Design and Applications of High Q Passive Devices on Multi-Layered Liquid Crystalline Polymer Based Substrates for Handset Applications Amit Bavisi, Wansuk Yun, Venky Sundaram, and Madhavan Swaminathan School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 Abstract- In the recent past, fully packaged RF modules suitable for integration in wireless handsets have been fabricated on organic packaging technology that uses a single sheet Liquid Crystalline Polymer (LCP) substrate. This paper demonstrates the RF characterization of inductors that were fabricated on two different stack-ups utilizing different configurations of the LCP substrate. The paper, then, shows the implementations of the embedded LC passives in RF front-end modules such as voltage controlled oscillators (VCOs) and tunable filters. The first application is the design and implementation of a 1.8 GHz feedback oscillator in a novel multi-layer laminate-type process technology that uses three layers of LCP substrate. The microstrip type oscillator measures a phase noise of -117 dBc/Hz at 100 KHz offset at 10 mW of power consumption. The oscillator meets the stringent phase noise specifications of cellular systems for both mobile-station and base-stations. The final application of the high quality factor (Q) passives is in the design and implementation of voltage tunable filters useful for WLAN applications. The filters were fabricated on a completely different stack-up that uses two layers of LCP substrate. The filter prototype is tunable from 1.75 to 2.03 GHz with an insertion loss of 2.5 dB using lossy surface-mount varactor diodes. I. INTRODUCTION Recent developments in the Liquid Crystalline Polymer (LCP) based processing technology have made LCP a promising technology for reliable system-in-package (SiP) applications at RF and microwave frequencies [ 1], [2]. Electrical characteristics such as (a) low and stable dielectric constant (£r = 2.95) and low loss (tan 6 = 0.002) upto microwave frequencies, and (b) low moisture absorption for dimensional stability [2] and high temperature tolerance make it usable in harsh environments. The entire process is done at a low temperature and is compatible with standard printed wiring board infrastructure [2]. Additionally, it is a large panel-area fabrication process (12" x 18") and has the mechanical strength to be the final printed circuit board (PCB). Both manufacturing and electrical merits, as will be presented in this paper, lead to a reduction in the manufacturing cost per component; thereby, making the technology useful for commercial RF applications. At mid-RF frequencies (- 6 GHz), embedded capacitors with Qs in the range of 200-300 and inductors with Qs greater than 50 can be designed in LCP [2]. Because of the embedded nature of the capacitors (Cs) and inductors (Ls), their characteristics can be controlled over a large frequency range. The above mentioned characteristics make LCP a feasible alternative to surface mount Ls and Cs, as the solution will become completely embedded. Unlike LTCC, components on LCP can be integrated into the inner layers of a PCB. Hence, integration using LCP improves reliability and reduces mounting costs. The above stated characteristics make LCP an excellent candidate for applications such as integrated filters [2], diplexers, duplexers, baluns, multiplexers, low noise amplifiers (LNAs) and VCOs [1],[3]. Present implementations of LCP based passive and active modules are mostly planar and use only one LCP sheet, which is bonded to multiple lower melt adhesives. But multi-band portable handsets require higher level of integrations for heavy signal routing, RF-digital isolation, and form-factor reduction. Furthermore, current trend in the volume reduction of portable phones has placed additional restrictions on the PCB thickness. The above mentioned restrictions map to a high Q process technology that can support large numbers of metal layers (- 10) and at the same time have a low overall thickness (height). This paper demonstrates novel, multiple cross-sections of stacked-LCP based packaging technologies. Depending on the application requirements the position and the number of LCP sheets is changed. Fully-packaged modules such as a VCO and tunable filters are then demonstrated. In particular, this paper presents a 10 mW, 1.8 GHz VCO on a three-LCP layer (6 metal layers) process, suitable for cellular applications. Additionally, this paper shows the first implementation of tunable filters on LCP substrate. The filters were fabricated on a two-LCP layer (8 metal layers) process and were tuned using commercially available silicon varactor diodes. The effect of lossy varactor diodes on the LCP based filters is studied. This paper is organized as follows: Section II shows the measured Qs of the Ls on the proposed technologies. Section III shows the measurement results of the fully-packaged, novel VCO that is fabricated in a volume of 5.5 x 4.8 x 0.7 mm3. Section IV summarizes the measured results of the tunable filter and discusses the effect of the lossy varactors on LCP based filters. Finally, the conclusions are made in section V. II. NOVEL LCP BASED PROCESS TECHNOLOGIES Upto 10 GHz, lumped-element inductors and capacitors are typically suitable for the design of RF front-end modules. An improvement in the VCO and filter design methodology, in 0-7803-9433-X/05/$20.00 02005 IEEE. APMC2005 Proceedings