Millimeter-wave and submillimeter-wave MHEMT LNA MMICs

Two metamorphic InAlAs/InGaAs based high electron mobility transistor (MHEMT) technologies have been developed for next generation active and passive millimeter wave imaging applications. The first technology features a 50 nm gate-length in combination with an In0.52Al0.48As/ In0.80Ga0.20As/In0.53Ga0.47As composite channel structure, resulting in an extrinsic transit frequency ft of 400 GHz and a maximum extrinsic transconductance gm, max of 1800 mS/mm. For the second MHEMT technology the gate length was reduced to 35 nm and a single InGaAs channel with an In content of 80 % was used. These modifications result in an ft of more than 500 GHz (Fig. 1) and a gm, max of 2500 mS/mm. The metamorphic HEMTs were grown on 4" semi-insulating GaAs wafers using molecular beam epitaxy (MBE). For the metamorphic buffer a linear graded InxAlyGa1-xAs transition was used. The gate definition was performed using electron beam lithography in a four layer resist (PMMA) process. For millimeter-wave and submillimeter-wave imaging applications requiring low noise figure and broadband gain characteristic, W-band (75-110 GHz), G-band (140-220 GHz) and H-band (220-325GHz) low-noise amplifier (LNA) MMICs were developed. Figure 2 shows the on-wafer measured small-signal gain and noise figure of a two-stage W-band LNA using the 50 nm MHEMT technology. The amplifier circuit was optimized to achieve high gain in combination with a very low noise figure. Therefore a cascode configuration, consisting of a series connection of one HEMT in common source and one in common gate configuration was utilized. The low-noise amplifier circuit demonstrates a linear gain of more than 20 dB and an average room temperature (T = 293 K) noise figure of only 1.9 dB between 80 and 100 GHz. Additionally, a four-stage 210 GHz LNA MMIC was realized based on conventional FETs in common-source configuration. This MMIC achieved a linear gain of more than 16 dB and a state-of-the-art noise figure of 4.8 dB between 180 and 220 GHz, as shown in Fig. 3. Based on our advanced 35 nm MHEMT technology, we could successfully realize first submillimeter-wave monolithic integrated circuits (SMMICs) demonstrating measured gain at 300 GHz, which is the threshold of the submillimeter-wave frequency regime. Fig. 4 shows a chip photograph of a coplanar 270 GHz single-stage LNA SMMIC, featuring a total chip-size of only 0.15 mm2. This circuit achieves a small-signal gain of more than 7 dB at 270 GHz, as illustrated in Fig. 5. Figure 6 shows the on-wafer measured S-parameters of a four-stage 300 GHz LNA SMMIC, demonstrating a linear gain of more than 15 dB between 268 and 306 GHz.