In this work, using 0.2 µm GaAs modulation doped FET (MODFET), a high performance downconverter MMIC was developed for direct broadcasting satellite (DBS) applications. The downconverter MMIC showed a noise figure of 4.3 dB which is lower by 5 dB than conventional ones, and required only a low LO power of -10 dBm for normal DBS operation. At a low LO power of -10 dBm, the power consumption was 175 mW, which is lower than 50 percent of conventional ones. The frequency response of conversion gain exhibited a low gain ripple of 0.9 dB, and the LO leakage power was suppressed to a lower value than -30 dBm under a LO input power of -10 dBm. The fabricated chip exhibited a small size of 0.840.9 mm2. The objectives of this work are to improve the traditional direct broadcasting satellite (DBS) downconverters by an efficient circuit design and to describe the techniques employed in the design.

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.