Glass viscosity and chemistry effects on the electrical properties of thick film resistors
Abstract
Glass viscosity and chemistry effects on the electrical properties of ruthenium dioxide based thick film resistors (TFR) using alumina modified lead borosilicate glasses and potassium modified borosilicate glasses were studied. Some physical properties of the glasses were studied as functions of glass composition and temperature. Glass viscosities were determined by the sphere method. At 850$\sp\circ$C, the glass viscosity was increased by a factor of 10 when the alumina content was changed from 2 to 14 weight percent. Glass viscosity ranges for some important microstructure development steps were determined. These are 10$\sp6$-10$\sp4$ Pa.s for glass sintering, 10$\sp4$-10$\sp3$ Pa.s for glass island formation, 10$\sp3$ - 50 Pa.s for glass infiltration and below 50 Pa.s the conductive particles are subject to Brownian motion. The resistivities of resistors were generally decreased as the viscosity of glass used increased. It was found that the sheet resistivity had a power dependence on glass viscosity (or system viscosity). It was attempted to correlate the power dependence on viscosity utilizing the theory of Brownian motion and hydrodynamics. A model was proposed to describe the observed glass viscosity dependence of sheet resistivities utilizing the probability of conductive particles leaving from the initial chain in terms of glass viscosity. The model was good for the resistors in the low glass viscosity region. It was found that the glass chemistry, keeping the same viscosity, significantly affected the microstructure development and eventually the final electrical properties. The sheet resistivities of the resistors with potassium glasses were decreased orders of magnitude compared to the resistors made with the lead borosilicate glasses. One possible speculation was that the conductive sintering in the potassium glasses had very fast kinetics, and this was supported by the much more positive TCR values for the resistors with potassium glasses compared to those with leadborosilicate glasses. Brownian motion of conductive particles and the movement of conductive chains in the liquid glass were considered in terms of microstructure development. Even through the glass viscosity retards the microstructure development kinetics, the overall microstructure development and network formation are favored for higher viscosity of glass, such that the sheet resistivities were decreased as the glass viscosity increased.
Degree
Ph.D.
Advisors
Vest, Purdue University.
Subject Area
Materials science
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