Girish Phatak

Study of glycine nitrate precursor method for the synthesis of gadolinium doped ceria (Ce0.8Gd0.2O1.90) as an electrolyte for intermediate temperature solid oxide fuel cells

The effects of the Glycine Nitrate Precursor (GNP) synthesis parameters, viz. fuel to oxidant molar ratio, oven temperature during combustion, calcination temperature, and calcination dwell time, on the structural, morphological and electrical properties of nanocrystalline gadolinium doped ceria (GDC) are reported. X-ray diffraction studies confirmed the FCC crystal structure with a lattice parameter of 5.4230 (±0.1) A under all conditions. Raman spectroscopy confirmed the FCC crystal structure with F2g symmetry. Depending upon preparation conditions, crystallite sizes between 15–40 nm were obtained, which was confirmed by TEM images. Good crystallinity, lower lattice strain and optimal crystallite size distribution, which result in high ionic conductivity at a stoichiometric and slightly above stoichiometric F/O ratio (1.7 to 2.5), indicated that a high adiabatic reaction temperature is of paramount importance. An oven temperature below 250 °C during the combustion reaction provides an insufficient heat of formation and causes a slow combustion reaction resulting in lattice strain and low crystallinity. Higher oven temperatures also caused low crystallinity and smaller crystallite size, indicating that 250 °C is the optimal oven temperature. A calcination temperature of 900 °C provided high crystallinity, low stress and high ionic conductivity, probably because of the optimal number of oxygen vacancies. The appropriate calcination dwell time was 8 h, even though its influence on the ionic conductivity was low. A good density of 94% of the theoretical density was obtained for pellets sintered at the relatively low sintering temperature of 1350 °C for 8 h at a F/O ratio of 1.7, oven temperature of 250 °C, calcination temperature of 800 °C and 8 h dwell time. These dense GDC pellets had an average grain size of 0.4–3 μm and showed a promising ionic conductivity of 9.7 × 10−3 S cm−1 at 700 °C. The activation energy calculated from Arrhenius plots revealed values as low as 0.19 ± (0.01) eV, which is also the lowest reported value for GDC.

Ultra-High-Frequency Behavior of BaFe

M-type barium hexaferrite (BaFe12O19) is investigated with an aim of using with low temperature co-fired ceramic (LTCC) substrate material. The as-calcined powders from combustion synthesis at neutral and acidic precursor solutions are used, which exhibit excellent properties of low coercive field values (up to 1350 Oe) and high magnetization (up to 60 emu/g). With an appropriate amount of Bi2O3 as sintering aid, high density ferrites have been realized at LTCC processing temperatures. The sintered ferrites possess bulk resistivity in excess of 109 Ω·cm, indicating their suitability for high-frequency applications. Complex magnetic permeability and magnetic loss factors are studied up to 1 GHz frequency. Complex permeability between 1.2 to 2.2 and magnetic loss tangent between 0.05-0.5 have been realized for the sintered ferrites. The influence of Bi2O3 content on resistivity and high-frequency magnetic properties is discussed. It is observed that the sample prepared by employing neutral pH during combustion preparation and calcined at 1200°C for 12 h shows low coercivity of 1350 Oe. After sintering at 900°C with 2 wt% Bi2O3, the sample shows better results with permeability of 1.5-1.7, magnetic loss tangent below 0.3 up to 700 MHz frequency and a high resonance frequency of 140 and 715 MHz in VHF and UHF band, respectively. Since the synthesis conditions provide better control over basic magnetic properties, the use of combustion synthesized BaFe12O19 material augers well for magnetic materials applications in LTCC technology.

_{12}

Purpose – The purpose of this paper is to investigate and report the impact of glass frit variation in silver thick film pastes used as surface conductors in low temperature co‐fired ceramics technology (LTCC), especially on the properties such as warpage of LTCC associated with conductors, microstructure of the fired thick films, sheet resistance and adhesion on LTCC.Design/methodology/approach – Silver thick film paste compositions were formulated by changing the silver glass frit ratio. The compatibility of these formulated paste compositions with LTCC (DP 951AX) substrate were evaluated. The properties such as microstructure developments, the change in sheet resistance, warpage of LTCC substrate with respect to glass frit ratio of the developed silver films on LTCC were evaluated.Findings – The results reveal that the glass frit percentage used in paste formulation is equally responsible for the disturbance in the properties such as microstructure, warping and electrical properties of the fired thick ...

O

Gadolinium doped Ceria (GDC) is a known oxygen ion conductor in intermediate temperature range. This is a preliminary work aimed at exploring the suitability of using nanocrystalline GDC as oxygen sensor in intermediate operating temperature range (500°C–700°C). The nanocrystalline Gadolinium doped Ceria (GDC) has been prepared by sol-gel method with EDTA as chelating agent. Particle size around 10±5nm was obtained after calcination at 600°C. Pellets prepared using this material were sintered 1350°C, which show 90% of the theoretical density. The dc and ac (1Hz–1MHz) conductivity of these pellet was measured in the temperature range 200–600°C and 500–700°C respectively. Highest conductivity of the order of 4.61X10⁻⁵ S/cm was recorded at 700°C. Possible reasons for low conductivity are discussed.

_{19}

Integrated SnO2: CuO thin-film based H2S gas sensor has been realized using low temperature co-fired ceramics (LTCC) tapes with heater and thermister buried inside the LTCC multilayer structure. The SnO2: CuO thin films are deposited on top of the structure. At operating temperature of 180°C, these films revealed sensing properties very similar to the reference films deposited on Alumina substrates. Further, effect of operating temperature on sensitivity was studied and sensor films on LTCC substrate were found to detect H2S with maximum sensitivity at a lower operating temperature of 100°C. The developed sensors have been tested for a period of more than one year and found to show a stable response.

Hexaferrite for LTCC Substrates

Todays high functionality electronic circuits require faster interconnection speed, better thermal conductivity and the good mechanical properties for reliability. These requirements calls for enhanced properties of the present solder materials. Appropriate reinforcements in the existing solder material will help in achieving much improved electrical, mechanical and thermal properties. Carbon Nano Tubes (CNTs) are one such material that can bring in considerable improvements in the properties of the solder material. CNT-Solder composite with less than 1% CNT is being explored for solder bumps in flip chip applications. This paper reports our work on co-deposition of CNT along with lead-free solder using electroplating process. For co-deposition of CNTs along with the solder, the processing of CNT is very important. Milling and CNT functionalisation are two such parameters that aid in its dispersion and make it active. The present studies include optimization of milling time for CNTs and selection of appropriate activators for functionalisation of CNTs in the electroplating bath.

Silver thick film pastes for low temperature co‐fired ceramics: impact of glass frit variation

This paper presents structural, morphological and electrical characterization of the in-house developed ruthenium oxide based thick film resistor pastes for buried heater applications in LTCC. The basic electrical characterization of heater shows that the designed test heater achieved temperature up to 238°C. The required power to raise the temperature up to 238°C was 1.9W. It is found that the in-house resistor paste has better shrinkage compatibility with commercial LTCC Tape as compared with the manufacturers own compatible resistor paste.

Nanocrystalline Gadolinium doped Ceria (Ce 0.8 Gd 0.2 O 3-δ ) for oxygen sensor and solid oxide fuel cell applications

Low Temperature Co-fired Ceramic (LTCC) technology is evolving. New materials now offer improved embedded passive components and kindle hope of integrating devices never before imagined. This rediscovery of LTCC is making it an important vehicle for systems integration. This chapter explores the current status of embedded capacitors and inductors in LTCC, providing a glimpse of the improved materials being developed. Investigations on materials for integrated nonreciprocal devices, such as, circulators and isolators are also discussed. For the first time, we report materials development for integrated solid oxide fuel cells within LTCC structures, opening up a new area of integrated power sources, hitherto unexplored.

Evaluation of compatibility of SnO 2 : CuO thin film based H 2 S sensor on LTCC substrates

Low Temperature Co-fired Ceramic (LTCC) is amongst the favoured technologies for preparing miniature integrated packages and devices for various sensor and actuators applications. It is known that semiconductor gas sensors work at elevated temperatures. We have developed LTCC based micro hotplates with integrated temperature sensors for preparing miniature gas sensors. We have devised way to fabricate small size (Long side 6.5mm) suspended hot plate design of LTCC based hotplate with integrated thermistor. This paper presents results of heater and thermistor characterization for solid rectangular block and suspended hotplate designs of the hot plate. It is seen that the heaters as well as the thermistors present a linear behavior for both the designs. The rectangular solid block design dissipates about 3.5W power while the suspended hot plate design requires only about 144mW reaching steady state temperature of 250°C.

CNT- lead free solder composite electrodeposition for obtaining high speed interconnect for memsapplication

Dependence of the resistance of metal-oxides thin films on environment is generally used to detect toxic gases at ppm levels. In order to obtain a fast response and recovery, sensing films are heated to high temperatures (upto 300°C). The heater assembly used to raise the film temperature not only makes the sensor bulky but also consumes high power. In our efforts to reduce the size of sensors, we have deposited SnO2: CuO thin film directly onto low-temperature co-fired ceramic (LTCC) substrates with integrated heater and temperature sensor. Sensor films were investigated for their compatibility with LTCC substrate and results show a stable response towards hydrogen sulphide gas for over a year. The stability of heater and thermistor embedded in LTCC substrate has also been monitored. The results of our study show films on LTCC substrate can be successfully applied in sensor technology.