Fabrication and Characterization of Roll-to-Roll Printed Air-Gap Touch Sensors

Abstract

Although printed electronics technology has been recently employed in the production of various devices, its use for the fabrication of electronic devices with air-gap structures remains challenging. This paper presents a productive roll-to-roll printed electronics method for the fabrication of capacitive touch sensors with air-gap structures. Each layer of the sensor was fabricated by printing or coating. The bottom electrode, and the dielectric and sacrificial layers were roll-to-roll slot-die coated on a flexible substrate. The top electrode was formed by roll-to-roll gravure printing, while the structural layer was formed by spin-coating. In particular, the sacrificial layer was coated with polyvinyl alcohol (PVA) and removed in water to form an air-gap. The successful formation of the air-gap was verified by field emission scanning electron microscopy (FE-SEM). Electrical characteristics of the air-gap touch sensor samples were analyzed in terms of sensitivity, hysteresis, and repeatability. Experimental results showed that the proposed method can be suitable for the fabrication of air-gap sensors by using the roll-to-roll printed electronics technology.

Organic Thin Film Transistors in Mechanical Sensors

“…It can be a simple parallel plate capacitor or integrated into an FET device as the gate capacitor. [ 47,65–68 ] The pressure sensitivity of a capacitive pressure sensor can be defined as: where C and C 0 are the capacitances with and without applied pressure, Δ C = C − C 0 , and p is the applied pressure. It is usually not constant and tends to decrease with large increases in pressure.…”

Cantilever Type Acceleration Sensors Made by Roll-to-Roll Slot-Die Coating

“…Since the electrical performance of our acceleration sensors is affected greatly by the air gap thickness, reducing the size of sensor samples is desired highly. In fact, the sensor samples made in this study are about 75% of our previous bridge type air gap-based touch sensors [55].…”

“…Some examples are motion sensors [52], touch sensors [53] and switching devices. [54] An air gap-based bridge type touch sensor was fabricated and reported by the authors [55], but studies on the fabrication of air gap acceleration sensors have not been reported and fabrication of air gap-based electronic devices using the productive roll-to-roll process has not been conducted either. The roll-to-roll printing process is difficult to optimize compared to the sheet-to-sheet approach using ordinary printing processes including screen printing, inkjet printing, and spin coating.…”

Fabrication and Characterization of Roll-to-Roll-Coated Cantilever-Structured Touch Sensors

“…It is found from our previous reports that poly(vinyl alcohol) (PVA) is more suitable for the sacrificial layer than those three materials in Table 1. 43,45 Since PVA is the representative water-soluble material, 46 As for fabrication processes of air-gap-structured electronic devices, inkjet printing and screen printing have been often used in printed electronics, 42−44 but roll-to-roll processes are considered more productive. 47−49 Printing/coating and curing are executed continuously during the roll-to-roll process, as the flexible substrate moves from the unwinder to the rewinder (Figure 1a).…”

“…This study aims at developing a roll-to-roll printed electronics technology for fabricating air-gap-based flexible sensors without relying on the MEMS process. The authors' previous work 45 presents bridge-structured touch sensors with an air-gap, but the sensitivity of 0.0026%/kPa needs a significant improvement. Herein, a new design with a smaller size and a cantilever structure is proposed.…”