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Dissertation/Thesis Abstract

Studying Integration of Diamond Hole-FET and GaN HEMT as Complementary-FET Inverters for High-Temperature Operation
by Ren, Chenhao, Ph.D., University of California, Davis, 2020, 113; 28255567
Abstract (Summary)

An increasing number of applications in power electronics, sensor signal conditioning, and RF communication are demanded to operate beyond 200°C (e.g., engine and geothermal wellbore monitoring). These applications require integrated circuits such as mixed-signal circuits featuring analog circuitry, analog to digital converters, embedded microcontrollers, and on-chip memories. The silicon-based complementary metal-oxide-semiconductor (CMOS) technology combining a p-type FET and n-type FET to achieve different logic functions is not reliable for stable and sustained operations at high temperatures (>125 °C). 

This study reports the successful development of an integrated high-temperature silicon CMOS kind of inverter using wide bandgap (WBG) complementary-FET (CFET) technology. Two high-temperature capable material systems, diamond and gallium nitride (GaN) were used to develop this novel inverter. The p-channel FET utilizes a hole accumulation channel achieved using a hydrogen-terminated diamond field-effect transistor. The n-channel FET is made out of an electron channel GaN high electron mobility transistor (HEMT). The proof-of-concept inverter was first achieved by thermocompression single-crystal diamond hole-FET on top of the GaN HEMT structure to prove the concept. This prototype demonstrated the inverter operations above 300 °C.

However, thermocompression integration is not ideal for large-scale production. Therefore, we first time demonstrate the monolithic integrated polycrystalline diamond hole-FET and GaN HEMT inverters on a single chip. The polycrystalline diamond layer was first deposited on the AlGaN/GaN HEMT structure using a microwave plasma chemical vapor deposition (MPCVD) system. Then we fabricated the hydrogen-terminated diamond hole-FET and GaN HEMT on the same chip simultaneously. As a highlight, the 450 °C ALD Al2O3 above 45 nm can effectively protect both diamond hole-FET and GaN HEMT from high-temperature above 300 °C. 

Diamond has one of the highest thermal conductivity in all semiconductor materials. Beyond its high-temperature performance, the deposited diamond on GaN HEMT can also work as a heat spreader for the integrated diamond and GaN technology. To study a diamond spreader's thermal impact on the GaN devices, we designed and fabricated a doped GaN FET with a 400 nm diamond on top as a heat sink. Compared to the reference, the diamond heat spreader effectively reduced the channel temperature up to 50 °C between 12 ~ 22 W/mm.

This comprehensive study demonstrates the different integration technology of diamond hole-FET and GaN HEMT together as inverters for high-temperature applications using 450 °C high-quality ALD Al2O3 passivation. The achieved inverters show excellent voltage transfer characteristic (VTC) operations above 300 °C. As an essential feature, the diamond as a heat spreader presents a noticeable reduction in GaN devices from self-heating.

Indexing (document details)
Advisor: Chowdhury, Srabanti
Commitee: Luhmann, Neville C., Ji, Dong
School: University of California, Davis
Department: Electrical and Computer Engineering
School Location: United States -- California
Source: DAI-B 82/9(E), Dissertation Abstracts International
Subjects: Electrical engineering
Keywords: Complementary Metal-Oxide-Semiconductor, Complementary Field Effect Transistor, Diamond, Gallium nitride, High Electron Mobility Transistor
Publication Number: 28255567
ISBN: 9798582546047
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