An effective lift-off method for patterning high-density gold interconnects on an elastomeric substrate.

More recently, there has been a growing trend toward making electronics fl exible and even stretchable, [ 1–7 ] e.g., in the applications of neural interfaces where mechanical compliance is critical. [ 8–12 ] Many challenges hinder the implementation of electronics on an elastomeric substrate with integration density and functionality comparable to that achievable on a silicon substrate. One major challenge lies in the diffi culty in connecting and packaging the soft electronics with standard rigid electronics. To address this issue, we have previously developed a via-bonding technology to facilitate high-resolution, high-density packaging of such stretchable electronics. [ 13 ] Another major challenge to implementing high-density stretchable electronics is the fabrication of high-density interconnects on the elastomeric substrate. To increase the interconnect density, there are two necessary aspects: 1) achieving multilayer electrical interconnects within the elastomeric substrate, and 2) patterning high-density interconnects on each individual conducting layer. To address the fi rst issue, we have implemented multilayer interconnects using an inclined-via technique. [ 13 ] For the second issue, the patterning of single 10 μ m-wide gold lines on elastomeric substrates has been achieved with both wet-etching [ 11 , 14 ] and lift-off methods, [ 15 ] but fi delity and viability diminish as interconnect length and density increase. Although the wiring of high-density devices such as microelectrode arrays frequently requires interconnects with these characteristics, no (universally) effective solution for patterning on elastomeric substrates has been reported so far. Therefore, the focus of this paper is to present an effective method for patterning highdensity thin-fi lm gold interconnects on an elastomeric substrate, specifi cally polydimethylsiloxane (PDMS). We have demonstrated 10 μ m-wide gold traces with a pitch as small as 20 μ m for both parallel and serpentine arrangements of wires as long as 3 cm. This approach provides more than one order of magnitude improvement on the density of interconnects patterned previously on elastomeric substrates. [ 8,9 , 11 , 14–16 ]