ZnO Thin Film Surface Acoustic Wave based Lab-on-a-Chip

Abstract

Lab-on-a-chip (LOC) is one of the most important microsystem applications with promise for use in microanalysis, drug development, diagnosis of illness and diseases etc. LOC typically consists of two main components: microfluidics and sensors. Integration of microfluidics and sensors on a single chip can greatly enhance the efficiency of biochemical reactions and the sensitivity of detection, increase the reaction/detection speed, and reduce the potential cross-contamination, fabrication time and cost etc. However, the mechanisms generally used for microfluidics and sensors are different, making the integration of the two main components complicated and increases the cost of the systems. A lab-on-a-chip system based on a single surface acoustic wave (SAW) actuation mechanism is proposed. SAW devices were fabricated on nanocrystalline ZnO thin films deposited on Si substrates using sputtering. Coupling of acoustic waves into a liquid induces acoustic streaming and motion of droplets. A streaming velocity up to ˜5cm/s and droplet pumping speeds of ˜1cm/s were obtained. It was also found that a higher order mode wave, the Sezawa wave is more effective in streaming and transportation of microdroplets. The ZnO SAW sensor has been used for prostate antigen/antibody biorecognition systems, demonstrated the feasibility of using a single actuation mechanism for lab-on-a-chip applications.

Novel ZnO nanorod films by chemical solution deposition for planar device applications

“…From the top and cross-sectional views of the SEM images, the obtained ZnO NR arrays have an improved structural orientation with the increase of seed layer thickness. With a thin seed layer, the size and number of the nucleus are limited and the crystal orientations would be random which is typically observed in physical vapor depositions [56]. These lead to a slow growth of the NRs with smaller diameters and more random crystal orientations as shown in figure 6(a 1 ).…”

“…A thicker seed layer could provide a larger size of the nucleus with well formed crystal orientations, the growth rate of the NRs increases, contributing to the larger aspect ratio of the NRs as shown in figure 6(b 1 ). This can be explained as follows: the initial layer of a sputtered seed layer has fine crystal structures with randomly distributed crystal orientation and the crystals become larger with a preferential orientation of (0002) as the sputtered layer becomes thicker [56].…”

“…In order to demonstrate the suitability of the smooth NR films for large area device applications by planar process fabrication, the NR films have been used to fabricate SAW devices as SAW devices are one of the building blocks for many applications ranging from communications, sensors [21][22][23], microfluidics to lab-on-a-chip [28,29,56]. When an alternating electric field is applied to an IDT on a piezoelectric substrate or a film such as ZnO on Si-substrate, acoustic waves are generated through the piezoelectric effect and propagate on the surface of the substrate.…”

Flexible Electronics: The Next Ubiquitous Platform

“…When the surface energy of the SAW device is reduced, using a self-assembly monolayer perhaps, the acoustic wave can be effectively used to pump droplets. Higher order mode waves, e.g., the Sezawa wave [96], are more effective in streaming and transportation of microdroplets. A SAW device on a ZnO island has also been used in [96] to pump and mix liquids remotely, thus avoiding direct contact of the extremely reactive ZnO film with biochemical solutions.…”

“…Higher order mode waves, e.g., the Sezawa wave [96], are more effective in streaming and transportation of microdroplets. A SAW device on a ZnO island has also been used in [96] to pump and mix liquids remotely, thus avoiding direct contact of the extremely reactive ZnO film with biochemical solutions. ZnO-based SAW devices have been utilized for biosensing [97].…”