Research Summary

Our research projects address the need for new sensor systems and material structures that can operate within extreme harsh environments. This technology can be utilized in a variety of applications (see figure below).
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Research Projects

Miniaturized Instrumentation for Deep Space Exploration

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Graphene-GaN UV Photodetector Arrays for Sun Sensing
GaN-based devices are studied for space environment applications. Metal semiconductor-metal (MSM) ultraviolet (UV) photodetectors, HEMTs and diodes integrating graphene and semi-transparent metals have been designed, fabricated and characterized under different irradiation sources (Cs-137, Co-60, protons) as well as UV light and dark conditions.

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AlGaN/GaN Pressure Sensors for Venus Exploration
The goal of this research is to investigate the high-temperature response of the 2-dimensional electron gas (2DEG) that occurs at the interface of gallium nitride (GaN) heterostructures upon mechanical deformation. Micro-pressure sensors are being designed, microfabricated, and characterized from AlGaN/GaN heterostructures. Extreme environment testing is being completed in oxidizing environments temperatures up to 600°C and within Venus simulated environments (supercritical CO2, 480°C, 90bar).

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Heat Flux Sensors for Thermal Protective Systems
This project is focused on the use of III-V nitrides for the development of temperature and heat flux sensors. Materials from the III-V Nitride family are utilized to make efficient thermoelectric structures using novel material combinations and in-house fabrication techniques. The end goal of this effort is to build a compact and reliable system (without the use of shielding) that can be used directly in aerospace and automobile thermal protective systems.

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AlGaN/GaN Sensors for Icy, Radiation-Rich Environments
There is rising interest in developing electronics for cold temperature environments. For example, NASA proposes sending a lander to the surface of Europa, the icy moon of Jupiter. This climate is extremely cold (-180°C) and highly radiative. The packaging required for electronics would add significant payloads, so an electronic system that can operate under harsh conditions is desired.

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Reliability Analysis of GaN, SiC and Si under Thermal and Radiative Stress
The operational limits of GaN, SiC and Si devices are studied using accelerated life testing. In addition, the electrical characteristics and microstructure of the devices are examined after exposure to very high doses of proton and gamma irradiation.

Robust Sensors for Energy and Environment

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GaN-Based Soot Particulate Sensors
For long-term monitoring of harmful soot particles in exhaust gases, development of GaN-based soot-particulate sensors using Schottky contacts and AlGaN/GaN HEMT architectures is underway.

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Nanoparticle-Enhanced AlGaN/GaN Carbon Dioxide Sensors
Inkjet printing process is being developed to integrate chemical sensitive nanoparticles onto AlGaN/GaN MEMS structures for carbon dioxide sensing in high temperatures. This can be used for industrial, environmental and automotive applications.

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High-Temperature Sensors for Smart Oilfields
While in-situ measurements of rock formations while drilling could improve drilling performance and prevent catastrophic events, sensing down hole is currently challenging. This project investigates different sensing schemes to characterize porous rock formations (e.g. sandstone and brine) during drilling to improve drill efficiency, safety and lifetime.

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Sensors for Smart Power Electronics Modules
Due to increased power densities on chip, future power electronics modules require parallel electrical and thermal optimization. The integration of on-chip sensors can be used for closed-loop control and optimization. GaN-based sensors are being developed for monolithic integration with GaN power electronics.

Advanced Fabrication Technology for GaN and SiC Materials Platforms

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4H-SiC Substrates Processed in Microgravity Environments
The effect of reduced gravity environments on 4H-SiC substrates at elevated temperatures is studied. Microstructural analysis through high resolution X-ray diffraction (HRXRD) is used to study crystal structure and stacking fault density. Further, the electrical responses and thermal properties of materials processed in the microgravity environments are characterized.

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Deep Plasma Etching of SiC Microstructures
The bulk micromachining of 4H-SiC is being studied for improved high aspect ratio features. This is of interest for the development of micro-channels for microfluidic thermal cooling applications as well as complex “3D” MEMS structures.

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High-Temperature Metal Contacts to GaN and SiC
The electrical and microstructural properties of Ti/Al/Pt/Au contacts to GaN at high temperatures (600°C) in air have been studied. Experimental results showed minimal change in contact resistance and surface roughness after 10 hours of thermal storage in air at 600°C. Our study supports the use of Ti/Al/Pt/Au multilayer metallization for GaN-based sensors and electronic devices that will operate within a high-temperature and oxidizing ambient.

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Metal Organic Chemical Vapor Deposition (MOCVD) of III-V Heterostructures
III-nitride heterostructures are grown by MOCVD in the Stanford Nanofabrication Facility using Aixtron Closed Coupled Showerhead reactor. The electrical characteristics and microstructures of the grown heterostructures are characterized to support MEMS sensor and device fabrication.