Research On InP-Based HEMT And Millimeter-Wave Monolithic Ampliifer Circuits

InP-based high electron mobility transistors (HEMTs) have shown extremely highelectron mobility, superior noise figure, low power consumption and high gainperformance, making them as the competitive candidates for millimeter waveapplications. In this dissertation, critical process, device fabrication and monolithicamplifier circuits for InP-based HEMTs have been studied. The main results aresummarized as follows:1. Critical fabrication technologies for InP-based HEMT have been developed: A)69nm T-shapped gate is successfully developed in PMGI/ZEP520A/PMGI/ZEP520Aby self-aligned exposure method, which avoids alignment deviation, decreases exposuretime and improves etch-resistant ability. B) Comparative experiments suggest thatTi/Pt/Au non-alloyed ohimic contact exhibits superior thermal stability and surfacemorphology, and the non-alloyed contact resistance is0.058Ω·mm. C) A series ofetching experiments have been carried out. The gate recess was formed by selective wetchemical etching. Etching selectivity ratio of InGaAs over InAlAs can exceed to100byadjusting the mixing proportion of succinic acid and hydrogen peroxide. The lowdamage dry-etching of InP stopper layer by ICP is explored to decrease gate-channelvertical distance and simultaneously ensure the protective effect of InP layer to theexposed gate-recess region.2. Based on the developed critical technologies, InP-based HEMTs have beensuccessfully fabricated on the lattice-matched epitaxial layer designed and optimized byourselves, which are quite suitable for W-band circuits. The current gain cutofffrequency (fT) and the maximum oscillation frequency (fmax) are150GHz and201GHzfor devices without InP etching-stop layer. With regard to ones with InP etching-stopperlayer, fTand fmaxare164GHz and389GHz, but decrease to135GHz and325GHzafter passivation.3. A full set of3inch InP-based HEMT MMIC process has been established,which includes: InP-based HEMT, TaN thin film resistance, Si3N4MIM capacitance,CPW transmission line and airbridges. It is suitable for the design and fabrication ofmillimeter wave integrated circuits.4. The impact of gate-recess lateral width and Si3N4passivation process on the DC and RF characteristics of InP-based HEMTs have been discussed to providetheoretical guidance for the optimization of device. The dependence of frequency andnoise characteristics on dimension and bias condition has been investigated to directchoosing the appropriate device and bias condition for millimeter-wave circuit design.5. Two chips of W-band monolithic amplifier circuits have been designed andfabricated in InP-based HEMT MMIC technology. The designed W-band low noiseamplifier is realized in cascode configuration and coplanar waveguid topology, leadingto a compact chip-size of0.992mm0.987mm and an excellent small-signal gain of15.2dB at95GHz. The noise figure is4.3dB at87.5GHz, and the saturated outputpower is8.05dBm at88GHz. The two-stage W-band cascode amplifier has a chip-sizeof1.85mm×0.932mm and a small-signal gain of25.7GHz at106GHz. Inter-digitalcoupling capacitor blocks low frequency signal, thus enhancing the stability of amplifier.The successful design experiments indicate that the InP-based HEMT technology has agreat potential for W-band applications.