A nonvolatile memory device made of a ferroelectric polymer gate nanodot and a single-walled carbon nanotube

Resistance switching of graphene by gate-controlled polarization reorientation of polyvinylidene fluoride in a field effect transistor

Ferroelectric β-phase crystals of a polyvinylidene fluoride (PVDF) polymer grown or deposited on a graphene channel of a field effect transistor would induce various degrees of electrostatic doping (i.e., various amounts of charge carriers) into graphene and in turn ON/OFF switching of the device, only if the electric field applied at the gate can reorient its polarization (i.e., the well-aligned F-to-H dipole moments perpendicular to the all-trans polymer backbone) around the polymer backbone. To assess the feasibility of achieving a β-PVDF/graphene ferroelectric field effect transistor or memory device, we mimic (1) the electric-field-controlled PVDF polarization reversal (with density functional theory calculations and molecular dynamics simulations) and (2) the conductance switching of β-PVDF/graphene by PVDF reorientations (F-, H- and FH-down) representing a cycle of gate-voltage sweep (with density functional theory combined with non-equilibrium Green's function formalism). The low energy barrier of the collective synchronous PVDF chain rotation around the backbone (0.22 eV per monomer) and the high electric field required to initiate the chain rotation (16 V nm-1) are compatible with the domain nucleation-growth theory and would support the polarization-induced resistance switching mechanism if the PVDF film is ultrathin and partially amorphous.

Non-Centrosymmetric Single Crystalline Biomolecular Nano-Arrays for Responsive Electronics

Herein, a novel strategy is reported for synthesizing libraries of single crystalline amino acid (AA) nanocrystals with control over size, anisotropy, and polymorphism by leveraging dip-pen nanolithography (DPN) and recrystallization via solvent vapor annealing. The crystals are prepared by first depositing nanoreactors consisting of a solvent with AAs, followed by water vapor-induced recrystallization. This leads to isotropic structures that are non-centrosymmetric with strong piezoelectric (g33 coefficients >1000 mVm N-1), ferroelectric, and non-linear optical properties. However, recrystallizing arrays of isotropic DL-alanine nanodot features with a binary solvent (water and ethanol) leads to arrays of 1D piezoelectric nanorods with their long axis coincident with the polar axis. Moreover, positioning nanoreactors containing AAs (the nanodot features) between micro electrodes leads to capillary formation, making the reactors anisotropic and facilitating piezoelectric nanorod formation between the electrodes. This offers a facile route to device fabrication. These as-fabricated devices respond to ultrasonic stimulation in the form of a piezoelectric response. The technique described herein is significant as it provides a rapid way of investigating non-centrosymmetric nanoscale biocrystals, potentially pivotal for fabricating a new class of stimuli-responsive devices such as sensors, energy harvesters, and stimulators.

Carbon Nanotube-Based Flexible Ferroelectric Synaptic Transistors for Neuromorphic Computing

Biological nervous systems evolved in nature have marvelous information processing capacities, which have great reference value for modern information technologies. To expand the function of electronic devices with applications in smart health monitoring and treatment, wearable energy-efficient computing, neuroprosthetics, etc., flexible artificial synapses for neuromorphic computing will play a crucial role. Here, carbon nanotube-based ferroelectric synaptic transistors are realized on ultrathin flexible substrates via a low-temperature approach not exceeding 90 °C to grow ferroelectric dielectrics in which the single-pulse, paired-pulse, and repetitive-pulse responses testify to well-mimicked plasticity in artificial synapses. The long-term potentiation and long-term depression processes in the device demonstrate a dynamic range as large as 2000×, and 360 distinguishable conductance states are achieved with a weight increase/decrease nonlinearity of no more than 1 by applying stepped identical pulses. The stability of the device is verified by the almost unchanged performance after the device is kept in ambient conditions without additional passivation for 240 days. An artificial neural network-based simulation is conducted to benchmark the hardware performance of the neuromorphic devices in which a pattern recognition accuracy of 95.24% is achieved.

Straightforward Patterning of Functional Polymers by Sequential Nanosecond Pulsed Laser Irradiation

Laser-based methods have demonstrated to be effective in the fabrication of surface micro- and nanostructures, which have a wide range of applications, such as cell culture, sensors or controlled wettability. One laser-based technique used for micro- and nanostructuring of surfaces is the formation of laser-induced periodic surface structures (LIPSS). LIPSS are formed upon repetitive irradiation at fluences well below the ablation threshold and in particular, linear structures are formed in the case of irradiation with linearly polarized laser beams. In this work, we report on the simple fabrication of a library of ordered nanostructures in a polymer surface by repeated irradiation using a nanosecond pulsed laser operating in the UV and visible region in order to obtain nanoscale-controlled functionality. By using a combination of pulses at different wavelengths and sequential irradiation with different polarization orientations, it is possible to obtain different geometries of nanostructures, in particular linear gratings, grids and arrays of nanodots. We use this experimental approach to nanostructure the semiconductor polymer poly(3-hexylthiophene) (P3HT) and the ferroelectric copolymer poly[(vinylidenefluoride-co-trifluoroethylene] (P(VDF-TrFE)) since nanogratings in semiconductor polymers, such as P3HT and nanodots, in ferroelectric systems are viewed as systems with potential applications in organic photovoltaics or non-volatile memories.

Piezoelectric polymer nanofibers for pressure sensors and their applications in human activity monitoring

Miniaturized, wearable and self-powered sensors are crucial for applications in artificial intelligence, robotics, healthcare, and communication devices. In particular, piezoelectric polymer-based sensing systems have the advantages of light weight, large piezoelectricity and mechanical flexibility, offering great opportunities in flexible and stretchable electronic devices. Herein, free-standing large-size nanofiber (NF) membranes have been fabricated by an electrospinning technique. Our results show that the as-synthesized P(VDF–TrFE) NFs are pure β-phase and exhibit excellent mechanical and thermal properties. Besides having high sensitivity and operational stability, the fibrous sensor can generate remarkable electrical signals from applied pressure, with an output voltage of 18.1 V, output current of 0.177 μA, and power density of 22.9 μW cm⁻². Moreover, such sensors also produce significant electrical performance of up to a few volts under human mechanical stress, thereby allowing for the monitoring of biomechanical movement of the human foot, elbow, and finger. Our study sheds light onto the use of piezoelectric polymers for flexible self-powered sensing electronics and wearable devices.

Miniaturized, wearable and self-powered sensors are crucial for applications in artificial intelligence, robotics, healthcare, and communication devices.

A conducting atomic force microscopy study of conducting filament nanobits in the epitaxial NiO thin film prepared precisely controlled by the oxidation time of the single crystalline Ni substrates

We report on the formation of conducting filament (CF) nanodots and the resistive random access memory (RRAM) characteristics of epitaxial NiO thin films with good crystallinity obtained by oxidation of the single crystal Ni substrates. The thickness of the epitaxial NiO thin films with good crystallinity was precisely controlled by the oxidation time. The local current mapping using conducting atomic force microscope (CAFM) showed that the NiO thin films had uniform resistance without conducting defects inside. In particular, it was confirmed that CF nanodots with a diameter of several nanometers in the 5-nm-thick NiO thin film and the storage density of about 16.7 Tbit/in² was achieved by arranging the CF nanodots.

In2O3 Nanowire Field-Effect Transistors with Sub-60 mV/dec Subthreshold Swing Stemming from Negative Capacitance and Their Logic Applications

Heat dissipation is a key issue for scaling metal-oxide-semiconductor field-effect transistors (MOSFETs). The Boltzmann distribution of electrons imposes a physical limit on the subthreshold swing (SS), which impedes both the reduction of the switching energy and the further increase of the device density. The negative capacitance effect is proposed to rescue MOSFETs from this phenomenon called "Boltzmann tyranny". Herein, we report In₂O₃ nanowire (NW) transistors with SS values in the sub-60 mV/dec region, which utilize the ferroelectric P(VDF-TrFE) as the dielectric layer. An ultralow SS down to ∼10 mV/dec is observed and spans over 5 orders of magnitude in the drain current. Meanwhile, a high on/off ratio of more than 10⁸ and a transconductance ( g_m) of 2.3 μS are obtained simultaneously at V_d = 0.1 V. The results can be understood by the "voltage amplification" effect induced from the negative capacitance effect. Moreover, the steep slope FET-based inverters indicate a high voltage gain of 41.6. In addition to the NOR and NAND gates, the Schmitt trigger inverters containing only one steep slope FET are demonstrated. This work demonstrates an avenue for low-power circuit design with a steep SS.

Single-Walled Carbon Nanotube Dominated Micron-Wide Stripe Patterned-Based Ferroelectric Field-Effect Transistors with HfO2 Defect Control Layer

Ferroelectric field-effect transistors (FeFETs) with single-walled carbon nanotube (SWCNT) dominated micron-wide stripe patterned as channel, (Bi,Nd)₄Ti₃O₁₂ films as insulator, and HfO₂ films as defect control layer were developed and fabricated. The prepared SWCNT-FeFETs possess excellent properties such as large channel conductance, high on/off current ratio, high channel carrier mobility, great fatigue endurance performance, and data retention. Despite its thin capacitance equivalent thickness, the gate insulator with HfO₂ defect control layer shows a low leakage current density of 3.1 × 10^-9 A/cm² at a gate voltage of - 3 V.

Fabrication of durable and flexible single-walled carbon nanotube transparent conductive films

Highly flexible, durable, and transparent conducting films are fabricated from the de-bundled SWCNTs in aqueous solutions of SPES with high conductivity (125 Ω sq⁻¹) and good transmittance (87%) without adopting any binder or post treatment techniques.

A high performance triboelectric nanogenerator for self-powered non-volatile ferroelectric transistor memory

We demonstrate an integrated module of self-powered ferroelectric transistor memory based on the combination of a ferroelectric FET and a triboelectric nanogenerator (TENG). The novel TENG was made of a self-assembled polystyrene nanosphere array and a poly(vinylidene fluoride) porous film. Owing to this unique structure, it exhibits an outstanding performance with an output voltage as high as 220 V per cycle. Meanwhile, the arch-shaped TENG is shown to be able to pole a bulk ferroelectric 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 (PMN-PT) single crystal directly. Based on this effect, a bottom gate ferroelectric FET was fabricated using pentacene as the channel material and a PMN-PT single crystal as the gate insulator. Systematic tests illustrate that the ON/OFF current ratio of this transistor memory element is approximately 10(3). More importantly, we demonstrate the feasibility to switch the polarization state of this FET gate insulator, namely the stored information, by finger tapping the TENG with a designed circuit. These results may open up a novel application of TENGs in the field of self-powered memory systems.

Organic Electronic Memory Devices

With the rapid development of the electronics industry in recent years, information technology devices, such as personal computers, mobile phones, digital cameras and media players, have become an essential part of our daily life. From both the technological and economic points of view, the development of novel information storage materials and devices has become an emergent issue facing the electronics industry. Due to the advantages of good scalability, flexibility, low cost, ease of processing, 3D-stacking capability and high capacity for data storage, organic-based electrical memory devices have been promising alternatives or supplementary devices to conventional inorganic semiconductor-based memory technology. The basic concepts and historical development of electronic memory devices are first presented. The following section introduces the structures and switching mechanisms of organic electronic memory devices classified as transistors, capacitors and resistors. Subsequently, the progress in the field of organic-based memory materials and devices is systematically summarized and discussed. Finally, the challenges posed to the development of novel organic electronic memory devices are summarized.

Ultralow-power non-volatile memory cells based on P(VDF-TrFE) ferroelectric-gate CMOS silicon nanowire channel field-effect transistors

Nanowire-based ferroelectric-complementary metal-oxide-semiconductor (NW FeCMOS) nonvolatile memory devices were successfully fabricated by utilizing single n- and p-type Si nanowire ferroelectric-gate field effect transistors (NW FeFETs) as individual memory cells. In addition to having the advantages of single channel n- and p-type Si NW FeFET memory, Si NW FeCMOS memory devices exhibit a direct readout voltage and ultralow power consumption. The reading state power consumption of this device is less than 0.1 pW, which is more than 10(5) times lower than the ON-state power consumption of single-channel ferroelectric memory. This result implies that Si NW FeCMOS memory devices are well suited for use in non-volatile memory chips in modern portable electronic devices, especially where low power consumption is critical for energy conservation and long-term use.

Fabrication of flexible, transparent and conductive films from single-walled carbon nanotubes with high aspect ratio using poly((furfuryl methacrylate)-co-(2-(dimethylamino)ethyl methacrylate)) as a new polymeric dispersant

We synthesized poly((furfuryl methacrylate)-co-(2-(dimethylamino)ethyl methacrylate)) (p(FMA-co-DMAEMA)) for the dispersion of single-walled carbon nanotubes (SWCNTs) while maintaining their high aspect ratios. The nanotubes' length and height were 2.0 μm and 2 nm, as determined by transmission electron microscopy and atomic force microscopy, respectively. Transparent conductive films (TCFs) were fabricated by individually dispersed long SWCNTs onto a flexible polyethylene terephthalate substrate. The sheet resistance (Rs) was 210 Ω □(-1) with 81% transmittance at a wavelength of 550 nm. To reduce their Rs, the TCFs were treated with HNO3 and SOCl2. After treatment, the TCFs had an Rs of 85.75 Ω □(-1) at a transmittance of 85%. The TCFs exhibited no appreciable change over 200 repeated bending cycles. Dispersing SWCNTs with this newly synthesized polymer is an effective way to fabricate a transparent, highly conductive and flexible film.

Flexible ferroelectric polymer devices based on inkjet-printed electrodes from nanosilver ink

High-quality silver (Ag) patterns were inkjet-printed with nanosilver ink on a flexible polyethylene terephthalate (PET) substrate. All-solution-processed flexible ferroelectric polymer devices that use inkjet-printed Ag to create their bottom and top electrodes were demonstrated. The active layer, a poly (vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) thin film, was spin-coated from solution. The devices have a remanent polarization of 8.03 μC cm(-2) and a coercive field of 68.5 MV m(-1), which is comparable to the device with evaporated-Ti electrodes on a silicon substrate. Based on the results presented in this paper, mass production of flexible ferroelectric devices is predictable.

Ordered arrays of a defect-modified ferroelectric polymer for non-volatile memory with minimized energy consumption

Ferroelectric polymers are among the most promising materials for flexible electronic devices. Highly ordered arrays of the defect-modified ferroelectric polymer P(VDF-TrFE-CFE) (poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene)) are fabricated by nanoimprint lithography for nonvolatile memory application. The defective CFE units reduce the coercive field to one-fifth of that of the un-modified P(VDF-TrFE), which can help minimize the energy consumption and extend the lifespan of the device. The nanoimprint process leads to preferable orientation of polymer chains and delicately controlled distribution of the defects, and thus a bi-stable polarization that makes the memory nonvolatile, as revealed by the pulsed polarization experiment.

Low-Programmable-Voltage Nonvolatile Memory Devices Based on Omega-shaped Gate Organic Ferroelectric P(VDF-TrFE) Field Effect Transistors Using p-type Silicon Nanowire Channels

A facile approach was demonstrated for fabricating high-performance nonvolatile memory devices based on ferroelectric-gate field effect transistors using a p-type Si nanowire coated with omega-shaped gate organic ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)). We overcame the interfacial layer problem by incorporating P(VDF-TrFE) as a ferroelectric gate using a low-temperature fabrication process. Our memory devices exhibited excellent memory characteristics with a low programming voltage of ±5 V, a large modulation in channel conductance between ON and OFF states exceeding 10⁵, a long retention time greater than 3 × 10⁴ s, and a high endurance of over 10⁵ programming cycles while maintaining an I _ON/I _OFF ratio higher than 10².

Non-volatile ferroelectric memory with position-addressable polymer semiconducting nanowire

One-dimensional nanowires (NWs) have been extensively examined for numerous potential nano-electronic device applications such as transistors, sensors, memories, and photodetectors. The ferroelectric-gate field effect transistors (Fe-FETs) with semiconducting NWs in particular in combination with ferroelectric polymers as gate insulating layers have attracted great attention because of their potential in high density memory integration. However, most of the devices still suffer from low yield of devices mainly due to the ill-control of the location of NWs on a substrate. NWs randomly deposited on a substrate from solution-dispersed droplet made it extremely difficult to fabricate arrays of NW Fe-FETs. Moreover, rigid inorganic NWs were rarely applicable for flexible non-volatile memories. Here, we present the NW Fe-FETs with position-addressable polymer semiconducting NWs. Polymer NWs precisely controlled in both location and number between source and drain electrode were achieved by direct electrohydrodynamic NW printing. The polymer NW Fe-FETs with a ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) exhibited non-volatile ON/OFF current margin at zero gate voltage of approximately 10(2) with time-dependent data retention and read/write endurance of more than 10(4) seconds and 10(2) cycles, respectively. Furthermore, our device showed characteristic bistable current hysteresis curves when being deformed with various bending radii and multiple bending cycles over 1000 times.

Tunable threshold voltage of an n-type Si nanowire ferroelectric-gate field effect transistor for high-performance nonvolatile memory applications

We successfully fabricated ferroelectric-gate field effect transistor (FEFET)-based nonvolatile memory devices using an n-type Si nanowire coated with omega-shaped-gate organic ferroelectric poly(vinylidene fluoride-trifluoroethylene) via a low-temperature fabrication process. Our FEFET memory devices with controllable threshold voltage via adjustment of the doping concentration exhibit excellent memory characteristics with ultra-low ON state power dissipation (≤3 nW), a large modulation in channel conductance between the ON and OFF states exceeding 10(5), a long retention time of over 3 × 10(4) s and a high endurance of over 10(5) programming cycles whilst maintaining an I ON/I OFF ratio higher than 10(3). This result may be promising for next-generation nonvolatile memory on flexible substrate applications.

Organic field-effect transistor memory devices using discrete ferritin nanoparticle-based gate dielectrics

Organic field-effect transistor (OFET) memory devices made using highly stable iron-storage protein nanoparticle (NP) multilayers and pentacene semiconductor materials are introduced. These transistor memory devices have nonvolatile memory properties that cause reversible shifts in the threshold voltage (Vth ) as a result of charge trapping and detrapping in the protein NP (i.e., the ferritin NP with a ferrihydrite phosphate core) gate dielectric layers rather than the metallic NP layers employed in conventional OFET memory devices. The protein NP-based OFET memory devices exhibit good programmable memory properties, namely, large memory window ΔVth (greater than 20 V), a fast switching speed (10 μs), high ON/OFF current ratio (above 10(4)), and good electrical reliability. The memory performance of the devices is significantly enhanced by molecular-level manipulation of the protein NP layers, and various biomaterials with heme Fe(III) /Fe(II) redox couples similar to a ferrihydrite phosphate core are also employed as charge storage dielectrics. Furthermore, when these protein NP multilayers are deposited onto poly(ethylene naphthalate) substrates coated with an indium tin oxide gate electrode and a 50-nm-thick high-k Al2 O3 gate dielectric layer, the approach is effectively extended to flexible protein transistor memory devices that have good electrical performance within a range of low operating voltages (<10 V) and reliable mechanical bending stability.

Ferroelectric memory based on nanostructures

In the past decades, ferroelectric materials have attracted wide attention due to their applications in nonvolatile memory devices (NVMDs) rendered by the electrically switchable spontaneous polarizations. Furthermore, the combination of ferroelectric and nanomaterials opens a new route to fabricating a nanoscale memory device with ultrahigh memory integration, which greatly eases the ever increasing scaling and economic challenges encountered in the traditional semiconductor industry. In this review, we summarize the recent development of the nonvolatile ferroelectric field effect transistor (FeFET) memory devices based on nanostructures. The operating principles of FeFET are introduced first, followed by the discussion of the real FeFET memory nanodevices based on oxide nanowires, nanoparticles, semiconductor nanotetrapods, carbon nanotubes, and graphene. Finally, we present the opportunities and challenges in nanomemory devices and our views on the future prospects of NVMDs.

Carbon nanotube memory by the self-assembly of silicon nanocrystals as charge storage nodes

A memory structure based on self-aligned silicon nanocrystals (Si NCs) grown over Al(2)O(3)-covered parallel-aligned carbon nanotubes (CNTs) by gas source molecular beam epitaxy is reported. Electrostatic force microscopy characterizations directly prove the charging and discharging of discrete NCs through the Al(2)O(3) layer covering the CNTs. A CNT field effect transistor based on the NC/CNT structure is fabricated and characterized, demonstrating evident memory characteristics. Direct tunneling and Fowler-Nordheim tunneling phenomena are observed at different programming/erasing voltages. Retention is demonstrated to be on the order of 10(4) s. Although there is still plenty of room to enhance the performance, the results suggest that CNT-based NC memory with diminutive CNTs and NCs could be an alternative structure to replace traditional floating gate memory.