A 5 mm ×5 mm ×1.37 mm hermetic FBAR duplexer for PCS handsets with wafer-scale packaging

Abstract

We describe the design and measured performance of a 5 mm x 5 mm x 1.37 mm antenna duplexer for the U.S. PCS band (Tx: 1850-1910 MHz, Rx: 1930-1990 MHz) for cellular handsets based on FBAR (Film Bulk Acoustic Resonator) technology. The FBARs are fabricated in a silicon-based IC process technology and are hermetically sealed in a wafer-level packaging process. Two dice, Tx and Rx, are attached to a 4-level printed circuit board, ballbonded, and encapsulated in plastic to form the final product. Guaranteed worst-case Tx insertion loss is 3.5 dB, worst-case Rx insertion loss is 4.0 dB. Minimum rejection is 50/40 dB in the Tx/Rx bands, guaranteed isolation is >52/42 dB.

Universal modeling of the bulk acoustic wave devices

“…Figure 1. Schematic of layered BAW system with parallel planes being perpendicular to X,Y, & Z axes, where the desired bulk acoustic waves propagate along X-direction (a), and the preferred configuration of the "top-side" electrode (Bradley et al, 2002) in an actual BAW device (b).…”

“…However, a usage of irregular polygon electrode, in which no two sides are parallel to one in the directions being perpendicular to Y-& Z-axes (Fig.1b), allows considerable suppression of parasitic movements in similar systems (Bradley et al, 2002). Thus, we must only introduce -on the phenomenological level -the proper imaginary addends to the wavenumbers in every layer, taking into account the losses caused by non-synchronous excitation and transformation to heat of parasitic modes (in addition to propagation losses of acoustic waves because of the material viscosity).…”

Comparison of Mode-Conversion, Energy-Trapping and Lateral Acoustic Coupling in FBAR and SBAR

“…However, energy leakage and also spurious resonances still occur due to conversion of energy between different acoustic modes at electrode edges. Reported measures to suppress spurious modes include special edge structures [3] and polygonal-shaped resonators [4]. In SBARs energy not associated with normal-incidence longitudinal waves can leak through the reflector.…”

A miniature BAW duplexer using flip-chip on LTCC

“…The latter serves to transform the low impedance short that the bare ladder type RX filter represents in the TX filter path over the range of the TX band into a high impedance open. This transformation can either be done by an LC matching network [2] or using a quarter wavelength delay line [3]. We have adopted the latter approach, since the delay line can quite easily be realized in the LTCC.…”

“…The main purpose of the duplexer is thus • to direct signals at RX band frequencies (US-PCS 1930 from the antenna to the Low Noise Amplifier (LNA) while sufficiently blocking all out-of-band signals, • to direct signals at the TX band frequencies (US-PCS 1850-1910MHz) from the Power Amplifier (PA) to the antenna, • to isolate the LNA from the high signal levels of the TX path Besides these basic prerequisites, the ideal duplexer should also provide a sufficient out-of-band rejection especially at higher frequencies in order to suppress higher harmonics arising from nonlinearities in the amplification characteristics of the PA. Until recently, these requirements could only be realized with rather bulky ceramic duplexer filters (at least for the above mentioned PCS band). Over the last few years, alternative technologies including SAW [1] and BAW [ 2,3] duplexers have been developed, mainly driven by the cellular phone industries demand for ever smaller component footprints.…”