Thick Ag Research Articles

Ultra-large resistance ratio of silver programmable metallization cell with stacked silicon oxide films

Characteristics of silver programmable metallization cells (Ag-PMCs) with single and stacked silicon oxide (SiOx) films were investigated. The oxygen to silicon intensity ratio of chemically-deposited SiOx and thermally-grown SiO2 films was analyzed by the energy dispersive X-ray spectroscopy (EDS). Though the set and reset voltages of Ag-PMCs with stacked SiOx films were increased owing to the high stoichiometry of thermally-grown SiO2 layer, the resistance ratio of more than 106 can be realized by the thick Ag conductive filament (CF) for the low resistance value at low resistance state (LRS). The thermally-grown SiO2 film can also prevent the regeneration of Ag-CF during retention test, leading to the superior retention properties for more than 104 s. The Ag-PMCs with stacked SiOx films can sustain a resistance ratio of five orders of magnitude for more than 400 times stable set and reset cycling, suitable for future multi-bit/cell nonvolatile memory operation.

Root-cause failure analysis of photocurrent loss in polythiophene:fullerene-based inverted solar cells.

Metal oxide transport layers have played a crucial role in recent progress in organic photovoltaic (OPV) device stability. Here, we measure the stability of inverted and encapsulated polythiophene:fullerene cells with MoO3/Ag/Al composite anode in operational conditions combining solar radiation and 65 °C. Performance loss of over 50% in the first 100 h of the aging is dominated by a drop in the short-circuit current (Jsc). We reveal a concurrent loss in reflectance from 85% to 50% above 650 nm, which is below the optical gap of the used photoactive materials, hence, excluding any major degradation in the bulk of this layer. Correlating the responses of aged devices to a series of test structures comprised of ITO/ZnO cathode, MoO3/Ag, and MoO3/Ag/Al anodes and their combinations with the active layer allowed us to identify that the presence of Al causes the reduced reflectance in these devices, independent of the presence of the active layer. Systematic single-stress aging on the test structures further indicates that elevated heat is the cause of the reflectance loss. Cross-section transmission electron microscopy coupled with elemental analysis revealed the unsuspected role of Al; notably, it diffuses through the entire 150 nm thick Ag layer and accumulates at the MoO3/Ag interface. Moreover, XRD analysis of the aged MoO3/Ag/Al anode indicates the formation of Ag2Al alloy. Depth profiling with X-ray photoelectron spectroscopy advanced our understanding by confirming the formation of Ag-Al intermetallic alloy and the presence of oxidized Al only at the MoO3/Ag interface suggesting a concomitant reduction of MoO3 to most probably MoO2. This latter compound is less reflective than MoO3, which can explain the reduced reflectance in aged devices as proven by optical simulations. On the basis of these results, we could estimate that 20% of the loss in Jsc is ascribed to reduction of MoO3 triggered by its direct contact with Al.

Growth and characterization of single phase AgInS2 crystals for energy conversion application through β-In2S3 by thermal evaporation

Silver indium sulfide thin films have been successfully synthesized out from β-In2S3 buffer layers using appropriate heat treatments of evaporated β-In2S3/Ag. X-ray analysis show that the β-In2S3/Ag crystalline films with 60nm thickness of Ag, which were annealed under sulfur atmosphere at 400°C, were mainly formed by the ternary AgInS2. Raman spectra confirmed that the observed peaks were characteristics to AgInS2 chalcopyrite of thin film structure. The optical band gap of AgInS2, which was evaluated as nearly 1.80eV, was confirmed by the electrical study which yielded a value in the order of 1.78eV. The electrical conductivity, conduction mechanism, dielectric properties and relaxation model of this thin film were studied using impedance spectroscopy technique in the frequency range 5Hz–13MHz under various temperatures (370–440°C). Besides, complex impedance, AC conductivity and complex electric modulus have been investigated on the basis of frequency and temperature dependence.

Structured metal thin film as an asymmetric color filter: the forward and reverse plasmonic halos.

We observe asymmetric color filtering under unpolarized incidence in a structured metallic (Ag) film, where the center of an optically thick circular Ag disk surrounded by a step gap appears dark when observed from one side, and bright from the other. The latter situation corresponds to abnormally high optical transmission through the optically thick film. We explain this by a three-step process: coupling of photons to surface plasmon polaritons (SPPs), wave interference of SPPs forming resonant cavity modes, and out-coupling from SPPs to photons. Full wave electromagnetic simulations based on the finite element method support our findings. These results may have potential applications in areas such as optical color filtering and biosensing via dielectric detection within the step gap plasmonic cavity.

Effect of Au, Ag and Cu thin films' thickness on the electrical parameters of metal-porous silicon direct hydrogen fuel cell

The effect of the thickness of the gold, silver and cupper films on the electrical properties such as open circuit voltage (Voc) and short circuit current (Isc), in the direct hydrogen fuel cell, which uses water as a source of hydrogen, is studied by fabricating Metal/Porous Silicon/n-Silicon/Indium structures. The Porous Silicon (PS) layer on n-type (111) oriented silicon wafers were prepared by anodization. The thin films of Au or Ag or Cu with different thicknesses between 120 and 600 nm were deposited onto the PS surface by the electron-beam technique. The obtained results indicated that Voc and Isc, strongly depend on the Au, Ag and Cu layer thicknesses. The Au/PS/n-Si structure generated highest Voc and Isc values for all thicknesses of Au film. The best values of Voc and Isc were obtained at 325 nm as 0.89 V and 0.021 mA for Au, at 350 nm as 0.75 V and 0.017 mA for Ag, at 350 nm as 0.50 V and 0.010 mA, respectively.

Schottky contact by Ag on In2O3 (111) single crystals

The barrier height of a metal-semiconductor contact was studied by means of angle-resolved photoemission spectroscopy, which was implemented through stepwise Ag deposition on the ultra-high vacuum cleaved (111) surface of melt-grown In2O3 single crystals. A small Schottky barrier height of 0.22 ± 0.08 eV was determined by following the band bending of the valence band and core level spectra with Ag thickness and corrected for the photovoltage effect. In addition, the work function of Ag and the electron affinity of In2O3 were measured in situ to be 4.30 ± 0.05 eV and 4.18 ± 0.06 eV, respectively. Agreement was observed when comparing the barrier height from band bending to the calculated one by applying the Schottky-Mott rule, yielding a value of 0.12 ± 0.11 eV. Due to an additionally appearing photovoltage, an explicit reference to the surface electron accumulation layer is not necessary when discussing the Schottky character of the Ag/In2O3 contact.

Ag 완충박막 두께에 따른 IGZO/Ag 적층박막의 특성 변화

IGZO/Ag bi-layered films were deposited on glass substrate at room temperature with radio frequency and direct current magnetron sputtering, respectively to consider the effect of Ag buffer layer on the electrical, optical and structural properties. For all deposition, while the thickness of Ag buffer layer was varied as 10, 15, and 20 nm, The thickness of IGZO films were kept at 100 nm, In a comparison of figure of merit, IGZO films with 15 nm thick Ag buffer layer show the higher figure of merit (<TEX>$1.1{\times}10^{-2}{\Omega}^{-1}$</TEX>) than that of the IGZO single layer films (<TEX>$3.7{\times}10^{-4}{\Omega}^{-1}$</TEX>). From the observed results, it is supposed that the IGZO 100 nm/Ag 15 nm bi-layered films may be an alternative candidate for transparent electrode in a transparent thin film transistor device.

Measurements of L shell X-ray yields of thick Ag target by 6–29keV electron impact

Abstract In this paper, the L shell X-ray yields for a thick Ag target have been measured at incident electron energies of 6–29 keV. The experimental values are compared with the Monte Carlo simulation results that are obtained by using the PENELOPE code, in which the inner-shell ionization cross sections by electron impact calculated in the theoretical frame of distorted wave Born approximation are used. The experimental and simulation values are in agreement with ~10% difference. Meanwhile, the L shell X-ray production cross sections are also obtained based on the measured L shell X-ray yields for a thick Ag target in this paper, and are compared with other experimental Ag L shell X-ray production cross section data by electron and positron impact measured previously and some theoretical models. Some factors that could affect these comparisons are also discussed in this paper.

Photoelectron spectroscopy study of thin Ag films deposited on to amorphous In–Ga–Zn–O surface

Ag was thermally evaporated onto amorphous In–Ga–Zn–O (a-IGZO) thin film, and the Ag-thickness (<0.3nm)-dependent chemical states of the Ag-deposited a-IGZO thin-film surfaces were investigated by high-resolution X-ray photoelectron spectroscopy. As Ag layer thickness increased, Ag 3d shifted towards the lower binding energy (BE) side and In 3d developed a lower-BE component; however, O 1s, Ga 3d, and Zn 3d showed much smaller spectral feature changes than Ag 3d or In 3d. The analysis suggests that Ag atoms preferentially interact and share electrons with In atoms. The Ag 4d split feature at the valence band and the metallic states near the Fermi edge were noticeably visible when the Ag thickness was greater than 0.1nm.

Effect of Ag layer thickness on the electrical transport and optical properties of ZnO/Ag/MoOx transparent composite electrodes and their use in P3HT:PC61BM-based organic solar cells

In this paper, the optoelectronic properties and morphological features of indium-free ZnO/Ag/MoOx electrodes deposited by in situ combination of RF and DC sputtering at room temperature for low-cost organic photovoltaics has been discussed. The transparent composite electrode (ZnO/Ag/MoOx) was optimized by inspecting the formation of a continuous Ag thin film on top of the ZnO layer. It was found that a 9nm thick Ag film had the best Haacke figure of merit. Organic solar cells on these composite electrodes revealed good optical and electrical properties, making them a promising alternative indium-free and PEDOT:PSS-free organic solar cells.

Long-range chemical interactions in solid-state reactions: effect of an inert Ag interlayer on the formation of L10-FePd in epitaxial Pd(0 0 1)/Ag(0 0 1)/Fe(0 0 1) and Fe(0 0 1)/Ag(0 0 1)/Pd(0 0 1) trilayers

The effect of 0, 0.5, and 1 μm-thick Ag interlayers on the chemical interaction between Pd and Fe in epitaxial Pd(0 0 1)/Ag(0 0 1)/Fe(0 0 1)/MgO(0 0 1) and Fe(0 0 1)/Ag(0 0 1)/Pd(0 0 1)/MgO(0 0 1) trilayers has been studied using X-ray diffraction, 57Fe Mössbauer spectroscopy, X-ray photoelectron spectroscopy, and magnetic structural measurements. No mixing of Pd and Fe occurs via the chemically inert Ag layer at annealing temperatures up to 400 °C. As the annealing temperature is increased above 400 °C, a solid-state synthesis of an ordered L10-FePd phase begins in the Pd(0 0 1)/Ag(0 0 1)/Fe(0 0 1) and Fe(0 0 1)/Ag(0 0 1)/Pd(0 0 1) film trilayers regardless of the thickness of the buffer Ag layer. In all samples, annealing above 500 °C leads to the formation of a disordered FexPd1−x(0 0 1) phase; however, in samples lacking the Ag layer, the synthesis of FexPd1−x is preceded by the formation of an ordered L12-FePd3 phase. An analysis of the X-ray photoelectron spectroscopy results shows that Pd is the dominant moving species in the reaction between Pd and Fe. According to the preliminary results, the 2.2 μm-thick Ag film does not prevent the synthesis of the L10-FePd phase and only slightly increases the phase’s initiation temperature. Data showing the ultra-fast transport of Pd atoms via thick inert Ag layers are interpreted as direct evidence of the long-range character of the chemical interaction between Pd and Fe. Thus, in the reaction state, Pd and Fe interact chemically even though the distance between them is about 104 times greater than an ordinary chemical bond length.

Improvement of transparent silver thin film anodes for organic solar cells with a decreased percolation threshold of silver

Organic solar cells (OSCs) using thermally evaporated Ag thin films as the transparent anode are investigated with poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) films as the active layer. The optimal power conversion efficiency (PCE) of 2.57% is obtained for the device with the 11nm thick Ag layer, namely the percolation threshold of Ag. Then an interlayer of MoO3 between the Ag anode and glass substrate is introduced. Two different thicknesses of MoO3 (2nm or 10nm) are chosen here, corresponding to the unclosed or closed MoO3 layer, respectively. It is observed that the introduction of the MoO3 interlayer can effectively improve the wetting of Ag on the substrate and reduce the percolation threshold of Ag. When the MoO3 thickness is 10nm, since the surface energy of Ag (γ=1.25Jm−2) is higher than that of MoO3 (γ=0.06Jm−2), the Ag–Ag interactions are stronger than the Ag-substrate interactions, weakening the surface-modifying effect. In contrast, since the 2nm thick unclosed MoO3 layer may create preferred nucleation sites on the substrate to enhance the lateral growth of Ag film effectively, a very low sheet resistance of 9.32 Ω/□ and a relatively high transmittance are obtained for MoO3 (2 nm)/Ag (9 nm) anode. The PCE of corresponding OSCs can be improved to 2.71%, comparable to that of ITO-based reference OSCs (PCE of 2.85%). From our results, it is concluded that the performance of the Ag thin film electrode can be improved by decreasing the percolation threshold of Ag with a MoO3 interlayer (especially when the MoO3 layer is thin). It may be instructive for the further research of metal thin film electrodes.

Influence of annealing on the optical, structural and electrical properties of ZnO:Al/Ag/ZnO:Al multilayer stack structures

Multilayer stack structures ZnO:Al(20 nm)/Ag(x)/ZnO:Al(20 nm) with different thickness of the middle Ag(x) layer – x = 6 nm, 10 nm, 12 nm, 16 nm and 20 nm, were prepared by r.f. magnetron sputtering. The ZnO:Al and Ag layers were deposited by magnetron sputtering on glass substrates without heating. The two-layer structures ZnO:Al(20)/Ag(x) were annealed in N2 + H2 at 180 °C, 50 min., and then capped by the top ZnO:Al(20 nm) layer. The optical, structural and electrical properties were studied of the as-deposited and of the annealed three-layer stacks. The TEM, SEM and AFM analyses demonstrated changes of the stack structure with the Ag film thickness and after annealing. The transmittance and reflectance spectra revealed bands of Ag electrons plasma oscillations and inter-band d-shell Ag electrons which were red-shifted after annealing. The as-deposited structures had low resistivity (1×10−3 to 4×10−5 Ω cm), which decreased with the thickness of the Ag film due to the change in the carrier transport mechanisms. The value of the resistivity increased after annealing.

Anomalous photoelectric emission from Ag on zinc-phthalocyanine film

Photoelectric emission from organic and metal thin films is generally observed with irradiation of photon energy larger than 4 eV. In this paper, however, we report photoelectric emission from Ag on a zinc-phthalocyanine (ZnPc) layer at a photon energy of 3.4 eV. The threshold energy for this photoelectric emission is much smaller than the work function of Ag estimated by conventional photoelectron spectroscopy. The photoelectric emission by low-energy photons is significant for Ag thicknesses of less than 1 nm. Photoelectron spectroscopy and morphological study of the Ag/ZnPc suggest that the anomalous photoelectric emission from the Ag surface is caused by a vacuum level shift at the Ag/ZnPc interface and by surface plasmons of the Ag nanoparticles.

Infrared reflective properties of AZO/Ag/AZO trilayers prepared by RF magnetron sputtering

AZO/Ag/AZO trilayer films were prepared on glass substrates by radio frequency (RF) magnetron sputtering technology. Crystal structure, surface morphology, visible transmittance, and color scale of the AZO/Ag/AZO coated trilayers as functions of Ag and AZO layers thickness were investigated by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Atomic Force Microscopy (AFM), optical transmittance spectra and CIELAB system. In addition, the electrical and infrared reflection properties of the coated trilayers were examined by four-point probe system and Fourier Transform Infrared Spectroscopy. The results indicated that the Ag inner layer started forming a continuous film at the thickness of 10nm which was supported by XRD result of the distinct 200 and 220 Ag peaks. Besides, the highest average visible transmittance of 80.5% was obtained by the AZO (30nm)/Ag (10nm)/AZO (30nm) structure. Furthermore, the lowest sheet resistivity of 4.36Ω/sq and the highest infrared reflection rate of 96% in FIR region can be obtained by the AZO (30nm)/Ag (13nm)/AZO (30nm) structure. The high infrared reflection property of the AZO/Ag/AZO trilayers makes it a promising candidate for energy conservation coatings.

Evaluation of Corrosion Resistance of Multilayered Sn/Ag3Sn Electroplating on Cu Alloys for Electric Connectors

The anti-corrosion performances of multilayered Sn/Ag3Sn films with Ag thickness of 50 nm on Cu alloy materials were evaluated through a sulfidizing test in (NH4)2Sx solutions and an aging test at 473 K up to 2000 h, comparing with a commercial pure Ag film and a conventional reflowed Sn film on Cu alloy materials. The multilayered Sn/Ag3Sn films succeeded in the accelerated sulfidizing test, with unchanged appearance and stable electrical contact resistance, even after immersion in a 0.2 ml/L (NH4)2Sx solution for 120 h. Moreover, the multilayered Sn/Ag3Sn films exhibited low and stable electrical contact resistances equivalent to as-plated samples even after heating at 473 K for 2000 h. The excellent corrosion resistance of the multilayered Sn/Ag3Sn films can be mainly ascribed to the chemical stable Ag3Sn covered with a thin Sn oxide film and the inward Ag diffusion that suppressing outward Cu diffusion during aging.

Inelastic tunneling conductance and magnetoresistance investigations in dual ion-beam sputtered CoFeB(110)/MgO/CoFeB (110) magnetic tunnel junctions

Magnetic tunnel junctions (MTJs) comprising Ta(5)/NiFe(5)/IrMn(15)/CoFeB(5)/Mg(1)/MgO(3.5)/ CoFeB(5)/Ta(5)/Ag(20) (thickness in nm) with (110) oriented CoFeB layers are grown using dual ion beam sputtering. The tunnel magnetoresistance (TMR) of MTJs is found to be significantly bias dependent and exhibits zero bias anomaly (ZBA) which is attributed to the presence of magnetic impurities or diffusion of Mn from antiferromagnetic IrMn in the barrier. Adjacent to the ZBA, two peaks at 24 ± 3 mV and 34 ± 3 mV are also observed, which differ both in intensity as well as their position in the antiparallel and parallel magnetic states, suggesting that they are due to magnon excitations. In addition to this, a phonon peak at 65 ± 3 mV is also observed. The effect of temperature on the inelastic and elastic tunneling contributions is studied in detail in 25–300 K range using the Glazman and Matveev model. Ten series of localized states are found to be involved in hopping conduction in the forbidden gap of MgO barrier. The effect of presence of such inelastic channels is found to be insignificant at low temperatures yielding sizeable enhancement in TMR.

Contact Resistance Measurement of Electrode on Silicon Prepared By Autocatalytic Electroless Metallization Using Metal Nanoparticles

We reported the adhesive metal-film formation by autocatalytic electroless metallization on silicon (Si) by using gold (Au) nanoparticles1). Autocatalytic electroless deposition, which is a conventional method to metalize nonmetallic substrates, has several advantages including simplicity of process, uniformity of films, and the covering of complicated structures. So, the process is expected to replace sputtering of back metal of power devices and screen-printing of thick film electrodes of solar cells. In this study, we determined contact resistance (Rc) between electrolessly deposited metal electrode and Si semiconductor by using TLM (transfer length model) method shown in Fig.1.Figure 2 shows photo and dimension of test sample, and Fig.3 shows schematic process flow of preparing two test samples; 1. Photoresist pattern formation: 2. Au nanoparticles formation by displacement reaction using a mixture solution of HAuCl4 and HF: 3. Autocatalytic electroless deposition of nickel-phosphorus alloy (Ni-P) film for sample (A), and: 4. Electron-beam silver (Ag) deposition on electrolessly deposited Ni-P film for sample (B). The thickness of Ni-P films was 0.25 mm and Ag thickness on Ni-P film was 1.15 mm.We measured Rt of samples and determined ρc. Rt and ρc are given byRt = 2Rm + 2Rc+ Rs ρc = Rm + Rc.Figure 4 shows TLM result of samples (A) and (B). The values of ρc were 140 mΩ cm2 in (A) and 13 mΩ cm2 in (B). These results indicate that the ρc is mainly determined by resistance of bulk metal (Rm) and the contact resistance (Rc) of these samples is lower than 13 mΩ cm2. The Rc of screen-printed-and-fired Ag electrodes of crystalline Si solar cells was reported as 2~3 mΩ cm2 lower than ρc of sample (B)2). Contact resistance (Rc) is important for devices rather than ρc 3). The Rc of electrode prepared by the autocatalytic electroless metallization using Au nanoparticles is approaching the value of conventional electrodes without any heat treatment. We also review interface structure and contacting mechanism between Au nanoparticles and Si semiconductor4).ACKNOWLEDGEMENTSThe present work was partly supported by JSPS KAKENHI (23560875) and A-STEP from JST.REFERENCE1) S.Yae, et al., ECS Trans., 53(6), 99 (2013).2) Yi Yang, et al., Energy Proc., 8, 607 (2011).3) P.L.Hower, et al., Semicon. Semimet., 7A, 147 (1971).4) H. Atsushiba, et al., Abst. 225th ECS meeting (D2), (2014).

Growth of polycrystalline Ag/Ni multilayers at room temperature

Ag/Ni multilayers have been grown on oxidized Si(100) substrates by dc magnetron sputtering at room temperature. The Ag thickness is varied in the range 2.5–20Å. A combination of X-ray reflectivity, diffraction and transmission electron microscopy shows that the films have excellent layering for all Ag thicknesses. This is due to the use of an amorphous AlZr wetting layer which promotes smooth, layered growth of the Ag and Ni. The results demonstrate the feasibility of growing good quality multilayers of high mobility metals on oxide substrates without substrate cooling.

Anisotropic electronic conduction in metal nanofilms grown on a one-dimensional surface superstructure

We performed in situ conductivity measurements by multiple microscopic probes of Ag nanofilms grown on a periodic array of indium atomic wires on Si(111). Within the investigated thickness range the transport properties differ markedly from the bulk case. The ratio between the in-plane conductivity along and perpendicular to the In wires is 1.4 for the 3 monolayer (0.7 nm) thick Ag film and approaches unity with increasing film thickness. The observed anisotropy at the initial stage of the film growth is far larger than expected from the quasi-one-dimensional quantum well electronic structure of the films and ascribed to the carrier scattering at the film/vacuum and film/substrate interfaces. Our findings show that an ordered monolayer inserted at the interface enables drastic changes of the transport behavior of the whole metal nanofilm.