Inorganic Barrier Layer Research Articles

Energy storage performances of polymer-based composite dielectrics containing an in-situ-grown boron nitride layer

Polymer-based energy storage materials are widely utilized in the fields of electrical and electronics due to their high-power density and excellent charge-discharge efficiency. In this study, polyetherimide (PEI) composite films with outstanding energy storage properties were prepared by growing an inorganic barrier layer of boron nitride (BN) on the surface of PEI films through the in situ chemical vapor deposition (PECVD) method. The effects of BN deposition time on the dielectric properties, leakage current density, and energy storage properties of the composite films were investigated. The results reveal that the BN inorganic barrier layer, prepared by the PECVD method, demonstrates excellent interfacial compatibility with the PEI polymer matrix and forms a densely deposited layer. The BN inorganic barrier layer effectively suppresses carrier injection at the electrode, reduces the current density inside the PEI composite film, and improves the breakdown strength of the composite film. The composite film exhibits optimal performance when BN is deposited for 20 min. At an electric field strength of 660 MV/m, the energy storage density of the composite film reaches 6.08 J/cm3, which is 1.53 J/cm3 higher than that of pure PEI, while maintaining a charge-discharge efficiency of 90.43%. The findings of this study provide valuable theoretical support for the design of polymer-based energy storage materials.

A novel paper-based composite film with enhanced oxygen and water vapor barrier properties

Paper-based composite films have demonstrated significant potential in the field of packaging materials. However, the gas barrier properties of these films have been found to be less than satisfactory, primarily due to the inherent porosity and hydrophilic nature of cellulose-based paper. Consequently, the challenge of enhancing the gas barrier performance, particularly in relation to oxygen and water vapor, remains a formidable obstacle. In this study, drawing inspiration from the well-established multilayer composite model, which incorporates both organic and inorganic layers, an efficient strategy has been devised to enhance the gas barrier performance of paper-based packaging materials. The organic barrier layers in this approach utilize polyvinyl alcohol and polyacrylate. Meanwhile, the critical inorganic barrier layer is composed of functionalized SiO2@polydopamine nanoparticles (SiO2@PDA NPs). Importantly, due to the isotropic nature of the SiO2@PDA NPs, concerns related to the orientation control and exfoliation of 2D layered materials are alleviated within this system. The introduction of a crosslinker, 3-aminopropyl triethoxysilane, serves to bridge the gap between SiO2@PDA NPs, facilitating the tight concatenation of NPs through Schiff base or Michael addition reactions. Utilizing coating technology, a paper-based multilayer film was fabricated. As a result, the oxygen transmission rate of the composite film was substantially reduced to 0.3077 cm3/cm2·24 h·0.1 MPa, and the water vapor transmission rate was lowered to 4.1109 g/m2·24 h. Significantly, these composite films exhibit exceptional water resistance and mechanical properties, rendering them highly suitable for the packaging of a wide range of sensitive products, including food items, pharmaceuticals, electronic devices, and other gas-sensitive products.

Enhancing the high-temperature energy storage performance of PEI dielectric film through deposition of high-dielectric PZT coating layer

Dielectric film capacitors are a highly ubiquitous and indispensable electronic component, serving a crucial role in a wide array of electronic devices and power systems. Despite their extensive use, polymer film capacitors are often hampered by the conduction loss that ensues when they are subjected to high electric fields and temperatures. As a result, this leads to a significant reduction in energy density and charge-discharge efficiency. To solve this issue, magnetron sputtering technology was used to create a sandwich structure made of polyetherimide (PEI) thin films with lead zirconate titanate (PZT) inorganic layers coated on both sides. This remarkable innovation has successfully introduced the high dielectric PZT layer in the PEI film/metal electrode, substantially augmenting the barrier height at the dielectric/polymer interface. This has also resulted in a marked decrease in conduction loss, as conclusively validated by the experimental findings. At 150 °C and with charge-discharge efficiency above 90%, the maximum discharged energy density is 3.26 J/cm3, which is increased by 263% compared to the pristine PEI films (1.24 J/cm3 at 290 MV/m and 150 °C). This study designed a unique inorganic barrier layer of PZT to increase the energy storage capability of polymer dielectric films in high-temperature environments.

Improved Energy Storage Performance of PVDF Nanocapacitors by Utilizing 2D Inorganic Barrier Layers

We demonstrated a rational approach for designing high-performance polymer-based energy storage capacitors. Two-dimensional paraelectric Ca2Nb3O10 nanosheets were deposited on a ferroelectric poly(vinylidene fluoride) (PVDF) film to form paraelectric/ferroelectric hetero-assemblies. Such an artificial structuring enabled tailoring of the breakdown strength and dielectric response, realizing an enhanced energy density (~10 J cm−3) compared to pristine PVDF film (~ 1 J cm−3).

A compact polymer\u2013inorganic hybrid gas barrier nanolayer for flexible organic light-emitting diode displays

Atomic layer infiltration technology allows the formation of a nanometer-thick polymer-inorganic hybrid barrier layer in polymer material for flexible organic light-emitting diode (OLED) displays. In this study, according to transmission electron microscopy and secondary-ion mass spectrometry analysis results under various process conditions, a compact polymer-inorganic hybrid nanolayer was successfully formed in a polymer and good barrier performance was revealed with a low water vapor transmission rate under optimal process conditions. Additionally, through gas chromatography-mass spectrometry measurements after ultra-violet radiation testing, polymer out-gassing decreased compared to bare polymers. Based on barrier properties, the polymer with a polymer-inorganic hybrid barrier nanolayer was applied to a flexible OLED display as a substrate. During storage tests and folding tests, the flexible OLED display exhibits good reliability and better flexibility compared to those with an inorganic barrier layer. These results confirm that the polymer-inorganic hybrid nanolayer is suitable for barrier layer formation in flexible OLED displays.

Origin of Contrasting Emission Spectrum of Bromide versus Iodide Layered Perovskite Semiconductors.

The origin of broadband emission is studied using temperature-dependent time-resolved photoluminescence (PL) spectra for two-dimensional (2D) layered halide perovskites (i.e., (PEA)2PbBr4 = phenylethylammonium lead bromide and (PEA)2PbI4 = phenylethylammonium lead iodide) semiconductors. Both perovskite systems show only a single peak exciton emission at room temperature, which becomes multipeak exciton emissions at low temperatures. For temperatures below 100 K, the (PEA)2PbBr4 film gives broad PL emission, Stokes shifted by 750 meV from narrow exciton emission peaks, whereas the (PEA)2PbI4 film does not show any broad emission. Kinetics of various peaks could provide useful insight to propose a consistent energy level scheme associated with a barrier (PEA) and well (PbX64-) material system's electronic states. This broad emission in (PEA)2PbBr4 perovskite is observed due to coupling of triplet states in the inorganic well (PbBr64-) and organic barrier (PEA) layer, which is in contrast to a proposed model based on self-trapped exciton.

Carbon-Based Fiber Materials as Implantable Depth Neural Electrodes.

Implantable brain electrophysiology electrodes are valuable tools in both fundamental and applied neuroscience due to their ability to record neural activity with high spatiotemporal resolution from shallow and deep brain regions. Their use has been hindered, however, by the challenges in achieving chronically stable operations. Furthermore, implantable depth neural electrodes can only carry out limited data sampling within predefined anatomical regions, making it challenging to perform large-area brain mapping. Minimizing inflammatory responses and associated gliosis formation, and improving the durability and stability of the electrode insulation layers are critical to achieve long-term stable neural recording and stimulation. Combining electrophysiological measurements with simultaneous whole-brain imaging techniques, such as magnetic resonance imaging (MRI), provides a useful solution to alleviate the challenge in scalability of implantable depth electrodes. In recent years, various carbon-based materials have been used to fabricate flexible neural depth electrodes with reduced inflammatory responses and MRI-compatible electrodes, which allows structural and functional MRI mapping of the whole brain without obstructing any brain regions around the electrodes. Here, we conducted a systematic comparative evaluation on the electrochemical properties, mechanical properties, and MRI compatibility of different kinds of carbon-based fiber materials, including carbon nanotube fibers, graphene fibers, and carbon fibers. We also developed a strategy to improve the stability of the electrode insulation without sacrificing the flexibility of the implantable depth electrodes by sandwiching an inorganic barrier layer inside the polymer insulation film. These studies provide us with important insights into choosing the most suitable materials for next-generation implantable depth electrodes with unique capabilities for applications in both fundamental and translational neuroscience research.

Protecting Perovskite Solar Cells against Moisture-Induced Degradation with Sputtered Inorganic Barrier Layers

We describe a general approach for protecting metal halide perovskite solar cells against degradation in high-humidity environments using a sputtered barrier coating. A SiO2 protective layer, applied to two different types of perovskite solar cells, was deposited without strongly impacting the initial device performance. The degradation of the cells was imaged in real time using laser beam-induced current (LBIC) measurements in an accelerated test. We show that SiO2 barrier films can improve the tolerance of the devices to extreme humidity conditions and extend lifetimes by a factor of ∼60 when a 45 nm SiO2 barrier layer is applied to CH3NH3PbI3 and by a factor of ∼600 when a 300 nm barrier is applied to a triple-cation perovskite material. The LBIC data revealed that the approach promises protection against degradation initiation at the edges of scribed lines, which will be necessary for the fabrication of monolithically integrated modules.

Constructing polyaniline nanowire arrays as efficient traps on graphene sheets to promote compound synergetic effect in the assembled coating for multifunctional protective cotton fabrics

Multifunctional protective coating with a novel trap structure containing Graphene oxide (GO) and Polyaniline (PANI) arrays is constructed on the surface of cotton fabrics through in–situ polymerization and spray assisted layer–by–layer assembly. The construction of nanoscale protective coatings with controllable thickness and different compounds on the surface of the cotton fabrics through spray assisted layer–by–layer assembly can better exert the molecular interaction between different layers and synergistic effect of different elements. More importantly, unique structure of PANI arrays are grown on the surface of the cotton fibers and GO sheets play very important role on the improvement of multifunctional performances for the cotton fabrics. PANI arrays can accept more APP molecules to promote the flame retardant behavior and construct nearly closed subspace to resist heat and oxygen, accompanying with the formation of inorganic barrier layer, excellent self–extinguishing ability can be achieved through nanoscale coating. Particularly, (GO–PANI1.0)3 coated cotton fabric with a weight gain of 12.7 wt% possesses the excellent self–extinguished ability and minimizes the total heat release value about 82.5% of pristine cotton. In addition, the PANI and GO reduced partially during in–situ polymerization of aniline can present good conductive pathway, as a result, the coated fabric also exhibits significant antistatic property, while can remarkably inhibit the growth of E. coli and S. aureus. Therefore this novel strategy with facile and scalable features can provide reference for developing various kinds of cheap composite nanocoating for multifunctional advanced textiles.

Charging Compensation Layer on Polyimide for Enhanced Device Stability in Flexible Technology

In this paper, we propose a structure that prevents the charging effects that occur in devices fabricated on polyimide (PI) substrates. In general, when fabricating a device on a PI substrate, an inorganic barrier layer is first deposited to prevent penetration of oxygen and moisture. In this study, we confirmed that fluorine ions were induced from PI by bias stress and proposed a SiOCH/SiO2 double layer as a barrier to prevent charging. Then, Al/PI/SiO2/Al and Al/ PI/SiOCH/SiO2/Al metal–insulator–metal capacitors were manufactured. The capacitor characteristics before and after application of bias stress were verified through current–voltage (I–V) and capacitance–voltage (C–V), which are electrical characterization methods, and secondary ion mass spectrometry (SIMS), which is a physical analysis method. As the voltage increased, the capacitance and current of the Al/PI/SiO2/Al capacitor varied, but those of the Al/PI/SiOCH/SiO2/Al device did not change. Finally, SIMS analysis confirmed that the PI-derived fluorine ions replaced the Si–CH3 bonds within the SiOCH film with Si–F bonds, thereby preventing capacitance and current fluctuations.

Halogen-free and phosphorus-free flame-retarded polycarbonate using cyclic polyphenylsilsesquioxanes

Organic–inorganic hybrid macrocyclic compounds, polyphenylsilsesquioxanes (cyc-PPSQ), have been synthesized through hydrolysis and condensation reactions of phenyl trichlorosilane. PC/cyc-PPSQ flame retardant materials were obtained by melt blending cyc-PPSQ and PC using a twin-screw extruder. The combustion and thermal decomposition behavior of PC/cyc-PPSQ composites were studied using UL-94, LOI, CONE, TG–FTIR and Py–GC/MS, which showed that the presence of cyc-PPSQ could improve flame retardancy and reduce the heat release and smoke release during combustion of PC. Incorporation of 2 wt% cyc-PPSQ produced a PC/cyc-PPSQ-2 composite which displayed LOI 37.5% and UL-94 V-0 (1.6 mm). The presence of cyc-PPSQ not only improved the flame retardancy of PC, but also did not diminish the glass transition temperature, good mechanical properties and transparency of PC. These results combined with those from TG–FTIR analysis suggest that cyc-PPSQ can promote the initial thermal induced chain-breaking reaction of PC, promote the cross-linking and charring of PC, and facilitate the formation of a dense carbon layer and external SiO2 inorganic barrier layer during combustion. Results from Py–GC/MS indicate that the presence of cyc-PPSQ promotes the generation of phenolic compounds when the composites are pyrolyzed at high temperature.

(Invited) Critical Parameters for GW Scale Perovskite PV Manufacturing

A recent NREL white paper proposing a new US Perovskite Energy Consortium states “Fulfilling the world’s demand for PV requires continued exponential growth of production capacity without exponential growth in capital expenditure and remains a major challenge due to the inadequate capital efficiency of PV using existing technologies. There is an opportunity and a need for disruptive and fundamentally profitable technologies to supplement the ongoing growth of the PV manufacturing industry”. Perovskite technology promises high conversion efficiency, low manufacturing cost, and low capital expense (CapEx) to build manufacturing capacity. Fulfilling that promise requires a manufacturing process with a very high throughput. The ability to fabricate perovskite films using low-temperature, solution based methods has been touted as a path to low cost and low CapEx manufacturing, however fast deposition of the perovskite layer alone is not sufficient to create the throughput that transforms the PV manufacturing landscape; an in-line process that integrates the deposition of all the functional layers of the device, as well as cell interconnects and module lamination, is required. Any slow vacuum deposition step (e.g., sputtering ITO for the transparent conductor) or long thermal annealing step (e.g., forming a charge transport barrier by forming a compact TiO2 layer) commonly used in lab-scale perovskite device fabrication must be avoided. Our cost modeling shows that the throughput of a single line needed to get to disruptive CapEx and manufacturing cost will be on the order of 45 m2/min. That results in over 3GW/year production capacity at conservative uptime and yield values. An integrated in-line roll-to-roll (RtR) process with a 1.5m wide web would require all deposition steps to run at 30 m/min; much faster than processes cited in the academic literature for lab scale devices. That line speed is not taxing to most commercially available RtR systems, but practical limitations on oven size means a tight window for drying and annealing steps of all solution coated layers. The challenges of creating high performance transparent conductors, inorganic charge transport and barrier layers, perovskite layers and cell interconnects at those speeds will be discussed. The implied TAKT time is less than 3 seconds for 2m2 modules coming off of a single production line. The final assembly and test operations take much longer for each module, so methods of dealing with the mismatch must be implemented. We will also describe the practical considerations, including material sourcing and process requirements for production at GW scale.

Mechanically Robust and Highly Flexible Nonvolatile Charge‐Trap Memory Transistors Using Conducting‐Polymer Electrodes and Oxide Semiconductors on Ultrathin Polyimide Film Substrates

AbstractFlexible charge‐trap memory thin‐film transistors (CTM‐TFTs) are fabricated and characterized for next‐generation highly functional consumer electronics. Poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and 1.2‐µm‐thick polyimide (PI) films are introduced as source/drain electrodes and plastic substrates, respectively, to realize highly flexible CTM‐TFTs with conducting polymers. A uniquely structured sacrificial layer is suggested for the lithography‐compatible transfer and patterning processes of PEDOT:PSS on inorganic Al2O3 barrier layers are prepared on the PI substrates. The CTM‐TFTs show significantly improved device performance compared with those of the previous proto‐type devices, including a memory window (MW) of 16.8 V and program speed of 100 µs at a program pulse amplitude of ±20 V. Furthermore, the MWs and on/off current ratio do not shown remarkable degradation, and total variations within a range of less than 7.5% are observed even under harsh bending strains with a curvature radius of 1 mm. Additionally, the mechanical robustness of the fabricated CTM‐TFTs is quantitatively discussed based on the contributions of the conducting polymer electrode and the ultrathin PI film to further improve device performance of the flexible CTM‐TFTs.

Insertion of an Inorganic Barrier Layer as a Method of Improving the Performance of Quantum Dot Light-Emitting Diodes

Quantum dot light-emitting diodes (QLEDs) are expected to be the basis of next-generation displays and have consequently been extensively investigated with the aim of commercialization. Herein, QLE...

Time-dependent water vapor permeation through multilayer barrier films: Empirical versus theoretical results

Multilayer films that comprise alternating inorganic barrier and polymer layers deposited on a flexible substrate are often used to protect organic electronic devices from degradation caused by oxygen and water vapor. We tested films consisting of up to 11 inorganic silicon oxide barrier and polymer layers to characterize the water vapor permeability, solubility and diffusivity of each layer based on measurements of water sorption, transient water vapor permeation and lag times. The time-dependency of transient water vapor transmission rates (WVTR) of the structures containing a barrier-polymer-barrier sequence was also estimated using a so-called quasi-steady-state (QSS) approximation. The permeability values and lag times in multilayer structures predicted by QSS approximation agreed with the values determined empirically based on time-dependent WVTR measurements. The steady-state WVTR of the multilayer barrier films was dominated by the permeability of the inorganic barrier layers, whereas the solubility coefficient and thickness of the interleaved polymer layers determined the lag times. The barrier performance and lag time of multilayer structures can be predicted using the parameters obtained from sorption measurements, thus significantly reducing the time required for experiments. The results of this study will allow us to design multilayer barrier films according to the lifetime requirements of flexible organic electronic devices.

Self-Healing Effect of Wet-Processed Organic SAM Diffusion Barrier Layer Using Polymer Capped Palladium Nanoclusters

In ultra-large scale integrated circuits (ULSIs), aluminum (Al) has been replaced by copper (Cu) as the interconnect material due to Cu has higher resistance to electromigration and lower electrical conductivity [1]. Unfortunately, Cu has high mobility in silicon (Si) and silicon dioxide (SiO2), thus impacting interconnect reliability and leading to inferior electrical performance or device failure. Therefore, it is necessary to form a good copper diffusion barrier between Si/SiO2 and Cu layer. In the past few decades, inorganic materials such as tantalum (Ta) or tantalum nitride (TaN) based compounds or metal-alloys has been successfully introduced as the diffusion barrier industrially. However, from the ULSI roadmap revealed by the International Technology Roadmap for Semiconductors report (ITRS), the necessary diffusion barrier thickness for the line-width of 22 nm is less than 2 nm [2], which challenges the current Ta or TaN technology by using the conventional vapor-phase deposition. Recently, a few reports use the organo-silane compounds such as 3-aminopropyltrimethoxysilane (APTMS) as the diffusion barrier to substitute inorganic Ta or TaN barrier layer [3-5], and show promising result. However, forming SAM is known to very sensitive to process conditions, particularly when SAM is prepared by wet-soaking. Imperfect SAM cannot block Cu diffusion efficiently and thus fails to compete with inorganic counterparts. In this study, we developed an all-wet, self-healing process to converge the copper diffusion blocking property on a Cu/SAM/SiO2 substrate. In particular, a 3-[2-(2-aminoethylamino)ethylamino] propyl-trimethoxysilane (ETAS) layer was deposited on SiO2 surface via wet soaking process. Then a 200 nm Cu film was electroless plated onto ETAS-treated SiO2 with the help of a home-made poly(vinyl alcohol)-capped palladium (PVA-Pd) nanoparticle catalysts. By varying ETAS soaking time and the ratio of PVA:Pd in the process, the sheet resistance of the Cu/SAM/SiO2 substrate after rapid thermal annealing (RTA) was investigated. As shown in Fig.1, it can be seen the sheet resistance increased rapidly after RTA over 300 oC in the case of no ETAS treatment, indicating the formation of copper silicide because of the absence of diffusion barrier layer. It is also found in the case of 30 minutes ETAS treatment (approaching SAM[6]) and 1:1 PVA to Pd ratio (ETAS-30-1xPVA-Pd), no copper silicide formation up to 500 oC. Interestingly, in 1 minute ETAS (ETAS-1) soaking samples, which is considered islandish ETAS coating rather than SAM, the PVA:Pd ratio affects the effectiveness of Cu diffusion barrier significantly. The more the PVA, the better Cu diffusion blocking capability is. Finally, in the sample processed by 1 minute islandish ETAS treatment and PVA:Pd ratio of 2 (ETAS-1-2xPVA-Pd), the Cu diffusion blocking capability is identical to the case of ETAS SAM, evidencing PVA can mend the imperfect SAM layer and thus converging the overall performance. Our study provides a simple and controllable process to utilize organic compound as the alternative for Ta or TaN diffusion barrier layer in fine line ULSI fabrication. REFERENCES [1] S. P. Murarka, Mater. Sci. Eng., 19 (1997) 87. [2] International Technology Roadmap for Semiconductors,2013 edition. [3] A. M. Caro, S. Armini, O. Richard, G. Maes, G. Borghs, C. M. Whelan and Y. Travaly, Adv. Funct. Mater., 20 (2010) 1125. [4] W. K. Han, G. H. Hwang, S. J. Hong, C. S. Yoon, J. S. Park, J. K. Cho and S. G. Kang, Appl. Surf. Sci., 255 (2009) 6082. [5] Y. Chung, S. Lee, C. Mahata, J. Seo, S. M. Lim, M. S. Jeong, H. Jung, Y. C. Joo, Y. B. Park, H. Kimd and T. Lee, RSC Adv., 4 (2014) 60123. [6] C. W. Hsu, W. Y. Wang, K. T. Wang, H. A. Chen and T. C. Wei, Sci. Rep., 7 (2017) 1. Figure 1

Helium permeation as a fast quality indicator for barrier properties of solar cell encapsulates

AbstractThe advent of flexible electronic devices and flexible thin‐film photovoltaic modules increases the need for transparent and flexible high‐barrier films. Conventional methods for measuring the barrier properties of such films are costly and time consuming. In our work, we present a method where we correlate water vapor and helium transmission rate measurements on strained barrier films with thin‐film solar module performance. We show that the detected properties correlate well with the performance of a CIGS mini module exposed to damp‐heat environment. The critical strain limit for a substantial decrease in barrier properties was identified for an ETFE‐based barrier film incorporating an inorganic barrier layer. It was found that the detection of the helium transmission rate provides a fast and reliable way to identify damage to barrier films and is therefore suitable as means for quality control or incoming goods inspection.

High-performance thin-film encapsulation for organic light-emitting diodes

Organic light-emitting diodes degrade rapidly by means of local cathode oxidation when exposed to the ambient atmosphere, resulting in visible non-emissive areas called black spots. High performance inorganic based encapsulations are required to protect the OLED. We have applied a hybrid thin-film encapsulation stack consisting of two inorganic barrier layers of silicon nitride deposited at low temperature with an organic layer in between. The resulting water permeation mechanism into the OLED is solely by means of lateral pinhole-to-pinhole transport. With the application of CaO nanoparticles in the organic layer the lateral water transport rate is reduced and we show that black spot formation in 8 cm2 OLEDs is delayed by 6000 h at accelerated climate conditions of 60°C/90% relative humidity. This is estimated to correspond to 20 years at ambient conditions.

(Invited) Flexible Memory Applications Using Oxide Semiconductor Thin-Film Transistors

Flexible nonvolatile memories (NVMs) have emerged as powerful assistants for future electronic systems featured to have wearable, stretchable, and bendable characteristics. There have been many unique flexible applications, such as radio frequency identification tag, electronic sensor arrays, flat-panel displays, and electronic circuit configuration. Furthermore, the suitable choice of NVM can effectively reduce the power consumption of set applications. From these technical backgrounds, flexible NVM devices with various operating origins have been fabricated on flexible plastic substrates. Among them, a charge-trap-type memory device composed of charge-storage layer is one of the most typical device configurations. However, conventional charge-trap NVMs have many problems such as asymmetric on- and off-program conditions, long program time for trap/detrap process, and unstable memory operations. Consequently, for the practical applications of flexible NVM devices, it is very important to realize both functions of a lower voltage operation and a more stable memory retention behavior. However, because it is difficult to simultaneously optimize these two functions owing to their trade-off relationship, device performances including the stable memory window and large on/off ratio should be guaranteed for low-power consumption and excellent device stability. Furthermore, the process temperature should be controlled to be as low as possible with the considerations of thermal stability of the flexible plastic substrate. In this work, we propose the flexible charge-trap memory thin-film transistor (f-MTFT) using all oxide-layers, in which sputter-deposited In-Ga-Zn-O (IGZO) and atomic-layer-deposited (ALD) ZnO thin films were used as an active channel and charge-trap layer (CTL), respectively. Poly(ethylene naphthalate) (PEN) was chosen as a flexible substrate due to its superior properties, such as a low linear thermal expansion coefficient, good chemical resistance, surface smoothness, and optical clarity, compared with the other types of plastic substrates. The main object of this work is to demonstrate the appropriate methodologies for high-performance f-MTFTs fabricated on flexible PEN substrate. Thus, fabrication procedures are carefully optimized for guaranteeing the stable memory device characteristics. As results, wide memory margin and very fast program speed are successfully demonstrated. Furthermore, the effect of mechanical deformation on the memory properties are examined as a flexible memory device. The operation stabilities at high temperature of 80 oC are also investigated. To realize the f-MTFTs with high performance and stability, following three strategies were introduced. First, the PEN substrate was pre-treated with hybrid barrier layer structure, which was composed of 3.6-μm-thick acrylic-based organic and 30-nm-thick inorganic Al2O3 films. These organic and inorganic barrier layers were prepared by spin-coating and ALD to obtain a smooth surface and to reduce a water vapor transmission rate, respectively. The second strategy was to optimize the deposition temperature for ZnO CTL, because the electronic natures of the ALD-grown ZnO sensitively depends on its deposition temperature. We previously fabricated the memory devices on glass substrate using the ZnO CTLs by controlling the deposition temperature to 100, 150, and 200 oC. As results, the 100-oC ZnO device exhibited wider memory window and stable retention properties than others. Thus, the ZnO deposition temperature was set as 100 oC. The third strategy was to optimize the patterning process of gate-stack structure. The double-layered structure of the Al2O3 tunneling layers was designed to prevent the wet-etching damages for the IGZO channel layer during the patterning process of CTL. When a single Al2O3 tunneling layer was prepared without an additional protection layer, the IGZO channel layer was decisively over-etched due to the differences in etch rates of each layer. On the contrary, the IGZO channel could be effectively protected by second tunneling layer by wrapping the side areas of the channel layer when the double-layered tunneling layer was introduced. Alternatively, a top-protection layer protected the surface of ZnO CTL during the lithography process. The obtained device characteristics of the fabricated f-MTFT can be summarized as follows. The memory margin, memory window width, and program time were evaluated as 4.7×107, 25.6 V, and 500 ns, respectively. These device characteristics were not markedly degraded even after the delamination, under the bending state with a curvature radius of 3.3 mm, and after the 104 times repetitive bending cycles at a curvature radius of 4.8 mm. Furthermore, the stable memory characteristics were successfully guaranteed even at a high temperature of 80 oC. Device parameters confirmed for the fabricated f-MTFTs presented remarkable improvements compared with previously reported various flexible memory devices. We can conclude that the proposed f-MTFTs on PEN substrates can be a suitable candidate for the highly-functional and stable flexible memory device embedded into the new-era flexible electronic systems.

Band Edge Modulated Polymer Layer to Decrease Back Electron Transfer and Increase Efficiency in Sensitized Solar Cells

Recombination of charges residing in the TiO2 and redox electrolyte is one of the factors affecting the efficiency of dye sensitized solar cells (DSSCs). To circumvent this recombination, inorganic oxide barrier layers and organic silanes have been coated on TiO2/dyes. Due to the insulating nature of these layers, the efficiency increase is not very impressive. Conducting polymers with different band edges are used to suppress the charge recombination. Amongst the four polymers that are used as barrier layers, a polymer with a highest occupied molecular orbital energy at −5.8 eV and lowest unoccupied molecular orbital at −3.1 eV is found to increase the electron life time at TiO2 and decrease the charge recombination. The electron life time is found to be 88 ms. In addition to the long electron life time, the recombination resistance of this polymer is also high (91 Ω). This resistance is 18% higher than that measured for DSSCs without polymer barrier layer. These factors impact the efficiency of DSSCs. DSSCs fabricated with this polymer as barrier layer exhibit an efficiency of 9.2%, which is 22% higher than that of DSSCs without polymer barrier layer.