Nonvolatile Organic Field-effect Transistor 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.

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.

Unveiling the Photoinduced Recovery Mystery in Conjugated Polymer-Based Transistor Memory.

A straightforward mechanism for the photorecovery behavior of photoresponsive nonvolatile organic field-effect transistor (OFET) memories is proposed by employing a commercially available conjugated polymer, the poly(9,9-dioctylfluorene) (PFO), the conjugated monomer fluorene (FO), and the nonconjugated poly(vinyl alcohol) (PVA), as charge storage layers beneath the semiconducting pentacene layer. As photoexcitons are generated upon light exposure, the respective charges recombine with the trapped charges in electrets and neutralize the memory device. However, whether the excitons are generated in the semiconducting layer or the electret part, the origin that mainly governs the photorecovery behavior remains unclear. In this study, we show that when PVA, a nonphotoactive electret, replaces PFO the photorecovery behavior is totally absent, and it confirms the photorecovery behavior dominated by the excitons in situ generated in a charged electret. Moreover, PFO as a photoactive electret, exhibiting an excellent hole-trapping ability over 24 h in the dark and high Ion/Ioff current ratio of 108, has successfully demonstrated rapid photoinduced recovery under UV light. The devices also display a reliable switching ability between electrical charge trapping and optical recovery cycles for optical-recording application. This report presents a clear understanding behind photorecovery phenomena that demonstrates useful guidance to boost the development of photoactive OFET memories based on conjugated polymer electrets.

High performance nonvolatile organic field‐effect transistor memory devices based on pyrene diimide derivative

AbstractDeveloping high‐quality electret layer is important for the fabrication of high‐performance nonvolatile organic field effect transistor memory devices (OFET‐NVMs). In this work, three representative aromatic diimide frameworks are employed for comparative studies as n‐type doping materials for the electret layers in OFET‐NVMs, which are naphthalene diimide (NDI), perylene diimide (PDI), and pyrene diimide (PyDI). When blended with polystyrene (PS) to prepare the electret layers, all the memory devices containing aromatic diimide dopants exhibited significantly improved performances compared with the undoped counterparts, indicating that low‐lying LUMO energy levels of these dopants are beneficial for charge injection. All the devices with n‐type dopants exhibited long retention times (more than 104 s) and good switching reliability in more than 400 continuous write‐read‐erase‐read cycles. Among them, the PyDI‐based memory device exhibited superior performance compared with other aromatic diimides, which achieved a memory window of 34.0 V, a trapping charge density of 1.98 × 1012 cm−2 along with an on/off ratio higher than 104. This work indicates that PyDI framework could be a new platform for the future design of n‐type dopant for high‐performance nonvolatile organic field‐effect transistor memory devices.image

Electrically programmable multilevel nonvolatile memories based on solution-processed organic floating-gate transistors

The development of nonvolatile organic field-effect transistor (OFET) memories with a satisfactory solution processability is highly desirable to fabricate the data storage media for flexible and printed electronic devices. In this study, we fabricate top-gate/bottom-contact OFET memories having an organic floating-gate structure by a spin-coating process and investigate their memory characteristics. An ambipolar polymer semiconductor of poly(N-alkyldiketopyrrolo-pyrrole-dithienylthieno[3,2-b]thiophene) (DPP-DTT) was used to fabricate an organic semiconductor layer, on which an organic composite of polystyrene and 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) was deposited to form an organic floating-gate structure through vertical phase separation. The existence of a deep lowest unoccupied molecular orbital (LUMO) level and the excellent electron transport property of the DPP-DTT enables the injection of electrons from the Au source-drain electrodes to the DPP-DTT semiconductor layer and the storage of electrons in the LUMO level of the TIPS-pentacene floating gates by programming under dark conditions. A high work function metal oxide layer of MoO3 was inserted at the Al gate electrode/CYTOP gate insulator interface to tune the energy level difference between the Au source-drain and Al gate electrodes. The DPP-DTT FET memories with MoO3/Al gate electrodes exhibit satisfactory retention characteristics and, because of the ambipolar trapping characteristics, allow the storing of holes in the highest occupied molecular orbital level of the TIPS-pentacene floating gates in the erasing process. Furthermore, the molecular floating-gate OFET memories exhibit a high storage capacity for multi-level data, and four state levels can be recorded with stable retention characteristics.

Study of the pyridyl-containing charge-trapping functional materials in the organic field effect transistor memory devices

Interface materials can effectively improve the storage characteristics of the memory devices. In this paper, a series of functional materials with propyl chain bridging pyridyl ring and triethoxysilyl group, 3-(3-(triethoxysilyl)propyl)pyridine (Pyridyl-C), N-(3-(triethoxysilyl)propyl)pyridin-3-amine (Pyridyl-N) and 3-(3-(triethoxysilyl)propoxy)pyridine (Pyridyl-O), were selected as the charge-storage interface materials to study the storage characteristics of nonvolatile organic field-effect transistor (OFET) memory devices. The results demonstrated that the memory performance could be enhanced by adding lone-pair-electron atoms (N, O) between pyridyl group and propyl chain. With the programming voltage of −30 V staying in dark condition for 1 s, the memory windows were increased from 12.48 V to 14.95 V, then to 21.99 V when the –O and N atoms were introduced, respectively. All memory devices could remain stable for more than 104 s. The morphology images indicated that there were aggregates on the interfacial layers, and the size was increased when the atoms (O, N) were added because of the hydrogen-bonding interaction. The aggregates can increase the contact area between pentacene and interface materials and further enlarge the effective tunneling area. In addition, the variation of self-assembling immersing time for preparing Pyridyl-N layers was studied, indicating that with the extension of the immersing time, the size of aggregates was increasingly enlarged and memory performance was improved correspondingly.

Nonvolatile photoelectric memory with CsPbBr3 quantum dots embedded in poly(methyl methacrylate) as charge trapping layer

Abstract Nonvolatile organic field-effect transistor (OFET) photoelectric memories have attracted tremendous attention due to special photoelectric memory mechanism and application area, such as image capture and light information storage. Unfortunately, conventional two-step preparation method of floating gate and tunneling layer is complex and not conducive to large-area. Here, a nonvolatile OFET photoelectric memory with perovskite quantum dots (QDs) embedded in poly(methyl methacrylate) (PMMA) as charge trapping layer is reported. The photoelectric memory can effectively accumulate and release photo-generated carriers during photo- or photoelectric programming operations and electrical erasing operation. The memory characteristics of the photoelectric memory are comparable to that of traditional memories with two-step preparation technique of floating gate and tunneling layer. In addition, the memory device presents well retention time and endurance property even after being exposed to air for two weeks. Hence, the memory using QDs/PMMA composites as charge trapping layer shows great potential for the application in photoelectric devices.

Optical memory characteristics of solution-processed organic transistors with self-organized organic floating gates for printable multi-level storage devices

Abstract Exploring optical memory functions in nonvolatile organic field-effect transistor (OFET) memories with top-gate/bottom-contact (TG/BC) configurations can offer effective routes for developing printable, high-density organic memory circuits capable of multi-level data storage. Here, we use a solution process to fabricate TG/BC OFET devices with organic floating-gate structures and investigate their memory characteristics under light illumination. A solution-processable organic composite of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) and poly(methylmethacrylate) is employed to self-organize organic floating-gate structures on a solution-processed semiconductor layer composed of poly(3-hexylthiophene) (P3HT). The floating-gate OFET devices programmed with blue, green, and red light exhibit large threshold voltage (Vth) shifts of approximately 30 V and stable charge retention characteristics even under light illumination. The devices also exhibit high sensitivity to incident light during programming, and the degree of Vth shift and the on-state current can be tuned using light and programming voltage to facilitate distinct storage and readout of multi-level data.

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.

9,10‐Imide‐Pyrene‐Fused Pyrazaacenes (IPPA) as N‐Type Doping Materials for High‐Performance Nonvolatile Organic Field Effect Transistor Memory Devices

AbstractThe fabrication of high‐performance nonvolatile organic field effect transistor (OFET) memory devices is reported using a series of pyrene‐fused pyrazaacene (PPA) and 9,10‐imide‐pyrene‐fused pyrazaacene (IPPA) derivatives as n‐type doping components. The obtained memory devices exhibit stable switching behaviors (>100 times) and good retention properties (>104 s). Devices based on chlorinated IPPA (IPPA‐Cl) show the largest memory window of 40.8 V, with a trapping charge density of 2.66 × 1012 cm−2 and on/off ratio higher than 106. Our investigation reveals that low‐lying lowest unoccupied molecular orbital energy levels and small dipole moment are key parameters for achieving high memory performance. This work provides a general guideline for the design of n‐type organic semiconductors as highly efficient doping materials for organic memory devices.

Charge-Storage Aromatic Amino Compounds for Nonvolatile Organic Transistor Memory Devices.

Here, charge-storage nonvolatile organic field-effect transistor (OFET) memory devices based on interfacial self-assembled molecules are proposed. The functional molecules contain various aromatic amino moieties (N-phenyl-N-pyridyl amino- (PyPN), N-phenyl amino- (PN), and N,N-diphenyl amino- (DPN)) which are linked by a propyl chain to a triethoxysilyl anchor group and act as the interface modifiers and the charge-storage elements. The PyPN-containing pentacene-based memory device (denoted as PyPN device) presents the memory window of 48.43 V, while PN and DPN devices show the memory windows of 24.88 and 8.34 V, respectively. The memory characteristic of the PyPN device can remain stable along with 150 continuous write-read-erase-read cycles. The morphology analysis confirms that three interfacial layers show aggregation due to the N atomic self-catalysis and hydrogen bonding effects. The large aggregate-covered PyPN layer has the full contact area with the pentacene molecules, leading to the high memory performance. In addition, the energy level matching between PyPN molecules and pentacene creates the smallest tunneling barrier and facilitates the injection of the hole carriers from pentacene to the PyPN layer. The experimental memory characteristics are well in agreement with the computational calculation.

Self-assembled oligosaccharide-based block copolymers as charge-storage materials for memory devices

Over the past few years, extremely high charge-storage capacities of glucose-based oligo- or polysaccharides have been discovered that enables such materials to hold a great potential in electronics applications due to their abundant and renewable materials. Typically, the introduction of an α-glucan-containing polysaccharide into the dielectric layer of a transistor-type memory device causes excellent irreversible electron-capture properties; hence, a transistor device embedded with oligosaccharide maltoheptaose domains expresses write-once-read-many (WORM)-type behavior, which confirms that green materials can be used for advanced electronics. However, their irreversible WORM-type characteristics also restrict the application α-glucan-containing polysaccharides in high-performance electronic devices. Recent advances in oligosaccharide-based block copolymers through the inherent immiscibility of different polymer segments can enhance not only the formation of self-assembled nanostructures but also the switching of memory properties. Furthermore, supramolecular structures composed of oligosaccharide-based block copolymers and conjugated moieties can be developed into high-performance nonvolatile organic field-effect transistor (OFET) memory devices. This mini review presents an overview of the recent literature in oligosaccharide maltoheptaose-based block copolymers and their promising applications in organic memory devices.

Bulky side chain effect of poly(N‐vinylcarbazole)‐based stacked polymer electrets on device performance parameters of transistor memories

ABSTRACTThree poly(N‐vinylcarbazole) (PVK)‐based polymer electrets were synthesized through Friedel‐Crafts postfunctionalization for the function of charge storage in nonvolatile organic field effect transistor (OFET) memory devices. The bulky side chain effect of these stacked polymer electrets on the morphology, water contact angles, and memory characteristics were examined with regard to those of precursor PVK. The introduction of steric hindrance groups could interrupt the large length of π‐stacked structures in PVK and block the form of region‐regular structures from region‐random on external electric field. As a result, the memories based on the three modified polymers exhibited approximate memory windows of 32 V increased by 13 V with respect to PVK. Besides, the write‐read‐erase‐read cycles stability of the modified polymers was superior to that of PVK. Furthermore, we found that the holes were mainly located in the region of local π‐stacked structures and bulky π‐conjugated groups also acted as additional electron trapping sites. Molecular engineering of charge trapping site with tunneling polymers will be a promise strategy for the advance of transistor memory. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3554–3564

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.

The effect of porous structure of PMMA tunneling dielectric layer on the performance of nonvolatile floating-gate organic field-effect transistor memory devices

In this paper, we used the low and high density porous structure of polymethylmethacrylate (PMMA) film as tunneling dielectric layer in the floating-gate organic field-effect transistor (OFET) memory devices. Compared to the thin/thick nonporous structure of PMMA tunneling layer, the porous structure of PMMA tunneling layer had positive impacts on the device performance of the floating-gate OFET memory devices. Moreover, it was found that the memory performance was also increased as pore density of PMMA film increased. The atomic force microscopy (AFM) results of both porous structure of PMMA film and pentacene film on porous structure of PMMA film revealed that high density porous structure of PMMA tunneling layer can produce larger tunneling area and more electron transfer paths between pentacene film and PMMA film, which resulted in high electron capture and release efficiency of the floating-gate OFET memory devices with porous structure of PMMA tunneling layer. In addition, our porous structure of PMMA tunneling layer as well as nonporous PMMA film has high electrical insulating property due to their semi-hollow structure film, which is favourable to maintain stable retention property. Eventually, the floating-gate OFET memory devices with high density porous structure of PMMA tunneling layer showed good nonvolatile memory properties with a large memory window of about 43 V, a high ON/OFF current ratio of about 104, and stable endurance and retention properties. Our results provided a new strategy to achieve the high performance floating-gate OFET memory devices.

Analysis of temperature-dependent electrical transport properties of nonvolatile organic field-effect transistor memories based on PMMA film as charge trapping layer

The temperature-dependent electrical transport properties of nonvolatile organic field-effect transistor (OFET) memories with Poly (methyl methacrylate) (PMMA) as a charge trapping layer were characterized at four typical temperatures (20 °C, 60 °C, 80 °C and −78.5 °C). It was found that the OFET memories showed strong temperature dependence. The performance degradations, including the memory windows and the retention characteristics, could be observed at both high and low temperatures. The degradations of the OFET memories at 60 °C, 80 °C and −78.5 °C were attributed to both the less electrons trapped by the PMMA film and the easier release of the trapped electrons from the PMMA film, which is caused by the lower crystallinity of pentacene film and the larger contact area between pentacene film and PMMA film, respectively.

Polymeric charge storage electrets for non-volatile organic field effect transistor memory devices

A review on polymeric charge storage electrets for constructing non-volatile organic field effect memory devices is presented.

Non-volatile organic memory with sub-millimetre bending radius

High-performance non-volatile memory that can operate under various mechanical deformations such as bending and folding is in great demand for the future smart wearable and foldable electronics. Here we demonstrate non-volatile solution-processed ferroelectric organic field-effect transistor memories operating in p- and n-type dual mode, with excellent mechanical flexibility. Our devices contain a ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) thin insulator layer and use a quinoidal oligothiophene derivative (QQT(CN)4) as organic semiconductor. Our dual-mode field-effect devices are highly reliable with data retention and endurance of >6,000 s and 100 cycles, respectively, even after 1,000 bending cycles at both extreme bending radii as low as 500 μm and with sharp folding involving inelastic deformation of the device. Nano-indentation and nano scratch studies are performed to characterize the mechanical properties of organic layers and understand the crucial role played by QQT(CN)4 on the mechanical flexibility of our devices.

Nonvolatile organic field-effect transistor memory devices using polymer electrets with different thiophene chain lengths

We report the synthesis of poly(5-hexyl-2-vinylthiophene) (PVT) and poly(5-hexyl-5′′-vinyl-2,2′:5,2′′-terthiophene) (PVTT) as charge storage electrets for nonvolatile organic field effect transistor (OFET) memory devices of n-type semiconducting N,N′-bis(2-phenylethyl)perylene-3,4,9,10-bis(dicarboximide) (BPE-PTCDI). The effects of the conjugated thiophene chain length on the morphology, OFET mobility and memory characteristics are explored and compared to those of the styrene or fluorene side chain. The mobility of the OFET memory device using PVTT as an electret is significantly smaller compared with that of PVT because its large torsional angle hinders the molecular packing of BPE-PTCDI. However, the OFET memory device using the PVTT electret has the largest hysteresis window of 81 V, compared to PVT, polystyrene (PS), and poly(styrene) para-substituted with fluorene (PSt-Fl). The highest HOMO energy level of PVTT facilitates the charge transfer from BPE-PTCDI and leads to the largest memory window. The backbone non-coplanarity prevents the back transfer of the charge for the nonvolatile memory characteristics. The device shows excellent nonvolatile behavior for bistable switching and the write–read–erase–read (WRER) cycles are operated over 100 cycles. The shifted threshold voltages of the OFET memory devices using PVTT are stable over 104 s, and the ON and OFF states could maintain 104 s with the Ion/Ioff current ratios of 103. This study suggests that the pendent conjugation length and the backbone coplanarity of polymer electrets significantly affect the charge mobility and electrical characteristics of OFET memory devices.

Nonvolatile organic field effect transistor memory devices using one-dimensional aligned electrospun nanofiber channels of semiconducting polymers

We report the nonvolatile memory characteristics of organic field effect transistors (OFETs) using one-dimensional aligned electrospun (ES) nanofibers of semiconducting poly(9,9-dioctyl-fluorene-co-bithiophene) (F8T2). The effects of the nanofiber diameter associated with the polymer chain orientation on the charge transport and storage ability were explored. The OFET devices using the F8T2 ES nanofibers exhibited a large average memory window of ∼30 V, an on–off ratio of 102–103 and a hole mobility of 10−4 to 10−2 cm2 V−1 s−1. The write, erase and read processes of the memory device were performed by voltages across the nanofiber channels for at least 100 cycles and could be stabilized for at least 1000 s. The reversible hysteresis characteristics were attributed to the shallow trapping in the ordered/disordered domains of the F8T2 nanofibers from the in situ grazing incidence wide angle X-ray scattering (GIWAXS) analysis. Our results suggest that the semiconducting ES nanofibers could have potential applications for high performance OFET-based nonvolatile organic memory devices.