New Diamond and Frontier Carbon Technology Vol. 17, No. 4 2007 MYU Tokyo NDFCT 540 * Corresponding author: e-mail: kawarada@waseda.jp 201 Microwave Operation of Diamond Metal-Insulator-Semiconductor Field-Effect Transistors Fabricated on Single-Crystal Chemical Vapor Deposition Substrate Kazuyuki Hirama, Hidenori Takayanagi, Shintaro Yamauchi, Hitoshi Umezawa 1 and Hiroshi Kawarada * School of Science and Engineering, Waseda University, 3-4-1 Ohkubo, Shinjuku-ku, Tokyo 169-8555, Japan 1 National Institute of Advanced Industrial Science and Technology (AIST), Diamond Research Center, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan (Received 19 April 2007; accepted 1 November 2007) Key words: diamond, hydrogen termination, RF, large signal, MISFET Diamond metal-insulator-semiconductor field-effect transistors (MISFETs) were MISFETs, and the RF power density was 2.14 W/mm at 1 GHz. This value is comparable to those of GaAs FETs and Si lateral-diffusion metal-oxide-semiconductor the highest cutoff frequency (f T ) of 30 GHz was obtained in 0.3-μm-gate-length (L G ) MISFET. The carrier velocity, which is extracted from the relationship between f T and L G , reached 6×10 6 cm/s. 1. Introduction Diamond has remarkable material properties, such as a wide band gap (5.5 eV), a 7 V/cm) and a high carrier velocity (hole: 1×10 7 cm/s, electron: 2×10 7 cm/s). Therefore, diamond is one of the most promising wide-band-gap semiconductors for high-power and high-frequency applications. However, improvements in device performance have been hampered by high activation energies (0.37 eV for boron, 0.63 eV for phosphorus). Impurity resistivity diamond substrate.