Monika Schmiedgen

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