BI-FET cascode power switch

1. A power switch device, comprising:

a depletion mode field effect transistor (D-FET);

an enhancement mode field effect transistor (E-FET) coupled in cascode with the D-FET such that turning off the E-FET turns off the D-FET and turning on the E-FET turns on the D-FET;

a bipolar transistor operably associated with the D-FET and the E-FET such that turning on the bipolar transistor drives current from the D-FET through the bipolar transistor to the E-FET to provide a charge that turns on the E-FET.

2. The power switch device of claim 1 , further comprising:

a first semiconductor substrate wherein the E-FET and the bipolar transistor are monolithically integrated into the first semiconductor substrate.

3. The power switch device of claim 2 wherein:

the first semiconductor substrate is a Gallium Arsenide substrate;

the E-FET is a HEMT; and

the bipolar transistor is an HBT.

4. The power switch device of claim 2 , further comprising:

a second semiconductor substrate, wherein the D-FET is formed in the second semiconductor substrate.

5. The power switch device of claim 4 wherein:

the first semiconductor substrate is a Gallium Arsenide substrate;

the E-FET is a HEMT;

the bipolar transistor is an HBT;

the second semiconductor substrate is one of a group consisting of a Gallium Nitride substrate, a Silicon Carbide substrate, and a Silicon substrate; and

the D-FET is an HEMT.

6. The power switch device of claim 1 wherein:

the E-FET has a drain, a source, and a gate;

the bipolar transistor has a collector, an emitter, and a base.

7. The power switch device of claim 6 , further comprising:

a first semiconductor substrate wherein the E-FET and the bipolar transistor are monolithically integrated into the first semiconductor substrate such that the drain and the collector are directly connected and the emitter and the gate are directly connected.

8. The power switch device of claim 7 further comprising a resistive component coupled between the emitter and the source.

9. The power switch device of claim 8 wherein the resistive component is a passive resistor.

10. The power switch device of claim 8 wherein the resistive component is operable to provide a variable resistance.

11. The power switch device of claim 6 wherein the bipolar transistor is configured to receive a power switch control signal at the base, wherein the bipolar transistor is operable to turn on when the power switch control signal is above a first threshold voltage.

12. The power switch device of claim 11 wherein the E-FET is operable to turn on when there is a second threshold voltage between the gate and the source and is operably associated with the bipolar transistor such that the E-FET is turned on when the power switch control signal is above the first threshold voltage added to the second threshold voltage.

13. The power switch device of claim 6 wherein the charge is provided at the gate of the E-FET in order to turn on the E-FET.

14. The power switch device of claim 1 wherein the E-FET and the bipolar transistor are arranged as a Darlington transistor pair.

15. The power switch device of claim 1 wherein:

the E-FET has a first drain, a first source, and a first gate;

the bipolar transistor has a collector, an emitter, and a base;

the D-FET has a second drain, a second source, and a second gate.

16. The power switch device of claim 15 further comprising:

a Gallium Arsenide substrate wherein the bipolar transistor and the E-FET are monolithically integrated into the Gallium Arsenide substrate;

a second semiconductor substrate that is one of a group consisting of a Gallium Nitride substrate, a Silicon Carbide substrate, and a Silicon substrate wherein the D-FET is formed by the second semiconductor substrate;

the first gate and the second source are each coupled to ground;

the first drain is configured to receive a power supply signal;

the first source is coupled to the collector and the second drain that are provided by the same structure; and

the base is configured to receive a power switch control signal.

17. The power switch device of claim 1 wherein the D-FET has a first breakdown voltage and the E-FET has a second breakdown voltage, the first breakdown voltage being higher than the second breakdown voltage.

18. The power switch device of claim 17 wherein the first breakdown voltage is significantly higher than the second breakdown voltage.

19. A power switch device, comprising:

a plurality of depletion mode field effect transistors (D-FETs);

a plurality of enhancement mode field effect transistor (E-FETs);

a plurality of bipolar transistors;

a plurality of transistor cells coupled in parallel to one another, each of the plurality of transistor cells having a corresponding D-FET of the plurality of D-FETs, a corresponding E-FET of the plurality of E-FETs, and a corresponding bipolar transistor of the plurality of bipolar transistors, and, wherein for each of the plurality of transistor cells:

the corresponding E-FET is coupled in cascode with the corresponding D-FET such that turning off the corresponding E-FET turns off the corresponding D-FET and turning on the corresponding E-FET turn on the corresponding D-FET; and

the corresponding bipolar transistor is operably associated with the corresponding D-FET and the corresponding E-FET such that turning on the corresponding bipolar transistor drives current from the corresponding D-FET through the corresponding bipolar transistor to the corresponding E-FET to provide a charge that turns on the corresponding E-FET.

20. The power switch device of claim 19 further comprising a first semiconductor substrate wherein, for each of the plurality of transistor cells, the corresponding E-FET and the corresponding bipolar transistor are monolithically integrated into the first semiconductor substrate.