High Output Power Density of 2DHG Diamond MOSFETs With Thick ALD-Al₂O₃

This article reports on the high operation voltage large-signal performance of two-dimensional hole gas diamond metal-oxide semiconductor field-effect transistors (MOSFETs) with thick atomic-layer-deposition (ALD)-Al ₂ O ₃ formed on high purity polycrystalline diamond with a (110) preferential orientation. MOSFETs with a 1- μm gate-length having a gate oxide layer of 200-nm-thick Al ₂ O ₃ , formed by ALD and asymmetric structures, to withstand high-voltage operations. The large-signal performances were evaluated at a quiescent drain voltage of greater than -60 V for the first time in diamond field-effect transistor (FET). As a result, an output power density of 2.5 W/mm under class-A operation at 1 GHz, which is higher than that of diamond FETs fabricated by a self-aligned gate process, was obtained. Moreover, an output power density of 1.5 W/mm was exhibited by the MOSFET when biased at a quiescent drain voltage of -40 V under class-AB operation at 3.6 GHz using an active load-pull system. This is the highest recorded value for diamond FETs at a frequency greater than 2 GHz, owing to the high-voltage operation. These results indicate that diamond p-FETs under high-voltage operations are the most suitable for high-power amplifiers with complementary circuits.