A one-by-four static frequency divider using AlGaAs/GaAs heterojunction bipolar transistors (HBTs) was designed to operate at a bias condition that gave a maximum cutoff frequency fT and a maximum oscillation freqency fmax. The fT and fmax applied to the divider were 68 GHz and 56 GHz, respectively. As a result of the tests, the circuit operated up to 34.8 GHz at a power supply voltage of 9 V and power dissipation of 495 mW. A low minimum input signal power level of 0 dBm was also achieved.

This paper describes small AlGaAs/GaAs HBT's for low-power and high-speed integrated circuits. The device fabrication is based on a new bridged base electrode technology that permits emitter width to be defined down to 1 µm. The new technology features oxygen-ion implantation for emitter-base junction isolation and zinc diffusion for extrinsic base formation. The oxygen-ion implanted emitter-base junction edge has been shown to provide a periphery recombination current much lower than that for the previous proton implanted edgs, the result being a much higher current gain particularly in small devices. The zinc diffusion offers high device yield and good uniformity in device characteristics even for a very thin (0.04 µm) base structure. An HBT with emitter dimensions of 12.4 µm2 yields an fT of 103 GHz and an fmax of 62 GHz, demonstrating that the new technology has a significant advantage in reducing the parasitic elements of small devices. Fabricated one-by-eight static frequency dividers and one-by-four/one-by-five two-modulus prescalers operate at frequencies over 10 GHz. The emitters of HBT's used in the divider are 12.4 µm2 in size, which is the smallest ever reported for AlGaAs/GaAs HBT IC's. These results indicate that the bridged base electrode technology is promising for developing a variety of high-speed HBT IC's.

Josephson junctions with semiconductor Te barriers have been studied. First, the junctions were fabricated with the process including oxidation of the evaporated Te film surface. The process was generally employed to avoid shorts through pinholes in Te film. Intensive studies on the influence of the Te barrier thickness and oxidation conditions on the junction characteristic parameters were made. The Te layer acts not only as the barrier for tunneling, that is the normal tunneling resistance shows exponential dependence on the Te layer thickness, but also induces proximity effect at the metal interface. The effect was found to play an important role in the junction performance. It was also found that, in the oxidation process, Te itself is oxidized and the junction performance is largely influenced by the Te oxide layer existance. In the second step, junctions free from oxide layer, which showed Josephson effect up to the Te barrier thickness of 40 nm, have been fabricated. By employing smooth surfaced Nb bottom electrode as well as the photolithographic technique comprising the trimming process, uniform junctions perfectly free from pinhole shorts have been realized.