David I. Shahin1, Travis J. Anderson2, Jordan D. Greenlee2, Virginia D. Wheeler2, Marko J. Tadjer2, Bradford B. Pate2, Jennifer K. Hite2, Andrew D. Koehler2, Karl D. Hobart2, Charles R. Eddy Jr.2, Francis J. Kub2, and Aris Christou1
1 Department of Materials Science and Engineering, University of Maryland, College Park, MD, USA
2 Naval Research Laboratory, Washington, DC 20375, USA
TiN and nanocrystalline diamond have been
evaluated as potential replacements for conventional Nibased
gate schemes in AlGaN/GaN HEMTs using reverse
bias electrical stressing. TiN gates deposited by atomic
layer deposition were found to be viable substitutes, as
TiN-gated devices exhibited improved on-state
characteristics in comparison to the Ni/Au-gated devices.
TiN was also determined to have a much higher critical
reverse gate voltage (Vgs = -210 V for TiN vs. -120 V for
Ni/Au) at which gate degradation occurs. The TiN gates
also catastrophically failed at slightly higher and much
less variable breakdown voltages than the Ni/Au gates.
Stressing at reverse gate biases slightly above the Ni/Au
critical voltage but well below the TiN critical voltage
(Vgs = -140 V) led to nearly an order of magnitude
increase in leakage current for the Ni/Au, but decreased
leakage in the TiN. Nanocrystalline diamond gates
exhibited critical voltages of Vgs = -90 V and broke down
at much lower reverse bias, possibly due to testing in air
without encapsulation to protect the gate material.
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