Session: 01-02-04: Phononic Devices

Paper Number: 167315

Manipulating Surface Acoustic Waves (Saw) in Radio Frequency (Rf) Saw Devices With Phononic Crystal Thin Films 

Surface acoustic wave (SAW) radio frequency (RF) devices are commonly used as filters in telecommunication applications. The much smaller wavelength of acoustic waves compared to electromagnetic waves at the same frequency enables the miniaturization of these devices.  These devices are constituted of a piezoelectric substrate with interdigitated transducers (IDT) on their surface serving as sources and detectors of SAW. The high quality (Q) factor of SAW RF devices is at the foundation of their filtering function. It is very desirable to impart new functionalities to SAW RF devices. We employ COMSOL © Multiphysics software to investigate the properties of SAW RF devices with phononic crystal thin film deposited on the device delay line between the source and detector IDTs. In these simulations the piezoelectric material is lithium niobate and the thin film is composed of a chalcogenide phase change material (PCM) based on germanium-antimony-tellurides (GST). The thin film is patterned with alternative regions of crystalline and amorphous GST along the direction of the delay line, thus forming a superlattice. This study focuses on devices operating at frequencies near 200MHz. At such frequencies, the SAW wavelength is on the order of 20 micrometer. By varying the geometric parameters of the phononic crystal thin film (thickness, period and length of the superlattice, filling fraction of crystalline and amorphous phases) we explore how the superlattice thin film impacts the propagation of the SAW in useful ways.  More specifically, we find that thin films thinner than 2 micrometers do not impact significantly the propagation of the SAW. The period and the filling fraction of 2 micrometer crystalline/amorphous GST phononic superlattice thin films are the dominant factors which effect the SAW propagation. We demonstrate that the superlattice thin film can introduce a stop band within the bandwidth of the SAW RF device thus converting the device into a SAW duplexer.  Such duplexer devices play a critical role in RF telecommunication by enabling simultaneous transmission and reception of signals with two different frequencies.  The superlattice thin film can also be designed to produce narrower bandwidth of the SAW device increasing its Q factor and subsequently improving its filtering capability.  Finally, the choice of GST-PCM for the phononic crystal thin film allows the integration of Compact Disk rewritable (CD-RW) technology with SAW RF device technology. Indeed, crystalline and amorphous regions in PCM films are laser writable and rewritable.  This integration enables us to envision the design fabrication and realization of low-cost high throughput reconfigurable SAW RF devices with multiple functionalities. 

Presenting Author: Farrukh Najmi University of Arizona

Presenting Author Biography: Dr. Farrukh Najmi is currently working as postdoc research associate in the NewFoS Science and Technology Center at the University of Arizona. Before joining he was working as assistant professor of physics at the University of Sialkot, Sialkot, Pakistan. He is a recipient of the prestigious Fulbright Scholarship to pursue his PhD at Auburn Universty, AL, USA. He has a decade long industrial experience on piezoelectric sensors and devices. He is four research articles and one US patent on his disposal. Currently he is working on surface acoustic wave devices and is responsible for the FEA simulations in COMSOL Multiphysics.

Authors:

Farrukh Najmi University of Arizona
Pierre A. Dymier University of Arizona
Keith Runge Univerity of Arizona
Krishna Muralidharan University of Arizona
Pierre Lucas University of Arizona