Thermal modeling and characterization of a thin-film heater on glass substrate for lab-on-chip applications

This paper presents an accurate thermal characterization of thin-film heaters manufactured on glass substrates. The characterization has been performed on Cr/Al/Cr meandered heaters. Techniques commonly adopted for measuring the temperature coefficient of resistance, the thermal resistance and thermal capacitance in the case of Si-based microheaters have been conveniently modified to consider the fundamentally different thermal parameters of a heater manufactured on glass. To reduce power consumption and thermal capacitance, a grating of 250- $\mu $ m wide trenches, stopped at $80~\mu $ m from the opposite metalized front surface, was manufactured on the back side of the heaters, obtaining an increase of the thermal resistance of about 110% and a decrease of the thermal capacitance of about 65% when the glass is in good thermal contact with a heat sink. The measured values of thermal resistance and time constants on a heat sink and in air have been justified starting from realistic physical considerations. Finally, a novel thermal model suitable for microheaters on glass immersed in air was presented and validated by comparing its predictions with the experimental cooling behavior of the microheater and with the predictions of an exponential model.