# Recent Advances in Fiber-Shaped Electronic Devices for Wearable Applications
## 3 Device Applications
### Electronic Devices  
#### 3.1.1 Transistors  
Transistors are one of the key electrical components of integrated electronic circuits that amplify and convert electrical signals simultaneously. They can also be applied to a variety of optoelectronic devices, such as displays, integrated circuits (ICs), memory devices, synaptic devices, and sensors. To date, most transistors have been fabricated on planar and rigid substrates. The development of flexible fiber-shaped transistors to give fabrics computational ability is still at an early stage because of the ongoing challenges involved in forming uniform films and high-resolution patterning on fiber substrates, and interconnecting fiber electrodes [2]. Thus, fabrication methods for electronic fibers and textile-compatible technology have been chosen as the primary focus of this research area. Fiber-shaped transistors have mainly been fabricated using mechanically flexible materials with a coaxial structure. The dielectric, semiconductor, and electrode materials are sequentially coated onto an electrode core using solution (dip-coating, spray, etc.) and vapor processes (sputtering, atomic layer deposition, chemical vapor deposition, etc.) [21; 22]. Various semiconducting materials have been applied to create a fibriform channel layer, such as polymers [23; 24], organic small molecules [3; 21; 25], single-walled carbon nanotubes (SWCNTs) [23; 26], and metal oxides [27; 28]. For instance, [PERSON] et al. fabricated organic field-effect transistor (OFET) fibers on Au microwires (Figure 2a) [29]. The OFET fiber was made from a coaxial bi-layer composed of 2,8-difluoro-5,11-bis (triethylsilylethylynyl)anthradithiophene (diF-TESADT) as an organic semiconductor and poly(methyl methacrylate) (PMMA) as the insulating polymer [29]. The diF-TESADT: PMMA blend solution was coaxially die-coated and solidified with vertical phase-separation. The dimension of the spirally wrapped CNT microelectrodes was controlled using a rolling-transfer method, and the OFET fiber showed a maximum field-effect mobility of 0.68 cm\({}^{2}\)V\({}^{-1}\)s\({}^{-1}\) and good output current characteristics [29]. 2D crystals of organic small molecules (2 DCOS) were used to fabricate fibriform OFETs through a jigsaw-puzzle physical-chemical method [25]. 2 DCOS film was prepared using a solution epitaxy method, and then transferred onto a planar substrate to fabricate the OFETs [25]. The 2 DCOS-based FETs were then peeled off and attached to the target fibers. The 2 DCOS fiber transistors showed competitive electronic characteristics: a high field-effect mobility of 1 cm\({}^{2}\)V\({}^{-1}\)s\({}^{-1}\), well-balanced ambipolarity via the p\(-\)n junction, high inverter gain up to 12.4, and a near-infrared photoresponsivity of 1.06 \(\times\) 10\({}^{4}\) A W\({}^{-1}\), with photodetectivity of 10\({}^{13}\) [PERSON] [25]. [PERSON] et al. reported reel-processed 1D complementary metal-oxide-semiconductor (CMOS) logic circuits based on SWCNT transistors (Figure 2b) [22]. P- and n-type SWCNT fiber transistors were demonstrated using selectively chemical doping and a photochemical patterning technique [22]. The device exhibited high hole mobility of 4.03 cm\({}^{2}\)V\({}^{-1}\)s\({}^{-1}\) (electron mobility of 2.15 cm\({}^{2}\)V\({}^{-1}\)s\({}^{-1}\)) and a gain of 6.76 with good dynamic operation at an applied voltage of 5.0 V [22]. [PERSON] et al. also fabricated fiber-shaped FETs with an Al\({}_{2}\)O\({}_{3}-\)MgO nanolaminate insulator and an In\(-\)Ga\(-\)Zn\(-\)O (IGZO) semiconductor [27]. The Al\({}_{2}\)O\({}_{3}-\)MgO and IGZO layers were deposited using a thermal atomic layer deposition system and radio-frequency sputtering, respectively [27]. The resulting fiber-shaped IGZO FETs exhibited an on- and off-current ratio above 10\({}^{8}\) and good electron mobility of more than 3 cm\({}^{2}\)V\({}^{-1}\)s\({}^{-1}\) with a leakage off-current of less than 10\({}^{-9}\) A [27]. Many obstacles continue to limit the practicality of using 1D FETs for electronic circuits.