Hsin-Chieh Yu

Nonvolatile Bio-Memristor Fabricated with Egg Albumen Film

This study demonstrates the fabrication and characterization of chicken egg albumen-based bio-memristors. By introducing egg albumen as an insulator to fabricate memristor devices comprising a metal/insulator/metal sandwich structure, significant bipolar resistive switching behavior can be observed. The 1/f noise characteristics of the albumen devices were measured, and results suggested that their memory behavior results from the formation and rupture of conductive filaments. Oxygen diffusion and electrochemical redox reaction of metal ions under a sufficiently large electric field are the principal physical mechanisms of the formation and rupture of conductive filaments; these mechanisms were observed by analysis of the time-of-flight secondary ion mass spectrometry (TOF-SIMS) and resistance–temperature (R–T) measurement results. The switching property of the devices remarkably improved by heat-denaturation of proteins; reliable switching endurance of over 500 cycles accompanied by an on/off current ratio (Ion/off) of higher than 103 were also observed. Both resistance states could be maintained for a suitably long time (>104 s). Taking the results together, the present study reveals for the first time that chicken egg albumen is a promising material for nonvolatile memory applications.

Negative differential resistance behavior and memory effect in laterally bridged ZnO nanorods grown by hydrothermal method.

A novel memory device based on laterally bridged ZnO nanorods (NRs) in the opposite direction was fabricated by the hydrothermal growth method and characterized. The electrodes were defined by a simple photolithography method. This method has lower cost, simpler process, and higher reliability than the traditional focused ion beam lithography method. For the first time, the negative differential resistance and bistable unipolar resistive switching (RS) behavior in the current-voltage curve was observed at room temperature. The memory device is stable and rewritable; it has an ultra-low current level of about 1 × 10(-13) A in the high resistance state; and it is nonvolatile with an on-off current ratio of up to 1.56 × 10(6). Moreover, its peak-to-valley current ratio of negative differential resistance behavior is greater than 1.76 × 10(2). The negative differential resistance and RS behavior of this device may be related to the boundaries between the opposite bridged ZnO NRs. Specifically, the RS behavior found in ZnO NR devices with a remarkable isolated boundary at the NR/NR interface was discussed for the first time. The memory mechanism of laterally bridged ZnO NR-based devices has not been discussed in the literature yet. In this work, results show that laterally bridged ZnO NR-based devices may have next-generation resistive memories and nanoelectronic applications.

Nonvolatile memory thin film transistors using CdSe/ZnS quantum dot- poly(methyl methacrylate) composite layer formed by a two-step spin coating technique

The nonvolatile memory thin film transistors (TFTs) using a core/shell CdSe/ZnS quantum dot (QD)-poly(methyl methacrylate) (PMMA) composite layer as the floating gate have been demonstrated, with the device configuration of n+-Si gate/SiO2 insulator/QD-PMMA composite layer/pentacene channel/Au source-drain being proposed. To achieve the QD-PMMA composite layer, a two-step spin coating technique was used to successively deposit QD-PMMA composite and PMMA on the insulator. After the processes, the variation of crystal quality and surface morphology of the subsequent pentacene films characterized by x-ray diffraction spectra and atomic force microscopy was correlated to the two-step spin coating. The crystalline size of pentacene was improved from 147.9 to 165.2 A, while the degree of structural disorder was decreased from 4.5% to 3.1% after the adoption of this technique. In pentacene-based TFTs, the improvement of the performance was also significant, besides the appearances of strong memory characteristic...

Characteristics of InGaAs Submonolayer Quantum-Dot and InAs Quantum-Dot Photonic-Crystal Vertical-Cavity Surface-Emitting Lasers

We have made InGaAs submonolayer (SML) quantum-dot (QD) and InAs QD photonic-crystal vertical-cavity surface-emitting lasers (PhC-VCSELs) for fiber-optic communications in the 990 and 1300 nm ranges, respectively. The active region of the InGaAs SML QD PhC-VCSEL contains three InGaAs SML QD layers, with each of the SML QD layer formed by alternating depositions of InAs and GaAs. The active region of the InAs QD PhC-VCSEL contains 17 undoped InAs-InGaAs QD layers. Both types of QD PhC-VCSELs exhibit single-mode characteristics throughout the current range, with side-mode suppression ratio (SMSR) larger than 35 dB. A maximum output power of 5.7 mW has been achieved for the InGaAs SML QD PhC-VCSEL. The near-field image study of the QD PhC-VCSELs indicates that the laser beam is well confined by the photonic-crystal structure of the device.

Impact of preparation condition of ZnO electron transport layer on performance of hybrid organic-inorganic light-emitting diodes

In this article, we have demonstrated the hybrid polymer light-emitting diodes (PLEDs) with a sol-gel derived or rf-sputtered ZnO electron transport layer (ETL). For the ZnO films prepared under different conditions, low annealing temperature (300 °C) leads to the film amorphous while the polycrystalline films is readily achieved by sputtering. Though the surface roughness can be improved by thermal annealing at 400 °C for sputtered films, the release of compressive stress after treatment has shrunk the optical band gap from 3.282 to 3.268 eV. As the ETL in PLEDs, the reduced band gap could increase potential barrier for electron injection and decrease the hole blocking capability. In our cases, luminance larger than 7000 cd/m2 can be obtained in device with pristine sputtered ZnO ETL. It is concluded that crystalline structure of ZnO films is important to facilitate the balance of carrier mobility to obtain high luminance and high efficiency devices.

Solution-Processable MoO x for Efficient Light-Emitting Diodes Based on Giant Quantum Dots

We report efficient quantum dot light-emitting diodes (QLEDs) using sizable 13-nm green-emission quantum dots as the emissive layer and solution-processable MoOx as the hole injection layer (HIL). The MoOx HIL was prepared by the decomposition of a solution of ammonium molybdate tetrahydrate at 80 °C under ambient conditions, further spin-coated onto an indium tin oxide substrate to facilitate hole injection. Compared with the reference sample with a polymeric hole injection material poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), the sMoOx film showed a higher work function of 5.6 eV, better transparency, and smoother surface morphology. The stable QLED with optimized MoOx film thickness achieved a higher maximum current efficiency of 10.8 cd/A at a lower turn-on voltage of 2.2 V versus the one with a PEDOT:PSS HIL, 9.9 cd/A and 2.9 V, respectively. Moreover, a small leakage current in sMoOx-device was found, which was attributed to the better surface morphology of sMoOx.

Enhanced Field Emission Properties of Ag Nanoparticle-Decorated ZnO Nanorods Under Ultraviolet Illumination

In this paper, pure ZnO and Ag nanoparticle (NP)-decorated ZnO nanorods (NRs) were successfully synthesized via a low-temperature hydrothermal method. The as-prepared samples were characterized through high-resolution transmission electron microscopy and selected-area electron diffractometry. The enhanced field emission (FE) behavior of the Ag NP-decorated ZnO NRs along the [0002] crystal c-axis and their single-crystalline hexagonal structures were characterized with surface-protruding Ag NPs. The resulting FE in the dark and under ultraviolet illumination had low turn-ON electric fields of 3.93 and 2.04 V · μm-2, whereas the enhanced field enhancement factors were 1593 and 57872, respectively.

Investigation of Nonvolatile Memory Effect of Organic Thin-Film Transistors with Triple Dielectric Layers

Pentacene thin-film transistor (TFT) memory using poly(2-hydroxyethyl methacrylate) (PHEMA)-based polymer dielectric layers has been developed. The electric performance and memory behaviors of memory TFTs can be significantly improved by using triple polymer dielectric layers consisting of PHEMA/poly(methyl methacrylate) (PMMA)/PHEMA. This can be attributed to the improvement of the channel/dielectric interface. This memory effect is due to the charge storage of the dipolar group or molecules in the dielectric. The devices exhibit a wide memory window (ΔVth, >20 V), switchable channel current, and long retention time.

Scalability of Phase Change Materials in Nanostructure Template

The scalability of In2Se3, one of the phase change materials, is investigated. By depositing the material onto a nanopatterned substrate, individual In2Se3 nanoclusters are confined in the nanosize pits with well-defined shape and dimension permitting the systematic study of the ultimate scaling limit of its use as a phase change memory element. In2Se3 of progressively smaller volume is heated inside a transmission electron microscope operating in diffraction mode. The volume at which the amorphous-crystalline transition can no longer be observed is taken as the ultimate scaling limit, which is approximately 5 nm3 for In2Se3. The physics for the existence of scaling limit is discussed. Using phase change memory elements in memory hierarchy is believed to reduce its energy consumption because they consume zero leakage power in memory cells. Therefore, the phase change memory applications are of great importance in terms of energy saving.

Cesium Azide—An Efficient Material for Green Light-Emitting Diodes With Giant Quantum Dots

A novel efficient and air-stable electron injection layer (EIL) of cesium azide (CsN3) was compared with conventional ones including CsF, Cs2CO3, LiF and without EIL in type-II quantum dot light-emitting diodes (QLEDs) with both organic electron and hole transport layers. Via directly decomposing to pristine cesium (Cs), the low-temperature evaporated CsN3 provided a better interfacial energy level alignment without damaging the underneath organic layer. Consequently, the current efficiencies of 7.45 cd/A was achieved in the CsN3-based green QLEDs consisting of giant CdSe@ZnS/ZnS quantum dots at 544 nm, which was 310% (at 10 mA/cm2) improvement over the LiF-based QLEDs. Moreover, the light turn-on voltage in CsN3-devices significantly decreased ~5.5 V in comparison with LiF-devices.A novel efficient and air-stable electron injection layer (EIL) of cesium azide (CsN3) was compared with conventional ones including CsF, Cs2CO3, LiF and without EIL in type-II quantum dot light-emitting diodes (QLEDs) with both organic electron and hole transport layers. Via directly decomposing to pristine cesium (Cs), the low-temperature evaporated CsN3 provided a better interfacial energy level alignment without damaging the underneath organic layer. Consequently, the current efficiencies of 7.45 cd/A was achieved in the CsN3-based green QLEDs consisting of giant CdSe@ZnS/ZnS quantum dots at 544 nm, which was 310% (at 10 mA/cm2) improvement over the LiF-based QLEDs. Moreover, the light turn-on voltage in CsN3-devices significantly decreased ~5.5 V in comparison with LiF-devices.