In the early development of the LEGEND-200 low-noise readout electronics (cf. July 2023 NSD newsletter), researchers in the NSD Neutrinos Program realized a supply issue of the junction field-effect transistors (JFETs) implemented in the design. The vendor that manufactured these low-noise devices has stopped making them, as have many of their competitors. NSD Senior Scientist Alan Poon’s group then embarked on a journey to find an alternative to these high-quality devices. In the summer of 2021, a Science Undergraduate Laboratory Internships (SULI) student, Jeremy Fleishhacker, from Carleton College, MN, was tasked with simulating the electronic response of a graphene field-effect transistor (GFET). His early findings showed that GFETs could be a viable alternative to JFETs.
This past summer, another SULI student, Phoebe Andromeda, from Oregon State University, joined the research team to investigate the actual device performance; in particular, the variation of electronic performance for graphene of different sizes, which acts as the “channel,” between the drain and the source of the GFET. They also measured the electronic characteristics at room and liquid nitrogen temperatures. Working with electronics in cryogens was a highlight of Andromeda’s summer term, as “running electrical tests on the GFETs was the culmination of all the hard work earlier in the internship.”
During the early development of this project, Marcos Turquetti, a staff engineer from the Lab’s Engineering Division, saw an increase in noise when he exposed the GFET device to light in the laboratory. He has since verified that GFETs are indeed sensitive to optical light. Lisa Schlüter, a postdoctoral fellow in the Neutrino Program since summer 2023, is now investigating the spectral response of GFETs over a broader wavelength spectrum, exploiting its utilities in other photo-sensing applications.
The team is exploring other practical uses of GFETs. For example, Lucas Brouwer of the Lab’s Accelerator Technology and Applied Physics (ATAP) Division is developing a magnetic sensor that exploits graphene’s high charge mobility. The goal is to develop a magnetosensor with nano-Tesla sensitivity for superconducting magnets operating at liquid helium temperature.
In 2022, the Department of Energy’s Office of Nuclear Physics funded this GFET development work as a two-year project under its Micro-electronics Initiative.
Figure 1. Layout of a Graphene FET (Image from Graphenea GFET-S31 datasheet).
Figure 2: SULI undergraduate Phoebe Andromeda presenting their GFET work at the Conference Experience for Undergraduates (CEU) poster session in Hawaii in November 2023. Andromeda summed up their poster presentation nicely: “It went exceedingly well. I spoke to many people in the nuclear science community during my presentation who were very interested in my research as it was new and cutting edge!”