Miniaturization of Electromagnetic Bandgap Structures with Thin Film Dielectrics for Si Interposer Applications
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1223-EE03-07
Miniaturization of Electromagnetic Bandgap Structures with Thin Film Dielectrics for Si Interposer Applications Koichi Takemura1, Noriaki Ando2, Hiroshi Toyao2, Takashi Manako1, and Tsuneo Tsukagoshi2 1 Device Platforms Research Laboratories, NEC Corporation, 1120 Shimokuzawa, Sagamihara, Kanagawa 229-1198, Japan. 2 System Jisso Research Laboratories, NEC Corporation, 1120 Shimokuzawa, Sagamihara, Kanagawa 229-1198, Japan. ABSTRACT We have developed miniaturized electromagnetic bandgap (EBG) structures on Si having a stopband that covers the 2.4 GHz band. By combining thin film dielectrics with inductanceenhanced EBG structures, the unit cell size can be reduced to 1 mm × 1 mm or less. Like the EBG structures embedded in conventional printed circuit boards, the stopbands can be designed using the transmission-line theory. The developed EBG structures can be integrated into Si interposers to suppress power noise. INTRODUCTION Continuous downsizing of mobile electronic equipment such as cellular phones, portable game machines, and laptop computers aggravates the electromagnetic interference (EMI) problem. Because digital and RF circuits are densely packaged in these products, power noise generated by high-speed digital LSIs causes EM coupling and unwanted EM emission, and consequently degrades the RF circuit performance. However, there are no crucial prescriptions for this so-called “autointoxication” problem, especially in the GHz range. An EBG, a feature of metamaterials, prevents EM wave propagation at the band-gap frequency. Thus, the use of EBG structures in power distribution networks has been proposed in order to suppress power noise [1,2]. EBG structures with a stopband in the microwave frequency region usually occupy a large area when embedded in conventional printed circuit boards and are therefore not suitable for use in portable electronic products. Consequently, it is strongly desired that the unit cell size be reduced for practical use. We previously reported the development of inductance-enhanced EBG structures to shrink the unit cell size down to 3 mm × 3 mm for wireless local area network (WLAN) applications at 2.4 GHz [3]. The advantages of miniaturization are not merely confined to saving occupied space. When package- or module-level integration of these EBG structures is realized, the noise suppression performance can be expected to improve because the EBG structures are placed in the immediate area of LSI chips that generate power noise. Therefore, we have studied a smaller EBG structure with thin film dielectrics for use in Si interposers, which are emerging platforms for system integration [4]. This paper describes the designs and fabrication process for miniaturizing EBG structures with a stopband that covers the 2.4 GHz WLAN band by using thin film dielectrics.
EXPERIMENTAL Designing EBG structures We adopted an inductance-enhanced EBG structure, as shown in Fig. 1(a). EBG structures have been developed based on a shielded mushroom-type structure [3]. The bottom metal plane is
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