Self-Aligned Gate Thin-Channel β-Ga 2 O 3 MOSFETs

Beta-phase gallium oxide $(\beta-\mathrm{Ga}_{2}\mathrm{O}_{3})$ has shown promise as a next-generation wide-bandgap semiconductor for use in power electronics. It possesses a bandgap and expected critical field strength of ~4.8 eV and ~8 MV/cm, respectively, surpassing the same measured characteristics of GaN and SiC [1]. Early work has been successful in demonstrating lateral metal-oxide-semiconductor field-effect transistors (MOSFETs), predominately for depletion mode operation, with high critical field strength [2], high current density [3], and high breakdown voltage [4], [5]. One limitation of $\beta-\mathrm{Ga}_{2}\mathrm{O}_{3}$ MOSFETs is source access resistance $(\mathrm{R}_{\mathrm{S}})$ , the ungated region between source and gate, with sheet resistance $(\mathrm{R}_{\mathrm{SH}})$ typically in the $\mathrm{k}\Omega/\mathrm{sq}$ range. The $\mathrm{R}_{\mathrm{S}}$ affects key device performance parameters such as transconductance $(\mathrm{G}_{\mathrm{M}})$ and drain-current density $(\mathrm{I}_{\mathrm{DS}})$ . Higher DC and RF performance can be expected from eliminating $\mathrm{R}_{\mathrm{S}}$ by self-aligning the gate and source contacts. We present, for the first time, a self-aligned gate (SAG) $\beta-\mathrm{Ga}_{2}\mathrm{O}_{3}$ MOSFET using a refractory metal gate-first design. MOSFET devices with $2\mathrm{x}50\mu \mathrm{m}$ gate periphery, $7.5 \mu \mathrm{m}$ source-drain distance $(\mathrm{L}_{\mathrm{SD}})$ and $2 \mu \mathrm{m}$ gate length $(\mathrm{L}_{\mathrm{G}})$ were directly compared with and without the SAG features. MOSFETs with SAG show a substantial increase in $\mathrm{G}_{\mathrm{M}}$ and $\mathrm{I}_{\mathrm{DS}}$ , from ~2 mS/mm to ~14 mS/mm and ~10 mA/mm to ~45 mA/mm, respectively, up to $\mathrm{V}_{\mathrm{GS}}=4$ V. Lastly, we report a laterally scaled device $(2\mathrm{x}50\mu \mathrm{m})$ with $\mathrm{L}_{\mathrm{SD}}=2.5\mu \mathrm{m}$ and $\mathrm{L}_{\mathrm{G}}=2\mu \mathrm{m}$ , achieving high current density $(\sim 140\mathrm{mA}/\mathrm{mm})$ , and high G M $(\sim 35\mathrm{mS}/\mathrm{mm})$ .