Low-cost and high-performance front-end module for WLAN

Abstract

In this paper, we have developed a Thin Film on Modified Ceramic (TFoMC) technology which provides not only a low-cost but also high-performance solution, especially for wireless local-area network (WLAN) related applications. To begin with, a warpage-controlled substrate model (WCSM) was developed and demonstrated to reduce/control the warpage and roughness of ceramic substrate, e.g., warpage is no more than 150 µm and average roughness is no more than 50nm respectively, which are the key requirements for thin-film processing on low-cost ceramic substrate, e.g., 96% alumina-based. Accordingly, a multi-layer thin-film structure could be fabricated on the low-cost ceramic substrate. The thin-film based passive components including capacitors, inductors, band-pass filters and baluns could be used for RF front-end module (FEM) related wireless applications. One key element is the thin-film-based integrated passive device (IPD). The characterization results of the fabricated IPD matched well with the HFSS simulation results, which demonstrated the good in-substrate uniformity. In order to evaluate the TFoMC substrate based technology, a WLAN FEM was designed and fabricated by integrating IPDs, power amplifier (PA) die and switch die on a modified ceramic substrate. The delivered FEM exhibited a 31-dB large signal gain with the power add efficiency over 10% in the pass band, and fulfilled the spectrum mask specifications under 802.11b/g modulations. The root-mean-sqaure (rms) error vector magnitudes of the FEM were 1.0% and 2.9% for 802.11b and 802.11g modulations respectively. The IPD and FEM characterization results met all the design requirements, indicating excellent performance of the TFoMC substrate and making it as a promising technology for the wireless-related applications.