A preview of the papers appearing in the March 2005 issue of the Journal of the SID, available on-line at www.SID.org.
Edited by Aris Silzars
Pieter van Lieshout
Erik van Veenendaal
Philips Research Laboratories, Eindhoven, The Netherlands
Abstract — A QVGA active-matrix backplane was produced on a 25-μm thin plastic substrate. A four-mask photolithographic process was used. The insulator layer and the semiconductor layer were organic material processed from solution. This backplane was a combination of the electrophoretic display effects supplied by SiPix Imaging and E-Ink Corp., resulting in electronic-paper displays with a thickness of 150 and 100 μm, respectively; this is the world's thinnest active-matrix display ever made.
Keywords — Plastic electronics, polymer electronics, active-matrix display, electrophoretic display, electronic paper.
The key features of this technology are that, first, a thin flexible foil is glued onto a rigid support, then the functional layer stack is processed, and, finally, the foil containing the microelectronic devices is delaminated from its support without degradation of the devices. The rigid support can be re-used. This allows the use of standard off-the-shelf patterning and deposition equipment. Typically, a registration better than 2.5 μm over a 150-mm wafer for a four-mask process is achieved. Integration of transistors over large areas with a relatively small overlap of 5 μm is possible. This allows the production of transistors with sufficiently small parasitic stray capacitances for active-matrix displays.
FIGURE 6 — A picture of the rollable QVGA active-matrix display withorganic TFTs combined with the E-Ink electrophoretic display effect. Theframe rate is 50 Hz, the image update time is ~0.5 sec.
Seiko-Epson Corp., Japan
Abstract — Thin-film transistors (TFTs) are field-effect transistors that can be used to create large-scale-integrated (LSI) circuits. The combination of high-performance TFTs and transfer technology of the TFTs has the potential to foster the rise of a new flexible microelectronics industry. This paper discusses the current status of flexible microelectronics, using a TFT fingerprint sensor (FPS) as an example. Technology used in active-matrix displays can easily be applied to the TFT FPS. TFT technology should not be confined to the display industry; its use should be expanded into the semiconductor industry. With the result presented in this paper, we declare a new era of flexible microelectronics open.
Keywords — TFTs, flexible microelectronics, fingerprint sensors.
Suftla (surface-free technology by laser annealing/ablation) is a superb technology that transfers TFT circuits from a glass substrate to a plastic sheet. The combination of Suftla and high-performance polysilicon TFT technologies will enable TFT large-scale integrations (TFT LSI) on plastic, thereby opening a new era in flexible microelectronics with semiconductor devices that are large in area, light-weight, thin, flexible, and shock resistant. Going forward, semiconductor devices will continue their remarkable advancement in flexible microelectronics.
FIGURE 6. TFT FPS on plastic.
C. Barron, J. Angelé,
L. Bajic, I. Dozov,
F. Leblanc, S. Perny,
J. Brill, J. Specht
Abstract — We have successfully fabricated BiNem® displays on thin flexible plastic substrates. The fabrication is based on the standard BiNem® process for glass, which has been adapted to plastic using new materials and technologies. The first application is targeted for an embedded display for smart-card products.
Keywords — BiNem®, bistable, flexible display, smart-card application, thin, robust.
BiNem® is a bistable nematic LCD technology based on switching between two stable textures. The uniform texture (no twist) and the 180°-twisted texture can be obtained by applying dedicated electronic waveforms to the display. The texture obtained depends on the pulse falling edge: if it is smooth, the elastic relaxation is dominant and the uniform texture is obtained. If the pulse falling edge is sharp, the LC backflow becomes the dominating factor, resulting in a twisted texture. Both states are stable over a very long period of time; switching is obtained by zenithal anchoring breaking on the weak anchoring layer and by applying a vertical electrical field.BiNem® displays can be used in both transmissive and reflective modes.
FIGURE 2 — BiNem® LCD structure in reflective mode (external reflector).
Willem den Boer
G. Scott Smith
ScanVue Technologies, U.S.A.
Abstract — In this paper, an alternative active-matrix LCD technology is described with scalable, low-cost processing. The Dual-Select-Diode (DSD) AMLCD needs less than 40% of the capital investment in the array process compared to a-Si TFT arrays and results in 20% lower-cost LCD modules. Development at several AMLCD manufacturers is in progress.
Keywords — AMLCDs, SiNx diode, thin-film diode, MIM diode.
To be considered for application in LCD TVs, a new AMLCD technology must be scalable to large area, compatible with wide-viewing-angle technologies, compatible with overdrive methods to improve response time, and have a lower manufacturing cost than existing TFT-LCD technology. It is believed that DSD AMLCDs satisfy all these requirements. SPICE simulations of a 40-in. DSD W-XGA AMLCD indicate that uniform gray-scale performance is possible with Vc = 0.875 V, row busline resistance of less than 1.3 kΩ, and column busline resistance of less than 20 kΩ. DSD technology is compatible with several wide-viewing-angle technologies, including multi-domain vertical alignment (MVA) and patterned vertical alignment (PVA).
FIGURE 10 — Image on 10-in. color VGA DSD AMLCD.
Cambridge University, U.K.
Abstract — We have optimized the low-temperature growth of microcrystalline silicon at 80°C. This material has been used to fabricate bottom-gate μc-Si:H TFTs by using a layer-by-layer nitrogenation process. By using this process, the amorphous incubation layer can be converted into silicon nitride and leads to an increase in a field-effect mobility of the TFT.
Keywords — Microcrystalline, low temperature, nitrogenation, plasma treatment.
Currently, the transistors used for AMLCDs are fabricated by using a-Si:H owing to its large-area deposition capability. Future displays will, however, demand a material with higher field-effect mobility than a-Si:H. Poly-Si can meet these requirements, but suffers from non-uniformity over large area and low-temperature substrate incompatibility. TFTs on lightweight and robust plastic substrates are in high demand for small- and medium-sized displays for mobile electronic applications such as mobile phones and PDAs. The fabrication of TFTs on plastic demands a very-low-temperature process <150°C. A new method to increase the mobility of bottom-gate μc-Si:H TFTs is achieved using a layer-by-layer nitrogenation technique in which the bottom 50 nm of the μc-Si:H is converted into silicon nitride so that, when the device is switched ON, the accumulation layer will form in a region of high crystallinity.
FIGURE 3 — Raman spectra of a typical film deposited at 80°C, with an amorphous peak at 480 cm–1 and a crystalline peak at 520 cm–1 (green line).
NEC SOG Research Laboratories, Japan
Abstract — We have developed a 470 x 235-ppi poly-Si TFT-LCD with a novel pixel arrangement, called HDDP (horizontally double-density pixels), for high-resolution 2-D and 3-D autostereoscopic displays. 3-D image quality is especially high in a lenticular-lens-equipped 3-D mode because both the horizontal and vertical resolutions are high, and because these resolutions are equal. 3-D and 2-D images can be displayed simultaneously in the same picture. In addition, 3-D images can be displayed anywhere and 2-D characters can be made to appear at different depths with perfect legibility. No switching of 2-D/3-D modes is necessary, and the design's thin and uncomplicated structure makes it especially suitable for mobile terminals.
Keywords — 3-D, high resolution, poly-Si TFT-LCD.
Figure 2 shows the principle of the HDDP arrangement. The HDDP arrangement incorporates rectangular pixels whose width is half that of their height. The horizontal pixel density is twice that of the vertical. As a result, each left-eye/right-eye set of pixels forms a square, and in a lenticular-lens-equipped 3-D mode, horizontal resolution will equal that of the vertical. This not only results in high 3-D image quality, it also means that 2-D characters can be displayed with perfect legibility without the need for any sort of 2-D/3-D conversion structure; that is, left and right pixels can simply be made to display the same content, in which case a full, perfectly proportioned character will be perceived. Further, horizontal (i.e., left-right) pixel shifting can be conducted in order to make 2-D characters appear at varying depths in the overall image. With this design, then, both 3-D and 2-D images can be displayed simultaneously in the same picture.
FIGURE 2 — HDDP arrangement. Right-eye pixel and left-eye pixel combine to form a square.
E. Y. Oh, S. H. Baik,
M. H. Sohn, K. D. Kim,
H. J. Hong, J. Y. Bang,
K. J. Kwon, M. H. Kim,
H. Jang, J. K. Yoon,
I. J. Chung
LG.Philips R&D Center, Korea
Abstract — In this paper, an active backlight control technology and a data-processing algorithm has been developed to improve the image quality in IPS-mode LCD TVs. The image-blinking problem caused by repeatedly abrupt changes in the backlight luminance was solved by using algorithms [Fba (flexible-boundary algorithm) and Cfa (cumulative feedback algorithm)] and an optimized number of backlight dimming steps based on human perception. In an IPS-mode 42-in. TFT-LCD panel, the dynamic contrast ratio can be more than twice the typical level by means of a lower black luminance and a higher white luminance. Addition-ally, the power consumption and LCD temperature were lowered.
Keywords — Backlight-control technology, data-processing algorithm, LCD TV, image blinking, backlight dimming.
As shown in Fig. 2, this technology consists of two steps and two algorithms. After inputing image data, an image analysis is performed by using the histogram method, which demonstrates the gray-level distribution of the pixels in one frame. According to the histogram, we can estimate whether the image is brighter or darker. In this histogram, three types of factors (maximum, average, and most frequent value) are investigated, which determine the type of image transmitted to the data-processing block.
FIGURE 2 — Concept of adaptive dynamic-image-control technology.
R. van Dijk
M. C. J. M. Vissenberg
S. T. de Zwart
Philips Research Laboratories, The Netherlands
Abstract — A new type of a flat and thin display with a secondary-emission electron source will be reported. In this display device, electrons are multiplied between two secondary emission plates under a high-frequency electric field. This has a number of advantages over a field-emission display: the emission comes from flat plates, which reduces the lifetime problems of ion bombardment of field-emitter tips. Furthermore, the electron emission is space-charge limited, which gives a uniform electron distribution. The electrons are extracted from the source and accelerated to a phosphor screen to generate light. Gray levels are made by pulse- width modulation.
Keywords — Multipactor, electrons, electron source, phosphor screen, field emission, matrix display, secondary emission yield, flat CRT.
The display consists of two facing glass plates that are covered with a metal layer. By applying a high-frequency alternating electric field, electrons are accelerated between the plates, creating additional free electrons as they collide with the plates. In this way, a source of electrons is created. To attract electrons to the phosphor screen, one of the glass plates contains tiny holes, one for each pixel, surrounded by a metal electrode. By applying a control voltage to each electrode, a precisely defined electron current can be drawn to the display pixels behind each hole. The first measurements indicate that this type of display has a uniform light distribution and is energy efficient.
FIGURE 9 — The display with a checkerboard pattern.
Yonsei University, Korea
Keywords — Fringe-field switching (FFS), a-C:H thin film, ion-beam alignment method, nematic liquid crystal.
a-C:H thin films were deposited on various substrates, such as indium tin oxide (ITO), single-crystalline Si, and glass by remote plasma-enhanced chemical-vapor deposition (RPECVD). The surface properties of a-C:H thin films were control-led by Ar-ion-beam irradiation. A Kaufman ion gun was used for the irradiation of a-C:H thin films. The argon-ion-beam irradiation time was 0, 1, and 5 min at an ion-beam energy of 200 eV. The IB (Kaufman-type Ar-ion gun) exposure sys-tem is shown in Fig. 1.
FIGURE 1 — Ion-beam exposure system used.
Tokyo University of Agriculture and Technology, Japan
Abstract — The development of fabrication processes for polycrystalline-silicon thin-film transistors (poly-Si TFTs) at low temperatures will be discussed. Rapid crystallization of silicon films through laser-induced melt regrowth has the advantage of having a low thermal budget. Solid-phase crystallization techniques have also been improved for low-temperature processing. Passivation of the SiO2/Si interface and crystalline grain boundaries is important in achieving high-carrier-transport properties. Oxygen-plasma and H2O-vapor heat treatments are proposed for the effective reduction of the density of defect states. TFTs with high performances will be reported.
Keywords — Laser crystallization, MIC, MILC, defect passivation, carrier mobility, threshold voltage.
Laser crystallization is one of most attractive methods for polycrystalline-film formation. Pulsed UV-laser light is effectively absorbed in the silicon surface because of the high absorption coefficient of ~106 cm–1 of silicon at wavelengths lower than 350 nm. The absorbed light simultaneously excites the electronic states of silicon. The energy of the excited states is relaxed to lattice vibration states within a time on the order of 10–12 sec. For the case of nanosecond-order pulsed laser irradiation, lattice heat is therefore the most important interaction. Crystallization methods without using a laser are also attractive for the low-cost formation of crystalline films. We have recently developed the electrical-current-induced Joule as a simple and rapid thermal annealing method.
FIGURE 1 — Plane view of bright-field TEM image of 30-nm-thick poly-Si films crystallized at 300 mJ/cm2.
Yoon-Ho Song, Kwang-Bok Kim,
Chi-Sun Hwang, Dong-Jin Park,
Jin Ho Lee, Kwang-Yong Kang,
Ji Ho Hur, Jin Jang
Abstract — An active-matrix field-emission display (AMFED), based on carbon-nanotube (CNT) emitters and amorphous-silicon thin-film transistors (a-Si TFTs), was developed. The AMFED pixels consisted of a high-voltage a-Si TFT and mesh-gated CNT emitters. The AMFED panel demonstrated high performance for a driving voltage less than 15 V. The low-cost large-area AMFED approach using a metal-mesh technology is proposed.
Keywords — Active-matrix field-emission display, carbon-nanotube emitter, mesh gate, high-voltage a-Si TFT.
For an active-matrix-driven display panel, the control device is integrated into each pixel. The driving voltage for the panel is the operation voltage of the control device, which is usually low enough to use general driving ICs for the display panel. In general, the variation of emission currents from field emitters is larger than that of on-currents in TFTs. The uniformity of the emission currents can be greatly improved by using TFT-controlled emission currents. The reduction of power consumption is another advantage of the AMFED.
FIGURE 5 — A moving image on a vacuum-packaged AMFED panel with 5-in. QQVGA resolution.
Seung Hoon Han
Sung Hwan Kim
Hye Young Choi
Sang Mi Cho
Myung Hwan Oh
Kyung Hee University, Korea
Abstract — A high-performance bottom-contact organic thin-film transistor (OTFT) array on plastic using a self-organized process has been developed. The effect of octadecyltrichlorosilane (OTS) treatment on the poly-4-vinylphenol (PVP) gate insulator on the performance of OTFT on plastic has been studied. The OTFT without OTS exhibited a field-effect mobility of 0.1-cm2/V-sec on/off current ratio of >107. On the other hand, the OTFT with OTS treatment exhibited a field-effect mobility of 1.3 cm2/V-sec and an on/off current ratio of >108. This is mainly due to the enhancement in grain size from less than 10 μm to more than 20 μm.
Keywords — Pentacene, organic TFT, self-organized process, flexible display.
For active-matrix displays and integrated circuits using pentacene TFTs, patterning with high resolution is the most important issue. In addition, the mobility is related to the grain size and to the surface treatment before pentacene growth. Thus far, the shadow-mask technique has been widely used because the shadow-mask process can make the shape of a pentacene active island and the source and drain as well. This is a top-contact structure and provides better TFT performance. But a top-contact structure is not a practical structure for the manufacture of high-resolution displays because of its high channel length and misalignment. Therefore, we studied a bottom-contact structure for high-resolution displays. In this work, the effect of the self-assembled mono-layer (SAM) treatment on the PVP was carried out to enlarge the grain size and also to improve the TFT performance.
FIGURE 7 — The optical image of a 4-in. pentacene OTFT array on PES.
National Taiwan University, Taiwan
Abstract — Top-emitting organic light-emitting devices (OLEDs) have several technical merits for application in active-matrix OLED displays. Generally, stronger microcavity effects inherent with top-emitting OLEDs, however, complicate the optimization of device efficiency and other viewing characteristics, such as color and viewing-angle characteristics. Using the rigorous classical electromagnetic model based on oscillating electric dipoles embedded in layered structures, the emission characteristics of top-emitting OLEDs as a function of device structures are analyzed. From comprehensive analysis, trends in the dependence of emission characteristics on device structures were extracted, and, accordingly, a general methodology for optimizing viewing characteristics of top-emitting OLEDs for display applications will be suggested. The effectiveness of the analysis and the methodology was confirmed by experimental results.
Keywords — Organic light-emitting devices, top-emitting organic light-emitting devices, microcavity effects.
The optical model used for performing the analysis adopts a classical approach based on the equivalence between the emission of a photon due to an electrical dipole transition and the radiation from a classical electrical dipole antenna, which can take into account loss due to the electrodes. With plane-wave expansion of the dipole field, the full-vectorial electromagnetic fields generated by a radiation dipole embedded in a layered structure is calculated, from which the distribution of the radiation power into different plane-wave modes and the far-field radiation related to emission characteristics of an OLED are obtained.
FIGURE 3 — Calculated contour plots of (a) out-coupling efficiency, (b) saturation offset, (c) color shift, and (d) Lambertian offset as a function of the Alq3 thickness and the m-MTDATA thickness with the TeO2 thickness fixed at 20 nm.