Periodic Reporting for period 3 - ULISSES (Ultra low-power integrated optical sensor systems for networked environmental multichannel gas Sensing)
Reporting period: 2022-07-01 to 2023-06-30
Within the ULISSES project, we have been faithful towards “Air sensors for everyone, everywhere”. The goal was to develop an integrated multi-gas sensor system based on waveguide technology with low-cost, low power consumption, and a small footprint.
The ULISSES partners strongly believed in the necessity for a gas sensor system that could satisfy the requirements and answer the questions of different segments of society, including researchers, industrial stakeholders, environmental scientists, farmers, administrations, and regular citizens. The importance of quantifying and qualifying the pollutants in both our outdoor and indoor environments was amplified by the important changes generated by climate change and the covid-19 pandemic. It resulted in the necessity to develop affordable gas sensor systems. The second key parameter is to integrate them, thanks to their small footprint and low-power consumption, into portable devices would be a game-changer, guaranteeing a fine mesh of devices measuring air quality in real-time.
The sensor developed within ULISSES consists of millimeter-sized on-chip optical gas sensors working in the mid-infrared spectral range, which can be mass-produced and integrated into portable devices (Figure 1a). Optical gas sensors require a light source, a light path, and a light detector.
The sensor principle is simple: an active 2D material, graphene, or platinum diselenide, generates light. The generated light is guided by an integrated waveguide on a chip that one can imagine as a micrometer size highway for light. In a perfect system, the light can either travel the entire path – several centimeters long, reaching the detector, another active layer of either graphene or platinum diselenide which can convert the recorded light into an electric signal or can be absorbed by the gas in the air – causing a difference in the quantity of light reaching the detector – and so giving us the information about the quantity of gas in the environment.
While the principle behind optical gas sensors is simple, developing such sensors requires satisfying strict constraints, making fabrication challenging.
To take full advantage of the ULISSES sensors, they must be connected to an Internet of Things (IoT) network (Figure 1b) to communicate their data from anywhere. This connection also enables data exchange to provide more reliable measurements, better calibration, and an increased lifetime. To this end, we developed machine learning algorithms that allow the sensors to communicate with each other to improve data reliability.
In summary, the goal of ULISSES was to advance the technologies required for the mass implementation of air quality sensors.
The ULISSES partners strongly believed in the necessity for a gas sensor system that could satisfy the requirements and answer the questions of different segments of society, including researchers, industrial stakeholders, environmental scientists, farmers, administrations, and regular citizens. The importance of quantifying and qualifying the pollutants in both our outdoor and indoor environments was amplified by the important changes generated by climate change and the covid-19 pandemic. It resulted in the necessity to develop affordable gas sensor systems. The second key parameter is to integrate them, thanks to their small footprint and low-power consumption, into portable devices would be a game-changer, guaranteeing a fine mesh of devices measuring air quality in real-time.
The sensor developed within ULISSES consists of millimeter-sized on-chip optical gas sensors working in the mid-infrared spectral range, which can be mass-produced and integrated into portable devices (Figure 1a). Optical gas sensors require a light source, a light path, and a light detector.
The sensor principle is simple: an active 2D material, graphene, or platinum diselenide, generates light. The generated light is guided by an integrated waveguide on a chip that one can imagine as a micrometer size highway for light. In a perfect system, the light can either travel the entire path – several centimeters long, reaching the detector, another active layer of either graphene or platinum diselenide which can convert the recorded light into an electric signal or can be absorbed by the gas in the air – causing a difference in the quantity of light reaching the detector – and so giving us the information about the quantity of gas in the environment.
While the principle behind optical gas sensors is simple, developing such sensors requires satisfying strict constraints, making fabrication challenging.
To take full advantage of the ULISSES sensors, they must be connected to an Internet of Things (IoT) network (Figure 1b) to communicate their data from anywhere. This connection also enables data exchange to provide more reliable measurements, better calibration, and an increased lifetime. To this end, we developed machine learning algorithms that allow the sensors to communicate with each other to improve data reliability.
In summary, the goal of ULISSES was to advance the technologies required for the mass implementation of air quality sensors.
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.
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.
The technologies related to graphene and other 2D materials struggle to advance beyond research levels due to production and integration techniques that rely on manual processes and therefore have poor reproducibility and yield. The acquired knowledge of graphene and platinum diselenide will lead to commercial products and not only related to the gas sensor industry once the market and technology around these materials will mature further.
The ULISSES breakthroughs on waveguide-integrated 2D material photodetectors and emitters and waveguide-based gas sensing aim at packing multiple sensors for different gases on a single chip to achieve multi-gas sensing with a three-order-of-magnitude reduction in sensor size and power consumption, thus enabling maintenance-free battery powered operation for the first time. The results showed a promising technology for developing a low-cost gas sensor with a small footprint and low power consumption.
By the end of the project, we demonstrated multi-gas sensing with our on-chip waveguides and detailed characterization of each component.
The technology developed during ULISSES is a step forward involving everyone to monitor and put demands on the quality of the air they breathe and provide authorities and industries with new tools to measure the air quality and trigger responsible interventions.
The ULISSES breakthroughs on waveguide-integrated 2D material photodetectors and emitters and waveguide-based gas sensing aim at packing multiple sensors for different gases on a single chip to achieve multi-gas sensing with a three-order-of-magnitude reduction in sensor size and power consumption, thus enabling maintenance-free battery powered operation for the first time. The results showed a promising technology for developing a low-cost gas sensor with a small footprint and low power consumption.
By the end of the project, we demonstrated multi-gas sensing with our on-chip waveguides and detailed characterization of each component.
The technology developed during ULISSES is a step forward involving everyone to monitor and put demands on the quality of the air they breathe and provide authorities and industries with new tools to measure the air quality and trigger responsible interventions.