Yein Lim

Biaxially stretchable, integrated array of high performance microsupercapacitors

We report on the fabrication of a biaxially stretchable array of high performance microsupercapacitors (MSCs) on a deformable substrate. The deformable substrate is designed to suppress local strain applied to active devices by locally implanting pieces of stiff polyethylene terephthalate (PET) films within the soft elastomer of Ecoflex. A strain suppressed region is formed on the top surface of the deformable substrate, below which PET films are implanted. Active devices placed within this region can be isolated from the strain. Analysis of strain distribution by finite element method confirms that the maximum strain applied to MSC in the strain suppressed region is smaller than 0.02%, while that on the Ecoflex film is larger than 250% under both uniaxial strain of 70% and biaxial strain of 50%. The all-solid-state planar MSCs, fabricated with layer-by-layer deposited multiwalled carbon nanotube electrodes and patterned ionogel electrolyte of poly(ethylene glycol) diacrylate and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide having high-potential windows, are dry-transferred onto the deformable substrate and electrically connected in series and parallel via embedded liquid metal interconnection and Ag nanowire contacts. Liquid metal interconnection, formed by injecting liquid metal into the microchannel embedded within the substrate, can endure severe strains and requires no additional encapsulation process. This formed MSC array exhibits high energy and power density of 25 mWh/cm(3) and 32 W/cm(3), and stable electrochemical performance up to 100% uniaxial and 50% biaxial stretching. The high output voltage of the MSC array is used to light micro-light-emitting diode (μ-LED) arrays, even under strain conditions. This work demonstrates the potential application of our stretchable MSC arrays to wearable and bioimplantable electronics with a self-powered system.

High-Density, Stretchable, All-Solid-State Microsupercapacitor Arrays

We report on the successful fabrication of stretchable microsupercapacitor (MSC) arrays on a deformable polymer substrate that exhibits high electrochemical performance even under mechanical deformation such as bending, twisting, and uniaxial strain of up to 40%. We designed the deformable substrate to minimize the strain on MSCs by adopting a heterogeneous structure consisting of stiff PDMS islands (on which MSCs are attached) and a soft thin film (mixture of Ecoflex and PDMS) between neighboring PDMS islands. Finite element method analysis of strain distribution showed that an almost negligible strain of 0.47% existed on the PDMS islands but a concentrated strain of 107% was present on the soft thin film area under a uniaxial strain of 40%. The use of an embedded interconnection of the liquid metal Galinstan helped simplify the fabrication and provided mechanical stability under deformation. Furthermore, double-sided integration of MSCs increased the capacitance to twice that of MSCs on a conventional planar deformable substrate. In this study, planar-type MSCs with layer-by-layer assembled hybrid thin film electrodes of MWNT/Mn3O4 and PVA-H3PO4 electrolyte were fabricated; when they are integrated into a circuit, these MSCs increase the output voltage beyond the potential of the electrolyte used. Therefore, various LEDs that require high voltages can be operated under a high uniaxial strain of 40% without any decrease in their brightness. The results obtained in this study demonstrate the high potential of our stretchable MSC arrays for their application as embedded stretchable energy storage devices in bioimplantable and future wearable nanoelectronics.

Design and Fabrication of Novel Stretchable Device Arrays on a Deformable Polymer Substrate with Embedded Liquid‐Metal Interconnections

Stretchable devices are fabricated on a newly designed deformable substrate. Active devices attached on the stiff islands are electrically connected by an embedded EGaIn interconnection, which ensures protection from external damage. In this structure, the local strain in the active device area is estimated to be less than 1% under applied strain of 30% by analysis of the strain distribution using the finite element method.