Seungmoon Pyo

Nonvolatile electrical bistability of organic/metal-nanocluster/organic system

Two-terminal electrical bistable devices have been fabricated using a sandwich structure of organic/metal/organic as the active medium, sandwiched between two external electrodes. The nonvolatile electrical bistability of these devices can be controlled using a positive and a negative electrical bias alternatively. A forward bias may switch the device to a high-conductance state, while a reverse bias is required to restore it to a low-conductance state. In this letter, a model to explain this electrical bistability is proposed. It is found that the bistability is very sensitive to the nanostructure of the middle metal layer. For obtaining the devices with well-controlled bistability, the middle metal layer is incorporated with metal nanoclusters separated by thin oxide layers. These nanoclusters behave as the charge storage elements, which enable the nonvolatile electrical bistability when biased to a sufficiently high voltage. This mechanism is supported by the experimental data obtained from UV–visible ...

Organic bistable light-emitting devices

An organic bistable device, with a unique trilayer structure consisting of organic/metal/organic sandwiched between two outmost metal electrodes, has been invented. [Y. Yang, L. P. Ma, and J. Liu, U.S. Patent Pending, U.S. 01/17206 (2001)]. When the device is biased with voltages beyond a critical value (for example 3 V), the device suddenly switches from a high-impedance state to a low-impedance state, with a difference in injection current of more than 6 orders of magnitude. When the device is switched to the low-impedance state, it remains in that state even when the power is off. (This is called “nonvolatile” phenomenon in memory devices.) The high-impedance state can be recovered by applying a reverse bias; therefore, this bistable device is ideal for memory applications. In order to increase the data read-out rate of this type of memory device, a regular polymer light-emitting diode has been integrated with the organic bistable device, such that it can be read out optically. These features make the ...

High Performance Polymer Light-Emitting Diodes Fabricated by a Low Temperature Lamination Process**

We report on the successful demonstration of high performance polymer light-emitting diodes (PLEDs) using a low temperature, plastic lamination process. Blue- and red-emitting PLEDs were fabricated by laminating different luminescent polymers and organic compounds together to form the active media. This unique approach eliminates the issue of organic solvent compatibility with the organic layers for fabricating multi-layer PLEDs. In addition, a template activated surface process (TAS) has been successfully applied to generate an optimum interface for the low temperature lamination process. Atomic force microscopy analysis reveals a distinct difference in the surfaces created by the TAS and the spin-coating process. This observation coupled with the device data confirms the importance of the activated interface in the lamination process.

Low-temperature processable inherently photosensitive polyimide as a gate insulator for organic thin-film transistors

We have fabricated organic thin-film transistors (OTFTs) on polyethersulfone substrate using low-temperature processable, inherently photosensitive polyimide as the gate insulator and pentacene as the active material. The polyimide was prepared through two-step reaction. The polyimide precursor, poly(amic acid), was prepared from a dianhydride and aromatic diamine through a polycondensation reaction, and subsequently converted to its corresponding polyimide by a chemical imidization. Photolithographic properties of the polyimide are investigated. The pattern resolution of the cured polyimide was about 50μm. The pentacene OTFTs with the patterned polyimide were obtained with a carrier mobility of 0.1cm2∕Vs and ION∕IOFF of 5×105. The OTFT characteristics are discussed in more detail with respect to the electrical properties of the photosensitive polyimide thin film. This low-temperature photopatternable polyimide paves the way for the easy and low-cost fabrication of OTFT arrays without expensive and compli...

Experimental study on thickness-related electrical characteristics in organic/metal-nanocluster/organic systems

Organic bistable devices with the trilayer structure, organic/metal-nanocluster/organic, interposed between two electrodes have been systematically studied by varying the thickness of the organic layers and the metal-nanocluster layer. Devices fabricated in this fashion exhibit either electrical bistability or current step, depending on the thickness of the metal-nanocluster layer. Electrical bistable devices have been studied by fixing the metal-nanocluster layer thickness at 20 nm and changing the organic-layer thickness from 20 to 60 nm. Device injection current at the on state shows an exponential decrease with an increasing organic-layer thickness, suggesting that the electron transmission probability of the devices decreases with an increasing thickness of the organic layer. This is in agreement with theoretical calculations based on the single-band Hubbard model. The evolution of the electrical current step is observed for devices fabricated by fixing the organic-layer thickness at 50 nm and changi...

Low-temperature processable inherently photosensitive polyimide gate dielectric for organic thin-film transistors : Synthesis, characterization, and application to transistors

Low-temperature processable inherently photosensitive polyimide was prepared from a dianhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, and aromatic diamines, 4,4′-diamino-3,3′dimethyl-diphenylmethane, through a polycondensation reaction, followed by a chemical imidization method. The photosensitive polyimide cured at 180 °C is used as a gate dielectric to fabricate flexible organic thin-film transistors with pentacene as an active semiconductor on polyethersulfone substrate. With the inherently photosensitive polyimide, the access to the gate electrode could be created easily without complicated and expensive lithographic techniques. A field effect carrier mobility of 0.007 cm 2 /V s was obtained for the pentacene organic thin-film transistors (OTFTs) with the photo-patterned polyimide as a gate dielectric. More detailed analysis for the pentacene OTFTs will be given with electrical properties of the thin polyimide film. Low-temperature processability and patternability of the polyimide give us more freedom to choose plastic substrates in OTFTs and facilitate the realization of low-cost organic electronics.

Investigation of the interfacial properties of laminated polymer diodes

Plastic lamination has become a promising approach to the fabrication of high-performance polymeric electronic devices. [T.-F. Guo, S. Pyo, S.-C. Chang, and Y. Yang, Adv. Funct. Mater. 11, 339 (2001)]. The major challenge for achieving high-performance laminated devices is the control of interface quality. In this letter, the various interfaces between two organic films have been investigated using atomic force microscope and impedance spectroscopy. Our results indicate the device performance is directly related to the formation of the interface. We attribute the better charge injection and higher electroluminescence efficiency of a laminated polymer light-emitting diode is due to the nanoscale surface roughness at the laminating interface.

High-performance flexible polymer light-emitting diodes fabricated via a low-temperature plastic laminated process

In this manuscript, we report on the successful fabrication of high performance polymer light emitting diodes (PLEDs) using a low temperature, plastic lamination process. Blue- and red-emitting PLEDs were fabricated by laminating different luminescent polymers and organic compounds together to form the active media. This unique approach eliminates the issue of organic solvent compatibility with the organic layers for fabricating multi-layer PLEDs. In addition, a template activated surface process (TAS) has been successfully applied to generate an optimum interface for the low temperature lamination process. The atomic force microscopy analysis reveals a distinct difference in the surfaces created by the TAS and the spin-coating process. This observation coupled with the device data confirms the importance of the activated interface in the lamination process.