Development of a volatile organic compounds sensor for the Internet of Things

Nowadays, there is a specific fields that tends to connect any devices creating useful or valuable data : the Internet of Things (IoT). The IoT can be seen has a network of many devices communicating together or to a central node. Collecting data anywhere it seems needed . The perspective of this network is to achieve more than billions of nodes 1 However, the specification of this network are : - Very low power consumption to be autonomous for a long time. - Small device size to be placed everywhere and anywhere it sounds needed. - Being able to communicate with the network and preferably in a secured way. - Cheap devices to have the opportunity to spread many nodes easily. Following this trends, this master thesis develops a sensors matrix to monitor volatile organic compounds (VOCs) in industrial workplaces or buildings and focus on the CMOS large scale production compatibility of these sensors, on the selectivity over the VOCs with electropolymerized "molecularly imprinted polymer" (MIP) patterned for a specific VOC and on the specificities required for an integration into the IoT. The sensors development realized in this work has three steps of investigation: 1. The design of masks to manufacture a wafer allowing the electro-polymerization of at least two different MIPs. The masks drawn allows two different MIPs to be electro-polymerized but the creation of new masks can increase the number of electro-polymerization up to nine different MIPs. The design has four different kind of sensors with different width and space for the IDEs shape. Two types of dies are drawn, 3x3 sensors dies and 2x2 sensors dies. The number of dies is optimised 2 with the constrain of a 3x3 mm2 maximum die size. In this way, the conditions of electro-polymerization are the closest to the foundries one. 2. The overall process is CMOS compatible including the most critical part: the electropolymerization. The electro-polymerization was successfully achieved on gold IDEs with a pulse deposition technique at a tension shifted from 1.1 V to 1.6 V by steps of 800 µV. This correspond to 625 pulses and the thickness of the MIP polymerized was ~1.4 µm. 3. The selectivity of the sensors over formaldehyde with a good sensitivity at room temperature. This step is still under investigation. Some variation of the resistance are visible. However, under 0%RH and a concentration of formaldehyde from 0 to 50 ppm the resistance variation is around 9.3%. Therefore, further investigations should be conducted. The IoT compatibility is considered as almost complete as the size of the sensors die is 9 mm2, it can provide data , its CMOS compatibility allows it to be added to a IC or SoC with a communication system and the price of process can be consider as cheap even with gold IDEs as many dies can created per wafer.