Effects of stress in passivation films on the electrical properties of (0001) AlGaN/GaN HEMTs are numerically analysed in the framework of the edge force model with anisotropical characteristics in elastic properties of group-III nitrides explicitly considered. Practical compressive stresses in passivation films induce negative piezoelectric charges below the gates and bring forth a-few-volt shallower threshold voltages. In addition, the shift in the threshold voltage due to the compressive stress is proportional to LG-1.1-1.5 with gate length LG, which is comparable to the expectation based on the charge balance scheme. These result suggest that passivation films with designed stress might play a crucial role in realising AlGaN/GaN HEMTs with shallow or positive threshold voltages.

We demonstrated the uniformity and stability as well as the high breakdown voltage of 0.1-µm-gate InP HEMTs with a double recess structure. To overcome the drawbacks regarding the uniformity and stability in the double recess structure, an InP passivation layer that functions as an etch-stopper and a surface passivator was successfully applied to the structure. It was confirmed that there was no degradation in the uniformity and stability of device performance for the double recess HEMTs that had the breakdown voltages in the on-state and off-state improved by a factor of 1.6.

A procedure for quickly developing highly integrated multifunctional MMICs by using the three-dimensional masterslice MMIC technology has been developed. The structures and advanced features of this technology, such as miniature transmission lines, a broadside coupler, and miniature function block circuits, enable multifunctional MMICs to be quickly and easily developed. These unique features and basic concept of the masterslice technology are discussed and reviewed to examine the advantages of this technology. As an example of quick MMIC development, an amplifier, a mixer, and a down-converter are fabricated on a newly designed master array.