As the demand for innovative flexible displays rises, one group wagers on its new printing technology as the perfect means to meet that demand.

Tanaka Kikinzoku Group's recently developed printing technology, which was unveiled at Semicon West, allows semiconductor manufacturers to produce accurate flexible touchscreen surfaces more quickly and cost effective, according to Matt Watson, director of business development for Tanaka America Inc. Dubbed “SuPR-NaP,” the technique can be carried out at standard temperature and pressure, while producing wiring so fine it’s invisible to the naked eye, he said in an telephone interview with EBN.

Tanaka’s SuPR-NaP method, developed in collaboration with AIST, is a nanoparticle chemisorption printing technique for conductive silver patterning, which provides for a short printing process, said Watson, that will enable manufacturers to cost-effectively mass produce more practical flexible touchscreen surfaces for any kind of device.

The process is summed up most simply by AIST: print production of ultrafine electronic circuits with 0.8µm linewidth is realised by simple surface coating of silver nanometal ink, followed by self-fusion phenomenon of silver nanoparticles is utilised, which occurs on patterned reactive surface produced by ultraviolet irradiation. This leads industrialisation of printed electronics technology as flexible touch-screen sensors.

As noted by AIST, print production technology for highly fine metal wiring has faced several technological difficulties such as in reproducibility due to the contamination of printing plates or other apparatus, in sintering or fusion of metal particles on substrates after printing, in avoiding distortion of plastic substrates by high-temperature post-treatment, and in avoiding peeling off the printed wires due to the substrate bending.

opto 01 Figure 1: Carboxyl groups that are generated by ultraviolet irradiation on substrate surface are connected with silver nanoparticles, and then the fusion reaction between the chemisorbed silver nanoparticles on the activated surface proceeds.

The SuPR-NaP technique enables easy and rapid production of ultrafine electronic circuits over a large-area substrate without using vacuum, with minimum linewidth of 0.8μm that strongly adhere to the plastic substrates. Essentially, it the creation of a very flat, but also very bendable surface, Watson said, and will deliver a better cost of ownership as compared to other common techniques, including ITO.

The flexibility and curvature provided by the techniques is expected to be required by the iPhone 8 and beyond, he said. One benefit will be the ability to sit on your phone and not crack. Tanaka has been doing reliability testing and the new material can survive 10,000 cycles of bending at sharp radiuses. Smartphones will the first segment to require the flexibility, said Watson.

There are limitations to the technology. Eighteen-inch capability is anticipated shortly, but “you can only go so big with this technology,” he said. Tanaka expects to provide roll-to-roll printing capabilities with OEM partners by January 2017 and to have the technology fully developed and ready to scale a year after that.

opto 02 Figure 2: Revenue from flexible displays will increase more than 300%, from just $3.7 billion in 2016 to $15.5 billion in 2022, according to IHS.

The demand for innovative flexible displays is being driven by the popularity and penetration of wearable and mobile devices, according to IHS, which is forecasting that revenue from flexible displays will increase more than 300%, from just $3.7 billion in 2016 to $15.5 billion in 2022. It also expects flexible displays will comprise 13% of total display market revenue in 2020.

Flexible displays are primarily used in smartphones and smartwatches in 2016; however, use in other applications, including tablet PCs, near-eye virtual reality devices, automotive monitors and OLED TVs is expected by 2022. Samsung Electronics and LG Electronics launched the first smartphones with flexible active-matrix organic light-emitting diode (AMOLED) displays in 2013, and both companies continue to adapt flexible AMOLED displays for their smartphones, smartwatches and fitness trackers.