Metal oxide semiconductor field effect transistors (MOSFETs) with Al2O3 passivation layer grown by atomic layer deposition (ALD) at 200 oC and 300 oC were fabricated on hydrogen-terminated polycrystalline diamond by using gold mask technology. The device with 200 oC grown Al2O3 dielectric shows high output current, low on-resistance, large threshold voltage and high transconductance compared to that with 300 oC grown Al2O3. A maximum drain current of 339 mA/mm has been achieved by the 2-μm device of the former kind, which, as we know, is the best result reported for the diamond MOSFETs with the same gate length except the NO2-adsorbed case. The current-voltage (I-V) of gate diodes of both kinds of devices show the gate forward leakage is dominated by the Frenkel-Poole (FP) emission mechanism at a high electric field, and the gate of the latter device can sustain higher forward bias. The stability of successive I-V measurements of both kinds of devices was proved. We expect that a high performance H-diamond MOSFET with high stability can be achieved by a double-layer dielectric structure with 200 oC grown Al2O3 stacked by another high-quality high κ dielectric.

High performance normally-off hydrogen-terminated diamond (H-diamond) MOSFETs were fabricated on single crystalline diamond grown in our lab. The device with 2-μm gate length shows threshold voltage of −1.0 V, and a drain current of 51.6 mA/mm at V GS = V DS = −4.5 V and an on-resistance of 65.39 •mm. The transconductance keeps increasing when V GS shifts from V TH toward more negative direction, and reaches the record high value of 20 mS/mm at V GS of −4.5 V, which benefitted from the almost constant mobility of the holes in the gate voltage range of −4 V < V GS < −2 V. The critical device process to realize these low on-resistance normally-off MOSFETs consists of 2-min UV ozone treatment of the H-diamond surface and thermal oxidation of aluminum film in the air to form an alumina gate dielectric. INDEX TERMS Single crystalline diamond, normally-off, MOSFET.

C-H diamond metal-oxide-semiconductor field effect transistors with different structures were fabricated on the same polycrystalline diamond plate. Devices A and B with 25-nm-thick high temperature (300 • C) atomic layer deposition grown Al 2 O 3 dielectric have the same source-to-drain distance of 6 µm and different gate length of 2 µm and 6 µm, respectively. Both devices show ultra-high on/off ratio of over 10 10 and ultra-low gate leakage of below 10 −10 A and continuous measurement stability. Device B with the source/drain-channel interspaces eliminated has achieved an on resistance of 46.20 •mm, which is record low in the reported 6-µm H-diamond MOSFETs with the gate dielectric prepared at high temperature (≥ 300 • C). Meanwhile, device B shows larger drain current in a large portion of the linear region at V GS = −6 V, and a just slightly smaller I Dmax compared with device A though its L G is three times of that of device A. A simple model of I D was used to explain the physics behind this phenomenon. In addition, the breakdown voltage is 145 V for device A and 27 V for device B, corresponding to the average breakdown field of about 0.72 MV/cm and 10.8 MV/cm, respectively.