Low‐Voltage Operable and Strain‐Insensitive Stretchable All‐Carbon Nanotube Integrated Circuits with Local Strain Suppression Layer

Abstract

Stretchable devices, which can intimately contact dynamic free‐form surfaces, show great promise for wearable and implantable devices for human beings and multifunctional electronic skins for soft robotics. Although some successful stretchable devices have been reported, there are still remaining issues; in particular, the fundamental requirements for wearable devices, including low‐voltage operation, operation speed, mechanical stretchability and robustness, and easy circuit design, are needed to be satisfied simultaneously. Here, a local strain suppression layer (L‐SSL) is introduced into all‐carbon nanotube (CNT) stretchable thin‐film transistors (TFTs) and integrated circuits (ICs) to address these issues. The L‐SSL, which has a high Young's modulus, is placed on top of the active channel region to suppress the induced local strain. The resulting CNT TFTs show no drain current degradation under externally applied tensile strain of up to 35%. Furthermore, stretchable all‐CNT ICs, such as inverters and ring oscillators, can operate at low supply voltage as 0.7 V, because high‐k material can be used underneath the L‐SSL. Biaxial stretching, an indispensable ability for wearable devices on 3D deformable surfaces such as the human body, is also achieved. The all‐CNT devices, equipped with an L‐SSL, demonstrate potential for strain‐insensitive stretchable devices with low‐voltage operation.

Developing the Nondevelopable: Creating Curved‐Surface Electronics from Nonstretchable Devices

“…Recent progress in this field has brought remarkable advances, leading to a variety of curved devices with unique applications in human–computer interaction, imaging, and environmental sensing. [ 17–19 ] Currently, deterministically patterned stretchable circuits (e.g., circuits employing an island–bridge structure or a local strain suppression layer) form the basis for the most complex, cutting‐edge examples of nondevelopable electronics, including thin‐film transistors, [ 20 ] ultrasonic transducers, [ 13 ] curved imagers, [ 14,21 ] and thermoelectric energy harvesters. [ 22 ] These devices integrate small chip devices, often made of high‐performance electronic materials such as silicon or metal, with wavy or kirigami‐inspired interconnects, ensuring that any tensile strain applied to the system is concentrated in the wiring instead of the chips.…”

Stretchable Electronics with Strain‐Resistive Performance

“…Reproduced with permission. [288] Copyright 2017, Wiley-Blackwell. g) Device structure schematic of stretchable CNT FET with L-SSL, and FEA of stretchable PDMS substrate with L-SSL under 50% uniaxial tensile strain.…”

Manipulating Strain in Transistors: From Mechanically Sensitive to Insensitive

“…A representative design for strain suppression in the transistor region of a stretchable FET array was the study reported by Nishio et al. [ 38 ] In their work, an uniaxially stretchable electronic circuit was proposed by incorporating a low strain suppression layer (L‐SSL) of Parylene C into the conventional bottom‐gate‐top‐contacted CNT transistor array. By encapsulating the OSC channel with the L‐SSL, whose Young's modulus was different with the substrate material, strains were successfully controlled in the lower modulus interspace, with marginal strain distributed in the transistor region.…”