Owen Meilander, 2nd year Interdisciplinary Material Science PhD student in Dr. Mona Ebrish’s Lab in the Electrical Engineering department.
Summary of Research:
My work focuses on the fabrication and characterization of gallium nitride (GaN) semiconductor devices. GaN devices offer many benefits for high power and high frequency applications. It will allow for more efficient electronics that are smaller than current devices. Additionally, GaN is radiation tolerant making it an ideal choice for use in extreme environments such as in outer space.
Specifically, we are exploring the fabrication of GaN high electron mobility transistors (HEMTs) for efficient power conversion. When charging a laptop or other large electronic, the charging cord typically has a box that sits between the wall plug and the plug that goes into your device. This box is responsible for converting the power that the wall supplies into a form that can be used by your device. After charging your device for a while, this box begins to heat indicating that power is being lost! Most of this power loss is due to the semiconductor device within circuit. By replacing this device with a GaN HEMT, these converters can be made smaller and more efficient. This promises to have a significant impact on industries such as renewable energy and electric vehicles allowing for more efficient harvesting of energy and faster yet more efficient charging.
Nevertheless, despite the potential of these devices, GaN is not a mature material. This leads to numerous material issues that hinder both reliability and manufacturability of GaN devices. One such issue is the activation of a p-type dopant. While magnesium can readily be incorporated into GaN through mature processes such ion implantation or directly during material, it cannot be easily promoted to the correct lattice position leading to electrical activation. This activation is normally done by heating the sample to a temperature where the dopant can move to the correct position. However, GaN must be heated to a temperature greater than what the crystal can withstand for Mg to be activated. We are exploring multiple ways to overcome this challenge. First, we are attempting to use a novel annealing technique to quickly allow for the Mg to be activated before the crystal can decompose. Additionally, we are exploring techniques to diffuse the Mg into crystal through the surface. Both processes will allow for easier doping and device fabrication.
Finally, GaN devices can only be widely adopted if they can be easily integrated with modern electronics i.e. Si CMOS. While GaN can be directly grown on Si, this would introduce a long step that would add much complexity to the overall fabrication process. Therefore, other techniques for heterogeneous integration are being explored. We are currently working on developing micro-transfer printing processes to move GaN devices fabricated on one wafer to another. In this process, we release a chip from its native wafer using a XeF2 etch, pick up the chip using a PDMS stamp, and adhere the chip to a different wafer. This process allows for the precise placement of GaN devices into an otherwise Si system. We are researching ways to optimize this process for fast and scalable printing while managing thermal and electrical considerations to maintain the original operation of the device.
Life in VINSE:
Nearly every step of my research is heavily dependent on VINSE facilities. The analytical lab and advanced imaging allow for the characterization of our materials while the cleanroom facilitates the fabrication and testing of devices. I would not be able to do any of the work that I have done today with all the wonderful VINSE staff. Coming from a newly started lab, we have had to develop every recipe and process we use. During every step of this process, VINSE staff has trained me and given me advice that has allowed me to find success in my work. Because of this, I have tried to give back in the same ways they have helped me. I currently volunteer as a NanoGuide, the VINSE program where we get to teach students from local high schools and show them all the science happening in VINSE. Specifically, I have lectured and led groups through the Cleanroom Microfluidics and Solar Cell projects. Also, I work for VINSE as a cleanroom Super User. In this role, I train other students on many of the tools within the cleanroom and help them develop processes of their own. I am incredibly thankful for VINSE and all their staff for helping me achieve the success I have today and for supplying me with the opportunities to grow as a researcher.
Contact: Owen Meilander