This study presents monolithically integrated power circuits, fabricated in a high-voltage GaN-on-Si heterojunction technology. Different advanced concepts are presented and compared with solutions found in the literature. High switching transition slew rates are demonstrated by means of a monolithic power circuit with integrated gate driver. A highly linear temperature sensor is integrated in a GaN-high-electron-mobility transistor (HEMT) power device for the 600 V class and on-state resistance of 53 mΩ. An area-efficient HEMT structure with integrated freewheeling diodes is presented. This structure is applied in a monolithic multilevel converter chip, as well as in a 600 V class half-bridge chip. The multilevel chip is integrated by an advanced printed circuit board embedding technology and tested in inverter operation with a mains voltage output of 120 V
 RMS
. The performance of the half-bridge is demonstrated in a synchronous buck converter operation from 400 to 200 V and with a switching frequency of 3 MHz.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2017.0397

Monolithically integrated power circuits in high-voltage GaN-on-Si heterojunction technology

This work reports on a 600 V GaN-on-Si power transistor with monolithic integrated gate driver. The circuit is based on Schottky-gate depletion-mode technology and fabricated on a 2×3 mm2 chip. The push-pull gate driver stage implements a quasi-normally-off pull-up transistor, fabricated with monolithic integrated series-connected Schottky diodes for positive voltage-level shifting in the source path of a d-mode HEMT. The measured gate-source threshold voltage of the fabricated quasi-normally-off pull-up transistor is +2.7 V as compared to −2.9 V of the normally-on pull-down transistor. Pulsed-IV measurements determine an effective gate driver resistance of around 2 Ω. On-wafer measurements of the power transistor show low off-state leakage-currents up to 600 V blocking voltage with high wafer yield and 150 mΩ on-resistance. Finally, inductive-load switching measurements up to 450 V, 14.3 A show maximum switch node slew-rates during turn-on and turn-off transitions as high as 250 V/ns.

Monolithic integrated quasi-normally-off gate driver and 600 V GaN-on-Si HEMT

This work presents a monolithically-integrated power circuit with a single control input gate driver based on depletion-mode logic and a 600 V, 150 mΩ power HEMT in GaN-on-Si technology. The gate driver final-stage is a push-pull circuit, in which the pull-up transistor is indirectly driven through a depletion-load logic inverter, whereas the pull-down transistor is directly driven by the single external control input. Measurements of soft- and hard-switching turn-on transitions in an inductive-load half-bridge at 300 V/ 4 A demonstrate controllability of the turn-on speed by adding an external speedup resistor in parallel to the depletion-load. Gate-charge measurements show a 25-fold reduction of external pre-driver drive capability requirement during a 400 V turn-on transition, since the main power transistor gate-charge (8.5 nC)-related losses are provided and dissipated within the GaN power device, and only the pull-down gate driver transistor gate-charge of 0.34 nC has to be provided externally by the pre-driver circuit.

Single-input GaN gate driver based on depletion-mode logic integrated with a 600 V GaN-on-Si power transistor

A self-bootstrap integrated gate driver circuit with high driving speed, enhanced driving capability and rail-to-rail output. A capacitor (120) and a diode (118) are used with a first inverter (102) coupled to a control signal input terminal, a second inverter (104) coupled to the first inverter (102), a push-pull circuit (106) comprising a pull-up transistor (116) and a pull-down transistor (115) and a power device comprising a power device transistor (108) with a gate. The control signal input at one state controls the first inverter (102) to a first output state, turns on the pull-down transistor (115) to discharge the gate of the power device transistor (108), turns off the power device and charges the capacitor (120) through the diode (118). The control signal input in another state controls the first inverter (102) to a second output state, turns off the pull-down transistor (115) and turns on the pull-up transistor (116) via the capacitor (120) to turn on the power device.

Power device with integrated gate driver

Due to its remarkably high Johnson figure of merit, gallium nitride (GaN) has become the material of choice for applications requiring high output power at high frequencies. In this paper, we have reviewed high-speed switching work to date and we demonstrate a 28 V, 865-MHz switching speed step-down converter that can be applied to envelope tracking (ET). We report a GaN monolithic microwave integrated circuit technology utilized to fabricate a gate driver IC at a switching speed >1 GHz with 100 V breakdown GaN power switch. The on-chip integration of the power switch and gate driver allows in-circuit characterization of the power switch switching speed. Using the integrated gate driver and switch, we report a slew rate of the power switch of 152 V/ns at 50 V, which enables a down converter IC capable of ET with over 50-MHz tracking bandwidth. This paper shows the first demonstration of a GaN low-side gate driver capable of >1-GHz switching, monolithic integration with a 0.15- $\mu \text{m}$ T-gate suitable for up to Ka-band operation, and a >100 V breakdown voltage power switch on the same chip.

GaN HEMT-Based >1-GHz Speed Low-Side Gate Driver and Switch Monolithic Process for 865-MHz Power Conversion Applications

This work presents a quasi-normally-off gallium nitride (GaN) transistor with positive gate threshold voltage based on depletion-mode technology, suitable for gate drivers or logic circuits. Quasi-normally-off behaviour is achieved by the series connection of multiple Schottky diodes in the source path of an initially normally-on transistor. As opposed to conventional approaches, a novel quasi-normally-off gate driver circuit avoids the static shoot-through current path in the driver final stage and ensures a safe blocking state of a d-mode power switch in case of driver failure with only one negative driver supply voltage. For evaluation a hybrid integrated GaN power module is built, comprising a 2.4 A gate driver and 600 V/ 24 A boost converter switching cell. Measurements of pulsed inductive switching up to 274 V/ 12 A show gate voltage rise and fall times of 5.4 ns and 3.8 ns, boost converter switch node transition times as low as 1.6 ns and 1.2 ns, and maximum slew-rates up to 91 V/ns during turn-on transitions, and up to 177 V/ns during turn-off transitions, respectively.

S. Monch

Papers

Quasi-normally-off GaN gate driver for high slew-rate d-mode GaN-on-Si HEMTs