Metal and polySi (Ge) micromechanical devices for high frequency applications Sayanu Pamidighantam, Henri Jansen, Agnes Verbist, Harrie A.C. Tilmans, Kris Baert and Robert Puers 2 IMEC, MCP-MEMS, 2 K.U.Leuven, ESAT/MICAS, Kapeldreef 75, Kardinaal Mercierlaan 94, B-3001 Leuven, Belgium B-3001 Heverlee (Leuven) Belgium. Phone: +32 (0)16 288 235, Phone: +32 (0)16 321 082 E-mail: sayanu@imec.be E-mail: Bob.Puers@esat.kuleuven.ac.be Abstract —In the current communications market, there exists a great demand for devices, which func- tion as passive signal processing units. High perfor- mance and small size are identified to be the bottle- necks to meet market demand in communications area[1,3]. MEMS or micromachining technology can yield small, low weight and high performance components to replace the currently used off-chip components. This paper describes the microme- chanical devices currently under intense research at IMEC. These include RF-MEMS switches, tune- able capacitors, MEMS resonators and their de- rived units such as bandpass filters etc. Micro me- chanical resonators are realised using polySi (and poly SiGe ) surface micromachining and RF-MEMS components are realised from metal surface micro- machining technology. Keywords — RF-MEMS, switch , micromechanical resonators. I. Introduction The communications market is poised for a rapid growth over the next decade in the application ar- eas such as Wireless Local Area Networks (WLAN), Satellite communications, and automotive electronics, etc. Since the introduction of new frequency stan- dards WLAN systems are promoted to be functional at 5-6 GHz up from existing market available sys- tem at 2.4 GHz centre frequency [3]. This increment in the centre frequency means higher bandwidth ca- pability and thus larger information carrying capac- ity. Core functioning block of a WLAN system is the transceiver block, which is a transmitter and a re- ceiver unit. Existing transceivers not only operate at a lower frequency (e.g.: 2.4 GHz), but also consists of tens of off-chip external components such as Antenna, transmit/receive switch, bandpass filters, voltage con- trolled oscillator (VCO), etc. Without doubt, there is a growing need to build a miniaturised transceiver to enable attractive features of small size, low weight and portability, simultaneously retaining high perfor- mance characteristics. Micromechanical devices can play a prominent role in meeting these requirements. Few groups in the world have already demonstrated the potential ad- vantages of these MEMS components for RF and mi- crowave applications [6,7]. Yet, ultimate limitations and full potential of micromechanical devices in the context of RF application is not completely under- stood and explored. And therefore, further investiga- tion is necessary. At IMEC, research work has begun in the field of RF-MEMS to build, develop and charac- terise components and systems. Research work is on going at IMEC in the field of RF-MEMS with a unique approach called ”integrated design approach” [2]. By practising this approach, one can design the compo- nent with the input from several multi-disciplinary fields such as structural design, design of electrome- chanical transducer, microwave design and package design. With this approach designed component rep- resents close to the fabricated and characterised de- vice. An example of successful realisation by use of this approach can be found in the reference [8]. This paper focuses on RF-MEMS components tar- geted for two branches of super-heterodyne architec- ture of transceiver for WLAN applications. In sec- tion 2.1, Micromechanical resonators resonating in the flexural mode of vibration is described. These devices are realised from the use of poly Si and poly SiGe as structural layers. These devices are targeted for IF (Intermediate Frequency ≤ 500MHz) range applica- tions. The primary intention here is to build the de- vices with CMOS compatibility and also high quality factors. Poly Si and poly SiGe satisfy these require- ments very well. The current status of these devices are updated. In section 2.2, RF-MEMS components such as switches, tuneable capacitors and their de- rived units such as bandpass filters and how they are integrated with other passive building blocks such as inductors etc. In section 3, measurement results of RF-MEMS switch are discussed and finally conclu- sions are drawn in section 4. ISBN: 90-73461-24-3 673 c STW-2000 09 26-02:109