Liwei Shang

Organic thin-film transistor memory with gold nanocrystals embedded in polyimide gate dielectric

An all-organic memory device based on a copper phthalocyanine (CuPc) thin-film transistor (TFT) using gold nanocrystals embedded in a polyimide gate dielectric is demonstrated. Both the gate dielectric and the active semiconductor layer are organic materials. Discrete gold nanocrystals are adopted as the charge storage medium. Under proper gate bias, gold nanocrystals are charged and discharged, resulting in the modulation of the channel conductance. Current–voltage (I–V) measurements at room temperature show the memory behaviour of the fabricated devices. The detailed programming and erasing operations are discussed. Low fabrication temperature and low cost are two benefits of the fabricated memory devices, which could provide a low-cost solution for the all organic circuits.

Low-Voltage Organic Field-Effect Transistor With PMMA/

This paper reports on the application of a bilayer polymethylmethacrylate (PMMA)/ZrO2 dielectric in copper ph-thalocyanine (CuPc) organic field-effect transistors (OFETs). By depositing a PMMA layer on ZrO2, the leakage of the dielectric is reduced by one order of magnitude compared to single- layer ZrO2. A high-quality interface is obtained between the organic semiconductor and the combined insulators. By integrating the advantages of polymer and high-fe dielectrics, the device achieves both high mobility and low threshold voltage. The typical field-effect mobility, threshold voltage, on/off current ratio, and subthreshold slope of OFETs with bilayer dielectric are 5.6 times 10-2 cm2/V ldr s, 0.8 V, 1.2 times 103, and 2.1 V/dec, respectively. By using the bilayer dielectrics, the hysteresis observed in the devices with single-layer ZrO2 is no longer present.

\hbox{ZrO}_{2}

Applying a bidirectional sweeping gate voltage, the white-light illuminated copper phthalocyanine thin-film transistors (CuPc-TFTs) show obvious hysteresis effect and the hysteresis window is 32 V. This effect is dominated by the additional carriers generated by photoirradiation. Although small hysteresis exists in CuPc-TFTs without illumination, light makes the hysteresis more obvious. Thus, CuPc-TFTs are promising to realize light detection and/or light memory in a single organic device for future low-cost, ultrahigh-density organic photoelectric integration.

Bilayer Dielectric

The electrical switching characteristics of eicosanoic acid (EA)/zirconium oxide (ZrO2) bilayer thin films are investigated in this letter. The devices have a sandwich structure of aluminum (Al)∕EA∕ZrO2∕gold (Au) and exhibit asymmetric electrical bistable behavior with a rectifying effect through resistive switching. Reversible and reproducible bistable switching properties were observed by applying certain voltages. The asymmetry and rectifying bistable behavior is proposed to result from the Schottky barrier that is present by reason of the ZrO2 layer. The rectifying effect can significantly improve misreading in matrix crossbar memory based on bistable two-terminal devices, paving a way for a practical crossbar molecular memory.

Light-induced hysteresis characteristics of copper phthalocyanine organic thin-film transistors

In this work, a bilayer resist system with ZEP520 as the top layer and lift-off resist (LOR) as the bottom layer for lift-off process was investigated for the first time. The formation of undercut was studied as a critical step which makes lift-off process much more feasible in bilayer resist process. Using different dissolution rates of LOR layer, the length of undercut can be well controlled, providing reliable process. The top layer of ZEP520 is more efficient than other resists (PMMA etc.) for e-beam lithography, due to its high resolution and high sensitivity. Here, a set of process parameters have been optimized to fabricate Cr metal lines with a width of less than 70 nm. This bilayer lift-off resist system can be widely used in nano-fabrication for various nano-scale structures and devices.

Asymmetric electrical bistable behavior of an eicosanoic acid/zirconium oxide bilayer system with rectifying effect

In this letter, an organic memory cell based on tris(8-hydroxyquinolinato)aluminum doped with gold nanoparticles is reported. The device can achieve good resistive switching properties, such as a high on/off current ratio of about 104, and good retention (4 h at 0.1 V). The device remains in either state even after the power has been turned off and shows a good stability under stress test. The current-voltage characteristics are comprehensively investigated, and a possible mechanism is proposed and well fitted with the experiment data. The results show that the organic memory devices have promising potentials for future flexible electronic systems.

A ZEP520-LOR bilayer resist lift-off process by e-beam lithography for nanometer pattern transfer

In this letter, high-performance organic phototransistors and photoswitches based on an ultraclosely π-stacked organic semiconductor, i.e., titanyl phthalocyanine, are fabricated. The p-type transistor exhibited high performance with a hole mobility of ~ 4. 5 cm²·V^-1·s^-1 and an on/off ratio higher than 3.1 × 10⁷. Phototransistors exhibited high-photoresponse properties with a responsivity at 10.5 A/W and a photosensitivity up to 2.7 × 10⁵. The high performance of the devices showed their potential application in optoelectronic organic integrated circuits.

Organic Programmable Resistance Memory Device Based on

A low-voltage multilevel organic thin-film memory device is proposed and demonstrated for nonvolatile data storage. Charge carrier density in the storage field was tuned up to four discrete levels in pentacene organic thin-film transistor with poly(methyl methacrylate)-modified Al₂O₃ film as the dielectric layer through light-assisted program procedures. Charges can be stored over 1 × 10⁴ s at room temperature. The states can be clearly distinguished after 1 × 10⁴ write-read cycles.

\hbox{Au/Alq}_{3}/\hbox{gold-nanoparticle/Alq}_{3}/\hbox{Al}

In this letter, the effect of the interface on the electrical characteristics of a rectifier based on an organic diode with pentacene as the electroactive layer is studied. It was found that the on/off ratio had a strong correlation with the interface effect (i.e., the bottom electrode material). The rectification ratio was improved to 2 × 106 at 5 V by modifying the bottom electrode with copper tetracyanoquinodimethane. The ac rectification frequency exceeded 13.56 MHz, which is a main requirement for an organic radio-frequency identification application.

Structure

In this paper, organic thin film transistors based on titanyl phthalocyanine were fabricated on octadecyltrichlorosilane (OTS) stripe modified Si/SiO2 substrates. The p-type transistor exhibited high performance with a hole mobility of ∼4.25 cm2V−1s−1 and an on/off ratio greater than 3.1 × 107 on 1 µm wide OTS stripe modified substrates. The charge transport anisotropy was observed in devices fabricated with channels parallel and perpendicular to the OTS stripes, indicating that the molecular orientation was optimized and arranged in a more ordered style. The high performance of the devices showed their potential for application in organic circuits.