Nonvolatile Ferroelectric P(VDF‐TrFE) Memory Transistors Based on Inkjet‐Printed Organic Semiconductor

Nonvolatile ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) memory based on an organic thin‐film transistor with inkjet‐printed dodecyl‐substituted thienylenevinylene‐thiophene copolymer (PC12TV12T) as the active layer is developed. The memory window is 4.5 V with a gate voltage sweep of ?12.5 V to 12.5 V. The field effect mobility, on/off ratio, and gate leakage current are 0.1 cm²/Vs, 10⁵, and 10^?10 A, respectively. Although the retention behaviors should be improved and optimized, the obtained characteristics are very promising for future flexible electronics.     

Control of Current Hysteresis of Networked Single‐Walled Carbon Nanotube Transistors by a Ferroelectric Polymer Gate Insulator

Films made of 2D networks of single‐walled carbon nanotubes (SWNTs) are one of the most promising active‐channel materials for field‐effect transistors (FETs) and have a variety of flexible electronic applications, ranging from biological and chemical sensors to high‐speed switching devices. Challenges, however, still remain due to the current hysteresis of SWNT‐containing FETs, which has hindered further development. A new and robust method to control the current hysteresis of a SWNT‐network FET is presented, which involves the non‐volatile polarization of a ferroelectric poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) gate insulator. A top‐gate FET with a solution‐processed SWNT‐network exhibits significant suppression of the hysteresis when the gate‐voltage sweep is greater than the coercive field of the ferroelectric polymer layer (≈50 MV m^?1). These near‐hysteresis‐free characteristics are believed to be due to the characteristic hysteresis of the P(VDF‐TrFE), resulting from its non‐volatile polarization, which makes effective compensation for the current hysteresis of the SWNT‐network FETs. The onset voltage for hysteresis‐minimized operation is able to be tuned simply by controlling the thickness of the ferroelectric film, which opens the possibility of operating hysteresis‐free devices with gate voltages down to a few volts.     

Self‐Powered Trace Memorization by Conjunction of Contact‐Electrification and Ferroelectricity

Triboelectric nanogenerator (TENG) is a newly invented technology that can effectively harvest ambient mechanical energy from various motions with promising applications in portable electronics, self‐powered sensor networks, etc. Here, by coupling TENG and a thin film of ferroelectric polymer, a new application is designed for TENG as a self‐powered memory system for recording a mechanical displacement/trace. The output voltage produced by the TENG during motion can polarize the dipole moments in the ferroelectric thin film. Later, by applying a displacement current measurement to detect the polarization density in the ferroelectric film, the motion information of the TENG can be directly read. The sliding TENG and the single‐electrode TENG matrix are both utilized for realizing the memorization of the motion trace in one‐dimensional and two‐dimensional space, respectively. Currently, the ferroelectric thin film with a size of 3.1 mm² can record a minimum area changing of 30 mm² and such resolution can still be possibly improved. These results prove that the ferroelectric polymer is an effective memory material to work together with TENG and thereby the fabricated memory system can potentially be used as a self‐powered displacement monitor.     

Mechanical Manipulation of Nano-Twinned Ferroelectric Domain Structures for Multilevel Data Storage

Ferroelectric materials feature a switchable spontaneous electric polarization and can enable low-power logic and nonvolatile memories. These applications require reliable and precise control of ferroelectric domains and domain walls in ferroelectric thin films. Mechanical manipulation is a promising route to engineer ferroelectric domains, but it has proved ineffective when going beyond a critical thickness. Here, multi-step 90° switching polarization reversal processes in (111)-oriented PbZr_0.2Ti_0.8O₃ thin films by applying mechanical forces along the direction parallel to the domain bands are reported. By probing the interrelationships between the relevant order parameters, coupled lattice distortion and piezoelectricity is revealed to facilitate domain switching from downward to upward in PbZr_0.2Ti_0.8O₃, a mechanism that is supported by the evolution of domains and electrical performances at different temperatures and under varying pressures, respectively. The multi-step domain reversal processes render PbZr_0.2Ti_0.8O₃ thin films an excellent candidate for multilevel data storage. The study's results have implications for the manipulation of polarization switching in ferroelectrics and open an avenue to domain reversal driven by mechanical loads for the development of next-generation ferroelectric devices.     

High‐Performance Piezoelectric,Pyroelectric, and Triboelectric Nanogenerators Based on P(VDF‐TrFE) with Controlled Crystallinity and Dipole Alignment

Poly(vinylidenefluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)), as a ferroelectric polymer, offers great promise for energy harvesting for flexible and wearable applications. Here, this paper shows that the choice of solvent used to dissolve the polymer significantly influences its properties in terms of energy harvesting. Indeed, the P(VDF‐TrFE) prepared using a high dipole moment solvent has higher piezoelectric and pyroelectric coefficients and triboelectric property. Such improvements are the result of higher crystallinity and better dipole alignment of the polymer prepared using a higher dipole moment solvent. Finite element method simulations confirm that the higher dipole moment results in higher piezoelectric, pyroelectric, and triboelectric potential distributions. Furthermore, P(VDF‐TrFE)‐based piezoelectric, pyroelectric, and triboelectric nanogenerators (NGs) experimentally validate that the higher dipole moment solvent significantly enhances the power output performance of the NGs; the improvement is about 24% and 82% in output voltage and current, respectively, for piezoelectric NG; about 40% and 35% in output voltage and current, respectively, for pyroelectric NG; and about 65% and 75% in output voltage and current for triboelectric NG. In brief, the approach of using a high dipole moment solvent is very promising for high output P(VDF‐TrFE)‐based wearable NGs.     

High‐Density Periodically Ordered Magnetic Cobalt Ferrite Nanodot Arrays by Template‐Assisted Pulsed Laser Deposition

A novel nanopatterning method using pulsed laser deposition through an ultrathin anodic aluminium oxide (AAO) membrane mask is proposed to synthesize well‐ordered nanodot arrays of magnetic CoFe₂O₄ that feature a wide range of applications like sensors, drug delivery, and data storage. This technique allows the adjustment of the array dimension from ～35 to ～300 nm in diameter and ～65 to ～500 nm in inter‐dot distance. The dot density can be as high as 0.21 Terabit in.^?2. The microstructure of the nanodots is characterized by SEM, TEM, and XRD and their magnetic properties are confirmed by well‐defined magnetic force microscopy contrasts and by hysteresis loops recorded by a superconducting quantum interference device. Moreover, the high stability of the AAO mask enables the epitaxial growth of nanodots at a temperature as high as 550 °C. The epitaxial dots demonstrate unique complex magnetic domains such as bubble and stripe domains, which are switchable by external magnetic fields. This patterning method creates opportunities for studying novel physics in oxide nanomagnets and may find applications in spintronic devices.     

Materials for Multibit‐per‐Site Optical Data Storage

An approach for multibit‐per‐site optical data storage has been proposed and demonstrated using mesostructured composite films incorporated with uniformly dispersed photoacid generator and pH‐sensitive dye molecules. Upon light illumination, photoacid generator molecules produce acid, which induces a change in the absorption property of pH‐sensitive dye molecules. Because the amount of the generated acid is proportional to the illumination time, the resulting change in the absorption property of mesostructured composite films varies as a function of the illumination time. This function between the absorption property of mesostructured composite films and the illumination time can be used for multibit‐per‐site optical data storage. Recording is performed by using certain discrete values of the illumination time to represent information bits. Reading out is achieved by measuring the absorbance of composite films at a particular wavelength, from which the stored information bits can be determined. In general, N‐bit‐per‐site storage can be realized using 2^N discrete values of the illumination time. This multibit‐per‐site approach for optical data storage is compatible with the current single‐bit‐per‐site technology used for compact disks and digital versatile disks, and will provide significantly larger optical storage capacity. It is also suitable for two‐photon multilayer optical data storage if the photoacid generators and pH‐sensitive dyes are properly designed.     

Hierarchically Ordered Nano‐Heterostructured PZT Thin Films with Enhanced Ferroelectric Properties

Realization of ferroelectric (FE) devices based on the polarization effects of Pb(Zr_0.52Ti_0.48)O₃ (PZT) has reinforced the investigation of this material in multiple dimensions and length scales. Multi‐level hierarchical nanostructure engineering in PZT thin films offer dual advantages of variable length‐scale and dimensionality. Here, the growth of hierarchically ordered PZT nano‐hetero­structures (Nhs) from PZT seed‐layer deposited on SrTiO₃:Nb (100) substrates, using a physical/chemical combined methodology involving pulsed laser deposition (PLD) and hydrothermal processes, is reported. Systematic SEM, TEM, and Raman spectroscopy studies reveal mixed hetero‐ and homo‐epitaxial growth mechanism. In the final stage, 3D Nh units cross‐link and form a dense network‐like Nh PZT thin‐film. FE polarizations are measured without using any polymer fill‐layer which otherwise introduces huge dielectric losses and lowers the polarization values for a FE device. In benefit, well saturated and symmetric FE hysteresis loops are observed with high degree of squareness and a high remnant polarization (54 μC cm^‐2 at a coercive field of 237 kV cm^‐1). This work provides a pathway towards preparing hierarchical PZT Nhs offering coherent design of high‐performance FE capacitors for data storage technologies in future.     

Downscaling and Charge Transport in Nanostructured Ferroelectric Memory Diodes Fabricated by Solution Micromolding

Ferroelectric polymer memory diodes are interface devices where charge injection into the organic semiconductor is controlled by the stray electric field of the ferroelectric polymer. Key to high current density and current modulation is the areal density of well‐defined interfaces. Here, bistable diodes are fabricated by using the soft lithography method solution micromolding. First, the semiconducting polymer poly(9,9‐dioctylfluorene) is patterned into linear gratings. Subsequently, bilinear arrays are obtained by backfilling with the ferroelectric polymer poly(vinylidenefluoride‐co‐trifluoroethylene). The lateral feature size is scaled down from 2 μm to 500 nm. Comprising memory diodes show rectifying J–V characteristics with an On‐current density larger than 10³ A m^?2 and an On/Off current ratio exceeding 10³. The charge transport is explained by 2D numerical simulations. Since the dependence of polarization on electric field is explicitly taken into account, entire J–V characteristics can be quantitatively described. The simulations reveal that rectifying J–V characteristics are inherently related to the concave shape of the patterned ferroelectric polymer. It is argued that the exponential increase in current density with decreasing feature size can be due to confinement of the semiconductor. High On‐current density combined with downscaling, rectification, and simple fabrication yield new opportunities for low‐cost integration of high‐density solution‐processed memories.     

Combining Data Longevity with High Storage Capacity—Layer‐by‐Layer DNA Encapsulated in Magnetic Nanoparticles

In this paper the practical density of long‐term DNA storage is increased. Specifically, the DNA weight loading of silica sphere DNA storage is increased to 3.4 wt%, a ten‐fold increase compared to the previous state‐of‐the‐art. By applying a Layer‐by‐Layer (LbL) design with alternating layers of DNA and a polycationic molecule, namely polyethyleneimine (PEI), another dimension to DNA surface binding onto magnetic nanoparticles is added. A protective silica layer is grown on top of the multilayered nanoparticles to shield the DNA from external sources of damage. Accelerated aging experiments of the nanoparticles and the subsequent quantification of DNA stability via qPCR show a significantly lower degradation rate compared to unprotected DNA. The novel material is compared to previous DNA storage technologies, outperforming those in DNA storage density as well as stability. Finally, the storage of an 83 kB digital file in DNA through a successful readout of a 4991 oligonucleotide pool is demonstrated from particle encapsulation, through accelerated aging, to sequencing.     

Hierarchical Self‐Organization of Nanomaterials into Two‐Dimensional Arrays Using Functional Polymer Scaffold

Fabrication of two and three‐dimensional nanostructures requires the development of new methodologies for the assembly of molecular/macromolecular objects on substrates in predetermined arrangements. Templated self‐assembly approach is a powerful strategy for the creation of materials from assembly of molecular components or nanoparticles. The present study describes the development of a facile, template directed self‐assembly of (metal/organic) nanomaterials into periodic micro‐ and nanostructures. The positioning and the organization of nanomaterials into spatially well‐defined arrays were achieved using an amphiphilic conjugated polymer‐aided, self‐organization process. Arrays of honeycomb patterns formed from conjugated C₁₂PPPOH film with homogenous distribution of metal/organic nanomaterials. Our approach offers a straightforward and inexpensive method of preparation for hybrid thin films without environmentally controlled chambers or sophisticated instruments as compared to multistep micro‐fabrication techniques.     

Molecularly Imprinted Polymer Grafted Porous Au‐Paper Electrode for an Microfluidic Electro‐Analytical Origami Device

Molecular imprinting technique is introduced into microfluidic paper‐based analytical devices (μ‐PADs) through electropolymerization of molecular imprinted polymer (MIP) in a novel Au nanoparticle (AuNP) modified paper working electrode (Au‐PWE). This is fabricated through the growth of a AuNP layer on the surfaces of cellulose fibers in the PWE. Due to the porous morphology of paper as well as the high specific surface area and conductivity of the resulting AuNP layer on the cellulose fibers, the effective surface area and the sensitivity of the Au‐PWE is enhanced remarkably. Based on this novel MIP‐Au‐PWE and the principle of origami, a microfluidic MIP‐based electro‐analytical origami device (μ‐MEOD), comprised of one auxiliary pad surrounded by four sample tabs, is developed for the detection of D‐glutamic acid in a linear range from 1.2 nM to 125.0 nM with a low detection limit of 0.2 nM. The selectivity, reproducibility, and stability of this μ‐MEOD are investigated. This μ‐MEOD would provide a new platform for high‐throughput, sensitive, specific, and multiplex assay as well as point‐of‐care diagnosis in public health, environmental monitoring, and the developing world.     

Dynamic Data Migration in Hybrid Main Memories for In‐Memory Big Data Storage

For memory‐based big data storage, using hybrid memories consisting of both dynamic random‐access memory (DRAM) and non‐volatile random‐access memories (NVRAMs) is a promising approach. DRAM supports low access time but consumes much energy, whereas NVRAMs have high access time but do not need energy to retain data. In this paper, we propose a new data migration method that can dynamically move data pages into the most appropriate memories to exploit their strengths and alleviate their weaknesses. We predict the access frequency values of the data pages and then measure comprehensively the gains and costs of each placement choice based on these predicted values. Next, we compute the potential benefits of all choices for each candidate page to make page migration decisions. Extensive experiments show that our method improves over the existing ones the access response time by as much as a factor of four, with similar rates of energy consumption.     

Conductivity of SU‐8 Thin Films through Atomic Force Microscopy Nano‐Patterning

Processing flexibility and good mechanical properties are the two major reasons for SU‐8 extensive applicability in the micro‐fabrication of devices. In order to expand its usability down to the nanoscale, conductivity of ultra‐thin SU‐8 layers as well as its patterning by AFM are explored. By performing local electrical measurements outstanding insulating properties and a dielectric strength 100 times larger than that of SiO₂ are shown. It is also demonstrated that the resist can be nano‐patterned using AFM, obtaining minimum dimensions below 40nm and that it can be combined with parallel lithographic methods like UV‐lithography. The concurrence of excellent insulating properties and nanometer‐scale patternability enables a valuable new approach for the fabrication of nanodevices. As a proof of principle, nano‐electrode arrays for electrochemical measurements which show radial diffusion and no overlap between different diffusion layers are fabricated. This indicates the potential of the developed technique for the nanofabrication of devices.     

High Performance Multi‐Level Non‐Volatile Polymer Memory with Solution‐Blended Ferroelectric Polymer/High‐k Insulators for Low Voltage Operation

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. Furthermore, polymer Fe‐FETs have been recently of interest owing to their capability of storing data in more than 2 states in a single device, that is, they have multi‐level cell (MLC) operation potential for high density data storage. However, among a variety of technological issues of MLC polymer Fe‐FETs, the requirement of high voltage for cell operation is one of the most urgent problems. Here, a low voltage operating MLC polymer Fe‐FET memory with a high dielectric constant (k) ferroelectric polymer insulator is presented. Effective enhancement of capacitance of the ferroelectric gate insulator layer is achieved by a simple binary solution‐blend of a ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) (PVDF‐TrFE) (k ≈ 8) with a relaxer high‐k poly(vinylidene‐fluoride–trifluoroethylene–chlorotrifluoroethylene) (PVDF‐TrFE‐CTFE) (k ≈ 18). At optimized conditions, a ferroelectric insulator with a PVDF‐TrFE/PVDF‐TrFE‐CTFE (10/5) blend composition enables the discrete six‐level multi‐state operation of a MLC Fe‐FET at a gate voltage sweep of ±18 V with excellent data retention and endurance of each state of more than 10⁴ s and 120 cycles, respectively.     

Polymer Thin‐Film Transistor Arrays Patterned by Stamping

We present a process to stamp semiconductor polymers suitable for the parallel fabrication of thin‐film transistor island arrays. This process is compatible with roll‐to‐roll fabrication. When a chemically treated elastomeric stamp is pressed against a substrate previously coated with the polymer solution, a capillary force drives the polymer solution into the stamp recesses. Simultaneously, the raised features of the stamp in contact with the substrate absorb the solvent. The resulting polymer thin film reproduces the pattern of the raised features of the stamp. Features with lateral dimensions as small as 2 μm are faithfully reproduced. We use this stamping process to fabricate arrays of polymer thin‐film transistors (TFTs) using poly(fluorene‐co‐bithiophene) and poly(thiophene) semiconductors.     

Optical Data Storage and Multicolor Emission Readout on Flexible Films Using Deep‐Trap Persistent Luminescence Materials

The fast‐growing amount of data that is produced every year creates an urgent need for ultracapacity storage media. However, 2D spatial resolution in the conventional optical data storage media has almost reached the limit. Further enlargement of storage capacity may rely on the development of the next‐generation data storage materials containing multiplexed information dimensions. Herein, a series of novel deep‐trap persistent luminescence materials (Sr_1‐xBa_x)Si₂O₂N₂:Eu/Yb,Dy with multicolor emissions in the whole visible region is developed and demonstrated a bit‐by‐bit optical data storage and readout strategy based on photon trapping and detrapping processes in these materials. Optical data can be handily encoded on a flexible film by a commercially available 405 nm laser and decoded by heating or by 980 nm laser scanning. The decoded information contains tunable spectral characteristics, which allows for the emission–intensity–multiplexing or emission–wavelength–multiplexing. The storage and readout strategy not only shows a great promise in the application of multidimensional rewritable optical data storage, but also opens new opportunities for advanced display technology and information security system.     

Electrically Activated Ultrathin PVDF‐TrFE Air Filter for High‐Efficiency PM1.0 Filtration

Ultrafine particulate matter (PM) in indoor air has become a serious concern for public health. Therefore, there is a growing interest in filters that can be installed on the window frames of ordinary homes to improve the indoor air quality by natural passive ventilation without using expensive forced air circulation systems. Thus, these filters require a high filtering efficiency and high air permeability and visibility, which do not compromise the original functionality of the windows. The filters developed for this purpose to date have demonstrated a high filtering efficiency for PM_2.5 but a relatively low efficiency for PM_1.0. Here, the performance of the ultrathin poly[(vinylidenefluoride‐co‐trifluoroethylene) (PVDF‐TrFE) nanofiber air filter capable of high‐efficiency PM_1.0 filtration is reported. To enhance the PM_1.0 filtering efficiency, the filter is electrically activated by the polarization of dipoles and triboelectrification using the ferroelectric nature and triboelectrically negative property of the PVDF‐TrFE filter layer. The electrically activated PVDF‐TrFE filter demonstrates a PM_1.0 filtering efficiency of over ≈88% after polarization, which is further improved to ≈94% after triboelectrification. In addition, the filter is ultrathin and air‐permeable with 65% light transmittance. The methods introduced in this work can be adopted to develop high performance, highly visible, and air‐permeable filter media.     

Self‐Healing Materials for Energy‐Storage Devices

The booming development of electronics, electric vehicles, and grid storage stations has led to a high demand for advanced energy‐storage devices (ESDs) and accompanied attention to their reliability under various circumstances. Self‐healing is the ability of an organism to repair damage and restore function through its own internal vitality. Inspired by this, brilliant designs have emerged in recent years using self‐healing materials to significantly improve the lifespan, durability, and safety of ESDs. Extrinsic and intrinsic self‐healing materials and their working principles are first introduced. Then, the application of self‐healing materials in ESDs according to their self‐healing chemistry, including hydrogen bonds, electrostatic interactions, and borate ester bonds, are described in detail. Based on these, critical challenges and important future directions of self‐healing ESDs are discussed.