Charge transport mechanisms in thick film resistors
Abstract
A thick film resistor is one of the basic components used in a hybrid microcircuitry. One of the important characteristics of a thick film resistor is that the temperature coefficient of resistance (RCR) should be very low. The TCR values are derived from the temperature dependence of resistance of a thick film resistor, which is controlled by the microstructure and charge transport mechanisms. It is well known that the microstructure of a thick film resistor is a strong function of materials parameters such as volume fraction of the conductive and particle size of both conductive and glass, and also of processing conditions such as time and temperature of firing. In order to understand the charge transport mechanisms in thick film resistors, it is necessary to understand the effects of these variables on the temperature dependence of resistance. To study the effect of these variables on the temperature dependence of resistance, thick film resistors with varying amount of RuO$\sb2$ using three different RuO$\sb2$ particle sizes (13.5, 8.4, and 5.0 nm) and different processing conditions were studied. For all the resistors prepared, resistance values were measured and sheet resistivities were calculated. The changes observed in sheet resistivity with a change in conductive particle size or processing condition were correlated to the proposed microstructure development model. The temperature dependence of resistance behavior of all the resistors made were studied from 10 K to 500K using a computer controlled experimental system. Both hot and cold TCR values were calculated. The temperature dependence of resistance behavior and TCR values were significantly affected by a change in RuO$\sb2$ content, particle size of RuO$\sb2$, or processing condition. The changes observed in the temperature dependence of resistance behavior with a change in any one of these variables were qualitatively correlated to the microstructure development model. A multipath model was invoked to explain the temperature dependence of resistance in thick film resistors. By considering the interconnected microstructure, it was shown that higher activation energy mechanisms such as impurity conduction, Schottky emission, Frenkel-Poole emission, and space charge limited flow near the trap filled limit may be important for non-sintered contacts. By utilizing the multipath model, it was also shown that even though higher activation energy mechanisms may operate at the non-sintered contacts, the measured activation energy from the temperature dependence of resistance behavior can be very low. A varying activation energy model was proposed to explain the temperature dependence of resistance over a wide temperature range. The theoretically calculated temperature dependence of resistance behaviors using this model were in good agreement with experimentally observed behaviors.
Degree
Ph.D.
Advisors
Vest, Purdue University.
Subject Area
Materials science
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.