# Recent Advances in Fiber-Shaped Electronic Devices for Wearable Applications
## 3 Device Applications
### Electronic Devices
#### 3.1.2 Memory Devices  
Electronic memory is an essential element of electronic circuits that store information. To store electronic signals generated by wearable processors, sensors, and elec  
Figure 2: **(a)** Top: schematic of the rolling-transfer process of printed CNT microelectrodes (left) and photographs of the spirally wrapped CNT microelectrodes on fiber substrates (right). Bottom: schematic and photograph of a flexible fiber OFET (left), field-effect mobilities and on/off current ratio with various bending radii (right). Reproduced with permission Ref. [29]. Copyright 2020, American Chemical Society. **(b)** Left: schematic illustration of a fabrication process for fiber-shaped CMOS circuitry. Right: electrical properties of the 1D complementary inverters. Reproduced with permission Ref. [22]. Copyright 2017, Wiley-VCH. **(c)** Left: schematic illustration of a fabrication process of a fiber-shaped OFET with the twisted structure and a solid ion-gel electrolyte. Right: photograph and transfer characteristics of the fiber-shaped OFET embedded in a fabric. Reproduced with permission Ref. [30]. Copyright 2019, Wiley-VCH. **(d)** Left: schematic illustration and photograph of the ionogel-gated fiber transistor. Middle: transfer characteristics of the ionogel-gated transistor with different bending radii. Right: electrical characteristics of logic gate NAND (A and B curves: two logic gate inputs, Y curve: output from the circuit). Reproduced with permission Ref. [26]. Copyright 2019, American Chemical Society. tronic circuitry, researchers have fabricated soft and flexible fiber-shaped memory devices. There are two main types of fiber-shaped memory: resistor-type and transistor-type. [PERSON] et al. reported a stretchable resistive memory device using a graphene-poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) hybrid material dip-coated on a nylon thread [33]. Conductive filaments were generated by applying voltages to access charges trapped in the graphene flakes [33]. The resulting fiber-shaped memory device has write-once-read-many-times characteristics and a retention time of 10\({}^{6}\) s, with an on/off ratio of approximately 10\({}^{3}\)[33]. [PERSON] and coworkers developed a textile-based resistive switching random access memory (RRAM) [34]. The woven RRAM was fabricated using a carbon counter-electrode fiber and an Al\({}_{2}\)O\({}_{3}\) resistance switching layer formed on an Al-coated cotton fiber (Figure 3a) [34]. When the 3 \(\times\) 3 RRAM array was embroidered into a cloth, it exhibited stable resistance switching for more than 100 cycles with an on/off ratio exceeding 10\({}^{2}\) (Figure 3b) [34]. In another example, [PERSON] and his colleagues demonstrated a textile memristor array in a logic-in-memory circuit that acted as both nonvolatile memory and a logic gate [35]. Cotton yarn was dip-coated with aluminum as a metallic electrode, and then poly(ethylene glycol) dimethacrylate (pEGDMA) was deposited as a resistive switching layer using an initiated chemical vapor deposition (iCVD) process (Figure 3c) [35]. Two aluminum/pEGDMA layers on the yarn intersected with each other, forming a memristor unit [35]. The pEGDMA memristors were woven in a crossbar array of textile structure, with untreated yarns that acted as cell-to-cell barriers [35]. The fabricated devices showed outstanding nonvolatile memory characteristics, including low operation voltage (<1.5 V), long-term retention (>1.5 \(\times\) 10\({}^{7}\) s), and good cycling endurance (>500 cycles), mechanical robustness, and washability [35]. The textile memristor crossbar array composed as a logic-in-memory circuit successfully implemented basic Boolean functions, such as half-adder and NOT, NOR, OR, AND, and NAND logic gates (Figure 3d) [35]. The pEGDMA memristor-based crossbar array architecture is one possible application for smart textile systems that use energy-efficient, normally-off computing, which is compatible with the limited battery capacity of wearable devices [35].