Stretchable gold conductors embedded in PDMS and patterned by photolithography: fabrication and electromechanical characterization

Abstract

Stretchable gold conductors embedded in polydimethylsiloxane (PDMS) films were successfully prepared using standard photolithography. The minimum feature sizes patterned in the metal film and PDMS encapsulation are 10 μm and 20 μm, respectively. The micro-patterned conductors are robust to uni-axial (1D) and radial (2D) stretching with applied strains of tens of percent. The electrical response of the conductors follows a nonlinear increase with strain, and is reversible. The extensive stretchability of the conductors relies on a randomly and independently distributed network of micro-cracks (∼100 nm long) in the metal film on PDMS. The micro-cracks elongate to a few microns length both in the stretching and normal directions in 1D stretching but during 2D stretching, the micro-cracks grow and form 'dry mud' islands leaving the gold microstructure inside the islands intact. Patterning metallic thin films directly onto elastomeric substrates opens a promising route for microelectrodes and interconnects for soft and ultra-compliant MEMS and electronic devices.

Flexible and stretchable electrodes for dielectric elastomer actuators

“…This step is followed by the etching of the exposed metal (c), and finally the photoresist is stripped from the metal (d). This process, which is the standard patterning method used in the integrated-circuit (IC) industry, has been successfully demonstrated to pattern metallic electrodes on elastomeric membranes for DEA applications by several authors [9,27,50,53,64]. Compared to the shadow mask process, any shape can be realized with photolithography, and features with size down to 5 µm have been demonstrated on soft polymers [9].…”

“…In addition to the three types of thin-film electrodes presented above (patterned electrodes, buckled electrode and corrugated electrodes), there are a few other technologies that can be used for interconnects, while having a too large stiffening impact to be used as active electrode in a DEA. For example, several authors reports on large uni-axial strains (up to 30%) obtained with metallic thin-films deposited on a flat elastomeric substrate, greatly exceeding the usual 3-4% yield strain of metals [64,69]. The authors have discovered that microcracks are created in the strained metallic tracks.…”

“…As these cracks do not propagate completely across the track, a conduction path is conserved up to large strains. It is difficult to evaluate the importance of the deposition parameters and of the stretching profile (very small increments with long pauses between each steps [64,69]) on the elongation at break for metallic thin-films. As a comparison, we have previously strained sputtered gold layers on PDMS at a constant speed and observed loss of conductivity for strains as low as 3% [70].…”

Stretchable Magnetoelectronics

“…Additionally, an encapsulation layer (e.g. of PDMS 181 or parylene 16 ) may help to stabilize the restored contacts across the cracks during moderate deformations. In conclusion, the self-healed sensors complement the choice of already available flexible magnetic sensing elements prepared on flexible plastic membranes and relying on GMR 4,103,104 as well as on tunnel magnetoresistance (TMR) effects 5 or even printed GMR elements on paper 182,183 .…”

Flexible and stretchable micro-electrodes for in vitro and in vivo neural interfaces

“…Stretchable metallization was first reported in 2003 [1,12,32]: thin gold film conductors on PDMS membrane can stretch and relax by tens of percent strain without electrical failure and over thousands of cyclic loadings. The stretchability of the metal film on PDMS relies on the built-in microstructure of the gold film and on the extreme compliance of the elastomeric substrate [12,23].…”