Jung Ah Lim

Bio: Jung Ah Lim is an academic researcher from Korea Institute of Science and Technology. The author has contributed to research in topics: Thin-film transistor & Organic semiconductor. The author has an hindex of 34, co-authored 144 publications receiving 4832 citations. Previous affiliations of Jung Ah Lim include Seoul National University Hospital & Information Technology University.

Self-Organization of Ink-jet-Printed Triisopropylsilylethynyl Pentacene via Evaporation-Induced Flows in a Drying Droplet†

Abstract: We have demonstrated the influence of evaporation-induced flow in a single droplet on the crystalline microstructure and film morphology of an ink-jet-printed organic semiconductor, 6,13-bis((triisopropylsilylethynyl) pentacene (TIPS_PEN), by varying the composition of the solvent mixture. The ringlike deposits induced by outward convective flow in the droplets have a randomly oriented crystalline structure. The addition of dichlorobenzene as an evaporation control agent results in a homogeneous film morphology due to slow evaporation, but the molecular orientation of the film is undesirable in that it is similar to that of the ring-deposited films. However, self-aligned TIPS_PEN crystals with highly ordered crystalline structures were successfully produced when dodecane was added. Dodecane has a high boiling point and a low surface tension, and its addition to the solvent results in a recirculation flow in the droplets that is induced by a Marangoni flow (surface-tension-driven flow), which arises during the drying processes in the direction opposite to the convective flow. The field-effect transistors fabricated with these self-aligned crystals via ink-jet printing exhibit significantly improved performance with an average effective field-effect mobility of 0.12 cm2 V–1 s–1. These results demonstrate that with the choice of appropriate solvent ink-jet printing is an excellent method for the production of organic semiconductor films with uniform morphology and desired molecular orientation for the direct-write fabrication of high-performance organic electronics.

Few-Layer Black Phosphorus Field-Effect Transistors with Reduced Current Fluctuation

Abstract: We investigated the reduction of current fluctuations in few-layer black phosphorus (BP) field-effect transistors resulting from Al2O3 passivation. In order to verify the effect of Al2O3 passivation on device characteristics, measurements and analyses were conducted on thermally annealed devices before and after the passivation. More specifically, static and low-frequency noise analyses were used in monitoring the charge transport characteristics in the devices. The carrier number fluctuation (CNF) model, which is related to the charge trapping/detrapping process near the interface between the channel and gate dielectric, was employed to describe the current fluctuation phenomena. Noise reduction due to the Al2O3 passivation was expressed in terms of the reduced interface trap density values Dit and Nit, extracted from the subthreshold slope (SS) and the CNF model, respectively. The deviations between the interface trap density values extracted using the SS value and CNF model are elucidated in terms of t...

Effect of Crystallization Modes in TIPS-pentacene/Insulating Polymer Blends on the Gas Sensing Properties of Organic Field-Effect Transistors

Abstract: Blending organic semiconductors with insulating polymers has been known to be an effective way to overcome the disadvantages of single-component organic semiconductors for high-performance organic field-effect transistors (OFETs). We show that when a solution processable organic semiconductor (6,13-bis(triisopropylsilylethynyl)pentacene, TIPS-pentacene) is blended with an insulating polymer (PS), morphological and structural characteristics of the blend films could be significantly influenced by the processing conditions like the spin coating time. Although vertical phase-separated structures (TIPS-pentacene-top/PS-bottom) were formed on the substrate regardless of the spin coating time, the spin time governed the growth mode of the TIPS-pentacene molecules that phase-separated and crystallized on the insulating polymer. Excess residual solvent in samples spun for a short duration induces a convective flow in the drying droplet, thereby leading to one-dimensional (1D) growth mode of TIPS-pentacene crystals. In contrast, after an appropriate spin-coating time, an optimum amount of the residual solvent in the film led to two-dimensional (2D) growth mode of TIPS-pentacene crystals. The 2D spherulites of TIPS-pentacene are extremely advantageous for improving the field-effect mobility of FETs compared to needle-like 1D structures, because of the high surface coverage of crystals with a unique continuous film structure. In addition, the porous structure observed in the 2D crystalline film allows gas molecules to easily penetrate into the channel region, thereby improving the gas sensing properties.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Semiconducting π-conjugated systems in field-effect transistors: a material odyssey of organic electronics.

Abstract: Since the discovery of highly conducting polyacetylene by Shirakawa, MacDiarmid, and Heeger in 1977, π-conjugated systems have attracted much attention as futuristic materials for the development and production of the next generation of electronics, that is, organic electronics. Conceptually, organic electronics are quite different from conventional inorganic solid state electronics because the structural versatility of organic semiconductors allows for the incorporation of functionality by molecular design. This versatility leads to a new era in the design of electronic devices. To date, the great number of π-conjugated semiconducting materials that have either been discovered or synthesized generate an exciting library of π-conjugated systems for use in organic electronics. 11 However, some key challenges for further advancement remain: the low mobility and stability of organic semiconductors, the lack of knowledge regarding structure property relationships for understanding the fundamental chemical aspects behind the structural design, and realization of desired properties. Organic field-effect transistors (OFETs) are a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals (drain, source, and gate electrodes). OFETs are not only essential building blocks for the next generation of cheap and flexible organic circuits, but they also provide an important insight into the charge transport of πconjugated systems. Therefore, they act as strong tools for the exploration of the structure property relationships of πconjugated systems, such as parameters of field-effect mobility (μ, the drift velocity of carriers under unit electric field), current on/off ratio (the ratio of the maximum on-state current to the minimum off-state current), and threshold voltage (the minimum gate voltage that is required to turn on the transistor). 17 Since the discovery of OFETs in the 1980s, they have attracted much attention. Research onOFETs includes the discovery, design, and synthesis of π-conjugated systems for OFETs, device optimization, development of applications in radio frequency identification (RFID) tags, flexible displays, electronic papers, sensors, and so forth. It is beyond the scope of this review to cover all aspects of π-conjugated systems; hence, our focus will be on the performance analysis of π-conjugated systems in OFETs. This should make it possible to extract information regarding the fundamental merit of semiconducting π-conjugated materials and capture what is needed for newmaterials and what is the synthesis orientation of newπ-conjugated systems. In fact, for a new science with many practical applications, the field of organic electronics is progressing extremely rapidly. For example, using “organic field effect transistor” or “organic field effect transistors” as the query keywords to search the Web of Science citation database, it is possible to show the distribution of papers over recent years as shown in Figure 1A. It is very clear

π-Conjugated Polymers for Organic Electronics and Photovoltaic Cell Applications†

Abstract: The optoelectronic properties of polymeric semiconductor materials can be utilized for the fabrication of organic electronic and photonic devices. When key structural requirements are met, these materials exhibit unique properties such as solution processability, large charge transporting capabilities, and/or broad optical absorption. In this review recent developments in the area of π-conjugated polymeric semiconductors for organic thin-film (or field-effect) transistors (OTFTs or OFETs) and bulk-heterojunction photovoltaic (or solar) cell (BHJ-OPV or OSC) applications are summarized and analyzed.

Inkjet Printing—Process and Its Applications

Abstract: In this Progress Report we provide an update on recent developments in inkjet printing technology and its applications, which include organic thin-film transistors, light-emitting diodes, solar cells, conductive structures, memory devices, sensors, and biological/pharmaceutical tasks. Various classes of materials and device types are in turn examined and an opinion is offered about the nature of the progress that has been achieved.