Hydrogen-terminated diamond surface shows p-type conduction even if it is not intentionally doped. Metal-semiconductor (MES) and metal-insulator-semiconductor (MIS) field-effect transistors have been fabricated on hydrogen-terminated diamond surface conductive layers, and their high-frequency performance is demonstrated. Nano-fabrication on a hydrogen-terminated diamond surface is performed by controlling surface adsorbates, using an atomic force microscope (AFM) technique. Insulated areas are successfully obtained by changing hydrogen termination to oxygen termination. Single hole transistors are also fabricated by AFM oxidation, and are operated at liquid nitrogen temperature (77 K). Polycrystalline diamond FET is operated in electrolyte solution. A perfect pinch-off and saturated current-voltage characteristics have been obtained for bias voltages within the potential window. The threshold voltages are almost constant in the electrolytes with different pH values of 7−13. Using this pH insensitive surface, ion selective regions can be fabricated to form transistor-based biosensors.
