Fabrication and characterization of thermal conductivity detectors (TCDs) of different flow channel and heater designs

Abstract

Different flow channel designs and heaters made from different materials were tested for improving the performances of silicon-based thermal conductivity detectors. One of the designs involved an electric heater sandwiched between two identical flow channels for high heat transfer rates. The heater of the other design was suspended over a slot to reduce heat losses. The flow channels were etched in silicon wafers and nickel heating elements were deposited on Pyrex glass, polyimide, and silicon nitride membranes. The transient behaviors of the heaters and the wafer temperatures were measured and analyzed for different voltages. The effects of flow channel design and membrane material on the heat transfer characteristics and sensitivities of the detectors were examined. Simple heat transfer models were developed to aid in understanding and diagnosing detector behaviors and performances. The polyimide heater had the best signal conditions. The warm-up times of the TCDs were found to be primarily dependent upon the package dimensions and properties. The double-channel TCD exhibited 20% higher heat transfer rate compared to the single-channel design, but the sensitivities of these two designs differed only slightly.