Metal Insulator Semiconductor (MIS)-based III-Nitride transistors are promising for high frequency applications due to their high current and high breakdown voltage. Two MIS-based Field Effect Transistors, namely AlN/GaN and in-situ Si₃N₄/AlN/GaN MISFETs were studied based on simulation, fabrication, characterization and modeling.

AlN/GaN MISFETs with 1 µm long gates were fabricated and showed maximum current density (I_DSmax) of 380 mA/mm and transconductance (g_mo) of 85 mS/mm. Power characteristics showed output power of 850 mW/mm with 23.8% PAE at 2 GHz. This is the first report on the power performance of AlN/GaN MISFETs. Improvements of AlN/GaN MISFETs characteristics were achieved with in-situ deposited Si₃N₄ for the first time. Fabricated Si₃N₄/AlN/GaN MISFET (1µm) showed I_DSmax of 403 mA/mm and g_mo of 206 mS/mm. f _T and f_MAX were 10.2 GHz and 32.3 GHz respectively, which are a factor of 2 to 3 improvement. 150nm long gate devices on Si₃N ₄/AlN/GaN MISFETs exhibited promising high frequency characteristics with f_T = 50 GHz and f_MAX = 110 GHz.

A wideband balanced low noise amplifier with AlGaN/GaN HEMTs was reported for the first time, using Coplanar waveguide (CPW) Lange coupler. The LNA demonstrated broad bandwidth of 3–16 GHz and high gain of 20 dB with a minimum noise figure of 4 dB. High linearity was demonstrated with 38 dBm of OIP3 at 8 GHz.

Al_xGa_1–xN/GaN superlattice diodes were designed, fabricated and measured, DC measurement showed a stable Negative Differential Resistance (NDR) with 1.3 peak-to-valley ratio for the first time with GaN-based superlattice diode. C-V measurements showed negative capacitance effects, which are possibly caused by carrier trapping and emission in the superlattice.

Using the developed integrated device fabrication technology, integrated CPW-based sensors were studied for complex permittivity measurements of liquids, cell media and living cell suspensions. Commonly used cell media are characterized over the frequency range of 1 ∼ 32 GHz for the first time. Dimethyl sulfoxide toxicity tests on cell suspensions showed time dependent permittivity changes. This opens the way to the integration of microwave semiconductors and sensors based on III-Nitride technology due to biocompatibility, chemical inertness, high sensitivity in charge sensing and optical monitoring.