Dielectric charging in silicon nitride films for MEMS capacitive switches: Effect of film thickness and deposition conditions U. Zaghloul a,b, * , G. Papaioannou c , F. Coccetti a , P. Pons a , R. Plana a,b a CNRS, LAAS, 7 avenue du Colonel Roche, F-31077 Toulouse, France b Université de Toulouse; UPS, INSA, INP, ISAE; LAAS; F-31077 Toulouse, France c Solid State Physics Section, University of Athens, Panepistimiopolis Zografos, Athens 15784, Greece article info Article history: Received 30 June 2009 Available online 12 August 2009 abstract The paper presents a systematic investigation of the dielectric charging and discharging process in silicon nitride thin films for RF-MEMS capacitive switches. The SiN films were deposited with high frequency (HF) and low frequency (LF) PECVD method and with different thicknesses. Metal–Insulator–Metal capac- itors have been chosen as test structures while the Charge/Discharge Current Transient method has been used to monitor the current transients. The investigation reveals that in LF material the stored charge increases with the film thickness while in HF one it is not affected by the film thickness. The dependence of stored charge on electric field intensity was found to follow a Poole–Frenkel like law. Finally, both the relaxation time and the stored charge were found to increase with the electric field intensity. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Capacitive RF-MEMS switches are one of the most pioneering microelectromechanical systems (MEMS) devices for wireless applications. This is mainly due to their very high isolation, extre- mely low insertion loss and near-zero power consumption. In spite of this, their commercialization is still hindered by reliability prob- lems nonetheless the studies on the subject carried out by several laboratories and companies worldwide. The most critical reliability issue for electrostatic capacitive MEMS switches is the charging of the dielectric [1]. This charging process results in a change in the pull-in voltage and causes a stiction, limiting the functionality of the device. On the way to solve the problem of dielectric charging, several materials have been investigated among which the most inten- sively investigated ones are SiO 2 and Si 3 N 4 . In contrast to the extensive knowledge gathered on their electrical properties, a comprehensive understanding of the charging process in dielectric materials used in RF-MEMS capacitive switches is still missing. In dielectrics the charging effect arises from dipoles orientation and charge injection, displacement and trapping that occurs under the strong electric field during the down state of MEMS switches [2]. The charge injection was reported to follow the Poole–Frenkel effect, a fact that has been supported by the shift of pull-up voltage [3]. In the case of SiN, it has been shown that holes injection intro- duces metastable traps, which give rise to asymmetrical current– voltage characteristic in symmetrical Metal–Insulator–Metal capacitors [4]. Moreover the stored charge was found to increase with increasing the dielectric film thickness and the nitride depo- sition temperature [5]. Recently, the relaxation time determined using Kelvin Probe Microscopy was found to be larger in thinner dielectric films [6]. The main goal from this paper is to present for the first time a comprehensive investigation for the charging and discharging pro- cess in SiN dielectric films. The key issue parameters that affect the dielectric charging process that are the dielectric deposition condi- tions, the film thicknesses and the applied electric field intensity have been systematically investigated. Metal–Insulator–Metal (MIM) capacitors have been chosen as test structures while the charging and discharging currents of MIM capacitors are moni- tored through the Charge/Discharge Current Transient (C/DCT) method. The paper is organized as follows: first, we will briefly present the samples and the experimental approach that have been imple- mented. Then, a detailed section is devoted to the results analysis followed by some conclusive remarks. 2. Experimental approach 2.1. Investigated samples description Circular MIM capacitors of 500 lm diameter were used as the test structures for our experiments. SiN films were deposited using PECVD method at a constant chuck temperature of 200 °C. In order to investigate the effect of the dielectric deposition conditions on the charging and discharging mechanism, two deposition 0026-2714/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.microrel.2009.07.006 * Corresponding author. Address: CNRS, LAAS, 7 avenue du Colonel Roche, F-31077 Toulouse, France. Tel.: +33 646446242. E-mail address: usama.zaghloul@laas.fr (U. Zaghloul). Microelectronics Reliability 49 (2009) 1309–1314 Contents lists available at ScienceDirect Microelectronics Reliability journal homepage: www.elsevier.com/locate/microrel