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In order to realize a high resolution and high throughput printing method for thin film transistor application, a modified offset roll printing was studied. This roll printing chiefly consists of a blanket with low surface energy and a printing plate (cliche) with high surface energy. In this study, a finite element analysis was done to predict the blanket deformation and to find the optimal angle of cliche's sidewall. Various etching methods were investigated to obtain a high resolution cliche and the surface energy of the blanket and cliche was analyzed for ink transfer. A high resolution cliche with the sidewall angle of 90^o and the intaglio depth of [email protected] was fabricated by the deep reactive ion etching method. Based on the surface energy analysis, we extracted the most favorable condition to transfer inks from a blanket to a cliche, and thus thin films were deposited on a Si-cliche to increase the surface energy. Through controlling roll speed and pressure, two inks, etch-resist and silver paste, were printed on a rigid substrate, and the fine patterns of [email protected] width and [email protected] line spacing were achieved. By using this printing process, the top gate amorphous indium-gallium-zinc-oxide TFTs with channel width/length of 12/[email protected] were successfully fabricated by printing etch-resists.

In order to use Al–2 at.%Nd as the source-drain electrode of hydrogenated amorphous silicon thin film transistors (a-Si:H TFTs) without diffusion barrier, the diffusion characteristics of Al–2 at.%Nd into phosphorus-doped (n+) a-Si:H were studied, and diffusion between Al–2 at.%Nd and phosphorous-doped poly-Si (n + poly-Si) was also investigated for comparison. The electric resistance variation of Al–2 at.%Nd, n + a-Si:H, and n + poly-Si was measured by four-point probe method at every annealing step, and each surface was inspected by optical microscope. Auger Electron Spectroscopy and X-ray Photoelectron Spectroscopy were used to analyze atomic diffusion progress with the variation of annealing temperature. Through these analyses, we ascertain that the Nd element of Al–2 at.%Nd hinders the diffusion between Al and Si, and n + a-Si:H is stable up to 300 °C and n + poly-Si is stable up to 400 °C against the diffusion of Al–2 at.%Nd. Thus Al–2 at.%Nd can be utilized as the source-drain electrode of a-Si:H TFTs below 300 °C and poly-Si TFTs below 400 °C without diffusion barrier.

This paper introduces the technology behind developing of flexible AM-OLED displays with improved color and reduced bending radius. Developing a-Si TFT fabrication technology using 80-μm ultrathin stainless steel foil as the substrate and integrating driver electronic in the display panel, we were able to demonstrate a full-color AM-OLED displayed in a curvature of less than 5 cm bending radius. Total panel thickness of 0.30 mm, brightness of 100 cd/m2 and color reproducibility of 63% were achieved.

Hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) were fabricated on a flexible stainless-steel (SS) substrate. The stability of the a-Si:H TFT is a key issue for active matrix organic light-emitting diodes (AMOLEDs). The drain current decreases because of the threshold voltage shift (ΔVTH) during OLED driving. A negative voltage at a floated gate can be induced by a negative substrate bias through a capacitor between the substrate and the gate electrode without additional circuits. The negative voltage biased at the SS substrate can recover ΔVTH and reduced drain current of the driving TFT. The VTH of the TFT increased by 2.3 V under a gate bias of +15 V and a drain bias of +15 V at 65 °C applied for 3,500 s. The VTH decreased by -2.3 V and the drain current recovered 97% of its initial value under a substrate bias of -23 V at 65 °C applied for 3,500 s.

To integrate solution-processible organic semiconductors in the array of thin-film transistors, fine-patterned organic thin-film transistors were fabricated by photolithography. Gold, which has a high work function, was used as a source–drain electrode to reduce the energy barrier between the organic semiconductor and the source–drain. Stacked double layers of gold and chromium were deposited and etched on a glass substrate to enhance the poor adhesion of gold on glass, and then a self-assembled monolayer was formed on them. Solutions of an organic semiconductor and a low-k organic gate insulator were spun by a spin coater and patterned by dry etching using a gate metal as a mask. The devices fabricated by this method show good electrical properties, average field effect mobilities of 0.2–0.3 cm2 V-1 s-1, and an on/off current ratio of over 105 in device dimensions of W/L=84/6 µm. The leakage current through the gate insulator between the gate and the source–drain was similar to that of SiNx in amorphous silicon thin-film transistor (a-Si TFT), which is lower than 10 pA. When the bias-stress stability of organic thin film transistors (OTFTs) was compared with that of a-Si TFT, the threshold voltage shift of OTFT was comparable to that of a-Si TFT, which is smaller than 1 V. However, the stability of OTFT should be further improved and discussed.

A novel active matrix array approach suitable for a compact multi-channel gas sensor platform is presented. Each sensor site utilizes carbon nanotubes (CNT) on top of a pair of interdigitated electrodes (IDEs) as the gas sensing element. The proposed active matrix sensor array utilizes an array of P-I-N diodes each connected in series with an IDE. The use of P-I-N diodes enables row and column addressing of each sensor thus significantly reducing the required wiring compared to individually addressed sensors. In this work, P-I-N diodes were implemented using either silicon-on insulator (SOI) or Low Temperature Poly-Silicon (LTPS) thin film technology thus validating that both wafer and glass based approaches can be used for the mass manufacture of proposed multi-channel sensor platforms. The functionality of 8×8 and 16×16 sensor arrays is proven with the help of a PEDOT:PSS cover. Data are also presented for the 8×8 arrays and the detection of ammonia (NH3) and chlorine (Cl2) vapor sources is demonstrated.

Organic photovoltaic devices (OPVs) are realizing power conversion efficiencies that are of interest for commercial production. However, cell efficiencies are poor to modest when compared to their more traditional silicon and other inorganic based counterparts. Apart from material breakthroughs, there is immense need to therefore engineer novel approaches to improve OPV cell performance. In this work, we have demonstrated feasibility of “Electretic” organic solar cells with improved efficiency based on incorporating functional electret materials into optimized organic photovoltaic cells. Dielectric Materials with the capability of storing electrical excess charges and therefore generating an electric field to adjacent electrodes or semiconductors are known as electrets [1]. The most significant feature of electrets is that they can be charged, discharged and recharged in a very controlled manner after preparation of the whole device in which they are used. In this proof of concept work, we have demonstrated dramatic improvement achieved in the current-voltage characteristic of conventional, simple OPV cells by simulating the electric field effects of an embedded electret layer by external high voltage DC bias levels. The concept will be revolutionary in enabling organic solar cells to break through the efficiency/ cost barrier to become more broadly, more quickly adopted.

We have fabricated high performance amorphous IGZO TFTs and integrated circuits on flexible kovar (Ni-Fe 42 alloy) foils. Excellent dimensional stability on kovar foils is obtained by a pre-anneal process at 800°C that limits the thermal run-out to within 100ppm. After substrate annealing, Ni-Fe 42 alloy retains high yield strength and good flexibility with the re-crystallized structure containing large isotropic grains between 20-50μm. Amorphous IGZO TFTs and circuits with a staggered, bottom-gate architecture are fabricated and tested. Non-flexed TFTs have field effect mobility of 12 cm2/V.s, threshold voltage around 2 V and sub-threshold swing of 0.6 V/decade and ON/OFF current ratio exceeding 107. Under prolonged uniaxial tensile strain upto 0.8%, TFTs exhibited minimal change in performance which augers well for use of Ni-Fe foil as flexible substrates. To demonstrate the viability of oxide-based device integration, n-type pseudo logic ring oscillator circuits are also evaluated. Sub 300 ns propagation delay is confirmed at a rail-rail supply voltage of 40 V. The results suggest that device integration on such a highly flexible substrate is amenable to roll-to-roll processing of future electronics.

We report Fe-42%Ni as a novel high-performance substrate for a-IGZO TFT fabrication after evaluating 8 different metals for chemical compatibility, mechanical flexing and dimensional stability. Excellent flexibility and rollability indicates that Fe-42%Ni would be a good choice as flexible substrate for R2R process. Pre-annealing process for stabilizing the substrate is studied and applied to the Fe-42%Ni foil before TFT fabrication. Staggered bottom gate a-IGZO TFTs which were fabricated on this substrate have field effect mobility of 12 cm2/V.s, threshold voltage of 2V, sub-threshold swing of 0.6V/decade and on/off current ratio exceeding 107.

We have developed a 14-inch flexible color e-paper using thin-film transistors on a thin metal foil and Color Filters coated onto the plastic substrate. This prototype has color, paper-like look, and is bendable and durable while maintaining excellent display quality.

A 10.1 inch SVGA reflective type flexible active matrix electrophoretic displays were successfully fabricated on a thin metal foil substrate. It was developed a new multi-barrier structure in order to use a rough metal foil as display substrate and designed a new TFT array structure for obtaining good performance. The backplane comprises a-Si thin film transistor array fabricated using a conventional TFT manufacturing technologies. The 800×600 pixel display can be driven during extremely bending and measures only 0.3 mm in total thickness and weighs 32.8 grams. This prototype displays have a true paper-like look and feel, with wide-viewing angle and high contrast ratio.

Indium–tin–oxide (ITO) films doped using an ion implantation system were used as the anode electrode of organic light-emitting diodes (OLEDs). Changes in the characteristics of the doped ITO films were observed and measured in terms of sheet resistance, Hall mobility, contact angle, roughness, transmittance and work function. Boron dopant was used as an impurity to modify the surface of the ITO films. The depth profile of boron concentration was monitored by secondary ion mass spectrometry (SIMS) as a function of dose. Optimum dose was 5×1014 atoms/cm3 at which resistance was lowest. The resistance variation from 16 Ω/sq. of the conventional ITO to 11 Ω/sq. of doped ITO shows that the doped ITO films become more conductive after doping and thermal annealing. The Hall mobility and carrier concentration of boron-doped ITO was 40.4 cm2/Vs and -9.32×1020/cm3 respectively. Contact angle and roughness were investigated by the sessile drop technique and atomic force microscopy (AFM). After doping, the water contact angle of the film surface was changed from 55° to 38° and the root-mean-square roughness of the films was similar to that of conventional ITO. Transmittance in the visible spectrum range was increased from 91% to 96%. Work function was improved from 4.66 eV to 4.86 eV. An OLED device fabricated with a multilayer, boron-doped-ITO/CuPc/NPD/Alq3:C545T/Alq3/LiF/Al, was tested. The device had a luminance of 780 cd/m2 and the lifetime was also increased by approximately 25% compared with those of ITO devices produced under the same conditions.