Gyoujin Cho

All-Printed and Roll-to-Roll-Printable 13.56-MHz-Operated 1-bit RF Tag on Plastic Foils

An all-printed rectifier that can provide at least 10 V dc from a 13.56-MHz radio frequency identification (RFID) reader and an all-printed ring oscillator that can generate at least 100 Hz of clock signal to read a 96-bit RFID tag in a second under the dc power provided by the rectifier should first be printable on plastic foils for the realization of roll-to-roll (R2R) printed ultralow cost RFID tags. Here, we describe a practical way to provide all-printed and R2R-printable antenna, rectifiers, and ring oscillators on plastic foils and demonstrate 13.56-MHz-operated 1-bit RF tags. The all-printed and R2R-printable 13.56-MHz 1-bit tags can generate 102.8 Hz of clock signal as the tag approaches the 13.56-MHz RFID reader.

Fully Printed, High Performance Carbon Nanotube Thin-Film Transistors on Flexible Substrates

Fully printed transistors are a key component of ubiquitous flexible electronics. In this work, the advantages of an inverse gravure printing technique and the solution processing of semiconductor-enriched single-walled carbon nanotubes (SWNTs) are combined to fabricate fully printed thin-film transistors on mechanically flexible substrates. The fully printed transistors are configured in a top-gate device geometry and utilize silver metal electrodes and an inorganic/organic high-κ (~17) gate dielectric. The devices exhibit excellent performance for a fully printed process, with mobility and on/off current ratio of up to ~9 cm(2)/(V s) and 10(5), respectively. Extreme bendability is observed, without measurable change in the electrical performance down to a small radius of curvature of 1 mm. Given the high performance of the transistors, our high-throughput printing process serves as an enabling nanomanufacturing scheme for a wide range of large-area electronic applications based on carbon nanotube networks.

Scalability of Roll-to-Roll Gravure-Printed Electrodes on Plastic Foils

Roll-to-roll (R2R) gravure printing is considered to be a leading technology for the production of flexible and low-cost printed electronics in the near future. To enable the use of R2R gravure in printed electronics, the limits of overlay printing registration accuracy (OPRA) and the scalability of printed features with respect to the physical parameters of the gravure system, including given plastic substrates and inks, should be characterized. Important parameters of printed lines include surface roughness, thickness, line widening, and line-edge roughness. To date, there are no comprehensive reports regarding the limits of OPRA and the scalability of printed electrodes, including the control of surface roughness, thickness, line widening, and line-edge roughness using R2R gravure printing. In this paper, we examine ways of evaluating the OPRA limit of our gravure system. We find that OPRA is limited in the web moving direction to 40 μm and in the perpendicular direction to 16 μm, showing the importance of web handling on registration. Furthermore, we demonstrate the scalability of printed electrodes formed using a R2R gravure system to linewidths of 317 μm, with 440 nm thickness, 30 nm of surface roughness and edge waviness of 4 μm on PET foils, and describe optimization strategies to realize improved surface roughness, thickness, line widening, and line-edge roughness for future printed electronics applications.

Large-Area Compliant Tactile Sensors Using Printed Carbon Nanotube Active-Matrix Backplanes

A 20 × 20 pixel pressure sensor array based on a printed active-matrix single-wall carbon-nanotube thin-film transistor backplane is presented. Using a gravure printing process that is compatible with fully printed large-area roll-to-roll processing, a 97% device yield is obtained on the 400-transistor backplane. As a proof of concept, pressure sensors are integrated to map the applied tactile pressure across the array.

Fully Gravure-Printed D Flip-Flop on Plastic Foils Using Single-Walled Carbon-Nanotube-Based TFTs

Since D flip-flop is one of the indispensable building blocks in integrated circuit (IC) design, providing a successful way to print D flip-flop on plastic foils will be the first step to reach fully printed flexible IC. Here, the network structure of single-walled carbon nanotubes (SWNTs) as an active layer has been employed to print the driver and load thin-film transistors (TFTs) of the D flip-flop. The same physical dimensions of driver and load TFTs were first developed to fully gravure print the D flip-flop because of the advantage of tunable electrical properties of network density of SWNTs. Therefore, the circuit design and printing becomes simpler and more convenient than using general design rules. Furthermore, the SWNT network structure in the active layer can also minimize the fluctuation of threshold voltages (Vth) of SWNT-TFTs because of the use of the same physical dimensions in TFTs. The resulting gravure-printed D flip-flop shows a clock-to-output delay of 23 ms for 20-Hz clock signal. This is the first reported D flip-flop performance using all gravure-printing method yet achieved.

Fully roll-to-roll gravure printed rectenna on plastic foils for wireless power transmission at 13.56 MHz

Wireless power transmission to inexpensive and disposable smart electronic devices is one of the key issues for the realization of a ubiquitous society where sensor networks such as RFID tags, price tags, smart logos, signage and sensors could be fully interconnected and utilized by DC power of less than 0.3 W. This DC power can be provided by inductively coupled AC from a 13.56 MHz power transmitter through a rectenna, consisting of an antenna, a diode and a capacitor, which would be cheap to integrate with inexpensive smart electronic devices. To integrate the rectenna with a minimum cost, a roll-to-roll (R2R) gravure printing process has been considered to print the rectenna on plastic foils. In this paper, R2R gravure printing systems including printing condition and four different nanoparticle based inks will be reported to print the rectenna (antenna, diode and capacitor) on plastic foils at a printing speed of 8 m min(-1) and more than 90% device yield for a wireless power transmission of 0.3 W using a standard 13.56 MHz power transmitter.

Screen Printed Resonant Tags for Electronic Article Surveillance Tags

Screen printing has been employed to print resonant tags on a plastic film for using as a low cost electronic article surveillance tags. The resonant frequency of the printed resonant tags can be tuned by simply varying the lengths or sizes of printed inductors and capacitors. The quality factor (Q) of the printed resonant tags strongly depends on the sheet resistance of the printed inductive patterns. The maximum Q factor of printed resonant tags attained was about 45. Since this resonant tag can be printed roll-to-roll on plastic films, a number of tags with various resonance frequencies can be mass produced at a lower cost.

Fully roll-to-roll gravure printable wireless (13.56 MHz) sensor-signage tags for smart packaging.

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.

Roll-to-roll anodization and etching of aluminum foils for high-throughput surface nanotexturing.

A high-throughput process for nanotexturing of hard and soft surfaces based on the roll-to-roll anodization and etching of low-cost aluminum foils is presented. The process enables the precise control of surface topography, feature size, and shape over large areas thereby presenting a highly versatile platform for fabricating substrates with user-defined, functional performance. Specifically, the optical and surface wetting properties of the foil substrates were systematically characterized and tuned through the modulation of the surface texture. In addition, textured aluminum foils with pore and bowl surface features were used as zeptoliter reaction vessels for the well-controlled synthesis of inorganic, organic, and plasmonic nanomaterials, demonstrating yet another powerful potential use of the presented approach.

Fully Printed and Encapsulated SWCNT-Based Thin Film Transistors via a Combination of R2R Gravure and Inkjet Printing

Fully printed thin film transistors (TFT) based on poly(9,9-di-n-dodecylfluorene) (PFDD) wrapped semiconducting single walled carbon nanotube (SWCNT) channels are fabricated by a practical route that combines roll-to-roll (R2R) gravure and ink jet printing. SWCNT network density is easily controlled via ink formulation (concentration and polymer:CNT ratio) and jetting conditions (droplet size, drop spacing, and number of printed layers). Optimum inkjet printing conditions are established on Si/SiO2 in which an ink consisting of 6:1 PFDD:SWCNT ratio with 50 mg L-1 SWCNT concentration printed at a drop spacing of 20 μm results in TFTs with mobilities of ∼25 cm2 V-1 s-1 and on-/off-current ratios > 105. These conditions yield excellent network uniformity and are used in a fully additive process to fabricate fully printed TFTs on PET substrates with mobility values > 5 cm2 V-1 s-1 (R2R printed gate electrode and dielectric; inkjet printed channel and source/drain electrodes). An inkjet printed encapsulation layer completes the TFT process (fabricated in bottom gate, top contact TFT configuration) and provides mobilities > 1 cm2 V-1 s-1 with good operational stability, based on the performance of an inverter circuit. An array of 20 TFTs shows that most have less than 10% variability in terms of threshold voltage, transconductance, on-current, and subthreshold swing.