Novel Packaging Approach for Enhanced Performance Gas Sensor

Background Gas sensing is becoming more and more important driven by the need to increase safety and to reduce the emissions. Sensors must operate in a variety of conditions and are playing a major role in several applications. Sensors based on optical detection offer some advantages with respect to other techniques. The present work deals with NDIR (Non Dispersive Infra Red) sensors and related packaging technology for enhancing the performances. Method Light source and couple of detectors, used for differential reading, are placed on top of DIL. A lid, properly shaped, has been placed on top of them, creating a complete module. 3D optical simulator, has been used for optimizing the shape of the lid. The best solution is a biconical surface. Moreover, a reflector has been added on top of the DIL surface. Using multiple reflections from source to detector, we can enhance the performances of the gas sensor, keeping a small form factor and footprint. Thanks to multiple reflections, the detectors are not constrained to be in the foci. This permits to address easy placement and large tolerance, without any detrimental effect on the performances. The module has been tested and compared with benchmark. Results Discussion Gas sensor module packaged in DIL 24 was inserted to a control board (Figure 1)and then data was acquired. During testing, the CO2 concentration was varied in extensively, ranging from 0 to 10000 ppm, whereas commercial sensors are usually limited to 5000 ppm and its response was then evaluated in terms of resolution and noise. Results are shown in Figure 2; the yellow and red plot are the concentration trend in the controlled chamber and in green and blue the relative sensor responses. The sensor’s response to common disturbances such as temperature and humidity was also evaluated. The temperature in the chamber has been increased from 21ºC to 33ºC. the sensor was exposed to a relative humidity variation from 20% up to 70%. No drift has been detected for humidity variation, while there is a small drift vs temperature, that can be easily compensated through a firmware recalibration procedure since the sensor embeds a temperature-sensing channel. Conclusion, The proper packaging for a CO2 sensor module has been designed and realized. Thanks to selected solution, the module size is kept small, and the detectors are not forced to be in fixed position. The assemble doesn’t required fine alignment of the lid and the placement tolerances are quite high. The module has been tested, and good results have been obtained. Measurements are aligned with the reference commercial sensor. Repeatability and accuracy have been proven. The working range was tested from 0 up to 10.000 ppm, and the sensitivity is 30 ppm. Future work will focus on more extensive testing to refine accuracy, and noise rejection can be improved by working on the hardware components and power supply.