Microfluidics based on ZnO/nanocrystalline diamond surface acoustic wave devices

Area of Science:

• Materials Science
• Acoustics
• Microfluidics

Background:

• Surface acoustic wave (SAW) devices are crucial for various sensing and actuation applications.
• Achieving high-performance SAW devices requires substrates with excellent surface properties and wave confinement capabilities.
• Ultra-smooth nanocrystalline diamond (UNCD) offers a promising substrate material due to its unique properties.

Purpose of the Study:

• To fabricate and characterize SAW devices utilizing a zinc oxide (ZnO) film on an ultra-smooth nanocrystalline diamond (UNCD) layer.
• To evaluate the performance of these ZnO/UNCD SAW devices for microfluidic applications.
• To investigate the microdroplet manipulation capabilities, particularly jetting, induced by the ZnO SAW.

Main Methods:

• Fabrication of SAW devices on a ZnO film deposited on a UNCD layer with a 64 μm wavelength.
• Characterization of the frequency response to identify the operating mode (Rayleigh mode at ~65.4 MHz).
• Demonstration and characterization of microfluidic functions (streaming, pumping, jetting) using microdroplets (0.5 and 20 μl) under varying SAW power.

Main Results:

• Successful fabrication of ZnO/UNCD SAW devices with excellent ZnO film quality (c-axis orientation, low roughness).
• Observation of a Rayleigh mode at ~65.4 MHz, indicating efficient wave propagation.
• Demonstrated microfluidic control, including streaming, pumping, and notably, jetting of microdroplets, driven by the ZnO SAW.

Conclusions:

• The UNCD substrate provides a superior foundation for ZnO film growth, enabling high-quality SAW device fabrication.
• The developed ZnO/UNCD SAW devices are effective for microfluidic actuation, particularly for generating microdroplet jets.
• This technology holds potential for advanced microfluidic systems and lab-on-a-chip devices.