Miki Shibata

Self-Aligned Bank Formation of Organic Electroluminescent Devices Using Ink-Jet Printing Method

The self-aligned bank formation of organic electroluminescent devices using the ink-jet printing method was proposed and investigated. A solution of organic materials mixed with host and emission materials was printed on an indium–tin–oxide-coated glass substrate covered with an insulating polymer layer. The insulating material was dissolved in a solvent, and a mixture of organic materials was formed at the same position as that of the ink-jet-printed region, that is, a self-aligned organic electroluminescent device was realized. The diameter of the emission region was 200 µm and a luminance of 9,070 cd/m2 was obtained using an electrophosphorescent material.

Top-Emission Organic Light-Emitting Diodes with Ink-Jet Printed Self-Aligned Emission Zones

We have investigated a method of fabricating ink-jet printed self-aligned emission zones for top-emission organic light-emitting diodes. To obtain a bright emission, the number of ink-jet printed shots was varied. From the viewpoint of surface roughness of the bottom electrode, AlNd was used. To reduce sputtering damage, a buffer layer with the hole transport ability of MoO3 was also employed. As a result, the maximum luminance obtained was 1,000 cd/m2. By application of this fabrication technique, we have achieved a printed display panel 30×30 mm2 resolution of 300 pixels per inch.

Organic Bifunctional Devices with Emission and Sensing Abilities

Organic bifunctional devices with emission and sensing abilities were reviewed and a prototype of a matrix was demonstrated. There are two types of device structure: a bi-function matrix array (Bi-Matrix) with a stacked layer of organic light-emitting diode (OLED) and organic photodiode (OPD) matrix arrays, and a multi-function diode (MFD) which has a structure similar to that of conventional OLED and has two functions of emission and photosensing. For the Bi-Matrix, independent operations of emission and photosensing were achieved; the maximum luminance of its OLED was 77,400 cd/m2 and the ratio of photoconductivity to dark conductivity was 1×104. A prototype 4×4 Bi-Matrix was also demonstrated. For the MFD, a special organic material, the pyrazoline derivative, was used. The highest luminance obtained was 9,270 cd/m2 under a forward bias condition. The highest photocurrent density was 71 µA/cm2 and the highest ratio of photo- to dark-conductivity was 1×104 under a reverse-bias condition. Details of the prototype 16×16 MFD matrix were also described.

Current and Field Characteristics and Memory Mechanism of TFEL Devices

The apparent current-controlled negative resistance resulting from current and triangular voltages in memory and nonmemory devices is considered to be due to hot electron injection fom the ZnS layer into the insulating layer. Further studies of the current wave in memory devices has revealed a voltage-controlled negative resistance. This fact is used to construct a two-level model of primary electron sources for impact excitation to explain the memory behavior of such devices. The model takes account of the interface state for initial high-field excitation and the trap level for sustaining low-field excitation.

Investigation of Time-Resolved X-Ray Diffraction Analysis in Smectic A Liquid Crystal Cells

Time-resolved X-ray diffraction analysis of smectic A liquid crystal cells is investigated. Frequency and duty ratio dependence of smectic A layer motions is measured. From the experimental results, possible mechanisms of layer motions are discussed.

Multi-Color Organic Light Emitting Panels Using Self-Aligned Ink-Jet Printing Technology

We have investigated multi-color organic light emitting panels using a self-aligned (SA) ink-jet printing (IJP) technology. Emission ink with phosphorescent materials of an iridium(III) bis(2-(2′-benzothienyl) pyridinato-N,C3′) (acetylacetonate) (Btp2Ir(acac)) for red, an fac-tris(2-(p-tolyl)-pyridine)iridium (Ir(tpy)3 for green, and an iridium(III) bis(2-(4,6-difluorophenyl) pyridinato-N,C2′) picolinate (FIrpic) for blue were printed on an indium-zinc-oxide (IZO) coated glass substrate covered with an insulating poly-methylmethacrylate (PMMA) layer. The PMMA was dissolved in a solvent of ink, then, emission region was formed at the same position as that of the ink-jet-printed region. The device structure was IZO/PEDOT/PMMA (30 nm) ← Ink/BCP (20 nm)/LiF (1 nm)/Al (70 nm). Luminescence of the device with red, green and blue emission materials, were 655 2,640 and 857 cd/m2, respectively. We have also demonstrated 150 ppi resolution of multi-color light emitting panels using the self-aligned IJP method.

Self-Aligned Organic Light-Emitting Diodes with Color Changing by Ink-Jet Printing Dots

The self-aligned color-changeing organic light-emitting diodes with the ink-jet printing (IJP) dots have been investigated, and we have studied a device structure of a micro-area color-changeing method involving the IJP emission of dots and their periphery, where a side-coupling emission mode and double-area emission mode were used. The distance of the side-coupling emission from emission dot was estimated to be 10 µm. The brightnesses of the dots and their periphery at 100 mA/cm2 were 1,300 and 380 cd/m2, respectively.

Light-Emitting Seal Using Self-Aligned Organic Light-Emitting Structure

A light-emitting seal using a self-aligned organic light-emitting diode (OLED) and a laminate process is proposed and demonstrated. This device has a self-aligned ink-jet-printed structure where an insulating material is dissolved in a solvent, and a mixture of organic materials is formed at the same position as that of the ink-jet-printed region. A cathode electrode is laminated onto the above ink-jet-printed structure. The merits of the device are its simple fabrication without the need for photolithography or any vacuum process, and its lower cost. The typical luminance obtained was 6,810 cd/m2. The concept of the device is useful for light-emitting seals (LES), tags and graphics with noncontact electromagnetic electric supply but no electric supply line.

Unit-by-Unit Process of Bi2Sr2CuOy Film Growth with Molecular Beam Epitaxy by Separated Evaporation/Oxidation/Crystallization Technique

Thin films of Bi2Sr2CuOy were grown with MBE (Molecular Beam Epitaxy) by the separated evaporation/oxidation/crystallization technique on a MgO (100) substrate. The proposed technique is the unit-by-unit process consisting of three steps: multilayer deposition of (Bi-Sr-Cu-Sr-Bi)×2, low-temperature oxidation (300°C) in low concentration O3 (O2/O3(0.3%)) atmosphere (5×10-5 Torr) and crystallization (750°C, 1×10-8 Torr). After growth of ten units, clear streaks on the RHEED pattern showing the twin structure and a fairly fine X-ray diffraction pattern were observed.

Oscillation method for uniform formation of solution-processed organic films and its application to organic light-emitting devices

We propose an oscillation method of solution-processed organic film coating. This method hindered a flow of solvent with organic materials during drying process. We have applied this technique into fabrication of OLEDs. In this time, oscillation is induced using piezoelectric actuator and wetted plastic roller is used for coating the organic film. By doing this method, uniform organic film with a mean roughness of 3.8 nm was achieved. Spin-coated poly(ethylene dioxythiophene) /poly(styrene sulfonate) (PEDOT) was used for hole buffer layer. Polyvinylcarbazole (PVCz) as a hole transport material, (BND) as an electron transport material, and coumarin 6 (C6) as an emission material were used. Device structure of ITO /PEDOT (40 nm)/PVCz+BND+C6 (100 nm)/LiF (1 nm)/ Al with area of 30×30 mm2 were tested. Emission was dramatically improved by changing the oscillation condition and uniform emission was observed at higher frequencies. This technique will be promising for large-area production and short tact time. And this method is also applicable for other fabrication methods, such as, spray method and ink-jet printing method.