A K-band AlGaN/GaN HFET MMIC amplifier on sapphire using novel superlattice cap layer

We have developed a K-band AlGaN/GaN HFET MMIC amplifier by applying an AlGaN/GaN superlattice (SL) capped structure on sapphire substrate. Owing to the lowest (0.4 Ω · mm) source resistance of AlGaN/GaN HFETs, the HFETs exhibited excellent DC and RF characteristics, and sufficient ability to operate in the K-band frequency range is obtained. The fabricated MMIC with a CPW-line structure exhibited a small-signal gain higher than 10 dB with a 3-dB bandwidth of 20-24.5 GHz and that of 13 dB at 21.6GHz when biased at a supply voltage of 7 V. The 1dB compression point (P_1dB) referred to output of 15.4 dBm at 21.6 GHz was obtained. This work is the first report of MMIC amplifier fabricated on sapphire successfully operating in the K band.