Robert Frederick Milsom

Materials for bulk acoustic wave (BAW) resonators and filters

Abstract Thin film bulk acoustic wave (BAW) resonators and filters are appropriate for mobile communication systems operating at high frequencies between 1–10 GHz. The resonance frequency is mainly determined by the thickness of the piezoelectric layer. Piezoelectric films used for this application are, therefore, several 100 nm in thickness (up to approx. 2 μm) depending on frequency. Piezoelectric thin film materials used for bulk acoustic wave devices include AlN, ZnO thin films for small bandwidth applications and also PZT films for wide bandwidth applications. Within Philips piezoelectric AlN and PbZr x Ti 1− x O 3 (PZT) layers are investigated with respect to their potential for RF micro-electronic applications. High quality AlN films with strong c -axis orientation are achieved by optimum sputter deposition conditions and by applying suited nucleation layers. Electromechanical coupling factors k of 0.25±0.03, which are close to the bulk data, have been found in highly c-axis oriented AlN thin films. The relationship between sputter deposition conditions, AlN films structure on the one hand and electromechanical coupling factor k and relevant electrical parameters on the other hand will be discussed. A one-dimensional physical model is used to describe the bulk acoustic wave resonators electrical impedance data accurately. Thin PZT films are grown via sol–gel processing. These films show high electromechanical coupling factor k of 0.3–0.6 and are therefore attractive for wide bandwidth filter applications.

Comparison of mode-conversion, energy-trapping and lateral acoustic coupling in FBAR and SBAR

2D mode-matching theory is used to explore differences between the two types of thin-film bulk-acoustic wave (BAW) resonator, based on membrane (FBAR) and Bragg reflector (SBAR). Issues of mode-conversion and energy-trapping are explored. Lateral acoustic coupling is addressed in the presentation. The most significant finding is that the SBAR reflector plays a significant part in the reduction of spurious responses close to the fundamental frequency of BAW resonators and filters.

Passive integration on Si for RF circuits in wireless applications

A technology is described for the integration of high quality factor inductors and capacitors on high ohmic silicon. The performance is optimised for resonator and matching circuits in RF wireless applications. This is demonstrated by the design and measurement of an integrated output match for a GSM power amplifier which has comparable performance to a conventional hybrid module.

Efficient SPICE-compatible electromagnetic model of arbitrarily shaped integrated passive structure

A numerically efficient SPICE-compatible electromagnetic model of an arbitrarily shaped integrated passive structure is presented. It is suitable for modeling structures with electrically small, but geometrically complex features. The original model, developed for printed circuit board layout simulation, is shown to be inadequate for integrated circuits, and also not directly usable for time-domain analysis. Here, it is adapted for structures fabricated in a silicon passive-integration process, and then extended to allow nonlinear time-domain analysis of active multichip modules that employ this technology as the substrate. Special emphasis is placed on characterizing losses. Comparison with measurement shows that the model is accurate.

Filter system with bulk wave resonator having a reflection layer composition that varies with the layer thickness

The invention relates to a filter device equipped with at least one bulk acoustic wave resonator, which comprises a resonator unit and a reflection unit. The resonator unit comprises a first (3) and a second electrode (5) together with a textured piezoelectric layer (4) between the first (3) and second (5) electrodes.