In this paper, we report a reduction in the access resistance of InP/InGaAs composite-channel metal-oxide-semiconductor field-effect-transistors (MOSFETs) with a back-source electrode. The source region has two electrodes. The source electrode on the surface side is connected to the channel through a doped layer and supplies the electrons. The back-source electrode is constructed under the channel layer and is insulated from the doped layer in order to avoid current leakage. The function of the back-source electrode is to increase the carrier concentration in the channel layer of the source region. In the simulation, the electron density in the channel layer is almost doubled by the effect of the back-source voltage. The fabricated III-V MOSFET has a channel length of 6 µm. A 6% increase in the maximum drain current density (Id) and a 6.8% increase in the transconductance (gm) (Vd = 2 V) are observed. The increase in the carrier density in the channel is estimated to be 20% when the applied voltage of the back-source electrode is 6 V.

We report 0.15-µm T-shaped gate MODFETs using BCB (Benzocyclobutene) as low-k spacer dielectric material. The RF performance of pseudomorphic MODFET was improved by reducing the gate fringing capacitance using low-k material. The BCB film was deposited by plasma CVD technique at 100C and was patterned by lift-off technique. The dielectric constant of BCB film deposited by plasma CVD was confirmed 2.7, which is equal to that of spin-coated BCB, and is 35% lower than that of conventional SiO2. The leakage current was 4.710-5 A/cm2 at 3.6 MV/cm and was low enough for spacer material. 0.15-µm T-shaped gate MODFETs were fabricated by using BCB spacer and phase-shift lithography technique. More than 20 GHz increase of fmax was obtained in comparison with conventional SiO2 spacer by reducing the gate fringing capacitance.

The authors have developed V-band high electron mobility transistor (HEMT) MMICs adopting benzo-cyclo-butene (BCB) thin-film layers on GaAs substrates. Since the BCB thin-film layers, which can change the thickness of arbitrary parts on a circuit, are used for these MMICs, both a thin-film microstrip (TFMS) line, offering the advantages of great flexibility in layout and small size, and a coplanar waveguide (CPW), offering the advantage of low loss, can be used according to the purpose of the MMIC. Here we introduce the four types of V-band MMICs that we fabricated: low noise amplifier (LNA), mixer, voltage controlled oscillator (VCO), and power amplifier (PA). The optimum transmission lines were chosen from the TFMS line and the CPW for these MMICs. Miniaturization of the LNA MMIC and the mixer MMIC were attained by adopting the TFMS line, whereas adoption of the CPW enabled the VCO MMIC to achieve high performance. These results indicate that it is important to choose the optimum transmission line according to the purpose of the circuit function for each MMIC. It was confirmed that these newly developed MMICs using the BCB thin-film dielectric layers are attractive for millimeter-wave applications.

This paper describes a new millimeter-wave hybrid integrated circuit (HIC) technology which applies a thin film multi-layered dielectric substrate and flip-chip bonding technology employing stud bump bonding (SBB). We have previously proposed and demonstrated a novel HIC structure, named millimeter-wave flip-chip IC, (MFIC), applying an excellent dielectric material of benzocyclobutene (BCB) thin film and flip-chip bonding. In this paper, an advanced thin film multi-layer process using non-photosensitive BCB was newly developed. Characteristics of the transmission lines and the built-in MIM capacitor within the multi-layered structure were discussed. Furthermore, stud bump bonding was newly adapted to the MFIC as a flip-chip method, and the millimeter-wave characteristics of the bumps were examined. Using these technologies, we demonstrate characteristics of a miniaturized 25 GHz down converter MFIC. Our newly proposed HIC structure enabled us to bring down chip size to less than 1/3 of our conventional structure. Finally, we discuss future possibilities for high performance multi-chip-modules (MCMs) using SBB technology as a further improved HIC for compact millimeter-wave radio equipment.

A 60-GHz-band monolithic HEMT amplifier for which BCB thin film layers are adopted on GaAs substrate has been developed. The MMIC utilized a thin film microstrip line for the bias circuit and a coplanar waveguide for the RF circuit. The coplanar waveguide has the advantage of low loss, whereas the thin film microstrip line has the advantage of small size. Two different types of transmission lines were selected to coexist in the monolithic amplifier. As a result, the MMIC achieved high gain over a wider frequency range at a small size. This MMIC had a gain of over 15 dB in a frequency bandwidth of 11 GHz. In particular, the high-frequency characteristics of the transmission lines and the HEMTs were evaluated in detail for the conventional MMIC structure and the new MMIC structure. It was confirmed that this newly developed MMIC using BCB thin film layers is attractive for millimeter-wave applications.