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The decrease in the measured dielectric constant of sputter-deposited (Ba, Sr)TiO[sub 3] thin films having Pt electrodes with decreasing dielectric film thickness was analyzed by a combination of theories regarding the finite charge-screening length of the metal electrode and the intrinsic-dead layer of the dielectric surface. It was found that the decreasing dielectric constant was mainly due to the metal electrode capacitance rather than the intrinsic-dead-layer capacitance. The almost film-thickness-independent dielectric constant of the (Ba, Sr)TiO[sub 3] thin films with conducting oxide electrodes, IrO[sub 2] and SrRuO[sub 3], when the dielectric film thickness >20 nm, was attributed to the very high capacitance values of the charge-screening layer of the oxide electrodes. The very high capacitance value appeared to originate from the strain-induced high dielectric constant of the oxide electrodes. [ABSTRACT FROM AUTHOR]

Grazing incidence x-ray diffraction reveals that conventional post-deposition-annealed ZrO2 and in situ crystallized (by local epitaxy) ZrO2 thin films (<15 nm) have different internal strain states. A comparison between single- and two-step grown films enables the diverse strain components to be discretely identified. In particular, thickness-dependent intrinsic growth strain is unevenly distributed within the film according to the Volmer–Weber growth. Furthermore, extrinsic thermal strain, locally present in the annealed seed layer, does not spread over the in situ crystallized upper main layer of the two-step film. Post-deposition annealing of the two-step film renders the strain state identical to the single-step films by imposing thermal strain on the in situ crystallized main layer. Local strains created by diffused aluminum and yttrium dopants are also examined. Since each stress factor plays a vital role in the phase formation and electrical behaviors of ZrO2 and other fluorite-structure films, this method will pave the way for understanding the film's internal strain distribution and accompanying performance engineering. [ABSTRACT FROM AUTHOR]

Presents information on an article which reported variations of the leakage current density of capacitors after annealing. Experimental procedures; Results and discussion; Conclusion.

Presents information on a study which proposed a band model based on the partial depletion model to solve the contradiction on film thickness relationship in platinum electrodes. Experimental procedure; Results and discussion; Conclusion.

Focuses on a comparative study which examined the electrical conduction mechanisms of (Ba0.5Sr0.5)TiO3 thin films on Pt and IrO...electrodes. Information on the electrical conduction properties of bulk perovskite oxides; Details on the study; Discussion on the study.

The effects of in-plane strain on the dielectric constant of the Be0.25Mg0.75O rock salt superlattice are investigated through ab initio thermodynamics calculations. Based on a previous report that the long apical Be–O bond increased the dielectric constant, the in-plane compressive strain dielectric constant is expected to increase the dielectric constant. Unlike the zero-strain case, the apical Mg–O bonds also contribute to the increase in the dielectric constant under compressive strain. However, small Be ions tend to occupy narrow spaces in the MgO-based rock salt structure, which can lead to an increase in dielectric constant even under in-plane tensile strain, depending on the local position of Be ions and its interaction with O ions. At higher temperatures, several configurations under strain showed a significant increase in the dielectric constant due to the elongation of the apical Be–O bond. Considering temperature and strain comprehensively, this study suggests that the Be0.25MgO0.75O superlattice under −2% in-plane compressive strain could be a promising candidate structure for achieving a high-κ value of approximately 30. [ABSTRACT FROM AUTHOR]

Pt or Arsenic (As)-doped polycrystalline-silicon (poly-Si) gate/HfO2 or HfO2-Al2O3/p-type Si metal oxide semiconductor (MOS) capacitors were fabricated using an atomic-layer-deposition technique, and their compatibility with poly-Si gate was investigated using a comparison with the Pt gate. The HfO2-Al2O3 stack film was found to have better As diffusion-blocking properties as a result of the rather thick amorphous interlace layer including Al2O2 than that of the HfO2 film. N+ duped poly-Si gate/HfO2-Al2O3 MOS capacitors had a lower current density of - 1.1 × 10-9 A/cm² at - 1 V resulting in a small hysteresis voltage due to the lower As penetration and thick amophous interface layer. These results suggest that N+ doped poly-Si gate/HfO2-Al2O3, MOS capacitors are compatible with the poly-Si gate, which is also comparable to the Pt gate. [ABSTRACT FROM AUTHOR]

Probabilistic computing can solve complex combinatorial optimization problems more efficiently than conventional deterministic computing. A probabilistic bit (p‐bit) with an n‐p‐n bistable resistor (biristor) is demonstrated for probabilistic computing. It is fabricated on an 8‐inch wafer with complementary metal–oxide–semiconductor (CMOS) compatible technologies. Its stochastic behavior of threshold switching, which is based on the phenomenon of a single transistor latch, provides output with a Boltzmann distribution. The p‐bit is composed of a biristor, a serial resistor, and a comparator. The output probability of the biristor‐based p‐bits shows a sigmoidal relationship with the input voltage, showing typical p‐bit characteristics. Invertible Boolean logic operations with p‐bits are demonstrated, and weighted maximum Boolean satisfiability problems are solved with high energy efficiency and accuracy. The biristor‐based p‐bits with perfect CMOS compatibility show sufficient device stability, demonstrating the possibility of large‐scale integration with a p‐bit array for complex optimization solvers. [ABSTRACT FROM AUTHOR]

The phenomenological Landau–Ginzburg–Devonshire model provides a fundamental background for an understanding of the peculiar charge–voltage behavior of ferroelectric (FE) materials. However, the model cannot explain the polarization behavior of multidomain FE materials. The experimentally observed negative capacitance (NC) effect, which is interpreted as an emergence of the Landau barrier effect, involves particular conceptual difficulty. This work provides a new conceptual framework to explain the quasi‐static NC effect based on the energy formula for a stacked dielectric/ferroelectric (DE/FE) layer structure with the multidomain configuration with arbitrary shape. The presence of such domain configuration causes the energy–displacement curve of the inhomogenous Helmholtz energy term to have negative curvature. This is caused by the stray field between the neighboring domains. The model can be further extended to the DE/FE system with polycrystalline FE grains using the advanced phase‐field analysis. It is determined that the NC effect from the stray field is a universal phenomenon. These models provide quantitative explanations for the previously reported short‐pulse measurement results for various DE/FE material systems, which have lacked accurate interpretations. [ABSTRACT FROM AUTHOR]

This study examined the relationship between the conducting filament resistance and reset voltage during the resistance switching of TiO2 thin films assuming a filament with a conical shape. There was a critical resistance (∼20 Ω) of the set state above and below which the filament responded differently in response to the current. Maintaining a higher set state resistance was more beneficial in achieving a more uniform reset voltage. This filament model coincides well with the localized switching behavior and the recently microscopically observed filament shape. [ABSTRACT FROM AUTHOR]

The frequency dispersion of the dielectric constant of yttrium (Y)-doped (Ba,Sr)TiO3 thin films (Y-BST) in the high-frequency domain (10 kHz–67 GHz) was investigated. In order to remove the substantial parasitic capacitances, inductances, and resistances from the measured impedance data, test samples, short-circuit standard, and open-circuit standard structures were fabricated and their frequency response was measured. Before removing parasitic components, the measured dielectric response showed a rolloff at approximately 4 GHz. However, after circuit calibration, the dielectric constant was almost constant up to 40 GHz where another rolloff was observed. However, this rolloff was due to the uncompensated small parasitic components. Therefore, the dielectric constant of the Y-BST films (170 with a film thickness of 30 nm) showed small frequency dispersion corresponding to the Curie–von Schweidler dispersion, of which the exponent is -0.0131, up to 40 GHz. Furthermore, the decrease of the capacitance was 17% in the frequency range from 10 kHz to 40 GHz. [ABSTRACT FROM AUTHOR]

This study investigated the variations in the dielectric constant with film thickness and measurement temperature of (Ba0.48Sr0.52)TiO3 thin-film capacitors with thicknesses ranging from 65 to 273 nm. The films were prepared by an on-axis rf magnetron sputtering, having Pt top and bottom electrodes. The thicker film showed a higher dielectric constant with a larger temperature dependence of the dielectric constant, and the maximum dielectric constant was observed at a higher temperature. The thickness-dependent dielectric constant at a given measurement temperature was explained by using the previously reported interfacial capacitance model, containing the intrinsic dead layer and electrode polarization. The temperature-dependent dielectric property could be explained using a modified Curie-Weiss (C-W) behavior of the film taking the nonferroelectric interfacial capacitance components into consideration. However, the C-W constant and Curie temperature of the ferroelectric layer must be modified in order to obtain a reasonable interfacial layer thickness. [ABSTRACT FROM AUTHOR]

The electrical conduction behavior of sputter-grown (Ba, Sr)TiO[sub 3](BST) thin films having IrO[sub 2] electrodes were studied under the assumption of a fully accumulated film. In the film-thickness range studied (40-80 nm), the dielectric constants and their electric field dependencies were found to be independent of the film thickness. Contrary to similar BST films grown on Pt electrodes, the leakage current density decreased with increasing film thickness at a given field. The phenomena were explained from the electric-field depression effect inside the film due to the accumulated negative space charges in the films. The leakage current conductions were controlled by the Poole-Frenkel mechanism in the low field whereas it changed to thermionic field emission in the high-field region. The dielectric constant obtained from the Poole-Frenkel fitting was approximately 300, which was in a qualitative agreement with the value obtained from the low-frequency capacitance measurement. The calculated interfacial potential-barrier height at zero volt and effective mass of electrons were 1.03 eV and 0.06m[sub 0], respectively, from the thermionic field emission fittings. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Multi-valued logic has been a significant focus of research in various fields with the advancement of information technology. One approach to realizing ternary logic is integrating of a threshold switching (TS) device with a transistor, but this method often entails a complex fabrication process. This work suggests a ternary gate-connected threshold switching thin-film transistor (TS-TFT) by serially connecting the TS device with a bottom-gate thin-film transistor (TFT). The fabrication process is simplified with a structure that shares electrodes and insulators. Different threshold voltages from TS and TFT devices produce stable multiple states. The Pt/HfO2/TiN TS device has an electronic trapping/detrapping switching mechanism that exhibits low power consumption and high reliability. With the superior electrical performance of an amorphous indium gallium zinc oxide TFT, the TS-TFT has stable endurance. Furthermore, pulse switching and ternary inverter are demonstrated from the practical point of view. [ABSTRACT FROM AUTHOR]

Analog and digital switching performances in a Ta/HfO2/RuO2 (THR) memristor are studied to implement a density‐based spatial clustering of applications with noise (DBSCAN) algorithm in a low‐power, parallel‐computing memristor crossbar structure. In the analog mode THR memristor, more than 256 states can be stored through a fine‐tuning process with a denoising scheme. The analog mode crossbar array facilitates Euclidean distance calculation between any points in the given graphic dataset. In the digital mode, the on/off ratio of more than three orders of magnitude between the binary states is achieved, providing functionality to cluster the data points with a reduced number of operations. The parallel computing capacity of the adopted crossbar decreases the time complexity of the original DBSCAN from O(n2) to O(n). Through array‐level simulations, the effectiveness of hardware functionality is validated using representative synthetic datasets and single‐cell RNA sequences datasets. [ABSTRACT FROM AUTHOR]

The ferroelectric negative capacitance (NC) draws a great deal of attention for low‐power negative capacitance field‐effect transistors (NCFET) and NC capacitors. The fabrication of steep‐slope FET (subthreshold swing < 60mVdec−1) is reported, followed by modeling approaches. While the device fabrication favors a ferroelectric gate structure without interlayer metal, many NCFET models adopt interlayer metal between the ferroelectric layer and metal–insulator–semiconductor structure. The metal interlayer averages out spatial variation in the ferroelectric polarization, enabling a compact charge‐based relation between the layers. In addition, the approach assumes that the NC effect emerges from the ferroelectric layer regardless of the metal interlayer, which is not necessarily probable. This work reinvestigates the possible NC effect in ferroelectric–dielectric capacitors connected by a metal interlayer. The experiment confirms that the NC effect in the metal–ferroelectric–dielectric–metal structure does not appear in the metal–ferroelectric–metal–dielectric–metal structure. These results are inconsistent with the multidomain‐1D Landau–Ginzburg‐Devonshire model. In contrast, the suppression of the NC effect in the structure is fully explained by the advanced inhomogeneous stray‐field energy model, which simulates the dynamic evolution of polarization and screening charges. Therefore, an NCFET with a metal interlayer is impractical. [ABSTRACT FROM AUTHOR]

The mechanism of the differential negative resistance behavior observable in transition metal oxides such as TiO2, NiO, and Nb2O5 is theoretically developed in terms of the order to disorder transition of local conducting pathways, so called filaments, by applying statistical mechanics. Joule heat is taken as a heat source giving rise to an increase of temperature in the filaments. The free energy of the filaments is evaluated by taking the site percolation model as well as the nonhomogeneity of an order parameter into account. It is concluded that the transition of a filament from the conducting state, which is dominated by the internal bonding energy term, to the nonconducting state is due to an increased contribution of the entropy term to the system’s total energy at a higher temperature. The calculation results also show that the rupture of a filament occurs in the middle of the filament when the filaments are in contact with thermally conducting metal electrodes, such as Pt. [ABSTRACT FROM AUTHOR]

Phase control in Hf1-xZrxO2 (HZO) is crucial for optimizing its electrical properties, such as ferroelectricity and high dielectricity. However, phase optimization in HZO has remained challenging due to limited theoretical understanding. This work devised an atomistic methodology based on density functional theory calculations to predict the phase fractions in HZO. The detailed phase evolution and phase fractions during the sequential processes of crystallization, annealing, and cooling were predicted by calculating the nucleation barrier from amorphous, the transition barrier between polymorphs, and Boltzmann fractions, considering the combined effects of composition (x), grain size (dT), and annealing temperature (Tannealing). The findings revealed that the polar orthorhombic (PO) phase exhibited the highest fraction at Tannealing = 770 K in Hf0.5Zr0.5O2, resulting in maximum ferroelectricity. Meanwhile, the fractions of PO and tetragonal phases are similar at dT = 7 nm in Hf0.4Zr0.6O2 and dT = 11 nm in Hf0.3Zr0.7O2, both at Tannealing = 770 K, leading to the highest dielectricity. These results are highly consistent with the experimental results. This work demonstrates that the comprehensive interpretations of both thermodynamic and kinetic effects are essential for quantitatively predicting the phase fraction and their corresponding electrical functionality. [ABSTRACT FROM AUTHOR]

This work systematically studies the TiN, Ru, and RuO2 top electrodes (TEs) effects on the ferroelectric properties of Hf0.5Zr0.5O2 (HZO) films. The Ru top electrode significantly improves the ferroelectric performance even with the conventional TiN bottom electrode. The high two‐remanent polarization (2Pr) value (≈65 µC cm−2) is obtained with the capacitor with Ru TE, which is ≈1.5 times higher than that of the capacitors with the TiN and RuO2 TEs. Moreover, it does not break down to 1 × 109 cycling with a high cycling electric field of 4.0 MV cm−1, while others do lower cycle numbers. Further enhancement can be achieved by inserting a 2‐nm‐thick HfON interfacial layer between the HZO film and TiN bottom electrode while keeping the Ru/HZO top interface structure. The capacitor does not break down even at an electric field strength of 4.8 MV cm−1, at which a 2Pr value of ≈67 µC cm−2 is achieved. Furthermore, it can endure 1 × 1011 switching cycles while a 2Pr value of 45–53 µC cm−2 is retained. Therefore, this study elucidates that interfacial engineering is an important technology that can overcome the trade‐off relationship between Pr and endurance, a critical issue in ferroelectric doped HfO2‐based films. [ABSTRACT FROM AUTHOR]

Review: [132 refs. [ABSTRACT FROM AUTHOR]

The negative capacitance (NC) effect, recently discovered in a fluorite‐based ferroelectric thin film, has attracted great attention as a rescue to overcome the scaling limitations of the conventional memory and logic devices of highly integrated circuits. The NC effect manifesting an S‐shaped polarization–voltage (P–V) curve is initially interpreted by a 1‐dimensional Landau Ginzburg Devonshire (LGD) model. However, a series of recent studies have found that this effect can also be explained by the inhomogeneous stray field energy (ISE) model. In this study, by extending the ISE model in the ferroelectric (FE)‐dielectric (DE) layered structure, an analytical model that considers the influence of the interfacial screening charge distribution is presented. This model showed that the NC effect in the FE‐DE heterostructure can be manifested in various forms other than a single S‐shaped P–V curve. In particular, a double S‐shaped P–V curve is expected from the fully compensated anti‐parallel domain structure, confirmed experimentally in the actual Al2O3/(Hf0.5Zr0.5)O2/Al2O3 triple‐layer structure. Furthermore, to reveal the origin of the double S‐shaped P–V curve, a multidomain LGD model is presented. It is confirmed that this phenomenon is attributed to the evolution of inhomogeneous stray field energy. [ABSTRACT FROM AUTHOR]

3-D integrations are unavoidable task for new emerging memories, including resistive switching random-access memory (RRAM), in order to overcome the market-leading nand flash. However, an RRAM crossbar array (CBA) suffers severe read margin degradation due to the sneak current, which becomes even more critical as the memory density increases with the 3-D integration. In this paper, we extend the two-port readout scheme for a 2-D CBA, proposed in our previous work, to the 3-D vertical structure. A closed-form expression of the operating principle is derived, and HSPICE simulation using a $32\times 32\times8$ vertical RRAM CBA considering practical circuit parameters verifies feasibility of the two-port scheme to the 3-D CBA. [ABSTRACT FROM AUTHOR]

The interface between amorphous ZnSnO3 and amorphous SiO2 was investigated by ab initio molecular dynamic simulations. The radial distribution function at the interfacial region shows the significant reduction of the coordination numbers of Zn and Sn and slight decrease in the bond lengths of Zn-O and Sn-O, while keeping those of Si. These phenomena were explained in terms of the differences in both the coordination states of oxygen polyhedra and the connectivity of oxygen polyhedra between amorphous ZnSnO3 and amorphous SiO2. The interfacial energy was calculated to be 0.73 J cm−2 by the annealing at 300 K, while it was 0.29 J cm−2 by the annealing at 900 K, respectively. The reduction of the interfacial energy at higher annealing temperature was considered to be attributed to the increase of the number of M-O-Si bonds (M=Zn and Sn). The interfacial states in the density of states observed at the interface region was induced by the 2p states of oxygen having the decreased coordination number, and the interfacial gap states were not removed even by the 900 K annealing. [ABSTRACT FROM AUTHOR]

The influences of low-dielectric interfacial layers on the dielectric properties of Pt/(Ba,Sr)TiO[sub 3]/Pt capacitors were investigated before and after postannealing. The interfacial layer is believed to be the intrinsic dead layer (low-dielectric layer) due to the termination of chemical bonds of the (Ba,Sr)TiO[sub 3] (BST) material at the interfaces. The dielectric constant of the capacitor decreases with decreasing BST film thickness owing to the low dielectric constant of the dead layer. The dead-layer capacitance varies with processes such as film deposition temperature, and postannealing. Higher deposition temperatures result in a larger dead-layer capacitance and a higher bulk dielectric constant. Although annealing under a N[sub 2] atmosphere is less effective in reducing the dead-layer effect than under an O[sub 2] atmosphere, it is more effective in increasing the bulk dielectric constant. Therefore, a N[sub 2], rather than an O[sub 2] atmosphere, results in a larger increase in the overall dielectric constant. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The electric-field-induced rejuvenation behavior of the degraded ferroelectric properties of integrated Pt/SrBi[sub 2]Ti[sub 2]O[sub 9]/Pt capacitors was investigated. Integration processes, especially plasma-enhanced chemical vapor deposition of the passivation layers, generate hydrogen ions and electrons which act as domain pinning centers and a source of a negative internal electric field. Domain pinning was found to reduce the remanent polarization (P[sub r]) and internal field that induces an imprint to the positive bias direction. Alternating current cyclings with peak voltages of +/-6 V rejuvenated the degraded ferroelectric performance of the capacitors. Cycling with a negative bias was more effective in fixing the damage than was a positive bias. Baking at 125 °C again degraded the rejuvenated ferroelectric performance. The degree of re-degradation was also dependent on the polarity of the rejuvenating bias. The polarity-dependent behavior of rejuvenation was explained on the basis of a negative-internal-field model due to preferential capture of electrons from the plasma at the top electrodes. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The retention behavior of a HfO2 resistive switching memory device with a diameter of 28 nm and an ultra-thin (1 nm) HfO2 layer as the switching layer was examined. Ta and TiN served as the oxygen vacancy (VO) supplying the top and inert bottom electrodes, respectively. Unlike the retention failure phenomenon reported in other thicker oxide-based resistance switching memory devices, the current of both the low and high resistance states suddenly increased at a certain time, causing retention failure. Through the retention tests of the devices in different resistance states, it was concluded that the involvement of the reset step induced the retention failure. The pristine device contained a high portion of VO-rich region and the location of the border between the VO-rich and VO-free regions played the critical role in governing the retention performance. During the reset step, this borderline moves towards the Ta electrode, but moves back to the original location during the retention period, which eventually induces the reconnection of the disconnected conducting filament (in a high resistance state) or strengthens the connected weak portion (low resistance state). The activation energy for the retention failure mechanism was 0.15 eV, which is related to the ionization of neutral VO to ionized VO. [ABSTRACT FROM AUTHOR]

Neuromorphic engineering aims to mimic brain functions to achieve energy‐efficient artificial intelligence. Since researchers have indicated that memristors can mimic synapses and neurons, various studies have demonstrated the operation of neural networks using memristive dot product engine (MDPE) hardware. However, although several feasible implementations of synapse and neuron behaviors have been reported, few studies have demonstrated the system‐level energy‐efficient operation on the hardware. This work proposes a novel system inspired by the neuromodulation of the brain, referred to as a "stashing system." In the system, the trained synapses are stashed temporarily during the training of the spiking neural network and then merged for inferencing. The software simulation first confirmed the working principle of the stashing system. Then, a hardware demonstration is performed at an integrated 32 × 32 MDPE embodying a self‐rectifying and electroforming‐free memristor cell to validate the system. The results confirm that energy consumption in the memristor array is reduced by 37% for the unsupervised learning of the MNIST dataset. [ABSTRACT FROM AUTHOR]

This study introduces the atomic layer deposition (ALD) of tin selenide thin films using Sn(N(CH3)2)4 and Se(Si(CH3)3)2 with NH3 co-injection. The co-injection of NH3 with Se(Si(CH3)3)2 is essential for film growth to convert the precursor into a more reactive form. The most critical feature of this specific ALD process is that the chemical composition (Sn/Se ratio) could be varied by changing the growth temperature, even for the given precursor injection conditions. The composition and morphology of the deposited films varied depending on the process temperature. Below 150 °C, a uniform SnSe2 thin film was deposited in an amorphous phase, maintaining the oxidation states of its precursors. Above 170 °C, the composition of the film changed to 1 : 1 stoichiometry due to the crystallization of SnSe and desorption of Se. A two-step growth sequence involving a low-temperature seed layer was devised for the high-temperature ALD of SnSe to improve surface roughness. [ABSTRACT FROM AUTHOR]

Electronic bipolar resistive switching and its degradation in the Pt/TiO2/Pt structure were studied. The electronic bipolar switching was induced from the asymmetric trap distribution of the structure under its unipolar reset state. The imbalanced migration of oxygen accompanied by electronic switching significantly degrades switching endurance. Instead, the anti-serial connection of Pt/TiO2/Pt cells resulted in substantial improvements in endurance, underscoring the importance of vacancy migration in device reliability. In addition, the independent control of resistance states of the two connected cells provides the freedom to control resistance ratio, switching direction, and reliability. [ABSTRACT FROM AUTHOR]

Abstract: Chemically conformal deposition of SrTiO3 (STO) thin films was successfully achieved by ALD using conventional metal organic precursors and remote-plasma activated H2O. It was found that the ALD behavior of the STO film was critically dependent on the Sr(thd)2 source bubbling temperature. When the Sr-source bubbling temperature was &#60;∼200 °C (Sr(thd)2 melting temperature), the deposition proceeded in a genuine ALD mode and stoichiometric STO films were deposited with a good process reliability. Relatively good electrical properties were obtained from a planar capacitor structure with Pt top and Ru bottom electrodes. A 19.5-nm-thick STO film showed an equivalent oxide thickness (EOT) of 0.8 nm and a leakage current density of 1.98×10−6 A/cm2 at 1V after post-annealing. [Copyright &y& Elsevier]

Thermal stability and interfacial charge trap properties of the multi-metal (Ir/Pt/Au) top electrode of a metal–insulator–metal cathode for field emission display applications were examined. The thin (∼5 nm) multi-metal electrode did not show sufficient thermal stability during the post-annealing stage, which is needed to obtain good emission properties of the cathode, due to inter-diffusion and agglomeration of the layers. Reactively sputtered IrO2 thin films as the top electrode were examined considering their excellent thermal stability and low work function. However, the proper sputtering conditions of thin IrO2 (<10 nm) films were different from those of thick films (>100 nm) and should be optimized again due to the serious resputtering of the substrate at the initial deposition stage. Increasing the oxygen concentration (25%) during sputtering, which is the condition that results in a non-uniform film when the film is thick (>100 nm), was essential to ensure that the film was a well oxidized IrO2 when the film was very thin (<10 nm). Excellent thermal stability in terms of the non-varying resistivity and surface roughness of the 8-nm-thick IrO2 films compared to the multi-metal electrode film were confirmed. [Copyright &y& Elsevier]

In this study, the influence of the HfOxNy interfacial layer (IL), interposed between the atomic layer deposited ferroelectric (FE) Hf0.5Zr0.5O2 thin film and TiN top electrode, on the FE properties of such a film was examined. The HfOxNy IL decreased the relative proportion of the non-FE monoclinic phase, possibly due to the N-doping effect. Furthermore, the oxidation of the TiN top electrode was also suppressed by the sacrificial oxidation of the HfOxNy IL during the rapid thermal process. As a result, the double remanent polarization of a Hf0.5Zr0.5O2 thin film could be enhanced from 40.2 to 48.2 μC/cm2 by the positive-up-negative-down test, and its degradation by fatigue during the endurance test can also be decreased. This result demonstrates the significance of interfacial engineering to optimize the FE properties of Hf0.5Zr0.5O2 films. [ABSTRACT FROM AUTHOR]

Combining Boolean logic and nonvolatile memory functions, memristor‐based stateful logic circuits can minimize data movement during the computing process to achieve futuristic in‐memory computing. This may solve the problem of the von Neumann bottleneck in the current computing architecture. Herein, the recent developments in memristor‐based stateful logic computation are discussed from several perspectives, including the device, circuit, operational principles, and applications. Stateful logic gates correspond to in‐memory logic gates, with the inputs and outputs having identical physical entities, such as resistance. The developments in stateful logic primitive gates reported in the past decade are summarized. The influential factors in their actual implementation for stateful logic computation are also discussed. Then, methods for allocating the logic gates into the crossbar array are explained, which are for implementing the complex computing instances in the crossbar array. Finally, several data‐intensive applications achieved using the in‐memory computing method are discussed for the practical application of stateful logic in future computing systems. [ABSTRACT FROM AUTHOR]

Y2O3/TiO2 bilayer thin films and Y-doped TiO2 (YTO) thin films were deposited on a Ge substrate by atomic layer deposition at a substrate temperature of 250 °C. They were used as gate insulators to examine the electrical properties of Pt/TiN/TiO2/Y2O3/p-Ge and Pt/TiN/YTO/p-Ge metal–oxide–semiconductor capacitors. A 7 nm thick bilayer thin film showed a lower leakage current density by more than one order of magnitude compared to a YTO thin film with the same thickness due to the high conduction band offset between the Y2O3 layer and Ge substrate. However, the bilayer thin film showed a large hysteresis of 950 mV. On the other hand, the YTO thin film showed significantly reduced hysteresis of 120 mV due to the smaller slow trap density. The voltage acceleration factors of the bilayer thin film and YTO thin film were 1.12 and 1.25, respectively, higher in the YTO thin film. The interfacial trap density of the 7 nm thick bilayer and YTO thin films were 3.5 × 1011 cm−2 eV−1 and 2.7 × 1011cm−2 eV−1, respectively. The equivalent oxide thickness of the YTO film could be scaled down to 0.9 nm, and a leakage current density of 1.4 × 10−4A cm−2 at flat band voltage −1 V was achieved. This study confirmed that the YTO film can be used as a promising ternary high-k oxide for a Ge-based field-effect-transistor. [ABSTRACT FROM AUTHOR]

For ferroelectric applications, wurtzite (WZ)‐phase (Al,Sc)N is investigated using ab initio calculations. The key ferroelectric properties, such as the ferroelectric switching barrier and spontaneous polarization, are examined in (AlN)n/(ScN)m superlattice (SL) structures by varying the ScN fraction, and compared with an (Al,Sc)N solid solution (SS). The reduction of the switching barrier is dominated by the local structural instability rather than the flattening of the buckled monolayer composed of metal–nitrogen pairs in WZ‐stacking. This argument is supported by the doping effects of other metal elements as well as the reduction of the switching barrier in the SL, which does not accompany the flattening of the buckled monolayer. The decrease in the spontaneous polarization along the ScN fraction is explained by structural parameters (the in‐plane area and the buckling parameter) and the Born effective charge (BEC). The slight decrease in the spontaneous polarization in the SL is attributed to the larger increase in the in‐plane area rather than the BEC. In contrast, the decrease in the buckling parameter in the SS is suggested to more significantly reduce the spontaneous polarization along the ScN fraction. [ABSTRACT FROM AUTHOR]

A charge‐trap flash (CTF) device is fabricated using atomic‐layer‐deposited zinc tin oxide (ZTO) as an n‐type amorphous oxide semiconductor (AOS) channel layer and its program/erase characteristics are examined. When a positive voltage of 20 V is applied to the gate electrode, electrons are fluently injected into the adopted SiNx charge trap layer, resulting in a program operation showing a threshold voltage (Vth) shift of 3.7 V. However, even when −20 V is applied for up to 10 s, the trapped electrons are not detrapped. Instead, it is possible to recover Vth to its initial value only by the irradiation of white light. To understand this phenomenon, a ZTO CTF device is modeled using the technology computer‐aided design (TCAD) simulation package. The high hole injection barrier between the source/drain and the ZTO channel prohibits hole injection, which is the cause of the inefficient erasing. It is also confirmed that an AOS CTF with sufficient program and erase speed would be limited by the inherent energy band structure of AOS with its wide bandgap of over 3 eV. An alternative method of using the fringing field effect according to channel length scaling is proposed. [ABSTRACT FROM AUTHOR]

This work proposes an efficient and accurate methodology of ab initio thermodynamics to predict phase diagrams of III–V pseudobinary systems. The innumerable configurations of solid solutions are efficiently considered while maintaining accuracy by calculating the energies of freely relaxed configurations with the combined methodology using density functional theory calculations and cluster expansion. Then, the thermodynamic properties are calculated following a grand canonical ensemble framework that takes into account the local compositional fluctuation. The local strain energy induced by this local compositional fluctuation is found to be independent of the configuration; hence, it is calculated separately and added to the energy of a freely relaxed configuration, which significantly reduces the computational cost. This novel methodology is applied to calculate the phase diagrams of Ga(As,Sb) and (In,Ga)As, showing a good agreement with previous experimental reports. Notably, the strain energy is indispensable to predict phase diagrams accurately. It implies both the validity and the applicability of this method to other III–V pseudobinary systems. From an understanding of the crucial role of the strain energy in phase separation, an intuitive prediction is suggested through a simple estimation of the strain energy using the ratio of lattice parameters between various III–V semiconductor materials. [ABSTRACT FROM AUTHOR]

The gate‐induced electrical instability of SnO thin‐film transistors (TFTs) with SiO2 and Al2O3/SiO2 gate dielectric layers is evaluated. The hysteresis voltage (Vhy) and threshold voltage (Vth) in the transfer characteristics of SnO TFTs depend on the sweep range and rate of gate voltage (VGS). The TFT with an Al2O3/SiO2 gate dielectric layer exhibit reduced Vhy and stable Vth compared with the device without an Al2O3 layer. The introduction of an Al2O3 layer between the SnO channel and the SiO2 layer suppresses the electron and hole trapping at the channel/dielectric interface and contains mobile oxygen vacancies that counteract the hole trapping effect. [ABSTRACT FROM AUTHOR]

The resistive switching (RS) behavior of a gallium oxide (Ga 2 O 3) thin film for use in resistive random access memory (RRAM) was investigated. Ta/Ga 2 O 3 /Pt memory devices exhibited favorable RS behavior, such as a small distribution of switching parameters and switching cycles of more than 3 × 106. X-ray photoelectron spectroscopy and the current transport mechanism indicated that that the RS behavior was attributed to the local variation on the Schottky barrier near the Pt electrode interface due to oxygen vacancies. A hybrid system for self-powered data storage and deletion was built by combining the RRAM device with a commercial Pb(Zr 1-x Ti x)O 3 piezoelectric ceramic as a pressure sensor/power generator. The excellent anti-interference and reuse performance of the system indicated promising potential for the application of this memory device. [ABSTRACT FROM AUTHOR]

Herein, electronic bipolar resistive switching of Pt/Al2O3/Si3N3.0/Ti device is investigated. The Pt/Si3N3.0/Ti device demonstrates bipolar resistive switching with set (reset) at negative (positive) bias, and the mechanism is revealed to be that the conduction filament, formed by percolation of the traps in defective silicon nitride thin film, is involved in the resistive switching. However, instead of the conduction filament, trapping and detrapping of the electrons in the trap sites of Si3N3.0 become the dominant switching mechanism by introducing an Al2O3 barrier layer between Pt and Si3N3.0, and the device has forming‐free, self‐rectifying, and nonlinear characteristics, which are necessary to the cross‐bar array (CBA) configuration. The optimized thickness of the Al2O3 barrier layer is 4 nm. A detailed electrical analysis is performed to identify the switching mechanism of the device. Also, the read/write margin is calculated using H simulation program with integrated circuit emphasis (HSPICE) to estimate the available CBA cell size. [ABSTRACT FROM AUTHOR]

Abstract: The electronic structure of amorphous semiconductor InGaO3(ZnO)0.5 thin films, which were deposited by radio-frequency magnetron sputtering process, was investigated using X-ray photoelectron spectroscopy and O K-edge X-ray absorption spectroscopy. The overall features of the valence and conduction bands were analyzed by comparing with the spectra of Ga2O3, In2O3, and ZnO films. The valence and conduction band edges are mainly composed of O 2p and In 5sp states, respectively. The bandgap of the films determined by spectroscopic ellipsometry was approximately 3.2 eV. Further, it is found that the introduction of oxygen gas during the sputter-deposition does not induce significant variations in the chemical states and band structure. [Copyright &y& Elsevier]

Based on the first-principles calculations, the authors study defect-defect interactions between cation vacancies in rutile TiO2 and monoclinic HfO2. It is found that vacancies are greatly stabilized at small separations because of a large reconstruction of nearby oxygen atoms that have two broken bonds. As a result, O–O bonds resembling O2 or O3 molecules are formed near the divacancy site. The defect levels originated from antibonding states of O p orbitals are identified within the energy gap, which can affect leakage currents and the density of trapped charges of oxides substantially. [ABSTRACT FROM AUTHOR]

The resistance switching mechanism of TiO2 films under voltage sweep mode was investigated. From the observed soft set of Pt/TiO2/Pt sample and from the polarity-dependant switching behavior of Ir(O)/TiO2/Pt sample, local rupture and recovery of conducting filaments near the anode interface wer identified as the switching mechanism. This is consistent with the authors’ recent observation [K. Kim et al., Electrchem. Solid-State Lett. 9, G343 (2006)] of the resistance switching property of Al2O3/TiO2 multilayers, where switching was controlled by the layer close to the anode. It appears that most parts of the filaments are preserved during switching and only a small portion of the film near the anode contributes to switching. [ABSTRACT FROM AUTHOR]

The effect of the carbon residue on the reliability of HfO2 thin films was investigated. HfO2 films were deposited on Si wafers by atomic layer deposition at a wafer temperature of 250 °C using Hf[N(CH3)2]4 and O3 oxidant with two different densities (160 and 390 g/m3). The films deposited at the higher O3 density contained a lower concentration of carbon impurities. The leakage current density was lower and the time-dependent dielectric breakdown was improved in the higher O3 density films. First principles calculations confirmed that trap sites were generated in the band gap of HfO2 when carbon was interstitially or substitutionally present. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) on Ta-doped SnO 2 thin films is proposed as a methodology for the fabrication of capacitor electrodes, for application in dynamic random-access memories (DRAMs). In ALD of doped materials, dopant concentration gradients inevitably occur due to the cyclic process-based characteristics of ALD. In this study, the dopant distribution improves drastically by the decrease in the growth per cycle of TaO x ALD. The modified ALD recipe exploits the low reactivity between Ta and Sn precursors to facilitate a reduction in the growth per cycle. The Ta-doped SnO 2 films grown based on this modified ALD recipe exhibit improved crystallinity and conductivity. The ALD process yields excellent conformality of the Ta-doped SnO 2 film over a hole structure with a high aspect ratio of ~10, both in terms of physical thickness and composition. Additionally, the Ta-doped SnO 2 films serve as a template for the overgrowing dielectric TiO 2 film, which induces the formation of a high-temperature phase with a high dielectric constant, rutile TiO 2 , and exhibit excellent thermal stability even after annealing at 400 °C in forming gas atmosphere. These findings demonstrate that the proposed methodology for the growth of Ta-doped SnO 2 can facilitate the fabrication of capacitor electrodes for application in DRAMs. Unlabelled Image • A new ALD process of Ta-doped SnO 2 films is demonstrated. • Potential applications include use as reduction-resistant capacitor electrode. • Dopant distribution improves by decrease in the growth per cycle of TaO x ALD. • Films reveal ease of formation of high-k rutile TiO 2 and excellent thermal stability. [ABSTRACT FROM AUTHOR]

The effects of the isoelectronic Al doping of epitaxial GaN films grown by metalorganic chemical vapor deposition on a (0001) Al2O3 single crystal substrate were investigated. It was found that the threading screw and edge dislocation densities of the GaN film decreased to less than half of that of the undoped GaN film up to Al doping concentration of 0.45%. The in-plane and out-of-plane strains were simultaneously reduced with the decrease in dislocation density as a result of the solution hardening effect. Accordingly, the electron mobility of the 0.45% Al-doped GaN film (524 cm2/Vs) was greatly improved compared to that of the undoped GaN film (178 cm2/Vs). However, the threading dislocation densities and strains were increased at a 0.64% Al concentration, and the electron mobility decreased accordingly. Therefore, the improvement in the electron mobility by Al doping up to 0.45% is the result of a decrease in the threading dislocation density and not a decrease in the number of point defects (Ga-site vacancy) as suggested earlier [Lee et al., Appl. Phys. Lett. 83, 917 (2003)]. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We demonstrate an electrostatic force microscopy based on a quartz tuning fork with 50 nm spatial resolution and 1 pN force sensitivity. We use a tuning fork with a spring constant of 1300 N/m and a Q factor of 3000. A sharpened nickel tip is attached to a prong of the tuning fork as well as electrically connected to the electrode of the prong. By applying a dc bias to the tip, ferroelectric domain patterns are recorded and read out on piezoelectric thin film. [ABSTRACT FROM AUTHOR]

Ferroelectric Hf0.5Zr0.5O2 (HZO) films were grown by the atomic layer deposition (ALD) technique on an ALD or physical-vapor-deposited (PVD, sputtering) TiN bottom electrode (BE). The PVD TiN film showed small grains with flat surface morphology, mainly consisting of the (111) crystallographic plane. In contrast, the ALD TiN film exhibited a larger diameter and faceted grain shapes, with the (200) crystallographic surface planes. The 10-nm-thick HZO film on the ALD TiN BE showed a lower internal field, enhanced endurance (>1 × 1010 cycle at 2.5 MV/cm), and decreased leakage current than identical HZO films on the PVD TiN BE. Lower interfacial oxidation of the ALD TiN BE as a result of the smaller grain boundary area of the ALD TiN induced a lower defect density in the HZO film. The higher work function of the ALD TiN film also contributed to the lowering of the leakage current. [ABSTRACT FROM AUTHOR]

The electronic structure of an amorphous SnO (a-SnO) thin film was examined by using spectroscopic methods including tender and soft x-ray absorption spectroscopies (XAS) and spectroscopic ellipsometry (SE). XAS at the Sn L1−, L3−, and O K-edges revealed that in a-SnO, the Sn 5px/y orbital states, which comprise the conduction band minimum (CBM), are broadened significantly compared to the case of crystalline SnO, whereas the hybridized Sn 5spz-O 2p states above the CBM are persistent. A lowering of the 5px/y states at the CBM by −0.4 eV and a reduction of the indirect bandgap were also observed. These orbital-dependent evolutions upon amorphization were caused by weakened interlayer couplings in the disordered quasi-2-dimensional semiconductor. However, the functionality of a-SnO as a p-type semiconductor would not be degraded significantly because the isotropic Sn 5s orbital states dominate in the valence band states. [ABSTRACT FROM AUTHOR]

Many applications, most notably memory and optical devices use ferroelectric materials. For many years the evolution of the field has revolved around understanding the materials science behind complex structures like artificial superlattices based mainly on perovskite-structure oxides. The recent discovery of ferroelectricity in fluorite-structure oxides has opened a new research direction. However, the formation of unstable or metastable phases in atomic layer deposited fluorite oxides has inhibited a full understanding of the origin of ferroelectricity in these materials. This work reports a comprehensive study of the structural and electrical properties of HfO2 and ZrO2 nanolaminates and superlattices of various layering combinations and thicknesses. The structural investigations provide insight into how to optimize conditions during atomic layer deposition to avoid the formation of unstable phases. Investigations showed that the starting layer of the material, the thickness ratio between HfO2 and ZrO2 layers, and the single-layer thickness strongly effected the ferroelectric properties. The influence of single-layer thickness related most strongly to the presence of interfacial nonferroelectric layers between the HfO2 and ZrO2 deposits. These features make the structures highly promising candidates for next-generation memory applications. Potentially other fluorite-structure oxides might also function as building blocks for nanolaminates and superlattices. [ABSTRACT FROM AUTHOR]