Thin reduced graphene oxide interlayer with a conjugated block copolymer for high performance non-volatile ferroelectric polymer memory

Polymer ferroelectric-gate field effect transistors (Fe-FETs) employing ferroelectric polymer thin films as gate insulators are highly attractive as a next-generation non-volatile memory. For minimizing gate leakage current of a device which arises from electrically defective ferroelectric polymer layer in particular at low operation voltage, the materials design of interlayers between the ferroelectric insulator and gate electrode is essential. Here, we introduce a new solution-processed interlayer of conductive reduced graphene oxides (rGOs) modified with a conjugated block copolymer, poly(styrene-block-paraphenylene) (PS-b-PPP). A FeFET with a solution-processed p-type oligomeric semiconducting channel and ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) insulator exhibited characteristic source–drain current hysteresis arising from ferroelectric polarization switching of a PVDF-TrFE insulator. Our PS-b-PPP modified rGOs (PMrGOs) with conductive moieties embedded in insulating polymer matrix not only significantly reduced the gate leakage current but also efficiently lowered operation voltage of the device. In consequence, the device showed large memory gate voltage window and high ON/OFF source–drain current ratio with excellent data retention and read/write cycle endurance. Furthermore, our PMrGOs interlayers were successfully employed to FeFETs fabricated on mechanically flexible substrates with promising non-volatile memory performance under repetitive bending deformation.     

UV assisted non-volatile memory behaviour using Copper (II) phthalocyanine based organic field-effect transistors

In this report, we have demonstrated the optical non-volatile memory characteristics using CuPc OFET. The memory operation was comprehensively demonstrated with different programming conditions. It was found that the programming of CuPc OFET with an electric pulse at the gate terminal under UV-light photo-illumination compared to other programming conditions, could substantially increase the memory window due to massive charge trapping in the polymer electret layer, which causes shift in the device transfer characteristics from low-conduction state (“OFF state”, or logic 0) to high conduction state (“ON state”, or logic 1) at V_GS = 0V. From device operation at −50V, a memory window of greater than 45V could be achieved by applying a programming voltage of +70 V at the gate terminal under UV-light photo-illumination. Moreover, it was completely erased by applying −100 V at the gate terminal in dark.     

（英）界面极化层引起P(VDF-TrFE)电容器的电容-电压的不对称

通过研究Au/P(VDF-TrFE)/Al 电容器的变温(200 K 到310 K)电容-电压曲线,室温下观察到两个极化方向下的电容不对称,这个现象可以应用于非挥发性存储器.电容不对称程度随着温度的降低而变小,当温度低于230 K,电容不对称现象消失.P(VDF-TrFE)与Al电极之间的界面极化层可以解释观察到的电容不对称现象.     

Microcavity polymer electroluminescent devices with solution-processed dielectric distributed Bragg reflectors utilizing inorganic copper (I) thiocyanate and insulating polymers

The concept of using printed inorganic/organic hybrid distributed Bragg reflectors (DBRs) utilizing inorganic semiconductor and insulating polymers in microcavity polymer electroluminescent devices is introduced to provide an approach to achieve the spectral narrowing and the strong forward directionality. The large refractive index contrast of approximately 0.5 (0.44) between inorganic copper(I) thiocyanate, CuSCN, and insulating polymer of poly(vinylidene fluoride-trifluoroethylene), P(VDF-TrFE) (cellulose acetate, CA) results in the fabrication of solution-processed inorganic-organic hybrid dielectric DBRs with high reflectivity (>90%) from nanostructures consisting of only four (five) bilayers. For DBRs composed of CuSCN/CA alternative dielectric layers, all-solution processed microcavity polymer light-emitting diode based on highly conductive poly(ethylenedioxythiophene):poly(styrenesulfonate) anode except for Ag cathode exhibits the narrowing of EL spectrum with a full width at half maximum of approximately 25 nm and the maximum luminance of above 10,000 cd/m². From the viewpoint of dielectric DBRs based on ferroelectric polymer P(VDF-TrFE) with both low refractivity and high permittivity, we demonstrate a microcavity AC voltage-driven polymer electroluminescent device (μcACEL) which exhibits the spectral narrowing and the strong forward directionality. This work is anticipated to be useful for the development of solution-processed μcACEL with unique device architecture.     

Phase Segregation in Thin Films of Conjugated Polyrotaxane– Poly(ethylene oxide) Blends: A Scanning Force Microscopy Study

Scanning force microscopy (SFM) is used to study the surface morphology of spin‐coated thin films of the ion‐transport polymer poly(ethylene oxide) (PEO) blended with either cyclodextrin (CD)‐threaded conjugated polyrotaxanes based on poly(4,4′‐diphenylene‐vinylene) (PDV), β‐CD–PDV, or their uninsulated PDV analogues. Both the polyrotaxanes and their blends with PEO are of interest as active materials in light‐emitting devices. The SFM analysis of the blended films supported on mica and on indium tin oxide (ITO) reveals in both cases a morphology that reflects the substrate topography on the (sub‐)micrometer scale and is characterized by an absence of the surface structure that is usually associated with phase segregation. This observation confirms a good miscibility of the two hydrophilic components, when deposited by using spin‐coating, as suggested by the luminescence data on devices and thin films. Clear evidence of phase segregation is instead found when blending PEO with a new organic‐soluble conjugated polymer such as a silylated poly(fluorene)‐alt‐poly(para‐phenylene) based polyrotaxane (THS–β‐CD–PF–PPP). The results obtained are relevant to the understanding of the factors influencing the interfacial and the intermolecular interactions with a view to optimizing the performance of light‐emitting diodes, and light‐emitting electrochemical cells based on supramolecularly engineered organic polymers.     

PEO作阴极修饰层提高有机光伏电池的稳定性

采用聚氧化乙烯(PEO)作为聚合物太阳能电池的阴极修饰层,以P3HT:PCBM为活性层制备了聚合物本体异质结太阳能电池。考察了PEO的厚度对器件光伏性能及稳定性的影响。比较了加入PEO修饰层前后器件的稳定性,研究了采用PEO修饰层前后器件电阻的差异。结果表明:加入PEO作为阴极修饰层后器件的光电性能(JSC,VOC,FF,PCE)均有明显提高,而器件的串联电阻Rs则有了明显降低。没有阴极修饰层的器件的初始光电转换效率为1.92%,90 h后衰减为初始值的5%;而加入PEO修饰层后初始光电转换效率为3.36%,90 h后仅衰减为初始值的20%,光电转换效率提高了75%,稳定性提高了3倍。     

Epitaxy of BaTiO3 thin film on Si(0 0 1) using a SrTiO3 buffer layer for non-volatile memory application

In this study we report the epitaxial growth of BaTiO₃ films on Si(0 0 1) substrate buffered by 5 nm-thick SrTiO₃ layer using both MBE and PLD techniques. The BaTiO₃ films demonstrate single crystalline, (0 0 1)-oriented texture and atomically flat surface on SrTiO₃/Si template. The electrical characterizations of the BaTiO₃ films using MFIS structures show that samples grown by MBE with limited oxygen pressure during the growth exhibit typical dielectric behavior despite post deposition annealing process employed. A ferroelectric BaTiO₃ layer is obtained using PLD method, which permits much higher oxygen pressure. The C-V curve shows a memory window of 0.75 V which thus enable BaTiO₃ possibly being applied to the non-volatile memory application.     

Synthesis of the PZT films deposited on pt-coated (100) Si substrates for nonvolatile memory applications

Ferroelectric lead-zirconate-titanate (PZT) thin films were deposited by the pulsed laser deposition technique on Pt-coated (100) Si substrates. This study was focused on the investigation of the PZT film growth on (100) Si substrate at varying deposition parameters and electrical characterization of the films including hysteresis loop and fatigue properties by RT66A Standardized Ferroelectric Test System. PZT deposited at higher temperature (575°C in 450 mTorr O₂ partial pressure) showed the best crystalline structure. The remnant polarization and the retained polarization of the ferroelectric capacitors were 13 μC/cm² and 20 μC/cm², respectively. The crystallographic properties of the films were determined using the x-ray diffractometer method. The cross-sectional transmission electron microscope results showed very smooth interfaces among different layers of films.     

Preparation of (Pb0.88La0.12)TiO3 thin films for dynamic random access memory by low pressure-metalorganic chemical vapor deposition

La-modified lead titanate (PLT) thin films were prepared by hot-wall type low pressure-metalorganic chemical vapor deposition method. Pb(dpm)₂, La(dpm)₃, and titanium tetraisopropoxide were used as source materials. The films were deposited at 500°C under the low pressure of 1000 mTorr and then annealed at 650°C for 10 min in oxygen ambient. Sputter-deposited platinum electrodes and 180 nm thick PLT thin films were employed to form MIM capacitors with the best combination of high charge storage density (26.7 μC/cm² at 3V) and low leakage current density (1.5 × 10^-7 A/cm² at 3V). The measured dielectric constant and dielectric loss were 1000∼1200 and 0.06∼0.07 at zero bias and 100 kHz, respectively.     

All‐Inorganic CsPbI3 Perovskite Phase‐Stabilized by Poly(ethylene oxide) for Red‐Light‐Emitting Diodes

Despite the excellent photoelectronic properties of the all‐inorganic cesium lead iodide (CsPbI₃) perovskite, which does not contain volatile and hygroscopic organic components, only a few CsPbI₃ devices are developed mainly owing to the frequent formation of an undesirable yellow δ‐phase at room temperature. Herein, it is demonstrated that a small quantity of poly(ethylene oxide) (PEO) added to the precursor solution effectively inhibits the formation of the yellow δ‐phase during film preparation, and promotes the development of a black α‐phase at a low crystallization temperature. A systematic study reveals that a thin, dense, pinhole‐free CsPbI₃ film is produced in the α‐phase and is stabilized with PEO that effectively reduces the grain size during crystallization. A thin α‐phase CsPbI₃ film with excellent photoluminescence is successfully employed in a light‐emitting diode with an inverted configuration of glass substrate/indium tin oxide/zinc oxide/poly(ethyleneimine)/α‐CsPbI₃/poly(4‐butylphenyl‐diphenyl‐amine)/WO₃/Al, yielding the characteristic red emission of the perovskite film at 695 nm with brightness, external quantum efficiency, and emission band width of ≈101 cd m^?2, 1.12%, and 32 nm, respectively.     

Molecular orientation anisotropy and hole transport properties of diluted semiconducting films of poly(p-phenylenevinylene) derivative

The electrical and optical properties of certain semiconducting polymers are improved in blend films with inert host materials. The improvements have been attributed to the dilution effect of electron traps and interchain species in semiconductor materials. In this paper, we report on anisotropy in the blend films of poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and its strong dependence on an inert host material, such as polystyrene (PS) or polyvinylcarbazole (PVK). We found that the orientation of the MEH-PPV backbone in the blend film changed from horizontal to random on dilution with PS. Moreover, the in-plane hole conductivity was enhanced in the MEH-PPV:PVK blend film, although the out-of-plane conductivity reduced owing to excessive dilution. Mott–Schottky analysis of the capacitance–voltage characteristics revealed opposite trends for dilution with PS and PVK; i.e., PS increased the accumulated charge density in the bulk of the blend film, whereas PVK reduced it. These results demonstrate that isotropy was induced in the PS blend films, whereas anisotropy was induced in the PVK blend films. Anisotropy is an important factor for understanding the hole transport characteristics in the diluted films.