  Thin dielectric stacks comprising a main insulating layer and a hydrophobic
top coating are commonly used in low voltage electrowetting systems. However,
in most cases, thin dielectrics fail to endure persistent electrowetting
testing at high voltages, namely beyond the saturation onset, as electrolysis
indicates dielectric failure. Careful sample inspection via optical microscopy
revealed possible local delamination of the top coating under high electric
fields. Thus, improvement of the adhesion strength of the hydrophobic top
coating to the main dielectric is attempted through a plasma-deposited
fluorocarbon interlayer. Interestingly enough the proposed dielectric stack
exhibited a) resistance to dielectric breakdown, b) higher contact angle
modulation range, and c) electrowetting cycle reversibility. Appearance of
electrolysis in the saturation regime is inhibited, suggesting the use of this
hydrophobic dielectric stack for the design of more efficient electrowetting
systems. The possible causes of the improved performance are investigated by
nanoscratch characterization.
