Heater patterns for planar gas sensors

This disclosure relates to planar gas sensors, and, more particularly, to heater patterns for planar gas sensors that yield a reduction in the incidence of cracking attributable to tensile stresses at the edges of the planar gas sensors. A heater pattern for a heater of a gas sensor in which a temperature profile is manipulated utilizes a thermistor element arranged in an electrically serial configuration and disposed on a substrate. The thermistor element is arranged so as to define an edge pattern extending about a perimeter of the substrate and a center pattern serially connected to the edge pattern. The center pattern extends over a portion of the substrate that is intermediate the perimeter of the substrate. In a preferred embodiment, the thermistor element is screen printed onto the substrate to a thickness of about 5 microns to about 50 microns, and preferably to a thickness of about 10 microns to about 40 microns. The edge and center patterns are furthermore preferably formed of materials having differing coefficients of thermal resistivity, e.g., platinum and platinum/palladium blends. A method of heating the gas sensor includes disposing the thermistor element in an electrically serial configuration about a perimeter of the substrate and over a portion of the substrate intermediate the perimeter of the substrate and pass an electric current through the thermistor element.