Stretchable Organic Thin-Film Transistors Fabricated on Elastomer Substrates Using Polyimide Stiff-Island Structures

Abstract

We demonstrate stretchable organic thin-film transistors (OTFTs) on a polyimide stiff-island/elastomer substrate. All processes are performed entirely at elastomer-compatible temperatures. We confirm the basic properties of the poly(vinylidene fluoridetrifluoroethylene) [P(VDF-TrFE)] with a poly(methyl methacrylate) (PMMA) blended film on the elastomer substrate and evaluate the characteristics of the fabricated stretchable OTFTs. A field-effect mobility of 3.4 × 10 −3 cm 2 V −1 s −1 , an I on /I off ratio greater than 10 3 , a subthreshold voltage swing of 12.5 V/decade, and a gate leakage current of 10 −10 A were obtained. The endurable maximum strain was approximately 50% for the OTFTs without degrading the field-effect mobility formed on the elastomers.The increasing need for flexible and stretchable circuitries, flexible and wearable displays, soft and human-friendly devices, has increased the industrial importance of portable and flexible devices. 1,2 As a result, the future development of electronics is expected to incorporate multifunctional electronic systems on the human body or clothing, requiring stable device performance under conditions of high strain and extreme body motion such as bending, folding, twisting, compressing, and stretching. 3 One of the key technologies toward the realization of these ultimate goals is the development of transistors and circuits that afford arbitrary form factors. 4 In particular, transistors that can stretch are the most essential component of stretchable electronics. Thin-film transistors (TFTs) are generally composed of gate stacks using metals and oxides, which are extremely brittle and fracture easily upon small mechanical deformation. Silicon integrated circuits are made of stiff active device films that fracture under a tensile strain of 1%. 5 Single-crystal gold films also rupture under a tensile strain of 1-1.5%. 6 To solve these problems, a few studies have focused on the fabrication of a stiff platform on elastomer substrates. 7-9 For example, diamond-like carbon islands on polydimethysiloxane (PDMS) substrate remain intact, even under 25% tensile strain. 7 Graz et al. reported a silicone substrate with in-situ strain relief for stretchable TFTs. Vacuum-processed pentacene transistors sustain an applied strain up to 13% without electrical degradation and mechanical fracture. 4 In this paper, we propose new stiff-island structures that act as a platform for stretchable electronic devices with high stretchability (approximately 50%). The stiff islands are defined by conventional photolithography on a stress-free elastomeric substrate. Thin-film islands within a stiff region are fabricated on an elastomeric substrate, and electronic devices are fabricated on these stiff islands. When the substrate is stretched, the deformation is mainly accommodated by the substrate, and the stiff islands and electronic devices experience relatively small strains. The stretchable OTFTs are fabricated onto polyimide (PI) stiff-island structures on elastomer substrates using a l...

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