Nobutaka Oi

Role of carboxyl and amine termination on a boron-doped diamond solution gate field effect transistor (SGFET) for PH sensing

In this paper, we report on the effect of carboxyl- and amine terminations on a boron-doped diamond surface (BDD) in relation to pH sensitivity. Carboxyl termination was achieved by anodization oxidation in Carmody buffer solution (pH 7). The carboxyl-terminated diamond surface was exposed to nitrogen radicals to generate an amine-terminated surface. The pH sensitivity of the carboxyl- and amine-terminated surfaces was measured from pH 2 to pH 12. The pH sensitivities of the carboxyl-terminated surface at low and high pH are 45 and 3 mV/pH, respectively. The pH sensitivity after amine termination is significantly higher—the pH sensitivities at low and high pH are 65 and 24 mV/pH, respectively. We find that the negatively-charged surface properties of the carboxyl-terminated surface due to ionization of –COOH causes very low pH detection in the high pH region (pH 7–12). In the case of the amine-terminated surface, the surface properties are interchangeable in both acidic and basic solutions; therefore, we observed pH detection at both low and high pH regions. The results presented here may provide molecular-level understanding of surface properties with charged ions in pH solutions. The understanding of these surface terminations on BDD substrate may be useful to design diamond-based biosensors.

Vertical-type two-dimensional hole gas diamond metal oxide semiconductor field-effect transistors

Power semiconductor devices require low on-resistivity and high breakdown voltages simultaneously. Vertical-type metal-oxide-semiconductor field-effect transistors (MOSFETs) meet these requirements, but have been incompleteness in diamond. Here we show vertical-type p-channel diamond MOSFETs with trench structures and drain current densities equivalent to those of n-channel wide bandgap devices for complementary inverters. We use two-dimensional hole gases induced by atomic layer deposited Al2O3 for the channel and drift layers, irrespective of their crystal orientations. The source and gate are on the planar surface, the drift layer is mainly on the sidewall and the drain is the p+ substrate. The maximum drain current density exceeds 200u2009mAu2009mm−1 at a 12u2009µm source-drain distance. On/off ratios of over eight orders of magnitude are demonstrated and the drain current reaches the lower measurement limit in the off-state at room temperature using a nitrogen-doped n-type blocking layer formed using ion implantation and epitaxial growth.

Heteroepitaxial Diamond Field-Effect Transistor for High Voltage Applications

The exceptional performance of diamond-based field-effect transistor technology is not restricted to devices that use single crystalline diamond alone. This letter explores the full potential of the heteroepitaxial diamond field-effect transistor (HED-FET). HED-FET devices were fabricated with a long gate–drain length (<inline-formula> <tex-math notation=LaTeX>

Evaluation of high frequency performance of ALD-Al 2 O 3 2DHG diamond MOSFET for high power at high voltage operation

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Vertical 2DHG Diamond MOSFET with improvement the structure for high breakdown voltage and miniaturization

</tex-math></inline-formula>) configuration using C–H bonded channels, and a high maximum current density of 80 mA/mm and a high <inline-formula> <tex-math notation=LaTeX>

Influence of SiO 2 thin films formed on the hydrogen-terminated diamond surface on two-dimensional-hole-gas

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improvement of vertical type 2DHG diamond FET

</tex-math></inline-formula> ratio of 10⁹ were achieved. Additionally, the HED-FETs showed an average breakdown voltage of ≥500 V and comparatively high breakdown voltage of more than 1 kV. This letter represents a significant step toward the realization of the potential of widely available heteroepitaxial diamond for use in FET applications.