Abstract
Metal oxide gas sensors with integrated micro-hotplate structures are widely used in the industry and they are still being investigated and developed. Metal oxide gas sensors have the advantage of being sensitive to a wide range of organic and inorganic volatile compounds, although they lack selectivity. To introduce selectivity, the operating temperature of a single sensor is swept, and the measurements are fed to a discriminating algorithm. The efficiency of those data processing methods strongly depends on temperature uniformity across the active area of the sensor. To achieve this, hot plate structures with complex resistor geometries have been designed and additional heat-spreading structures have been introduced. In this work we designed and fabricated a metal oxide gas sensor integrated with a simple square planar indium tin oxide (ITO) heating element, by using conventional micromachining and thin-film deposition techniques. Power consumption–dependent surface temperature measurements were performed. A 420 °C working temperature was achieved at 120 mW power consumption. Temperature distribution uniformity was measured and a 17 °C difference between the hottest and the coldest points of the sensor at an operating temperature of 290 °C was achieved. Transient heat-up and cool-down cycle durations are measured as 40 ms and 20 ms, respectively.
Highlights
Metal oxides are widely used in gas sensing applications, such as chemo-resistive [1] and optoelectronic sensors [2,3]
Those research studies present innovative integrated micro-hotplate technologies based on Micro Electro Mechanical Systems (MEMS) to achieve optimized thermal properties such as low power consumption and good temperature uniformity across the active layer [4]
The structure of the metal oxide gas sensor is shown in Figure 1, which demonstrates the cross-section of the gas sensor
Summary
Metal oxides are widely used in gas sensing applications, such as chemo-resistive [1] and optoelectronic sensors [2,3]. Metal oxide–resistive gas sensors are being investigated, developed, and used due to their simplicity, production flexibility, low cost and sensitivity to a wide variety of volatiles [1]. Due to increasing interest in those sensors, micro-hotplate structures are being developed with enhanced device performance, decreased power consumption, and low cost [1,4]. Research activities aimed at enhancing the sensitivity and selectivity as well as lowering the response time and power consumption are still under active research. Those research studies present innovative integrated micro-hotplate technologies based on Micro Electro Mechanical Systems (MEMS) to achieve optimized thermal properties such as low power consumption and good temperature uniformity across the active layer [4]. With the development of MEMS technologies in the 1990s, new generations of gas sensors with integrated micro-hotplates were realized. The optimization of device geometry, membrane, Sensors 2016, 16, 1612; doi:10.3390/s16101612 www.mdpi.com/journal/sensors
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