Yuya Kitabayashi

Durability-enhanced two-dimensional hole gas of C-H diamond surface for complementary power inverter applications

Complementary power field effect transistors (FETs) based on wide bandgap materials not only provide high-voltage switching capability with the reduction of on-resistance and switching losses, but also enable a smart inverter system by the dramatic simplification of external circuits. However, p-channel power FETs with equivalent performance to those of n-channel FETs are not obtained in any wide bandgap material other than diamond. Here we show that a breakdown voltage of more than 1600 V has been obtained in a diamond metal-oxide-semiconductor (MOS) FET with a p-channel based on a two-dimensional hole gas (2DHG). Atomic layer deposited (ALD) Al2O3 induces the 2DHG ubiquitously on a hydrogen-terminated (C-H) diamond surface and also acts as both gate insulator and passivation layer. The high voltage performance is equivalent to that of state-of-the-art SiC planar n-channel FETs and AlGaN/GaN FETs. The drain current density in the on-state is also comparable to that of these two FETs with similar device size and VB.

High voltage breakdown (1.8 kV) of hydrogenated black diamond field effect transistor

We fabricated and characterized black polycrystalline diamond field effect transistors. By implementing a C-H bonded channel with a wide gate-drain length up to 20 μm, a breakdown voltage of 1.8 kV was achieved, which is the highest value reported for a diamond field effect transistor (FET) to date. Several of our devices achieved a breakdown voltage/wide gate-drain length ratio > 100 V/μm. This is comparable to the performance of lateral SiC and GaN FETs. We investigated the effects of voltage stress up to 2.0 kV, and showed that the maximum current density fell to 26% of its initial value of 2.42 mA/mm before the device eventually broke down at 1.1 kV.

Diamond MOSFETs using 2D hole gas with 1700V breakdown voltage

More than 1600V breakdown voltages have been obtained in hydrogen terminated (C-H) diamond planar p-channel MOSFETs with gate-drain distance of 16-22 μm. The drain current density exceeds 100mA/mm in the FETs. The blocking voltage and drain current characteristics are comparable to those of n-channel AlGaN/GaN FETs and planar SiC MOSFETs in a similar device size. Atomic layer deposited Al2O3 works as gate insulator and passivation layer. It also induces the 2 dimensional hole gas ubiquitously on C-H diamond surface not only in planar, but in a trench gate structure. The first diamond vertical MOSFET has also operated using the trench structure.

Trench-channel MOSFET using C-H Diamond Surface

Hydrogen-terminated diamond metal –oxide-semiconductor field-effect transistors (C-H diamond MOSFETs) with trench channels were fabricated. The trench structure was formed by inductive coupled plasma etching. The side walls of the trenches can be used for p-channel. This result indicates that, in principal, a vertical diamond MOSFET with trench gate and bottom drain is feasible for power device application.