Electrowetting on a semiconductor

TL;DR

This paper demonstrates reversible electrowetting on silicon surfaces using mercury droplets, showing how the contact angle varies with voltage depending on doping type and level, explained by modulation of the metal-semiconductor junction capacitance.

Contribution

It introduces the first demonstration of electrowetting on a semiconductor surface, linking the effect to the modulation of junction capacitance and providing a theoretical model.

Findings

Electrowetting on silicon is reversible and voltage-dependent.

Doping type and level influence the electrowetting behavior.

A model combining junction capacitance and Young-Lippmann equation matches experimental data.

Abstract

We report electrowetting on a semiconductor using of a mercury droplet resting on a silicon surface. The effect is demonstrated using commercial n-type and p-type single-crystal (100) silicon wafers of different doping levels. The electrowetting is reversible - the voltage-dependent wetting contact angle variation of the mercury droplet is observed to depend on both the underlying semiconductor doping density and type. The electrowetting behaviour is explained by the voltage-dependent modulation of the space-charge capacitance at the metal-semiconductor junction - current-voltage and capacitance-voltage-frequency measurements indicate this to be the case. A model combining the metal-semiconductor junction capacitance and the Young-Lippmann electrowetting equation agrees well with the observations.