Endurance Characteristics Research Articles

Enhanced Ferroelectricity in Hf‐Based Ferroelectric Device with ZrO2 Regulating Layer

AbstractHfAlO film‐based ferroelectric memory is a strong contender for the next‐generation nonvolatile memories. However, the remanent polarization intensity of HfAlO films is small compared to other Hf‐based ferroelectric films at low annealing temperatures. In order to further improve the remnant polarization of the device, the ferroelectric memory with metal‐ferroelectric‐metal structure using ZrO2 as the regulating layer (RL) is designed and fabricated. Experimental results show that the device with the ZrO2 regulating layer exhibits triple enhancement, which may be due to the fact that ZrO2 RL has an effect on the enhancement of the ferroelectric phase. In addition, the device with ZrO2 regulating layer exhibits a superior ON/OFF conductance ratio, endurance, and retention characteristics, demonstrating potential for application to memory. This work provides an effective way to improve the ferroelectricity in HfAlO films at low annealing temperatures.

Improved ferroelectric and endurance properties of Hf0.5Zr0.5O2 thin films by a replacement indium-tin-oxide top electrode process

The ferroelectricity in HfO2-based thin films offers a potential alternative to non-volatile memories and logic devices. Special top electrodes such as nitride metal serving as a mechanical capping layer are used to induce the ferroelectricity in HfO2, which hinders the extensive application of HfO2 ferroelectrics. Indium-tin-oxide (ITO) is a transparent, highly conductive electrode or semiconductor, widely used in microelectronics. Here, we comprehensively investigated the impact of ITO electrodes on the ferroelectric polarization and endurance properties of Hf0.5Zr0.5O2 (HZO) thin films. The remnant polarization (2P r) of ∼23.6 μC cm−2 was obtained for the ITO#/HZO/TiN capacitors with an electrode-replacement technique. The relatively enlarged coercive field of ±1.25 MV cm−1 was observed in the ITO/HZO/TiN capacitors compared with TiN/HZO/TiN structures (±0.94 MV cm−1). This might be owing to the work function difference between top ITO and bottom TiN electrodes, as well as the depletion effect of the ITO interface. Furthermore, stable endurance characteristics after 108 cycles were obtained in the ITO#/HZO/TiN capacitors. This work provides a new strategy to obtain excellent ferroelectricity and good reliability in HfO2-based ferroelectric thin film integration with other oxide electrodes.

Linear and symmetric synaptic weight update characteristics by controlling filament geometry in oxide/suboxide HfOx bilayer memristive device for neuromorphic computing

Memristive devices have been explored as electronic synaptic devices to mimic biological synapses for developing hardware-based neuromorphic computing systems. However, typical oxide memristive devices suffered from abrupt switching between high and low resistance states, which limits access to achieve various conductance states for analog synaptic devices. Here, we proposed an oxide/suboxide hafnium oxide bilayer memristive device by altering oxygen stoichiometry to demonstrate analog filamentary switching behavior. The bilayer device with Ti/HfO2/HfO2−x(oxygen-deficient)/Pt structure exhibited analog conductance states under a low voltage operation through controlling filament geometry as well as superior retention and endurance characteristics thanks to the robust nature of filament. A narrow cycle-to-cycle and device-to-device distribution were also demonstrated by the filament confinement in a limited region. The different concentrations of oxygen vacancies at each layer played a significant role in switching phenomena, as confirmed through X-ray photoelectron spectroscopy analysis. The analog weight update characteristics were found to strongly depend on the various conditions of voltage pulse parameters including its amplitude, width, and interval time. In particular, linear and symmetric weight updates for accurate learning and pattern recognition could be achieved by adopting incremental step pulse programming (ISPP) operation scheme which rendered a high-resolution dynamic range with linear and symmetry weight updates as a consequence of precisely controlled filament geometry. A two-layer perceptron neural network simulation with HfO2/HfO2−x synapses provided an 80% recognition accuracy for handwritten digits. The development of oxide/suboxide hafnium oxide memristive devices has the capacity to drive forward the development of efficient neuromorphic computing systems.

Multi-Level Resistive Al/Ga2O3/ITO Switching Devices with Interlayers of Graphene Oxide for Neuromorphic Computing.

Recently, resistive random access memory (RRAM) has been an outstanding candidate among various emerging nonvolatile memories for high-density storage and in-memory computing applications. However, traditional RRAM, which accommodates two states depending on applied voltage, cannot meet the high density requirement in the era of big data. Many research groups have demonstrated that RRAM possesses the potential for multi-level cells, which would overcome demands related to mass storage. Among numerous semiconductor materials, gallium oxide (a fourth-generation semiconductor material) is applied in the fields of optoelectronics, high-power resistive switching devices, and so on, due to its excellent transparent material properties and wide bandgap. In this study, we successfully demonstrate that Al/graphene oxide (GO)/Ga2O3/ITO RRAM has the potential to achieve two-bit storage. Compared to its single-layer counterpart, the bilayer structure has excellent electrical properties and stable reliability. The endurance characteristics could be enhanced above 100 switching cycles with an ON/OFF ratio of over 103. Moreover, the filament models are also described in this thesis to clarify the transport mechanisms.

Sodium–tungsten–titanium phosphate glasses: an investigation of the structure, chemical endurance, and kinetic characteristics

Sodium–tungsten–titanium phosphate glasses: an investigation of the structure, chemical endurance, and kinetic characteristics

Modulating the Performance of MoS2-Based Nanocrystal Memory via Ag Ion Implantation

Nonvolatile flash memory is an important component of the semiconductor memory device, which is widely used in a variety of portable electronic equipment. As traditional flash memory approaches its physical limit, reduced reliability and performance degradation have become unavoidable. Two-dimensional (2D) layered materials exhibit excellent electronic properties even at the atomic level and have been considered as a promising development direction for future flash memory. Here, we report a MoS2-based Ag nanocrystal memory. The fabricated memory device can form the memory stack in one step through metal ion implantation, omitting tedious deposition steps compared to the conventional process. The fabricated silver nanocrystal memory exhibits a 9 V memory window and a high ON/OFF current ratio (>107). In addition, the device also exhibits good endurance characteristics of more than 104 cycles. The ion implantation technology and the 2D nature of the channel can be used for the fabrication of flexible nanoelectronic memory devices with large-scale integration.

Reliability Test of Inkjet-Printable Silver Conductive Ink

Inkjet printing is a promising technique for fabricating printed electronics. This technique acquires the utilization of conductive ink to form a fine and thin resolution conductive structure on a flexible substrate. The challenges are to design a stable conductive ink with a controlled properties to prevent nozzle clogging. Furthermore, a fine structure construction often demonstrated poor device performance due low mechanical durability. In this work, we have characterized morphology of the newly developed inkjet-printable nanosilver conductive ink (Mi-Ag) in our laboratory. The ink shows a stable colloidal ink zeta potential of-79.1 mV with nanoparticle size less than 100 nm properties has been tailored for compatibility with inkjet printing of conductive pattern on polyethylene terephthalate (PET) flexible substrate. It has been ascertained that the flexible electronic form factor affects the quality of the physical and electrical properties of printed pattern and the device performance. Hence, the bending test of the printed RFID patterns fabricated with different layer of thicknesses was investigated. Electrical properties of the samples were monitored by in-situ conductivity and resistivity measurement under cyclic bending testing. Pattern with thinnest layer of 1.31μm (1X) had the smallest electrical properties percentage drop (38.4%) at 12,000 bending cycles due to the fact that in thick layer, the interparticle network started to change during bending and became weaker due to the large amount of the particles in the dense printed layer. In contrast, printed device exhibited minimal increase in resistivity. Consequently the particle gap increased which allowed the movement of electrons, leading to the increased of electrical resistance. The device endurance characteristic is crucial to satisfy future design requirement of flexible electronic applications.

Role of Postdeposition Annealing and Doping with Si and Al Impurities in the Formation of HfxSi1–xO2 at the SiO2/FE:HfO2 Interface in a Ferroelectric Field-Effect Transistor

Characterization of the composition and extension of the SiO2/HfO2 interface in the model systems Si-sub./SiO2 (7.5 nm)/FE:HfO2 (9.5 nm)/TiN (9 nm) for standard impurity concentrations and annealing temperatures (Si 3.6%, 1000 °C; Al 5.5%, 850 °C) were carried out using X-ray photoelectron spectroscopy with high kinetic energies. In addition, the crystalline properties of HfO2 were characterized by transmission electron microscopy and grazing incidence X-ray diffraction depending on the type of impurity. Formation of HfxSi1–xO2 at the SiO2/HfO2 interface was revealed, and the dependence of its thickness dsilicate and stoichiometry X on the formation of the tetragonal phase P42/nmc of HfO2 was established. It is shown that doping with aluminum followed by annealing prevents the formation of a tetragonal phase and reduces both dsilicate and X by about 20% (with respect to undoped HfO2 annealed at the same temperature), in contrast to doping with Si followed by annealing, which practically does not affect dsilicate and X. The results obtained are important for the problem of imbalance in the voltage drop across the gate oxides stack in a ferroelectric field-effect transistor and improvement of its endurance and retention characteristics.

Improved Endurance of Ferroelectric Hf0.5Zr0.5O2 Using Laminated-Structure Interlayer.

In this article, the endurance characteristic of the TiN/HZO/TiN capacitor was improved by the laminated structure of a ferroelectric Hf0.5Zr0.5O2 thin film. Altering the HZO deposition ratio, the laminated-structure interlayer was formed in the middle of the HZO film. Although small remanent polarization reduction was observed in the capacitor with a laminated structure, the endurance characteristic was improved by two orders of magnitude (from 106 to 108 cycles). Moreover, the leakage current of the TiN/HZO/TiN capacitor with the laminated-structure interlayer was reduced by one order of magnitude. The reliability enhancement was proved by the Time-Dependent Dielectric Breakdown (TDDB) test, and the optimization results were attributed to the migration inhibition and nonuniform distribution of oxygen vacancies. Without additional materials and a complicated process, the laminated-structure method provides a feasible strategy for improving HZO device reliability.

Ferroelectric Tunnel Thin-Film Transistor for Synaptic Applications

In this work, a ferroelectric tunnel thin-film transistor (FeT-TFT) with polycrystalline-silicon (poly-Si) channel and ferroelectric HfZrOx gate dielectric is demonstrated with analog memory characteristics for the application of synaptic devices. The FeT-TFT exhibits a much lower conduction current of ∼0.032 times in transfer characteristics and maximum conductance (Gd) of ∼ 0.14 to 0.2 times in potentiation and depression operation than the FeTFT due to FeT-TFT’s carrier transport mechanism: interband tunneling. This work employed pulse widths of 75, 150, and 300 ns to modulate Gd, and it was found that using a pulse width of 75 ns could achieve low asymmetry ∼ 1 and high Gd ratio ∼ 20.63 under the consideration of operation speed. When the pulse time is increased, the potentiation and depression voltages can be significantly decreased to maintain the low asymmetry, but the Gd ratio is also reduced. In addition, the endurance characteristic of poly-Si FeT-TFT is found to be strongly related to the degradation effect of subthreshold swing due to the dynamic stress effect in the endurance measurement. This result reveals that the reliability of ferroelectric devices is not only owing to the degradation of the remanent polarization.

Digital and analog resistive switching in Lu-doped piezoelectric [formula omitted] film

Recently, in the field of artificial intelligence, neuromorphic devices have received significant attention for building artificial neural networks. Nano-scale resistive random access memory (RRAM) is one of the emerging electrical components for neuromorphic computing. In the present study, the synaptic characteristics are investigated in the piezoelectric BiFe1−xLuxO3 (BFLO) and Bi1−xLuxFeO3 (BLFO) (x = 0.05) based RRAM devices in a vertical configuration. Both devices show bipolar resistive switching behavior with good endurance characteristics. However, analog switching with potentiation and depression response is observed in Ag/BFLO/FTO device. The change in resistance and leakage current flow across the device is explained by the space charge limiting current conduction mechanism with regard to thermally generated and injected charge carriers. Both films possess strong electro-mechanical response with the ferroelectric and ferro-elastic domain walls oriented along 710, 1090, and 1800 directions. The electro-mechanical response and resistive switching properties make the materials viable for sensing, energy harvesting, and non-volatile memory technology. Moreover, the BFLO-based synaptic device has potential application in neuromorphic computation.

Highly Enhanced Polarization Switching Speed in HfO2‐based Ferroelectric Thin Films via a Composition Gradient Strategy

AbstractThe next‐generation semiconductor memories are essentially required for the advancements in modern electronic devices. Ferroelectric memories by HfO2‐based ferroelectric thin films (FE‐HfO2) have opened promising directions in recent years. Nevertheless, improving the polarization switching speed of FE‐HfO2 remains a critical task. In this study, it is demonstrated that the composition‐graded Hf1‐xZrxO2 (HZO) ferroelectric thin film has more than two times faster polarization switching speed than the conventional composition‐uniform one. Meanwhile, it has excellent ferroelectricity and improved endurance characteristics. It is also discovered that when the HZO thin film has a gradient composition, the polarization‐switching dynamics shifts from the nucleation‐limited‐switching mechanism to the domain‐wall growth mechanism. Moreover, the transition of switching dynamics is responsible for the faster speed and better endurance of the composition‐graded HZO thin film. These findings not only reveal the physical mechanisms of this material system but also provide a new strategy for memory devices having faster speed and higher endurance.

Deep-trap dominated degradation of the endurance characteristics in OFET memory with polymer charge-trapping layer

Organic field-effect transistors (OFETs) with polymer charge-trapping dielectric, which exhibit many advantages over Si-based memory devices such as low cost, light weight, and flexibility, still suffer challenges in practical application due to the unsatisfied endurance characteristics and even the lack of fundamental of behind mechanism. Here, we revealed that the degradation of endurance characteristics of pentacene OFET with poly(2-vinyl naphthalene) (PVN) as charge-storage layer is dominated by the deep hole-traps in PVN by using the photo-stimulated charge de-trapping technique with the fiber-coupled monochromatic-light probes. The depth distribution of hole-traps in PVN film of pentacene OFET is also provided.

Nanostructures Stacked on Hafnium Oxide Films Interfacing Graphene and Silicon Oxide Layers as Resistive Switching Media.

SiO2 films were grown to thicknesses below 15 nm by ozone-assisted atomic layer deposition. The graphene was a chemical vapor deposited on copper foil and transferred wet-chemically to the SiO2 films. On the top of the graphene layer, either continuous HfO2 or SiO2 films were grown by plasma-assisted atomic layer deposition or by electron beam evaporation, respectively. Micro-Raman spectroscopy confirmed the integrity of the graphene after the deposition processes of both the HfO2 and SiO2. Stacked nanostructures with graphene layers intermediating the SiO2 and either the SiO2 or HfO2 insulator layers were devised as the resistive switching media between the top Ti and bottom TiN electrodes. The behavior of the devices was studied comparatively with and without graphene interlayers. The switching processes were attained in the devices supplied with graphene interlayers, whereas in the media consisting of the SiO2-HfO2 double layers only, the switching effect was not observed. In addition, the endurance characteristics were improved after the insertion of graphene between the wide band gap dielectric layers. Pre-annealing the Si/TiN/SiO2 substrates before transferring the graphene further improved the performance.

Understanding the Resistive Switching Mechanism of 2-D RRAM: Monte Carlo Modeling and a Proposed Application for Reliability Research

The 2-D materials have become promising candidates for resistive random access memory (RRAM) devices as more unique resistive switching (RS) characteristics have recently been revealed. However, endurance is a major challenge for industrialization. Unlike the well-developed and recognized conductive filament (CF) model for oxide-based RRAM, the RS mechanism for 2-D RRAM is not well understood. In this article, we first review the dissociation–diffusion–adsorption (DDA) model and the cluster model proposed in previous works on monolayer 2-D RRAM devices. The use of a Monte Carlo (MC) simulator for multilayer 2-D RRAM devices to expand the application of DDA and cluster models is then discussed. A simulator was designed to provide an intuitive physical view by visualizing the stochastic behaviors of the RS process in multilayer 2-D RRAM devices. By comparing the simulated results with experimental data, the endurance characteristic was found to be mainly determined by the formation and collapse of an effective switching layer. We also found that the thickness of the effective switching layer is independent of the total thickness of the multilayer 2-D material and the initial status of the device, which is consistent with the experimental observations. The model and results discussed in this work provide additional insights and guidance for improving the reliability of 2-D RRAM devices.

Highly hard modified Novikov gears for special purpose drive gearboxes

A comparison of the technical and economic characteristics of the drive gearbox of oil pumping units with different versions of modified Novikov gears with thermally improved and highly hard teeth is considered. The advantages of the latter are shown. Keywords: Novikov gearing, thermally improved teeth, highly hard teeth, contact endurance, bending endurance, technical and economic characteristics of the gearbox. vkorotkin@sfedu.ru

The improvement of endurance characteristics in a superlattice-like material-based phase change device

Improvement of endurance characteristics has been a hot area of phase-change memoryresearch. The properties of a phase-change material are believed to play an important role in device endurance. Repeated SET–RESET operation always leads to material failure problems, such as composition deviation and phase separation. Moreover, the quality of the electrode and the electrode contact also determine the endurance characteristics. In this study, C nanolayers were periodically inserted into the phase-change material Ge2Sb2Te5 (GST) to fabricate a superlattice-like (SLL) structure. Although some of C bonded with some of the Ge, Sb and Te atoms, more C atoms prefer nanometer-scale clusters at the grain boundary in the SLL film. The typical local configuration of GST was unchanged when artificial C nanolayers were inserted. Transmission electron microscopy experiments revealed that the bonded C atoms and nanometer-scale C clusters may occupy the spontaneously created holes and defects, preventing composition deviation of the phase-change material and prolonging the electrode service life. The contact surface between the phase-change material and the electrode is also improved. As a result, we found that the endurance cycle could be improved by up to 106 for a GST/C SLL film-based device.

Experimental study of endurance characteristics of Al-doped HfO2 ferroelectric capacitor

In this work, the endurance characteristics of Al-doped HfO2 (HAO)-based metal-ferroelectric-metal (MFM) capacitors (which were annealed at 1000 °C) with various doping concentrations were investigated. The doping concentration was optimized for the high annealing temperature (1000 °C) process. To investigate the impact of cycling pulses on the endurance characteristics of HAO-based MFM capacitor, the rise/fall time (t r/f ) and hold time (th ) for the cycling pulses were varied. Moreover, by adopting the recoverable fatigue process, the endurance characteristics under repetitive wake-up/fatigue processes were studied. The HAO capacitors achieved the remnant polarization (2Pr) of 23.767 μC cm−2 at pristine state under the high annealing temperature. Furthermore, it was demonstrated that the endurance characteristics (∼108 cycles) of the HAO capacitors were comparable to them of other HfO2-based ferroelectric capacitors. Lastly but not least, it turned out that the amount of oxygen and oxygen vacancies in the HAO thin film was dependent of doping concentrations for the film. The impact of oxygen and oxygen vacancies was quantitatively analyzed, in detail, with TEM, XPS and GIXRD analysis.

Graphene Oxide-Based Memristive Logic-in-Memory Circuit Enabling Normally-Off Computing.

Memristive logic-in-memory circuits can provide energy- and cost-efficient computing, which is essential for artificial intelligence-based applications in the coming Internet-of-things era. Although memristive logic-in-memory circuits have been previously reported, the logic architecture requiring additional components and the non-uniform switching of memristor have restricted demonstrations to simple gates. Using a nanoscale graphene oxide (GO) nanosheets-based memristor, we demonstrate the feasibility of a non-volatile logic-in-memory circuit that enables normally-off in-memory computing. The memristor based on GO film with an abundance of unusual functional groups exhibited unipolar resistive switching behavior with reliable endurance and retention characteristics, making it suitable for logic-in-memory circuit application. In a state of low resistance, temperature-dependent resistance and I-V characteristics indicated the presence of a metallic Ni filament. Using memristor-aided logic (MAGIC) architecture, we performed NOT and NOR gates experimentally. Additionally, other logic gates such as AND, NAND, and OR were successfully implemented by combining NOT and NOR universal logic gates in a crossbar array. These findings will pave the way for the development of next-generation computer systems beyond the von Neumann architecture, as well as carbon-based nanoelectronics in the future.

Uniform resistive switching and highly stable synaptic characteristics of HfOx sandwiched TaOx-based memristor for neuromorphic system

Emerging nanoscale devices, including memristors, have been extensively studied to implement biological synaptic functions such as learning and plasticity, which are the fundamental building blocks of brain-inspired neuromorphic computing. The memristor with analog switching ability exhibits linear tuning of weight during neural network training is a desirable synaptic device behavior. The importance of inserting a HfOx sandwiched layer in a TaOx/HfOx/TaOx memristor is to achieve analog set/reset operation along with improved spatial/temporal switching uniformity. The optimal resistive switching (RS) behavior can be attributed to asymmetric oxygen vacancy distribution in the stacked structure leading to the formation of an hourglass-shaped conductive filament. Furthermore, confining filament formation/rapture in the narrow fixed region displays superior endurance characteristics (dc cycles >2000 and ac cycles > 106) and uniform resistive switching with the set (reset) voltage variation constrained to 1.8 (2.9) %. Paired-pulse facilitation (PPF), a form of short-term synaptic plasticity is stimulated to replicate bio-synapse behavior. The stable long-term potentiation (LTP) and depression (LTD) behavior for more than 1000 epochs (>105 pulses) with excellent symmetry and linearity is achieved with 50 ns voltage pulse stimulation. The pattern recognition accuracy of 93% was achieved for an image of size 10 × 10 pixels after 13 epochs by deploying 100 synapses in Hopfield Neural Network (HNN) simulation. This comprehensive study demonstrates that the HfOx-inserted TaOx memristor has tremendous potential for application in future neuromorphic computing.