Tantalum nitride （TAN） and nichrome （NiCr） are the two most common materials used as thin film resistors （TFR） for monolithic microwave integrated circuits （MMIC） based on AlGaN/GaN high electron mobility transistors （HEMTs）. In this study,we compare the reliability of the two materials used as TFRs on a semi-insulation 4H SiC substrate. Through the comparison between NiCr and TaN thin-film resistor materials, we find the square resistor （Rs） of TaN TFR increases as the annealing temperature increases. However, the R s of NiCr TFR shows the opposite trend. We also find the change of the TaN Rs and contacted resistor （Re） is smaller than the NiCr. After O2 plasma exposure in RIE,the TaN R s only decreases 0.7Ω,or about 2.56%, and R c increases 0.1Ω,or about 6.6%, at an annealing temperature of 400℃. In contrast, the NiCr R s and R c show large changes at different annealing temperatures after O2 plasma exposure. In conclusion,TaN is more stable during plasma exposure after 400℃ annealing in N2 ambient.
A 4-12GHz wideband power amplifier,using a balanced configuration with a strip line Lange coupler, is designed and fabricated. This power amplifier shows a maximum continuous wave output power of 29.5dBm at 8GHz center frequency with an associated gain of 8.5dB and a gain flatness of ＋ /- 0.6dB in the 4-12GHz frequency range.
A power amplifier MIC with power combining based on AlGaN/GaN HEMTs was fabricated and measured. The amplifier consists of four 10 × 120μm transistors. A Wilkinson splitters and combining were used to divide and combine the power. By biasing the amplifier at VDS = 40V, IDS = 0.9A, a maximum CW output power of 41.4dBm with a maximum power added efficiency （PAE） of 32.54% and a power combine efficiency of 69% was achieved at 5.4GHz.
