Optimization of thin film heater/sensor design for miniature devices using finite element analysis

Hoang, V.N., Kaigala, G.V., Backhouse, C.J.
ECERF, University of Alberta, Edmonton, Alberta, Canada

Localized heating is poised to become an integral part of microfluidic devices in various life-science applications. This is catalyzed by the scale of economics, the advantageous fluidic behavior at small volumes, and the ever increasing need for rapid and high throughput assays for pharmaceutical industry and other combinatorialbased studies. For precision confined heating, thin film resistive heaters have proven to be superior to the conventionally used Peltier elements, which are bulky, consume a large amount of power and are often a hindrance to miniaturization and funtionality integration for thermally sensitive applications.

The resistivity of certain metals varies predictably with temperature, making them suitable for use as temperature sensors. If a thin film heater could be designed so that it preserves a uniform temperature distribution during heating, its total resistance would accurately reflect its temperature, allowing it to simultaneously act as both a temperature sensor and a heater. Such a heater/sensor design would eliminate the need for two metal films (heater and sensor) on a chip, reducing the real-estate usage of electronics and rendering the chip more readily adaptable for higher levels of integration.

Through finite element analysis (FEA), certain guidelines for designing such a heater/sensor have been laid down and can be used generically for chip designs having different materials and geometries.