Organic Transistor Memory Research Articles

Tailoring the Tunneling‐Effect‐Boosted Interfacial Charge Trapping via Effective Conjugation Length

AbstractHighly efficient charge injection and charge trapping stability of the tunneling layer are of desirable and practical importance to transistor memory applications. However, both of which can be contradictory to the nature properties of its material. It is herein demonstrated that lowering the energy mismatch of the tunneling layer by employing a longer conjugation length of the polymer can improve the charge injection efficiency, albeit the trapped charges will be easily diminished and finally losing its memory characteristics, and vice versa. To further elaborate and verify this concept, both materials are blended with distinct nature of properties as the tunneling layer in pentacene‐based transistor devices. As the results, the device using 300 nm SiO2 with optimum blending ratio displays a broad memory window of ≈77.6 V which is superior to the non‐blended tunneling layer carrying appropriate energy levels and band gap energy, not to mention, revealing fast operation time (≈1 s), low driving voltage (≈20 V), long retention (>104 s), and high switching stability over 50 cycles with on–off ratio of >104. Most importantly, this finding shed insight into the design of tunneling materials for advancing organic transistor memory technologies based on tunneling‐effect‐boosted interfacial charge trapping.

A floating-gate field-effect transistor memory device based on organic crystals with a built-in tunneling dielectric by a one-step growth strategy.

A floating-gate organic field-effect transistor (FG-OFET) memory device is becoming a promising candidate for emerging non-volatile memory applications due to the advantages of its sophisticated data-storage mechanism and reliable long-term data retention capacity. However, a conventional FG-OFET memory device suffers from complex fabrication technologies and poor mechanical flexibility, which limits its practical applications. Here, we propose a facile one-step liquid-surface drag coating strategy to fabricate a layered stack of 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (Dif-TES-ADT) crystals and high-quality insulating polymer polystyrene (PS). The liquid surface enhances the spreading area of an organic solution and facilitates the unidirectional growth of organic crystals. In the bilayer-structured blend, the bottom PS polymer and the top Dif-TES-ADT semiconductor serve as a tunneling dielectric and an active memory layer of an FG-OFET memory device, respectively. Consequently, a flexible FG-OFET memory device with a large memory window of 41.4 V, a long retention time of 5000 s, and a high current ON/OFF ratio of 105 could be achieved, showing the best performance ever reported for organic thin film-based FG-OFET memory devices. In addition, multi-level data storage (3 bits per cell) can be achieved by tuning the gate voltage magnitude. Our work not only provides a general strategy for the growth of high-quality organic crystals, but also paves the way towards high-performance flexible memory devices.

Optoelectronic Synaptic Characteristics of Organic Transistor Memories with Organic Semiconductor Floating Gates

Optoelectronic Synaptic Characteristics of Organic Transistor Memories with Organic Semiconductor Floating Gates

Polyarylamine-Based Polymeric Electret with Tunable Pendant Groups for Photorecoverable Organic Transistor Memory

Polyarylamine-Based Polymeric Electret with Tunable Pendant Groups for Photorecoverable Organic Transistor Memory

Electret Molecular Configuration Induced Programmable Photonic Memory for Advanced Logic Operation and Data Encryption

AbstractNonvolatile organic photonic transistor (OPT) memories have attracted widespread attention due to their nondestructive readout, remote controllability, and robust tunability. Developing electrets with similar molecular structures but different memory behaviors and light‐responsive features is crucial for light‐wavelength‐modulated data encryption. However, reported OPT memories have yet to meet this challenge. Here a new electret molecule (“H‐PDI”) is developed via reconfiguring the linear perylene diimide molecule (“L‐PDI”) to a helical shape. Respectively incorporating H‐PDI and L‐PDI into the floating gate layer results to H‐PDI OPT and L‐PDI OPT. Attributing to their remarkably different electronic structures and energy bandgaps, H‐PDI OPT and L‐PDI OPT preferably respond to 405 and 532 nm light irradiation, respectively. Upon electrical programming, data can be written and stored in both memories with good retention features and a high “1”/“0” state current ratio over 105, though the data can only be erased by light with correct wavelengths, rather than the electrical field. Moreover, data stored in a memory array consisting of both H‐PDI OPT and L‐PDI OPT can only be read out by correct inputs, and wrong inputs will lead to highly deceptive outputs. This study provides a general design strategy of OPT for advanced data encryption and protection.

Organic Phase-Change Memory Transistor Based on an Organic Semiconductor with Reversible Molecular Conformation Transition.

Phase-change semiconductor is one of the best candidates for designing nonvolatile memory, but it has never been realized in organic semiconductors until now. Here, a phase-changeable and high-mobility organic semiconductor (3,6-DATT) is first synthesized. Benefiting from the introduction of electrostatic hydrogen bond (S···H), the molecular conformation of 3,6-DATT crystals can be reversibly modulated by the electric field and ultraviolet irradiation. Through experimental and theoretical verification, the tiny difference in molecular conformation leads to crystalline polymorphisms and dramatically distinct charge transport properties, based on which a high-performance organic phase-change memory transistor (OPCMT) is constructed. The OPCMT exhibits a quick programming/erasing rate (about 3 s), long retention time (more than 2h), and large memory window (i.e., large threshold voltage shift over 30V). This work presents a new molecule design concept for organic semiconductors with reversible molecular conformation transition and opens a novel avenue for memory devices and other functional applications.

Water-Soluble Reactive Polymer Blends for Stable Memory Layers in Low-Voltage Nonvolatile Organic Memory Transistors with High Mobility and Data-Retention Characteristics.

Here low-voltage nonvolatile organic memory transistors, featuring high charge-carrier mobility and outstanding data-retention characteristics, by employing water-soluble reactive polymer blends as a gate-insulating memory layer are demonstrated. Blend films of poly(vinyl alcohol) (PVA) and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA) (PVA:PAMPSA) are prepared from their aqueous solutions with various molar ratios of PAMPSA (0-18mol%) and thermally annealed at 70 and 110°C. Organic field-effect transistors (OFETs) are fabricated by depositing poly(3-hexylthiophene) (P3HT) channel layers on the thermally treated PVA:PAMPSA films. Results show that the hole mobility of OFETs is remarkably increased (≈294 times at 70°C and ≈42 times at 110°C) by adding only 2mol% PAMPSA to the PVA films and further improved at 10mol% PAMPSA (>11.7cm2 V-1 s-1 at 70°C and >3.8cm2 V-1 s-1 at 110°C). The hysteresis characteristics are rather strengthened for the PVA:PAMPSA layers by annealing at 110°C due to the formation of cross-linking sites, even though the OFETs with the pristine PVA layers do almost lose hysteresis characteristics at 110°C. The optimized OFETs with the PVA:PAMPSA layers (10mol%, 110°C) deliver excellent data retention characteristics during >10000 memory cycles at a voltage range of -5 to +5V.

Synthesis of a novel A-b-(B-co-C)-type terpolymer with a regioregular poly(3-hexylthiophene) segment and its application to intrinsically stretchable transistor memory

To date, a variety of organic semiconductors with high stretchability have been developed for applications in wearable electronic devices. However, there is still a problem of irreversible damage by repeated stretching/releasing cycles, resulting in a low lifetime for the devices. In this study, a novel A-b-(B-co-C)-type terpolymer, where A and B-co-C were regioregular poly(3-hexylthiophene) (P3HT) and poly(nbutyl acrylate-co-acrylic acid) segments, respectively, was successfully synthesized by the copper-catalyzed azide-alkyne cycloaddition reaction of α-chain-end-functionalized P3HT with an azide moiety and α-chain-end-functionalized poly(nbutyl acrylate-co-tbutyl acrylate) with an alkyne moiety, followed by deprotection of tbutyl groups with trifluoroacetic acid. The AFM and OM images of the terpolymer films showed that no cracks formed even when stretched up to 100%. This may be due to the synergistic effect of the low Tg-inducible nbutyl acrylate and hydrogen-bonding-inducible acrylic acid repeating units in the copolymer segment. In addition, the results of organic transistor memory using terpolymer thin films showed that the transferred/stretched electrets could preserve their device performance and produce stable bipolar charge trapping by applying electrical writing/erasing processes.

In situ memory characteristics of thermal disturbance in low-voltage organic field-effect transistors

Low-voltage organic memory transistors (LOMTs) in situ operation from 25 °C to 100 °C were studied. The interface between charge trapping and active layers exhibited a correlation between the performances of LOMTs and the temperature of environment. Effective microstructures and interface properties need to be investigated to understand the physical mechanisms of the LOMTs in situ operation at various temperatures. When the temperature increased, the thermal disturbance fluctuated the channel, leading to the variety of memory characteristics for the LOMTs. The memory window of LOMTs can reach 1.87 V at 25 °C and maintain most memory stability below 40 °C.

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.

Thickness Effect of Polar Polymer Films on the Characteristics of Organic Memory Transistors

Thickness Effect of Polar Polymer Films on the Characteristics of Organic Memory Transistors

3D Steric Bulky Semiconductor Molecules toward Organic Optoelectronic Nanocrystals

With minimal defects, few grain boundaries, and high-performance optoelectronic characteristics, organic semiconductor nanocrystals (OSNCs) have emerged as promising solutions for miniaturized organic devices and related optoelectronic circuits. To realize this, it is crucial that the OSNCs should possess desired morphologies and unique optoelectronic attributions. After the planar π-conjugated building blocks, the steric bulky molecules with a three-dimensional (3D) framework enable the multiscale self-assembly architectures and superior charge storage properties, as well as high-performance optoelectronic applications, such as organic transistor memory, organic light-emitting diodes, organic lasers and organic photovoltaic cells. However, this type of 3D steric bulky molecule-based OSNCs are not easily to get, and molecular design principles must be developed. In this Review, recent advances in the efficient theories that have arose in building varied nanoarchitectures of 3D steric bulky molecule-based OSNCs, especially the 2D and 3D in morphology, are highlighted. The obtained steric OSNCs exhibited rich optoelectronic properties, including the charge storage, ion transmission, crystallization-enhanced emission, and so on. Further architectural optimization of the steric OSNCs to cater for optoelectronic device based on them is necessary to strive to develop this research direction.

Porous p–n junction-induced memory characteristics in low-voltage organic memory transistors

Low-voltage organic memory transistors (LOMTs) as data storage units are crucial for the advancements of future flexible electronics. However, charge storage mechanism remains a great challenge. In this work, we used poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno(3,2-b)thiophene) (PBTTT-C14) as the active layer and incorporated poly(methyl methacrylate) (PMMA) with the PBTTT-C14 through a simple blending process to fabricate LOMTs with porous structure. The function of the porous structure was to improve the carrier traps, which can effectively capture the holes at the charge trapping regions during the programming process. A maximum threshold voltage shift of 1.01 V was achieved when the weight ratio of PBTTT-C14 and PMMA is 7:3, and the LOMTs were operated under the programming process of −4 V/1 s. Impedance-admittance analyses were used to investigate the interfacial trap density of charge trapping regions, which is a supporter of the programming capability of LOMTs. An ultrathin dioctyl perylene tetracarboxylic diimide film was deposited on the active layer with porous structure in LOMTs. This film can increase the carriers’ erasing capability. A wide memory window of 1.64 V was obtained in LOMTs when the devices are operated under the erasing process of bias pulse of 3 V/1 s with the assistance of 2.5 mW cm−2 light irradiation. This study facilitates the development of high-performance LOMT device in fresh-type memory.

Complementary of Ferroelectric and Floating Gate Structure for High Performance Organic Nonvolatile Memory

AbstractOrganic thin film transistor (OTFT) based nonvolatile memory has made significant progress due to its biocompatibility, flexibility, and low cost, in which ferroelectric transistor memory and floating gate transistor memory play the main roles in organic nonvolatile transistor memory. Here, a novel layered hybrid structure OTFT nonvolatile memory is invented by combining ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) P(VDF‐TrFE) with a floating gate layer utilizing CdSe/ZnS quantum dots (QDs), which integrates the advantages of ferroelectric memory and floating gate memory. The core–shell structured CdSe/Zns QDs are acted as robust charge trapping centers due to their band structure similar to a quantum well, preventing the back diffuse of trapped charges, while P(VDF‐TrFE) provides additional polarized electric field to modulate the capture of charge. The resultant devices exhibit high on‐state current (≈10−5 A), low off‐state current (≈10−10 A), excellent switch ratio (≈105), and retention characteristic (>104 s). Furthermore, a superior memory window, more than 85.6% of scanning voltage range, higher than most reported organic transistor memories, is achieved, which endows the device wide operating condition and significant discrimination between on and off state. The fine‐structured OTFT memory opens up a unique path for desirable memory to meet the growing demand of microelectronic industry.

An organic field effect transistor memory adopting octadecyltrichlorosilane self-assembled monolayer

An organic nonvolatile memory is proposed based on octadecyltrichlorosilane self-assembled monolayer (ODTS SAM) and copper hexadecafluorophthalocyanine (F16CuPc) heterostructure, where F16CuPc acts as the active layer of the organic thin film transistor memory device, and ODTS SAM functions as the charge trapping layer. By adopting N-type active layer, sufficient electrons ensure the erasing process that is independent of the light illumination, indicating a fully electrically driving memory device, where large memory window is obtained. AFM images demonstrates that the monolayer provides the trapping sites. The trapping mechanism is analyzed based on the electric dipoles theory, the dipoles orientation in the monolayer is critical for providing trapping sites, which fixes the mobile carriers at the ODTS SAM/F16CuPc interface. The writing–reading–erasing–reading (WRER) tests and the retention time are shown, and they can be further optimized by involving a thin polystyrene tunneling layer between active layer and charge trapping layer, with an retention time of approximately 125 d, and a sufficient WRER reading current ratio of more than 103 for practical fully electrically driving binary nonvolatile memory device applications.

Enhancement of Optical Memory Characteristics of Solution-Processed Organic Transistor Memories with Polymer-Small-Molecule Composite Charge Storage Layers

Proceedings of the International Display Workshops Volume 27 (IDW '20),Enhancement of Optical Memory Characteristics of Solution-Processed Organic Transistor Memories with Polymer-Small-Molecule Composite Charge Storage Layers

High-Performance Nonvolatile Organic Photonic Transistor Memory Devices using Conjugated Rod-Coil Materials as a Floating Gate.

A novel approach for using conjugated rod-coil materials as a floating gate in the fabrication of nonvolatile photonic transistor memory devices, consisting of n-type Sol-PDI and p-type C10-DNTT, is presented. Sol-PDI and C10-DNTT are used as dual functions of charge-trapping (conjugated rod) and tunneling (insulating coil), while n-type BPE-PDI and p-type DNTT are employed as the corresponding transporting layers. By using the same conjugated rod in the memory layer and transporting channel with a self-assembled structure, both n-type and p-type memory devices exhibit a fast response, a high current contrast between "Photo-On" and "Electrical-Off" bistable states over 105 , and an extremely low programing driving force of 0.1 V. The fabricated photon-driven memory devices exhibit a quick response to different wavelengths of light and a broadband light response that highlight their promising potential for light-recorder and synaptic device applications.

Solution-Processable Anion-doped Conjugated Polymer for Nonvolatile Organic Transistor Memory with Synaptic Behaviors

Brain-inspired synaptic transistors have been considered as a promising device for next-generation electronics. To mimic the behavior of a biological synapse, both data processing and nonvolatile memory capability are simultaneously required for a single electronic device. In this work, a simple approach to realize a synaptic transistor with improved memory characteristics is demonstrated by doping an ionic additive, tetrabutylammonium perchlorate (TBAP), into an active polymer semiconductor without using any extra charge storage layer. TBAP doping is first revealed to improve the memory window of a derived transistor memory device from 19 to 32 V (∼68% enhancement) with an on/off current ratio over 103 at VG = -10 V. Through morphological analysis and theoretical calculations, it is revealed that the association of anion with polymers enhances the charge retention capability of the polymer and facilitates the interchain interactions to result in improved memory characteristics. More critically, the doped device is shown to successfully mimic the synaptic behaviors, such as paired-pulse facilitation (PPF), excitatory and inhibitory postsynaptic currents, and spike-rate dependent plasticity. Notably, the TBAP-doped device is shown to deliver a PPF index of up to 204% in contrast to the negligible value of an undoped device. This study describes a novel approach to prepare a synaptic transistor by doping conjugated polymers, which can promote the future development of artificial neuromorphic systems.

Light-Sensitive Material Structure-Electrical Performance Relationship for Optical Memory Transistors Incorporating Photochromic Dihetarylethenes.

Photoswitchable organic field-effect transistors (OFETs) with embedded photochromic materials are considered as a promising platform for development of organic optical memory devices. Unfortunately, the operational mechanism of these devices and guidelines for selection of light-sensitive materials are still poorly explored. In the present work, a series of photochromic dihetarylethenes with a cyclopentenone bridge moiety were investigated as a dielectric/semiconductor interlayer in the structure of photoswitchable OFETs. It was shown that the electrical performance and stability of the devices can be tuned by variation of the substituents in the structure of the photochromic material. In particular, it was found that dihetarylethenes with donor substituents demonstrated the best light-induced switching effects (wider memory windows and higher switching coefficients) in the devices. The operation mechanism of the light-triggered memory devices was proposed based on the differential in situ Fourier transform infrared (FTIR) spectroscopy data and regression analysis of the threshold voltage-programming time experimental dependencies. The established relationships will facilitate further rational design of new photochromic materials, thus paving a way to fast and durable organic optical memories and memory transistors (memristors).

Non-Volatile Organic Transistor Memory Based on Black Phosphorus Quantum Dots as Charge Trapping Layer

High performance organic nano-floating gate transistor memory (NFGTM) has important prerequisites of low processing temperature, solution–processable layers and charge trapping medium with high storage capacity. We demonstrate organic NFGTM using black phosphorus quantum dots (BPQDs) as a charge trapping medium by simple spin-coating and low processing temperature ( 104 over 10,000 sec by introducing PMMA as the tunneling layer.