Comparative Study on Microfluidic Performance of ZnO Surface Acoustic Wave Devices on Various Substrates

Abstract

ZnO thin film-based surface acoustic wave (SAW) devices have been fabricated on Si, glass and polyimide (PI) substrates, and their microfluidic performances were compared. The Rayleigh and Sezawa mode waves were observed from the ZnO/Si devices, the Rayleigh and Lamb modes from the ZnO/PI, and only the Rayleigh mode from the ZnO/glass devices. The ZnO/Si devices have the best performance with the highest acoustic streaming velocity of about 10 cm/s and the shortest particle concentration time of less than 10 sec. The ZnO/glass SAW devices deliver comparable performances to that on Si substrate, while the ZnO/PI devices perform not as good as the devices on other two types of substrates due to the large acoustic attenuation, but still can deliver a streaming velocity up to 1.0 cm/s and reasonable particle concentration function with a particle concentration time of ~70 sec.Owing to its low cost, easy fabrication and compatible with traditional glass-based biochemical analysis systems, ZnO/glass SAW device is believed to have better potential for lab-on-a-chip application.In recent years, lab-on-a-chip (LOC) technology has attracted great attentions for research and development, and has been widely utilized in chemical, biological and medical applications. 1-8 Microfluidics including liquid transportation, pumping, mixing, digitizating etc, and sensors are the two main components of LOC microsystems. Various effects have been utilized to develop microfluidics such as bimorph structure, electrostatic and piezoelectric mechanisms. Moving part-free microfluidics based on kinetic energy such as electroosmosis, 9, 10 electrophoresis, 11, 12 dielectrophoresis 13, 14 etc are preferred owing to its advantages of excellent reliability, easy fabrication and operation etc.Surface acoustic wave (SAW) device is one of the building blocks for electronics and microsystems, 15-17 and can also be utilized for accurate sensing, efficient fluidic actuation and manipulation. 18-23 Therefore SAW-based microfluidic devices and sensors will play an important role in single mechanism based-LOCs in the future. SAW-based microfluidics have the advantages of low cost, high stability, easy fabrication and operation, 24 and have been intensively investigated and studied in recent years. Wixforth demonstrated the principle of SAW-based microfluidic. 25 Li et al demonstrated the particle concentration effect on LiNbO 3 substrate 26 and Alghane et al conducted numerical simulation for liquid mixing and particleconcentration. 27 They also discussed the frequency effect and scaling effect on the performance of SAW-based microfluidics. 28,29 Shi et al showed that standing surface acoustic wave (SSAW) can be used for particle sorting and manipulation. 30 Reboud et al reported the ability to do cell lyses using SAW on LiNbO 3 substrate. 31 One of the key issues for widespread application of LOCs and microfluidics is the cost of the materials and devices involved, which is the same for the SAW-based microfluidics and LOCs. At the early study, SAW-based...

Bimorph material/structure designs for high sensitivity flexible surface acoustic wave temperature sensors

“… Comparison of TCF readings between ZnO/Al SAWs in this study and ZnO based SAWs on other commonly used substrates reported in literature 16 , 22 , 23 , 25 , 33 – 39 . …”

“…This could dramatically increase the thermal expansion of the devices during heating/cooling and result in significant variations in the wave velocities with temperature.

Figure 5 Comparison of TCF readings between ZnO/Al SAWs in this study and ZnO based SAWs on other commonly used substrates reported in literature 16 , 22 , 23 , 25 , 33 – 39 .

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“…A further essential challenge in temperature sensing is to detect or monitor changes on a curved or bendable surface, such as those for healthcare applications, and for this purpose, a temperature sensor needs to be mechanically flexible or bendable. High TCF readings have previously been reported for ZnO film based SAW devices fabricated onto polymer (such as polyimide), which are flexible substrates 22 – 24 . For SAW devices with frequencies of 132 MHz and 427 MHz, TCF values were reported to be −423 ppm/K and −258 ppm/K, respectively 23 , attributed to the large thermal expansion coefficient (TEC) of the polymer substrate.…”

Microfluidics for ZnO micro-/nanomaterials development: rational design, controllable synthesis, and on-chip bioapplications

“…ZnO thin film-based surface acoustic wave (SAW) devices have been successfully utilized to fabricate microfluidic pumps. 83,86,89,90 Among different deposition substrates (Si, glass, and polyimides), ZnO deposited on a Si substrate exhibits the highest acoustic streaming velocity of about 10 cm s −1 and the shortest particle concentration time of less than 10 seconds. 90 When introdu-cing ultra-smooth nanocrystalline diamond films with highacoustic wave velocity as an interlayer into a ZnO-based SAW device, the microfluidic efficiency was found to be further enhanced due to reduced acoustic energy dissipation into the Si substrate and improved acoustic properties of SAW devices.…”

AlScN thin film based surface acoustic wave devices with enhanced microfluidic performance

“…silicon, glass, metal, or polymer). 7,[10][11][12][13] Currently, piezoelectric thin films such as ZnO have been extensively explored for SAW based sensors and microfluidics. 6,7,14 AlN, another extensively used piezoelectric film materials in microelectro mechanical system (MEMS), has great advantages such as high acoustic velocity, outstanding stability at high temperatures, excellent chemical inertness and good compatibility with CMOS process.…”