METAMORPHIC HEMT TECHNOLOGY FOR SUBMILLIMETER- WAVE MMIC APPLICATIONS A. LEUTHER, A. TESSMANN, I. KALLFASS, H. MASSLER, R. LOESCH, M. SCHLECHTWEG, M. MIKULLA, O. AMBACHER Fraunhofer Institute for Applied Solid State Physics (IAF), Tullastrasse 72, D-79108 Freiburg, Germany e-mail: arnulf.leuther@iaf.fraunhofer.de Abstract — Metamorphic high electron mobility transistor (mHEMT) technologies with 50 and 35 nm gate length were developed for the fabrication of submillimeter-wave monolithic integrated circuits (S-MMICs) operating at 300 GHz and beyond. Heterostructures with very high electron sheet density of 6.110 12 cm -2 and 9800 cm 2 /Vs electron mobility were grown on 4” GaAs substrates using a graded quaternary InAlGaAs buffer layer. For proper device scaling channel-gate distance and source resistance were reduced. Maximum transconductance of 2500 mS/mm and a transit frequency of 515 GHz were achieved for the 35 nm mHEMT with 2  10 μm gate-width. Already the 50 nm technology allows the realization of S-MMIC operation frequencies up to 320 GHz, the current limit of on-wafer probe availability. A compact four-stage H-band amplifier circuit based on a grounded coplanar waveguide (GCPW) layout is presented in 50 and 35 nm technology, respectively. The 50 nm mHEMT amplifier has a linear gain of 19.5 dB at 320 GHz and more than 15 dB between 240 and 320 GHz. The same amplifier utilizing 35 nm gate-length transistors achieves more than 20 dB gain within the entire H-band from 220 to 320 GHz. I. INTRODUCTION The submillimeter-wave range of the electromagnetic spectrum which means frequencies above 300 GHz is attracting increasing interest in science and technology. The terahertz frequency regime is the transition between electronics and optics. Until recent years the electronic access to submillimeter-wave frequencies was limited to non-amplifying devices like Schottky-diodes. But now due to the progress in transistor technologies submillimeter-wave MMICs (S-MMICs) can be successfully fabricated. This opens up opportunities for new types of applications like high-resolution active and passive imaging systems (Fig.1), high data rate wireless communication links as well as ultra- wideband transmitter and receiver components, e. g. for use in explosive detection spectroscopy or measurement instrumentation. Due to the fairly high absorption of submillimeter-waves in the atmosphere, medium range applications will be limited to the atmospheric windows at 340, 480, and 670 GHz. The relative high absorption coefficient is caused by the excitation of molecular rotation Fig. 1. 220 GHz inverse synthetic aperture radar (ISAR) image of person with gun. The distance between the person on a turn table an the radar system was 170m [1]. modes which on the other hand enables molecule spectroscopy for many different applications. Due to the short wavelength very compact antennas can be used in high resolution imaging or detector systems. Another advantage of the submillimeter-wave is the availability of wide non- restricted frequency bands which can be used in active systems for ultra fast data transfer or radar. Currently, the InGaAs channel high electron mobility transistor (HEMT) is the most advanced semiconductor device technology for S-MMICs [2-4]. Besides the high transistor gain at these frequencies the HEMT has the advantage of the lowest noise figures which is a very important parameter for many system applications. The high frequency performance of the HEMT was continuously improved over the years by reducing the gate length and increasing the In content in the channel layer. The advantages of the higher In concentration up to pure InAs are the higher electron mobility and the better charge confinement due to larger band offsets. InP, GaAs or even Si can be used as substrates for the epitaxial growth of