Development of solid state thick film zirconia oxygen gas sensors.

Aspects relating to and including the development of thick film amperometric zirconia oxygen sensors were investigated. These devices, which were operated in the range 550-950°C, had a laminated structure in which a cathode, an electrolyte and an anode were printed, in that order, onto a planar alumina substrate. The anode and electrolyte were porous and during sensor Operation also acted as a diffusion barrier, restricting the rate of oxygen diffusion to the cathode. A thick film platinum heater was also developed to maintain the sensor at its operating temperature while acting simultaneously as a résistance thermometer; it was screen-printed onto the substrate on the reverse side to the sensor. The individual components were characterised and optimised prior to assembly of complete sensors. Zirconia films were deposited by screen-printing onto alumina substrates. Careful attention was paid to formulation of zirconia inks, drying and firing procedures. Temperatures above 1350°C were necessary to sinter the zirconia to a low (<0.1%) though not zero porosity. The high sintering temperatures were found to result in the diffusion of impurities from the 96% alumina Substrate into the zirconia film which accelerated grain growth. X-ray diffraction showed that the grain growth resulted in transformation of the metastable tetragonal zirconia to the monoclinic form: where this occurred frequency response analysis of the films showed the expected decrease in ionic conductivity. These effects were absent on high purity (99.6%) alumina substrates. Platinum-zirconia cermets were investigated as possible electrodes. When screen-printed and fired at 1000°C for 1 hour and operated in the range 500-700°C, electrode activity was orders of magnitude greater than for pure porous platinum electrodes and increased substantially with increasing zirconia fractions provided electronic continuity was maintained within the film. High firing temperatures (> 1000°C), which were necessary for preparing a sensor with co-fired electrolyte and electrodes, decreased electrode activities although cermets remained greatly superior to pure platinum. Planar amperometric zirconia oxygen sensors were prepared using thick-film technology exclusively. When a voltage (0.5-1.4 V) was applied between the electrodes, a current flowed which was directly proportional to the oxygen concentration in the range up to 21%; this has not previously been achieved with such sensors. Characteristics were shown to be dependent upon firing temperature and substrate purity. Interestingly, temperature coefficients of the output were positive and negative for sensors fired at temperatures up to 1400 and above 1450°C respectively. Operation in the combustion products of a gas-burning flue demonstrated linear dependence upon calculated oxygen concentration. Heaters, printed using either fritted or unfritted platinum inks, were given extended treatments in a furnace at elevated temperatures (1000-1300°C) to accelerate ageing effects. Measurements were made of résistance (at 20°C), platinum evaporation rate and film cross-sectional area and these were correlated with the microstructure. The variation of résistance (at 20°C) of the films was analysed using effective medium theory invoked in order to quantify the blocking effect of the non-metallic fractions. During the initial phase (résistance decreasing) the governing factor was probably the high resistance of necks between contacting platinum particles. During the subsequent phase (resistance increasing) the resistance was controlled principally by the formation and growth of voids

Proceedings of the 1977 NASA/ISHM Microelectronics Conference

Current and future requirements for research, development, manufacturing and education in the field of hybrid microelectronic technology were discussed

Hybrid construction of a 10MHz DC-DC converter for distributed power systems

Thesis (Elec. E.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1989.Includes bibliographical references (leaves 204-208).by Brett Andrew Miwa.Elec.E

Analysis and evaluation in the production process and equipment area of the low-cost solar array project

The effect of solar cell metallization pattern design on solar cell performance and the costs and performance effects of different metallization processes are discussed. Definitive design rules for the front metallization pattern for large area solar cells are presented. Chemical and physical deposition processes for metallization are described and compared. An economic evaluation of the 6 principal metallization options is presented. Instructions for preparing Format A cost data for solar cell manufacturing processes from UPPC forms for input into the SAMIC computer program are presented

Review of Bi2O3-based glasses for electronics and related applications

The present work critically reviews the scientific and patent literature on low-melting bismuth-based oxide glass frits in materials for electronics, sensors and related applications such as sealing glasses, solar cells, architectural and automotive glass, the main motivation being to replace lead-based materials by environmentally more benign ones. Due to similar glass-forming properties of Bi and Pb, Bi-based glasses are the closest "drop-in" alternative for lead-bearing formulations, and are therefore actually replacing them in many applications, helped also by previous experience with Bi-containing materials in thick-film technology and component metallisations. The outstanding issues are discussed, e.g. matching the lowest processing temperatures achieved by the classical lead-based glasses without sacrificing durability and stability, as well as stability vs. chemical reduction. Finally, consideration is also given to special "heavy" glasses (often containing Bi and Pb together) that are useful in fields such as optics, superconductors and nuclear technology, as well as to specific Bi2O3-containing crystalline compounds

From the Laser-doped Semiconductor Fingers to the Advanced Semiconductor Fingers Silicon Solar Cell

To reach the goal of grid parity for photovoltaic-generated power, the efficiency of conventional screen-printed p-type silicon solar cells should be increased without significant increase in the manufacturing cost. The semiconductor fingers (SCF) screen-printed silicon solar cell technology fabricated by laser-doping the SCF can potentially achieve this aim. Previous laser-doped SCF p-type silicon solar cell efficiencies were too low, limited by the achievable SCF doping and therefore sheet resistance levels using available laser technology. Recently, the new Spectra Physics Millennia Prime laser introduced new laser technology apparently with the potential to produce laser-doped features with sheet resistances low enough for the SCF cell. The objective of this thesis is to design and develop an n-type SCF with this laser so as to demonstrate high efficiency laser-doped SCF solar cells on p-type Czochralski (Cz) silicon wafers. Since the sheet resistance of the laser-doped SCF (lines) is important to the efficiency of the SCF solar cell, appropriate methods to measure the sheet resistance of these laser-doped lines were investigated. A method widely-used to measure the sheet resistance of a laser-doped line was demonstrated here to produce unreliable results and thus not used. Instead, a new measurement method was presented along with a new upper sheet resistance limit concept. A theory was also presented that relates these two different measurement methods, and was experimentally-supported within an error of 10 %. The Spectra Physics laser was also demonstrated to produce laserdoped lines that can be as conductive as 2 Ω/□. Thus, this laser is suitable for high efficiency SCF solar cells. Beside the benefits that highly-conductive SCF can bring to a SCF cell, there are drawbacks that appear mainly in the form of SCF effective shading losses. To account for them, a model was built to simulate the efficiencies of laser-doped SCF solar cells with different SCF sheet resistance and junction depths. The cell efficiency potential of SCF laser-doped by the Spectra Physics laser was then assessed. With the most optimistic assumptions for contact resistance, and with experimentally-derived SCF sheet resistances and junction depths, the highest efficiency was predicted to be 18.81 % and was only 1.13 % relatively higher than that of an optimised screen-printed silicon solar cell. High SCF effective shading loss was the limiting factor. Subsequently, laser-doped SCF solar cells screen-printed with appropriate lowreactivity silver pastes were fabricated. From these cells, the contact resistance was determined to be too high and not uniform enough for high efficiency laser-doped SCF solar cells from being demonstrated in the duration of this thesis work. Plating the SCF with metal was then proposed as a solution that can overcome both challenges of high effective shading loss and low contact quality. This new metalplated SCF solar cell is known as the advanced SCF solar cell. A laser-doping and metallisation sequence in the order of screen-printing, laser-doping, and nickel/copper stack plating was analysed to be a practical sequence to fabricate the advanced SCF cell. During the development of the recipe, nickel was found to not uniformly plate across the cell and these nickel voids resulted in higher series resistance levels. A modified dopant dispense method for the laser-doping step was developed to significantly reduce these nickel voids. By applying this solution to a batch of six advanced SCF solar cells, an average batch and highest efficiency of 18.40 % and 18.82 % respectively were achieved on p-type Cz 1 Ωcm textured silicon wafers. Modelling and simulation of the advanced SCF solar cell show that this new cell design can have a direct ≈ 0.7 % absolute and ≈ 3.8 % relative efficiency gain over the laser-doped SCF solar cell. This is mainly due to the ability of the advanced SCF solar cell to space the screen-printed silver fingers much wider apart and to use narrower SCF. The predicted efficiency potential of the advanced SCF solar cell with a full area back surface field exceeds 20 %. Of secondary importance and it was discovered while developing techniques to minimise the contact resistance between a screen-printed metal and a high sheet resistance diffused emitter, that using dilute hydrofluoric acid to improve the contact resistance can increase the cell s recombination impact and reduce its pseudo-fill factor. It was also demonstrated that by treating the cell in phosphoric acid, this impact can be significantly reduced or eliminated. Chemical analyses suggest lead to be the likely recombination source

Reactive Ink Metallization for Next Generation Photovoltaics

abstract: In order to meet climate targets, the solar photovoltaic industry must increase photovoltaic (PV) deployment and cost competitiveness over its business-as-usual trajectory. This requires more efficient PV modules that use less expensive materials, and longer operational lifetime. The work presented here approaches this challenge with a novel metallization method for solar PV and electronic devices. This document outlines work completed to this end. Chapter 1 introduces the areas for cost reductions and improvements in efficiency to drive down the cost per watt of solar modules. Next, in Chapter 2, conventional and advanced metallization methods are reviewed, and our proposed solution of dispense printed reactive inks is introduced. Chapter 3 details a proof of concept study for reactive silver ink as front metallization for solar cells. Furthermore, Chapter 3 details characterization of the optical and electrical properties of reactive silver ink metallization, which is important to understanding the origins of problems related to metallization, enabling approaches to minimize power losses in full devices. Chapter 4 describes adhesion and specific contact resistance of reactive ink metallizations on silicon heterojunction solar cells. Chapter 5 compares performance of silicon heterojunction solar cells with front grids formed from reactive ink metallization and conventional, commercially available metallization. Performance and degradation throughout 1000 h of accelerated environmental exposure are described before detailing an isolated corrosion experiment for different silver-based metallizations. Finally, Chapter 6 summarizes the main contributions of this work. The major goal of this project is to evaluate potential of a new metallization technique –high-precision dispense printing of reactive inks–to become a high efficiency replacement for solar cell metallization through optical and electrical characterization, evaluation of durability and reliability, and commercialization research. Although this work primarily describes the application of reactive silver inks as front-metallization for silicon heterojunction solar cells, the work presented here provides a framework for evaluation of reactive inks as metallization for various solar cell architectures and electronic devices.Dissertation/ThesisDoctoral Dissertation Materials Science and Engineering 201