An Ultrasonic MEMS Particle Separator with Thick Film Piezoelectric Actuation

Hill, Martyn, Townsend, Rosemary J., Harris, Nicholas R., White, Neil M., Beeby, Steve P. and Ding, Jiexiong (2005) An Ultrasonic MEMS Particle Separator with Thick Film Piezoelectric Actuation. In 2005 IEEE International Ultrasonics Symposium, 18-21 Sep 2005, Rotterdam, Netherlands. IEEE. pp. 1160-1163 .

Abstract

An ultrasonic resonator has been microfabricated from layers of silicon and Pyrex. A fluid channel of approximately 200?m in depth is etched into the Pyrex and allows particles within the fluid to be moved by acoustic radiation forces into the pressure nodal planes of the ultrasonic standing wave. Depending on the required application this can be used to generate a particle-free fluid sample, to concentrate particles prior to analysis, or to move particles to a surface within the resonator to aid analysis. In previously published work this resonator has been driven using a thickness mode bulk piezoceramic. While this has provided reasonable performance, the adhesion of the piezoceramic plate to the silicon has proved both the least repeatable and the least reliable element of the fabrication process. It has also been a factor in the long-term failure of test devices. To overcome these issues, multilayer thickfilm printed actuators have been developed to replace the bulk piezoceramic. Thick-film processing offers an effective means of depositing active materials onto substrates, and the technique is compatible with the microfabrication process, allowing multiple actuators to be printed onto a wafer comprising multiple devices. A variety of structures has been tested on ceramic substrates and shown to provide acceptable acoustic outputs when compared with bulk transducers mounted on identical substrates. A two layer actuator provides a good performance without excessive complexity and this configuration has been used on the resonator. Further acoustic and flow modeling of the device is described, and this has been used both to improve the channel geometry and to select better operating conditions for the system. It is shown that the thick-film actuated device working at the new operating conditions provides significantly improved performance when compared with the bulk piezoceramic device, and in particular is able to offer a five-fold reduction in concentration for 1?m latex particles, which had previously proved difficult to manipulate successfully.

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Contributors

Author: Martyn Hill

Author: Nicholas R. Harris

Author: Neil M. White

Author: Steve P. Beeby

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