Experimental study of heat-treated thin film Ti/Pt heater and temperature sensor properties on a Si microfluidic platform

Design, fabrication and characterization of thin film Ti/Pt heaters and integrated temperature sensors on a Si microfluidic platform are presented. Ti/Pt heaters and sensors provide controlled heating of microchannels realized on the opposite side of the Si platform. Ti/Pt heaters and sensors were fabricated simultaneously by a dc sputtering method and a lift-off process. Thermal annealing of deposited Ti/Pt layers in the temperature range of 300-700 degrees C was investigated revealing a strong impact on the Ti/Pt resistivity and, consequently, on the final resistance of fabricated heaters and sensors. Furthermore, it was determined that the temperature coefficient of resistance (TCR) for Ti/Pt temperature sensors and the heater increased with the annealing temperature. Microstructural analysis of deposited and annealed Ti/Pt layers carried out by AES and AFM revealed that recrystallization followed by a grain growth process of heat-treated Ti/Pt layers started at around 500 degrees C and correlated well with the behavior of electrical properties, but not with the TCR behavior of annealed layers. To reduce the heat losses of the heated Si platform, the heater and temperature sensors were covered hermetically by anodically bonded Pyrex glass with a prefabricated insulating cavity. According to this approach the power consumption was reduced by more than 25% due to the improved thermal insulation. Additional insulation steps implemented during thermal characterization of the assembled microfluidic platform further reduced the power consumption, but also increased the time response of the microfluidic reactor.