Transistor Memory Devices Research Articles

Plasma Etch of IGZO Thin Film and IGZO/SiO2 Interface Diffusion in Inductively Coupled CH4/Ar Plasmas

ABSTRACTIn this work, the etching characteristics of InGaZnO4 (IGZO) thin films were systemically investigated in inductively coupled CH4/Ar plasmas with various gas ratios, bias voltages, and surface temperatures. The ion flux in the CH4/Ar plasmas was analyzed using bias power and voltage, whereas the relative densities of CH and H radicals were quantified through optical actinometry. The change in CH3 radical density was also estimated based on plasma kinetics analysis. The correlations between the plasma properties and IGZO etch rate were investigated. In CH4/Ar plasmas with CH4 ratios below 80%, the IGZO etch rate increases with a higher CH4 proportion, aligning with the ascending trend of CH3 radical density, which suggests that CH3 radical density acts as a limiting factor (radical‐limited regime). However, the IGZO etch rate decreases when the CH4 ratio exceeds 80%, corresponding to the reduction in ion flux, which indicates that ion flux becomes a limiting factor in this ion‐limited regime. The IGZO etch rate shows a linear relationship with bias voltage and follows the Arrhenius equation with varying surface temperature in plasmas without bias voltage. A spontaneous etch model was proposed based on these relationships. In this model, the IGZO etch rate depends on CH3 radical density and IGZO surface reactivity, where ion bombardment contributes more significantly to surface reactivity than high surface temperature. IGZO thin film was deposited on SiO2 during the fabrication of a 3D stacked ferroelectric field‐effect transistor (FeFET) memory device. The interaction between IGZO and SiO2 during CH4/Ar plasma processing was investigated using time‐of‐flight secondary ion mass spectrometry. The efficacy of removing IGZO atoms that had diffused into the SiO2 network was enhanced when subjected to plasma with a bias voltage, compared to the process without a bias voltage. However, exposure to CH4/Ar plasma resulted in a deeper diffusion of IGZO atoms into the SiO2 network, primarily attributed to ion bombardment rather than elevated surface temperature. A significant improvement in surface smoothness was achieved after IGZO and SiO2 etch by introducing BCl3 into the SiO2 etching chemistry.

Ambipolar charge-trapping in self-assembled nanostructures of a supramolecular miktoarm star-shaped copolymer with a zinc phthalocyanine core

Supramolecular miktoarm star-shaped copolymers with a zinc phthalocyanine core exhibit phase-separated nanostructures that enhance ambipolar charge-trapping capabilities in the organic field-effect transistor memory devices.

A sustainable biomass-based electret for face mask and non-volatile transistor memory

An electret filter on the middle layer of disposable medical face masks has a similar function to the charge storage layer on the transistor memory devices. Both applications require a polymer electret to trap charges so that it could establish electrostatic attraction to effectively enhance the filtration efficiency of face mask or modulate the electrical behaviours of transistor memory. By virtue of that very same function, we demonstrate the charge storage performance and memory characteristics of transistor memory using the electret filters of face mask material, from the non-renewable polypropylene (PP) to the biomass-based polymers. We demonstrate dextrin, a biomass-derivative, as a sustainable alternative electret. Due to dextrin being produced natural starch products, it is a renewable material that is biocompatible and eco-friendly. Furthermore, by adding sodium methylsiliconate (SMS), the hydrophobic blended dextrin-SMS transistor memory can maintain inherent prolonged electrostatic charges for over 100 days along with relatively wide memory window of 39.5 V. Ultimately, the non-woven nanofiber electret filter using dextrin-SMS can be successfully produced using an industrial compatible electrospinning technique combined with the addition of polyethylene oxide (PEO) to improve the electrospinability of the mat filter and potentially utilized for future biodegradable face masks and green electronics.

Rubrene/CuInP2S6 organic/inorganic heterojunctions for ferroelectric organic transistor memory devices

Ferroelectric organic field-effect transistor (Fe-OFET) memory devices exhibit low power consumption, low cost and good flexibility, which are indispensable to next generation flexible and wearable memory devices. However, up until the present, the ferroelectric materials used in Fe-OFETs have been limited to ferroelectric polymers, i.e. poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)], and suffer from large surface roughness and high-risk of depolarization. This work integrates a new two-dimensional CuInP2S6 crystal into Fe-OFET, which can introduce excellent ferroelectric property due to its single crystalline smoothness and noncentrosymmetric crystal structure. Meanwhile, the high-mobility rubrene crystal is selected as the channel material to construct rubrene/CuInP2S6 organic/inorganic van der Waals heterojunctions. Associated with synergetic effect of single-crystalline nature of the heterojunction and atomically flat/defect-free interface, the memory devices possess a high programming speed of 0.5 s and long retention time of 104 s with a current ratio larger than 103. Furthermore, the performance of flexible devices is also demonstrated, including a programming/erase cycle of 1000 with a current on/off ratio approaching 103, data retention time of 104 s with a current on/off ratio of 103 and a current on/off ratio maintained at 102 even after 100 bending cycles under a bending radius of 25 mm, which are qualified for memory buffer usage or short-term data storage especially when they are integrated with other flexible electronics. The proposed configuration of memory transistors using organic/inorganic heterojunctions provides a rational design of device structure toward flexible Fe-OFET non-volatile memory applications.

Large-Area Arrays of Polymer-Tethered Gold Nanorods with Controllable Orientation and Their Application in Nano-Floating-Gate Memory Devices.

In this work, it is reported that large-area (centimeter-scale) arrays of non-close-packed polystyrene-tethered gold nanorod (AuNR@PS) can be prepared through a liquid-liquid interfacial assembly method. Most importantly, the orientation of AuNRs in the arrays can be controlled by changing the intensity and direction of electric field applied in the solvent annealing process. The interparticle distance of AuNR can be tuned by varying the length of polymer ligands. Moreover, the AuNR@PS with short PS ligand are favorited to form orientated arrays with the assistance of electric field, while long PS ligands make the orientation of AuNRs difficult. The orientated AuNR@PS arrays are employed as the nano-floating gate of field-effect transistor memory device. Tunable charge trapping and retention characteristics in the device can be realized by electrical pulse with visible light illumination. The memory device with orientated AuNR@PS array required less illumination time (1 s) at the same onset voltage in programming operation, compared to the control device with disordered AuNR@PS array (illumination time: 3 s). Moreover, the orientated AuNR@PS array-based memory device can maintain the stored data for more than 9000 s, and exhibits stable endurance characteristic without significant degradation in 50 programming/reading/erasing/reading cycles.

Selective Release of Excitatory‐Inhibitory Neurotransmitters Emulated by Unipolar Synaptic Transistors via Gate Voltage Amplitude Modulation

AbstractOrganic field‐effect transistor (OFET) memory devices are benefiting from their independent gate modulation advantages for hardware implementation of synaptic functionalities. However, the imitation of selective release of excitatory–inhibitory neurotransmitters in a unipolar synaptic OFET is challenging due to the unbalanced mobile carrier concentration. Here, a p‐type synaptic OFET memory with CsPbBr3 quantum dots (QDs) as nano‐floating gates (NFGs) is developed, which can emulate both the excitatory–inhibitory responses of the biological synapse and their reconfigurable nature. By controlling the offset difference between stimulus voltage and reading voltage, the concomitant and independently expressed excitatory and inhibitory responses are successfully implemented in a negative gate modulation manner, but without introducing an ambipolar semiconductor or additional optical terminal. This reconfigurable modulation is ascribed to the dynamic competition between external electric field and built‐in electric field assisted by charge trapping in shallow traps. The proposed gate voltage‐offset method can be generally adapted to other unipolar synaptic OFETs. These results provide insight into OFET memory devices for building neuromorphic hardware elements with tailorable synaptic plasticity.

Influence of Molecular Weight of Polymer Electret on the Synaptic Organic Field‐Effect Transistor Performance

AbstractChargeable polymer electret‐based organic field‐effect transistor (OFET) memory devices are attractive for intrinsically flexible artificial synapse. However, the effects of molecular weight (Mw) of polymer electret on the charge trapping properties, especially the implementation of synaptic functions, are not yet well‐understood. In this work, the authors study pentacene‐based synaptic OFET memory made from two different molecular weight polymer electrets, with poly(N‐vinylcarbazole) (PVK) as the case study. Utilizing the synergistic effect of smooth surface morphology, higher polymer chain‐end density and lower dielectric constant, OFET memory device with lower Mw PVK electret showed a larger memory window (28.2 V) and faster write speed (1 ms) compared to that with higher Mw PVK. Benefiting from its charge‐trapping ability, the synaptic OFETs with lower Mw PVK delivered a better modulation of synaptic weight. The co‐modulation of photonic and electric operations enabled the reconfigurable short‐term plasticity and long‐term plasticity (LTP) in lower Mw PVK devices, further leading to the STP‐based emulation of visible color recognition and LTP‐based neural network simulation. This work enlightens a detailed understanding of the molecular weight‐dependent charge trapping behavior for the future integration of visible information sensing‐memory‐processing in optoelectronic OFET memory.

Gate‐Deterministic Remote Doping Enables Highly Retentive Graphene‐MXene Hybrid Memory Devices on Plastic

AbstractIn this work, a highly retentive and synaptic‐functional transistor memory device architecture based on the gate‐deterministic remote doping of graphene via surface‐oxidized Ti3C2TX MXene nano‐floating‐gates (NFG) is presented. By using solution‐phase size‐sorting followed by controlled surface oxidation process, a regulated distribution of MXene nanoflakes comprising metallic Ti3C2TX as the core surrounded by TiO2‐a high dielectric constant insulator‐as the shell is achieved. The size‐sorted core/shell‐like MXene nanoflakes show a self‐sustainable charge trapping/detrapping behavior, which is highly feasible for realizing non‐embed NFGs for transistor memory devices. Interestingly, unlike the conventional NFG‐embedded architecture, the introduction of core/shell‐like MXene under an electrolyte‐gated graphene field‐effect transistor (GFET) architecture induces a cooperative evolution of the hysteresis loop associated with ionic motion in the electrolyte gates and charge trapping/detrapping in the nanoflakes, resulting in a deterministic remote doping of the graphene layer. The resulting device exhibited a highly retentive memory behavior, which can be optimized by the nanoflake size distribution. In addition, synaptic functions having mechanical flexibility can be successfully emulated using MXene‐based GFETs fabricated on a flexible polyethylene naphthalate substrate.

Ultrathin Metal–Organic Framework Nanosheets as Nano‐Floating‐Gate for High Performance Transistor Memory Device

AbstractMetal–organic framework (MOF) is an emerging important class of functional materials in the fields of information storage, wearable electronics and optoelectronic devices. The interaction of electrons or holes with MOFs is important for the systematic exploration of MOFtronics and to investigate the related structure–performance correlation. Herein, MOF flat nanosheets of copper tetrakis(4‐carboxyphenyl)porphyrin with sub‐10 nanometer scale in thickness are employed as the charge‐trapping layer in organic field‐effect floating‐gate transistor memory device fabricated by an air–liquid interfacial assembly and subsequent stamping operation. As charge trapping sites, MOF nanosheets with ultrathin nanoporous arrays significantly improve in comparison with the memory device using its counterpart ligand of tetrakis(4‐carboxyphenyl)porphyrin as the trapping elements. As compared to the reported widely applied nanofloating gate materials of gold nanoparticles, graphene, or macromolecular nanomaterials, a short pulse (≈20 ms) on the device gets a considerable memory window of ≈37.5 V at a programming voltage of ‐80 V, with a retention time longer than 104 s and good ON/OFF ratio of >103. Furthermore, the hybrid structure composed of metal and organic components endows it with electron and hole trapping capability. This work could push forward the fundamental research of organic–inorganic–hybrid electronics in future microelectronic research.

Photoinduced-reset and multilevel storage transistor memories based on antimony-doped tin oxide nanoparticles floating gate

Recently, antimony-doped tin oxide nanoparticles (ATO NPs) have been widely used in the fields of electronics, photonics, photovoltaics, sensing, and other fields because of their good conductivity, easy synthesis, excellent chemical stability, high mechanical strength, good dispersion and low cost. Herein, for the first time, a novel nonvolatile transistor memory device is fabricated using ATO NPs as charge trapping sites to enhance the memory performance. The resulting organic nano-floating gate memory (NFGM) device exhibits outstanding memory properties, including tremendous memory window (∼85 V), superhigh memory on/off ratio (∼109), long data retention (over 10 years) and eminent multilevel storage behavior, which are among the optimal performances in NFGM devices based on organic field effect transistors. Additionally, the device displays photoinduced-reset characteristic with low energy consumption erasing operation. This study provides novel avenues for the manufacture of simple and low-cost data storage devices with outstanding memory performance, multilevel storage behavior and suitability as platforms for integrated circuits.

Multiband Photoresponding Field‐Effect Transistor Memory Using Conjugated Block Copolymers with Pendent Isoindigo Coils as a Polymer Electret

AbstractIn this study, the authors report a series of conjugated block copolymers, PF‐b‐Piso comprising poly[2,7‐(9,9‐dihexylfluorene)] (PF), and poly(pendent isoindigo) (Piso) for polymer electret in the photonic field‐effect transistor (FET) memory device. The optical properties, surface morphology, and molecular organization of these BCPs are investigated systematically. Accordingly, Piso with absorption in the Ultraviolet C range (UVC, 200–280 nm) possibly rendered the device with a multiband photoresponse, and a good memory performance is achieved by optimizing the polymer composition. Therefore, the memory device comprising PF‐b‐Piso could perform a high current contrast of 106 to 405 nm light and 105 to 254 nm light over 104 s. In addition, a current contrast of 104 and 102 is achieved in response to 650 and 530 nm light, and this phenomenon can be attributed to the charge transfer between channel and memory layers. The experimental results indicate that the block copolymer design not only conduces to forming a self‐assembled microphase separation to stabilize the trapped charge in the polymer electret, but also triggers multiband photoresponding of the photonic FET memory.

High-k polymer dielectrics with different cross-linked networks for nonvolatile transistor memory device

Nonvolatile OFET memory devices using different pPFPA/bPEI cross-linked polymers as the dielectric layer are fabricated. The influence of bPEI content on the electrical property and memory performance of devices are systematically investigated. The results demonstrate that the introduction of bPEI into pPFPA can significantly enhance the capacitance and dielectric constant of the pPFPA/bPEI cross-linked polymer dielectrics, but it also causes a slight increase in the leakage current density. Besides, the excess bPEI induces more morphology defects of the semiconductor film, leading to an apparent decrement in charge mobility. Transistors with the 119:250 pPFPA/bPEI dielectric layer exhibit the highest on/off current ratio (~107 at Vg = − 20V) and a relatively low hole mobility of 0.38 cm2 V−1s−1. Moreover, the corresponding memory devices show good reliability in information record with a data retention time over 105 s, indicating that an appropriate amount of bPEI is crucial for improving the stability of the memory devices.

Realizing fast photoinduced recovery with polyfluorene‐block‐poly(vinylphenyl oxadiazole) block copolymers as electret in photonic transistor memory devices

AbstractPhotonic field‐effect transistor (FET) memory devices offer unique advantages owing to their solution processability, low cost production, and their lightweight and structural flexibility. Despite the plethora of research demonstrated the photon based programming process, limited reports are available for photoinduced recovery mechanism in such devices. To investigate the influence of polymer electret design on photonic memory performance, poly(9,9‐dioctylfluorene) (PFO)–block–poly (vinylphenyl oxadiazole) (POXD) conjugated block copolymers were employed to a photonic FET memory with n‐type semiconducting channel. The studied device exhibited bistable ON/OFF current states after electrical programming and photoinduced recovery (erasing) processes. The device operating mechanism was elaborated by comparing the device performance with respective electrets of PFO‐b‐POXD and PFO‐b‐polystyrene (PS) and PFO homopolymer. We found that PFO‐b‐POXD can efficiently generate photoexciton under UV illumination to neutralize the trapped hole, and assuage the hole trapping propensity of PFO segment, simultaneously. By optimizing the POXD content in the block copolymer, a decent memory ratio (ION/IOFF) of ~105 was achieved after 104 s, indicating its superior long‐term stability and data discernibility. This research shows the judicious strategy to design polymer electret for photonic memory, and it opens up the possibility of developing photonic memory, human perception and futuristic communication systems using simple, convenient and reliable optoelectronic technique.

Multilevel Photonic Transistor Memory Devices Based on 1D Electrospun Semiconducting Polymer /Perovskite Composite Nanofibers

AbstractPhotonic field‐effect transistor (FET) memory devices offer unique advantages over conventional voltage‐driven memory devices, such as noncontact programming capability, rapid data transmission, and low power consumption. In this article, the first example of a nanofiber‐only photonic FET memory device is reported. Perovskite nanocrystal (βNC)‐embedded polythiophenes are employed as 1D semiconducting channels of the nanofiber matrix. A decent On/Off current ratio of ≈103 is reached for the best device with a prolonged data retention of over 104 s, attributing to the favorable energy level alignment and molecular packing of conjugated polymers in nanofibers. The composite nanofiber system exhibits superior photoresponsivity and charge retention, outperforming its film‐based counterpart owing to its regular 1D confined structure, and well‐dispersed βNCs. Collectively, the structurally fine‐tuned conjugated polymer and the 1D confined structure in the nanofiber promise good data discriminability and a highly fault‐tolerant photonic memory device. In addition, the fiber‐based flexible memory device exhibits excellent photonic memory performance, indicating its integrity for application in wearable electronics. The current system represents the first application of 1D perovskite nanocrystal/conjugated polymer composite nanofibers for high‐performance photonic memory devices, which reveals their potential to make composite nanostructures for novel pioneering photonic applications.

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

Pyrene-Incorporated Side Chain in π-Conjugated Polymers for Non-Volatile Transistor-Type Memory Devices with Improved Stretchability

The direct application of a conjugated polymer as the single active layer in a field-effect transistor (FET) memory device is in high demand to integrate the conventional charge-transport and charg...

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.

Improving the performance of photonic transistor memory devices using conjugated block copolymers as a floating gate

We report the synthesis, morphology and photo-memory device applications of a block copolymer (BCP) consisting of poly(9,9-dioctylfluorene) (PFO) and polystyrene (PS).

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.

Recent advance in renewable materials and green processes for optoelectronic applications

With the growing global environmental awareness, the development of renewable and green materials has gained increased worldwide interest. Being at the heart of current scientific research studies, renewable polymers, include natural, semisynthetic, and microbial polymers, have a scope in vast diverse applications in packaging, agriculture, medicine, and optoelectronic technological fields. In recent years, research interest has been increasingly focused on integrating biodegradable polymers into optoelectronic devices for the sake of reducing non-degradable waste and conserving our environment. Numerous biobased materials have been successfully incorporated in organic field-effect transistor memory, resistor memory, and organic photovoltaic (OPV) devices. Besides natural biomaterials, there are also various biobased synthetic polymers used in electronic devices; for example, sugar-based block copolymers have been synthesized to fabricate stretchable memory devices. Several recent studies have also been devoted to integrating green materials into OPV devices in hope of fulfilling sustainable development. In this mini-review, science development of exploiting renewable materials, introducing environmentally friendly processing solvents, and their corresponding applications toward an environmental sustainable life will be briefly narrated.