RF and Noise Optimization of Pseudomorphic inP HEMT Technology

Licentiate thesis, 2006

The InGaAs-InAlAs-InP high electron mobility transistor (InP HEMT) is the electronic device utilized for the highest frequency and/or the lowest noise applications known to date for analog transistor-based circuits. Hence it is of both scientific and technological interest to explore the InP HEMT for even further improvement in device performance. This thesis deals with the fabrication, modeling and epitaxial optimization of pseudomorphic InP HEMTs with nominal gate lengths between 50 and 100 nm. In particular, the epitaxial heterostructure of the InGaAs channel and the InAlAs Schottky layer design have been investigated. Furthermore, the integration of the InP HEMTs with passive components in a microstrip monolithic microwave integrated circuit (MMIC) process is reported. Two different channel designs have been studied. InP HEMTs based on 65 % and 80 % indium in the channel exhibited a maximum gm of 0.9 and 1.4 S/mm, respectively. Since the output conductance also increased with increasing indium concentration the RF results were similar for the two channel designs with an fmax and fT of approximately 300 and 200 GHz, respectively. The effect of the Schottky layer thickness on the InP HEMT performance has been investigated with respect to RF and noise performance. An optimum gate-to-channel distance was found with maximum gm, fmax, fT and noise temperature of 1.1 S/mm, 200 GHz, 170 GHz and 140 K respectively, for 2x50 µm devices biased at VDS=0.7 V. Two different one-stage amplifiers have been designed and demonstrated in MMICs based on pseudomorphic InP HEMTs, 300 pF/mm2 silicon nitride metal-insulator-metal (MIM) capacitors and tantalum nitride thin film resistors (TFRs) with sheet resistances of 80-85 Ω/□. A broadband feedback amplifier operating between 0-42 GHz with an average noise figure of 3 dB and a W-band amplifier with a gain above 8 dB from 75-94 GHz were fabricated.