We have developed a fabrication technique for high-performance high-thermal-stability InP/InGaAs heterojunction bipolar transistors (HBTs) for use in 40-Gb/s ICs. The HBT's T-shaped emitter electrode structure simplifies the fabrication process and enables high controllability of spacing between the emitter and the base electrodes. A highly-C-doped base, grown by gas-source MBE, and a new Pt-based metal system results in a low base resistance. An InP subcollector suppresses thermal runaway of HBTs at high collector current better than a conventional InGaAs subcollector does. Using these techniques, we fabricated a very-high-performance HBT with an extremely high cutoff frequency fT of 235 GHz. The RF measurements show that the collector current at the peak cutoff frequency is inversely proportional to collector thickness. We also fabricated a static 1/2 frequency divider, that can be used for 40-Gb/s optical transmission systems, operating up to 44 GHz. This divider confirmed that the developed HBT is applicable to 40-Gb/s optical transmission ICs.

A design method for an ultra-wideband bandpass filter (BPF) with four coupled lines has been developed. For demonstration purposes, 50 Ω-matched self-complementary antennas integrated with the ultra-wideband, differential-mode BPF with four coupled lines, a notch filter, and a low-pass filter (LPF) were prepared and tested. An optimized structure for a single-stage, broadside-coupled and edge-coupled four-lines BPF was shown to exhibit up to 170% fractional bandwidth and an impedance transformation ratio of 1.2 with little bandwidth reduction, both analytically and experimentally. Using the optimized structure, 6-stage BPFs were designed to transform the self-complementary antenna's constant input impedance (60πεe- 1/2(Ω)) to 50 Ω without degrading bandwidth. In addition, two types of filter variations--a LPF-embedded BPF and a notch filter-embedded BPF--were designed and fabricated. The measured insertion loss of both filter systems was less than 2.6 dB over the ultra-wideband (UWB) band from 3.1 GHz to 10.6 GHz. The filter systems were embedded in the wideband self-complementary antennas to reject unnecessary radiation over the next pass band and 5-GHz wireless LAN band.

Microwave circuits embedded in a multi-layer resin PCB are demonstrated using low loss resin materials. Resin materials for microwave frequencies were compared with conventional FR-4 with respect to dielectric and conductor loss factors, which proved that losses could be reduced drastically with the low loss material and design optimizations. Baluns, switches and BPFs were designed and fabricated to estimate microwave performances. Measured and simulated insertion losses of the circuits for 2.5 GHz band, were 0.3 dB for a switch, 0.4 dB for a balun and 2.0 dB for a 3-stage Chebyshev BPF. An integration of a switch, a BPF and two baluns was successfully implemented in a multi-layer PCB. Insertion losses of the fabricated integrated circuit were less than 3 dB with 0.1 dB additional loss compared with a sum of individual circuit losses. With estimated results of temperature characteristics and reliability as well as low loss performances, microwave circuits in resin PCBs can be considered as a viable candidate for microwave equipments.