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This paper addresses the key issues that must be overcome to realize fully printed TFT-based flexible devices via commercially viable methods. In particular the threshold voltage ( $V_{\rm th} $ ) variation in printed TFTs is a serious impediment to the successful launch of fully printed TFT-based devices in the market. The underlying causes of the $V_{\rm th} $ variation in fully printed TFTs were analyzed by considering the misalignment of printed drain-source to gate electrodes, the rheology of electronic inks and effects from external sources of charge. By alleviating the influences of external sources of charge using a printed passivation layer, $V_{\rm th} $ variation is maintained below 30% using a fully printed process. Based on the attainable variation range, the required number of integrated TFTs was estimated to fabricate a fully printed TFT-based radio frequency (RF) sensor device. A practical compromise enables fully printed RF sensors to be realized via the scalability of printing processes that mitigate $V_{\rm th} $ variation by minimizing the level of TFT integration. Prototypes of fully printed RF sensors with human interactive capability—an RF sensor label, and an RF $e$ -sensor (cyclic voltammetry) tag—are enabled with as few as 26 printed TFTs, demonstrating that low-cost and high throughput manufacturing of printed electronics is feasible.

We prepared monodispersed silica–polypyrrole core-shell spheres (SiO 2 –Ppy) using adsorbed surfactant bilayers on silica as templates and demonstrated the construction of photonic crystal with tunable stop band from SiO 2 –Ppy core-shell spheres. Since the photonic stop band is very dependent on the refractive index, it can be tuned by simply changing the refractive index of Ppy shell via changing doping level. In fact, the stop band was shifted about 15 nm when the photonic crystal was exposed to fuming sulfuric acid due to the change of the doping level of Ppy shell.

A disposable cyclic voltammetry (CV) tag is printed on a plastic film by integrating wireless power transmitter, polarized triangle wave generator, electrochemical cell and signage through a scalable gravure printing method. By proximity of 13.56 MHz RF reader, the printed CV tag generates 320 mHz of triangular sweep wave from +500 mV to −500 mV which enable to scan a printed electrochemical cell in the CV tag. By simply dropping any specimen solution on the electrochemical cell in the CV tag, the presence of solutes in the solution can be detected and shown on the signage of the CV tag in five sec. 10 mM of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) was used as a standard solute to prove the working concept of fully printed disposable wireless CV tag. Within five seconds, we can wirelessly diagnose the presence of TMPD in the solution using the CV tag in the proximity of the 13.56 MHz RF reader. This fully printed and wirelessly operated flexible CV tag is the first of its kind and marks the path for the utilization of inexpensive and disposable wireless electrochemical sensor systems for initial diagnose hazardous chemicals and biological molecules to improve public hygiene and health.

For the first time, fully gravure printed wireless cyclic voltammetry (CV) tag is reported as a platform for the disposable wireless sensor tags by utilizing Ag nano-particle based conducting ink, BaTiO 3 nano-particle based dielectric ink and single-walled carbon nanotube based semiconducting ink. The printed CV tag contains four functional units for the disposable wireless sensor tag: the rectenna to generate polarized DC volt through coupled 13.56 MHz AC, triangle wave generator to scan electrochemical cell by ±500 mV at lower frequency (< 500 mHz), amplifier to enhance the output signal and signage to indicate detected level of specimens. Those printed four units will be used as a platform to further develop disposable wireless sensor tags by simply replacing sensor unit.

Integration of sensing capabilities with an interactive signage through wireless communication is enabling the development of smart packaging wherein wireless (13.56 MHz) power transmission is used to interlock the smart packaging with a wireless (13.56 MHz) reader or a smart phone. Assembly of the necessary componentry for smart packaging on plastic or paper foils is limited by the manufacturing costs involved with Si based technologies. Here, the issue of manufacturing cost for smart packaging has been obviated by materials that allow R2R (roll-to-roll) gravure in combination with R2R coating processes to be employed. R2R gravure was used to print the wireless power transmission device, called rectenna (antenna, diode and capacitor), and humidity sensor on poly(ethylene terephtalate) (PET) films while electrochromic signage units were fabricated by R2R coating. The signage units were laminated with the R2R gravure printed rectenna and sensor to complete the prototype smart packaging.

To use conducting polymers as substitutes for metals and conventional semiconductors in device fabrication, a cost-effective process for the reproducible deposition of the conducting polymers is needed. In this letter, we report a simple solution casting method for the fabrication of micro- to nanopatterns using the conducting block copolymer, poly(thiophene-block-ethyleneoxide), which shows rectifying characteristics dependent on the pattern width.