Chip on a fiber toward the e-textile computing platform

Fiber electronics are of considerable interest for wearable applications and smart textiles, and they can facilitate communication and the interaction between humans and surroundings. As a basic element of functional textiles, the one-dimensional (1D) form of thread-like fibers offers high flexibility,isotropic deformations, breathability, and light weight in fabric structures. The 1D functional fibers can be further processed into two-dimensional (2D) textile and three-dimensional (3D) yarn configurations through traditional textile engineering techniques, such as twisting, weaving, sewing, knitting, knotting, and interlacing. Owing to such intrinsic merits, in recent years, fiber-based device components that perform optoelectronic functions, such as health/environmental monitoring, displays, sensing, energy harvesting, energy storage, electromagnetic shielding, and information processing, have been integrated directly into fabrics to demonstrate futuristic clothes. The existing electronic fiber platforms are generally composed of only one type of electronic component with a single function on a fiber substrate that is attributed to all around wrapping of an active layer on the entire fiber without patterning at the desired area on the surface of the fiber during the manufacturing process. Moreover, a precise connecting process between each electronic fiber is essential to configure the desired electronic circuits or systems into the 2D textile while minimizing the degradation of the device performance. Although assembly of those functional fibers can be used for recording, detecting, and readout data sequentially, similar to conventional integrated circuits and multifunctional devices on 2D wafers, both limitations on scaling down and difficulty in the configuration of the electronic circuit remain major obstacles for the implementation of practical electronic fiber systems. To impart multiple functions to the textile, the methods of inserting small electronic components into a fiber strand or yarn have been considered emerging candidates, enabling the implementation of a thermally drawn digital fiber and e-yarn. However, a limitation to the thermal drawing approach and the mounting of small components on the top surface of a filament is the low device density. A new strategy to fabricate a high-density electronic microfiber possessing multiple electronic components and circuits as well as maintaining excellent electrical performance has not yet been reported. In this work, we present a new electronic fiber platform that enables LSI of electronic device components on the surface of a 1D fiber, defined as a monofilament with a diameter of 150 μm. By using high-resolution maskless photolithography with a capillary tube-assisted coating method, multiple miniaturized device units are integrated onto a very narrow and thin fiber surface.

As a proof-of-concept demonstration, basic electronic devices (field-effect transistors, inverters, and ring oscillators) and sensors (photodetectors, signal transducer, and distributed temperature sensors consisting of thermocouples) are fabricated onto the two different sides of the rectangular fiber. The chip on a fiber exhibits various electronic functions (UV detection and switching electrical signals in a single transistor, symmetric input/output behaviour in the n-type inverter, oscillation characteristics of 5-stage ring oscillator) and thermal sensing performance. We believe that our approach is one of the big steps to implement a high-density electronic fiber platform for integrated electronic textiles.

Fibre electronics are of considerable interest for wearable applications and smart textiles, and they can facilitate communication and the interaction between humans and surroundings. As a basic element of functional textiles, the one-dimensional (1D) form of thread-like fibres offers high flexibility, isotropic deformations, breathability, and light weight in fabric structures. The 1D functional fibres can be further processed into two-dimensional (2D) textile and three-dimensional (3D) yarn configurations through traditional textile engineering techniques, such as twisting, weaving, sewing, knitting, knotting, and interlacing. Owing to such intrinsic merits, in recent years, fibre-based device components that perform optoelectronic functions, such as health/environmental monitoring, displays,sensing, energy harvesting, energy storage, electromagnetic shielding, and information processing, have been integrated directly into fabrics to demonstrate futuristic clothes. The existing electronic fibre platforms are generally composed of only one type of electronic component with a single function on a fibre substrate that is attributed to all around wrapping of an active layer on the entire fibre without patterning at the desired area on the surface of the fibre during the manufacturing process. Moreover, a precise connecting process between each electronic fibre is essential to configure the desired electronic circuits or systems into the 2D textile while minimizing the degradation of the device performance. Although assembly of those functional fibres can be used for recording, detecting, and readout data sequentially, similar to conventional integrated circuits and multifunctional devices on 2D wafers, both limitations on scaling down and difficulty in the configuration of the electronic circuit remain major obstacles for the implementation of practical electronic fibre systems. To impart multiple functions to the textile, the methods of inserting small electronic components into a fibre strand or yarn have been considered emerging candidates, enabling the implementation of a thermally drawn digital fibre and e-yarn. However, a limitation to the thermal drawing approach and the mounting of small components on the top surface of a filament is the low device density. A new strategy to fabricate a high-density electronic microfibre possessing multiple electronic components and circuits as well as maintaining excellent electrical performance has not yet been reported.

In this work, we present a new electronic fibre platform that enables LSI of electronic device components on the surface of a 1D fibre, defined as a monofilament with a diameter of 150 μm. By using high-resolution maskless photolithography with a capillary tube-assisted coating method, multiple miniaturized device units are integrated onto a very narrow and thin fibre surface. As a proof-of-concept demonstration, basic electronic devices (field-effect transistors, inverters, and ring oscillators) and sensors (photodetectors, signal transducer, and distributed temperature sensors consisting of thermocouples) are fabricated onto the two different sides of the rectangular fibre. The chip on a fibre exhibits various electronic functions (UV detection and switching electrical signals in a single transistor, symmetric input/output behaviour in the n-type inverter, oscillation characteristics of 5-stage ring oscillator) and thermal sensing performance. We believe that our approach is one of the big steps to implement a high-density electronic fibre platform for integrated electronic textiles.