Transparent Touch Sensor Research Articles

Transparent Touch Sensors on Wood: Sustainable Development with Aesthetic Integrity

Transparent Touch Sensors on Wood: Sustainable Development with Aesthetic Integrity

Self‐Powered e‐Skin Based on Integrated Flexible Organic Photovoltaics and Transparent Touch Sensors

There is a growing interest in the large area, lightweight, low‐power electronic skin (e‐Skin), consisting of a multitude of sensors over conformable surfaces. The use of multifunctional sensors is always challenging, especially when their energy requirements are considered. Herein, the heterogeneous integration of custom‐made flexible organic photovoltaic (OPV) cells is demonstrated with a large area touch sensor array. The OPV can offer power density of more than 0.32 μW cm−2 at 1500 lux, which is sufficient to meet the instantaneous demand of the array of touch sensors. In addition to energy harvesting, it is shown that the OPVs can perform shadow sensing for proximity and gesture recognition, which are crucial features needed in the e‐Skin, particularly for safe interaction in the industrial domain. Along with pressure sensing (sensitivity of up to 0.26 kPa−1 in the range of 1–10 kPa) and spatial information, the touch sensors made of indium tin oxide and monolayer graphene have shown >70% transparency, which allow light to pass through them to reach the bottom OPV layer. With better resource management and space utilization, the presented stacked integration of transparent touch‐sensing layer and OPVs can evolve into a futuristic energy‐autonomous e‐Skin that can “see” and “feel.”

Stretchable, self-healing, transparent macromolecular elastomeric gel and PAM/carrageenan hydrogel for self-powered touch sensors

The booming of next-generation soft electronics has aroused great demand for the flexible touch sensors, and their key problem is to ensure good transparency and durability. Herein, glycerin and hydroxyethyl cellulose elastomer (GHEC), and PAM/carrageenan double network (DN) hydrogel are prepared by a simple one-pot polymerization method. The as-prepare DN hydrogel are sandwiched between two GHEC layers to act as a self-powered and self-healing triboelectric nanogenerator (SS-TENG), with the average peak value of VOC and ISC reaching 347.5 V and 0.98 μA respectively. When the SS-TENG is damaged, it can complete self-healing without degradation of the electrical output performance and mechanical property, guaranteeing good durability. The prepared SS-TENG exhibits excellent flexibility and high transmittance up to 93%. Further, a 3 × 3 sef-powered transparent touch sensor array based on the SS-TENG is developed. Our SS-TENG paves the way for the development of new flexible self-powered touch screen sensors.

A Highly Accurate, Stretchable Touchpad for Robust, Linear, and Stable Tactile Feedback

AbstractA stretchable and steady performance of human–machine interfaces and localized tactile perception is a broad concerning problem. Existing tactile sensors and touchpads claim to be stretchable for location detection failing to offer a location with uniformity during inevitable flexible movements, as well as linearity. The fabrication of a highly stretchable and transparent touch sensor, which is made of hydrogels and PDMS, could simultaneously and precisely determine location and pressure while being stretched or unstretched. It is noteworthy that the sensor introduces a new structure of resistant‐system into stretchable sensors, which needs only four electrodes in 3D helical structure without sacrificing linearity. A few drops of silicone oil are added to the interfaces to prevent the dehydration of the hydrogels, which is a common problem leading to device failure. In the same time, the transparency is improved significantly from 84.3% to 96%. Its interface application is demonstrated by practically using it for drawing, dialing numbers, calculating, and playing cards. Finite element analysis based on Ogden models indicates that the sensor shows instant response without delay, which is vital for super‐elastic materials based electronics.

Highly Conductive, Stretchable, and Transparent PEDOT:PSS Electrodes Fabricated with Triblock Copolymer Additives and Acid Treatment.

Here, we report on a highly conductive, stretchable, and transparent electrode of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) fabricated via modification with triblock copolymer, poly(ethylene glycol)- block-poly(propylene glycol)- block-poly(ethylene glycol) (PEO20-PPO70-PEO20, Pluronic P123), and post-treatment with sulfuric acid. The fabricated electrode exhibits high transparency (89%), high electrical conductivity (∼1700 S/cm), and minimal change in resistance (∼4%) under repetitive stretch-release cycles at 40% tensile strain after stabilization. P123 acts as a secondary dopant and plasticizer, resulting in enhanced electrical conductivity and stretchability of PEDOT:PSS. Furthermore, after sulfuric acid post-treatment, P123 helps the electrode to maintain its stretchability. A successful demonstration of the stretchable interconnection was shown by stretching the P123-modified PEDOT:PSS electrodes, which were connected with light-emitting diodes (LEDs) in series. Finally, a stretchable and transparent touch sensor consisting of our fabricated electrodes and an LED array and stretchable semitransparent supercapacitor were presented, suggesting a great potential of our electrodes in the application to various deformable devices.

Revisiting the thickness reduction approach for near-foldable capacitive touch sensors based on a single layer of Ag nanowire-polymer composite structure

Although a percolated network of silver nanowires (AgNWs) is considered the most promising flexible transparent electrode because of its high conductivity, high transmittance, excellent flexibility, and facile patternability, it has encountered a serious delay in its application to most optoelectronic devices. Here, we analyzed the reasons and tried to resolve the current issues to achieve near-foldable transparent touch sensors by employing an inverted layer processing method. A hydroxylated polydimethylsiloxane (PDMS) was used as a preliminary substrate for deposition and patterning of AgNWs, and then the nanowires were completely transferred to the newest version of colorless polyimide (cPI) by hydrophobic recovery of the PDMS surface. For the first time, we designed an automatic apparatus for testing the foldability of the fabricated composite film by a spacer inserting method. The testing of various AgNWs/cPI films with this method revealed that the thickness reduction approach could be an efficient and powerful tool to attain near-foldable electrodes if the AgNWs are solidly adhered to the substrate. Based on these findings, we could successfully demonstrate a near-foldable touch sensor, which is capable of sensing human touches even in the folded state.

Stretchable, Transparent, and Stretch-Unresponsive Capacitive Touch Sensor Array with Selectively Patterned Silver Nanowires/Reduced Graphene Oxide Electrodes.

Stretchable and transparent touch sensors are essential input devices for future stretchable transparent electronics. Capacitive touch sensors with a simple structure of only two electrodes and one dielectric are an established technology in current rigid electronics. However, the development of stretchable and transparent capacitive touch sensors has been limited due to changes in capacitance resulting from dimensional changes in elastomeric dielectrics and difficulty in obtaining stretchable transparent electrodes that are stable under large strains. Herein, a stretch-unresponsive stretchable and transparent capacitive touch sensor array was demonstrated by employing stretchable and transparent electrodes with a simple selective-patterning process and by carefully selecting dielectric and substrate materials with low strain responsivity. A selective-patterning process was used to embed a stretchable and transparent silver nanowires/reduced graphene oxide (AgNWs/rGO) electrode line into a polyurethane (PU) dielectric layer on a polydimethylsiloxane (PDMS) substrate using oxygen plasma treatment. This method provides the ability to directly fabricate thin film electrode lines on elastomeric substrates and can be used in conventional processes employed in stretchable electronics. We used a dielectric (PU) with a Poisson's ratio smaller than that of the substrate (PDMS), which prevented changes in the capacitance resulting from stretching of the sensor. The stretch-unresponsive touch sensing capability of our transparent and stretchable capacitive touch sensor has great potential in wearable electronics and human-machine interfaces.

Laser-assisted fabrication of single-layer flexible touch sensor.

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 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.

Fabrication of Novel Transparent Touch Sensing Device via Drop-on-Demand Inkjet Printing Technique.

PSS) and dielectric poly(methylsiloxane) were deposited on a desired area to form a capacitive touch sensor structure. The properties of the printed sensors (optical transparency, electrical resistance and touch sensing performance) were investigated with varying PSS printing passes. A novel transparent touch sensor fabricated with an all-inkjet-printing method is demonstrated for the first time. This process holds industrially viable potential to fabricate transparent touch sensors with an inkjet printing technique on both rigid and flexible substrates for a wide range of applications.

A flexible graphene touch sensor in the general human touch range

We present a transparent touch sensor based on single layers of graphene that works under a gentle touch. Using the flexible characteristics of graphene, a touching event and a vertical force are measured by a change in the channel conductance. In contrast to the previous graphene gauge sensors, this is an alternative scheme that responds to a vertical force using the contacting properties of two isolated and patterned single graphene layers. This sensor responded to pressures ranging from 1 to 14 kPa, corresponding to the lowest human perception. In addition, we outline the processing methods for handling single layers of graphene for the integration of devices on transparent and flexible substrates.

Fabrication of a Flexible and Transparent Touch Sensor Using Single-Walled Carbon Nanotube Thin-Films

Reported herein are the fabrication and demonstration of a flexible and transparent touch sensor using carbon nanotube thin films (CNTFs). The CNTF was fabricated by vacuum filtration and was transferred CNTF to polydimethylsiloxane (PDMS) by water-assisted stamping method. The sheet resistance of the CNTF decreased by approximately 74% after HNO3 treatment. The CNTF touch sensor was fabricated similarly to the conventional four-wire touch screen structures. PDMS was used for the upper plate to absorb the tensile and compressive strain and polyethylene terephthalate (PET) for the lower plate to provide device stability during bending action. The CNTF touch sensor showed high optical transmittance (over 80%) and high sensitivity with the measured touch activation pressure of 23 kPa. Cyclic pressure (38 kPa) was applied at 0.5 Hz and good repeatability was found for several hundred cycles. The results show that the CNTF flexible touch sensor can be applied to future flexible electronic interfaces such as, e-paper and flexible displays.