Current-voltage characteristics of in situ doped polycrystalline diamond field-effect transistors

The authors report the first demonstration of a polycrystalline diamond (PCD) FET which exhibits saturation and pinchoff. The PCD material was grown by a microwave enhanced chemical vapor deposition technique. Following room-temperature characterization, the devices were tested at elevated temperatures in atmosphere. As the temperature was increased, the current level increased significantly. At a temperature of 150 degrees C, the zero gate-bias drain-to-source current was -34 nA at -20 V and the channel resistance had dropped to 990 M Omega . The drain to source I-V characteristics were linear at this temperature. Gate voltages were applied in 8-V steps while the drain-to-source voltage was swept from 0 to -30 V. The I-V characteristics clearly showed evidence of saturation. Also, at applied gate biases in excess of 32 V, the active channel is pinched off. The peak transconductance at 150 degrees C was 6.4 nS/mm. Device failure occurred at a temperature above 200 degrees C and was due to failure of the gate oxide layer.