An integrated multi-element ultra-thin-film gas analyzer

The authors reports a multi-element gas analyzer realized in silicon as the hybrid of two dual-element detector chips and a control/interface chip. The detectors utilize ultra-thin metal sensing films supported by a selectively micromachined dielectric window. Boron-diffused silicon heaters under the windows permit the window temperature to he varied between ambient and over 1000 degrees C with a heating efficiency in vacuum of 20 degrees C/mW. The detector control chip contains interface circuitry for four such detectors. Window temperature is controlled from ambient to 1200 degrees C with eight-bit accuracy. Film conductivity is similarly measured to eight-bit accuracy for full-scale resistances from 5 ohms to 1.3 Mohms. Film conductivity measurements (magnitude and phase) can be made from DC to 2 MHz using the on-chip circuitry. On the output side, the interface chip utilizes a standard eight-line interface to a VLSI microcontroller, allowing the implementation of the analyzer as a smart peripheral. The detectors are realized using a six-mask process while the control chip is implemented in an eleven-mask 2 mu m CMOS process in a die size of 4.4 mm*6.6 mm.<>