FET—bipolar transistor combination

1. A current flow control device, comprising:

a bipolar transistor in series combination with a field effect transistor inside an isolated region of semiconductor; and

a drive field effect transistor having a gate formed within a trench arranged to isolate the gate of the drive field effect transistor from the bipolar transistor.

2. A current flow control device as claimed in claim 1 , in which the current flow control device is a three terminal device having a first terminal connected to an emitter region of the bipolar transistor, a second terminal connected to a drain region of the field effect transistor, and a control terminal connected to the gate of the drive field effect transistor to control current flow through the current flow control device, and wherein the three terminals are provided on a same side of the current flow control device.

3. A current flow control device as claimed in claim 1 , in which the current flow control device is formed vertically within the isolated region and a drain region of the field effect transistor is formed in a lowermost portion of the current flow control device below a surface of the current flow control device having terminals for connection to the current flow control device.

4. A current flow control device as claimed in claim 3 , further including vertical regions doped similar to the drain region and disposed away from an emitter region of the bipolar transistor to enable the drain/collector current to be brought to a surface of the current flow control device for connection to metallic contacts.

5. A current flow control device as claimed in claim 1 , in which the bipolar transistor is an NPN transistor having a gain greater than 50.

6. A current flow control device as claimed in claim 1 , in which the trench is closed opposite a contact to the gate.

7. A current flow control device as claimed in claim 1 , in which the field effect transistor is configured to pinch off when the voltage at a drain region of the field effect transistor exceeds the voltage of at the gate of the drive field effect transistor by a predetermined threshold.

8. A current flow control device as claimed in claim 7 , in which the gate of the drive transistor is also within a second trench arranged to isolate the gate of the drive field effect transistor from the bipolar transistor, in which the trench and the second trench are opposing structures, and in which the field effect transistor is formed between the opposing structures so as to define a channel between the opposing structures, and where a pinch-off voltage for the field effect transistor is based on a distance between the opposing structures.

9. A current flow control device as claimed in claim 8 , in which the opposing structures are spaced apart by less than 5 microns.

10. A current flow control device as claimed in claim 8 , in which the pinch-off voltage for the field effect transistor is based on a collector doping concentration in a region between the opposing structures.

11. An integrated circuit comprising at least one current flow device as claimed in claim 1 .

12. A device comprising:

a bipolar transistor;

a first field effect transistor in series with the bipolar transistor;

a second field effect transistor comprising a source electrically connected to a base of the bipolar transistor and a drain electrically connected to a node between the first field effect transistor and the bipolar transistor; and

an insulating well surrounding the bipolar transistor, the first field effect transistor, and the second field effect transistor, wherein the insulating well is configured to insulate the device from other circuit elements disposed on the same die as the device.

13. The device as claimed in claim 12 , wherein the first field effect transistor comprises a gate electrically connected to an emitter of the bipolar transistor.

14. The device as claimed in claim 12 , wherein a source of the first field effect transistor and a collector of the bipolar transistor each comprise a common region within the insulating well.

15. The device as claimed in claim 12 , wherein the bipolar transistor is configured to inject carriers into a depleted region of the first field effect transistor so as to turn the first field effect transistor on.

16. The current flow control device as claimed in claim 1 , wherein a conductivity of a channel in the current flow control device is controlled by a signal received at the gate of the drive field effect transistor.

17. A current flow control device, comprising:

a bipolar transistor; and

a field effect transistor in series combination with the bipolar transistor,

wherein the bipolar transistor and the field effect transistor are disposed within an isolated region of semiconductor, and

wherein the bipolar transistor is configured to inject carriers into a depleted region of the field effect transistor so as to turn the field effect transistor on.

18. The current flow control device as claimed in claim 17 , further comprising a drive field effect transistor having an isolated gate, the drive field effect transistor being coupled to both the field effect transistor and the bipolar transistor.

19. The current flow control device as claimed in claim 18 , further comprising:

a gate terminal disposed on a first side of the current flow control device and connected to the isolated gate of the drive field effect transistor;

an emitter terminal disposed on the first side of the current flow control device and connected to the bipolar transistor; and

a collector terminal disposed on the first side of the current flow control device and connected to the field effect transistor.

20. The current flow control device as claimed in claim 18 , wherein a source of the drive transistor is electrically connected to a base of the bipolar transistor.

21. The current flow control device as claimed in claim 17 , wherein the field effect transistor comprises a gate formed within a trench arranged to isolate the gate from the bipolar transistor.