GaN-based heterojunction transistors are being developed with intensive efforts for the next-generation high-efficiency power converters, owing to their capabilities to deliver lower conduction and switching losses, higher switching frequency, and higher operating temperatures compared with the conventional Si power devices. The commercialized GaN-based high-voltage lateral power devices almost feature the grounded substrate termination. However, it is still unclear whether the grounded substrate termination is the optimum choice while considering the dynamic performance.

The commercialized GaN power devices have already outperformed the Si counterparts. However, in GaN-based power converters, the peripheral logic control or drive modules are still Si-based. Such a hybrid scheme...[ Read more ]

GaN-based heterojunction transistors are being developed with intensive efforts for the next-generation high-efficiency power converters, owing to their capabilities to deliver lower conduction and switching losses, higher switching frequency, and higher operating temperatures compared with the conventional Si power devices. The commercialized GaN-based high-voltage lateral power devices almost feature the grounded substrate termination. However, it is still unclear whether the grounded substrate termination is the optimum choice while considering the dynamic performance.

The commercialized GaN power devices have already outperformed the Si counterparts. However, in GaN-based power converters, the peripheral logic control or drive modules are still Si-based. Such a hybrid scheme with GaN power devices and Si integrated circuits usually consumes more board space and features larger parasitic inductances, which inevitably limit the performance of GaN power switches to some extent. And this parasitic effect will cause reliability concern on the valuable p-GaN gate, leading to the unexpected issues on the GaN-based power converters, especially when the GaN power switches work with high switching frequency.

In this work, we focused on the GaN-based power device characterization and power integrated circuit development. The work was devoted into three parts:

1. The impact of the substrate termination on GaN power devices’ dynamic performance was investigated. The dynamic R_ON was characterized with a grounded and floating substrate termination. Comparing to the grounded substrate termination, the floating substrate can lead to a better dynamic R_ON during high-voltage switching operations, because of the negative charge removal in the silicon substrate and alleviated trapping effect in the buffer region. The observed dynamic performance with a floating substrate termination indicates a potential for a 600-V half-bridge integration.

2. Although the commercialized discrete GaN power devices have already delivered the superior performance than the Si-based power MOSFETs, the control/drive circuits are still implemented in CMOS technology. The interconnection between the Si integrated circuits and GaN power devices will cause inevitable parasitic inductance in the gate drive loop. To fully eliminate the parasitic-inductance-induced circuit reliability issue, the gate drive loop could be shortened to micrometer scale by integrating the gate driver and the power device on the chip. Thus, it is necessary to develop the 650-V GaN power integration platform where the transistors, diodes, resistors and capacitors can be all implemented. The characteristics and design guidance of the GaN-based devices/elements are included.

3. Based on the afore-mentioned GaN power integration platform, the GaN-based digital integrated circuits have been demonstrated. By selectively etching the ρ-GaN layer, both the E/D-mode HEMTs can be achieved on the same GaN-on-Si wafer without the additional process steps. The demonstrated logic circuits consisting of E/D-mode devices show superior performance, indicating that the control circuits can be achieved based on GaN device technology. Furthermore, the fabricated ring oscillator exhibits a small propagation delay, meaning that the GaN-based integrated circuits can work properly in the high-speed mixed-signal circuit applications.

4. To address the issue of parasitic inductance in the gate driver loop, the GaN power device with integrated gate driver was demonstrated on the GaN-on-Si platform. The integrated gate driver with introduced charge pump unit could solve the existing issues in the conventional GaN-based gate driver circuit. The designed gate driver could deliver a rail-to-rail output and higher driving capability. The fabricated GaN power device with integrated gate driver features high switching speed. Also, the devices can work properly under the 300V/15A switching condition without the extra need of negative power supply for the gate driver. The additionally introduced under-voltage lock-out (UVLO) module in the gate driver circuit can effectively protect the gate driver from the undesired supply voltage.