Illuminating the connection between contact angle saturation and dielectric breakdown in electrowetting through leakage current measurements

Abstract

Recent findings on the connection between the dielectric breakdown strength and the contact angle saturation in electrowetting triggered further investigation of the underlying mechanisms towards reporting the consequences of the proposed relation. High sensitivity current measurements are conducted to monitor the dielectric leakage current during a standard electrowetting experiment by testing thin (15–500 nm) dielectric films of materials widely used in microelectronics industry (SiO2, tetra-ethoxy-silane, Si3N4). The measurements confirmed that the current is negligible as long as the applied, direct current, voltage is kept below a critical value at saturation onset. This current, however, exhibits a sharp increase at higher voltages. By exploiting the increased breakdown strength of stacked oxide-nitride-oxide dielectrics, the appearance of the contact angle saturation is inhibited, suggesting the use of such composites for the design of efficient electrowetting devices.

Leakage current study for dielectric breakdown in electrowetting systems

“…The increase of leakage current indicates damage to the dielectric layer, this local damage was found to be reversible as long as the leakage current was kept low [10]. However, when excessive current was passed through the dielectric layer, breakdown occurred and the failure was irreversible.…”

“…However, the reduction of contact angle is actually limited by the well known phenomenon of contact angle saturation (CAS) [8], that is, the contact angle ceases to decrease beyond a certain angle no matter how much the applied voltage is increased. Fully understanding towards the mechanism for CAS is still lacking, but several models have been proposed to account for the origin of CAS, including zero interfacial tension, gas ionization, charge trapping, contact line instability, and dielectric breakdown [8][9][10]. Among them, the dielectric breakdown model assumes that the dielectric layer near triple contact line (TCL) becomes conductive, and screens the applied electric field and reduces electrodynamic forces applied on droplet surface.…”

REVIEW OF PAPER-LIKE DISPLAY TECHNOLOGIES (Invited Review)

“…Amorphous materials with only CF 2 groups, for example Cytop [84], while excellent insulators are not sufficiently hydrophobic to be used on the standard architecture shown in Figure 5. At the same time there remain opportunities to enhance device performance by introducing stacked dielectrics with a hydrophobic top layer [85,86].…”

Annealing Effect of High Dielectric Material for Low Voltage Electrowetting on Dielectric (EWOD)

“…Many studies have used SiO 2 with a low dielectric-constant of about 3.8 as the insulating layer, leading to a large operating voltage of several tens of volts (Smith, Abeysinghe, Haus, & Heikenfeld, 2006;Papathanasiou, Papaioannou, & Boudouvis, 2008;Cho, Fan, Moon, & Kim, 2002;Cho, Moon, & Kim, 2003). The larger operating voltage will cause electrical breakdown and reliability.…”