This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. JOURNAL OF MICROELECTROMECHANICAL SYSTEMS 1 Capacitive RF MEMS Switches With Tantalum-Based Materials Anna Persano, Adriano Cola, Giorgio De Angelis, Antonietta Taurino, Pietro Siciliano, and Fabio Quaranta Abstract—In this paper, shunt capacitive RF microelectro- mechanical systems (MEMS) switches are developed in III–V technology using tantalum nitride (TaN) and tantalum pentox- ide (Ta 2 O 5 ) for the actuation lines and the dielectric layers, respectively. A compositional, structural, and electrical character- ization of the TaN and Ta 2 O 5 films is preliminarily performed, demonstrating that they are valid alternatives to the conven- tional materials used in III–V technology for RF MEMS switches. Specifically, it is found that the TaN film resistivity can be tuned from 0.01 to 30 Ω · cm by changing the deposition parameters. On the other hand, dielectric Ta 2 O 5 films show a low leakage- current density of few nanoamperes per square centimeter for E ∼ 1 MV/cm, a high breakdown field of 4 MV/cm, and a high dielectric constant of 32. The realized switches show good actu- ation voltages, in the range of 15–20 V, an insertion loss better than −0.8 dB up to 30 GHz, and an isolation of ∼−40 dB at the resonant frequency, which is, according to bridge length, between 15 and 30 GHz. A comparison between the measured S-parameter values and the results of a circuit simulation is also presented and discussed, providing useful information on the operation of the fabricated switches. [2010-0236] Index Terms—Capacitive switches, RF microelectromechanical systems (MEMS), tantalum nitride (TaN), Ta 2 O 5 . I. I NTRODUCTION T HE RF microelectromechanical systems (MEMS) repre- sent a viable solution to overcome the limitations ex- hibited by semiconductor-based switches (pin diode, FET switches, ...) owing to the very low power dissipation and in- sertion loss, high isolation, and linearity [1]. Moreover, the use of III–V technology for RF MEMS switch fabrication may pave the way for the implementation of future-generation transmit/ receive modules owing to the monolithic integration of MEMS and HEMT components in a single fabrication process [2]. However, in spite of the attractive capabilities, RF MEMS reliability is of major concern for long-term applications, and it is currently the subject of an intense research effort [3]–[7]. To date, the device lifetime is reduced in RF MEMS ohmic switches by the degradation of the metal-to-metal contact be- Manuscript received August 4, 2010; revised November 29, 2010; accepted January 3, 2011. This work was supported in part by the Italian Ministry for Education, University, and Research (MIUR) under Project DM25810 of the Basic Research Investment Fund (FIRB). Subject Editor C.-J. Kim. A. Persano, A. Cola, A. Taurino, P. Siciliano, and F. Quaranta are with the Institute for Microelectronics and Microsystems, National Research Council (IMM-CNR), Unit of Lecce, 73100 Lecce, Italy (e-mail: anna.persano@le. imm.cnr.it). G. De Angelis is with the Institute for Microelectronics and Microsystems, National Research Council (IMM-CNR), Unit of Rome, 00133 Rome, Italy. 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/JMEMS.2011.2107884 tween the actuation electrode and the bridge. This degradation can be due to different phenomena, such as the contamination and the electromigration of materials across the contact, the creeps, the ductile, and the brittle wearing of the contact, and the hardening of the contact area [8]. However, this drawback can be managed by proper design guidelines which allow actu- ation voltages not exceeding 50 V and a switch lifetime beyond one trillion cycles [9], [10]. In capacitive switches, the metal-to- metal contact is eliminated by covering the actuation pad with a dielectric layer, which also offers the benefit to provide a high ratio between the switch capacitance in the down and up states (C down /C up ). However, this dielectric layer usually undergoes charging effects in the area (approximately 100 μm × 100 μm in typical configurations) under the bridge [5], [7], [11]–[13] which can cause stiction phenomena between the dielectric layer and the bridge metal or an increase in the pull-down volt- age, depending on the polarity of the injected charge. Dielectric charging increases with the applied electric field [7], and hence, efforts to control the actuation voltage have been made by the optimization of the bridge fabrication process [14]. Nowadays, most of the technological issues limiting the RF MEMS switches are still open, particularly in III–V technol- ogy, which is much less mature than the Si-based fabrication process. Hence, the investigation of alternative materials with respect to the ones commonly used in III–V technology for both dielectric and actuation components of MEMS switches becomes mandatory. In this paper, RF MEMS shunt capacitive switches in copla- nar configuration are fabricated in III–V technology materials which are alternative to the standard ones. Specifically, films of tantalum nitride (TaN) and tantalum pentoxide (Ta 2 O 5 ) are chosen for the realization of actuation lines and dielectric layers, respectively. This paper is organized as follows. In Section II, the compositional, structural, and electrical charac- terization of TaN and Ta 2 O 5 thin films is reported. Deposition parameters, such as the substrate temperature and the sputtering gas mixture composition, have been varied. The resistivity of TaN films is obtained from Hall-effect measurements, while I –V characteristics allow identifying the conduction mecha- nisms which are responsible for the leakage current in the Ta 2 O 5 films. Capacitance measurements have also been per- formed, allowing the estimation of the static dielectric constant of Ta 2 O 5 films. In Section III, the steps for the fabrication of shunt capacitive switches in III–V technology using TaN and Ta 2 O 5 films are described. Finally, in Section IV, the results of the RF characterization performed on the fabricated switches are presented and compared with the results obtained by a circuit simulation. 1057-7157/$26.00 © 2011 IEEE