Distributed constant passive devices using wafer-level chip scale package technology for one-chip wireless communication circuits

Large losses of on-chip passive devices are crucial problem for CMOS RF circuits. This paper proposes the use of wafer-level chip scale package (WL-CSP) technology to realize on-chip distributed-constant passive devices on Si CMOS substrates. In this paper, a 3 dB 90deg directional coupler using WL-CSP technology is investigated. Algebraic comparison of simulation results with measurement results are performed, which express the same tendency. The coupler has insertion loss of -0.5 dB, isolation of -29.8 dB and VSWR of 1.2 in the measurement results. The WL-CSP coupler has almost the same characteristics as those fabricated on GaAs and Al₂O₃ substrates. The WL-CSP technology contributes to realize low-loss RF passive devices on Si CMOS chip, which is indispensable to achieve small-size, low-price and low-power-consumption RF circuits