Faculty Candidate Seminar

Developing and Deploying Gallium Nitride Magnetometers for Harsh Environments

Karen DowlingPostdoctoral Research StaffLawrence Livermore National Laboratory

Magnetic sensors are quite common in every day life, with a variety of uses in mobile devices, electric machines, cars, motors, navigation, and planetary exploration. They are incredibly useful due to their non-perturbing nature. For example, they infer information about position, velocity, and current in power systems. Silicon Hall effect sensors are popular for many applications due to their low cost and ease of integration with silicon circuits. However, silicon Hall-effect plates cannot operate at extreme temperatures (< -100°C or above 300°C) due to carrier freeze out or intrinsic carrier leakage, respectively. In addition, Hall-effect plates have challenges with thermal drift, offset, and flicker noise.

Gallium nitride (GaN) and silicon carbide (SiC) are two key WBG materials rapidly replacing silicon in high-speed communications and power systems. These materials also can operate in extreme temperature ranges, from cryogenic temperatures to 1000°C. GaN, in particular, has the ability to support a confined charge layer, commonly referred to as a two-dimensional electron gas (2DEG). This phenomenon is key to high-frequency, high-power RF transmission in 5G networks, and is also a great sensing layer for various environmental stimuli (i.e. Thermal, Magnetic, Strain). Additionally, various GaN sensors and transistors can be fabricated with the same fabrication process, which can lead to monolithically integrated systems on a single chip. Thus GaN Hall plates are attractive to further this technology.

In this talk, I will describe an AlGaN/GaN 2DEG Hall-effect plate with ~100 ppm/K drift, 0.5 micro-Tesla offset, and 200 Hz corner frequency. In addition, the GaN 2DEG Hall-effect plates have operated in an extended temperature range from 50 K to 600°C. These metrics beat out state-of-the-art silicon Hall-effect sensors. Through this work, I have created a record-low offset in GaN 2DEG Hall devices, presented a framework for studying noise in GaN Hall sensors, and initiated steps towards integration of Hall-effect devices in microsystems for Low earth orbit and current sensing in transformers. I will conclude with new concepts for novel GaN sensors with a micromachined substrate and highlight additional work with plasma etched SiC. These contributions will enable a future monolithically integrated GaN platform for power electronics and extreme environments.


Karen Dowling received her B.S. degree in electrical engineering from the California Institute of Technology, Pasadena CA in 2013 and M.S. degree in electrical engineering from Stanford University, CA in 2015. She received her Ph.D. in electrical engineering at Stanford University in 2019.

In 2011, she was a Systems Engineering Intern at Crane Aerospace Electronics, Burbank CA. In 2012, she was a Research Assistant at the Wireless Integrated Microsystems center at the University of Michigan, Ann Arbor. In 2015, she was an intern at MIT Lincoln Laboratory, Lexington MA, and in 2018 she was an intern at Infineon Technologies in Munich, Germany. Currently, she is a postdoctoral researcher at Lawrence Livermore National Laboratory with a focus on opto-electronics for power and RF devices. Her research interests include the use of wideband gap materials for the development of sensors for extreme environments, in particular magnetic field sensors for power electronic systems and navigation for exploration. Dr. Dowling is a National Science Foundation Graduate Research Fellow and was the student president of the NSF engineering research center for power optimization of electro-thermal systems.


Faculty Host

Zetian MiProfessor, Electrical Engineering and Computer ScienceUniversity of Michigan