Bidirectional GaN FET with single gate
A bidirectional GaN FET with a single gate formed by integrating a single-gate bidirectional GaN FET in parallel with a bidirectional device formed of two back-to-back GaN FETs with a common source. The single-gate bidirectional GaN FET occupies most of the integrated circuit die, such that the integrated device has a low channel resistance, while also capturing the advantages of a back-to-back bidirectional GaN FET device.
1 . A bidirectional GaN FET switch with a single gate, comprising:
a substrate, a GaN layer on the substrate, an AlGaN layer on the GaN layer, a first power electrode and a second power electrode, a third power electrode and a gate, wherein the bidirectional GaN FET switch is formed of a first sub-switch and a second sub-switch integrated together in the bidirectional GaN FET switch on a die having an area and connected in parallel in an equivalent circuit, wherein:
the first sub-switch comprises a single gate GaN field effect transistor (FET), wherein the first and the second power electrodes serve as source/drain electrodes and wherein the gate is centrally located between the first and second power electrodes, whereby the gate is spaced an equal distance from the first and second power electrodes;
the second sub-switch comprises a first GaN FET and a second GaN FET connected in a back-to-back configuration having a common gate, wherein the third power electrode acts as a common source, and wherein the first power electrode and the second power electrode serve as the respective drain electrode of the first GaN FET and the second GaN FET; and
the gate of the single gate GaN FET of the first sub-switch is electrically connected to the common gate of the first and second back-to-back GaN FETs of the second sub-switch to form the single gate of the bidirectional GaN FET switch;
wherein the first sub-switch occupies most of the die area, and the second sub-switch occupies only a small percentage of the die area, such that current passing through the bidirectional GaN FET switch, when the switch is ON, flows primarily under the single gate of the first sub-switch.
2 . The bidirectional GaN FET switch of claim 1 , wherein the substrate is electrically connected to the single gate.
3 . The bidirectional GaN FET switch of claim 1 , wherein the substrate is electrically connected to the common source of the second sub-switch.
4 . The bidirectional GaN FET switch of claim 1 , further comprising at least one field plate, wherein the at least one field plate is connected to the common source of the second sub-switch.
5 . The bidirectional GaN FET switch of claim 2 , further comprising a protection circuitry between the common source of the second sub-switch and the single gate, which is electrically connected to the substrate, to protect the single gate from an overvoltage.
6 . The bidirectional GaN FET switch of claim 1 , wherein the substrate is electrically connected to the power electrodes of the first sub-switch by respective diodes.
7 . The bidirectional GaN FET switch of claim 6 , further comprising a Zener diode connected between each respective diode and the single gate of the bidirectional GaN FET switch to provide overvoltage protection for the single gate.
8 . The bidirectional GaN FET switch of claim 1 , wherein the substrate is electrically connected to the power terminals of the first sub-switch by an active circuit comprising a comparator connected to first and second transistors which are respectively connected between the first and second power electrodes and the substrate, wherein the comparator is configured to:
compare electrical potentials of the first and second power electrodes; and
turn on the one of the first and second transistors corresponding to the power electrode having a lower potential.
9 . The bidirectional GaN FET switch of claim 1 , wherein the substrate is connected to ground.
10 . The bidirectional GaN FET switch of claim 1 , further comprising a voltage divider electrically connected between the single gate and ground, the voltage divider being electrically connected to the substrate, such that the substrate has a potential which follows a potential of the single gate at a fraction of the potential of the single gate.