Diamond FET using high-quality polycrystalline diamond with fT of 45 GHz and fmax of 120 GHz

Using high-quality polycrystalline chemical-vapor-deposited diamond films with large grains (similar to 100 mu m), field effect transistors (FETs) with gate lengths of 0.1 mu m were fabricated. From the RF characteristics, the maximum transition frequency f(T) and the maximum frequency of oscillation f(max) were similar to 45 and similar to 120 GHz, respectively. The fT and f(max) values are much higher than the highest values for single-crystalline diamond FETs. The dc characteristics of the FET showed a drain-current density-I-DS of 550 mA/mm at gate-source voltage V-GS of -3.5 V and a maximum transconductance g(m) of 143 mS/mm at drain voltage V-DS of -8 V. These results indicate that the high-quality polycrystalline diamond film, whose maximum size is 4 in at present, is a most promising substrate for diamond electronic devices.