title: Monolithically Integrated GaN MIS-HEMT Blocks for Power Conversion System
Creators: name: Li, Ang
Publisher: name: University of Liverpool Repository
Year: 2028

description: Gallium nitride (GaN), a wide bandgap material, has grand success for high-brightness light-emitting diodes (LEDs) and high-frequency power amplifiers. GaN devices demonstrate superior performance compared to conventional silicon devices, including higher operation temperatures, higher breakdown voltages and faster switching speeds. In recent years, GaN-based power converters have become a focus of research, with GaN power devices enabling the reduction of passive components, decrease in overall system size and improvement in power efficiency. GaN power devices have recently entered the market and are being widely adopted for applications such as chargers, data centers, and electric vehicles. Despite the significant progress in GaN technology, its maturity has not been fully achieved. To further unlock the potential of GaN in power converters, a high-performance GaN device and multifunctional GaN integrated circuits (ICs) are required. A fully functional GaN power converter requires control, drive, sensing, and protection blocks to enable robust control and enhanced functionality. In the short term, the peripheral controller can be implemented with separate Si ICs. However, in the long term, a monolithically integrated solution with GaN technology is desirable to meet the significant demand for high-temperature applications, such as electric vehicles, the oil industry and aerospace. This paper aims to advance the design of highly integrated GaN power conversion systems by demonstrating the GaN metal-insulator-semiconductor high-electron-mobility transistor HEMT (MIS-HEMT) technology from both a device to circuit perspectives: (1) The GaN MIS-HEMT based on threshold voltage modulation is optimised to yield highly tunable D-mode devices. The devices are capable of achieving a range of threshold voltages from −2 to −8 V, and a maximum gate operating voltage of 15.5 V. Furthermore, the performance of the Vth-tunable devices are modelled using a compact model as advanced spics HEMT model (ASM-HEMT), and the results were experimentally verified at circuit level. (2) A novel pulse width modulation (PWM) control block is presented, comprising a comparator, hysteresis comparator, and sawtooth generator. The control block is able to operate at temperatures up to 250°C, frequencies up to 500 kHz with an output amplitude of 6.1 V. This block can be directly applied to the gate driver circuit, allowing for the monolithic integration of GaN control and driver circuits. (3) A GaN-based voltage reference block with a simple design consisting of only two transistors (2T), a high-temperature operation (−25 to 250 °C), a high supply voltage range (VDD: 4.8 to 50 V) and a fast start-up (387 ns) is demonstrated. This block can be applied to comparators and under voltage lock-out (UVLO), to effectively provide a more compact design by simplifying external power supply requirements. (4) Two GaN-based temperature sensing blocks are demonstrated: a four-transistor (4T) design with good sensitivity (31.28 mV/°C), linearity (R2 = 0.995) and accuracy (±2.74 °C); and a two-transistor (2T) design with supply voltage insensitivity (8 to 50 V) and adjustable proportional-to-absolute-temperature/complementary-to-absolute temperature (PTAT/CTAT). These temperature sensors are capable of operating up to 250°C and are validated for over-temperature protection. This work is focused on enhancing the performance of GaN devices to enable circuit design, optimisation, and implementation of monolithic integration of various functional blocks. The system volume has been reduced, while design flexibility has been greatly improved. The device-to-circuit co-design and co-optimisation approach facilitates the practical deployment of GaN technology in power electronics.