# Skin-Compatible Amorphous Oxide Thin-Film-Transistors with a Stress-Released Elastic Architecture
## 1 Introduction  
Mechanically stretchable electronic devices are attracting great attention due to their conformable adaptability to the human body [1; 2; 3]. The advantage of being conformable devices leads to the creation of utilization of wearable s and healthcare monitoring systems, as well as human-machine interfaces, smart skin, and robotics applications [4; 5; 6; 7; 8]. In addition to the above promise, the capability of resisting various deformations may enable the realization of rollable and stretchable displays [9]. The meaningful realization of skin-compatible electronic devices requires achievement of physical parameters that approximate those of the human epidermis to be properly compliant and contact with the skin. To do this, the skin-compatible electronic applications should not only be bent to conform to the skin topography but also to be stretchable to accommodate strain from various body motions. Thus, skin-compatible devices can elastically deform with a minimum 15% strain of the epidermis [2]. To meet these needs, one of the most commonly used elastomeric materials is polydimethylsiloxane (PDMS), which has an elastic modulus similar to that of human skin, shows optimal conformability and good contact and adhesion to the skin [2; 10].  
The achievement of practical skin-compatible electronic applications requires progress in the robustness of stretchable thin film transistors (TFTs) as the indispensable basic components of various systems. Among a variety of semiconductor materials, amorphousindium-gallium-zinc oxide (_a_-IGZO) thin films have been extensively employed in switching components in large area displays, sensors and functional circuits because of their outstanding electrical performance and excellent features such as low off current, high mobility, good transparency, and easy fabrication from inexpensive precursors [1; 11; 12; 13; 14]. However, the oxide materials have inherent limitations in mechanical properties, such as high brittleness and fragileness [15]. Therefore, it has been a significant challenge to implement highly reliable and robust oxide thin films onto complaint and ultraflexible substrates, allowing tolerance of large strains without significant degradation of electrical properties and the fracture of _a_-IGZO TFTs and their integrated circuits.  
To implement stretchable amorphous metal-oxide electronics with high mechanical stability, diverse unique structures have been suggested such as transferred device architectures on heterogeneous rigid island substrates, and strain-minimized device structures on dome-like deformable substrates [16; 17]. For example, prestrained wavy geometry of ZnO TFTs [18] and integrated _a_-IGZO TFTs on a strain-relief rigid island to protect the electronic devices from severe cracking [19; 20] have been demonstrated. Although previous advances are noteworthy, heterogeneous structures including stiff islands located under TFT devices often exhibit operational failures possibly due to the delamination between elastomeric parts and rigid islands in the substrates, which may be caused by enhanced strain from remaining portion of the stiff islands [17; 21].  
Despite these advances, more versatility and feasibility of stretchable electronic devices, it is highly desirable to achieve enhanced mechanical properties along with high density of device integration for simple process. Thus, to realize skin-compatible electronics, we propose reverse-trapezoid-structured _a_-IGZO TFTs in a stretchable matrix by employing a complementary metal-oxide semiconductor-compatible photolithography process with commercialized homogeneous elastomeric materials.