FET—bipolar transistor combination, and a switch comprising such a FET—bipolar transistor combination
A transistor switch device is provided that exhibits relatively good voltage capability and relatively easy drive requirements to turn the device on and off. This can reduce transient drive current flows that may perturb other components.
1. A current flow control device, comprising:
a bipolar transistor; and
a vertical junction field effect transistor in series with the bipolar transistor, wherein a first region of semiconductor is shared by the bipolar transistor and the vertical junction field effect transistor, wherein the vertical field effect transistor comprises a buried region of doped semiconductor in physical contact with a conductor disposed between insulating walls, wherein the vertical junction field effect transistor has a pinch off voltage and is configured to limit a voltage across the bipolar transistor to the pinch off voltage.
2. A current flow control device as claimed in claim 1 , wherein the first region forms a collector of the bipolar transistor and a drain of the vertical junction field effect transistor.
3. A current flow control device as claimed in claim 2 , wherein the collector of the bipolar transistor is bounded by insulating trenches and connects with a less doped region of semiconductor that forms an extended channel of the vertical junction field effect transistor, wherein the insulating trenches include the insulating sidewalls.
4. A current flow control device as claimed in claim 3 , wherein an emitter region and a base region of the bipolar transistor are bounded by the insulating trenches.
5. A current flow device as claimed in claim 1 , wherein the bipolar transistor is an NPN device.
6. A current flow device as claimed in claim 1 , wherein the buried region of doped semiconductor and another buried region comprise an opposing type of semiconductor to that of a collector of the bipolar transistor and are formed to encircle a carrier flow path from the bipolar transistor, the buried region and the another buried region configured to modulate a channel width of the vertical junction field effect transistor.
7. A current flow control device as claimed in claim 1 , wherein a connection to a gate region of the vertical junction field effect transistor is by way of the conductor.
8. A current flow control device as claimed in claim 1 , further comprising a discontinuity formed in a channel of the vertical junction field effect transistor so as to cause carriers to disperse within the channel.
9. A current flow control device as claimed in claim 1 , wherein the device further comprises a drive field effect transistor integrated with the bipolar transistor to provide a base current for the bipolar transistor.
10. A current flow control device as claimed in claim 9 , wherein a doped region for a source of the drive field effect transistor abuts or is electrically connected by another conductor to a doped region forming a base of the bipolar transistor.
11. A current flow control device as claimed in claim 1 , wherein the bipolar transistor is configured to inject carriers into a depleted region of the vertical junction field effect transistor to initiate current flow when the vertical junction field effect transistor is pinched off.
12. A current flow control device as claimed in claim 1 , wherein the vertical junction field effect transistor comprises a vertical channel, wherein the vertical channel is bounded by opposing regions of semiconductor and a separation between the opposing regions and a doping concentration within the vertical channel define the pinch off voltage.
13. A current flow control device as claimed in claim 1 , further comprising a drive field effect transistor configured to provide a base current to the bipolar transistor, wherein the drive field effect transistor comprises a gate in an insulating well that is separated from the conductor by additional insulating walls.
14. A current flow control device as claimed in claim 9 , wherein the drive field effect transistor is a metal oxide semiconductor field effect transistor.
15. A current flow control device comprising:
an emitter region connected to a first current flow node;
a collector region connected to a second current flow node, wherein the collector region is spatially extended; and
buried doped regions abutting a spatially extended portion of the collector region, the buried doped regions being in physical contact with a conductor disposed between insulating sidewalls, the buried doped regions arranged so as to cause a portion of the spatially extended portion of the collector region to pinch off when a collector voltage exceeds a first value, and where a base region and the emitter region are operable in response to a base current to inject carriers into the pinched off portion of the spatially extended collector region to cause a current to flow.
16. A current flow device as claimed in claim 15 , wherein the buried doped regions are oppositely doped to the adjacent regions of the spatially extended portion of the collector region and, in use, form a vertically formed junction field effect transistor.
17. A current flow control device as claimed in claim 15 , wherein the current flow device is an insulated gate bipolar transistor.
18. A current flow control device as claimed in claim 17 , in which a base of the insulated gate bipolar transistor is connected to a different node than a gate of a vertical junction field effect transistor of the insulated gate bipolar transistor.
19. A current flow control device comprising:
a bipolar transistor;
a vertical junction field effect transistor in series with the bipolar transistor, wherein a first region of semiconductor is shared by the bipolar transistor and the vertical junction field effect transistor, wherein the vertical field effect transistor comprises a conductor disposed between insulating walls of a first trenched region and in physical contact with a buried region of doped semiconductor, wherein the vertical junction field effect transistor has a pinch off voltage and is configured to limit a voltage across the bipolar transistor to the pinch off voltage; and
a drive field effect transistor configured to provide a base current to the bipolar transistor, wherein the drive field effect transistor comprises a gate in an insulating well in a second trenched region, wherein additional insulating walls separate the first trenched region and the second trenched region.
20. A current flow control device as claimed in claim 19 , wherein the first trenched region and the second trenched region encircle the bipolar transistor in a plan view.