Benjamin P. Abbott

A coupling-of-modes formalism for surface transverse wave devices

Surface transverse wave (STW) devices exhibit two substantial advantages over conventional surface acoustic wave (SAW) devices. These are a substantially higher velocity and power handling capability. Each of these characteristics are often great assets in frequency control applications. However, STW devices have found little commercial application. This may be attributed to a lack of a practical and accurate analysis method. By applying the recent advances in the analysis of STW devices by Plessky (1993), Hashimoto and Yamaguchi (1994), a new COM analysis of STW devices has been developed. This new COM formalism is applied to the analysis of STW coupled resonators to demonstrate the accuracy of the method.

Transformation of acoustic waves in periodic metal grating sandwiched between piezoelectric and dielectric

The mechanism of SAW transformation with variation of film thickness is investigated in a piezoelectric substrate with a metal grating overlaid by a dielectric film, via simulation and visualization of the acoustic fields. By way of example, two orientations of lithium niobate substrates are analyzed, YX-LN and 128°YX-LN, with a Cu grating and an isotropic silica glass overlay. The motions, which follow the wave propagation in the sagittal plane, are visualized within two periods of the grating, with added contour plots showing the shear horizontal displacements. The continuous transformation of the waves nature is investigated for each wave propagating in the analyzed material structures when the film thickness is increased from zero to a few wavelengths. The examples of the SAW transformation into boundary waves and into plate modes of different polarization have been found and investigated. The behavior of the SAW characteristics in the grating is correlated with transformation of the wave structure with increasing overlay thickness.

Acoustic wave device employing reflective elements for confining elastic energy

An acoustic wave device includes electrodes carried on a surface of a piezoelectric material and an array of reflective obstacles such that elastic energy resulting from a piezoelectric effect is preferentially directed along a primary wave propagation path. The array of reflective obstacles are positioned generally parallel to the surface of the piezoelectric material and redirect acoustic waves typically reflected in other than a desirable direction to along a desired direction generally along the primary propagation path. The obstacles improve performance for SAW and BAW devices by effecting reflected energy and suppressing spurious modes.

Characterization of bonded wafer for RF filters with reduced TCF

In order for SAW duplexers to successfully meet the stringent requirements of insertion loss and skirt steepness required for applications such as the US-PCS duplexer, new technologies are required to reduce the temperature coefficient of frequency (TCF). SAW duplexer manufacturers (1), (2), (3), (4) are aggressively pursuing various methods to accomplish this reduction in TCF, at the wafer level. Their methods will necessarily result in changes to other properties of importance to duplexer design. This paper examines the effect bonding of Lithium Tantalate (LT) to Silicon has on the properties of the leaky SAW (LSAW) resonators.

A phenomenological coupling-of-modes formalism for surface transverse wave devices

Surface transverse wave (STW) devices exhibit two substantial advantages over conventional surface acoustic wave (SAW) devices. These are a substantially higher velocity and power handling capability. Each of these characteristic are often great assets in frequency control applications. However, STW devices have found little commercial application. This may be attributed to a lack of a practical and accurate analysis method. By applying the recent advances in the analysis of STW devices by Plessky (1993) and Hashimoto et al. (1994), a new COM analysis of STW devices has been developed. This new COM formalism is applied to the analysis of STW coupled resonators to demonstrate the accuracy of the method.

SAW filters with reconfigurable transition bands

A surface acoustic wave (SAW) filter with a reconfigurable upper transition band is presented. This is achieved through the reuse of SAW resonators by incorporating single pole double throw (SPDT) GaAs switches. The reconfigurable filter with two states is demonstrated around the 700 MHz frequency range currently allocated to LTE bands. The EM simulation results are obtained from a 3D EM model built in Ansys HFSS. Fabricated SAW dies and GaAs switch dies are assembled in a 7×9×1.4 mm3 SMP package. Measured results agree well with the EM simulations. In the first state the center frequency is 687.8 MHz and the BW is 2.4%. In the second state the center frequency is 691.1 MHz and the BW is 3.4%. The shift in the upper transition band is 0.95%.

A modular SAW filter design approach for multiband filtering

This paper presents two novel modular ladder type surface acoustic wave (SAW) filters. The first topology realizes a shift of center frequency and bandwidth (BW) and the second topology a shift of band edge. In the designs, the acoustic resonators are reused and the need for passive elements is reduced. Experimental results are presented for the 700 MHz frequency band currently allocated to Long Term Evolution (LTE). Parasitics caused by the packaging, interconnect and non-ideal switches are incorporated in the design using a linear circuit solver and three dimensional electro-magnetic (3D EM) commercial simulator. The measured results agree well with the simulations. In the filter with shifted center frequency and BW, two filter states with a BW of 1.4% and 1.7% are realized with a center frequency shift of 3.1%. In the filter with shifted lower band edge, two filter states with a BW of 3% and 1.7% are obtained.