Double-Framed Thin Elastomer Devices

Abstract

Elastomers and, in particular, polydimethylsiloxane (PDMS) are widely adopted as biocompatible mechanically compliant substrates for soft and flexible micro-nanosystems in medicine, biology, and engineering. However, several applications require such low thicknesses (e.g., <100 μm) that make peeling-off critical because very thin elastomers become delicate and tend to exhibit strong adhesion with carriers. Moreover, microfabrication techniques such as photolithography use solvents which swell PDMS, introducing complexity and possible contamination, thus limiting industrial scalability and preventing many biomedical applications. Here, we combine low-adhesion and rectangular carrier substrates, adhesive Kapton frames, micromilling-defined shadow masks, and adhesive-neutralizing paper frames for enabling fast, easy, green, contaminant-free, and scalable manufacturing of thin elastomer devices, with both simplified peeling and handling. The accurate alignment between the frame and shadow masks can be further facilitated by micromilled marking lines on the back side of the low-adhesion carrier. As a proof of concept, we show epidermal sensors on a 50 μm-thick PDMS substrate for measuring strain, the skin bioimpedance and the heart rate. The proposed approach paves the way to a straightforward, green, and scalable fabrication of contaminant-free thin devices on elastomers for a wide variety of applications. KEYWORDS: double-framed thin elastomer devices, contaminant-free epidermal devices, thin PDMS devices, epidermal electronics, peel-off, Kapton-paper frame

Thin PDMS-on-Sacrificial-PCB Devices

“…First, the UV-protection film of the sacrificial PCB was cut by removing an inner part so that the residual protection film constitutes a frame for facilitating the subsequent handling of the device (Figure S2 shows the selective removal of the UV-protection film on the PCB substrate and the resulting frame). As an advantage, instead of manufacturing , or attaching the frame, , it is sufficient to pattern an existing film. Afterward, we spin-coated and cured in an oven (3 h at 80 °C) the thin PDMS layer.…”

“…Additional constraints can be introduced by the typically high coefficients of thermal expansion of elastomers ( e.g ., the linear and the volumetric thermal coefficients of PDMS–Sylgard 184 are about 320 and 960 ppm/°C, respectively) and by their swelling characteristics . Several strategies have been reported for mitigating these issues, including proper coatings of the carrier before PDMS deposition, − PDMS doping, an intermediate parylene layer, laser pulses through a transparent glass substrate for removing an intermediate polyimide (PI) layer deposited on glass before PDMS and a double-framed strategy . However, for very thin devices, it is often preferable to chemically, rather than mechanically, release the devices.…”

Twin-Wire Networks for Zero Interconnect, High-Density 4-Wire Electrical Characterizations of Materials

“…A second paper frame was used for neutralizing the adhesive of the polyimide tape in order to facilitate both peeling and the subsequent handling of the device. Details can be found in [32]. 4.2.…”

“…This problem can be critical for devices where conductors (e.g., thin metals on soft polymers) are so delicate that R PAD may be significantly increased even when connecting with instrumentation. For validation, we fabricated [32] zero interconnect twin-wire gold resistors on PDMS (Figure 2(a)). In practice, 10 nm chromium adhesion layer and 100 nm gold were thermally evaporated on 50 μm thick PDMS.…”

“…In practice, 10 nm chromium adhesion layer and 100 nm gold were thermally evaporated on 50 μm thick PDMS. The devices were double-framed [32] for simplifying both fabrication and handling. As schematically shown in Figure 2(b), the order of magnitude of the worst case parasitic pad resistance R PAD,WC can be estimated by considering a hypothetical resistor with length, width, and thickness equal to X L , X W , and t, respectively, so that…”