IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 54, NO. 11, NOVEMBER 2007 2843 AlGaN/GaN HEMTs on a (001)-Oriented Silicon Substrate Based on 100-nm SiN Recessed Gate Technology for Microwave Power Amplification Sanae Boulay, Salim Touati, Abdourahmane A. Sar, Virginie Hoel, Christophe Gaquière, Jean-Claude De Jaeger, Sylvain Joblot, Yvon Cordier, Fabrice Semond, and Jean Massies Abstract—AlGaN/GaN high-electron mobility transistors on (001)-oriented silicon substrates with a 0.1-μm gamma-shaped gate length are fabricated. The gate technology is based on a silicon nitride (SiN) thin film and uses a digital etching technique to perform the recess through the SiN mask. An output current density of 420 mA/mm and an extrinsic transconductance g m of 228 mS/mm are measured on 300-μm gate-periphery devices. An extrinsic cutoff frequency f t of 28 GHz and a maximum oscilla- tion frequency f max of 46 GHz are deduced from S-parameter measurements. At 2.15 GHz, an output power density of 1 W/mm that is associated to a power-added efficiency of 17% and a linear gain of 24 dB are achieved at V DS = 30 V and V GS = -1.2 V. Index Terms—AlGaN/GaN, high electron mobility transistors (HEMTs), microwave devices, Si (001). Manuscript received February 9, 2007; revised June 29, 2007. This work was supported in part by the French Office “Ministère de l’Economie, des Finances et de l’Industrie” under Project “Nano 2008.” The review of this paper was arranged by Editor M. Anwar. S. Boulay was with the Institut d’Electronique de Microélectronique et de Nanotechnologie, Unité mixte de Recherche, Centre National de la Recherche Scientifique (CNRS) 8520, Université des Sciences et Technologies de Lille, 59652 Villeneuve d’Ascq, France. She is now with the University of Manchester, Manchester, M601QD, U.K. S. Touati was with the Institut d’Electronique de Microélectronique et de Nanotechnologie, Unité mixte de Recherche, Centre National de la Recherche Scientifique (CNRS) 8520, Université des Sciences et Technologies de Lille, 59652 Villeneuve d’Ascq, France. He is now with Delfmems, 59650 Villeneuve d’Ascq, France. A. A. Sar was with the Institut d’ Electronique de Microélectronique et de Nanotechnologie, Unité mixte de Recherche, Centre National de la Recherche Scientifique (CNRS) 8520, Université des Sciences et Technologies de Lille, 59652 Villeneuve d’Ascq, France. He is now with the University of Groningen, 9700 AB Groningen, The Netherlands. V. Hoel, C. Gaquière, and J.-C. De Jaeger are with the Institut d’Electronique de Microélectronique et de Nanotechnologie/THALES, IEMN, GaN, Elec- tronics, Research (TIGER), Unité Mixte de Recherche, Centre National de la Recherche Scientifique (CNRS) 8520, Université des Sciences et Technologies de Lille, 59652 Villeneuve d’Ascq, France (e-mail: Virginie.hoel@iemn.univ- lille1.fr). S. Joblot is with the University of Nice Sophia-Antipolis, 06103 Nice, France, the CRHEA-CNRS, 06560 Valbonne, France, and also with STMicro- electronics, 38926 Crolles, France. Y. Cordier, F. Semond, and J. Massies are with the Centre de Recherche sur l’Hétéroépitaxie et ses Applications (CRHEA), CNRS, 06560 Valbonne, France. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TED.2007.907189 I. INTRODUCTION A lGaN/GaN high-electron mobility transistors (HEMTs) represent the most promising devices for microwave and millimeter-wave power applications. In this paper, devices are fabricated on a (001)-oriented silicon substrate. Up to now, the Si(111) orientation, which provides a hexagonal symmetry surface, has been preferred for GaN-based devices grown on silicon because it is more suitable for the epitaxial growth of a wurtzite phase. Several reports concerning the performance of HEMT structures have demonstrated the relevance of this approach [1]–[3]. Nevertheless, among the existing silicon ori- entations, the (001) orientation is the one that is most widely used in silicon mainstream technology and presents advantages for processing and integration, including the use of locally misoriented areas. However, the square surface symmetry of Si(001) and the presence of two types of terraces with a 2 × 1 reconstruction alternatively rotated by 90 ◦ induce the growth of hexagonal GaN with two orientations rotated by 30 ◦ [4], [5]. In previous studies, the growth by molecular beam epitaxy (MBE) of AlGaN/GaN HEMTs on Si(001) demonstrated a layer quality approaching that obtained from materials grown on Si(111) [4], [6], [7]. Devices with a 3-μm gate length were reported with drain current and transconductance exceeding 500 mA/mm and 120 mS/mm, respectively. The goal of this paper is to demonstrate the power and frequency capabilities of short-gate-length devices. The gamma-gate technology based on nitride, permitting a high yield for short-gate fabrication, is proposed. In this case, the 0.1-μm gate foot is surrounded by silicon nitride (SiN), and the top of the gate is supported by SiN. This process provides a good control of the gate length. The main interest is AlGaN etching through the SiN opening. Digital etching is chosen to perform the recess using SiN as a mask. The main drawback is the increase of the parasitic capacitive elements due to the SiN layer. In this paper, the state- of-the-art microwave and power performances of AlGaN/GaN devices on highly resistive silicon (001) substrate are reported. It opens a new field of interest for GaN-based devices on silicon substrates. Due to the commonly used Si(001) orientation, it makes GaN-based HEMTs well suited for processing and integration in silicon mainstream technology. The growth and device processing are first described and then followed by the presentation of microwave device performances. Finally, pulsed current–voltage (I –V ) measurements and correlated large-signal results are given. 0018-9383/$25.00 © 2007 IEEE