RF-MEMS: Materials and technology, integration and packaging
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RF-MEMS: Materials and technology, integration and packaging Harrie A. C. Tilmans IMEC, Division MCP Kapeldreef 75, B-3001 Leuven, Belgium ABSTRACT MEMS technology is rapidly emerging as an enabling technology to yield a new generation of highperformance RF-MEMS passives, like switches, tunable capacitors, high-Q resonators and tunable filters. This paper presents the progress in RF-MEMS device and package development with focus on relevant technology and material issues. The importance of wafer-level or 0-level packaging of the RF-MEMS devices is elucidated. Examples of 1-level packaging, e.g., chip-on-board or plastic molded 1-level package, are briefly described. The paper concludes in stipulating how integration of RF-MEMS passives with other passives (as inductors, LC filters, SAW devices) and active circuitry (RFICs) can lead to socalled "RF-MEMS system-in-a-package (RF-MEMS-SiP)" modules. The evolution of the RF-MEMS-SiP technology is illustrated using IMEC's microwave multi-layer thin film MCM-D technology.
INTRODUCTION Wireless communication is showing an explosive growth of emerging consumer and military applications of radio frequency (RF), microwave, and millimeter-wave circuits and systems. Future wireless communication systems as mobile phones, wireless local area networks (WLAN), satellite communications and automotive radar will require very low weight, volume and power consumption in addition to higher data rates and increased functionality. Improvements in the size and component count have been achieved by increasing the level of onchip integration. Currently, in a mobile phone, all active functions are already integrated, also in the RF front-end with on the average 3-4 RFICs per terminal. Continuing integration and chip scaling will at this point only marginally contribute to the size reduction [1-3]. Today, the situation has been reached where the presence of the rather bulky expensive off-chip (or discrete) passive RF components, like high-Q inductors, capacitors, varactor diodes and ceramic filters, plays a limiting role in further reducing size. Moreover, despite many years of research, the IC industry is facing a technological barrier to further integration. On-chip passive components, fabricated along with the active elements as part of the semiconductor wafer in various RFIC technologies as BiCMOS, SiGe and GaAs, did not result in components with the required highquality factors offered by the off-chip passives. The inductor, sometimes designated as "the most crucial passive" [4], best illustrates this. Inductor Q’s for low cost (Bi)CMOS or bipolar technologies, used for application below 10GHz, are typically limited to around 10, whereas Q’s of at least 30 are desired in the RF front-end of heterodyning transceivers. The absence of onchip passives becomes particularly troublesome for more specific, yet indispensable, off-chip passives like the very high-Q (>10,000) quartz-crystal reference resonators, high-Q ceramic and SAW filters, high-Q varactor diodes and PIN diode or FET swi
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