Ag Paste Electrode Research Articles

Electrical contact effects of flexible self-supporting DNA thin films for storage devices

The development of flexible DNA thin films embedded with diverse functional nanomaterials might be beneficial for electronic devices and biosensors. In this work, we fabricated two different types of electrodes (i.e. metal paste spotted electrodes and metal layer electrodes) on flexible drug- and dye-embedded DNA thin films to examine their electrical and capacitance properties for conduction and energy storage, respectively. Enhanced current and reduced capacitance of drug-embedded DNA thin films compared with pristine DNA with Ag paste electrodes were observed due to the intrinsic characteristics of the drugs. We used the electron-beam deposition process to fabricate relatively large-area metal-coated (e.g. Au and Al) electrodes, which ensures the creation of metal layers on both sides of the flexible thin films while improving metal contact. There was a significant current increase in DNA thin films with metal layer electrodes compared with DNA thin films with Ag paste electrodes. Furthermore, capacitances measured from Au/DNA/Au and Al/DNA/Al capacitors were relatively more stable than from Ag paste DNA thin films. The physical properties of our samples might be easily controlled by manipulating functional nanomaterials in DNA thin films and various types of metal layer electrodes. Our self-supporting DNA thin films with integrated nanomaterials and durable metal layer electrodes might be employed in flexible electronic devices such as nanogenerators, skin electronics and biosensors in the future.

Screen-Printable Silver Paste Material for Semitransparent and Flexible Metal-Semiconductor-Metal Photodetectors with Liquid-Phase Procedure.

Photodetectors are widely applied in modern industrial fields because they convert light energy into electrical signals. We propose a printable silver (Ag) paste electrode for a highly flexible metal–semiconductor–metal (MSM) broadband visible light photodetector as a wearable and portable device. Single-crystal and surface-textured silicon substrates with thicknesses of 37.21 μm were fabricated using a wet etching process. Surface texturization on flexible Si substrates enhances the light-trapping effect and minimizes reflectance from the incident light, and the average reflectance is reduced by 16.3% with pyramid-like structures. In this study, semitransparent, conductive Ag paste electrodes were manufactured using a screen-printing with liquid-phase process to form a flexible MSM broadband visible light photodetector. The transmittance of the homemade Ag paste solution fell between 34.83% and 36.98% in the wavelength range of visible light, from 400 nm to 800 nm. The highest visible light photosensitivity was 1.75 × 104 at 19.5 W/m2. The photocurrents of the flexible MSM broadband visible light photodetector were slightly changed under concave and convex conditions, displaying stable and durable bending properties.

Fabrication of conductive silver paste recovered from leaching of waste catalyst using hydrochloric acid.

Transition metal compounds based on silver (Ag) and palladium (Pd) are extensively used as catalysts in the petrochemical industries. The catalytic activities of Ag and Pd decrease over time and hence need to be discarded. The recovery of elements like Ag from waste catalyst is essential because of its limited availability and cost, and it is environmentally beneficial with regards to recycling. In this study, Pd and Ag were leached from waste catalyst providing an alternative source suitable for a Ag paste electrode. Through an efficient reduction process, AgCl particles were obtained which serve as a precursor to synthesize Ag using ammonia as the solvent. The obtained Ag was fabricated to Ag paste by using mixed dispersion and solvent. The electrical resistivity of the Ag paste was recorded as 6.14 μΩ cm at 417 °C in a hydrogen atmosphere.

Hydrophilicity Control of Ag-Paste Electrodes by UV/Ozone Treatment.

Ag-paste is used as an electrode material in various fields as a manufacturing advantage that enables solution processing. However, when a subsequent thin film is formed on the solidified Ag-paste electrode, there is a fear that the bonding force between the Ag-paste electrode and the subsequent thin film is weakened and peeled off due to the low surface energy of the Agpaste electrode. It is necessary to increase the surface energy of the Ag-paste electrode surface since it ultimately directly affects the yield of the device or product. In this study, the UV/ozone treatment process was introduced to increase the Ag-paste surface energy, thereby making the surface hydrophilic. Additionally, it was confirmed that the UV/ozone treatment process affected only the surface of the Ag-paste electrode by extracting the contact resistance.

Chemical treatment of Ag paste electrodes for surface energy control

Though various metal powders are used as the main components of conductive pastes, silver is most widely used owing to its high conductivity and strong corrosion resistance. Hence, silver paste is required for the manufacturing of many items, such as large-area display panels and semiconductor chips. However, electrodes made of silver paste commonly have low surface energy levels, resulting in hydrophobicity. To strengthen the adhesive force between films when silver paste is used as a component in items consisting of many film layers, the silver paste must have high surface energy. In other words, it must show low contact angles in water-drop measurements. Despite the proposal and practicality of the plasma treatment method, this method can cause radical damage, and it is undesirable for batch processes. In this study, the surface energy of a silver paste electrode was changed by dipping it into a sulfuric acid solution. A simple but effective controllable method by which to manage the surface energy is demonstrated, which may be useful for the selective control of specific films on large-area substrates in the future.

Electrical characterization of thermoelectric generators based on p-type Yb0.6Co4Sb12 and n-type Fe2.0Co2.0Sb12 thermoelectric materials

In this study, thermoelectric power generation (TEPG) device (D) was fabricated. The device based on p-Yb0.6Co4Sb12 and n-Fe2.0Co2.0Sb12, fabricated by using the solid state microwave. 8-couples of legs connected and attached to alumina substrates by Ag paste–Cu plate–Ag paste electrodes, with dimensions of 25 mm by 25 mm were used to fabricate the device. The maximum output power (Pmax) and the open-circuit voltage (Voc) was estimated based on the temperature difference (∆T) of 210 K and the hot-side temperature (TH) of 603 K for the module. We found the obtained open-circuit voltage (Voc) was 18.046 mV and the maximum output power (Pmax) was 12.732 μW.

Flexible piezoresistive pulse sensor using biomimetic PDMS mold replicated negatively from shark skin and PEDOT:PSS thin film

We propose a newly designed and fabricated flexible piezoresistive pulse sensor (FPPS) using a biomimetic PDMS mold replicated negatively from shark skin and PEDOT:PSS thin film. Its feasibility to measure physiological signals from the human body using FPPS was tested. The FPPS consists of a sensor element with PEDOT:PSS film coated on the PDMS substrate and two electrodes with copper tape as a counter electrode almost covering the surface of the sensor element and an Ag paste electrode on the edge of one side of the sensor element. The PDMS substrate was negatively replicated from shark skin as a biomimetic mold, and the PEDOT:PSS sensing film was coated on the replicated PDMS substrate to fabricate the sensor element of the FPPS. The unique geometry of shark skin remarkably affects the decrease of contact resistance by about 700-fold until the pressure range of ˜500 Pa compared to using PEDOT:PSS film on the planar PDMS substrate. The reason why the contact resistance decreases with increasing pressure is that the conducting points increase in the PEDOT:PSS chains with increasing pressure. In the low pressure range (<0.7 kPa) and high pressure range (0.7 through ˜6 kPa), the sensitivities were 62.56 kPa−1 and 8.32 kPa−1, respectively. For the feasibility test, physiological pulse signals were measured from a human subject’s body using the FPPS, the S.I. of 6.73 m/s and R.I. of 64.03% were close to the normal range of S.I. and R.I., which are 5.72 ± 0.28 m/s and 48.19 ± 9.51%, respectively. The calculated vascular age, 24.5 years old, was similar to 24.9 years old, the actual age of the subject.

Microscopic investigation on sintering mechanism of electronic silver paste and its effect on electrical conductivity of sintered electrodes

In view of extensive application of silver (Ag) paste metallization in the manufacture of electronic devices, it is of great significance to accurately grasp the factors affecting the Ag paste electrode conductivity and the relevant mechanism. Although so far many progresses have been made in the improvement of Ag paste technology, there is still a lack of comprehensive understanding of the microscopic mechanism about Ag paste sintering. Herein, this article tries to relate the conductivity of Ag paste electrodes sintered at different temperatures to those factors, including the morphology, grain size and aggregation state of Ag powder used, as well as the glass frit additive by investigating the microstructure evolution of silver powder (paste) in the sintering process. The results show that these factors determine the grain growth rate and the structure densification during the Ag paste sintering, and thus make an important influence on the electrode conductivity. In general, the larger the grain size and the denser the structure, the greater the electrode conductivity. Therefore, the high electrode conductivity can be achieved by using the flake shaped or spherical Ag powder with a nano-assembly structure. According to the microscopic observations, we suggest that the sintering process should include three stages at temperatures from 300 to 800 °C, i.e. the merging of nanocrystallites in assemblies, interconnection of separated particles, and sintering completion. The influence of glass frit additive on Ag powder sintering is attributed to the dissolution of Ag grain surface by glass melt. This effect may help to increase the grain growth rate and structure densification degree. However, the entry of glass phase matter into Ag grain boundaries would impede the electron transport between grains. Therefore, with increasing the amount of glass phase additive in the Ag paste, the electrode conductivity increased first and then decreased rapidly.

Resistive random access memories fabricated by using solution-processed AlZnSnO semiconductor films and indium ball electrodes

Resistive random access memories (ReRAMs) using solution-processed AlZnSnO (AZTO) oxide semiconductor films as resistive switching layers were fabricated. Electrodes were prepared by applying Ag paste or by pressing indium balls onto the AZTO surface. Vacuum processes were not required. The resistive switching behavior was not found for the ReRAM using a Ag paste electrode. However, a significant resistive switching characteristic could be obtained when using an In ball as the electrode. In addition, by adjusting compliance current from 80 mA to 20 mA, a stable resistance difference between high and low resistance state of 1839 Ω could be obtained over 500 operations. The ReRAM also exhibited good data retention capability and read disturb immunity for at least 103 s. Physical mechanisms of current conduction and resistance switching behavior were also investigated.

Influence of the contact interface on the electrical characteristics of a ZnO microwire with silver paste electrodes

We investigate the influence of the contact interface on the electrical properties of a ZnO microwire (MW) with silver (Ag) paste electrodes. The ZnO MW devices that are produced by dropping Ag paste on the ZnO MW surface followed by a curing step at an elevated temperature exhibit linear current-voltage characteristics, whereas the devices with Ag paste electrodes dropped upon a heated ZnO MW exhibit a non-linear electrical behavior. The results of electron microscopy and cathodoluminescence show the effect of the contact interface properties, such as interfacial defects and/or charge trap sites, between the ZnO MW and Ag paste electrodes. An energy band model is suggested to explain the charge transport mechanism for different types of Ag contacts on the ZnO MW.

Effects of Electrode on Dielectric Properties of Barium Iron Niobate Ceramics Doped with Gallium Oxide

Ba (Fe0.8Ga0.2)0.5Nb0.5O3 ceramics were synthesized via a solid state reaction method. The Raman spectrum analysis indicated that the sample presented a cubic structure. Dielectric measurement on the ceramics with Ag-paste and Au-sputtered electrodes showed that all ceramic samples exhibited very high dielectric constants with a strong frequency dispersion. The Au-sputtered electrode samples presented higher dielectric tunability the dielectric constant than Ag-paste electrode samples.This behaviour was related with the electrode effect, occured in the studied samples.

Highly Flexible Magnetoelectronic Device Integrated With Embedded Ag Nanoparticle Electrode

A flexible magnetoresistance (MR) device is fabricated through the hybrid process of embedding an Ag nanoparticle electrode by thermal imprinting and magnetic multilayer sensor element by sputtering on a polyethylene naphthalate (PEN) substrate. The MR signal profiles for a ring type sensor deposited on the PEN substrate show typical anti-symmetric curves centered for the field H=0, and the maximum signal and its field sensitivity are nearly the same as those of sensors deposited on Si and glass substrates. The root mean square (rms) roughnesses and magnetic properties of magnetic thin film deposited on the different substrates show that Hex was decreased with increasing roughness. Further, MR change with temperature had no significant effect on the sensor performance. The stability of Au electrode and Ag paste electrode were compared during the bending of MR sensor, revealing the cracking of Au electrode above 45°. However, Ag paste electrode was stable up to 90°. The field sensitivity of the MR signal for the full range of fields is inversely proportional to the effective anisotropy field, which is the sum of exchange-bias and stress-induced anisotropy fields. As a whole, the field sensitivity of MR signal depends on bending stress at the sensor position.

Electrical characterization of thermoelectric generators based on p-type Bi0.4Sb1.6Se2.4Te0.6 and n-type Bi2Se0.6Te2.4 bulk thermoelectric materials

In this study, we fabricated two thermoelectric (TE) generation (TEG) devices based on p-Bi0.4Sb1.6Se2.4Te0.6 and n-Bi2Se0.6Te2.4 bulk TE materials. The overall dimensions of these devices, which comprise 9 (D1)-and 18(D2)-couples of legs connected and attached to alumina substrates by Ag paste–Cu plate–Ag paste electrodes, are 50mm ×25mm and 50mm ×50mm, respectively. The open-circuit voltage (Voc) and the maximum output power (Pmax) were estimated in terms of the temperature difference (ΔT) between hot (TH) and cold (TC) junctions as well as the number of p–n couples of the TEG devices. The significance of the resistances, including the internal resistance (Rin) and contact resistance (Rc) between legs and electrodes, are discussed. Pmax obtained with the D2 device was 273mW under thermal conditions of TH=523K and ΔT=184K.

High Temperature Phase Transition in Cs3D(SO4)2

The M3XðYO4Þ2 type crystals have so-called zerodimensional hydrogen bonds consisting of isolated YO4{X{YO4 dimers, where M 1⁄4 NH4, K, Rb, Cs; X 1⁄4 H, D; Y 1⁄4 Se, S. It is well known that some of the member crystals undergo successive structural phase transitions, and show marked isotope effects on the antiferroelectric (ferroelectric) phase transitions below room temperature. On the other hand, above room temperature, most of the members exhibit the ferroelastic-superionic phase transitions, and show a high electric conductivity above the transition points. The high temperature phase transitions are due to the destruction and the reconstruction of hydrogen bonds. However, for most cases, the phase transition points do not exhibit the normal type of isotope effect on deuteration. These show the negative isotope effect in which lowering of the transition temperature is seen by the deuteration, for example, Cs3H(SeO4)2 ! Cs3D(SeO4)2. Tricesium hydrogen disulfate, Cs3H(SO4)2, (abbreviated as TCHS) also belongs to M3XðYO4Þ2 type crystals. So far no phase transition point has been reported in TCHS above and below room temperature. Then the deuterated compound TCDS may exhibit the ferroelastic-superionic phase transition at a some point above room temperature, if this compound follows the negative isotope effect on ferroelastic-superionic transition temperature (Ti). In order to confirm the effect on Ti in TCDS, the measurements of the dielectric constant, the electric conductivity and the differential scanning calorimetry (DSC) are performed. Single crystals of TCDS were prepared by successive recrystallizations from D2O solution containing Cs2SO4 and H2SO4 with molar ratio 3 : 1. Both (001) and (00 1) planes of the sample crystal were coated with Ag paste electrodes. The electric capacity and the complex impedance were measured in the direction perpendicular to the (001) plane, in the temperature region from 350K to 450K, with an automatic LCR-meter, HIOKI-3531, using 100KHz electromagnetic wave. The dielectric constant and the electric conductivity of TCDS were calculated from the data of electric capacity and the complex impedance, respectively. The temperature fluctuation of the sample is suppressed within 0:1K by a precise temperature controller. The measurement by DSC was performed in the temperature region from 350K to 470K in the heating rate of 3 C/min. It was also comfirmed by DSC signals that no protonated compounds TCHS exhibited the phase transition in the temperature region from 350K to 490K. In Fig. 1, the temperature dependence of the dielectric constant of TCDS is shown; the dielectric constant increases with increasing temperature and jumps discontinuously at about 422K. On further heating, it decreases rapidly. when temperature is increased further, the dielectric constant increases exponentially. The temperature dependence of the dielectric constant around 422K seen in Fig. 1 is similar to those found in the cases of the ferroelastic-superionic phase transitions of Cs3D(SeO4)2 and K3H(SeO4)2. 5,6) The temperature dependence of the electric conductivity of TCDS is plotted in Arrhenius coordinates as shown in Fig. 2. The conductivity has a value of about 5:0 10 8 cm 1 at 350.1K (1000=T 2:86) and increases sharply with increasing temperature up to about 422K (1000=T 2:37). The electric conductivity jumps suddenly from 7:3 10 7 cm 1 to 9:7 10 4 cm 1 at 422K, and drops just above this temperature as seen also in the case of the dielectric constant in Fig. 1. On further heating, it increases exponentially. The temperature dependence of the electric conductivity shown in Fig. 2 is very similar to that of AgI which undergoes the superionic phase transition. High values of dielectric constant above 422K in Fig. 1 may be considered as due to high electric conductivities in this temperature region. However, the reason for the dropping of just above 422K is unknown. According to Fig. 1. Temperature dependence of the real part of dielectric constant 0 of Cs3D(SO4)2 along the direction perpendicular to the (001) plane at 100KHz.

A.c. powder electroluminescence devices using ZnGa2O4:Mn phosphor

Zinc gallate, ZnGa2O4 was recently investigated for the application to vacuum uorescent displays (VFDs) utilizing low-voltage cathodoluminescence. The ZnGa2O4 host lattice without dopant shows blue emission [5, 6]. The phosphor shows green [1±3] and red [4] emmision when it is doped with Mn2‡ and Cr3‡ activators. A high luminous ef®ciency had been obtained when the phosphor was operated at low voltage (10±300 V). The results of low accelerating voltage and high luminous ef®ciency led us to study the electroluminescence (EL) characteristics of the ZnGa2O4:Mn phosphor. There are a few papers reporting the electroluminescence (EL) of the ZnGa2O4:Mn phosphor. Thin ®lm electroluminescence devices (TFEL) had been developed using ZnGa2O4:Mn phophor thin ®lms which were deposited by RF magnetron sputtering on polished BaTiO3 ceramic sheets [7]. In this paper, we report the fabrication of the a.c. powder electroluminescence (ACPEL) devices. The ZnGa2O4:Mn ACPEL device was developed by the printing technique. First, ZnO (99.999%), Ga2O3 (99.999%) and MnO (99.9%) powders were mixed in 1 : 1 :0.001 mole ratio and ball-milled with alcohol for 24 h. The mixed powders were dried at 100 8C and sintered at 1375 8C for 5 h in air to form the doped zinc gallate (ZnGa2O4:Mn) phosphor powder. The phase identi®cation of the phosphor powder was carried out on a Siemens D5000 X-ray diffraction (XRD) equipment with CuKa radiation. Fig. 1 shows X-ray diffraction patterns of ZnGa2O4:Mn and ZnGa2O4 powders. There are no ZnO-phase or Ga2O3-phase peaks discernible in any of the samples. The subsolidus equilibria study of the ZnO-Ga2O3 system showed no appreciable solid solubilities of ZnO or Ga2O3 in the ZnGa2O4 compound [1]. All the sintered powders exhibit the spinel structure of the ZnGa2O4 powder. The lattice constant of the ZnGa2O4:Mn powder was calculated to be 0.8365 nm. The result is consistent with the value of 0.837 nm [8]. It is shown that the concentration of Mn dopant is much less so that it cannot in uence the crystal structure of host lattice. The a.c. powder electroluminescence (ACPEL) devices were prepared by the printing method. The cross-sectional structure of the ZnGa2O4:Mn ACPEL device is shown in Fig. 2. The device consisted of the indium tin oxide (ITO) coated glass, ZnGa2O4:Mn emitting layer, BaTiO3 insulating layer, and Ag paste electrode. Initially, an ITO coated glass substrate was etched in the requisite manner. Secondly, the ZnGa2O4:Mn phosphor powder was mixed with the dielectric organic binder (cyanoethyl cellulate) and deposited on the ITO substrate by printing. The high dielectric material (BaTiO3) was printed upon the phosphor ®lm to protect against breakdown. Finally, the Ag paste was printed as an electrode ®lm. Fig. 3 shows the scanning electron microscope (SEM) image and the corresponding cathodulminescence (CL) image of the ACPEL device in its cross-sectional view. It is interesting to note that the interface between the ZnGa2O4:Mn phosphor layer and the BaTiO3 insulator layer cannot be apparently distinguished in the SEM image (Fig. 3a). In contrast, we can easily characterize the thicknesses of each of the layers of the ACPEL device with the CL image (Fig. 3b). The thickness of the phosphor, the BaTiO3 and the Ag are evaluated to be 10, 13 and 6 im respectively. We can calculate the electric ®eld in the printed phosphor layer by evaluating the thickness of the phosphor layer. Among transition-metal ions, Mn2‡ ions are usually used as luminescent centres in the phosphor powder. Mn2‡ centres in the ZnGa2O4 host lattices show green luminescence with a peak at 508 m, which is due to 3d intra-shell transitions. The wave-

Inductance effect in the AC impedance of conducting polypyrrole films

It was found that a conducting polypyrrole (PPy) film strip with two Ag-paste electrodes exhibited an inductance in the AC impedance measurement. An equivalent circuit was proposed for an approximate analysis of experimental data. The effect of the physical dimensions on the parameters of the elements of the equivalent circuit is given. The parameters were found to be sensitive to the applied AC field strength. Although the DC conductivity of a conducting PPy film is isotropic in the film plane, the conductivity for the applied field in the thickness direction is some 4 orders of magnitude smaller and highly non-ohmic even at low fields of over 4Vmm −1. The anisotropy in the thickness direction of AC impedance is also very pronounced.

The effect of Ag electrode processing on (Nb, Ba) doped TiO2 ceramics

Since the characteristics of the electrode made from Ag paste greatly affect the dielectric properties of (Nb, Ba) doped TiO2 ceramics, the processing condition, i.e., baking temperature, was investigated. Low melting glass binder contained in Ag paste reacted with TiO2 ceramics to form an interface layer between Ag electrode and TiO2 ceramics during baking. The interface layer was identified as Bi2Ti2O7 by x-ray diffraction (XRD), and the thickness of the Bi2Ti2O7 layer was estimated from line profiles of EPMA and dielectric properties. The interface layers were found to increase with baking temperature. Increased baking temperature lowered the relative dielectric constant and dielectric dissipation factor of TiO2 ceramics, while it raised the resistivity. Controlling the baking condition of the Ag paste electrode on TiO2 ceramics resulted in reasonably good dielectric properties and excellent temperature stability.

Switching behavior in II-IV-V 2 amorphous semiconductor systems

The electrical characteristics and switching behavior of amorphous ternary semiconducting CdGeAs 2 were studied under DC and AC conditions. The samples tested were fabricated as as-quenched bulk compounds, roller splat-quenched ribbons, and Ar-sputtered thin films. Vapor deposited Ag, Au and Al behaved similarly as electrical contacts while the commercial Ag-paste electrodes revealed variable contact resistance. The threshold electric field of ribbon sample was ∼ 5 × 10 3 V/cm, smaller than ∼ 1.5 × 10 4 V/cm for the sputtered thin films. The electrical band gap of amorphous CdGeAs 2 was determined to be 1.2 eV (n-type). The “forming” process was believed to occur during the first switching cycle whereby highly conductive amorphous channels formed through the width of the samples. The effects of current on switching were investigated and shown not to be significant. The response time for switching decreased approximately exponentially with the applied voltage. The thermal assisted electronic model was postulated for the OFF-ON transition in these materials.