Patterning sub-30 µm liquid metal wires on PDMS substrates via stencil lithography and pre-stretching

Presented is a simple method combining a pre-stretching process with stencil lithography for high-resolution patterning of liquid metal wires on polydimethylsiloxane (PDMS) substrates. The PDMS substrate is pre-stretched to several times its original length before casting liquid metals, it is released and restores back to its original length after casting liquid metals through a stencil mask; hence, the width and spacing of the patterned liquid metal wires decrease simultaneously with the PDMS substrate. The degree to which the width and spacing of liquid metal wires decrease is approximately equal to the times that the PDMS substrate is pre-stretched. An ultraviolet-ozone surface modification method was used to enhance the adhesion between liquid metals and PDMS substrates, and an alternative method based on applying an external electric field was proposed to remove excess liquid metals over the stencil mask. Sub-30 µm liquid metal wires were successfully patterned. As a demonstration, a liquid metal based flexible strain sensor was fabricated, the sensor exhibited excellent stretchability, stability, sensitivity and durability. (paper)