Polymer-based surface acoustic wave device operating in ultra-high frequency
The high cost of conventional surface acoustic wave (SAW) devices limits its widespread use as micro-sensor and actuator for lab-on-a-chip applications. Solution-processed, inexpensive SAW device based on poly[(vinylidenefluoride-co-trifluoroethylene] [P(VDF-TrFE)], a ferroelectric polymer, is an alternative route to address this issue. However, incompatibility of P(VDF-TrFE) films with photoresist strippers and temperature intensive steps, often used in the optical lithography process, impede the development of efficient SAW device. This paper describes suitability of methanol as an alternative photoresist stripper without compromising the ferroelectric property of P(VDF-TrFE). Furthermore, a novel Bilayer-IDT architecture based SAW device is presented, which can be easily poled after temperature intensive fabrication steps to restore its ferroelectric property prior to SAW characterization. The SAW device, presented here, shows resonant frequency in the ultra-high frequency (UHF) range (≈451 MHz), which is quite superior to the highest reported value for P(VDF-TrFE) based SAW. The result is in good agreement with FEM simulations.
Ultra high frequency acoustic wave propagation in fully polymer based surface acoustic wave device
Surface acoustic wave (SAW) device, which integrates the generation, propagation and detection of acoustic waves into the same device, has been known to be an essential functional unit for sensors and electromechanical systems. However, high substrate cost and process complexity of traditional inorganic SAW devices have triggered extensive research efforts to seek for alternative low cost solution, especially for disposable application. Poly(vinylidenefluoride)[P(VDF)] and its co-polymer, despite being promising materials for acoustic transducer with inexpensive processing technique, have rarely been used in SAW device due to exhibiting extremely low operating frequency (few tens of MHz) compared to the traditional SAW device (few hundreds of MHz to GHz) based on inorganic piezoelectric material. Here we demonstrate SAW device, which is entirely based on Poly(vinylidenefluoride-trifluoroethylene) [P(VDF-TrFE)], as piezoelectric material, offering transduction and propagation of acoustic waves with a frequency around 450 MHz. The drawbacks of the previous attempts by the others are addressed and rectified systematically to obtain high operating frequency comparable to the traditional SAW. The influence of periodicity of interdigitated transducer and thickness of polymer film on device performance is thoroughly investigated. Temperature dependent variation of resonance frequency, which can be exploited as temperature sensor in integrated systems, is also demonstrated.