions is entirely within the buffer region.
4. A device according to claim 2 , wherein at least one of the electrically floating island region is entirely within the drift region.
5. A device according to claim 2 , wherein at least one of the electrically floating island regions is partly within the buffer region and partly within the drift region.
6. A device according to claim 1 or claim 2 , wherein the device is a lateral device having opposed edges between the active area of the device and any unused area, at least one of the electrically floating island regions being positioned at or towards said edges.
7. A device according to claim 1 or claim 2 , wherein the device is formed within a layer of semiconductor layer placed above a thin buried insulating layer or placed above a dielectric layer or placed above a thin insulating layer within a membrane, the electrically floating island regions having a depth substantially equal to the depth of the semiconductor layer.