Habbo Heinze

Appropriate Methods to Suppress Spurious FBAR Modes in Volume Production

Standards like CDMA in combination with the US PCS band impose challenging demands on the duplexer unit in the RF circuit of mobile phones. FBAR filters are candidates to fulfil the latest cutting-edge requirements for temperature stability, insertion loss, power durability, bandwidth, and filter skirts. Unfortunately, these filters suffer from spurious resonator modes. In this work we have investigated several suppression methods, which are capable of being applied to volume production

3.8 /spl times/ 3.8 mm/sup 2/ PCS-CDMA duplexer incorporating thin film resonator technology

Bulk acoustic wave (BAW) technology based on piezoelectric thin films has recently emerged as a preferred technology for the realization of miniaturized high performance RF filters and duplexers for wireless applications like mobile telephones. We present a duplexer for PCS-CDMA applications with a footprint of 3.8 mm /spl times/ 3.8 mm and a height of 1.1 mm. The duplexer consists of a transmit (TX) and a receive (RX) filter, both mounted as bare dies on a low temperature co-fired ceramic (LTCC) multilayer substrate incorporating additional matching elements. The filters are realized using solidly mounted resonator (SMR) technology, where an acoustic mirror separates the active resonator part from the substrate. Duplexer packaging is based on the EPCOS proprietary CSSP technology developed for the miniaturization of chip sized SAW packages including a cavity between the package and the acoustically active filter areas. The front-end technology for realizing the RF filters uses standard 200 mm CMOS technology and the deposition of AlN piezoelectric thin films with high thickness uniformity over the wafer. The duplexer is fully matched to 50 ohms with low insertion attenuation in the pass band, a superior stop band characteristic up to 10 GHz, and a temperature coefficient of frequency (TCF) of -20 ppm/K.

Baw components for PCS-CDMA applications

Bulk Acoustic Wave (BAW) technology is highly investigated due to its silicon-based technology for further integration in the RF part of e.g. mobile phones. This paper shows the current performance of various components suitable for the US PCS-CDMA band. In particular, new results of a duplexer are presented as well as new designs for a transmit filter and a receive filter. Besides the transfer functions, measurements of the temperature coefficient for left and right skirts are shown as well. The presented results show clearly our improvements within solidly-mounted-resonator (SMR) -BAW technology. Our process flow using a 200 mm manufacturing line uses only the minimum required process steps by still keeping a high yield in combination with high process stability and high process robustness.

Suppression of spurious modes in mirror-type thin film BAW resonators using an appropriate shape of the active area

F ilm bulk acoustic resonators (FBARs) have emerged as an important new technology for realization of GHz filter components. Two different technologies are commonly used: bridge-type and mirror-type resonator layer stacks. Both resonator configurations are susceptible to unwanted lateral modes beside the main resonance. Filters composed of FBARs, e.g. bandpass ladder-type filters, suffer from those spurious modes: they show a higher insertion loss, a lower bandwidth and several ripples in their passbands. Therefore, a practical method is needed to suppress spurious modes in FBARs. In the past, using membrane-type resonators with non-parallel edges of the active area (apodization) has been successfully applied to suppress lateral spurious modes. In contrast, for mirror-type FBARs the focus has been on mode suppression by means of a lateral edge design (frame-like resonators). In this paper we investigate in detail, if apodization works for acoustically more complicated mirror-type FBARs. We have processed a lot of eight 200-mm-wafers using a special test reticle set comprising resonators and filters with both distinct shapes of the active area, lateral edge design as well as combinations thereof. Our measurement results clearly single out optimum electrode shapes for apodization, but also manifest the superior performance of the lateral edge design. I. INTRODUCTION