Wide bandgap GaN-based power switching devices promise to deliver low ON-resistance, high breakdown voltage and high switching frequency owing to the superior material properties of group III-nitride materials. These high-performance devices are emerging as highly attractive candidates for the next-generation power converters as they promise higher power conversion efficiency (i.e. lower loss) within a more compact size. For a fully functional GaN-based power converter, sensing/control/protection circuits are necessary to provide robust control, increased functionality and enhanced reliability to the core high-voltage GaN power components, and to protect them against harmful operating conditions such as over-current, over-voltage and over-temperature. While the peripheral controller cou...[ Read more ]

Wide bandgap GaN-based power switching devices promise to deliver low ON-resistance, high breakdown voltage and high switching frequency owing to the superior material properties of group III-nitride materials. These high-performance devices are emerging as highly attractive candidates for the next-generation power converters as they promise higher power conversion efficiency (i.e. lower loss) within a more compact size. For a fully functional GaN-based power converter, sensing/control/protection circuits are necessary to provide robust control, increased functionality and enhanced reliability to the core high-voltage GaN power components, and to protect them against harmful operating conditions such as over-current, over-voltage and over-temperature. While the peripheral controller could be implemented with separate Si ICs in the near term, it is desirable to develop a system-on-chip solution with GaN smart power IC technology that can better take advantage of GaN’s capability of operating at higher temperatures. This dissertation focuses on developing gate-protection techniques and mixed-signal functional blocks for GaN smart IC implementation.

Aiming at developing circuit techniques that take full advantage of the various devices and the device-circuit interactions on a robust planar GaN smart power IC technology platform, this dissertation focuses on three parts including 1) an integrated gate-protected power HEMT; 2) mixed-signal functional blocks for continuous expansion of GaN mixed-signal design library; and 3) GaN-based temperature sensing and over-temperature protection circuits. The first GaN high electron mobility transistor (HEMT) with integrated gate protection is demonstrated by embedding a depletion-mode HEMT (D-HEMT) into the gate of an enhancement-mode HEMT (E-HEMT). The gate remains safe (i.e. no shift in threshold voltage and no gate failure) even when the input bias exceeds 20 V, with no penalties to the ON-state current and off-state breakdown voltage. Several key mixed-signal functional blocks (e.g. a 2-level quantizer circuit and a set/reset flip-flop) are demonstrated on the GaN smart power IC platform for the first time, showing proper operations at 250 ℃ with low power consumption. Since GaN devices exhibit strong temperature dependence, temperature sensing circuits play an important role in providing feedback signals for circuit tuning and adjustments. An over-temperature protection circuit and an accurate temperature sensor, such as a proportional-to-absolute-temperature (PTAT) voltage source are demonstrated using monolithically integrated GaN transistors and diodes. The former circuit shows a sharp transition of control signal at a designated critical temperature (up to 250 ℃) that is set by a reference voltage, while the latter one exhibits an output with a +0.35 mV/℃ temperature coefficient and an excellent linearity of R² = 0.9931 between 25 and 250℃.