Introduction of a Chemical-Free Metal PDMS Thermal Bonding for Fabrication of Flexible Electrode by Metal Transfer onto PDMS

Abstract

Polydimethylsiloxane (PDMS) is a flexible and biocompatible material widely used in the fabrication of microfluidic devices, and is often studied for the fabrication of flexible electrodes. The most popular method of fabricating a flexible electrode using PDMS is done by transferring a metal electrode onto said PDMS. However, the transfer process is difficult and the transferred metal layer is easily damaged due to inherently weak adhesion forces between the metal and PDMS, thus requiring a chemical treatment or sacrificial layer between the two. The fabrication process using a chemical treatment or sacrificial layer is complicated and expensive, which is the major limitation of using PDMS in the fabrication of flexible electrodes. This paper discusses the findings of a possible solution to create strong bonding between PDMS and various metals (copper, nickel and silver) using a chemical-free metal to PDMS thermal bonding technique. This method is the same as the PDMS curing process, but with a variation in the curing condition. The condition required to create strong bonding was studied by observing copper transferred by various PDMS curing conditions, including the standard condition. The condition creating the strong bonding was baking PDMS (5:1 = base polymer: curing agent) at 150 °C for 20 min. Experimentation showed that the optimum thickness of the transferred metal shows that the optimum thickness is approximately 500 nm, which allows for a higher resistance to stresses. The successful transfer of copper, nickel and silver layers onto PDMS with a stronger adhesion force opens up many new applications dealing with the fabrication of flexible electrodes, sensors, and flexible soft magnets.

3D Printing High‐Resolution Conductive Elastomeric Structures with a Solid Particle‐Free Emulsion Ink

“…Such resolutions are hardly achievable for solid‐particle‐loaded conductive elastomer inks. [ 20,35,36 ] This work, together with the silicone oil‐elastomer ink reported by our group previously, [ 15 ] demonstrates that the particle‐free emulsion design enables high‐resolution printing (<30 μm) of very different functional inks.…”

“…[13,14] These methods currently lack useful capabilities to integrate soft and conductive materials in three dimensions.Patterning metallic components on soft substrates such as poly (dimethyl siloxane) (PDMS) provides one method to improve the electrical functionality of composite structures, but the bonding of most metals with the elastomer is susceptible to delamination, potentially limiting the performance of such devices without adoption of specific modifications to improve adhesion. [15] To overcome this weakness, the approach of embedding conductive fillers into PDMS to render it inherently conductive has been adopted, where fillers such as metal or carbon particles are added to PDMS above a certain percolation threshold. The successful fabrication of electrically conductive soft structures has been reported using carbon nanofibers, MWCNT, and PDMS-grafted CNTs, [16][17][18] but these structures either lack well-defined 3D shapes or require complex/timeconsuming methods of preparation to provide them.…”

State‐of‐the‐Art Electronic Materials for Thin Films in Bioelectronics

“…Such processing is often not compatible with fabrication of more sophisticated devices requiring several fabrication steps. [ 132 ] Next option of adhesion improvement is deposition of adhesion layer like Ti using high‐energetic deposition method such as high‐power impulse magnetron sputtering. [ 133 ] PDMS can withstand relatively high temperatures.…”

Double-Framed Thin Elastomer Devices

“…23 As an alternative, metals and, subsequently, PDMS can be, first, deposited on a substrate and, after a thermal procedure for strengthening the PDMS-metal adhesion, removed by conventional peeling. 24 Nevertheless, these techniques can still be problematic because of, for instance, complex equipment, additional materials or steps, and unwanted materials changes or residuals. As an interesting approach, in principle, a frame 25−27 attachment, undesired contact with PDMS (i.e., contamination) and, if the frame is stiff enough, formation of wrinkles.…”

“…Likewise, an intermediate polyimide (PI) layer, deposited on glass before PDMS, can be released by laser pulses through a transparent glass substrate . As an alternative, metals and, subsequently, PDMS can be, first, deposited on a substrate and, after a thermal procedure for strengthening the PDMS-metal adhesion, removed by conventional peeling . Nevertheless, these techniques can still be problematic because of, for instance, complex equipment, additional materials or steps, and unwanted materials changes or residuals.…”