Impact of Polyimide Film Thickness for Improving the Mechanical Robustness of Stretchable InGaZnO Thin-Film Transistors Prepared on Wavy-Dimensional Elastomer Substrates

Abstract

We report on the In-Ga-Zn-O thin-film transistors (IGZO TFTs) with outstanding mechanical stretchability, which were fabricated on ultrathin polyimide (PI) film/prestrained elastomer with a wavy-dimensional structure. The device characteristics of the fabricated devices were evaluated under mechanically strained conditions with various strains. The operational reliabilities against the bias stress conditions and during the cyclic stretching tests were also carefully examined. The stretchable IGZO TFTs exhibited good device operations without any marked degradation under stretching/compressed conditions with a strain of 40%. Under positive bias stress with a prestrain of 50%, the turn-on voltage instabilities for the TFTs prepared on 0.9 and 2.0 μm-thick PI films were estimated to be 1.5 and 3.9 V, respectively. During the cyclic stretching tests with a strain of 50%, the device operations failed after 20,000 and 100,000 stretching cycles for the TFTs fabricated on 2.0 and 0.9 μm-thick PI films, respectively. As a result, the IGZO TFTs fabricated on a thinner PI film presented more reliable operations after the repeated stretching events. The robust mechanical stretchability dependent on the PI film thickness was suggested to be due to the difference in critical values of bending radii and the influence of the local strain induced by the spatial fluctuations of the wavy structures.

Interface Design for Stretchable Electronic Devices

“…Introducing buckling, islands, or high relief structures into the interfaces could adjust the strain applied to the two different layers. [142][143][144][145][146][147][148][149][150][151][152][153][154][155][156][157][158][159][160][161] The adhesion between the two layers was increased by introducing microstructured surfaces at the interfaces, such as interlocking metal nanopiles, [162] hydrogels, [164] and SBS block copolymers. [165,166] Interfacial adhesion between the multiple device components is an important issue for integrated stretchable devices.…”

“…After Rogers and co-workers demonstrated the buckling-based stretchable electronic devices, [142][143][144][145][146][147] buckling has been used extensively to fabricate stretchable devices. Buckling occurs when compressive force is exerted to a double layer with a large modulus difference, and the buckled structure depends on the moduli of the interfacing layers, dimension of the buckled film, the prestrain applied to the substrate, the thickness of the substrate, and the interfacial adhesion.…”

“…Those variables result in different buckling deformations, such as in-plane buckling, out-of-plane buckling, locally delaminated buckling, or a combination of all. [142][143][144][145] Initially, the approach was used for changing the Si-based conventional devices stretchable. [146,147,150] Khang et al produced a stretchable form of Si ribbons structured into out-of-plane wavelike geometries.…”

“…The buckling and rigid islands approaches can be readily applied to low-resolution devices. [142][143][144][145][146][147][148][149][150][151][152][153][154][155][156][157][158][159][160][161] On the other hand, the intrinsically stretchable device approach may provide high integration, but the stretchable functional materials are still far behind their practicality. Therefore, there is a need for a new approach that can overcome simultaneously the issues of the high-resolution integration and the lack of materials.…”

Stretchable Systems

“…So far, two major approaches have been commonly utilised to realise stretchable systems: (1) a fully stretchable system, which involves the fabrication of the devices that are intrinsically stretchable and deform in response to mechanical strain; and (2) a semi-stretchable system, which involves the usage of stretchable interconnects to connect the rigid islands of silicon or inorganic semiconductor-based devices (Figure 1.1) [27][28][29][30][31][32]. These are discussed in detail in Section 2.…”