Interlayer Research Articles

Improved interface properties of an HfO2 gate dielectric GaAs MOS device by using SiNx as an interfacial passivation layer

A GaAs metal-oxide-semiconductor (MOS) capacitor with HfO2 as gate dielectric and silicon nitride (SiNx) as the interlayer (IL) is fabricated. Experimental results show that the sample with the SiNx IL has an improved capacitance—voltage characteristic, lower leakage current density (0.785 × 10−6 A/cm2 at Vfb + 1 V) and lower interface-state density (2.9 × 1012 eV−1 cm−2) compared with other samples with N2− or NH3—plasma pretreatment. The influences of post-deposition annealing temperature on electrical properties are also investigated for the samples with SiNx IL. The sample annealed at 600°C exhibits better electrical properties than that annealed at 500°C, which is attributed to the suppression of native oxides, as confirmed by XPS analyses.

Inter-Layer FEC Aided Unequal Error Protection for Multilayer Video Transmission in Mobile TV

Layered video coding creates multiple layers of unequal importance that enables us to progressively refine the reconstructed video quality. When the base layer (BL) is corrupted or lost during transmission, the enhancement layers (ELs) must be dropped, regardless of whether they are perfectly decoded or not, which implies that the transmission power assigned to the ELs is wasted. In this treatise, we propose an inter-layer forward error correction (FEC) coded video transmission scheme for mobile TV. At the transmitter, the proposed interlayer (IL) coding technique implants the systematic information of the BL into the ELs by using exclusive-OR operations. At the receiver, the implanted bits of the ELs may be utilized for assisting in decoding the BL. Furthermore, the data partition mode of H.264 video coding is utilized as the source encoder, where the type B and type C partitions will assist in protecting the type A partition. The IL coded bitstream will then be modulated and transmitted over a multifunctional multiple input multiple output (MF-MIMO) scheme for the sake of improving the system's performance in mobile environments. The proposed system may be readily combined with the traditional unequal error protection (UEP) technique, where extrinsic mutual information (MI) measurements are used for characterizing the performance of our proposed technique. Finally, our simulation results show that the proposed system model outperforms the traditional UEP aided system by about 2.5 dB of E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> or 3.4 dB of peak signal-to-noise ratio (PSNR) at the cost of a 21% complexity increase, when employing a recursive systematic convolutional code. Furthermore, unlike the traditional UEP strategies, where typically stronger FEC-protection is assigned to the more important layer, employing our proposed IL coding technique requires weaker FEC to the more important layer. For example, the system relying on channel coding rates of 0.85, 0.44, and 0.44 for the type A, type B, and type C H.264 video partitions, respectively, achieves the best system performance when employing a recursive systematic convolutional (RSC) code.

Large active area inverted tandem polymer solar cell with high performance via insertion of subnano-scale silver layer

We propose the deposition of ultra-thin silver layer (in subnano-scale) between bottom subcell and the hole-transport sublayer in the interlayer (IL), poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), in the inverted tandem polymer solar cell (t-PSC) for improving the wettability of aqueous hole-transport interlayer on hydrophobic active layer so that the performance is significantly improved and larger active area is allowed. The inverted t-PSC is composed of bottom subcell (regioregular poly(3-hexylthiophene) (P3HT): indene-C60-bisadduct (ICBA)) and the top subcell (thieno[3,4-b]thiophene/benzodithiophene (PTB7) with [6,6]-phenyl C71-butyric acid methyl ester (PC71BM)) along with the IL, PEDOT:PSS/ZnO nanoparticles. For the small-area (0.03cm2) t-PSC, the power conversion efficiency (PCE) can be improved from 7.06% without Ag layer to 7.81% with depositing 0.5nm Ag layer, and the device production yield from 40% (4 out of 10 devices) to near 100% (10 out of 10 devices), which can be ascribed to more efficient hole collection and reducing leakage current for the bottom subcell due to improvement of film forming of PEDOT:PSS. As the active area is increased to 1cm2, a PCE of over 6% (6.11%) can also be achieved by this approach, which is much higher than that without such Ag layer (2.19%) by a factor of 2.78. The reported active area of inverted t-PSC is in the range 0.02–0.15cm2; while the present method allows an inverted t-PSC to enlarge its active area to 1cm2, yet the PCE can maintain over 6%.

Understanding Process Impact of Hole Traps and NBTI in HKMG p-MOSFETs Using Measurements and Atomistic Simulations

The impact of the gate insulator process on interlayer (IL) hole traps in IL/high-K dual-layer p-MOSFET gate-stack is studied by physical and electrical measurements along with atomistic simulations. Processes that lead to higher concentrations of Hf and N in IL, measured by angle-resolved X-ray photoelectron spectroscopy, result in higher IL hole traps measured by flicker noise in prestress and verified by atomistic simulations. The influence of these process induced preexisting IL hole traps on parametric degradation of p-MOSFETs during Negative bias temperature instability (NBTI) stress is studied. The mechanism responsible for superior NBTI of thermal IL stack, having lower Hf and N content in the IL as compared with Chem-Ox IL stack, is explained.

X-ray spectroscopic study of SrTiOx films with different interlayers

Air-exposed systems SrTiOx/B/Si with different film thickness (7 nm and 15 nm) and different interlayers (ILs) (B: SiO2, Si3N4, and HfO2) grown by the atomic layer deposition (ALD) technique were studied using near edge x-ray absorption fine structure (NEXAFS), soft x-ray photoelectron spectroscopy (XPS), and hard x-ray photoelectron spectroscopy (HAXPES). It was established that the material of the IL influences strongly the lowest unoccupied bands and local atomic structure of the SrTiO3 film. In the case of SiO2 IL, the SrTiO3 film is characterized by nearly ideal cubic structure. The Si3N4 IL supports the Sr-enrichment of the air-exposed film. Presumably the enrichment of Sr occurs predominantly in the near surface range of the film. The HfO2 IL promotes the violation of the structure creating numerous defects inside the film. The surfaces of all the investigated SrTiOx films are carbonate-rich surfaces in the form of SrCO3. The SrCO3 content is minimal/maximal in the film grown on the SiO2/HfO2 IL.

(Invited) Metal Gate/High-κ Dielectric Gate Stack Reliability; or How I Learned to Live with Trappy Oxides

Over the last couple of scaling generations the gate stack in leading edge technology has migrated from Poly-Si and SiON to a metal gate with a bi-layer of a Hafnium based dielectric with a SiON interlayer (IL). This switch yielded immediate gains in gate leakage (Ig) and reliability, allowing a thinning of the inversion thickness (tinv) from ~20Å to less than 14Å. Even though gate length scaling and performance would drive further thinning of the dielectric stack, reliability considerations limit this. Understanding the fundamental reliability mechanisms enables mitigation with process changes and an optimization of reliability, performance, and operating voltage (Vmax). This paper will explore the main reliability mechanisms that are limiting scaling and the processes that improve reliability. Furthermore, the relationship between device level reliability and circuit reliability will be broached with ring oscillator data that shines light on the dominant reliability mechanism limiting Vmax.

Bentonite pore distribution based on SAXS, chloride exclusion and NMR studies

AbstractWater-saturated bentonite is planned to be used in many countries as an important barrier component in high-level nuclear waste (HLW) repositories. Knowledge about the microstructure of the bentonite and the distribution of water between interlayer (IL) and non-interlayer (non-IL) pores is important for modelling of long-term processes. In this work the microstructure of water-saturated samples prepared from MX-80 bentonite was studied with nuclear magnetic resonance (NMR) and small-angle X-ray scattering spectroscopy (SAXS) coupled with chloride exclusion modelling. The sample dry densities ranged between 0.7 and 1.6 g/cm3. The NMR technique was used to get information about the relative amounts of different water types. Water in smaller volume domains has a shorter relaxation time than that in larger domains due to the average closer proximity of the water to the paramagnetic Fe at the layer surfaces. The results were obtained using1H NMRT1ρrelaxation time measurements with the short inter-pulse CPMG method. The interpretation of the NMR results was made by fitting a sum of discrete exponentials to the observed decay curves. The SAXS measurement on bentonite samples was used to get information about the size distribution of the IL distance of montmorillonite. The chloride porosity measurements and Donnan exclusion calculations were used together with the SAXS results to evaluate the bentonite microstructure. In the model, the montmorillonite layers were organized in stacks having IL water between the layers and non-IL water between the stacks. In the modelling, the number of layers in the stacks was used as fitting parameters which determined the IL and non-IL surface areas. The fitting parameters were adjusted so that the modelled chloride concentration was equal to the measured one. The NMR studies and SAXS studies coupled with the Cl porosity measurements provided very similar pictures of how the porewater is divided in two phases in bentonite.

Scaled Gate Stacks for Sub-20-nm CMOS Logic Applications Through Integration of Thermal IL and ALD HfOx

The impact of gate insulator processes to achieve deeply scaled interlayer (IL)/high-k (HK) bilayer stacks for sub-20-nm CMOS on negative-bias temperature instability and positive-bias temperature instability is studied. IL scaling is done by novel low-thermal-budget rapid-thermal-process-based ultrathin IL and monolayer IL. Innovative IL top surface treatment enables integration of IL and atomic-layer-deposition-based hafnium oxide HK without vacuum break. Fully integrated stacks show scaling of equivalent oxide thickness down to ~6Å, with excellent gate leakage, mobility, and world-class BTI. The mechanism responsible for improved BTI is discussed.

NMR Study of Interlayer and Non-interlayer Porewater in Water-saturated Bentonite and Montmorillonite

ABSTRACTBentonite is planned to be used in many countries as an important barrier in high-level waste repositories. Assessment of the barrier with regard to,inter alia, its ability to hinder transport of dissolved radionuclides leaking from a damaged canister containing spent nuclear fuel, requires quantitative data about the pore structure inside bentonite. The present NMR study was made in order to determine the number of distinguishable porewater phases in compacted water-saturated samples of MX-80 bentonite and Na-montmorillonite. The samples were compacted to dry densities in the interval 0.7-1.6 g/cm3and subsequently saturated with Milli-Q water or 0.1 M NaCl solution in equilibrium cells. The NMR measurements were performed with a high-field 270 MHz NMR spectrometer using a short inter-pulse CPMG method to study proton T1ρrelaxation. The measured relaxation curves were found to consist of one faster and one slower proton relaxation. Subsequent analysis of the data indicated that the faster relaxation was associated with interlayer (IL) water between montmorillonite unit layers, while the slower one was associated with non-interlayer (non-IL) water located outside the interlayer spaces. The results indicate for compacted samples with a dry density of ≥ 1.0 g/cm3, that Na montmorillonite contains a larger relative volume of non-IL water than the corresponding MX-80 bentonite. This in turn, suggests that the stacking number in Na-montmorillonite is smaller than in MX-80 bentonite. Changing the porewater chemistry seemed to have some effect on the non-IL water content in the Na montmorillonite but not in the MX-80 bentonite.

Unraveling the interlayer-related phonon self-energy renormalization in bilayer graphene

In this letter, we present a step towards understanding the bilayer graphene (2LG) interlayer (IL)-related phonon combination modes and overtones as well as their phonon self-energy renormalizations by using both gate-modulated and laser-energy dependent inelastic scattering spectroscopy. We show that although the IL interactions are weak, their respective phonon renormalization response is significant. Particularly special, the IL interactions are mediated by Van der Waals forces and are fundamental for understanding low-energy phenomena such as transport and infrared optics. Our approach opens up a new route to understanding fundamental properties of IL interactions which can be extended to any graphene-like material, such as MoS2, WSe2, oxides and hydroxides. Furthermore, we report a previously elusive crossing between IL-related phonon combination modes in 2LG, which might have important technological applications.

Band alignment in Ge/GeOx/HfO2/TiO2 heterojunctions as measured by hard x-ray photoelectron spectroscopy

We investigate the interlayer (IL) thickness dependence of band offsets in a germanium based bilayer metal-oxide-semiconductor sandwich with an amorphous plasma enhanced atomic layer deposited (PE-ALD) HfO2 IL and PE-ALD grown TiO2 high k gate dielectric using hard x-ray photoelectron spectroscopy. The native Ge oxide shifts to higher oxidation state as the thickness of the IL layer was increased. The Hf 4f core line shows a broadening with increasing thickness, indicating the formation of Hf-Ge germanate. We observed a deviation from the bulk offset for films with ultra thin layers of HfO2.

Interaction of the dual effects triggered by AlN interlayers in thick GaN grown on 3C-SiC/Si substrates

In this work, the stress distribution of a thick GaN layer, which was realized with multiple AlN interlayers (ILs) on a 3C-SiC/Si (1 1 1) substrate, was mapped by low-temperature cathodoluminescence spectroscopy. A relaxation of compressive stress was distinguished in the top GaN layers above the AlN ILs by the inhomogeneous luminescent property. Through cross-sectional transmission electron microscopy, misfit dislocations (MDs) transformed from threading dislocations were observed. Analysis confirmed that the transformation process of dislocations should account for a part of compressive stress relaxation. As a result, a trade-off between compressive stress induction and dislocation transformation effects, both of which were induced by the AlN ILs, was proposed. In this model, the mean length of MDs in the GaN/AlN multi-layer structure was evaluated as L = 84 nm.

Study on the effects of AlN interlayer in thick GaN grown on 3C-SiC/Si substrates

For epitaxy of GaN on 3C-SiC/Si substrates, optimization of growth temperature of AlN interlayers (ILs) was performed. With a proper growth condition of AlN IL, crack-free 3.5μm thick GaN layer was realized by multiple AlN ILs on 3C-SiC/Si (111) substrate. The distribution of D0X peak position in low temperature cathodoluminescence spectra was mapped to investigate the stress in as-grown wafer. An increase of tensile stress was found in the top GaN layers above AlN ILs. Cross-sectional transmission electron microscopy images confirmed that AlN ILs could induce compressive stress and reduce threading dislocations in the GaN epilayer grown on 3C-SiC/Si. The reduction of dislocations should account for the part of incremental tensile stress revealed by the inhomogeneous distribution of luminescence.

The influence of AlN interlayers on the microstructural and electrical properties of p-type AlGaN/GaN superlattices grown on GaN/sapphire templates

AlN with different thicknesses were grown as in- terlayers (ILs) between GaN and p-type Al0.15Ga0.85N/GaN superlattices (SLs) by metal organic vapor phase epitaxy (MOVPE). It was found that the edge-type threading dis- location density (TDD) increased gradually from the mini- mum of 2.5 × 10 9 cm −2 without AlN IL to the maximum of 1 × 10 10 cm −2 at an AlN thickness of 20 nm, while the screw-type TDD remained almost unchanged due to the interface-related TD suppression and regeneration mech- anism. We obtained that the edge-type dislocations acted as acceptors in p-type AlxGa1−xN/GaN SLs, through the comparison of the edge-type TDD and hole concentration with different thicknesses of AlN IL. The Mg activation en- ergy was significantly decreased from 153 to 70 meV with a 10-nm AlN IL, which was attributed to the strain modula- tion between AlGaN barrier and GaN well. The large acti- vation efficiency, together with the TDs, led to the enhanced hole concentration. The variation trend of Hall mobility was also observed, which originated from the scattering at TDs.

Highly stable charge generation layers using caesium phosphate as n-dopants and inserting interlayers

Highly stable and efficient charge generation layers (CGLs) comprising caesium phosphate (Cs3PO4) doped 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) as n-type organic semiconductor and molybdenum trioxide (MoO3) doped N,N′-di-(naphthalen-1-yl)-N,N′-diphenyl-benzidine (α-NPD) as p-type organic semiconductor, respectively, are presented. By inserting narrow-gap organic copper-phthalocyanine (CuPc) and wide-gap insulating aluminum oxide (Al2O3) as interlayer (IL), we show that the long-term stability of the CGL can be improved. The variation of the CuPc IL thickness yields an optimum of 8 nm as a trade-off between minimal operating voltage and maximum voltage stability of the CGL. Luminance-current density-voltage characteristics and lifetime measurements of stacked green organic light emitting diodes (OLEDs) confirm the functionality and high voltage stability of the presented CGL. The luminous efficacy of the stacked OLED compared to the non-stacked reference device is nearly unchanged. However, the lifetime of the stacked device is enhanced by a factor of 3.5. Consistent with our experimental findings, we propose a model of the energy-level diagram of a fully doped CGL with IL based on a field-assisted tunneling mechanism.

Different strain relief behaviors in Al0.35Ga0.65N/GaN multiple quantum wells on GaN/Sapphire templates with AlN/GaN supperlattices and low-temperature AlN interlayers

Strain relief behaviors in Al0.35Ga0.65N/GaN multiple quantum wells (MQWs) grown on GaN/sapphire templates with either AlN/GaN supperlattices (SLs) or low-temperature AlN (LT-AlN) interlayers (ILs) between the MQWs and templates have been investigated. These two IL techniques can both effectively relieve the tensile strain in the MQWs, leading to crack-free surfaces and high crystalline quality. Further analysis shows that there are two distinct strain relief channels. In the case of adopting AlN/GaN SLs IL, microcracks and misfit dislocations account for strain relief in the MQWs. Microcracks are first generated in the IL, followed by activating formation of misfit dislocations. Then, the microcracks are immediately filled up by the subsequent epilayers. Contrastively, strain relief by using LT-AlN IL is mainly through the self relaxation process of the MQWs by surface roughening and strain compensation effect of LT-AlN IL.

420 DLC/WC-12Co溶射複合皮膜を有するアルミニウム合金A5052の疲労挙動に及ぼす中間層厚さの影響(GS 材料力学2)

420 DLC/WC-12Co溶射複合皮膜を有するアルミニウム合金A5052の疲労挙動に及ぼす中間層厚さの影響(GS 材料力学2)

Enhancement of STT-RAM Characteristics by Wet Clean Treatment after MTJ Etch Process

ABSTRACTThe effect of wet chemical treatment on the magnetic tunneling junction (MTJ) was examined. The tunneling magneto-resistance (TMR) increased and the resistance of anti-parallel state and parallel state decreased when a wet cleaning treatment was carried out after a reactive ion etching process. Furthermore, the exfoliation between the capping layer and Inter layer Dielectric (ILD) was prevented. Presumably, these were due to the elimination of the damaged layer and the residues. This investigation showed that the wet treatment after the MTJ patterning using RIE process could improve the MTJ properties without degradation of Hc, such as TMR and Rlow.

Strain–Stress Analysis of AlGaN/GaN Heterostructures With and Without an AlN Buffer and Interlayer

Abstract: The strain–stress analysis of AlxGa1−xN/GaN (x = 0.3) heterostructures with and without a high‐temperature HT‐AlN interlayer (IL) grown on sapphire (Al2O3) substrates and AlN buffer/Al2O3 templates via metal organic chemical vapour deposition (MOCVD) was carried out based on the precise measurement of the lattice parameters by using high‐resolution X‐ray diffraction (HRXRD). The a‐ and c‐lattice parameters were measured from the peak positions that were obtained by rocking the theta axis at the vicinity of the symmetric and asymmetric plane reflection angles, followed by the in‐plane and out‐of‐plane strains. Then, the biaxial and hydrostatic components were extracted from the total strain values that were obtained and were then discussed in the present study as the effect of the HT‐AlN buffer and IL. The AlN buffer layer (BL) affects the strain values of the AlGaN ternary layer (TL). A further effect was realized by inserting an AlN IL between GaN BL and AlGaN TL. However, the experimental results also show that an AlN IL changes the strain behaviour in the a‐ and c‐directions of the AlGaN TL from the tensile to compressive and the compressive to tensile type, respectively. These similar behaviours were observed in hydrostatic strain, biaxial strain and stress. Their reasons are explained with an effective a‐lattice parameter, post‐growth cooling and lattice and thermal mismatches.

Study of the Cesium Carbonate (Cs2CO3) Inter Layer Fabricated by Solution Process on P3HT:PCBM Solar Cells

In this paper, we studied the effect of the electron injection layer, Cesium carbonate (Cs2CO3), thickness on the performance of organic solar cell (OSC) based on blends of poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester fullerene derivative (PCBM). The polymer solar cell consists of molybdenum-oxide (MoO3) as a hole injection layer, P3HT and PCBM bulk hetero junction as an active layer, and Cesium carbonate (Cs2CO3) as an electron injection layer. We measured each device by current-voltage measurement and impedance spectroscopy which is widely used for equivalent circuit analysis of solid state structures. The device with the Cs2CO3 layer showed about 8–10% higher JSC and about 6–8% higher power conversion efficiency compared with the devices without the Cs2CO3 layer.