Tez No	İndirme	Tez Künye	Durumu
508865		High performance InP-based HEMTs with dry etched gate recess / Yazar:HALİT CELALEDDİN Danışman: Prof. WERNER BäCHTOLD ; Prof. H. MELCHIOR Yer Bilgisi: EIDGENOSSISCHE TECHNISCHE HOCHSCHULE ZURICH (ETH) / YURTDIŞI ENSTİTÜ Konu:Bilgisayar Mühendisliği Bilimleri-Bilgisayar ve Kontrol = Computer Engineering and Computer Science and Control ; Bilim ve Teknoloji = Science and Technology Anahtar Kelime:	Onaylandı Doktora İngilizce 1998 132 s.
During the course of this work, a reproducible fabrication process for InP-based high electron mobility transistors (HEMTs) with 0.2 mm gate length has been developed. Millimeter-wave circuits were designed and fabricated using these transistors. The results demonstrate the potentially high impact of the technology for future microwave communication applications. First, a methane-hydrogen (CH4/H2) reactive ion etching (RIE) process was developed for selective gate recess etching of lattice-matched InGaAs/InAlAs/InP HEMTs. Chemical and physical analysis of the dry etched surface revealed changes in the stoichiometry and a slight increase in surface roughness. These effects lead to poor quality Schottky contacts and consequently to high gate diode leakage currents. The surface damage problems were overcome using a post- RIE cleaning process established for this application. The high selectivity of the dry etching process leads to superior uniformity of the HEMT devices when compared with conventional wet etching techniques. This is a key issue for transistors in microwave applications. The resulting InP HEMTs showed transit frequencies ft of up to 150 GHz and maximum frequencies of oscillation fmax of up to 220 GHz. The minimum noise figure Fmin was measured to be as low as 0.8 dB at 26 GHz with an associated gain Gass of 9 dB. These results are state-of-the art values for 0.2 mm InP HEMT technology. The dry etched HEMTs showed comparable or better electrical and microwave noise performance than corresponding wet etched reference devices. This indicates that the channel of the devices is not damaged by the dry etching process. Low-frequency noise characterization of the HEMT devices revealed a significantly lower normalized 1/f noise for the dry etched HEMTs at all bias conditions. By varying the temperature between 77 and 340 K, four electron traps could be identified in the drain current noise spectra for both dry and wet etched devices. No additional traps were introduced by the dry etching step. The concentration of the main trap in the Schottky layer is one order of magnitude lower for the dry etched HEMTs. Hydrogen passivation of the deep levels is suggested as the cause for the trap density reduction. The kink effect, associated with the output characteristics of HEMTs, was found to be significantly reduced for dry etched devices. This observations provides further evidence of trap passivation during dry etching. An accurate small-signal electrical and noise model of the InP HEMT was developed for use in the design of millimeter-wave circuits. Special equivalent circuits for discontinuities in the coplanar waveguide lines were developed for this work since there were no reliable coplanar models available in the standard software packages used for circuit design. The simulations of the designed circuits show a good agreement with measurements on the fabricated circuits. Several integrated amplifiers, key elements of microwave communication systems, were fabricated using dry etched HEMTs. A single-stage amplifier with serial impedance matching networks yielded a gain of 11.9 dB at 61 GHz, a third order input intercept point IP3 at 19.5 dBm and a 1-dB compression point at 8.7 dBm output power. A low-noise amplifier (LNA) showed a noise figure of 2.9 dB at 42 GHz with a gain of 9.2 dB. A dielectric resonator oscillator (DRO) operating in the frequency range of 23.2-24.8 GHz was designed and fabricated using dry and wet etched InP HEMTs. The active oscillator was designed in coplanar waveguide technology. This monolithic microwave integrated circuit (MMIC) was connected to a microstrip line for external coupling to the mechanically tunable dielectric resonator (DR). An output power of 12 dBm and a phase noise of -107 dBc/Hz at 100 kHz offset from the carrier were measured for DROs with dry etched HEMTs. These values were superior to those obtained with wet etched devices. The 10 dB reduction in phase noise is attributed to the hydrogen passivation of deep level traps during dry gate recess etching. The results of this work demonstrate the feasibility of dry etching technology for the fabrication of high-performance MMICs.