Winfried Nessler

Bulk-acoustic-wave filters: performance optimization and volume manufacturing

Performance parameters of BAW devices are reviewed and ranked corresponding to their importance for RF-filters in mobile phone applications. The most important performance parameters - such as resonator bandwidth and Q-values - critically depend on the quality of the piezolayer and other relevant layers in the acoustic stack. The design of the complete layer stack in a Solidly Mounted Resonator (SMR) concept in combination with a proper design of lateral resonator-boundaries will be revealed to be extremely important for the suppression of spurious resonances. Challenges in manufacturing of BAW filters will be briefly reviewed. Examples of state-of-the-art in BAW filters in production and ramp-up status will be presented.

Coupled bulk acoustic wave resonator filters: key technology for single-to-balanced RF filters

Coupled Resonator Filters (CRF) are a new type of Bulk Acoustic Wave (BAW) device in which two piezoresonators are stacked on top of each other in a way that a certain degree of acoustic interaction occurs. CRFs feature complete galvanic isolation between input and output and thus enable to offer BAW filters with mode-conversion (single-ended to balanced) as well as impedance transformation. The basic concept behind these devices is reviewed. The size of a CRF BAW filter is excitingly small as compared to SAW filters. First experimental results for CRFs operating at 1.8 GHz which have been manufactured at Infineon Technologies will be presented. Certain manufacturing issues are discussed and measurements of the temperature coefficient TCF are shown.

Wafer-level-package for Bulk Acoustic Wave (BAW) filters

Silicon based Bulk-Acoustic-Wave (BAW) filters utilize mainstream wafer processing and can create significant customer benefit in terms of cost, performance and size. Similar to conventional SAW filters the package is a dominant cost contributor as long as ceramic cavity packages are used. For both SAW and BAW the active area may not be coated with any package material. We report on an innovative process which enables to manufacture BAW filters in cheap plastic SMD packages similar to packages in use for diodes and transistors. Our process is based photo-epoxy SU-8 which allows to build air-cavities above the active areas of a filter. The process is cheap as it is done on wafer level and fits well into a CMOS manufacturing environment.

Control positioning of torsional electrostatic actuators by current driving

In this paper, a novel charge control procedure of the moveable electrode of a torsional electrostatic actuator is presented It is demonstrated that pull-in charge limits the controllable range not only with parasitic capacitances but also without them. Charge is injected into the actuator by means of a switched current source. Current injection is controlled measuring voltage drop on a series capacitance, and a

BAW resonator having piezoelectric layers oriented in opposed directions

@flop closing the loop provides the synchronous operation of the system. In fact, the control circuit is a current sigma-delta control.