ダイヤモンド薄膜表面の導電性制御によるハイパワー高周波トランジスタの開発

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Four of the elemental techniques were developed to improve the performance and the stabilization of the diamond transistors. (1)Fabrication technique of the low resistive layer, less than 1kΩ/sq, utilizing focused ion beam. (2)Deposition technique of the thermally stable ultrahigh-concentration boron doped diamond(specific resistance : 2×10^<-4>[Ωcm], boron concentration 1.4×10^<22>cm^<-3>]). (3)Film formation technique of high quality Al_2O_3 gate insulator with very low gate leakage current, three orders of magnitude smaller than the conventional CaF_2 insulator film. (4)Control of the threshold voltage with ozone treatment aimed at low dissipation power.De-embedding method, the most widely used method for the evaluation of RF devices, was employed to evaluate the intrinsic characteristics of the diamond MISFETs. And the normal effective field dependency of the mobility of the hole accumulation layer was clarified aimed at analyzing the carrier traveling mechanism in the accumulation … More layer. As device fabrication process technology, the self-alignment technique for the fabrication of the fine gate with less than 0.2μm gate length, and the T-shape gate electrode fabrication process for lowering the gate resistance were established.The diamond MISFETs were fabricated utilizing the fine process technology described before. An f_T cut-off frequency of 30GHz and an f_<max> cut-off frequency of 48GHz were obtained for the 0.15μm gate length MISFETs. And the fabrication of diamond MISFETs with Al_2O_3 gate insulator has been succeeded. They yield f_T=30GHz and f_<max>=6oGHzz for the thickness of gate insulator of 3nm and the gate length of 0.3μm. In addition, we have employed load-pull measurement on diamond MISFETs for the first time and obtained 2.14W/mm output power density at 1GHz for the gate length of 100μm and the gate length of 0.3μm. The value is superior to the reported power density of GaAs FETs or Si LDMOS ; therefore it confirms the advantage of the diamand MISFETs as high power RF transistor. Less