Study on the resistivity behaviour of graphite-based resistors used in sol-gel thick film heaters

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Datec Coating Corporation is a Canadian manufacturer of custom heating elements and high-performancecoatings based primarily on patented and proprietary sol gel technologies. The company was founded by 2PhD scientists from Queen's University in the mid 1990's and has since grown into a leader in thick filmheating technology over various segments including automotive (electric vehicle battery heaters), medicaldevices and electronics. Two product platforms involve graphite-based resistors created using Datec's sol-gel chemistry. One utilizes mica as the heater substrate and the other utilizes aluminum substrate. Although the graphite-based heater has significant competitive advantages over the state of the art, the resistivity of thegraphite heater has been observed in some instances to drift significantly and in an unpredictable way, depending on application variables (power density, temperature, relative humidity, voltage, current density,duty cycle) as well as on the history of the device. The resistance drift behaviour is different for mica heaters than aluminum heaters. The first objective of the project is to design and execute experiments to identify and systematically evaluate the variables governing resistance drift for the purpose of predictive modelling. Due tothe complexity of the phenomenon and the apparently numerous factors affecting resistivity drift, it isenvisioned that an artificial neural network model will be developed with the support of the R&D capability at Datec. Additionally, experiments will be designed and executed following scientific method to test hypothesesregarding the mechanisms governing resistivity drift. The results of this work will inform the next generation of resistor design, which represents core technology to Datec.