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.

A K-band monolithic driver amplifier with equalizer circuits has been developed. It is necessary for the equalizer circuit to be low losses in the high-frequency range and for its S21 values to increase as the operation frequency increases. In order to realize these features, it is desirable for the equalizer to have element location considering high-frequency current flows. In this paper, we present a novel low-loss, high-pass equalizer circuit layout that has superior characteristics in the high-frequency range. We used a high-pass filter as the equalizer circuit and performed a detailed evaluation of the high-frequency characteristics of the filter circuit test element groups (TEGs) for three layout types. It was found that the best filter circuit layout for the three types consisted of two capacitors and one resistor, placed with parallel connections. The resistor is located at the center and the capacitors are located at both sides of the resistor. This filter is called the CRC-type in this paper. An MMIC test sample, a K-band monolithic amplifier with CRC-type filter circuits, was fabricated. The amplifier had a gain of 21.6 dB, a Rollett stability factor K of 28.9, an input VSWR of 1.63, an output VSWR of 1.92, and a 1 dB compressed output power of 22.6 dBm at 26 GHz.

A GaAs HEMT with flip-chip interconnections using a suitable transmission line has been developed. The underfill resin, which was not used for the conventional flip-chip interconnection structure, was adopted between GaAs chip and assembly substrate to obtain high reliability. The underfill resin is effective in relaxing the thermal stress between the chip and the substrate and in encapsulating the chip. There are various possible ground current paths for the GaAs chip in the structure with flip-chip interconnections. An actual ground current path is determined depending on the transmission line type for the chip. For an active device, it is important to utilize an assembly structure capable of realizing excellent high-frequency characteristics. In addition, each transmission line for the chip has its own transmission characterizations such as characteristic impedance. Therefore, it is necessary to choose a suitable transmission line for the chip. We evaluated the high-frequency characteristics of the HEMT test element groups (TEGs) with flip-chip interconnection for three types of transmission lines: with a microstrip line (MSL), with a coplanar waveguide (CPW), and with an inverted microstrip line (IMSL). All three types of TEGs had similar values of a maximum available power gain (MAG) at 30 GHz. However, it was found that the IMSL-type TEG, which had superior characteristics in high-frequency ranges of more than 30 GHz, is the most suitable type. The IMSL-type TEG had an MAG of 10.02 dB and a Rollett stability factor K of 1.20 at 30 GHz.