Diamond RF Transistor Technology with f t =41 GHz and fmax=44 GHz

Initial results for diamond RF transistor technology are presented. Field Effect Transistors (FETs) were fabricated with gate lengths $(\mathbf{L}_{\mathrm{g}})$ ranging from $\mathbf{4}\pmb{\mu}\mathbf{m}$ to 50nm. The FETs have total gate width $(\mathbf{W}_{\mathrm{g}})$ of 40 or $\mathbf{120}\pmb{\mu}\mathbf{m}. \mathbf{L}_{\mathbf{g}}=\mathbf{100\ nm}$ devices show DC drain current $\mathbf{I}_{\mathbf{D}}=\mathbf{600\ mA}/\mathbf{mm} (>\mathbf{V}_{\mathbf{GS}}=-\mathbf{3V},\mathbf{V}_{\mathbf{DS}}=-\mathbf{10V}$ ) with transconductance $\mathbf{g}_{\mathbf{m}}=\mathbf{140mS}/\mathbf{mm} (>\mathbf{V}_{\mathbf{GS}}=-\mathbf{0.3V},\mathbf{V}_{\mathbf{DS}}=-\mathbf{4V}$ ). Small signal S-parameters were measured to evaluate the high-frequency performance of the diamond FETs. Extrinsic $\mathbf{f}_{\mathbf{t}}$ and $\mathbf{f}_{\mathbf{max}}$ were measured to be 41GHz and 44GHz, respectively. Load pull measurements were used to characterize the devices under large signal excitation. The $\mathbf{L}_{\mathbf{g}}=\mathbf{200nm},\ \mathbf{W}_{\mathbf{g}}=\mathbf{40}\pmb{\mu}\mathbf{m}$ device, tested at 2GHz, shows peak efficiency of 30.5% at $\mathbf{V}_{\mathbf{DS}}=-\mathbf{5V}$ . Both peak gain of 19.5dB and peak output power density of 0.66W/mm were achieved at $\mathbf{V}_{\mathbf{DS}}=- \mathbf{30V}$ , Biasing the device at $\mathbf{V}_{\mathbf{DS}}=-\mathbf{15V}$ provides a trade off point for the large signal parameters - gain of ~15dB, efficiency of ~20%, and output power of ~0.5W/mm.