Dielectric constant enhancement of BaTiO3/SU-8 for low-voltage droplet actuation

Digital microfluidics (DMF) technology, which called lab-on-a-chip will bring technological innovations to the field of biochemistry. Electro-wetting-on-dielectric (EWOD) is one of the forms of DMF which actuate independent droplets through electric field enabling more accurate and efficient actuation. Nowadays, the high driving voltage required for droplet actuation remains a major obstacle to the practical application of this technology. Dielectric layer is the main factor affecting the driving voltage. In this study, we fabricate a dielectric layer film that can reduce the driving voltage by doping BaTiO₃ nanoparticles with high dielectric constant in SU-8 at room temperature. The volume ratio of dopant particles and spin coating speed are studied to determine the optimal processing conditions for low-voltage droplet actuation. As the volume ratio of the dopant particles increased, the dielectric layer dielectric constant firstly increases and then decreases. When the volume ratio of BaTiO₃:SU-8 is 1:10, the maximum dielectric constant is achieved. The dielectric wetting properties follow the same trend as the change in dielectric layer dielectric constant. Thus, the parameters of a volume ratio of 1:10 and spin coating speed of 7500 rad/min are finally selected for the preparation of the dielectric layer. These measures resulted in lower threshold voltages for droplet actuation, which contributes to advancing the application and widespread adoption of DMF technology.