Number Of Stacked Layers Research Articles

What Will Come After V‐NAND—Vertical Resistive Switching Memory?

AbstractThe NAND flash memory serves as the key enabler of the flourishing of portable handheld information devices, such as the cellular phone. The recent upsurge in the sales of vertical NAND flash memory (V‐NAND) entails a further increase in the available information capacity at the edge devices and the servers with higher performance and lower power consumption compared with the magnetic hard‐disc drives. Nonetheless, there will certainly be an upper limit for the number of stacked layers, which will be the point at which further memory density increase will stop. While V‐NAND is a supreme outcome of semiconductor memory technologies, it still relies on conventional Si‐based materials. The newly explored memory materials and concepts, such as the resistance‐based memories, can therefore be an appealing contender to or successor of V‐NAND. In this review, the current state of V‐NAND is first briefly looked into, and then the eventual limitation of memory density increase and performance boost are discussed. Most importantly, the possible strategies of integrating the resistance‐based memories into the vertical architecture are then discussed. Finally, the outlook for such resistance‐based vertical memories is presented.

RGB-Colored Cu(In,Ga)(S,Se)2 Thin-Film Solar Cells with Minimal Efficiency Loss Using Narrow-Bandwidth Stopband Nano-Multilayered Filters.

Colorful Cu(In,Ga)(S,Se)2 (CIGSSe) thin-film solar cells were achieved by integrating a narrow-bandwidth stopband filter (NBSF) on a CIGSSe cell. The full range of visible color of NBSF could be realized by depositing one-dimensional nano-multilayers of alternating high-index (Al2O3) and low-index (SiO2) films while controlling the thickness of each layer and the number of stacked layers. Particularly, high-purity red, green, and blue (RGB) colors were generated on black CIGSSe cells with minimal harvest efficiency drop, showing power conversion efficiency (PCE) losses for the red and green CIGSSe cells of 4.2 and 1.2%, respectively, with no reduction in the PCE of the blue CIGSSe cell. The minimal drop in the harvest efficiency was attributed to the antireflection effect of the NBSF and the low overlap between the reflectance spectrum of NBSFs with a narrow stopband and the absorption spectrum of CIGSSe. The esthetic value could be further enhanced through the color variation of the RGB NBSF with viewing angle, so-called pearl-like colors. The synergetic effect of minimal efficiency loss, full color realization, and the pearl-like color change of the newly developed NBSFs can make CIGSSe cells applicable to building-integrated photovoltaics.

Thermal effect in ultra-high density 3D vertical and horizontal RRAM array

Thermal induced reliability issues in ultra-high density storage arrays are becoming increasingly significant, especially in 3D stacks. In this paper, research into the reliability issues of a stacked 3D TaOx vertical resistive random access memory (VRRAM) is demonstrated first through experiments. The results indicate that the thermal induced reliability issues of a 3D VRRAM are very severe. To further study the thermal effect and its impact on a 3D VRRAM, finite element analysis models of the 3D VRRAM are established in CMOSOL Multiphysics. Parameters including different feature sizes (F), metal layer thickness (tm), isolation layer thickness (ti) and the number of stacked layers (Ns) are simulated and investigated to clarify the relationship between heat dissipation performance and the device’s integration density. In addition to this, the influence of electrode materials is also discussed. The results reveal that scaling down F and tm are the main reasons for bad heat dissipation performance, and optimizing the thermal conductivity in both electrodes and the isolation layer can improve the heat dissipation performance. In addition, a comparative investigation into the heat dissipation performance in a 3D horizontal RRAM (HRRAM) has also been performed under the same conditions. Finally, by evaluating the influence of the integration parameters on the thermal effect related reliability performance, design guidelines for a 3D VRRAM and HRRAM are proposed.

Deep Haar Scattering Networks in Pattern Recognition: A Promising Approach

The aim of this paper is to discuss the use of Haar scattering networks, which is a very simple architecture that naturally supports a large number of stacked layers, yet with very few parameters, in a relatively broad set of pattern recognition problems, including regression and classification tasks. This architecture, basically, consists of stacking convolutional filters, that can be thought as a generalization of Haar wavelets, followed by non-linear operators which aim to extract symmetries and invariances that are later fed in a classification/regression algorithm. We show that good results can be obtained with the proposed method for both kind of tasks. We have outperformed the best available algorithms in 4 out of 18 important data classification problems, and have obtained a more robust performance than ARIMA and ETS time series methods in regression problems for data with strong periodicities.

Electrical characterization, crosstalk compensation and experimental examination of AlN-based piezoelectric micro resonators

Aluminum nitride based micro resonators are fabricated and measured with an all-electrical excitation and detection method in this paper. Low resistivity single crystal silicon is used as resonating element, serving simultaneously as bottom electrode for the piezoelectric layer. The elimination of the bottom metal electrodes reduces the number of stacked layers and stress in the cantilever; however, the short circuit connection between drive and sense port silicon grounds induces serious feedthrough capacitance effect. Electrical measurement results indicate that, the resonator output is a superposition of mechanical resonance behavior and electrical crosstalk from feedthrough capacitance. A general equivalent circuit model is derived to analyze the resonator’s electromechanical performance. To eliminate the electrical crosstalk, a compensation solution has been developed, by applying an inverted adjustable voltage to the common bottom electrode. Further experimental investigations of the device under different controlled pressures show that, the output amplitude after compensation is precisely symmetric around the resonance peak, and phase shift of -90° occurs at resonance, indicating that the feedthrough has been adequently cancelled out.

Design of Multilayer Ring Emitter Based on Metamaterial for Thermophotovoltaic Applications

The objective of this study is to design a broadband and wide-angle emitter based on metamaterials with a cut-off wavelength of 2.1 µm to improve the spectral efficiency of thermophotovoltaic emitters. To obtain broadband emission, we conducted the geometric parameter optimization of the number of stacked layers, the inner and outer radii of the nano-rings, and the thickness of the nano-rings. The numerical simulation results showed that the proposed emitter had an average emissivity of 0.97 within the targeted wavelength, which ranged from 0.2 µm to 2.1 µm. In addition, the presented multilayer nano-ring emitter obtained 79.6% spectral efficiency with an InGaAs band gap of 0.6 eV at 1400 K.

Morphological changes in graphene materials caused by solvents

The aim of this work is to determine the changes in morphology caused in thermally reduced graphene oxide (rGO) after it has been mixed with organic molecules with different surface properties. The morphology of the dried rGO after being mixed with 16 organic solvents was evaluated using statistically SEM analysis. The results obtained indicate that this process led, in some cases, to an increase both in the number of stacked layers and in the corrugation of each rGO sheet. The largest modifications were obtained after contact with organic solvents undergoing intramolecular interactions mainly governed by the hydrogen-bonding interactions (measured as the Hansen δh parameter) and the dipole-dipole molecular interactions (expressed by the Hansen δp parameter). On the other hand, the morphology of the rGOs remained unaltered when solvents with values of δp + δh in the range 10–26 MPa1/2 were used. These results represent a useful guide for the preparation of graphene-based composites in which the morphology of the graphene in the mixture is a crucial parameter which affects their characteristics.

DREM2: a facile fabrication strategy for freestanding three dimensional silicon micro- and nanostructures by a modified Bosch etch process

Three dimensional (3D) silicon micro- and nanostructures enable novel functionalities and better device performances in various fields. Fabrication of real 3D structures in a larger scale and wider applications has been proven to be limited by the technical difficulties during the fabrication process, which normally requires multiple process steps and techniques. Direct top-down fabrication processes by modifying a plasma etch process have been proposed and studied in previous studies. However, the repeatability, size uniformity and the maximal number of stacked layers were limited. Here we report a facile single run fabrication strategy for three dimensional silicon micro- and nanostructures. A good uniformity of suspended layer thickness has to be achieved and up to 10 stacked layers have been fabricated in a single run without other additional steps or post-process procedures. This is enabled by a modified multiplexed Bosch etch process, so called DREM (deposit, remove, etch, multistep), while the DREM etch is used to transfer the patterns into silicon, an extra isotropic etch creates a complete undercut and thus freestanding structures come into form. This method is easy to program and provides well-controlled etch profiles.

Analysis for deformation behavior of multilayer ceramic capacitor based on multiscale homogenization approach

Given the rapid improvements in the miniaturization, functionality, and efficiency of electronic products in recent years, the dielectric layers and electrodes of multilayer ceramic capacitors have become thinner, with the number of stacked layers also increasing. As a result, the deformation defects induced during manufacturing of the capacitors have increased. In this study, the deformation behavior of a multilayer ceramic capacitor composed of ceramic dielectric layers and Ni electrode layers during the compression process was analyzed numerically using the FEM. To analyze the deformation behavior of the capacitor, which consisted of several hundred laminated ceramic and Ni layers, in the plane direction, the material properties were represented by equivalent material properties based on the multiscale homogenization approach. Then, the deformation of the capacitor in the plane direction owing to the residual stress arising during the compression process was analyzed based on the calculated equivalent material properties. Finally, the possibility of a product defect with the size of the ceramic dielectric and electrode layers during the cutting process was predicted.

Structural and electronic properties of SnS2 stacked nanosheets: An ab-initio study

We present an ab-initio study of the structural and electronic properties of SnS2 stacked nanosheets using the standard LDA and GGA functionals as well as the newly developed variants of the non-local van der Waals (vdW) exchange correlation functionals, namely vdW-DF-revPBE and vdW-DF2-C09. We have examined different stacking configurations of the two, three and four SnS2 layers. The GGA-PBE functional fails to describe the interlayer binding energies and interlayer spacing of SnS2 nanosheets, while a good agreement is observed between the calculated and available experimental values when the van der Waals corrected functionals are used, mostly the vdW-DF2-C09. It is found that the interlayer interactions in the SnS2 films are not only vdW type but, the overlap of wave functions of neighboring layers have to be taken into account. We have observed a systematic reduction in the band gap with the increase in the number of stacked layers. This can be another way of controlling the band gap of SnS2 nanosheets as required for electronic devices.

Synthesis of fluorinated graphene oxide by using an easy one-pot deoxyfluorination reaction

The fluorination of two types of graphene oxides conducted by an easy and scalable deoxyfluorination reaction is reported. This reaction was carried out using diethylaminodifluorosulfinium tetrafluoroborate, a stable compound and an efficient reagent for replacing oxygenated functional groups of graphene oxide by fluoride. The graphene oxide produced by the Hummers’ method (GOH) showed lower reactivity than that produced by the Brodie’s method (GOB). X-ray photoelectron spectroscopy indicated that the highest fluorination degree achieved was 4.7 at.% when GOB was used, and the CF character corresponds to semi-ionic bonds. Additionally, a partial reduction of GO was concomitant with the functionalization reaction. The deoxyfluorination reaction changed the crystalline structure of GO, favoring the reconstruction of Csp2 structure of the graphene lattice and reducing the number of stacked layers. The fluorination led to the modification of the electronic band structure of this material, increasing the band gap from 2.05 eV for GOB to 3.88 eV for fluorinated GOB, while for GOH the low flurionation led to a slight increase of the band gap, from 3.48 eV to 3.57 eV.

Direct Imprinting of Scalable, High-Performance Woodpile Electrodes for Three-Dimensional Lithium-Ion Nanobatteries.

The trend of device downscaling drives a corresponding need for power source miniaturization. Though numerous microfabrication methods lead to successful creation of submillimeter-scale electrodes, scalable approaches that provide cost-effective nanoscale resolution for energy storage devices such as on-chip batteries remain elusive. Here, we report nanoimprint lithography (NIL) as a direct patterning technique to fabricate high-performance TiO2 nanoelectrode arrays for lithium-ion batteries (LIBs) over relatively large areas. The critical electrode dimension is below 200 nm, which enables the structure to possess favorable rate capability even under discharging current densities as high as 5000 mA g-1. In addition, by sequential imprinting, electrodes with three-dimensional (3D) woodpile architecture were readily made in a "stack-up" manner. The height of architecture can be easily controlled by the number of stacked layers while maintaining nearly constant surface-to-volume ratios. The result is a proportional increase of areal capacity with the number of layers. The structure-processing combination leads to efficient use of the material, and the resultant specific capacity (250.9 mAh g-1) is among the highest reported. This work provides a simple yet effective strategy to fabricate nanobatteries and can be potentially extended to other electroactive materials.

Investigation for the Feasibility of High-Mobility Channel in 3D NAND Memory

As the number of stacked layers in 3D NAND flash memory increases, the cell current for reading scheme is continuously decreased. The purpose of this paper is to study the integration of alternative channel materials with electron mobility higher than poly-Si (e.g., SiGe, InGaAs) in 3D NAND, as a feasible approach to improve current conduction and to enable further-scaling for future 3D NAND generations. Meanwhile, the industrial-relevant “Macaroni” channel geometry can also be applied in this new type of memory device for better gate controllability and higher cell drive current. A series of simulations are performed with Sentaurus TCAD to clarify the advantages of high-mobility channel materials in 3D NAND. It has been confirmed from the simulation results that the drive-current (Id) reduction for 3D NAND with high-mobility channel is much lower than that for counterpart with poly-Si channel as the number of memory stacked layer increases. Meanwhile, the variation of threshold voltage (Vth) and sub-threshold swing (SS) for high-mobility channel is also small. Therefore, the introduction of high-mobility channel material can be regarded as an effective and practical solution to enable further scaling for future 3D NAND generations with a channel-hole diameter down to 50 nm.

Organic Photovoltaics with Stacked Graphene Anodes

Graphene has recently been used to achieve power conversion efficiencies (PCEs) equal to those of ITO-based devices, although they remain a challenging and costly replacement for ITO. Herein, we employed chemical vapor deposition to grow graphene islands and transferred them onto a transparent substrate. The resulting stacked graphene films were characterized by Raman and UV–vis spectroscopies and conductivity measurements. Solar cells fabricated with stacked graphene (one to four layers)/PEDOT:PSS/P3HT:PCBM/Ca/Al architecture showed an enhancement of PCE as a function of the number of stacked layers. The highest efficiency was measured for the double-layered graphene anode because of its optimal conductance and transmittance. This work establishes that readily prepared layered graphene islands are a viable and economical substitute for ITO.

Nitrocellulose-based collodion gate insulator for amorphous indium zinc gallium oxide thin-film transistors

ABSTRACTA novel organic material named ‘collodion’ was suggested as a gate insulator for amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs). To find the optimized condition of the collodion gate insulator (CGI), the following three parameters of collodion solution were controlled: (1) the concentration of collodion solution; (2) the number of stacked layers; and (3) the spin-coating speed. The single-layered diluted CGI (collodion:ethanol=1:1) that was fabricated with a 3 krpm spin-coating speed exhibited an acceptable dielectric strength (J < 10−10 A/cm2 in the range of 1.1 MV/cm) and a high-dielectric constant (∼6.57) for the gate insulator layer. As a result, a-IGZO TFTs with CGI showed high-field effect mobility (∼17.11 cm2/Vs).

Stacked Self‐Assembled Cubic GaN Quantum Dots Grown by Molecular Beam Epitaxy

We have investigated the stacking of self‐assembled cubic GaN quantum dots (QDs) grown in Stranski–Krastanov (SK) growth mode. The number of stacked layers is varied to compare their optical properties. The growth is in situ controlled by reflection high energy electron diffraction to prove the SK QD growth. Atomic force and transmission electron microscopy show the existence of wetting layer and QDs with a diameter of about 10 nm and a height of about 2 nm. The QDs have a truncated pyramidal form and are vertically aligned in growth direction. Photoluminescence measurements show an increase of the intensity with increasing number of stacked QD layers. Furthermore, a systematic blue‐shift of 120 meV is observed with increasing number of stacked QD layers. This blueshift derives from a decrease in the QD height, because the QD height has also been the main confining dimension in our QDs.

Microemulsion-mediated hydrothermal synthesis of flower-like MoS2 nanomaterials with enhanced catalytic activities for anthracene hydrogenation

Flower-like intercalated MoS2 nanomaterials have been successfully synthesized via a microemulsionmediated hydrothermal (MMH) method, and characterized by X-ray diffraction, Raman spectroscopy, element analysis, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and Fourier transform infrared spectroscopy in detail. Their catalytic performance for anthracene hydrogenation was evaluated using a slurry-bed batch reactor with an initial hydrogen pressure of 80 bar at 350 °C for 4 h. The intercalated MoS2 nanoflowers synthesized from Na2MoO4 (MoS2-S) and H2MoO4 (MoS2-A) as molybdenum precursors have diameters of about 150 and 50 nm, respectively. MoS2 nanosheets on MoS2-S and MoS2-A possess stacking layer numbers of 5–10 and 2–5, and slab lengths of about 15 and 10 nm, respectively. The interlayer distances of MoS2-S and MoS2-A are both enlarged from 0.62 nm to about 0.95 nm due to the intercalation of NH4 + and surfactant molecules. The MoS2 nanoflowers have high catalytic activities for anthracene hydrogenation. The selectivity for octahydroanthracene, a deeply hydrogenated product, over MoS2-A is 89.8%, which is 31.0 times higher than that over commercial bulk MoS2. Fully hydrogenated product (perhydroanthracene) was also detected over MoS2 nanoflowers with a selectivity of 3.7%. The enhanced hydrogenation activities of MoS2 nanoflowers can be ascribed to the high exposure of catalytic active sites, resulting from the smaller particle size, fewer stacking layer, shorter slab length and enlarged interlayer distance of MoS2 nanoflowers compared with commercial bulk MoS2. In addition, a possible growth mechanism of MoS2 nanoflowers synthesized via the MMH method was proposed.

Spectroscopic investigations on the origin of the improved performance of composites of nanoparticles/graphene sheets as anodes for lithium ion batteries

Composites of nanoparticles/graphene sheets show an improved lithium storage capacity and cycling stability compared to bare graphene sheets (GSs). They are therefore considered as one of the promising candidates of anode materials for portable electrochemical energy storage devices requiring lightweight and ultrathin batteries. The practical application of these materials relies on the in-depth understanding of the origin of their improved performance. In this work, a composite of silver nanoparticles and graphene sheets (Ag/GSs) has been used as a model material to investigate the origin of the improved electrochemical performance by impedance, ex situ XPS and in situ Raman spectroscopy. We found that the Ag/GSs composite electrode has higher electrical conductivity than GSs. AgLix alloy was formed during the lithiation. Insertion of Ag nanoparticles into the interlayers between graphene sheets reduced the mean number of graphene stacking layers in the composite and provided a better site accessibility for Li+ insertion. Comparative in situ Raman measurements of them showed a completely reversible structural evolution of graphene sheets in Ag/GSs during the first lithiation/de-lithiation process, while for GSs the structural stability was worse. In combination, these effects are favorable for improving the reversible capacity and retaining the cycle stability of the Ag/GSs composite.

Structural control in porous/compact multilayer systems grown by magnetron sputtering

In this work we analyze a phenomenon that takes place when growing magnetron sputtered porous/compact multilayer systems by alternating the oblique angle and the classical configuration geometries. We show that the compact layers develop numerous fissures rooted in the porous structures of the film below, in a phenomenon that amplifies when increasing the number of stacked layers. We demonstrate that these fissures emerge during growth due to the high roughness of the porous layers and the coarsening of a discontinuous interfacial region. To minimize this phenomenon, we have grown thin interlayers between porous and compact films under the impingement of energetic plasma ions, responsible for smoothing out the interfaces and inhibiting the formation of structural fissures. This method has been tested in practical situations for compact TiO2/porous SiO2 multilayer systems, although it can be extrapolated to other materials and conditions.

Curvature of BEOL Cantilevers in CMOS-MEMS Processes

This paper presents the curvature characterization results of released back-end-of-line $5~\mu \text{m}$ -wide cantilevers for two different 0.18- $\mu \text{m}$ 1P6M complementary metal–oxide semiconductor microelectromechanical systems processes. Results from different runs and lots from each foundry are presented. The methodology and accuracy of the characterization approach, based on optical measurements of test cantilever curvature, are also discussed. Special emphasis is given to the curvature average and variability as a function of the number of stacked layers. Analythical equations for modeling the bending behavior of stacked cantilevers as a function of the tungsten (W) vias that join the metal layers are presented. In addition, the effect of various post-processing conditions and design techniques on the curvature of both single and stacked cantilevers is analyzed. In particular, surpassing certain time-dependent temperature stress conditions after release lead to curvature shifts larger than one order of magnitude. Also, the W via design was found to strongly affect the curvature of the test cantilevers. [2016-0293]