Youngjun Yun

Pentacene thin film transistors with a poly(methyl methacrylate) gate dielectric : optimization of device performance.

The electrical characteristics of pentacene-based organic thin film transistors (OTFTs) using poly(methyl methacrylate) (PMMA) as the gate dielectric are reported. Uniform pinhole-free and crack-free films of PMMA could be obtained by spin coating, with a lower limit of thickness of about 150 nm. The effects of the insulator thickness and channel dimensions on the performance of the devices have been investigated. Leakage currents, which are present in many polymeric gate dielectrics, were reduced by patterning the pentacene active layer. The resulting devices exhibited minimal hysteresis in their output and transfer characteristics. Optimized OTFT structures possessed a field-effect mobility of 0.33 cm2 V−1 s−1, a threshold voltage of −4 V, a subthreshold slope of 1.5 V/decade, and an on/off current ratio of 1.2×106.

A pentacene-based organic thin film memory transistor

An organic memory device based on a pentacene thin film transistor is demonstrated. Gold nanoparticles have been used as the charge storage elements while a thin film of polymethylmethacrylate formed the gate insulator. The electrical characteristics and the memory behavior of the organic thin film memory transistor (OTFMT) are reported. Under an appropriate gate bias (1 s pulses), the gold nanoparticles are charged and discharged, resulting in significant threshold voltage shifts of the OTFMT. The detailed programing and erasing procedures are reported.

Charge Storage in Pentacene/Polymethylmethacrylate Memory Devices

The electrical behavior of organic metal-insulator-semiconductor (MIS) structures incorporating a layer of self-assembled metallic nanoparticles is described. These have been based on thermally evaporated pentacene (semiconductor) and spin-coated polymethylmethacrylate (insulator). The MIS devices containing the nanoparticles exhibited significant hysteresis in their capacitance-versus-voltage and conductance-versus-voltage characteristics, which was attributed to the charging and discharging of the nanoparticles. The memory structure reported here offers a useful advance in the development of flexible organic memory structures.

An Ion Sensitive Organic Field-Effect Transistor Incorporating the Ionophore Valinomycin

We report on the effect of depositing the ionophore valinomycin onto the polymethylmethacrylate (PMMA) gate insulator of an ion-sensitive organic field-effect transistor (ISOFET) based on poly(3-hexylthiophene). The ionophore was deposited onto the PMMA using the Langmuir-Blodgett (LB) technique; thin films based on pure valinomycin and those in which valinomycin was mixed with arachidic acid were investigated. The pH sensitivity of the reference ISOFET could be improved significantly when the devices were coated with an LB film of arachidic acid. However, the response to was low. By adding a small amount (5% w/w) of the ionophore valinomycin to the fatty acid LB film, an improved response to potassium ions was achieved, but no selectivity over sodium. It was necessary to use an LB membrane of pure valinomycin in order to realise an ISOFET with some selectivity. We suggest that the presence of the ionophore in the fatty acid matrix disrupts the packing of the hydrocarbon chains in the mixed LB film and that the monovalent ion response originates from interactions with the carboxylic acid groups in the fatty acid. In contrast, for the case of the pure valinomycin coating, it is thought that response is controlled by complex formation with the ionophore.

Bootstrapped inverter using a pentacene thin-film transistor with a poly(methyl methacrylate) gate dielectric

A bootstrapped inverter incorporating pentacene organic thin-film transistors (OTFTs), with poly(methyl methacrylate) as the gate dielectric, has been designed, fabricated and tested. The inverter uses capacitive coupling and bootstrapping effects, and exhibits superior performance to the normal diode-connected load inverter. The pentacene OTFTs used for the inverter possess a field-effect mobility of 0.32 cm2/V/s, a threshold voltage of −10.0 V, a subthreshold slope of 1.5 V per decade and an on/off current ratio of 2.2×106. The inverter has a 30 µs rise time and a 450 µs fall time, at an operating frequency of 1 kHz and 30 V drive voltage.

Improvement of Interpixel Uniformity in Carbon Nanotube Field Emission Display by Luminance Correction Circuit

Interpixel uniformity is critical to image quality, and is hard to be improved by structural reformation of emissive elements because of nonuniformity in luminance characteristics of subpixels in self-emissive device like the carbon nanotube field emission display (CNT-FED). In this paper, we discuss the improvement of the interpixel uniformity by individually controlling the luminance of all subpixels in a display panel. We propose a prototype CNT-FED with improved interpixel uniformity using luminance correction circuitry. The analysis of interpixel uniformity with the proposed luminance correction circuit shows that the index of interpixel uniformity increases about 8% with only about 10% luminance reduction ratio that is a relatively small penalty compared to the enhancement of the interpixel uniformity. The proposed correction method can also be used to ensure improvement of the interpixel uniformity in large-size CNT-FED panels.

Color filters for reflective display with wide viewing angle and high reflectivity based on metal dielectric multilayer

We report high performance reflective color filters based on one-dimensional metal-dielectric multilayer. Wide viewing angle of ±50°, far beyond that with conventional all-dielectric multilayers, is achieved while maintaining approximately 100% peak reflectance and color reproducibility. Reflectance of 40% in white mode and color gamut of 47% to the United States National Television Systems Committee (NTSC) standard is demonstrated. The proposed color filter is integrated into 3.5-in. color reflective display and shows 30% increase in brightness than conventional dye color filters.

Design of system-on-glass for poly-Si TFT OLEDs using mixed-signals simulation

Abstract AMOLEDs (active-matrix organic light emitting diodes) employing poly-Si TFT have been used to integrate peripheral circuits on a glass to reduce the cost through the use of dead space on the glass. The system-on-glass (SOG) development provides enormous challenges to the developers, usually verifying the SOG by transistor-level simulation. IR-drop modeling is needed to reduce the uniformity degradation in the OLED image quality. This paper presents a full panel simulation technique for OLED driver and pixels that is integrated on a glass using the mixed-signals circuit design and the proposed process shows excellent capabilities relating to the capacity and the speed.