Monitored vacuum deposition of dielectric coatings over surface acoustic wave devices Sergei Zhgoon a, * , Alexander Shvetsov a , Kushal Bhattacharjee b , Ouarda Legrani c, d , Philippe Pigeat c , Omar Elmazria c a National Research University Moscow Power Engineering Institute, 14 Krasnokazarmennaja, 111250 Moscow, Russia b Qorvo Inc., 7628 Thorndike Road, 27409-9421 Greensboro, NC, USA c Institut Jean Lamour UMR 7198, Universit e de Lorraine e CNRS, Vandoeuvre les Nancy, France d LMOPS EA 4423, CentraleSup elec e Universit e de Lorraine, 2 rue Edouard Belin, F-57070 Metz, France article info Article history: Received 17 January 2015 Received in revised form 14 February 2015 Accepted 16 February 2015 Available online 4 March 2015 Keywords: Magnetron sputtering In-situ monitoring Surface acoustic wave SAW Resonator Electrical response abstract We report on our experience in the control of magnetron sputtering process by in-situ monitoring of a surface acoustic wave (SAW) device (resonator or delay line) electrical response during the deposition of dielectric layers on the SAW device surface. While the electrical response changes with the growth of different layers, the response monitoring provides a useful feedback for layer thickness control in a multiple layer system. The monitoring approach is reproducible and gives physical insight into the SAW propagation changes occurring during the fabrication. It serves as a good tool for obtaining acoustic wave dispersion curves and helps in verifying theoretical and design principles of building multiple layer microwave acoustics devices. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Surface acoustic wave (SAW) devices found wide application in standard communication systems as filters, resonators or delay lines. Moreover, because of their extreme sensitivity to external environments (temperature, strain, gas pressure), these devices are also widely used as sensors. In all these applications the technical development of SAW devices depends on advances in new design approaches and in new technological processes. Notably, in many modern devices coatings with dielectric layers are required. Some of them serve for modification of the physical properties of the devices such as the temperature coefficient of frequency (TCF), electromechanical coupling coefficient and/or acoustic velocity [1]. However, more important is the use of coatings for packaging of SAW devices, which cannot operate without protection of their surface from the environment. Known hermetic packaging tech- niques do not respond to all challenges, especially in the field of sensors that work at elevated temperatures (up to 1000  C). Indeed constitutive components of standard sealed boxes can withstand a temperature up to about 250  C. Thus, new packaging approaches need to be found. Coatings may serve for formation of acoustically isolated waves and thus they may replace additional packages for hermetically sealing the sensitive surface from the aggressive environment [2]; on the contrary, sensitivity-enhancing coatings work in chemical, biological and physicals sensors [3]. In some cases, very thin dielectric coatings can be used for monitored trimming of the working frequency of a SAW device [4]. In all such cases the coatings drastically change the properties of the SAW and thus of the actual devices, so that understanding and control of the incurred changes are required. Sometimes, analysis of the moni- tored deposition results allows making conclusions on the process parameters that lead to faults, such as layer delamination; intro- ducing corrections at a specific stage improves the processing reliability. Besides, the in-situ monitoring of the thickness depen- dence of electrical properties provides dispersion characteristics of the waves as the natural output, thus becoming a powerful in- strument for acoustic wave investigation. In this way, one can study some physical properties of deposited layers together with their dependence not only on the film thicknesses, but also on elastic and * Corresponding author. E-mail address: zhgoon@ieee.org (S. Zhgoon). Contents lists available at ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum http://dx.doi.org/10.1016/j.vacuum.2015.02.022 0042-207X/© 2015 Elsevier Ltd. All rights reserved. Vacuum 116 (2015) 1e6