From the beginning, we studied and fabricated platinum, graphene, and platinum diselenide infrared emitters, different designs for waveguides (Figure 2a, 2b), graphene and platinum diselenide photodetectors (Figure 2c,2d). We also designed tunable optical filters (Figure 2e) to measure different infrared wavelengths and, thus, different gases on the same chip (Figure 2f). We developed a technique to place small protective gas-permeable caps on the gas sensors to keep them safe from dirt and dust. The fabrication techniques required to produce the sensors in large volumes, particularly the methods to integrate 2D materials, graphene, and platinum diselenide, on semiconductor wafers was improved.
Platinum diselenide can be grown with thermally assisted conversion (TAC) and metal-organic chemical vapor deposition (MOCVD). TAC is a two-step process in which a thin layer of platinum is first deposited and then converted (selenized) into platinum diselenide. With MOCVD, instead, the platinum diselenide is grown in a single-step process, and the resulting material is of better quality. The main achievements are the in-situ growth of this 2D material on waveguides and the development of a 4” wafer scale platinum diselenide deposition process.
We developed wafer-scale dry transfer processes of graphene that result in good graphene quality, even on suspended waveguide topography, which are suitable for mass production. Furthermore, a new seed-free graphene encapsulation process was developed (patent pending).
By the end of the project, we fabricated and characterised most of the components individually, and we reached the goal of demonstrating multi-gas sensing by using the ULISSES-designed waveguides and external light sources and detectors. We could measure the presence of methane (Figure 3a) and carbon dioxide (Figure 3b) and determine the concentration of carbon dioxide.
We developed machine learning algorithms for networked cloud-connected sensors to achieve the most from the sensors and make them more reliable by incorporating them in an IoT ecosystem. This way, the sensors can improve their lifetime by staying calibrated, thanks to other peers or superior sensors. Each sensor can learn from its own and other sensors’ history and self-estimate its reliability.
While developing the system-on-a-chip (SoC), we also prepared wireless cloud-connected air quality sensing units for our on-chip gas sensors using traditional gas sensors. Several deployments have taken place since the beginning of the ULISSES project, one involving multi-gas sensing for hydrocarbon detection as safety systems (Figure 4a) and several involving carbon dioxide sensors for mapping air quality in several areas of Sweden, by using electric vehicles in Stockholm (Figure 4b, 4c) or cars in rural Sweden (Figure 4d, 4e). The data collected in the deployment suggested ways to achieve better performances, but they are also useful for various applications. For example, we developed a route planning tool that works as a Google Maps plug-in and identifies the route with the lowest exposure to exhaust gas based on the measured air quality data. To ensure that our new sensors meet the needs and expectations of future users, we established a forum of stakeholders that follow the project, providing insights into the challenges they face, as well as valuable feedback and ideas.
