To save this undefined to your undefined account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your undefined account.
Find out more about saving content to .
To save this article to your Kindle, first ensure firstname.lastname@example.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
In the last few years, industrial research into materials fulfilling the needs of the maturing OLED display industry has intensified considerably. A first generation of polymers (phenyl- PPVs) is now being commercially exploited in first monochrome polymer LED display applications. Based on these materials, non-planar displays have already been demonstrated. However, those proof of concept devices have been monochrome. Especially the RGB materials need considerable improvement to be suitable for flexible full color displays.
We will therefore report on the progress in the development of polymers for red, green, and blue emission. Our main focus here is on improving the properties of various polymers derived from the spiro-bifluorene core.
Depending on the color, the main issues vary strongly: For BLUE polymers, efficiency, color coordinates, and processibility are already at a commercial level while operational lifetime still needs strong improvement. RED materials are in an almost contrary situation: here, the operational lifetime is excellent, whereas the efficiency and the driving current are requiring further improvement. For GREEN, achieving saturated emission, whilst maintaining the other properties (high efficiency, long operational lifetime), is still challenging. We will demonstrate the current status of material development within Covion.
In addition, we achieved advances in full-color patterning, especially techniques based on Ink-Jet printing. This technology potentially allows the efficient manufacturing of high resolution RGB devices on a variety of substrates, including flexible layers.
Flexible magnetic lithography is a process qualitatively analogous to contact optical lithography which transfers information from a patterned magnetic mask (analog of optical photomask) to magnetic media (analog of photoresist), and is interesting for applications in instantaneous parallel magnetic recording. The magnetic mask consists of patterned soft magnetic material (FeNiCo, FeCo) on a flexible plastic substrate, typically Polyethylene Teraphtalate (PET). When uniformly magnetized media is brought into intimate contact with the magnetic mask, an externally applied magnetic field selectively changes the magnetic orientation in the areas not covered with the soft magnetic material. Flexible substrate of the magnetic mask o.ers superior compliance to magnetic media which is likely to have imperfect flatness and surface particulate contamination.
Although magnetic in physical nature, flexible magnetics draws interesting parallels to flexible electronics, especially in challenges of fabrication of sub-micron patterns on thin flexible plastic substrates. We fabricated samples of sub-micron patterned FeCo and FeNiCo magnetic masks on PET substrates by using combined lamination/release process of PET films. Rigid substrates, typically silicon or quartz were initially laminated with PET films and processed using standard fabrication procedures. After completing magnetic mask device fabrication, PET films were released from the rigid substrates.
We successfully transferred patterns from magnetic masks to hard disk CrPtCo-based magnetic media. The details of the method, including physics of the magnetic lithography pattern transfer, fabrication of the magnetic mask on flexible PET substrates, lamination and release of PET films, and magnetic force microscopy (MFM) images of the magnetic transition patterns are reported.
An electronic imaging system using a curved image sensor can use a faster lens, and cover a greater field of view, than an imaging system using a planar sensor. The simpler lens systems also weight less, a decisive advantage in portable applications.
This paper describes a method to fabricate a curved silicon substrate from a flat wafer containing appropriate circuits. To curve the substrate, the processed wafer is diced, by dry-etching from the backside, into 1x1cm tiles. The tiles are separated by 0.5mm gaps, which are bridged, in turn, by a dense array of 45x100μm gold leads formed by electroplating using lithographically defined leads as seeds. Two methods were used to curve the wafer. In the first one, the wafer was bonded with epoxy to a PMMA disk, and then curved by heating the sandwich, under a load of ∼ 230gr, for 1.5 hrs at 130°C in a concave metal mold with a radius of curvature of 7.8cm. In the second method, the wafer was put into a curved metal mold, radius 14cm, loaded with 230gr, and heated to 290°C for 2 hrs. The normal and shear strains accommodated by the flexible interconnects were measured by analyzing their deformation. The experimentally measured strains are compared with a model that calculates the deformation required to deform a flat sheet into a spherical surface.
Highly transparent and conductive ZnO:Ga thin films were produced by rf magnetron sputtering at room temperature on polyethylene naphthalate substrates. The films present a good electrical and optical stability, surface uniformity and a very good adhesion to the polymeric substrates. The lowest resistivity obtained was 5×10-4 Ωcm with a sheet resistance of 15 Ω/sqr and an average optical transmittance in the visible part of the spectra of 80 %. It was also shown that by passivating the polymeric surface with a thin SiO2 layer, the electrical and structural properties of the films are improved nearly by a factor of 2.
Stretchable, elastic metal interconnects are a key to the fabrication of 3-D conformal circuits and electrotextiles. The basic concept for reversibly stretchable, elastic metallization is a corrugated stripe of thin-film metal that is expanded by stretching. The maximum elongation is reached when the stripe is stretched flat. We prepared wavy metal stripes by evaporating gold onto pre-stretched strips of the elastomer, poly-dimethyl siloxane (PDMS). We experimented with gold metal line width and thickness and substrate elongation. We measured the film structure, amplitude, and wavelength, as well as electrical resistance in relaxed and various stretched states. So far we have reached elastic strains of 15% while maintaining the initial resistance and 80% with a rise in the resistance. We discovered a rich macroscopic and microscopic film morphology. Presented are the fabrication, electro-mechanical performance, and data on the film structure of these wavy metal interconnects.
PMOD (Photochemical Metal Organic Deposition)-based DTFI (Direct Thin Film Imaging) methodology is a demonstrated means for patterning organic materials on flexible (plastic) substrates. This process is used to pattern 1-micron features at an aspect ratio of 8:1 using contact lithography. Use of oxygen plasma RIE etch to transfer the hard mask pattern to the organic material allows for good sidewall angle control. High etch selectivity between the novolac polymer and PMOD TiOX hard mask (< 800:1) makes the use of very thin hard masks (∼ 200 angstroms) to pattern thick organic films (<10 microns) possible. Selective removal of the PMOD TiOX (TiO2) hard mask makes this process amenable to patterning of functional organic structures fabricated from materials chosen for their desired properties (e.g., glass transition temperature (Tg), etch resisitance, optical properties, mechanical properties, etc.) not their ability to be photopatterned (e.g., photoresist).
The complex dielectric constants of several π-conjugated materials were measured, and generalized Langevin equation was used to analyze the dielectric behavior in the frequency domain. From the results of the fitting the experimental data using the generalized Langevin equation, we suggest that the charge carriers are electrically screened by the neighboring charges through the structural relaxation, and the carriers are not interact each other. We confirmed that the generalized Langevin equation offers a very good approach to analyze and understand the transport properties of charge carriers in π-conjugated materials.
Textiles are a suitable substrate for large area, flexible and wearable electronics because of their excellent flexibility, mechanical properties and low cost manufacturability. The ability to fabricate active devices on fiber is a key step for achieving large area and flexible electronic structures. We fabricated transistors and inverters with a-Si film and pentacene film on Kapton film and cut them into fibers. The a-Si TFT showed a threshold voltage of 8.5 V and on/off ratio of 103 at a drain voltage of 10 V. These are similar to the characteristics of a TFT fabricated on a glass substrate at the same time. The maximum gain of the inverter with an enhancement n-type load was 6.45 at a drain voltage of 10 V. The pentacene OTFT showed a threshold voltage of -8 V and on/off ratio of 103 at a drain voltage of -30 V. The inverter with a depletion p-type load showed a voltage inversion but the inversion occurred at the wrong voltage. The antifuse was successfully programmed with a voltage pulse and also a current pulse. The resistance decreased from 10 GΩ to 2 kΩ after the programming.
The X-ray diffraction measurement for superionic conducting glasses nAgI-3Ag2O-2V2O5 (n = 2, 5, 10) has been performed at 12, 100, 200 and 290 K. The temperature dependence of structure factor S(Q) of nAgI-3Ag2O-2V2O5 has been discussed based on the theoretical treatment including the thermal vibration of atoms in noncrystalline materials. The effective overall Debye-Waller temperature parameter B increases with the increase of temperature and also with AgI concentration.
In order to tailor the synthesis of new robust organic materials for electronic applications and to guarantee the required life time for the emerging commercial plastic electronic applications it is of key importance to understand the underlying degradation mechanisms. Since plastic electronics is a rather young technology introducing new material systems, its reliability is characterized by new failure and degradation mechanisms, a relatively high amount of early failures and multi-modal failure distributions. To understand the mechanism responsible for a given failure or degradation mode, it is essential to study it separately, through appropriate test structures and test techniques. Powerful techniques for this purpose are a.o. analytical techniques (SEM, TEM, SPM,…), in-situ electrical measurement techniques and spectroscopical techniques (in-situ FTIR, in-situ UV-Vis, PDS). The benefits of these in-situ techniques in the reliability study of organic based electronics will be illustrated in this contribution.
With market opportunities continuing to drive electronic products to smaller size, significant research efforts continue to shrink semiconductor devices in accordance with Moore's Law. However, a new set of market opportunities is emerging for which the significant driver is not semiconductor complexity, but rather lower product cost arising from the novel integration of technologies making use of organic and flexible substrates. These new technologies present opportunities for research into new materials and fabrication processes. These new research opportunities extend from embedding passive devices, microfluidics, and polymeric optical waveguides in printed wiring boards, to organic transistors. This paper will discuss these new technologies and present some of the market forces driving these efforts.
Direct fabrication of organic light emitting diodes (OLED) on a polymeric substrate, i.e., polymeric waveguide substrate to form a flexile optical integrated devices has been realized. The OELD was fabricated by organic molecular beam deposition (OMBD) technique on a polymeric substrate and a glass substrate, for comparison. The device fabricated on a polymeric substrate shows similar device characteristics to that on a glass substrate. Optical signal of faster than 100 MHz has been created by applying pulsed voltage directly to the OLED with emissive layers utilizing rubrene or porphine doped in 8-hydoxyquinolinum aluminum derivatives. Optical signal transmission with OLED fabricated on a polymeric waveguide with optical connectors has been successfully realized. Optical photo detectors (OPD) utilizing phthalocyanine derivatives with superlattice structure provide increased pulse response with input optical signals, and the OPD with 5 MHz of cut-off frequency has been realized with superlattice structure under reverse bias voltage to the OPD.
Pentacene is one of the most promising organic materials for organic transistor fabrication, since it offers higher mobility, better on-off ratio, improved environmental stability, and better reliability than most other organic semiconductors. However, its severe insolubility renders it useless for the solution-based fabrication of electronic devices. Solution-based processing is the key to enabling ultra-low-cost circuit fabrication, since it eliminates the need for lithography, subtractive processing, and vacuum-based film deposition. Using a recently developed soluble pentacene precursor, we demonstrate the first inkjet-printed pentacene transistor fabricated to date. This is achieved using a substrate-gated transistor structure in conjunction with an inkjetprinted pentacene precursor active layer. After deposition, the precursor is converted to pentacene via heating, through the decomposition of the Diels-Alder product. As the anneal temperature increases above 120°C, performance increases dramatically. The process is therefore compatible with numerous low-temperature plastics. As the anneal time is increased to several minutes, performance likewise increases through increased precursor decomposition. However, exposure to excess temperatures or times tends to degrade performance. This is caused by morphological and chemical changes in the pentacene film. Optimization of the anneal process alone has resulted in the demonstration of transistors with an on-off ratio of >105 and field-effect mobility of >0.01cm2/V-s, attesting to the great promise of this material.
We have investigated the growth mechanism and thin film morphology of pentacene thin films by the process of low-pressure gas assisted organic vapor deposition (LP-GAOVD). As the source temperature, flow rate of the carrier gas, substrate temperature and chamber pressure were varied, the growth rate, morphology and grain size of the films were differently obtained. The electrical properties of pentacene thin films for applications in organic thin film transistor and electrophoretic displays were discussed
The properties of ZnO thin film are currently of great commercial and scientific interest due to its particular properties such as highly conductive, transparent as well as chemical stability and nontoxic. The Ti doping ZnO thin films were deposited by simultaneously magnetron co-sputtering from both Zn and Ti targets in a mixture of oxygen and argon gases onto heated Corning 7059 glass substrates in this study. The experimental results show that deposition rate of ZnO films are strongly dependent on DC power of Ti target. The growth rate initially increases and changes to decrease when the DC power of Ti target further rises. The content of Ti in the ZnO films increases with the applied DC power of Ti target. The lattice constant of ZnO (002) increases with DC power of Ti target due to incorporated Ti into the lattice of ZnO. The crystalline size becomes smaller when the DC power of Ti target was raised. The visible transmittance is a little lowered when slight Ti incorporated but still average maintains above 80%. The lowest resistivity of undoped ZnO film obtained in this study is 4.14×10-3 ohm-cm and further decreased to 1.02×10-3 ohm-cm after being doped a trace of Ti.
The mechanical properties of two cured silicone monolithic specimens with targeted bulk moduli of 300 and 10 MPa have been evaluated by DMA and regionally by CSM nanoindentation. The results showed that the mechanical properties of the monolithic samples were heterogeneous, with the DMA and nanoindention results only in agreement at the midplane of cleaved bulk samples. The specimens showed a significantly higher modulus at the sample surfaces compared to the bulk. Thin films of the same silicones displayed a modulus closer to that of the bulk sample surface. The nanoindentation results of this study were reliable and consistent, and are being used to assess the effects of material and microelectronic device integration processes on the mechanical properties of a series of low modulus photopatternable silicone thin film dielectrics.
Low temperature copper-induced crystallization of amorphous germanium (a-Ge) has been significantly enhanced by applying mechanical compressive stress during thermal post-treatment. Manipulation of this technique, alongside with proper patterning of the a-Ge layer before thermo-mechanical process, has led to growth of device-quality poly-Ge layer on flexible PET substrate at temperatures as low as 130°C. Flexibility of the substrate allows the efficient application of uniaxial compressive stress by bending the PET sheets inward. Effects of compressive stress and ultimate crystallization of the Ge layer has been verified by electrical sheet resistance and Hall mobility measurements, and analyzed by XRD, SEM, TEM and RAMAN spectroscopy.
In this study, we have investigated microencapsulation of magenta, yellow, and cyan color polymer balls with white pigment for multi-color electrophoretic display implementation. The charged color pigments have been prepared by physical coating of magenta, yellow, and cyan with functionalized polymers, then surface charging with charge control agent. These color balls with white pigment were microencapsulated in suspending fluid through in-situ polymerization.
In the most fundamental approach, e-Textile circuits will be made by weaving component fibers into circuits. The weaving pattern will determine the circuit function. A key requirement of such e-Textile circuits is reliable electrical contact between fibers. Contacts which rely only on the pressure between fibers are preferred since they preserve the drapability of real fabrics. Since thin-film device fabrication technology is planar, the component fibers, made by the slit-film technique, are flat. Thus a slight edge-to-edge curvature (with a radius of curvature as large as 500mm) can either prevent or promote electrical contact. Using fibers with thin-film transistors of amorphous silicon, we study the processes that produce the desired fiber curvature. A layer of stressed silicon nitride is used to create the curvature. The stress in this layer can be controlled by the deposition parameters. We present successful fabrication of curved fibers with vastly improved electrical contact. We also present electrical characterization of woven transistor circuits
The dielectric and thermal properties of three-layer structured films were studied. The two outer layers were about 1 μm and the thickness of the middle layer was varied. We measured the thickness dependence of the dielectric constant of the three-layer structured films. The dielectric results were evaluated with a simple serial three-capacitance model. Local thermal property of these polymer films were also measured using a micro-tip local thermal analysis method. Local glass transition of the film was compared with the one expected from bulk data.