In this paper, we describe the operation of circuits capable of more than 40-Gbit/s that we have developed using InP HEMT technology. For example, we succeeded in obtaining 43-Gbit/s operation for a full-rate 4:1Multiplier (MUX), 50-Gbit/s operation for a Demultiplexer (DEMUX), 50-Gbit/s operation for a D-type flip-flop (D-FF), and a preamplifier with a bandwidth of 40 GHz. In addition, the achievement of 90-Gbit/s operation for a 2:1MUX and a distributed amplifier with over 110-GHz bandwidth indicates that InP HEMT technology is promising for system operations of over 100 Gbit/s. To achieve these results, we also developed several design techniques to improve frequency response above 80 GHz including a symmetric and separated layout of differential elements in the basic SCFL gate and inverted microstrip.

We fabricate and characterize a GaAsSb/InGaAs backward diode (BWD) toward a realization of high sensitivity zero bias microwave rectification for RF wave energy harvest. Lattice-matched p-GaAsSb/n-InGaAs BWDs were fabricated and their current-voltage (I-V) characteristics and S-parameters up to 67 GHz were measured with respect to several sorts of mesa diameters in μm order. Our theoretical model and analysis are well fitted to the measured I-Vs on the basis of WKB approximation of the transmittance. It is confirmed that the interband tunneling due to the heterojunction is a dominant transport mechanism to exhibit the nonlinear I-V around zero bias regime unlike recombination or diffusion current components on p-n junction contribute in large current regime. An equivalent circuit model of the BWD is clarified by confirming theoretical fitting for frequency dependent admittance up to 67 GHz. From the circuit model, eliminating the parasitic inductance component, the frequency dependence of voltage sensitivity of the BWD rectifier is derived with respect to several size of mesa diameter. It quantitatively suggests an effectiveness of mesa size reduction to enhance the intrinsic matched voltage sensitivity with increasing junction resistance and keeping the magnitude of I-V curvature coefficient.

A wide-bandwidth fundamental mixer operating at a frequency above 110GHz for precise spectrum analysis was developed using the InP HEMT technology. A single-ended resistive mixer was adopted for the mixer circuit. An IF amplifier and LO buffer amplifier were also developed and integrated into the mixer chip. As for packaging into a metal block module, a flip-chip bonding technique was introduced. Compared to face-up mounting with wire connections, flip-chip bonding exhibited good frequency flatness in signal loss. The mixer module with a built-in IF amplifier achieved a conversion gain of 5dB at an RF frequency of 135GHz and a 3-dB bandwidth of 35GHz. The mixer module with an LO buffer amplifier operated well even at an LO power of -20dBm.

We developed a 300-GHz high gain amplifier MMIC in 75-nm InP high electron mobility transistor technology. We approached the issues with accurate characterization of devices to design the amplifier. The on-wafer through-reflect-line calibration technique was used to obtain accurate transistor characteristics. To increase measurement accuracy, a highly isolated structure was used for on-wafer calibration standards. The common source amplifier topology was used for achieving high gain amplification. The implemented amplifier MMIC exhibited a gain of over 25 dB in the 280-310-GHz frequency band.