Full Integration of Stretchable Inorganic Transistors and Circuits on Molecularly Tailored Elastic Platforms

The incorporation of amorphous oxide semiconductors in flexible electronics is promising due to their high carrier mobility, operational stability, and transparency. The advantages of metal-oxide (MO) semiconductors make them excellent candidates for use as channel materials in thin-film transistors (TFTs), particularly for applications like flexible displays, wearable devices, and smart windows. Extensive research on incorporating MO semiconductor devices onto elastomeric substrates has laid the foundation for developing deformable electronics, including technologies like electronic skins and bio-integrated devices. However, their rigid nature poses challenges when integrating them into highly stretchable systems. Because the inherent rigidity and fragility of MO materials make it difficult to directly implement MO devices on highly stretchable substrates, a bridge structure combining embedded rigid islands with adjacent stretchable areas is proposed. These rigid islands, with their high elastic modulus, protect the fragile active components from mechanical stress by redirecting the strain to the surrounding stretchable areas. As a result, most of the stress is focused on the outer edges of the rigid islands. The rigid island and stretchable bridge layout have been the subject of extensive research for stretchable electronic devices due to its stress dissipation capability, but issues such as stress concentration leading to damage or delamination of the devices can still occur.
In this study, we investigate highly integrated, strain-insensitive metal-oxide transistors and circuitry, achieving a density of 442 transistors/cm² using a photolithography-based bottom-up process. These transistors, connected via fluidic liquid metal interconnections, are embedded in large-area, molecularly tailored heterogeneous elastic substrates (5×5 cm²), offering stretchability without compromising performance. The use of molecularly tailored elastomer substrates, comprising of poly epoxy acrylate (PEA) and poly urethane acrylate (PUA), which form strong adhesion between photo-patterned polymeric rigid islands and soft substrate, prevents delamination at the interface and avoids strain-induced failure. Crucially, fluidic liquid metal interconnects and dual-island structures further enhance the architecture, providing mechanical and electrical resilience. The 7×7 arrays of amorphous indium-gallium-zinc-oxide transistors, various logic gates and ring-oscillator demonstrated excellent durability under mechanical deformation. The transistors achieved an average mobility of 12.7 (± 1.7) cm²/Vs, with an on/off current ratio greater than 10⁷, exhibiting less than 20% performance variation when stretched up to 50% and 10,000 cyclic stretching of 30%. Additionally, a ring oscillator composed of 14 cross-connected transistors confirmed the cascading of multiple stages and device uniformity, exhibiting an oscillation frequency of approximately 70 kHz.