Lead Ruthenate Thick Film Resistors
Y. M. Chiang, L. E. Silverman, R. H. French, R. M. Cannon, "The Thin
Glass Film between Ultrafine Conductor Particles in Thick Film Resistors", Journal
of the American Ceramic Society, 77,
1143-52 (1994).
No
Titania
Additive
With Titania Additive
Distribution in the apparent film thickness of glass
films in samples with and without titania, measured from STEM bright field
images under slight underfocus conditions. As discussed in text, these results overestimate the absolute film
thickness, but clearly show the greater average film thickness of the titania
containing samples.
The
Thin Glass Film between Ultrafine Particles in Thick Film Resistors
Yet-Ming
Chiang
Department
of Materials Science and Engineering, Massachusetts Institute of Technology,
Cambridge, MA 02139
Lee A.
Silverman and Roger H. French
Central
Research and Development
, DuPont Company,
Wilmington, DE 19880
Rowland
M. Cannon
Lawrence
Berkeley Laboratory, Berkeley, CA
Abstract
Thick
film resistors are electrical composites containing ultra-fine particles of
ruthenate conductor (Pb2Ru2O7 in the present materials) distributed in a highly modified silicate glass. We show that conductor particles remain flocced in the absence of any
applied or capillary pressures, but are separated at equilibrium by a nanometer
thick film of glass. Microstructures show evidence for liquid phase sintering,
i.e. contact flattening of particles, under van der Waals attraction alone. Titania addition, which in dilute concentrations markedly increases the
resistivity, decreases the temperature coefficient of resistance, and improves
voltage stability and noise, is found to increase the equilibrium film thickness
between particles by a few angstroms. STEM
analyses show that the added titania preferentially concentrates in the silicate
rich grain boundary film, as well as at particle-glass interfaces. The roles of interparticle forces and adsorption on the glass film
thickness with and without titania are discussed. The large increase in resistivity caused by titania additions
is attributed to the increase in film thickness as well as to local chemical
changes of two possible types. Titania
enrichment within the glass film itself is expected to decrease the local
ruthenium ion solubility, which along with the possible formation of a more
insulating titania-substituted surface layer on ruthenate grains will decrease
the tunneling conductivity between conductor grains.
Key
words: Grain boundaries,
interfaces, thick film resistors, electrical composites, electroceramics, nanocrystal, analytical electron microscopy.
