David Penunuri

Coordinate-free, frequency-independent universal functions for BAW analysis in SAW devices

We critically consider the boundary element method (BEM) as applied to SAW devices and describe a convenient way for increasing the accuracy of the numerical data, while significantly reducing the required computer resources. We construct appropriately defined frequency-scaled Greens functions and show that a function A(|X|) exists such that, say, for the interaction between the k/sup th/ and l/sup th/ substrips in BEM applications the relationship A/sub kl/=A(|a/sub kl/|)-A(|b/sub kl/|)-A(|c/sub kl/|)+A(|d/sub kl/|) holds true, even for the more complicated self-action elements (k=l). The various arguments of the function A(|X|) are related to the geometrical data of the aforementioned substrips. The coordinate-free, frequency-independent universal function A(|X|) merely involves the associated Greens functions, and thus can be tabulated for any material and cut only once. We validate our approach by comparing simulation results with experimental data.

A tunable SAW duplexer

The success of SAW technology for RF front end filtering in high performance hand held mobile phones and radios is well demonstrated. The small size, high rejection and relatively low insertion loss which can be achieved using SAW impedance resonators gives this technology a significant advantage over competing approaches. One of the remaining issues for SAW impedance resonator filters has been to further improve the performance margins, particularly in the case of pass band edge insertion loss, in order to reduce average insertion loss and improve manufacturing yield. This paper describes the development of a SAW duplexer component that tunes the response of the Tx filter over a frequency range in order to improve its effective performance. The duplexer is fabricated using multi-layer LTCC technology that permits the easy interconnection of numerous diverse components, including SAW filter die, inductors, transmission lines, capacitors and voltage variable capacitors. The duplexer is designed for the dual-mode AMPS/CDMA cellular system, i.e., for transmission in the band from 824-849 MHz and for reception in the band from 869-894 MHz. The duplexer is packaged in a 9 mm/spl times/10 mm/spl times/2.5 mm form factor, attains 0.8 dB minimum insertion loss in the Tx band and 1.0 dB average insertion loss and provides good return loss in a 50 ohm system. The duplexer can be tuned under software control through the use of external DC voltages which are readily available at the RF board.

Calculation and measurement of scattering parameters of SAW-devices employing leaky waves

A software package for modeling SAW-device characteristics using dyadic Greens functions has been extended to allow for the calculation of scattering parameters of SAW-devices utilizing substrates which support leaky waves. This package employs our fast version of the method-of-moments which has already reduced our simulation times on digital computers by more than one order of magnitude. However, the efficient solution of large systems of equations, had remained a challenge to be mastered. To this end wavelet bases can be used in order to convert the original dense matrices into band- or nearly band-matrices. We briefly outline important features of the wavelet bases. Subsequently, we use this technique to calculate the scattering parameters of a group of open, shorted and loaded electrodes. We compare measured scattering parameters to simulations of several SAW devices on high coupling, leaky wave substrates such as LiNbO/sub 3/.

Single-phase, unidirectional transducer design for charge transport devices

Expressions for calculating the per-stripe reflectivity of aluminum stripe and grooved reflectors as a function of stripe width and thickness are given. These results are used to predict the performance of unidirectional SAW (surface acoustic wave) transducers on gallium arsenide substrates for ACT and HACT (heterojunction acoustic charge transport) applications. The objective is to build the transducers using the same materials used for the NDS (nondestructive sense) Schottky barriers in (H)ACT devices, minimizing the number of photolithographic steps required and maintaining SAW equiphase front alignment to the NDS structures across the devices channel width. In turn, the optimization of the materials systems for large reflectivity in the SAW transducer structure dictates that the NDS structures be designed to minimize net acoustic reflections by these taps in order to maintain the low acoustic standing wave ratio required for high charge transfer efficiency.<<ETX>>

Mechanical loading effect of rectangularly-shaped shallow electrodes on SAW devices

We present a perturbation analysis of mechanical loading effect for rectangularly-shaped shallow electrodes on SAW devices. The model utilized assumes on the plane surface of a piezoelectric semi-space a layer of thickness d with piecewise constant material constitution. The method relies on eigenequations of the form L/spl psi//spl I.oarr/=/spl part//sub z//spl psi//spl I.oarr/. Our analysis technique provides a convenient perturbative solution of this equation in the substrate and layer regions subject to certain interface and boundary conditions. We validate our theory by calculating the dispersion curves related to waves propagating along corrugated surfaces.