Low voltage electrowetting-on-dielectric platform using multi-layer insulators

A low voltage, two-level-metal, and multi-layer insulator electrowetting-on-dielectric (EWD) platform is presented. Dispensing 300 pl droplets from 140 nl closed on-chip reservoirs was accomplished with as little as 11.4 V solely through EWD forces, and the actuation threshold voltage was 7.2 V with a 1 Hz voltage switching rate between electrodes. EWD devices were fabricated with a multilayer insulator consisting of 135 nm sputtered tantalum pentoxide (Ta2O5) and 180 nm parylene C coated with 70 nm of CYTOP. Furthermore, the minimum actuation threshold voltage followed a previously published scaling model for the threshold voltage, VT, which is proportional to (t/ɛr)1/2, where t and ɛr are the insulator thickness and dielectric constant respectively. Device threshold voltages are compared for several insulator thicknesses (200 nm, 500 nm, and 1 μm), different dielectric materials (parylene C and tantalum pentoxide), and homogeneous versus heterogeneous compositions. Additionally, we used a two-level-metal fabrication process, which enables the fabrication of smaller and denser electrodes with high interconnect routing flexibility. We also have achieved low dispensing and actuation voltages for scaled devices with 30 pl droplets.