Resistive switching characteristics of Cu/ZnO0.4S0.6/Al devices constructed on plastic substrates

In this study, Cu/ZnO0.4S0.6Al devices are fabricated on plastic substrates using the sputtering method at room temperature. The ratio of O/S in the zinc oxysulfide thin film is confirmed to be 0.4/0.6 from the Auger depth profiling. The Cu/ZnO0.4S0.6/Al devices show unipolar resistive switching behaviors and the ratio of the measured resistance in the low-resistance state (LRS) to that in the high-resistance state (HRS) is above 10(4). The conduction mechanism of the LRS is governed by Ohm's law. On the other hand, in the HRS, the conduction mechanism at low voltages is controlled by Ohm's law, but that at high voltages results from the Poole-Frenkel emission mechanism. The Ohmic and Poole-Frenkel conduction mechanisms observed in the LRS and HRS support the filament model of unipolar resistive switching. The memory characteristics of the Cu/ZnO0.4S0.6/Al devices are retained for 10(4) sec without any change.     

An RMS Digital Voltmeter/Calibrator for Very-Low Frequencies

A portable rms digital voltmeter (DVM) has been developed at NBS to support vibration measurements over the ranges of 0.1 to 50 Hz and 2 mV to 10V. A self-contained calibrator provides for self-calibration and may be used for calibrating other VLF voltmeters. The calibrator basically consists of a Kelvin-Varley divider fed by a reference voltage (either dc or sinewave generated by a ROM-DAC combination) A multijunction thermal converter (MJTC) was selected as the sensing device in the rms/dc converter of the DVM since its low ac/dc difference facilitates calibration of the ac calibrator. Factors affecting accuracy and response time are analyzed. The DVM response time is 40 s for the lowest input frequency. Its accuracy (percent of reading) is 0.1 percent above 0.5 Hz and 5 mV and 0.2 percent below these values. The ac calibrator accuracy is 0.02 percent. Measurement accuracy improves by a factor of about 4 for transfer measurements (comparing input voltages with ac calibrator voltages) Means for extending this accuracy to 0.01 percent are discussed.     

Synthesis of cobalt-based nanocrystal layer in silicon dioxide for nonvolatile memory applications

Cobalt silicide (CoSi) nanocrystal (NC) layer distributed within narrow spatial region is synthesized by thermal annealing of a sandwich structure comprised of a thin cobalt (Co) film sandwiched between two silicon-rich oxide (SiO(x)) layers. It is shown that the size of the CoSi NCs can be controlled by varying the Co film thickness, an increase in the size with increasing thickness. Capacitance-voltage (C-V) measurements on a test metal/oxide/semiconductor (MOS) structure with floating gate based on CoSi NCs of 3.8 nm in diameter and 1.4 x 10(12) cm2 in density are shown to have C-V characteristics suitable for nonvolatile memory applications, including a C-V memory window of about 9.5 V for sweep voltages between -15 V and +8, a retention time >10(8) s, and an endurance > 10(6) program/erase cycles.     

Y5U multilayer ceramic capacitors with high-specific capacitance and low-equivalent series resistance

A dielectric powder material, for Y5U multilayer ceramic capacitors was developed in the Pb(Mg(1/3)Nb(2/3))O (3)-Pb(Ni(1/3)Nb(2/3))O(3)-PbTiO (3) ternary system by using an alkoxide process. Multilayer ceramic chip capacitors (10 muF) with high specific capacitances were fabricated using this powder. A Ag80%-Pd20% alloy was used for the internal electrodes. The alkoxide-derived capacitor had an extremely high specific capacitance of about 500 muF/cm(3) and a small temperature dependence meeting Y5U specifications of the EIA standard. The equivalent series resistance was approximately 20 mOmega at 500 kHz. The breakdown voltages of the capacitor were 300 V or higher. In accelerated load life tests and load humidity tests, no degradation of insulation resistance was found during 1000 h of testing.     

反应溅射TiN纳米晶薄膜的结构特征和耐蚀性

利用直流反应溅射技术在不锈钢和硅基体上沉积了TiN纳米晶薄膜,采用场发射扫描电镜(FESEM)、X射线衍射(XRD)和电化学阻抗谱(EIS)技术研究了薄膜的表面形貌、相结构和耐蚀性与偏压的关系。结果表明,TiN薄膜的表面结构明显取决于所施加的偏压,适当提高偏压有利于获得细小、均匀、致密和光滑的膜层。XRD分析发现,TiN薄膜为面心立方结构,其择优取向为(111)面。实验显示,对应0V和-35V偏压的薄膜为欠化学计量比的,而偏压增加至-70V和-105V时的薄膜为化学计量比的TiN。EIS结果表明,较高偏压下的TiN薄膜几乎在整个频率范围内均表现为容抗特征,其阻抗模值明显高于低偏压下的膜层,这主要与较高偏压下的薄膜具有相对致密的微结构有关。较低偏压的TiN薄膜因结构缺陷较多其耐蚀性低于基体不锈钢。EIS所揭示的薄膜结构特征与FESEM观测结果一致。可见,减少穿膜针孔等结构缺陷有利于改善反应溅射TiN纳米晶薄膜耐蚀性。     

LiMgPO4-Coating-Induced Phosphate Shell and Bulk Mg-Doping Enables Stable Ultra-High-Voltage Cycling of LiCoO2 Cathode

Stable cycling of LiCoO₂ (LCO) cathode at high voltage is extremely challenging due to the notable structural instability in deeply delithiated states. Here, using the sol–gel coating method, LCO materials (LMP-LCO) are obtained with bulk Mg-doping and surface LiMgPO₄/Li₃PO₄ (LMP/LPO) coating. The experimental results suggest that the simultaneous modification in the bulk and at the surface is demonstrated to be highly effective in improving the high-voltage performance of LCO. LMP-LCO cathodes deliver 149.8 mAh g⁻¹@4.60 V and 146.1 mAh g⁻¹@4.65 V after 200 cycles at 1 C. For higher cut-off voltages, 4.70 and 4.80 V, LMP-LCO cathodes still achieve 144.9 mAh g⁻¹ after 150 cycles and 136.8 mAh g⁻¹ after 100 cycles at 1 C, respectively. Bulk Mg-dopants enhance the ionicity of Co O bond by tailoring the band centers of Co 3d and O 2p, promoting stable redox on O²⁻, and thus enhancing stable cycling at high cut-off voltages. Meanwhile, LMP/LPO surface coating suppresses detrimental surface side reactions while allowing facile Li-ion diffusion. The mechanism of high-voltage cycling stability is investigated by combining experimental characterizations and theoretical calculations. This study proposes a strategy of surface-to-bulk simultaneous modification to achieve superior structural stability at high voltages.     

A 0.2 V Micro‐Electromechanical Switch Enabled by a Phase Transition

Micro‐electromechanical (MEM) switches, with advantages such as quasi‐zero leakage current, emerge as attractive candidates for overcoming the physical limits of complementary metal‐oxide semiconductor (CMOS) devices. To practically integrate MEM switches into CMOS circuits, two major challenges must be addressed: sub 1 V operating voltage to match the voltage levels in current circuit systems and being able to deliver at least millions of operating cycles. However, existing sub 1 V mechanical switches are mostly subject to significant body bias and/or limited lifetimes, thus failing to meet both limitations simultaneously. Here 0.2 V MEM switching devices with ?10⁶ safe operating cycles in ambient air are reported, which achieve the lowest operating voltage in mechanical switches without body bias reported to date. The ultralow operating voltage is mainly enabled by the abrupt phase transition of nanolayered vanadium dioxide (VO₂) slightly above room temperature. The phase‐transition MEM switches open possibilities for sub 1 V hybrid integrated devices/circuits/systems, as well as ultralow power consumption sensors for Internet of Things applications.     

Thermal stability of metal-silicide nanocrystal nonvolatile memory with barrier engineered tunnel layers

WSi2 nanocrystal nonvolatile memory devices were fabricated with a silicon oxide-nitride-oxide (SiO2: 2 nm/Si3N4:2 nm/SiO2:3 nm) tunnel layer. WSi2 nanocrystals of 2.5 nm diameters and a density of 3.6 x 10(12) cm(-2) were formed using radio frequency magnetron sputtering and annealing processes. The WSi2 nanocrystal nonvolatile memory device exhibited strong thermal stability during writing/erasing operations at temperatures up to 125 degrees C. When the writing/erasing voltages were applied at +10 V/-10 V for 500 ms, the memory window of the initial approximately 2.6 V decreased by approximately 1.1 V at 25 degrees C and 0.4 V at 125 degrees C after 10(4) sec, respectively. These results show that WSi2 nanocrystals with barrier-engineered tunnel layers are possible for application in nonvolatile memory devices.     

聚吡咯/聚多巴胺的电化学合成及其对铝合金耐蚀性的影响

为了提高铝合金有机涂层的耐蚀性,通过电化学方法在7075铝合金表面制备了海岛结构的聚吡咯（PPy）/聚多巴胺（PDA）复合涂层,利用FE-SEM、原子力显微镜、FTIR分析了PPy/PDA涂层的表面形貌、表面粗糙度和化学成分,并通过交流阻抗图谱分析了涂层的阻抗特性,通过极化曲线分析了具有PPy/PDA涂层的铝合金的极化电压和极化电流,研究其耐蚀特性。结果显示,通过一步法电化学聚合方法,吡咯和多巴胺在铝合金表面同时发生电化学聚合,生成PPy/PDA复合涂层,PPy/PDA涂层具有海岛结构,纯PPy和PPy/PDA涂层的粗糙度分别是（74.582±7.227）nm和（73.740±7.811）nm。交流阻抗和极化曲线说明PPy/PDA涂层相比于纯PPy涂层具有更大的阻抗力,PPy/PDA涂层的腐蚀电流和腐蚀电压分别是4.1825×10-6 Acm-2和-0.6919 V,相对于纯PPy（腐蚀电流和腐蚀电压分别是7.618×10-6 Acm-2和-0.7403 V）具有更好的防腐特性。      

Dielectric properties of anodized Al-Ta alloy films with high Al content

At 1 mA cm^-2 the anodization voltage of sputtered Al-Ta alloy films with about 7 at.% Ta content rises linearly with time at a rate of 0.45 V s^-1. The Al-Ta thickness-anodization voltage ratio and the oxide growth constant have been determined, for 7–14 at.% Ta in the films with 1% citric acid electrolyte, to be 1.03-0.94 nm V^-1 and 1.42–1.5 nm V^-1, respectively. The permittivity was found to range from 10.0–11.4, corresponding to a capacitance density of about 330 pF mm^-2 for an anodization voltage of 200 V. The temperature coefficient of capacitance (t.c.c.) was 500 ppm K^-1. The capacitance between 400 Hz and 1 MHz remained constant within ±1%. At 1 kHz the disspation factor tan δ was 0.6%.Nearly all leakage currents were between 0.1 and 0.5 nA using 5.6 nF test capacitors and 50 V as the test voltage. This corresponds to an insulation resistance R of 10¹¹ Ω or more, or a time constant τ ( = RC) of approximately 1000 s. For the 50 V test the yield was about 90% and at least 80% of the capacitors had no short circuits after step stress tests up to 90 V.The current-voltage characteristics of capacitors made from Al-Ta (7 at.% Ta) films showed non-destructive breakdown voltages greater than 100 V. Only a slight deviation from symmetry was noticed whether the Al-Ta electrode was positive or negative, indicating that the capacitors were virtually non-polar. In some cases non-shorting breakdown was observed.     

Electrical conduction and low voltage blue electroluminescence in vacuum-deposited organic films

Bright blue (400–500 nm) recombination electroluminescence (EL) has often been observed from anthracene crystals with solid electrodes; external quantum efficiencies of 1%–8% have been seen and the theoretical efficiency is approximately 40%. The power efficiency has always been greatly degraded by the high voltages necessary to obtain reasonable currents through the comparatively thick crystals used. We report the preparation, and the structural, electrical and EL properties of approximately 0.6 μm vacuum-deposited anthracene films through which large steady state current densities can be passed at rather low applied voltages. The films showed the critical optimization effect, various structural and electrical properties exhibiting sharp singularities when the films were prepared at substrate temperatures within a narrow range near ?60 °C. EL visible in normal room lighting was obtained at applied voltages of only about 30 V and up; in thinner films, EL could be seen in a darkened room at only about 12 V. This is apparently the first time that clearly visible EL has been reported from an organic material at voltages significantly less than 100 V. Broadly similar results were obtained for perylene and 1,12-benzperylene films; EL does not appear to have been observed before from these substances in any form. We discuss in some detail the prospects for practical EL devices based on organic films. In view of our results, and of the great improvements which are now probably feasible, we conclude that the prospects are promising; if these improvements can be realized, such devices could include high efficiency blue light-emitting diodes, and large-area broader wavelength systems for illumination applications.     

Nano-scaled Pt/Ag/Ni/Au contacts on p-type GaN for low contact resistance and high reflectivity

We synthesized the vertical-structured LED (VLED) using nano-scaled Pt between p-type GaN and Ag-based reflector. The metallization scheme on p-type GaN for high reflectance and low was the nano-scaled Pt/Ag/Ni/Au. Nano-scaled Pt (5 A) on Ag/Ni/Au exhibited reasonably high reflectance of 86.2% at the wavelength of 460 nm due to high transmittance of light through nano-scaled Pt (5 A) onto Ag layer. Ohmic behavior of contact metal, Pt/Ag/Ni/Au, to p-type GaN was achieved using surface treatments of p-type GaN prior to the deposition of contact metals and the specific contact resistance was observed with decreasing Pt thickness of 5 A, resulting in 1.5 x 10(-4) ohms cm2. Forward voltages of Pt (5 A)/Ag/Ni contact to p-type GaN showed 4.19 V with the current injection of 350 mA. Output voltages with various thickness of Pt showed the highest value at the smallest thickness of Pt due to its high transmittance of light onto Ag, leading to high reflectance. Our results propose that nano-scaled Pt/Ag/Ni could act as a promising contact metal to p-type GaN for improving the performance of VLEDs.     

Microwave-Assisted Synthesis of Highly Active Single-Atom Fe/N/C Catalysts for High-Performance Aqueous and Flexible All-Solid-State Zn-Air Batteries

The development of low-cost single-atom electrocatalysts for oxygen reduction reaction (ORR) is highly desired but remains a grand challenge. Superior to the conventional techniques, a microwave-assisted strategy is reported for rapid production of high-quality Fe/N/C single-atom catalysts (SACs) with profoundly enhanced reaction rate and remarkably reduced energy consumption. The as-synthesized catalysts exhibit an excellent ORR performance with a positive half-wave potential up to 0.90 V, a high turnover frequency of 0.76 s⁻¹, as well as a satisfied stability with a lost half-wave potential of just 27 mV over 9000 cycles (much better than that of Pt/C with 107 mV lost) and good methanol resistance. The open-circuit voltages of as-constructed aqueous and flexible all-solid-state Zn-air batteries (ZABs) are 1.56 and 1.52 V, respectively, higher than those of 20% Pt/C-based ones (i.e., 1.43 and 1.38 V, respectively). Impressively, they afford a peak power density of 235 mW cm⁻², which exceeds that of Pt/C (i.e., 186 mW cm⁻²), and is comparable to the best ones of Fe/N/C-based ZABs ever reported.     

Nanotechnology for next generation Josephson voltage standards

We have developed two voltage standard systems: 1) the programmable Josephson voltage standard and 2) the Josephson arbitrary waveform synthesizer. The programmable system is fully automated and provides stable programmable dc voltages from -1.2 V to +1.2 V. The synthesizer is the first quantum-based ac voltage standard source. It uses perfectly quantized Josephson pulses to generate arbitrary waveforms with low harmonic distortion and stable, calculable time-dependent voltages. Both systems are presently limited to output voltages less than 10 V as a result of frequency requirements and the limits of junction fabrication technology. We describe the development of fabrication technology for these systems and describe the circuit- and fabrication-related constraints that presently limit system performance. Finally, we propose the use of lumped arrays of junctions to achieve higher practical voltages through development of a nanoscale junction technology, in which 13 000 junctions are closely spaced at 50 nm-100 nm intervals     

Electrode effect on resistive switching of Ti-added amorphous SiOx films

Ti-added amorphous SiO_x films were sputter-deposited into stacks of Pt/SiO_x/Pt and Cu/SiO_x/Pt. Optimally prepared Pt/SiO_x/Pt exhibits unipolar resistive switching over 10² cycles, resistance ratio ∼ 10³, yet wide voltage distribution (2 ∼ 7 V for SET, 0.5 ∼ 1.5 V for RESET). Cu/SiO_x/Pt exhibit similar endurance, resistance ratio up to 10⁷, and SET and RESET voltages reduced to 1.8 ∼ 4.2 V and 0.5 ∼ 1 V, respectively. Cu diffusion into SiO_x at the virgin state may play a role in resistive switching of Cu/SiO_x/Pt stack besides of filament conduction. Ti-added amorphous SiO_x films incorporating Cu electrode shows potential for resistive memory.     

Electrical stress effect on the leakage current of metal-induced laterally crystallized p-channel poly-Si TFTs

A p-type polycrystalline silicon thin-film transistor (TFT) was fabricated using the metal-induced lateral crystallization (MILC) technique at 550 degrees C. To reduce the leakage current in the MILC TFT, electrical stress (ES), newly developed in this work, was applied prior to the I(D)-V(G) measurements. It was found that ES is effective only when the TFT is under off-state. The stress gate voltage is related to the leakage current at high gate voltages and the electric field between the source and the drain to the leakage current at low gate voltages. The leakage current of the MILC TFT could be lowered to 10(-11) A for width/length ratios of 1/2 measured at the drain voltage of 3 V. A new plausible model has been suggested to explain the ES effect on the leakage current behavior in low-temperature polycrystalline silicon TFTs.     

Room-temperature gas-sensing ability of PtSi/porous Si Schottky junctions

Gas-sensing ability of n-type PtSi/porous Si Schottky junctions is investigated at room temperature. These junctions exhibit a breakdown-type current-voltage (I-V) curve at low reverse bias voltages (5-15 V) due to very large electric fringing fields (10/sup 5/-10/sup 6/ V/cm) developed at the sharp edges and the bottom of the pores. Experimental results for selected gases are presented. Gases with inherent dipole moments tend to decrease the breakdown voltage. Gases without dipole moments do not affect the I-V curve directly, but they can replace gas content inside the pores and decrease the dipole moment of the ambient gas, which results in an increase in breakdown voltage. Based on these experiments, the possible application of this structure as a gas sensor at room temperature is discussed.     

基于Fe/Co-MOF制备的高性能镍铁电池铁电极及其电化学性能

铁电极是构筑高性能镍铁电池的关键。本文报道了一种基于Fe/Co-MOF制备镍铁电池铁电极的新思路,并系统研究了该材料的电化学性能。XRD、SEM和HRTEM等结果表明,Fe/Co-MOF烧结产物以八面体颗粒为主,主要由Fe_3O_4相及少量Fe-Co合金构成。作为镍铁电池的阳极时,相比于未加入Co的材料,目标材料的电化学性能得到了明显改善。Fe/Co-MOF烧结产物的放电平台稳定在1.18V,比Fe-MOF烧结产物的放电平台(1.10V)高约0.08V。尽管Fe/Co-MOF烧结产物在前10次循环出现了明显的容量衰减,但之后保持了较好的循环稳定性能,在1.0A·g-1电流密度下循环90次后比容量稳定在233.1mAh·g-1,而Fe-MOF烧结后产物的比容量仅为181.2mAh·g-1。交流阻抗结果显示Fe/Co-MOF烧结产物表现出更低的电荷传递阻抗。     

Pentacene thin-film transistors and inverters with plasma-enhanced atomic-layer-deposited Al2O3 gate dielectric

The performances of pentacene thin-film transistor with plasma-enhanced atomic-layer-deposited (PEALD) 150 nm thick Al₂O₃ dielectric are reported. Saturation mobility of 0.38 cm²/V s, threshold voltage of 1 V, subthreshold swing of 0.6 V/decade, and on/off current ratio of about 10⁸ have been obtained. Both depletion and enhancement mode inverter have been realized with the change of treatment method of hexamethyldisilazane on PEALD Al₂O₃ gate dielectric. Full swing depletion mode inverter has been demonstrated at input voltages ranging from 5 V to − 5 V at supply voltage of − 5 V.     

Study on the dynamic resistance switching properties of NiO thin films

The resistive switching properties of NiO-based memory cells were investigated utilizing test structures with a storage contact size of 150 nm in diameter. Two well defined stable resistance states with high OFF/ON ratios were achieved by unipolar operation. Detailed electrical characterizations with respect to nonvolatile memory applications reveal fast (< 300 ns) and reliable switching performance at low operating voltages (< 2.5 V). Promising results of endurance data (> 1000 cycles) and retention tests up to 110 °C show excellent stability and indicate the competitive potential with respect to established nonvolatile memory devices.