With a large band gap and low intrinsic carrier concentration, β-Ga2O3 suggests a robust platform for operation of electronic devices at a high temperature. The performance Ga2O3 transistors with different gate metals has been characterized in vacuum and air at temperatures up to 500 C.
Devices fabricated with NiAu gate metal and Al2O3 gate dielectric exhibited stable operation up to 500 C in air. The measured ID-VD characteristics showed no current degradation up to 450 C. At 500 C, gate leakage dominates in the off-state. The characteristics recover when the device is returns to RT, even after 20 hours of operation at 500 °C, the device experiences minimal degradation.
Devices fabricated using TiW gate metal and Al2O3 gate dielectric exhibited stable operation up to 500 C in vacuum and up to 450 C in air. Transfer characteristics were measured at various temperatures in vacuum and air. Extracted IMAX/IMIN for the vacuum test reduced from ~104 to 102 as temperature was increased up to 500 C. During the vacuum characterization, the contact resistance remained unchanged at all temperatures and the device characteristics showed no degradation once devices were brought back to RT after several hours of operation at 500 C in vacuum.
For tests in air, both NiAu and TiW devices observed an increase in current with temperature due to activation carriers from dopants/traps in the device. Both devices exhibited IMAX/IMIN < 102 at 450 C because of contact degradation. Barrier heights of ϕB ~ 1.0 eV and 0.77 eV were calculated for the TiW/Al2O3 and the NiAu/Al2O3 interfaces, respectively using thermionic emission theory. Though the values of ϕB for the TiW was consistent with that expected from the work-function difference between TiW and Al2O3, the devices with NiAu yielded lower ϕB presumably due to the diffusion of Ni into the Al2O3 dielectric. The results suggest that with appropriate choice of metals and gate dielectrics, stable 500 C operation is achievable.