Lifetime estimation of thin-film transistors in organic emitting diode display panels with compensation.

Oxide semiconductor thin-film transistors (TFTs) are used in the pixel array and gate driver circuits of organic light emitting diode (OLED) display panels. Long-term reliability characteristics of the TFTs are a barometer of the lifetime of OLED display panels. The long-term reliability of the driver TFTs is evaluated in a short time under high voltages and high temperature for an accelerated degradation test. If reliability parameters from the power law or stretched-exponential functions are the same for individual devices and devices in an operating panel, the lifetime of the panel can be accurately estimated. However, since compensation circuits are designed into operating panels, an environmental discrepancy exists between the accelerated test of single devices and the operation of devices in the panel. Herein, we propose a novel compensation stretched-exponential function (CSEF) model which captures the effect of the threshold voltage compensation circuit in the panel. The CSEF model not only bridges the discrepancy between individual devices and panel devices, but also provides a method to accurately and efficiently estimate the long-term lifetime of all display panels that utilize compensation circuits.

Complementary Hybrid Semiconducting Superlattices with Multiple Channels and Mutual Stabilization.

An organic-inorganic hybrid superlattice with near perfect synergistic integration of organic and inorganic constituents was developed to produce properties vastly superior to those of either moiety alone. The complementary hybrid superlattice is composed of multiple quantum wells of 4-mercaptophenol organic monolayers and amorphous ZnO nanolayers. Within the superlattice, multichannel formation was demonstrated at the organic-inorganic interfaces to produce an excellent-performance field effect transistor exhibiting outstanding field-effect mobility with band-like transport and steep subthreshold swing. Furthermore, mutual stabilizations between organic monolayers and ZnO effectively reduced the performance degradation notorious in exclusively organic and ZnO transistors.

Ultrasensitive Electrical Detection of Hemagglutinin for Point-of-Care Detection of Influenza Virus Based on a CMP-NANA Probe and Top-Down Processed Silicon Nanowire Field-Effect Transistors.

Rather than the internal genome nucleic acids, the biomolecules on the surface of the influenza virus itself should be detected for a more exact and rapid point-of-care yes/no decision for influenza virus-induced infectious diseases. This work demonstrates the ultrasensitive electrical detection of the HA1 domain of hemagglutinin (HA), a representative viral surface protein of the influenza virus, using the top-down complementary metal oxide semiconductor (CMOS) processed silicon nanowire (SiNW) field-effect transistor (FET) configuration. Cytidine-5'-monophospho-N-acetylneuraminic acid (CMP-NANA) was employed as a probe that specifically binds both to the aldehyde self-aligned monolayer on the SiNWs and to HA1 simultaneously. CMP-NANA was serially combined with two kinds of linkers, namely 3-aminopropyltriethoxysilane and glutaraldehyde. The surface functionalization used was verified using the purification of glutathione S-transferase-tagged HA1, contact angle measurement, enzyme-linked immunosorbent assay test, and isoelectric focusing analysis. The proposed functionalized SiNW FET showed high sensitivities of the threshold voltage shift (ΔVT) ~51 mV/pH and the ΔVT = 112 mV (63 mV/decade) with an ultralow detectable range of 1 fM of target protein HA1.

Effect of Simultaneous Mechanical and Electrical Stress on the Electrical Performance of Flexible In-Ga-Zn-O Thin-Film Transistors.

We investigated the effect of simultaneous mechanical and electrical stress on the electrical characteristics of flexible indium-gallium-zinc oxide (IGZO) thin-film transistors (TFTs). The IGZO TFTs exhibited a threshold voltage shift (∆VTH) under an application of positive-bias-stress (PBS), with a turnaround behavior from the positive ∆VTH to the negative ∆VTH with an increase in the PBS application time, whether a mechanical stress is applied or not. However, the magnitudes of PBS-induced ∆VTH in both the positive and negative directions exhibited significantly larger values when a flexible IGZO TFT was under mechanical-bending stress than when it was at the flat state. The observed phenomena were possibly attributed to the mechanical stress-induced interface trap generation and the enhanced hydrogen diffusion from atomic layer deposition-grown Al2O3 to IGZO under mechanical-bending stress during PBS. The subgap density of states was extracted before and after an application of PBS under both mechanical stress conditions. The obtained results in this study provided potent evidence supporting the mechanism suggested to explain the PBS-induced larger ∆VTHs in both directions under mechanical-bending stress.

Effect of Oxygen Content on Current Stress-Induced Instability in Bottom-Gate Amorphous InGaZnO Thin-Film Transistors.

The effect of oxygen content on current-stress-induced instability was investigated in bottom-gate amorphous InGaZnO (a-IGZO) thin-film transistors. The observed positive threshold voltage shift (ΔVT) was dominated by electron trapping in the gate insulator (GI), whereas it was compensated by donor creation in a-IGZO active regions when both current flows and a high lateral electric field were present. Stress-induced ΔVT increased with increasing oxygen content irrespective of the type of stress because oxygen content influenced GI quality, i.e., higher density of GI electron traps, as well as typical direct current (DC) performance like threshold voltage, mobility, and subthreshold swing. It was also found that self-heating became another important mechanism, especially when the vertical electric field and channel current were the same, independent of the oxygen content. The increased ΔVT with oxygen content under positive gate bias stress, positive gate and drain bias stress, and target current stress was consistently explained by considering a combination of the density of GI electron traps, electric field relaxation, and self-heating-assisted electron trapping.

ZnO composite nanolayer with mobility edge quantization for multi-value logic transistors.

A quantum confined transport based on a zinc oxide composite nanolayer that has conducting states with mobility edge quantization is proposed and was applied to develop multi-value logic transistors with stable intermediate states. A composite nanolayer with zinc oxide quantum dots embedded in amorphous zinc oxide domains generated quantized conducting states at the mobility edge, which we refer to as "mobility edge quantization". The unique quantized conducting state effectively restricted the occupied number of carriers due to its low density of states, which enable current saturation. Multi-value logic transistors were realized by applying a hybrid superlattice consisting of zinc oxide composite nanolayers and organic barriers as channels in the transistor. The superlattice channels produced multiple states due to current saturation of the quantized conducting state in the composite nanolayers. Our multi-value transistors exhibited excellent performance characteristics, stable and reliable operation with no current fluctuation, and adjustable multi-level states.

Photoactivation of Noncovalently Assembled Peptide Ligands on Carbon Nanotubes Enables the Dynamic Regulation of Stem Cell Differentiation.

Stimuli-responsive hybrid materials that combine the dynamic nature self-assembled organic nanostructures, unique photophysical properties of inorganic materials, and molecular recognition capability of biopolymers can provide sophisticated nanoarchitectures with unprecedented functions. In this report, infrared (IR)-responsive self-assembled peptide-carbon nanotube (CNT) hybrids that enable the spatiotemporal control of bioactive ligand multivalency and subsequent human neural stem cell (hNSC) differentiation are reported. The switching between the ligand presented and hidden states was controlled via IR-induced photothermal heating of CNTs, followed by the shrinkage of the thermoresponsive dendrimers that exhibited lower critical solution temperature (LCST) behavior. The control of the ligand spacing via molecular coassembly and IR-triggered ligand presentation promoted the sequential events of integrin receptor clustering and the differentiation of hNSCs into electrophysiologically functional neurons. Therefore, the combination of our nanohybrid with biomaterial scaffolds may be able to further improve effectiveness, durability, and functionality of the nanohybrid systems for spatiotemporal control of stem cell differentiation. Moreover, these responsive hybrids with remote-controllable functions can be developed as therapeutics for the treatment of neuronal disorders and as materials for the smart control of cell function.

Highly efficient and fast pre-activation cyclization of the long peptide: Succinimidyl ester-amine reaction revisited.

A new method for the pre-activation cyclization of a long peptide is described. The approach involves the formation of a pre-activated succinimidyl ester species in advance of amidation, which completely eliminates the potentially troublesome amine end-capping side reaction. The cyclization reactions proceed with high efficiency and fast reaction kinetics for the long peptide with 25 residues. The exploration and large-scale preparation of synthetic cyclic peptides should become more accessible and feasible with this approach. This method has a potential to be further applied for the synthesis of much longer and more complex cyclic peptides.

Synthesis and conformational analysis of macrocyclic peptides consisting of both α-helix and polyproline helix segments.

Macrocycles are interesting molecules because their topological features and constrained properties significantly affect their chemical, physical, biological, and self-assembling properties. In this report, we synthesized unique macrocyclic peptides composed of both an α-helix and a polyproline segment and analyzed their conformational properties. We found that the molecular stiffness of the rod-like polyproline segment and the relative orientation of the two different helical segments strongly affect the efficiency of the macrocyclization reaction. Conformational analyses showed that both the α-helix and the polyproline II helix coexisted within the macrocyclic peptides and that the polyproline segment exerts significant effect on the overall helical stability and conformation of the α-helical segment.

Stabilization of α-helices by the self-assembly of macrocyclic peptides on the surface of gold nanoparticles for molecular recognition.

A novel strategy to stabilize the α-helical secondary structures of peptides upon binding to gold nanoparticles is described. Using a model protein-protein interaction system, we showed that AuNPs decorated with stabilized p53 α-helix peptides can mediate specific molecular recognition with their target protein.

Chameleon-like self-assembling peptides for adaptable biorecognition nanohybrids.

We present here the development of adaptable hybrid materials in which self-assembling peptides can sense the diameter/curvature of carbon nanotubes and then adjust their overall structures from disordered states to α-helices, and vice versa. The peptides within the hybrid materials show exceptionally high thermal-induced conformational stability and molecular recognition capability for target RNA. This study shows that the context-dependent protein-folding effects can be realized in artificial nanosystems and provides a proof of principle that nanohybrid materials decorated with structured and adjustable peptide units can be fabricated using our strategy, from which smart and responsive organic/inorganic hybrid materials capable of sensing and controlling diverse biological molecular recognition events can be developed.

Differential self-assembly behaviors of cyclic and linear peptides.

Here we ask the fundamental questions about the effect of peptide topology on self-assembly. The study revealed that the self-assembling behaviors of cyclic and linear peptides are significantly different in several respects, in addition to sharing several similarities. Their clear differences included the morphological dissimilarities of the self-assembled nanostructures and their thermal stability. The similarities include their analogous critical aggregation concentration values and cytotoxicity profiles, which are in fact closely related. We believe that understanding topology-dependent self-assembly behavior of peptides is important for developing tailor-made self-assembled peptide nanostructures.