Laser-assisted fabrication of single-layer flexible touch sensor

Seokwoo Son, Jong Eun Park, Joohyung Lee, Minyang Yang, Bongchul Kang
<span title="2016-10-05">2016</span> <i title="Springer Nature"> <a target="_blank" rel="noopener" href="" style="color: black;">Scientific Reports</a> </i> &nbsp;
Single-layer flexible touch sensor that is designed for the indium-tin-oxide (ITO)-free, bendable, durable, multi-sensible, and single layer transparent touch sensor was developed via a low-cost and one-step laser-induced fabrication technology. To this end, an entirely novel approach involving material, device structure, and even fabrication method was adopted. Conventional metal oxides based multilayer touch structure was substituted by the single layer structure composed of integrated silver
more &raquo; ... wire networks of sensors and bezel interconnections. This structure is concurrently fabricated on a glass substitutive plastic film via the laser-induced fabrication method using the low-cost organometallic/ nanoparticle hybrid complex. In addition, this study addresses practical solutions to heterochromia and interference problem with a color display unit. As a result, a practical touch sensor is successfully demonstrated through resolving the heterochromia and interference problems with color display unit. This study could provide the breakthrough for early realization of wearable device. Owing to the progress and popularization of portable devices, such as smart phones and tablet computers, the demand of touch sensors for user interfaces is dramatically increasing. From the early pressure-electric type, the touch sensor mechanisms have recently evolved to an electrostatic-capacitive type, which has many advantages such as coincident multiple sensing, high response rate, good durability, and high sensitivity, compared with other competitive methods 1 . A sensor array layer to detect a touch event and a bezel circuit to transmit the electric signal from the sensor to a drive integrated chip (IC) are the key components that directly affect the resulting engineering performance and physical properties such as transparency, resistance, size, and thickness. Indium tin oxide (ITO) is mainly used as a transparent conductive material in sensors, as it is characterized by high transparency within the visible wavelength range 2,3 . However, its application is limited to flexible, low-cost, and large area touch sensor because of its brittleness, high material cost, and relatively low conductivity 4 . In addition, the ITO-based device has some disadvantages in the fabrication process because its deposition requires expensive vacuum deposition methods, such as sputtering. Moreover, costly and complicated post-patterning processes, such as photolithography and chemical etching, are necessary. These processes should be repeated to fabricate the bezel circuit. Most previous studies attempting to resolve the issues of current touch sensors mainly focused on pioneering alternative transparent materials 5 , which can be representatively classified into four categories: conducting polymers 6 , carbon nanomaterials 7-9 , metallic one dimensional nanomaterials 10-13 , and hybrid materials 5,14,15 . These attempts do not come up with a definite answer because of the fundamental limitations represented by the limited conductivity and transparency of conducting polymers, the high junction resistance and weak adhesion of carbon nanotubes (CNT), challenging processibility of graphene, excessive haziness and low clarity of metallic nanowires, and process complexity of hybrid structures. Fundamentally, since these approaches have a conflicting relationship between conductivity and transparency, also depending on material thickness, it is considered that concurrently improving them is almost impossible 16, 17 . Metal-meshed transparent conductors, another approach adopted when using metals, consist of two dimensionally tangled metal traces of invisibly narrow width. This method provides outstanding advantages in device performance, structural simplicity, and manufacturing availability [16] [17] [18] . First, outstanding transparency and clarity are achievable without sacrificing its conductivity, since the transmittance is almost independent from a variation of structure thickness 17 . This approach supports a high design flexibility of touch sensors. Second,
<span class="external-identifiers"> <a target="_blank" rel="external noopener noreferrer" href="">doi:10.1038/srep34629</a> <a target="_blank" rel="external noopener" href="">pmid:27703204</a> <a target="_blank" rel="external noopener" href="">pmcid:PMC5050410</a> <a target="_blank" rel="external noopener" href="">fatcat:k4lsonk2nbbl5iw5wem5ulvbi4</a> </span>
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