Conductive Silver Paste Research Articles

Fabrication and properties of ultraviolet photo-detectors based on SiC nanowires

A new type of ultraviolet photo-detectors (UVPDs) based on a bundle of highly aligned SiC nanowires was fabricated and the photo-electric properties of the UVPDs including I–V characteristics and time response were studied in this work. SiC nanowires were prepared by pyrolysis of a polymer precursor with ferrocene as the catalyst by a CVD route. The diameters of SiC nanowires varied from 100 to 200 nm while they were some centimeters long and the SiC nanowires were with zinc blended cubic form (β-SiC) tested by X-ray diffraction. A bundle of nanowires was fixed onto two legs’ base by conductive silver paste to form the UVPDs. The electrical measurement of the device showed a significant increase of current when the device was exposed to 254 nm UV light, and the rising time of the device is very short, but the falling time is relatively long. Our results show that the UVPDs based on SiC nanowires have excellent electrical and optical properties which can be potentially applied.

Influence of Sn doping on ZnO sensing properties for ethanol and acetone

Nanostructured pure ZnO (PZO) and Sn doped ZnO (SZO) were deposited on glass templates by chemical deposition method. Before the deposition, electrically conductive silver paste was pasted at the two ends of the glass templates as electrodes. The gas sensing properties of the nanostructured PZO and SZO were systematically investigated by our home-made system, and the results show that Sn doping decreases the response to tested gases. However, it remarkably shortens the response time and recovery time of the sensor. Both PZO and SZO show higher response to acetone than to ethanol, while the response time and recovery time of PZO and SZO to ethanol are shorter than those to acetone, which indicates that the selectivity of ZnO nanostructures to ethanol and acetone are different.

SiC纳米线紫外光探测器光电性能的研究 Fabrication and Properties of Ultraviolet Photo-Detector Based on SiC Nanowires

基于一束高取向排列的SiC纳米线，本文制备了一种新型的紫外光探测器，并测试研究了其光电性能。采用传统化学气相沉积技术，以二茂铁为催化剂，通过聚合物热解的方法制备了长度达数厘米、直径为100~200 nm的SiC纳米线。探测器由导电银浆固定一束高取向排列的SiC纳米线到器件基座两个引脚上形成，其光电性能测试研究表明，器件暗电流很小、并且在254 nm紫外光照射时，其光电流迅速变大；器件反应时间很短而回复时间相对较长。 A new type of Ultraviolet Photodetector (UVPDs) based on a bundle of highly aligned SiC nanowires was fabricated and the photo-electric properties of the UVPDs including I-V characteristic and time response et al. were studied in this paper. SiC nanowires were prepared by pyrolysis of a polymer precursor with ferrocene as the catalyst by a CVD route. The diameter of SiC nanowires varied from 100 to 200 nm while they were some centimeters long. A bundle of nanowires was fixed onto two legs in a custom base by conductive silver paste to form the UVPDs. The electrical measurements of the device show a big increase of current when explored the device to 254 nm UV light, and the rise time of the device is very short, but the fall time is relatively long.

Silver content effect on rheological and electrical properties of silver pastes

The novelty of this work is laboratory formulation of environmentally friendly, water-based silver inks adapted for screen printing. The challenge was also to elaborate inks that can withstand temperatures as high as 900 °C. Indeed, when printed on ceramic substrate, they were sintered at these high temperatures. These inks can replace conductive silver pastes present in the market, today, and containing irritant solvents such as terpineol and other aromatic solvents. Besides, screen printing is considered as an additive technique, thus allowing reducing wastes. Furthermore, only with 72.5% silver, considered as low content compared to commercial inks (≥75%), prepared inks presented good electrical resistivity, 23 nΩ m, close to that of bulk silver resistivity, 16 nΩ m. Formulation of silver inks with spherical particles, 2–3 μm mean diameter, was performed. The aim of the study was to determine silver content effect on pastes rheological behaviour, lines properties (width, thickness and roughness) and electrical properties. Therefore, rheological behaviour of inks was studied; in particular, Casson and Bingham models were applied in order to determine the yield stress. Viscosity evolution as a function of shear rate was also determined. Besides, the thixotropic behaviour of inks was highlighted. Inks were then screen printed on alumina sintered substrates and cured at different temperatures during 15 min. Topography measurements were performed. Line resistivity as small as 35 nΩ m was measured on cured lines. These inks, printed on ceramic tapes, can be used to print microwave transmission lines, for which resistivities lower than 1 mΩ m are requested.

Towards highly conductive silver pastes for LTCC power electronics

The realization of high current conductors in LTCC multilayer architectures was studied. By mixtures of spherical silver powders, maximum tap densities above 7 g/cm3 could be obtained. On pressed cylinders a good correlation between tap density and total shrinkage was found. Pastes were made of the highly packed silver powders and detailed investigations regarding paste sintering kinetics and interactions between paste ingredients among one another as well as between paste ingredients and LTCC substrates were made. The pastes did not show a pronounced correlation between tap density and total densification. With increasing solid content of the pastes, the shrinkage printed-dry, the shrinkage dry-fired and the specific sheet resistance decreases. These findings can be used to control the filling degree of channels or grooves as well as the properties of the fired conductor. Expansion effects of the pure silver powders during sintering could be correlated to gas pressure effects, whereby there are obviously different kinds of gas formation in fine and coarse powders. Avoiding of camber of freely sintered LTCC should be attained if new LTCC materials are showing different sintering behavior, e. g. strong and early crystallization building of diffusion barriers or the possession of a glass phases which will not incorporate silver oxide. Research on this target should be done. The realization of high current conductors in constrained sintered LTCC was successfully shown. A paste comparable to standard values for direct copper bond (DCB) substrates with a thickness 35 μm of 0,48 mOhm/sq is introduced

Electromechanical coupling of lead zirconate titanate nanofibres

This Letter reports on the fabrication of piezoelectric nanofibres and the demonstration of voltage generation from them by performing three-point bending with a dynamic mechanical analyser (DMA). Partially aligned lead zirconate titanate (PbZr52Ti48O3, PZT) nanofibres were fabricated using a sol–gel electrospinning process. The diameters of the PZT nanofibres were tuned from 50 to 150 nm by changing the concentration of the sol–gel in the precursor. The nanofibres consist of nanocrystalline grains with an average grain size of 10 nm. A voltage generation device based on PZT nanofibres was fabricated by simply applying conductive silver paste to serve as electrodes. The output voltages from the nanofibres under different strains were recorded using a data acquisition (DAQ) card and Labview®. The output voltage increased with intensified, applied strain; and the highest value of the output voltage was 0.17 V. From the output voltage, the piezoelectric voltage coefficient, g33, was estimated as 0.0354 m2/C. The principle of the voltage generation is caused by the strain-induced piezoelectric effect. The results reveal that PZT nanofibres have great potential for nanosensor, nanoactuator and nanogenerator applications.

Fabrication of wireless sensors on flexible film using screen printing and via filling

Wireless sensors are fabricated on flexible plastic films by means of screen printing and via-hole filling. The wireless sensors are battery free with data and power transmission functions. The sensors, fabricated on polyethylene terephtalate films, are designed based on RFID technology. Using an additive patterning process known as screen printing, metallization on polymer films is created. Both sides of a polymer film are printed with metallic patterns and connected with micro vias filled with conductive paste. One side of the film consists of printed electrical traces for discrete components like resistors and transistors that would be mounted onto it; the other side consists of a printed inductive coil used for wireless data and power transmission. The micro vias, which have a diameter of 120 μm, are formed by mechanical punching and filled with conductive silver paste. The size of one sensor unit is approximately 2 cm × 1.5 cm; an array of 4 × 7 sensor units are printed over an area of 15 cm × 15 cm on a PET film. Details of manufacturing processes, component assembly and functionality test are presented in this paper.

A Homogeneous Electrically Conductive Silver Paste

A homogeneous electrically conductive silver paste was developed using silver i-propylcarbamate ((CH3)2CHNHCOOAg) as the precursor of functional phase. The precursor had good solubility in water and methanol, high silver content (about 50 wt.%) and low decomposition temperature (below 200 °C). The paste was a non-Newtonian fluid with the viscosity depending significantly on the content of thickening agent (ethyl cellulose). When the paste was applied in micro-pen direct-writing process, it was able to produce high-resolution (20 μm or so) array patterns. After a homogeneous paste with about 40 wt.% silver i-propylcarbamate as the precursor was directly written and sintered at 180 °C for 15 min, an electrically conductive network consisting of more than 95 wt.% silver was formed and the network had a volume electrical resistivity in the order of magnitude of 10-5-10-6 Ω · cm and a sheet electrical resistivity in the order of magnitude of 10-4 Ω/square.

Electrically Conductive Thick Film Made from Silver Alkylcarbamates

A homogeneous electrically conductive silver paste without solid or particle phase was developed using silver alkylcarbamates [(CnH2n� 1NHCOO)2Ag, n £ 4] as the precursor of the functional phase. The silver alkylcarbamates were light insensitive and had a low decomposition temperature (below 200� C). The paste was a non-Newtonian fluid with viscosity significantly depending on the content of the thickening agent ethyl cellulose. Array patterns with a resolution of 20 lm were obtained using this paste by a micropen direct-writing method. After the paste with about 48 wt.% silver methylcarbamate [(CH3NHCOO)2Ag] precursor was sintered at 180� C for 15 min, an electrically conductive network consisting of more than 95 wt.% silver was formed, and was found to have a volume electrical resistivity on the order of 10 � 5 X cm and a sheet electrical resistivity on the order of 10 � 2 –10 � 3 X/h. The cohesion strength within the sintered paste and the adhesion strength between the sintered paste layer and the alumina ceramic substrate were tested according to test method B of the American Society for Testing and Materials standard D3359-08. None of the sintered paste layer was detached under the test conditions, and the cohesion and adhesion strengths met the highest grade according to the standard.

High-performance electrically conductive silver paste prepared by silver-containing precursor

A high-performance electrically conductive silver paste with no solid particles before drying and/or sintering is developed, in which silver-containing precursor is employed as conductive functional phase. Thermogravimetry analysis, volume electrical resistivity tests and sintering experiments show that the paste with about 14 wt.% silver pristine content is able to achieve the volume electrical resistivity of (2–3) ×10−5 Ω cm after it is sintered at 220°C. A micro-pen direct-writing process indicates that it is very suitable for the fabrication of high-resolution (25 μm) and high-integration devices and apparatus.

The Effect of Particle Size on Sintering of Conductive Silver Paste in Electrode for LTCC

The Effect of Particle Size on Sintering of Conductive Silver Paste in Electrode for LTCC

Preparation of Conductive Silver Paste Using Bimodal Particles

Networking and density of silver particles is a great importance to obtain low electrical resistivity of silver paste. In order to improve packing density, interconnectivity and conductivity at low sintering temperature, silver paste was prepared from bimodal silver particles, i.e., consisting of micro- and nano-sized particles. In order to fit nano-Ag particle into the interstices of the micro-Ag particles of 1.6 microm in size, the interstices need to be approximate below 360 nm in size. Therefore, we prepared nano-Ag particles of 100-300 nm in size by chemical reduction method. The silver paste prepared by mixing the bimodal powders, Pb-free frit and vehicle were printed on an alumina substrate by screen printing and sintered at temperature of 400-500 degrees C. As increasing the amount of nano-Ag particles and sintering temperature, packing density and electrical conductivity were increased. The nano-Ag particles placed between the micro-Ag particles contributed to improve interconnectivity and densification of the printed films. Accordingly, as the amount of nano-Ag particles was increased, the electrical resistivity were decreased. The thick film at sintered 500 degrees C showed the lowest electrical resistivity of 3.9 microomega cm which can be compatible for application in microelectronics devices.

Sinterability and conductivity of silver paste with Pb-free frit

Abstract Conductive silver paste for low sintering temperature was prepared by mixing two commercial silver powders with different particle size of 0.8 μm and 1.6 μm, and nanoparticles of 20–50 nm. The silver nanoparticles were synthesized by a chemical reduction method using surfactant and 10 wt% of the nanoparticles was added as a low sintering temperature aid. About 3, 6 and 9 wt% of Pb-free frits were added to the mixed silver powder, respectively. Using the paste, thick films were prepared by a screen-printing on an alumina substrate and the films were sintered at temperatures from 400 to 550 °C. As increasing the sintering temperatures and glass frit contents, the thick films became dense and their sheet resistivity decreased corresponding to dense microstructure. The films had thickness of 4–6 μm and sheet resistivity of approximately 5–10 mΩ/□.

Investigation on a new silver photoimageable conductor

A new thick film photoimageable silver paste of improved properties has been elaborated. The paste is less sensitive to the visible light. Certain disadvantages of most commercially available materials, such as necessity of operating with the paste in the room illuminating with yellow, green or red light has been eliminated. Further improvement of conductive silver pastes to enable reducing lines width down to 10 μm has been done.

Pb-Free Silver Conductive Paste with High Reliability

We have been engaged in developmental activities aimed at improving the properties of Ag conductive paste which can be used for various kinds of electronic components including circuit boards and both chip and high frequency components. By applying the uniform ceramic coating technology to Ag powder, we produced a variety of options to achieving the goal of lead elimination. The properties, namely solder leaching, adhesives strength (aging, heat cycles, strength in high heat and humidity) and migration, have successfully been improved to a level which is the same or higher than those of Ag/Pd (80/20) and Ag/Pt (99/1), which are currently used for conductive paste material. In this study, we succeeded in eliminating not only lead, but also frit, which, as a result, paves the way for the application of Ag conductive paste to high-frequency components, LTCC (Low Temperature Co-fired Ceramic) terminations and surface electrodes.

Study on delayed cracking of conductive notch under electric field in PZT-5H ferroelectric ceramics

Electric-field-induced delay cracking of conducting notch in PZT-5H ferroelectric ceramics has been studied using a compact specimen with a notch filled in conductive silver paste. The critical electric field that induces instant failure of the PZT-5H specimen is shown to be EF = 14.7±3.2 kV/cm. When an electric field lower than EF, but higher than EDF = 9.9 kV/cm was applied, a micro-crack formed at the conductive notch tip instantly, propagating slowly until the specimen failure. When the electric field was lower than EDF, the micro-crack propagated a short distance, and then stopped. When the electric field was lower than EK = 4.9 kV/cm, no cracks formed at the conductive notch tip instantly, however, a delay micro-crack would form and propagate. When the electric field was lower than EDK=2.4 kV/cm, no cracks formed and delay propagation occurred. A model for electric charge emission and concentration at a conductive notch is proposed to explain the delay cracking of conducting notch.

Corrosion and Adhesion Properties of a Low-CTE Polybenzoxazole Film

The corrosion and adhesion properties between conductive silver pastes and a novel, solutionprocessable low-CTE polybenzoxazole (PBO) film were studied. In this study, a polyester and an epoxy resin were used as the binders of conductive pastes. The pastes were coated on the PBO film, then thermally cured. The samples obtained were cut using the SAICAS slant-cut method to analyze the corrosion caused by the corrosive gases and to measure the interfacial peel force. The system using epoxy resin as the paste binder showed excellent corrosion resistance and adhesion properties. The results revealed that PBO film is a promising candidate in the area of new insulation materials having not only heat resistance, low CTE, and low water absorption but also corrosion resistance and good adhesion.

High quality LTCC resonator for voltage-controlled oscillator

Design and technology of microwave conductor lines embedded in low-temperature cofired ceramic (LTCC) multilayer substrates are summarized with a focus on achieving the highest possible quality (Q) factor for a given line inductance. The work was initiated to test the integrability of base station voltage-controlled oscillators (VCOs) in ceramic multilayer substrates. This approach leads to a miniaturization of current versions by a factor of 2 to 4. However, base station specifications for phase noise and hence resonator Q are extremely demanding. Therefore, both the design and the processing technology were optimized. By choosing a twin-line design with two parallel lines vertically separated by a single LTCC layer, Q factors of 90 and 180 have been achieved for integrated 5.5 nH inductors at frequencies of 640 MHz and 1650 MHz, respectively. Application of this result to VCO modules in standard LTCC technology already yields low phase noise levels, e.g., -136 dBc/Hz at 100 kHz offset, which is suitable for base station applications. However, further noise reduction is expected from a dedicated high Q fabrication process that uses conventional via punching and filling steps to replace the ceramic material between the two lines by conductive silver paste. This raises the Q to 120 and 200, respectively, at the two frequencies and adds extra degrees of freedom to LTCC design for low-loss wireless solutions.

Corrosion and Protection of a Conductive Silver Paste

One of the possible uses for a conductive paste is as an adhesive in interconnect technology that could replace solder. The interconnections are expected to perform under a variety of environmental conditions, and with an applied voltage. Thus knowledge of their corrosion and dissolution resistance is of utmost importance. This is a study of the dissolution and protection of polymer/metal composite films, prepared with a high loading of silver or gold particles. Electrochemical tests were conducted in a droplet of triple‐distilled water with or without benzotriazole (BTA) and BTA derivatives. Results indicate that, in spite of some protection obtained by the polymer, silver paste dissolution at high anodic potentials is rapid, reaching values of 10−1 A/cm2, which corresponds to a catastrophic silver removal rate of at least 35.6 nm/s. With a reservoir of azole in the corrosive environment, this rate can be reduced by up to five orders of magnitude. This azole effect greatly reduces the probability of electrolytic silver migration, but the Ag dissolution rate is still higher than the anodic activity shown by Au paste under the same conditions.

Photoconduction of ZnO-Bi2O3 varistors

Zinc oxide (ZnO) ceramics with a few mol % Bi203, CoO, MnO, Sb203, etc., as additives exhibit a high non-ohmic property in their voltage-current characteristics [1, 2], and therefore they are called varistors and are widely used for surge protection against transient voltage and powder overload [3]. Another interesting property of ZnO is its high photoconductivity, as can be seen from the fact of many applications of ZnO in electrophotography [4, 5]. Bismuth sesquioxide (Bi203) is also known to create photoconductive materials, as Bi~2MO20 (M = Si, Ge or Ti) crystals with 7-form show a high photoconductivity [6, 7]. In addition the authors have found that photoconductive films with a &-related structure are obtained by roller-quenching Bi203 melts containing a small amount of second oxide [8-11]. From such photo-effects of ZnO and Bi203, it would be consistent to suppose that ZnO-Bi203 varistors have a photoconductivity. However, few studies have been made on the photoconductivity in ZnO-Bi203 varistors. In this work the photoconductivity of ZnO-Bi203 ceramics containing up to 20% Bi203 was measured and the influence of temperature on the photoconductivity was investigated. Reagent grade (99.9% pure) ZnO and Bi203 were used to prepare the ceramic samples. Powder mixtures of these oxides containing 1, 5, 10 and 20% Bi203 were heated at 800 ° C for 5 h in air. Following this preliminary heat treatment, they were finely ground, pressed into rods (5mm x 5mm × 30mm) and sintered under the same heating conditions. The sintered rods were cut into segments in the shape of rectangular parallelepipeds of length about 5mm, to measure the photoconductivity. Conductive silver paste was applied to both sides of the segments as electrodes. Applying 100V (d.c.) between the electrodes, the electrical resistivity was measured in the range of room temperature to 170°C using an electrometer (Advantest, TR8652) while irradiating one side of the samples with light from a spectro-irradiator (Jasco, CRM-FA) and scanning the wavelength of the light in the range 300 to 700 nm. As expected, all ceramic samples prepared were confirmed to show photoconductivity at room temperature. In the samples containing 5% Bi203 o r more, it was observed that the photoconductivity was influenced by temperature. As a typical example, electrical resistivity curves at various temperatures for the sample of composition 9ZnO.Bi203 are shown in Fig. 1 as a function of the wavelength of the incident light. The photoconductivity of this sample is characterized by a steep decrease in the resistivity at wavelength 400 to 500nm (blue-purplish to blue-greenish light). The doublet peak seen on the curves suggests