Memristive functional device and circuit on fabric for fibertronics

Abstract

Fabric-based electronic textiles (e-textiles) are the fundamental components of wearable electronic systems, which can provide convenient hand-free access to computer and electronics applications. However, e-textile technologies presently face significant technical challenges. These challenges include difficulties of fabrication due to the delicate nature of the materials, and limited operating time, a consequence of the conventional normally-on computing architecture, with volatile power-hungry electronic components, and modest battery storage.

In the first part, we report a polydopamine (PDA) based nonvolatile memory device using fully two-step solution dip coating method to deposit aluminum (Al) and PDA as metal electrodes and resistive switching layer (RSL) on cotton yarn as a backbone. This ‘PDA based Intersected Fabric Memory (PiFAM)’ was constructed by interweaving with PDA/Al coated yarns and untreated yarns for forming active memory cell and hampering cell-to-cell interaction, respectively. The PiFAM can potentially provide a promising memory component for fabric electronics and smart nanodevices.

In the second part, we demonstrate iCVD polymer-intercalated RRAM (i-RRAM). i-RRAM exhibits robust flexibility and versatile wear-ability on any substrate. Stable operation of i-RRAM, even in water, is demonstrated, which is the first experimental presentation of water-resistant organic memory without any waterproof protection package. Moreover, the direct observation of the carbon filament is also reported for the first time using transmission electron microscopy (TEM), which puts an end to the controversy surrounding the switching mechanism. Therefore, reproducibility is feasible through comprehensive modeling. Furthermore, the carbon filament is superior to a metal filament in terms of the design window and selection of the electrode material. These results suggest an alternative to solve the critical issues of organic RRAM and an optimized memory type suitable for the IoT era.

In the third part, we report a novel poly(ethylene glycol dimethacrylate) (pEGDMA)-textile memristive nonvolatile logic-in-memory circuit, enabling normally-off computing, that can overcome those challenges. To form the metal electrode and resistive switching layer, strands of cotton yarn were coated with aluminum (Al) using a solution dip coating method, and the pEGDMA was conformally applied using an initiated chemical vapor deposition (iCVD) process. The intersection of two Al/pEGDMA coated yarns becomes a unit memristor in the lattice structure. The pEGDMA-Textile Memristor (ETM), a form of crossbar array, was interwoven using a grid of Al/pEGDMA coated yarns and untreated yarns. The former were employed in the active memristor and the latter suppressed cell-to-cell disturbance. We experimentally demonstrated for the first time that the basic Boolean functions, including a half adder as well as NOT, NOR, OR, AND, and NAND logic gates, are successfully implemented with the ETM crossbar array on a fabric substrate. This research may represent a breakthrough development for practical wearable and smart fibertronics.

In the fourth part, we report a wearable and flexible temperature sensing circuitry for a diagnosis of skin temperature. This system is based on a novel carbon nanotubes (CNTs)-based temperature sensor (CTS) array, built on cotton yarn using a mixture of multi-walled (MW)-CNTs and PDMS (polydimethylsiloxane). To divide and select the unit thermistors, a memristor which operates in the normally-off state was utilized. To construct the memristors, an Al precursor-based solution dip coating method and initiated chemical vapor deposition (iCVD) were employed for the metal electrode and resistive switching layer (RSL), respectively. Using the aforementioned processes, aluminum (Al) electrode and poly (ethylene glycol methacrylate, pEGDMA)-RSL layers were deposited on a cotton yarn backbone. A unit temperature sensor based on the proposed circuitry was fabricated by intersecting the Al/pEGDMA-coated yarns to both sides of the CTS wire, while forming a 1-thermistor and 2-memristor (1T-2M). This architecture exhibited promising performance as a sensor-array system for a fully fabric-based wearable healthcare device.