INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF MICROMECHANICS AND MICROENGINEERING J. Micromech. Microeng. 16 (2006) 601–611 doi:10.1088/0960-1317/16/3/016 Microelectromechanical tunable capacitors for reconfigurable RF architectures Th G S M Rijks 1,4 , P G Steeneken 1 , J T M van Beek 1 , M J E Ulenaers 1 , A Jourdain 2 , H A C Tilmans 2 , J De Coster 3 and R Puers 3 1 Philips Research, Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlands 2 Interuniversity Micro-Electronics Center (IMEC), Kapeldreef 75, B-3001 Leuven, Belgium 3 KU Leuven, Department ESAT-MICAS, Kasteelpark Arenberg 10, B-3001 Leuven, Belgium Received 24 November 2005, in final form 23 January 2006 Published 14 February 2006 Online at stacks.iop.org/JMM/16/601 Abstract This paper reports on metal-based MEMS tunable capacitors, fabricated in a thin-film process on high-ohmic silicon. Continuous and reversible tuning has been demonstrated with an average tuning ratio of 4.5. A quality factor between 100 and 300 has been obtained in a frequency range of 0.5 to 4 GHz. The combination of a high quality factor and large tuning range makes these tunable capacitors very suitable as building blocks in many radio-frequency (RF) applications. The tuning speed, temperature stability and RF power handling have been studied in terms of self-actuation. Finally, the need for a hermetic package as well as a packaging concept which can potentially provide this has been demonstrated. After packaging, the devices can be handled as standard silicon dies, making them fit very well with a system-in-package approach. (Some figures in this article are in colour only in the electronic version) 1. Introduction In radio-frequency (RF) transceivers for wireless mobile communication, accurate and high-quality passive circuits are of prime importance. For example, the power-added efficiency of the transmit circuitry in the RF front end, consisting of power amplifiers, impedance matching networks, harmonic filters and switches, is to a large extent determined by the performance of the passives (including the switches) that constitute most of these circuits. Besides a high efficiency resulting in a low power consumption, small size and low cost are important drivers in the market of RF modules for mobile communication terminals. A very promising route of integrating high-quality passives in a cost-effective manner is using passive integration in a system-in-package (SiP) approach [1, 2]. In this approach, 4 Presently at Philips Lighting, LCD Backlighting, Hurksestraat 2c, 5652 AJ Eindhoven, The Netherlands. the passives are integrated on a chip or in a substrate using dedicated technologies, which are then combined with the active ICs in a modular fashion. In this way, different technologies and processes can easily be mixed and matched leading to an optimum of performance, cost and size of the RF module. This approach is illustrated in figure 1, showing an example of an RF transmit module [3]. A multilayer laminate substrate provides interconnect and embedded inductors, and acts as a mechanical carrier for the active ICs, passive ICs and surface mount device (SMD) components. The passive dies, indicated in the black rectangles, containing high-quality inductor/capacitor circuits, are manufactured in the Philips PASSI TM process and mounted by flip-chip assembly [4]. The next step to bring down module size and cost, and increase functionality, is to implement a reconfigurable front end in which adaptive components such as tunable/switchable capacitors and switches enable parts of the circuits to be used for more than one frequency. In addition, these adaptive networks can be used to actively optimize the power-added 0960-1317/06/030601+11$30.00 © 2006 IOP Publishing Ltd Printed in the UK 601