Sustainability assessment of sensor materials in applications

Abstract

Sensing technologies offer several advantages for industrial tooling. In mechanical processing and manufacturing environments, sensors can be used to monitor process conditions, support predictive maintenance, reduce unnecessary material losses, and improve overall production efficiency. Therefore, as manufacturing systems become more advanced and data-driven, the integration of sensors has become more and more common.
At the same time, the benefits of sensor integration should not be evaluated only from the perspective of performance at the stage of use. Sensors cannot function independently; they usually rely on additional functional materials to achieve their sensing capabilities. If this material dimension is ignored, some important sustainability issues may be overlooked. This is especially relevant for indium-based materials. Indium is mainly obtained as a by-product of zinc production, which means that its availability is closely related to the broader metal production system, not just direct mining. In addition, indium also involves problems such as supply chain concentration, relatively complex processing routes, and uncertainty in post-use recycling.
Against this background, this thesis examines indium-based thin-film sensing materials from the perspective of sustainability. The research focuses on indium oxide (In2O3) and indium tin oxide (ITO), paying special attention to their role in the sensor-integrated manufacturing applications. This study did not carry out a complete quantitative life cycle assessment (LCA), but adopted a life cycle-oriented exploratory method. This enables research to discuss major sustainability issues at different stages of the material life cycle, rather than reducing the analysis to numerical indicators alone.
This analysis also considers the upstream and downstream links of the material system. The research content includes raw material acquisition, supply chain risks, processing challenges, relevance of the use stage, material stewardship, concerns related to toxicity, and the possibility of recycling at the end of life. The manufacturing stage is also included in the discussion, but mainly as a technical background. The role of this part in this thesis is to help explain why these materials are related to sensor applications and why they need to be carefully considered in sustainability assessment.
The results indicate that the sustainability significance of In₂O₃- and ITO-based sensor materials cannot be evaluated solely on the basis of their small mass contribution to the final product. A broader material-system perspective is required, since these materials are embedded in supply and processing structures that may generate sustainability concerns beyond the sensor layer itself. The main hotspots identified in this study include the by-product dependence of indium supply, geographic concentration of refining capacity, limited transparency in processing routes, reliance on manufacturing scrap rather than mature end-of-life recycling systems, and the technical difficulty of recovering thin and spatially dispersed sensor layers from engineering products. At the same time, the use of indium-based sensor materials may be justifiable in applications where sensor integration can produce measurable reductions in scrap, rework, downtime, premature tool failure, or unnecessary energy consumption.
The thesis concludes that indium-based sensor materials should not be classified as inherently sustainable or unsustainable. Their sustainability performance depends on the balance between upstream and downstream burdens and the functional benefits achieved during the use phase. The study provides an initial analytical framework for assessing emerging sensor materials in sensor-integrated manufacturing systems and identifies key knowledge gaps that should be addressed in future application-specific life cycle assessment studies.

Popular Abstract

Popular Abstract
Sensors are becoming increasingly important in modern manufacturing. They can be integrated into tools, machines, or engineering components to monitor temperature, vibration, wear, and process stability. This information can help factories detect problems earlier, reduce defective products, avoid unnecessary downtime, and use materials and energy more efficiently. In this way, sensor technology may support smarter and more sustainable production.
However, sensors also depend on specific materials to perform their functions. This thesis focuses on two indium-based thin-film sensor materials: indium oxide and indium tin oxide, also known as ITO. These materials can be made into very thin functional layers and used in sensor systems. Although the amount of material used in each product may be small, the sustainability issues behind these materials should not be ignored.
The key issue is indium. Indium is usually not mined as a main metal, but is mainly recovered as a by-product from zinc production. This means that indium supply depends on zinc production, refining capacity, recovery technology, and economic conditions. Its supply is also geographically concentrated, which may make users more vulnerable to trade changes, policy decisions, or regional supply disruptions.
The downstream stage is also important. When indium oxide or ITO is integrated into engineering products, it becomes part of a multi-material system with substrates, coatings, wires, protective layers, and electronic components. During use, this integration may support monitoring and maintenance. However, after use, the thin indium-containing sensor layer may be difficult to identify, separate, and recycle. Health and handling issues may also arise during manufacturing, cutting, dismantling, or recycling if respirable indium-containing dust is generated.
This thesis does not simply judge indium-based sensor materials as good or bad. Instead, it shows that they should be understood through a trade-off. Their supply, processing, recycling, and handling challenges need to be considered together with possible use-phase benefits, such as reduced scrap, rework, downtime, tool failure, or energy consumption. The main message is that even very small functional material layers can be connected to larger sustainability challenges, and more application-specific data are needed to decide when their use can be justified.

• author: Wang, Ange
• supervisor: Christina Windmark
• organization: Production and Materials Engineering
• course: MMTM05 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Sustainability assessment, sensor materials, indium oxide, indium tin oxide, life-cycle-oriented assessment, sensor-integrated manufacturing.
• other publication id: LUTMDN/(TMMV-5390)/1-61/2026
• language: English
• id: 9233486
• date added to LUP: 2026-06-09 12:58:35
• date last changed: 2026-06-09 12:58:35