ZnO nanowires for LED and field‐emission displays

Abstract— The use of ZnO nanostructures in various display applications is reported. Single‐crystalline vertically oriented nanowires with typical diameters of 100 nm and a length of 1–2 μm were grown at deposition temperatures below 100°C. Homogeneous growth over areas up to 50 cm² on Si as well as on various metallic, transparent, and flexible substrates were obtained. Visible electroluminescence in the region between 400 and 900 nm and narrow‐line near‐ultraviolet (UV) electroluminescence is demonstrated. The physical conditions leading to single‐crystalline growth at low temperature, the role of defects, and the possibility of doping are discussed. These issues present the main challenges on the road towards high emission rates in LED operation. Under certain conditions, sharply tipped wires can be grown that hold promise for field‐emission applications.     

Switching of carbon‐nanotube emitters by an integrated MOSFET

Abstract— The integration of carbon‐nanotube (CNT) emitters with a metal‐oxide‐semiconductor field‐effect transistor (MOSFET) can stabilize and control the emission current of CNTs. CNTs were grown by using the resist‐assisted patterning (RAP) process and plasma‐enhanced chemical vapor deposition (PECVD) and were connected to the drain part of an external MOSFET. The electron‐emission current of CNTs was switched by applying a low gate voltage to the MOSFET, and the switching current was very stable because the MOSFET was operated in the saturation region. Based on these results, the emission current of CNTs was stabilized and switched by using a low‐voltage‐driven MOSFET.     

Suspension‐deposited carbon‐nanotube networks for flexible active‐matrix displays

Abstract— The unique properties of carbon nanotubes (CNTs) promise innovative solutions for a variety of display applications. The CNTs can be deposited from suspension. These simple and low‐cost techniques will replace time‐consuming and costly vacuum processes and can be applied to large‐area glass and flexible substrates. Single‐walled carbon nanotubes (SWNTs) have been used as conducting and transparent layers, replacing the brittle ITO, and as the semiconducting layer in thin‐film transistors (TFTs). There is no need for alignment because a CNT network is used instead of single CNTs. Both processes can be applied to glass and to flexible plastic substrates. The transparent and conductive nanotube layers can be produced with a sheet resistance of 400 Ω/□ at 80% transmittance. Such layers have been used to produce directly addressed liquid‐crystal displays and organic light‐emitting diodes (OLED). The CNT‐TFTs reach on/off ratios of more than 10⁵ and effective charge‐carrier mobilities of 1 cm²/V‐sec and above.     

Large‐area FEDs with carbon‐nanotube field emitter

Abstract— Application of carbon nanotubes (CNTs) as field emitters for large‐area FED panels is described. In 1998, we presented the first experimental devices: light‐source tubes for outdoor large‐area displays and a diode‐type flat‐panel display, both with screen‐printed CNT cathodes. The fisrt practical high‐luminance color CNT‐FED panel was built in 1999. It employed the new triode‐structure panel was x‐y addressable. The CNT‐FED structure was further optimized for large‐area display panels by improving the luminous uniformity. This paper also describes the design and performance of a new, experimental, 40‐in.‐diagonal panel, which showed that the CNT‐FED technology is suitable for use in large‐area displays.     

Film surface morphology and field‐emission characteristics of a carbon‐nanotube array pattern fabricated under a magnetic field

Abstract— This study focuses on the influence of sodium metasilicate binder on CNT paste and the arrangment of Mg‐Ni alloy multi‐walled carbon nanotubes on the surface of CNT film under the influence of a magnetic field. The CNT paste was prepared by mixing CNTs with silver epoxy resin and sodium metasilicate solution and coating them onto the surface of indium tin oxide (ITO) glass. The impact of sodium metasilicate solution and magnetic strength on the morphology of the paste film's surface and on the field‐emission (FE) characterics of the cathode was examined. The experimental results showed that the CNT paste provided good adhesion between the CNT array and silver epoxy resin when sodium metasilicate solution was presented. CNT paste containing sodium metasilicate showed a better dispersion with silver epoxy resin and a better CNT‐array pattern, and better vertical alignment of the CNT was obtained when the magnetic field and grid were both appied. An optimal condition for a better CNT‐array pattern for both the morphology and FE characteristics had a magnetic strength of 1 89 mT, magnetization time of 30 min, and a grid above the cathode.     

Design of carbon nanotubes for large‐area electron field‐emission cathodes

Abstract— Electron field‐emission displays offer a viable option for the next generation of flat‐panel screens. Boasting high‐quality images in terms of good color saturation, fast refresh rate, and high brightness, these displays have the potential to offer above and beyond what the current market leaders, LCD and plasma. However, for the realization of such a new display disrupting the incumbent LCD and plasma displays, not only does the image quality need to be better, but fabrication costs and suitable manufacturing processes need to be in place at reduced cost. Many viable cathode materials have been proposed in recent years, one of which being the use of carbon nanotubes (CNTs) in various forms (aligned growth, screen printing, and polymer matrix). In this review, a series of recent experiments investigating the field‐emission characteristics of carbon‐nanotube systems for possible use in the display industry is presented.     

Tetrahedrally bonded amorphous carbon for field‐emission displays

Abstract— Field emission from a series of tetrahedrally bonded amorphous‐carbon (ta‐C) films, deposited in a filtered cathodic vacuum arc, has been measured. The threshold field for emission and current densities achievable have been investigated as a function of sp³/sp² bonding ratio and nitrogen content. Typical as‐grown undoped ta‐C films have threshold fields of the order 10–15 V/μm and optimally nitrogen doped films exhibit fields as low as 5 V/μm. In order to gain further understanding of the mechanism of field emission, the films were also subjected to H₂, Ar, and O₂ plasma treatments and were also deposited onto substrates of different work function. The threshold field, emission current, and emission site densities were all significantly improved by the plasma treatment, but little dependence of these properties on work function of the substrate was observed. This suggests that the main barrier to emission in these films is at the front surface.     

Frequency‐dependent maximum average power‐handling capabilities of single and edge‐coupled microstrip lines on low‐temperature co‐fired ceramic (LTCC) substrates

The frequency‐dependent maximum average power‐handling capabilities (APHCs) of single and edge‐coupled microstrip lines (MLs) on low‐temperature co‐fired ceramic (LTCC) substrates are investigated in this article. Although LTCCs have excellent high‐frequency performance, the thermal conductivity is about 2.0–3.0 W/m°C, which is much smaller than that of sapphires, alumina, silicon, and GaAs. The method used to predict the APHC is based on the calculated conductive and dielectric attenuation constants for different modes, and the proposed multilayer thermal model for the temperature rise. Numerical investigations are carried out to examine the effects of geometric and physical parameters on the wideband pulse responses and maximum APHC for single finite‐ground thin‐film and coupled MLs, respectively. Methodologies to enhance the power‐handling capability which are useful in the design of high‐density microstrip interconnects on or embedded in multi‐layer LTCCs are proposed. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

Growth and characterization of carbon nanotubes for field‐emission‐display applications

Abstract— This paper will report on the production, dimensional control, and characterization of arrays of cold‐cathode field emitters based on multiwall carbon nanotubes, suitable for use in large‐area field‐emission‐based displays.     

Plasma damage‐free SiO2 deposition for low‐temperature poly‐Si AMLCDs

Abstract— High‐quality SiO₂ films have been fabricated at a substrate temperature of 300°C by utilizing a novel deposition method refered to as radical‐shower CVD (RS‐CVD), in which the substrates and material gases are completely separated from the plasma. On this account, SiO₂ deposition is achievable without plasma damage and excessive decomposition of the material gases. The electrical characteristics of RS‐CVD SiO₂ films are comparable to those of thermal SiO₂. Furthermore, the compact parallel‐plate structure of RS‐CVD is suitable for large‐area deposition.     

Annealing effect of low‐temperature (<150°C) Cat‐CVD gate dielectric silicon nitride films diluted with atomic hydrogen

Abstract— The effect of in‐situ hydrogen pretreatment on dielectric properties of silicon nitride (SiN^x) thin films for a gate dielectric layer has been studied. SiN^xthin films were grown at a low temperature (150°C) by Catalytic CVD followed by conventional furnace annealing at 150°C for 2 hours. The in‐situ hydrogen pretreatment was performed without vacuum break before the sample was transferred to the furnace for thermal annealing. Capacitance—voltage (C‐V) and current‐density—voltage (J‐V) measurement showed that the hydrogen pretreatment was effective in reducing the hysteresis in the C‐V curve and in increasing the breakdown voltage. Without the treatment, the 150°C annealing failed to produce reliable C‐V and I‐V characteristics. The C‐V hysteresis and the threshold voltage shift of SiN^x were improved by furnace annealing as the hydrogen dilution ratio increased. Also, addition of hydrogen to the deposition gas mixture helped to improve the dielectric properties of the SiN^x films after thermal annealing. The combination of hydrogen dilution of the source gas and the in‐situ hydrogen treatment was successful in producing low‐temperature SiN^x films applicable to a‐Si TFTs. The TFT fabricated by using these films showed a field‐effect mobility of 0.23 cm²/V‐sec and a Vth of 3.1 V.     

An averaging pixel structure using microcrystalline‐silicon films prepared at high temperature for AMOLED displays

Abstract— A new voltage‐addressed pixel using a multiple drive distribution has been developed to improve, in a simple way, the brightness uniformity of active‐matrix organic light‐emitting‐diode (AMOLED) displays. Moreover, circuits were realized using microcrystalline‐silicon (μc‐Si) films prepared at 600°C using a standard low‐pressure CVD system. The developed p‐channel TFTs exhibit a field‐effect mobility close to 6 cm²/V‐sec. The experimental results show that the proposed spatial distribution of driving TFTs improves the uniformity of current levels, in contrast to the conventional two‐TFT pixel structure. Backplane performances have been compared using circuits based on μc‐Si and furnace‐annealed polysilicon materials. Finally, this technology has been used to make an AMOLED demonstration unit using a top‐emission OLED structure. Thus, by combining both an μc‐Si active‐layer and a current‐averaging driver, an unsophisticated solution is provided to solve the inter‐pixel non‐uniformity issue.     

Surface‐light‐emitting transistors based on vertical‐type metal‐base organic transistors

Abstract— Light‐emitting transistors having a metal‐base organic transistor (MBOT) structure demonstrate both the function of an organic thin‐film transistor (OTFT) and organic light‐emitting diode (OLED). The MBOT is a vertical‐type organic transistor having a simple structure composed of organic/metal/organic layers demonstrating high‐current and low‐voltage operation. The light‐emitting MBOT was fabricated simply by inserting additional layers of hole‐transporting and emissive materials used in the OLED into the col lector layer. The device showed perfect surface emission similar to an OLED. A luminance modulation of 370 cd/m² was observed at a collector voltage of 20 V and a base voltage of 3 V. This device can be applied to an OLED display device to increase the numerical aperture or reduce the required current of the TFT backplane.     

Thermally adaptive response‐time compensation for LCDs

Abstract— This paper presents thermally adaptive driving (TAD) technology for response‐time compensation (RTC) of an LCD with an integrated sensor. The TAD system is comprised of an analog sensor, an analog sensor signal conditioning, and a digital feedback algorithm. The integrated thermal sensor provides accurate temperature measurement of the liquid‐crystal layer. The TAD controller has an eight‐step look‐up‐table (LUT) and compensates response time based on the panel temperature. The TAD system reduces response time by nearly 34% over the temperature range 0–60°C. This paper also presents a thermal sensor which has been integrated onto an LCD. The sensor uses metal (Mo/Al) film as a temperature detection layer, and its fabrication requires no manufacturing process changes. The sensor shows very good linearity, sensitivity, and reliability.     

Carbon nanotubes and semiconductor nanowires for active‐matrix backplanes

Abstract— Carbon nanotubes and semiconductor nanowires are a new class of materials currently being studied within the context of molecular electronics. Because of their excellent characteristics, transistors based on carbon nanotubes and semiconductor nanowires could become the workhorse of the post‐CMOS era. Since carbon nanotubes as well as Si or Ge nanowires can be grown at low temperature, using similar CVD‐type processes and on non‐crystalline and non‐refractory substrates, they could (and will) certainly be used in the near future for the fabrication of thin‐film transistors and active‐matrix backplanes. However, the development of these nanomaterials is hampered by the general problems posed by their manipulation, placement, and in‐plane organization. The possible use of CNT random networks (that do not need to be organised) for the fabrication of thin‐film transistors will be reviewed. Then a new way of organizing semiconductor NWs in a thin‐film transistor, based on the use of lateral porous anodic alumina templates, will be presented.     

Silicon‐nanocrystal‐based photosensor integrated on low‐temperature polysilicon panels

Abstract— A photodetector using a silicon‐nanocrystal layer sandwiched between two electrodes is proposed and demonstrated on a glass substrate fabricated by low‐temperature poly‐silicon (LTPS) technology. Through post excimer‐laser annealing (ELA) of silicon‐rich oxide films, silicon nanocrystals formed between the bottom metal and top indium thin oxide (ITO) layers exhibit good uniformity, reliable optical response, and tunable absorption spectrum. Due to the quantum confinement effect leading to enhanced phonon‐assisted excitation, these silicon nanocrystals, less than 10 nm in diameter, promote electron‐hole‐pair generation in the photo‐sensing region as a result resembling a direct‐gap transition. The desired optical absorption spectrum can be obtained by determining the thickness and silicon concentration of the deposited silicon‐rich oxide films as well as the power of post laser annealing. In addition to obtaining a photosensitivity comparable to that of the p‐i‐n photodiode currently used in LTPS technology, the silicon‐nanocrystal‐based photosensor provides an effective backlight shielding by the bottom electrode made of molybdenum (Mo). Having a higher temperature tolerance for both the dark current and optical responsibility and maximizing the photosensing area in a pixel circuit by adopting a stack structure, this novel photosensor can be a promising candidate for realizing an optical touch function on a LTPS panel.     

Applications of OLEDs that use VUV‐CVD films

Abstract— In photo‐CVD (chemical vapor deposition) in which vacuum‐ultraviolet (VUV) excimer lamps (VUV‐CVD) are used, thin films were deposited at room temperature because VUV photons have the energy to decompose material gases. For the use of OMCTS (octamethylcyclotetrasiloxane), an organic siloxane, we can deposit a self‐flatness film for high‐pressure conditions. The reactants generated by VUV photons have excellent migration characteristics for this condition. Also, the VUV‐CVD film demonstrates low stress, comparatively hard hardness, good electrical properties, and good thermal resistance. The VUV‐CVD film is optimum for planarizing film in the over‐coating deposition step in the production of OLEDs, which requires a low‐temperature process.     

Active‐matrix field‐emission display based on a CNT emitter and a‐Si TFTs

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.     

Composite silver electrode for double‐sided‐emitting stacked organic light‐emitting diode

Abstract— A reflective composite silver electrode is proposed and characterized as the middle electrode of a stacked organic light‐emitting diode (OLED) with double‐sided light emission. The proposed electrode is composed of a thermally evaporated stack of LiF (1 nm)/Al (3 nm)/Ag (70 nm) layers. The LiF/Al and the plasma‐treated Ag of the electrode function well as the respective cathode and anode of the bottom‐ and top‐emitting stacked OLEDs, with both being of the non‐inverted type. Power efficiencies of 10.3 and 12.1 lm/W at 100 cd/m² have been measured for bottom‐ and top‐emitting OLEDs, respectively, using dye doping. The stacked OLED having this bipolar middle electrode can be constructed as a two‐terminal‐only device, allowing for simpler driving schemes in double‐side‐emitting passive‐/active‐matrix OLED displays.     

Amorphous semiconductors for cold cathodes: A route to large‐area flat‐panel displays

Abstract— The field‐emission‐display (FED) technology examined in the early sixties used metal tips or Spindt cathodes in order to extract electron beams to excite phosphors. The tips were necessitated by the large work function the electrons needed to overcome in order to be released into the vacuum. In the early nineties it was noticed that “flat” diamond surfaces emitted electrons at relatively low electric fields. Just as its crystalline counterparts, amorphous‐carbon thin films also showed that this class of materials were also capable of electron emission at low threshold fields. By using flat emitters, technologist can remove a number of fabrication steps that otherwise would have been required to produce large‐area arrays of field emitters and therefore reduce the cost of production significantly. This paper will review the progress of the use of flat amorphous semiconductors as cold cathodes. New results that appear to point towards a space‐charge‐controlled emission mechanism as opposed to a purely surface emission process based upon Fowler‐Nordheim tunneling will be introduced, which have implications on the type of device structure that will ultimately be needed for electron field‐emission devices. Two possible cold‐cathode materials, namely, amorphous‐carbon and amorphous silicon, will be examined.