Low temperature poly-Si TFT technology is reviewed and is discussed from a view point of device, fabrication process, and its possibility as FPD (Flat Panel Display) application. After the appearance of crystallization technique of SPC (Solid Phase Crystallization) using FA (Furnace Annealing) or ELA (Excimer Laser Annealing) using UV (Ultra-Violet) beam, the electronic property of poly-Si thin-film, which relates to the crystalinity of the grains, was improved drastically, and the process temperature for the TFT fabrication had been reduced below 600° down to 400°. As a result, improvement of device characteristic of poly-Si TFT such as an enhancement of carrier mobility or a reduction of leakage current has been studied intensively for the application to FPD (Flat Panel Display) on glass. Currently, extensive study is being done in order to realize a more functional SOG (System on Glass). By reducing the TFT process temperature down to 200° or below and by modifying a design for the device structure or the circuit in the pixel, O-LED (Organic LED) FPD addressed by uniform poly-Si TFTs is expected to mount on flexible plastic substrate such as on PES (PolyEtherSulphone). The poly-Si TFT has a possibility to develop as a smart system on plastic panel for unique applications as well as the conventional Si LSI in the ubiquitous IT (Information Technology) era.

Poly-Si Thin-Film Transistors (TFTs) are currently used in commercial active-matrix displays. They provide superior performance with respect to their amorphous silicon counterparts and allow integration of driving electronics directly on the display glass plates.

For several applications, it can be desirable to have active-matrix displays made on flexible substrates. However, a direct application of a standard TFT process to plastic substrates is not in general possible, mostly because of temperature limits and related dimensional stability issues. In addition, standard flat-panel manufacturing tools are not capable of automatically handling non-rigid floppy substrates.

Therefore, a new process has to be developed, compatible with a suitable way of handling plastic substrates. A process was developed in which plastic sheets are laminated on glass carrier wafers and run through all the automated tools. A low-temperature process using excimer laser annealing is developed and optimized. High-quality TFT backplanes are manufactured with a pixel layout designed for active-matrix OLED (AMOLED) displays. Field-effect mobility in excess of 70 cm2Vs on p-channel TFTs are achieved, together with leakage currents lower than 2 pA per micron gate width.

Challenges include low-temperature gate dielectric development, reduction of intrinsic film stress, protection of plastic from laser damage, and contact formation. Solutions to these challenges are discussed and TFT transfer characteristics on glass and plastic substrates are presented. Finally, images from prototype monochrome AMOLED displays are presented, with 64 × 64 pixels and 80-dpi resolution.

Polymer optoelectronics and microelectronics have been recognized as next generation technologies. One of the widely investigated materials for photodiode, LED and solar cell applications is the insoluble conjugated polymer poly(p-phenylene vinylene) or PPV. In this paper we present experimental results of a blended polymer-organic compound photodiode. This diode is based on a soluble derivative of PPV, poly(2-methoxy-5- (2,9-ethyl-hexyloxy)-1,4- phenylene vinylene) or MEH-PPV, and the organic material ethyl viologen dibromide or EVD. In making the photodiodes, solutions of MEH-PPV and EVD were spin-coated on indium tin oxide coated glass substrates. The thicknesses of these polymer-organic thin films were approximately 190 nm. An aluminum cathode was deposited by thermal evaporation. These devices were illuminated under monochromatic light in UV and visible range wavelengths. These thin polymer-organic blend photodiodes have shown an eight-fold increase in responsivity and quantum efficiency compared to pure MEH-PPV photodiode devices. The increase in photoconductivity of blended MEH-PPV:EVD photodiodes may be due to charge transfer by EVD dication. The results from this work clearly demonstrate the application of the reported approach for the realization of polymer photodiodes with increased photoconductivity characteristics.

The effects of various ambient gases (N2, O2, H2O) to the electron mobility of tris(8-hydroxyquinoline) aluminum, Alq3, were examined. For a clean Alq3, the electron transport is non-dispersive and essentially trap-free as revealed by optical time-of-flight measurements. At 295K, the electron mobility (μe) spans the range 0.2-1×10−6cm2V−1s−1 when the field varies from 0.4-0.9 MV cm−1. Exposing the sample to oxygen dosages in the range 1-100 Torr.s does not cause any noticeable changes in μe. The effect of oxygen on μe can be observed only at much higher oxygen dosages (>105 Torr.s). In contrast, exposing pristine Alq3 to moisture of same dosages causes a gradual reduction in μe by a factor of 4. It is proposed that oxygen diffuses into Alq3 during exposure and subsequently acts as charge scattering centers for externally injected free electrons. On the other hand, water induces charge traps at high dosages. Moisture control appears to be the most critical factor for the long-term operation of Alq3-based organic light-emitting diodes.

We present a new type of system architecture to fabricate thin film silicon devices on flexible substrates, which uses the inherent advantages of a cluster tool normally used in the production of amorphous silicon thin film transistors, solar cells, etc. In this, the flexible substrate material is contained within a cassette which includes a reel to reel operation. As in the current cluster tools used for planar substrates, the cassette is transported to a process chamber using a robotic arm. When the entire roll in the cassette has been processed, it is transported into other chambers for further processing. We also show that a four terminal device structure (e.g. amorphous Si and stable low band gap nano-crystalline Si cells) potentially can lead to high efficiency (>15%), stable, low cost solar cells on a plastic substrate. Lastly we discuss the use of a pulsed PECVD deposition technique, which allows that the structure of the nano-crystalline Si films can be altered from 111 to 220 in a controllable way at a low temperature of <170C.

In view of its maturity and low-cost, the amorphous silicon (a-Si) technology is an attractive candidate for active matrix organic light emitting diode (AMOLED) display backplanes on flexible substrates. However, the a-Si material comes with significant intrinsic shortcomings related to speed (mobility) and stability of operation, requiring novel threshold-voltage-shift (ΔVT) compensated thin-film transistor (TFT) pixel circuits and architectures to enable stable OLED operation. But given the dramatic progress in efficiency of OLED materials over recent years, the drive current requirement has been significantly lowered, thus relaxing the constraints on a-Si TFTs. For compatibility to plastic substrates, the a-Si TFT process temperature must be reduced from the conventional 300°C to ∼150°C or below, which tends to compromise the integrity of thin- film materials and device performance. Hence, optimizing the TFT process for high device performance with limited thermal budget is a necessary step towards flexible AMOLEDs with a-Si backplanes. This paper reviews the design and process challenges, and specifically examines the performance of TFTs and ΔVT-compensated integrated pixel driver circuits on plastic substrates with respect to current driving ability and long term stability. More importantly, lifetime tests of circuit degradation behaviour over extended time periods demonstrate highly stable drive currents and its ability to meet commercial standards.

In the given report we present results of investigation of possibility to produce gas sensors on flexible substrates (polymer roll base). As gas sensitive materials were chosen glass chalcogenide semiconductors on the base of solid solutions of (As2S3)x-(As2Se3)1−x (where x=0; 0.3; 0.5; 0.7 and 1.0) and also solid solutions of As-Tl-S-Se system. Thin films of the mentioned above materials were deposited on lavsan roll film by means of thermal evaporation under vacuum conditions 10-5 Torr. At the thickness of 1-2 um the deposited layers are possessed the specific resistance in the range of 1010-1014 Ohm.cm on dependence on chemical composition.

The change of conductivity of these films in the presence of gas impurity in atmosphere was used as sensitive parameter. Gas sensitive characteristics of obtained structures were tested with such toxic and inflammable environmental pollutant gases as carbon monoxide, methane, nitrogen dioxide, hydrogen and other. All measurements of gas sensitivity were performed at room temperature. For further increase of the gas sensitivity and selectivity the very thin layer of Pd was deposited onto the surface of semiconductor layer. The last one has allowed to increasing the gas sensitive characteristics by order.

Through routine technology mode ready gas sensors were created. Dimensions of the developed gas sensitive elements were 1000×1000×350 μm.

In order to fabricate flexible microelectronic devices, fabrication of metallization lines and metal electrodes on the flexible substrate is essential. Cu lines are often used as interconnect lines in electronic devices and Au as microelectrodes in organic transistors and bioelectronics devices due to its good electrochemical stability and biocompatibility. For minimizing the size of device, the realization of metallization lines and microelectrodes with the scale of a few micrometers on the flexible substrate is very important. In this work, micro-scale metallization lines of Cu and Au were fabricated on the flexible polyimide (PI) substrate by electroplating using the patterned mask of a negative-tone SU-8 photoresist. Surface of PI substrate was treated by O2 inductively coupled plasma for improvement in the adhesion between the Cr layer and the PI and in-situ sputter-deposition of 100-nm-thick Cu seed layers on the sputter-deposited 50-nm- thick Cr adhesion layer was followed. Electroplating of Cu and Au lines using a sulfuric acid and a noncyanide solution with the patterned SU-8 mask, respectively, removal of SU-8, and selective wet etch of Cr adhesion and Cu seed layers were carried out. Micro-scale Au electrode lines were successfully fabricated on the PI substrate. Micro-scale gap-filled Cu lines with spin- coated polyimide on the PI substrate with the thickness of 6 ∼ 12 νm and the aspect ratio of 1~3 were successfully fabricated.

Simple, cost-effective roll-to-roll processes for the manufacturing of patterned conductor films have been developed. The technique involves printing proprietary masking patterns, depositing conductive material, and stripping away undesired areas. In one approach, a pattern is printed on the plastic substrate with a masking coating. Then, conductive material is deposited on the patterned substrate and the undesired areas are stripped away, leaving behind the patterned electrode structures. In another approach, a first masking pattern is printed, followed by a second masking coating which is repelled by the first masking layer and forms the negative pattern. The first masking pattern is stripped off, a conductive layer is deposited, and the second masking pattern is stripped off, leaving a high resolution conductor pattern on the web. No photolithographic exposure, development or chemical etching is needed. These processes are useful for producing rolls of electrodes with features as small as 25 microns for the roll-to-roll manufacturing of flexible display applications.

In this work, transparent flexible substrates based on polyimides(PI) with indium tin oxide (ITO) thin films for organic electroluminescent devices have been prepared. 2,2'-bis-(3,4- dicarboxyphenyl) hexafluoropropanedianhydride (6FDA) and 2,2'-bis-(trifluoromethyl)-4,4'- diaminobiphenyl (TFDB) PI films were used for transparent flexible substrates. ITO thin films were prepared at two substrate deposition temperatures of 25°C and 150°C with a typical radio- frequency (r.f.) planar magnetron sputtering system. The sheet resistance and the optical transmission properties of the fluorinated PI substrate were comparable with those for the slide glass substrate. The substrate properties are better when the deposition temperature is higher. SiO2 coating onto the fluorinated PI substrate by sol-gel reaction was also attempted to improve the optical transmission of the ITO/PI substrate. It was found that the coating of SiO2 affected on the morphology of the PI substrates.

NASA is currently developing a host of deployable structures for the exploration of space. These include balloons, solar sails, space-borne telescopes and membrane-based synthetic aperture radar. Each of these applications is driven by the need for a thin, low mass, large area structure (e.g., polymer-based) which could not be implemented using conventional engineering materials such as metals and alloys. In each case, there is also the need to integrate sensing and control electronics within the structure. However, conventional silicon-based electronics are difficult to integrate with such large, thin structures, due to a variety of concerns including mass, reliability and manufacturing issues. Flexible electronics, particularly thin film transistors (TFTs), are a potentially key enabling technology that may allow the integration of a wide range of sensors and actuators into these types of structures. There are numerous challenges, however, regarding the survivability of such devices during stowage and deployment of the structure, as well as during operation in the harsh environments of space. We have fabricated TFTs on polyimide substrates, and are investigating the durability of these devices with respect to relevant space environments. We are also developing flexible sensor technologies for the integration of distributed sensor networks on large area structures.

Large area p-i-n image sensors deposited on plastic substrates were produced at low temperatures (110 °C) by PE-CVD and compared with similar sensors deposited on glass substrates. The same sensing element structure ZnO:Al/p(SiC:H)/i(Si:H)/n(SiC:H)/Al was used for both devices. In this work the efforts are focused mainly on the optimization of the output characteristics of the sensor when fabricated on plastic substrates. The role of the sensor configuration and readout parameters in the image acquisition process is analyzed. The optical- to-electrical transfer characteristics show a reasonable quantum efficiency under a red light pattern, broad spectral response, and reciprocity between light and image signal.

First results show that the sensors deposited on flexible substrate present smaller light to dark sensitivity than those deposited on glass. In both, the non ohmic behavior of the transparent conductive oxide front contact blocks the carrier collection and leads to a surprising linear dependence of the image signal with the applied voltage.

Here we report on OTFTs made from a novel thermoresponsive thiophene based oligomer. The functionalized oligomer is soluble in common solvents, but loses its solubility upon thermolysis. Devices with channel lengths from 5 to 40 νm were fabricated from solution then subjected to thermolysis at temperatures ranging from 150-250°C. The initially amorphous materials reorganize into highly crystalline films upon thermolysis. Crystallinity was characterized by x-ray diffractometry and atomic force imaging. AFM studies depicted the nucleation of molecular terraces, where the formation and overall height of terraces was observed to be dependent upon the thermolysis temperature and solvent choice. These factors correlated to overall performance. For both dip-cast and spin-cast samples, devices were fabricated at a process temperature of 180°C with mobilities of 0.07 cm2/Vs and on/off ratios > 105. The deves were relatively stable in both air and common solvents, with their mobility degrading only by ∼25% upon immersion in the original casting solvents. The solubility characteristics and process temperatures for these devices may be particularly suitable for solution processing on flexible substrates.

This paper examines the variations in performance of amorphous silicon (a-Si:H) thin-film transistor (TFT) pixel driver circuits for active-matrix organic light-emitting diode (AMOLED) displays, which are subject to compressive or tensile mechanical strain. The external strain is induced by bending of the TFT substrate, and is measured by the observed changes in resistance of in-situ strain gauges. Mechanical strain impacts the performance of the circuit in terms of its drive current, which may be attributed to mobility and Fermi energy shifts in the individual TFTs. The effect of strain-induced shifts in the TFTs as a function of strain orientation (longitudinal or transverse) with respect to direction of current flow is also examined. Our measurements show that the variation in the drain current of a longitudinally oriented TFT can be as much as ∼ 1.5% for strains as high as 10−3. Proper layout and circuit design can suppress the effect of strain-induced shifts, and should be taken into consideration when designing stable TFT driver circuits for mechanically flexible AMOLED displays.

A simple idea is proposed for the realization of organic photovoltaic devices on flexible substrates. According to this, a poly(ethylene terephtalate) layer (Mylar), transparent, a few micrometers thick and completely flexible, works as mechanical support. It is an insulating material, which has good mechanical and dielectric properties and, most important, it is completely transparent to ultraviolet light. For this reason it could be suitable for being used as transparent supporting layer for large area photovoltaic devices. Furthermore, its mechanical properties allow to employ it in a roll-to-roll lamination procedure that could give rise to low cost extended films carrying solar cells on the surface.

This report present results of study of some organic materials suitable for creation of photothermoplastic media (on flexible base) for optical information recording. In particular, speech is about donor-acceptor systems on the base of carbazolyl containing polymers, in particular, carbzolylethylmethacrylates (CEM) with oktylmethacrylates (OMA) and polyepoxypropylcarbazolyl (PEPC) copolymers sensibilization of which was made by means of 5-20% of trinitrofluorenone (TNF), N-fenylamino-2,4,7-trinitrofluorenone (FNF) and ditianomethylen-2,4,7-trinitrofluorenone (DTF) (containing donor-acceptor group) and additives of photochromic substances of indolynospirobenspyran series.

There were studied the dependencies of photosensitivity on sensibilizer's concentration and temperature of heating of polymeric material and also the spectral diapason of photosensitivity. It was established that maximum of photosensitivity is observed at the concentration of sensibilizing agent 12-14%. Heating above 60°C leads to sharp decrease of photosensitivity of developed organic materials.

It was established that donor-acceptor systems as photoplastic layers possess photosensitivity on the level 10−3-10−4 J/cm2. The introduction of PP layers of 6-10% photochromic additives leads to 2-3 times increasing of the photosensitivity of the given donor- acceptor system. At that the essential growth of photosensitivity is observed in the blue-green part of visible spectrum. Also, it was established that 8'-nitro-1,3,3- trimethylindolynospirobenzopyrane possess the greatest effect of sensibilization. The fact that adsorption band (500-600 nm) is in the visible part of spectrum confirms the amplification of concentration of donor-acceptor group in PP layers and, as result, considerable growth of photosensitivity. The received results are discussed.

Thus, donor-acceptor systems, developed on the base of photopolymer CEM:OMA, demonstrate photosensitivity of 10−6 J/cm2. at 80-85°C that 2-3 times higher than in case of usual donor-acceptor systems.

Although it is tempting to begin with a standard opening statement like “Flexible displays have been generating much recent interest,” the fact is that flexible displays have fascinated people for about 50 years and have been discussed seriously for at least 20 years. The difference now is that display and backplane technology have evolved to the point where reasonably attractive-looking demonstrations of flexible screens are possible.

We have proposed nitrous oxide (N2O) plasma pre-treatment in order to reduce the oxide charge densities as well as to increase the breakdown field of silicon dioxide film for flexible display. Our experimental results show that the proposed treatment improved both the flat-band voltage from –3V to –1.8V and the breakdown voltage of gate oxide from 7MV/cm to 9.5MV/cm, respectively. The proposed treatment also improved poly-Si TFT characteristics such as low sub-threshold swing of 0.43V/dec.

Flexible printed circuits are a technology and product enabler for miniature, high density electronic systems, especially mobile communications and automotive applications. Over the past ten years, flexible printed circuit densities have increased, dramatically, while the area they occupy has decreased. The ever shrinking circuit form factor and increasing I/O and interconnect densities are driving flex circuit configurations from single sided to double sided constructions. In addition, the need for high performance steers circuit construction towards thinner dielectrics. Adhesiveless flex circuit constructions, for example, enable direct metal and lamination bonding without the use of added adhesive materials. Removing adhesive layers, such as epoxies or acrylics allows for a thinner more flexible device with a homogeneous dielectric stack (e.g., all polyimide construction), resulting in superior electrical performance. High resolution flexible circuit processes established using General Electric ULTEM [registered trademark] polyetherimide materials have shown ULTEM resin to have excellent electrical properties including dielectric constant and dissipation factor. Adhesiveless single and double sided flexible circuits have been fabricated and tested for performance (electrical, mechanical, thermal) and reliability (thermal cycling, tear propagation, flexural endurance, and solderability). Critical flex circuit fabrication processes such as metal adhesion, micro-via formation, lamination, photolithography, and module singulation have been evaluated. This paper addresses the key steps for flexible substrate fabrication describing the key advantages and disadvantages of the approach.

We will demonstrate a novel approach to the problem of patterning organic small molecule layers, which is compatible with printing techniques. By locally changing the chemistry of the dielectric surface by means of Self-Assembly Monolayers (SAM), we predefine active and passive areas of the circuit. The subsequent growth of the organic film by sublimation takes place under growth conditions which cause the formation of a high-mobility, well- connected two-dimensional (2D) grains in the predefined active area contrasting with ill- connected, low-mobility 3D-grains in the passive area. We will explain this patterned growth in terms of a microscopic theory of nucleation of organic semiconductor on inert substrates and present experimental results.