Qijing Wang

Boost Up Carrier Mobility for Ferroelectric Organic Transistor Memory via Buffering Interfacial Polarization Fluctuation

Ferroelectric organic field-effect transistors (Fe-OFETs) have been attractive for a variety of non-volatile memory device applications. One of the critical issues of Fe-OFETs is the improvement of carrier mobility in semiconducting channels. In this article, we propose a novel interfacial buffering method that inserts an ultrathin poly(methyl methacrylate) (PMMA) between ferroelectric polymer and organic semiconductor layers. A high field-effect mobility (μFET) up to 4.6 cm2 V−1 s−1 is obtained. Subsequently, the programming process in our Fe-OFETs is mainly dominated by the switching between two ferroelectric polarizations rather than by the mobility-determined charge accumulation at the channel. Thus, the “reading” and “programming” speeds are significantly improved. Investigations show that the polarization fluctuation at semiconductor/insulator interfaces, which affect the charge transport in conducting channels, can be suppressed effectively using our method.

Fabrication and optical properties of two-dimensional ZnO hollow half-shell arrays

Two-dimensional optically active ZnO shells on polystyrene (PS) templates have been fabricated using a sputtering technique. Periodic ZnO hollow half-shell structure has been obtained by removing PS templates. It exhibits several anomalous dips in transmission spectra that have not been reported. The dips can be tuned up by changing the shell thickness and PS sphere size. The PL spectra confirm that the structure has enhanced defect emission of ZnO.

UV-blue photoluminescence from close-packed SiC nanocrystal film

We observed stable photoluminescence from close-packed cubic SiC nanocrystals that are self-assembled into thin solid film. The peak wavelength shifts from blue to near UV with increasing excitation energy and follows well the quantum-confinement effect. The photoluminescence excitation spectrum indicates a 3.47 eV bandgap corresponding to a particle size of 2.3 nm. The nanocrystal film shows triple-exponential photoluminescence decay with lifetimes of 2.3, 8.5, and 36.9 ns. The results open the possibility of the solid state UV-blue light emitting by use of the SiC nanocrystals in photonics and photonics/electronics integration.We observed stable photoluminescence from close-packed cubic SiC nanocrystals that are self-assembled into thin solid film. The peak wavelength shifts from blue to near UV with increasing excitation energy and follows well the quantum-confinement effect. The photoluminescence excitation spectrum indicates a 3.47 eV bandgap corresponding to a particle size of 2.3 nm. The nanocrystal film shows triple-exponential photoluminescence decay with lifetimes of 2.3, 8.5, and 36.9 ns. The results open the possibility of the solid state UV-blue light emitting by use of the SiC nanocrystals in photonics and photonics/electronics integration.

Unidirectional coating technology for organic field-effect transistors: materials and methods

Solution-processed organic field-effect transistors (OFETs) are essential for developing organic electronics. The encouraging development in solution-processed OFETs has attracted research interest because of their potential in low-cost devices with performance comparable to polycrystalline-silicon-based transistors. In recent years, unidirectional coating technology, featuring thin-film coating along only one direction and involving specific materials as well as solution-assisted fabrication methods, has attracted intensive interest. Transistors with organic semiconductor layers, which are deposited via unidirectional coating methods, have achieved high performance. In particular, carrier mobility has been greatly enhanced to values much higher than 10 cm2 V−1 s−1. Such significant improvement is mainly attributed to better control in morphology and molecular packing arrangement of organic thin film. In this review, typical materials that are being used in OFETs are discussed, and demonstrations of unidirectional coating methods are surveyed.

Speed up Ferroelectric Organic Transistor Memories by Using Two-Dimensional Molecular Crystalline Semiconductors

Ferroelectric organic field-effect transistors (Fe-OFETs) have attracted intensive attention because of their promising potential in nonvolatile memory devices. The quick switching between binary states is a significant fundamental feature in evaluating Fe-OFET memories. Here, we employ 2D molecular crystals via a solution-based process as the conducting channels in transistor devices, in which ferroelectric polymer acts as the gate dielectric. A high carrier mobility of up to 5.6 cm2 V-1 s-1 and a high on/off ratio of 106 are obtained. In addition, the efficient charge injection by virtue of the ultrathin 2D molecular crystals is beneficial in achieving rapid operations in the Fe-OFETs; devices exhibit short switching time of ∼2.9 and ∼3.0 ms from the on- to the off-state and from the off- to the on-state, respectively. Consequently, the presented strategy is capable of speeding up Fe-OFET memory devices by using solution-processed 2D molecular crystals.

Tunable interference of light behind subwavelength apertures

We demonstrate in this letter that electromagnetic waves passing through the subwavelength apertures on a silver film interfere with each other in the airgap behind the apertures. Depending on the width of the airgap, either constructive or destructive interference occurs. It is shown that constructive interference enhances the extraordinary optical transmission and evidently improves the quality factor, whereas destructive interference weakens the extraordinary optical transmission. We suggest that our results provide a unique approach to construct plasmonic structures and devices.

Reducing contact resistance in ferroelectric organic transistors by buffering the semiconductor/dielectric interface

The reduction of contact resistance in ferroelectric organic field-effect transistors (Fe-OFETs) by buffering the interfacial polarization fluctuation was reported. An ultrathin poly(methyl methacrylate) layer was inserted between the ferroelectric polymer and organic semiconductor layers. The contact resistance was significantly reduced to 55 kΩ cm. By contrast, Fe-OFETs without buffering exhibited a significantly larger contact resistance of 260 kΩ cm. Results showed that such an enhanced charge injection was attributed to the buffering effect at the semiconductor/ferroelectric interface, which narrowed the trap distribution of the organic semiconductor in the contact region. The presented work provided an efficient method of lowering the contact resistance in Fe-OFETs, which is beneficial for the further development of Fe-OFETs.

High-performance non-volatile field-effect transistor memories using an amorphous oxide semiconductor and ferroelectric polymer

Ferroelectric field-effect transistors (Fe-FETs) are of great interest for a variety of non-volatile memory device applications. High-performance top-gate Fe-FET memories using ferroelectric polymers of poly(vinylidene fluoride–trifluoroethylene) (P(VDF–TrFE)) and the inorganic oxide of InSiO were fabricated. The extracted electron mobility was as high as 84.1 cm2 V−1 s−1 in a low-frequency state. The interfacial charge transfer between the P(VDF–TrFE) and InSiO during annealing of the P(VDF–TrFE) layer benefits improvement in the device performance. The results show the potential of our Fe-FET memories for next-generation electronics.

Spin-Coated Crystalline Molecular Monolayers for Performance Enhancement in Organic Field-Effect Transistors

In organic field-effect transistors, the first few molecular layers at the semiconductor/dielectric interface are regarded as the active channel for charge transport; thus, great efforts have been devoted to the modification and optimization of molecular packing at such interfaces. Here, we report organic monolayers with large-area uniformity and high crystallinity deposited by an antisolvent-assisted spin-coating method acting as the templating layers between the dielectric and thermally evaporated semiconducting layers. The predeposited crystalline monolayers significantly enhance the film crystallinity of upper layers and the overall performance of transistors using these hybrid-deposited semiconducting films, showing a high carrier mobility up to 11.3 cm2 V-1 s-1. Additionally, patterned transistor arrays composed of the templating monolayers are fabricated, yielding an average mobility of 7.7 cm2 V-1 s-1. This work demonstrates a promising method for fabricating low-cost, high-performance, and large-area organic electronics.

Low-voltage, High-performance Organic Field-Effect Transistors Based on 2D Crystalline Molecular Semiconductors

Two dimensional (2D) molecular crystals have attracted considerable attention because of their promising potential in electrical device applications, such as high-performance field-effect transistors (FETs). However, such devices demand high voltages, thereby considerably increasing power consumption. This study demonstrates the fabrication of organic FETs based on 2D crystalline films as semiconducting channels. The application of high-κ oxide dielectrics allows the transistors run under a low operating voltage (−4 V). The devices exhibited a high electrical performance with a carrier mobility up to 9.8 cm2 V−1 s−1. Further results show that the AlOx layer is beneficial to the charge transport at the conducting channels of FETs. Thus, the device strategy presented in this work is favorable for 2D molecular crystal-based transistors that can operate under low voltages.