Organic Field-effect Transistor Nonvolatile Memory Research Articles

Graphdiyne particles as nano-floating gates for high-performance nonvolatile organic field-effect transistor memory

Graphdiyne particles (GDYP), newcomers of carbon family, were employed as nano-floating gates in organic field-effect transistor (OFET) memories. The charge-trapping layer was prepared by blending GDYP into a polystyrene (PS) matrix. The effect of GDYP doping ratio on memory performances was investigated, and the OFET memory with the optimal doping concentration of the GDYP (0.3 mg/mL) exhibits ambipolar memory behavior with a wide memory window as large as 86 V, excellent retention time over 104 s with a high ON/OFF current ratio of 7.5 × 105. This work demonstrates that graphdiyne is a promising charge-trapping material for high-performance nonvolatile OFET memory devices.

Intramolecular Alkyne Aromatization: Unexpected Synthesis of Expanded [9]Helicene and π‐Extended Double [4]Helicene, and Their Molecular Geometry Effect on Transistor Memory

Intramolecular alkyne aromatization is a powerful tool that enables the synthesis of nonplanar polycyclic aromatic hydrocarbons. Herein, an unexpected intramolecular alkyne aromatization via a trifluoroacetic acid‐promoted cyclization is described, in which two structural isomers, expanded [9]helicene (1) and π‐extended double [4]helicene (2) are obtained. A possible rearrangement mechanism is proposed to account for the formation of 1. The geometric and optoelectronic properties of these two nonplanar molecular nanocarbons are comprehensively investigated by single‐crystal X‐ray, UV–vis absorption, photoluminescence spectra, and cyclic voltammetry analysis. These two structural isomers exhibit wide energy gaps with similar energy levels, which further apply them as molecular floating gate in organic field‐effect transistor nonvolatile memory (OFET‐NVM) devices. The nonplanar geometry of 1 and 2 shows a remarkable effect on charge‐trapping behaviors in OFET‐NVMs; the 1‐based device displays a more than threefold wider memory window (MW, 44.5 V) than that of the 2‐based device (14.2 V), and a large charge‐trapping density of 1.08 × 1013 cm−2. The distinct different charge‐trapping behavior is likely attributed to the different molecular geometries, resulting in different molecular‐packing modes. It is revealed in this study that controlling the geometry of molecular nanocarbons is a new strategy for application in organic electronics.

A flexible floating-gate based organic field-effect transistor non-volatile memory based on F8BT/PMMA integrated floating-gate/tunneling layer

The solution mixing method was adopted to build polymer semiconductor poly(9,9-dioctylflfluorene-co-benzothiadiazole) (F8BT) nanoparticles (NPs), which were mixed with poly (methyl methacrylate) (PMMA) in a solution to prepare an integrated floating-gate/tunneling layer. On this basis, flexible floating-gate based organic field-effect transistor non-volatile memories (F-OFET-NVMs) were prepared. The intrinsic correlations of the microstructures in the integrated floating-gate/tunneling layer of the memory devices with the device performance were explored. Moreover, correlations of the charge injection and discharge, physical mechanism of memory, and charge trapping capacity of the floating-gate/tunneling layer with different F8BT/PMMA mass ratios with the key parameters of memory devices were investigated. Relevant results indicate that the memory devices are able to well trap charges inside the F8BT NPs during operation at a programming voltage of +40 V, an erasing voltage of −40 V, and a pulse width of 1 s. The floating gate acquires the injected and trapped bipolar charges (electrons and holes). The optimized high-performance memory device is found to have an average memory window of 9.5 V, remain stable for more than three years, and have reliable stability in more than 100 erase/write cycles. Furthermore, the memory device also exhibits outstanding durability under mechanical bending and still has high storage stability after 6,000 times of bending with a bending radius of 3 mm. The research results powerfully promote the research progress of applying semiconductor polymers to memory devices.

High-performance flexible pentacene transistor memory with PTCDI-C13 as N-type buffer layer

Flexible organic field-effect transistor nonvolatile memories (OFET-NVMs) with polymer electrets have aroused great attention for its important role in next-generation flexible data storage devices application. However, the OFET-NVMs to date still hardly reach the requirements for practical applications. In air environment, the positively charged defects formed in pentacene near the interface with polymer, result in unsatisfied high programming/erasing (P/E) voltages. Here, we propose an OFET memory structure, in which an n-type semiconductor N, N′-Bis(3-pentyl) perylene-3, 4, 9, 10-bis(dicarboximide) (PTCDI-C13) is inserted between pentacene and poly(4-vinyl phenol. Based on the electrostatic induction effect, electrons are induced on the surface of PTCDI-C13 due to the electrostatic field generated by the positive charges at the interface of pentacene/polymer, and compensate part of the positive charges at the interface, resulting in the reduction of the height of hole-barrier. The flexible memory device with PTCDI-C13 exhibits a memory window of larger than 7 V at P/E voltages (±20 V), fast switching speeds (0.5 ms), good P/E endurance (>400 cycles), large field-effect mobility (0.026 cm2 V−1 s−1), and long retention time (over 104 s).

UV-Enabled Multibit Organic Transistor Memory With High Controllability and Stability

An organic field-effect transistor nonvolatile memory with multibit storage capability and selective UV response was demonstrated, which showed good retention for all the memory states. The programming/erasing of the device operating at a low voltage was enabled by solar-blind UV light of 254 nm, and it had no response to 365 nm UV light and visible light. The stepwise switching between the memory states was controlled only by the number of the programming/erasing pulses, rather than by programming/erasing voltage or duration. The multibit memory feature is ascribed to the cumulative and reversible charge trapping in the employed polymer electret layer, and this architecture may offer a promising approach to multibit organic-based memories.

Nanostructured interfacial dipole layers for high-performance and highly stable nonvolatile organic field-effect transistor memory

An interfacial dipole layer formed between the solution-processed charge trapping nanostructures and the active layer enables significant improvement of the charge storage capability and stability.

Solution-processed flexible nonvolatile organic field-effect transistor memory using polymer electret

Flexible organic field-effect-transistor (OFET) memory is one of the promising candidates for next-generation wearable nonvolatile data storage due to its low price, solution-processability, light-weight, mechanically flexibility, and tunable energy level via molecular tailoring. In this paper, we report flexible nonvolatile OFET memory devices fabricated with solution-processed polystyrene-brush electret and organic semiconductor blends of p-channel 6, 13-bis-(triisopropylsilylethynyl)pentacene (TIPS-PEN) and n-channel poly-{[N,N′-bis(2- octyldodecyl)-naphthalene-1,4,5,8-bis-(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (P-(NDI2OD-2T); N2200). Fabricated flexible OFET memory devices exhibited high memory window (30 V) and ON/OFF current ratio (memory ratio) over 103. Furthermore, we obtained reliable memory ratio (~103) over retention time of 108 s, 100 times of repeated programming/erasing cycles, and 1000 times of bending tests at a radius of 3 mm.

High-performance polymer semiconductor-based ferroelectric transistor nonvolatile memory with a self-organized ferroelectric/dielectric gate insulator

Ferroelectric organic field-effect transistor nonvolatile memories (Fe-OFET-NVMs) offer attractive features for future memory applications, such as flexible and wearable electronics. Polymer semiconductor-based top-gate Fe-OFET-NVMs possess natural advantages in the device structure and processing manufacturing, compared to small-molecule semiconductor-based bottom-gate Fe-OFET-NVMs. However, their performances, such as mobility and operating voltages, should be further improved to be comparable to those of the latter. In this Letter, we develop a route to achieve high-performance top-gate Fe-OFET-NVMs, by employing a polymer semiconductor channel and self-organized ferroelectric/dielectric gate insulators, which were processed by a solution spin-coating technique. The optimal Fe-OFET-NVM exhibits a high mobility of 1.96 cm2/V s on average, a reliable endurance over 400 cycles, a stable retention capability over 6 × 104 s, and a life more than one year. Furthermore, the operating voltage of the Fe-OFET-NVM is reduced to ±20 V by scaling down the thickness of the ferroelectric/dielectric gate insulator. The whole performances of our memories are comparable to or better than those of the previous Fe-OFET-NVMs.

High-performance Nonvolatile Organic Photoelectronic Transistor Memory Based on Bulk Heterojunction Structure.

Depending on the storage mechanisms, organic field-effect transistor (OFET) memory is usually divided into floating gate memory, ferroelectric memory, and polymer-electret-based memory. In this work, a new type of nonvolatile OFET memory is proposed by simply blending a p-type semiconductor and a n-type semiconductor without using an extra trapping layer. The results show that the memory window can be effectively modulated by the dopant concentration of the n-type semiconductor. With the addition of a 5% n-type semiconductor, blending devices exhibit a large memory window up to 57.7 V, an ON/OFF current ratio (ION/IOFF) ≈ 105, and a charge retention time of over 10 years, which is comparable or even better than those of most of the traditional OFET memories. The discontinuous n-type semiconductor is set as a charge-trapping center for charge storage due to the quantum well-like organic heterojunctions. The generalization of this method is also investigated in other organic systems. Moreover, the blend devices are also applied to optical memory and show multilevel optical storage, which are further scaled up to 8 × 8 array to map up two-dimensional (2D) optical images with long-term retention and reprogramming characteristic. The results reveal that the novel system design has great potential application in the field of digital image memory and photoelectronic system.

Pentafluorosulfanylated polymers as electrets in nonvolatile organic field-effect transistor memory devices

Styrenic polymer electrets with pentafluorosulfanylated sidechains demonstrate their charge-storage capabilities in organic nonvolatile memory devices.

Solution Processed Organic Transistor Nonvolatile Memory With a Floating-Gate of Carbon Nanotubes

In this letter, an organic field-effect transistor nonvolatile memory (NVM), based on single-walled carbon nanotubes (SWNTs) as a nano floating-gate, is demonstrated, for which a four-layer stacked core architecture was processed by following the sequential solution spin-coating method. The SWNTs, separated by spin-coating, are distributed in the matrix of copolymer poly (styrene-block-paraphenylene) to act as the charge trapping sites. The memory of the floating-gate organic transistor so prepared exhibits excellent NVM characteristics,with a large memory window of 26.7 V, memory on/off ratio larger than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , stable charge storage retention capability for over 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> s with a memory on/off ratio over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and the reliable memory endurance property of over 500 Hz.

Solution-Processed Wide-Bandgap Organic Semiconductor Nanostructures Arrays for Nonvolatile Organic Field-Effect Transistor Memory.

In this paper, the development of organic field-effect transistor (OFET) memory device based on isolated and ordered nanostructures (NSs) arrays of wide-bandgap (WBG) small-molecule organic semiconductor material [2-(9-(4-(octyloxy)phenyl)-9H-fluoren-2-yl)thiophene]3 (WG3 ) is reported. The WG3 NSs are prepared from phase separation by spin-coating blend solutions of WG3 /trimethylolpropane (TMP), and then introduced as charge storage elements for nonvolatile OFET memory devices. Compared to the OFET memory device with smooth WG3 film, the device based on WG3 NSs arrays exhibits significant improvements in memory performance including larger memory window (≈45 V), faster switching speed (≈1 s), stable retention capability (>104 s), and reliable switching properties. A quantitative study of the WG3 NSs morphology reveals that enhanced memory performance is attributed to the improved charge trapping/charge-exciton annihilation efficiency induced by increased contact area between the WG3 NSs and pentacene layer. This versatile solution-processing approach to preparing WG3 NSs arrays as charge trapping sites allows for fabrication of high-performance nonvolatile OFET memory devices, which could be applicable to a wide range of WBG organic semiconductor materials.

High-Performance Nonvolatile Organic Field-Effect Transistor Memory Based on Organic Semiconductor Heterostructures of Pentacene/P13/Pentacene as Both Charge Transport and Trapping Layers.

Nonvolatile organic field‐effect transistor (OFET) memory devices based on pentacene/N,N′‐ditridecylperylene‐3,4,9,10‐tetracarboxylic diimide (P13)/pentacene trilayer organic heterostructures have been proposed. The discontinuous n‐type P13 embedded in p‐type pentacene layers can not only provide electrons in the semiconductor layer that facilitates electron trapping process; it also works as charge trapping sites, which is attributed to the quantum well‐like pentacene/P13/pentacene organic heterostructures. The synergistic effects of charge trapping in the discontinuous P13 and the charge‐trapping property of the poly(4‐vinylphenol) (PVP) layer remarkably improve the memory performance. In addition, the trilayer organic heterostructures have also been successfully applied to multilevel and flexible nonvolatile memory devices. The results provide a novel design strategy to achieve high‐performance nonvolatile OFET memory devices and allow potential applications for different combinations of various organic semiconductor materials in OFET memory.

Solution Processed Top-Gate High-Performance Organic Transistor Nonvolatile Memory With Separated Molecular Microdomains Floating-Gate

In this letter, a top-gate high-performance floating-gate organic field-effect transistor nonvolatile memory (FG-OFET-NVM), where the four-layer stacked core architecture is processed by a successive solution spin-coating method, is demonstrated. The floating-gate layer is prepared by spin-coating from a blend solution consisting of poly(styrene) (PS) and 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pen). As a result of phase separation, TIPS-Pen aggregates and forms many separated microdomains, which uniformly distribute in thematrix of PS as the charge-trapping sites. The optimal FG-OFET-NVM exhibits excellent memory characteristics, with a large memory window of 26 V, a desired reading voltage of 0 V, a memory ON/OFF ratio larger than 3500, programming/erasing switching endurance over 500 cycles, and good charge-storage retention with a memory ON/OFF ratio larger than 103 over 5000 s.

Achieving high mobility, low-voltage operating organic field-effect transistor nonvolatile memory by an ultraviolet-ozone treating ferroelectric terpolymer.

Poly(vinylidene fluoride–trifluoroethylene) has been widely used as a dielectric of the ferroelectric organic field-effect transistor (FE-OFET) nonvolatile memory (NVM). Some critical issues, including low mobility and high operation voltage, existed in these FE-OFET NVMs, should be resolved before considering to their commercial application. In this paper, we demonstrated low-voltage operating FE-OFET NVMs based on a ferroelectric terpolymer poly(vinylidene-fluoride-trifluoroethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] owed to its low coercive field. By applying an ultraviolet-ozone (UVO) treatment to modify the surface of P(VDF-TrFE-CTFE) films, the growth model of the pentacene film was changed, which improved the pentacene grain size and the interface morphology of the pentacene/P(VDF-TrFE-CTFE). Thus, the mobility of the FE-OFET was significantly improved. As a result, a high performance FE-OFET NVM, with a high mobility of 0.8 cm2 V−1 s−1, large memory window of 15.4~19.2, good memory on/off ratio of 103, the reliable memory endurance over 100 cycles and stable memory retention ability, was achieved at a low operation voltage of ±15 V.

Physical implication of transition voltage in organic nano-floating-gate nonvolatile memories

High-performance pentacene-based organic field-effect transistor nonvolatile memories, using polystyrene as a tunneling dielectric and Au nanoparticles as a nano-floating-gate, show parallelogram-like transfer characteristics with a featured transition point. The transition voltage at the transition point corresponds to a threshold electric field in the tunneling dielectric, over which stored electrons in the nano-floating-gate will start to leak out. The transition voltage can be modulated depending on the bias configuration and device structure. For p-type active layers, optimized transition voltage should be on the negative side of but close to the reading voltage, which can simultaneously achieve a high ON/OFF ratio and good memory retention.

High reliable and stable organic field-effect transistor nonvolatile memory with a poly(4-vinyl phenol) charge trapping layer based on a pn-heterojunction active layer

In this letter, we demonstrate a high reliable and stable organic field-effect transistor (OFET) based nonvolatile memory (NVM) with a polymer poly(4-vinyl phenol) (PVP) as the charge trapping layer. In the unipolar OFETs, the inreversible shifts of the turn-on voltage (Von) and severe degradation of the memory window (ΔVon) at programming (P) and erasing (E) voltages, respectively, block their application in NVMs. The obstacle is overcome by using a pn-heterojunction as the active layer in the OFET memory, which supplied a holes and electrons accumulating channel at the supplied P and E voltages, respectively. Both holes and electrons transferring from the channels to PVP layer and overwriting the trapped charges with an opposite polarity result in the reliable bidirectional shifts of Von at P and E voltages, respectively. The heterojunction OFET exhibits excellent nonvolatile memory characteristics, with a large ΔVon of 8.5 V, desired reading (R) voltage at 0 V, reliable P/R/E/R dynamic endurance over 100 cycles and a long retention time over 10 years.

Synergistic effect in organic field-effect transistor nonvolatile memory utilizing bimetal nanoparticles as nano-floating-gate

A solution-processed bimetal nano-floating-gate, with a combination of stabilized Ag and Pt nanoparticles, is utilized to achieve high-performance organic field-effect transistor nonvolatile memories. The device based on the Ag–Pt nano-floating-gate shows the synergistic superiority in memory performance compared with the corresponding Ag-only and Pt-only devices. The Ag and Pt nanoparticles are found to prefer hole and electron trapping, respectively. Upon the blending of the Ag and Pt nanoparticles, both hole and electron trapping are significantly enhanced and thus realize a large memory window. The dipole enhancement induced local work function change for both Ag and Pt is proposed to be responsible for the synergistic effect, and this physical picture is supported by the electronic structure results. It is concluded that using a hybrid nano-floating-gate is a promising strategy to optimize the device performance of organic field-effect transistor nonvolatile memories.

Direct probing of electron and hole trapping into nano-floating-gate in organic field-effect transistor nonvolatile memories

Electron and hole trapping into the nano-floating-gate of a pentacene-based organic field-effect transistor nonvolatile memory is directly probed by Kelvin probe force microscopy. The probing is straightforward and non-destructive. The measured surface potential change can quantitatively profile the charge trapping, and the surface characterization results are in good accord with the corresponding device behavior. Both electrons and holes can be trapped into the nano-floating-gate, with a preference of electron trapping than hole trapping. The trapped charge quantity has an approximately linear relation with the programming/erasing gate bias, indicating that the charge trapping in the device is a field-controlled process.

Organic field-effect transistor nonvolatile memories utilizing sputtered C nanoparticles as nano-floating-gate

High-performance organic field-effect transistor nonvolatile memories have been achieved using sputtered C nanoparticles as the nano-floating-gate. The sputtered C nano-floating-gate is prepared with low-cost material and simple process, forming uniform and discrete charge trapping sites covered by a smooth and complete polystyrene layer. The devices show large memory window, excellent retention capability, and programming/reading/erasing/reading endurance. The sputtered C nano-floating-gate can effectively trap both holes and electrons, and it is demonstrated to be suitable for not only p-type but also n-type organic field-effect transistor nonvolatile memories.