3D Heterogeneous Integration using MEMS Devices for RF Applications
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3D Heterogeneous Integration using MEMS Devices for RF Applications Fumihiko Nakazawa1,2, Xiaoyu Mi1,2, Takeaki Shimanouchi1,2, Tadashi Nakatani1,2, Takashi Katsuki1,2, Hiroaki Inoue1,2, Osamu Toyoda1,2, and Satoshi Ueda1,2 1
3D-Integration Technology Research Department, Association of Super-Advanced Electronics Technologies, 64, Nishiwaki, Ohkubo-cho, Akashi, Japan 2 Device & Materials Laboratories Fujitsu Laboratories 64, Nishiwaki, Ohkubo-cho, Akashi, Japan ABSTRACT This paper presents novel 3D heterogeneous integrations using MEMS Devices for RF applications. We propose a 3D heterogeneous integration method that combines the advantages of LTCC, passive integration, and MEMS technologies. The basic concept is to form a large-size LTCC wiring wafer and then to form high-Q passives or MEMS filters directly on the wafer surface. Other functional devices such as ICs, SAWs, and MEMS switches are mounted above the surface-formed devices. A miniaturized duplexer consisted of IPD, SAW, and film bulk acoustic resonator (FBAR); and a next generation duplexer module consisted of an MEMS tunable filter and a piezoelectric transducer (PZT)-actuated RF MEMS switch were constructed to demonstrate its feasibility and effectiveness. INTRODUCTION Advanced RF systems are becoming more complicated and involve more and more devices such as ICs, high-Q passives, and MEMS to support filtering, tuning, and switching functions, which cannot be effectively integrated on active silicon nowadays. Good RF performances and high integration density are required. In terms of these factors, the future RF system necessitates 3D heterogeneous integration instead of building everything on a single chip [1]. LTCC (low temperature co-fired ceramics) and organic wiring substrates with passive components incorporated inside are used as an interposer for RF system integration. But, the quality factor and integration density of the built-in passives are still low [2]. Si carriers with TSV (through-silicon-via) and integrated passives enable a fine structure and high integration density, but still have the drawback of poor RF performance. RF performances can be improved to some degree by introducing some special processing measurements that are usually complex and costly [3-5]. They are still not enough for many important RF circuit functions. We propose a 3D heterogeneous integration method to combine the advantages of the LTCC, thin-film passive integration, and MEMS technologies. We also demonstrate 3D heterogeneous integrated devices using the proposed integration method. CONCEPT The concept of the 3D heterogeneous integration method is to form a large-size LTCC wiring wafer and then to form high-Q passive circuits or RF-MEMS directly on the wafer surface (Fig. 1). The surface-formed devices are fabricated using photolithography and thin-film technology, enabling a fine structure and high integration density. Some low-k materials can be used easily for inductors so that a small inductor can provide a large inductance and high SRF compared to a
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