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Flexible non-volatile memories have attracted tremendous attentions for data storage for future electronics application. From device perspective, the advantages of flexible memory devices include thin, lightweight, printable, foldable and stretchable. The flash memories, resistive random access memories (RRAM) and ferroelectric random access memory/ferroelectric field-effect transistor memories (FeRAM/FeFET) are considered as promising candidates for next generation non-volatile memory device. Here, we review the general background knowledge on device structure, working principle, materials, challenges and recent progress with the emphasis on the flexibility of above three categories of non-volatile memories.

DOI: 10.1002/adma.201201195 Flash memories have recently attracted considerable attention as promising next-generation nonvolatile memories owing to their higher chip density, multi-bit per cell storage properties, and compatibility with the current complementary metal– oxide–semiconductor (CMOS) process. [ 1–4 ] The fl ash memories based on fi eld-effect transistors (FETs) with a fl oating gate architecture work on the variation of the threshold voltage ( V th ) by trapping/detrapping the charge carriers of the semiconductor under external gate bias. To meet the requirements of manipulating the trap levels (work functions of metal) and trap sites (directly related to memory window which can be controlled by varying the density of nanoparticles), employment of nanocrystals fl oating gate is considered to be an alternative approach to replace the planar fl oating gate for information storage. [ 5 , 6 ] Gold nanoparticles (Au NPs) are appropriate material to serve as fl gate due to their chemical stability and high work function. [ 7 ] The Au NPs charge trapping layer can be created by several methods including thermal evaporation, [ 8 , 9 ] chemical process such as electrostatic self-assembly

A metal–insulator–metal field‐effect transistor has been fabricated. The device performance was achieved by reducing the density of states by only partially covering the substrate, which increases the relative field effect. An infinite on–off ratio, no lower limit to device dimensions, a generally enhanced flexibility in design, and low production costs are all advantages of this device.

The electrical transport properties of DNA films in field‐effect transistor structure are analyzed. As‐depositedfilms did not show electrical conductivity; no DNA network wasobserved between the DNA moleculesbridging the electrodes. When the DNA molecules were stretchedinto a thin film an interpenetratingnetwork formed, and the devicesshowed pronounced field‐effects withambipolar behavior. Devices producedby electrostatic trapping of DNA molecules exhibited large bulk parallelcurrents and relatively small field effects.

Efficient white organic light‐emitting devices with uncomplicated architectures are fabricated employing phosphorescent platinum(II) complexes containing extended π‐conjugated cyclometalated ligands as a yellow‐light source, and fluorescent material 9,10‐bis‐(β‐naphthyl)‐anthrene as a blue‐light source. Peak external quantum (power) efficiencies of 11.8 % (18.4 lm W–1) are demonstrated (see figure).

Oligo(arylacetylene)‐based organic thin‐film transistors (OTFTs) possess good structural order and smooth film morphologies, and exhibit field‐effect mobilities of 0.3 cm2 V–1 s–1, one of the highest field‐effect mobilities reported for an OTFT device that does not possess a self‐assembled‐layer configuration. The Figure shows the measured output characteristics (drain–source current, IDS versus drain–source voltage, VDS) at different gate voltages (VG).

Because of current fabrication limitations, miniaturizing nonvolatile memory devices for managing the explosive increase in big data is challenging. Molecular memories constitute a promising candidate for next-generation memories because their properties can be readily modulated through chemical synthesis. Moreover, these memories can be fabricated through mild solution processing, which can be easily scaled up. Among the various materials, polyoxometalate (POM) molecules have attracted considerable attention for use as novel data-storage nodes for nonvolatile memories. Here, an overview of recent advances in the development of POMs for nonvolatile memories is presented. The general background knowledge of the structure and property diversity of POMs is also summarized. Finally, the challenges and perspectives in the application of POMs in memories are discussed.

Flexible sensors that efficiently detect various stimuli relevant to specific environmental or biological species have been extensively studied due to their great potential for the Internet of Things and wearable electronics applications. The application of flexible and stretchable electronics to device-engineering technologies has enabled the fabrication of slender, lightweight, stretchable, and foldable sensors. Here, recent studies on flexible sensors for biological analytes, ions, light, and pH are outlined. In addition, contemporary studies on device structure, materials, and fabrication methods for flexible sensors are discussed, and a market overview is provided. The conclusion presents challenges and perspectives in this field.