Thermally regenerated volatile organic compound sensors based on IGZO-transistor functionalization with metal-organic frameworks

Promovendus/a: Maider Calderon González

Promotor(en): Prof. dr. ir. Jan Genoe, Prof. dr. ir. Rob Ameloot

We are constantly surrounded by smells: from your favourite dish, air freshener, cigarette smoke, or even old garbage. But what if I told you that by studying smells, we could do incredible things? For instance, scientists can detect the early signs of certain diseases or find out if food that looks fine is actually unsafe to eat.

Although a lot of progress has been made, smell detectors are either too big, too costly, or not very precise. Therefore, we are still trying to find useful alternatives capable of overcome these limitations. In this work, we propose a novel smell detector composed by three key elements.

The first component is something you can find in almost every electronic device: a transistor. Transistors are used to regulate the flow of electric current, and they are very popular since they are very small, fast, and cheap. When a transistor comes into contact with certain odours, the way it controls the electricity can experience changes, and we can use those changes to ‘read’ the amount and properties of the smell.

The second element is a very particular material, called metal-organic framework. This material can be understood as a ‘sponge’ which is able to trap and concentrate certain types of odours. By doing this, it helps to produce a stronger signal (sensitivity), and can improve the ability to distinguish target odours from interfering ones (selectivity).

The third element is a microheater, used to increase the temperature of the sensor. This is very helpful to eliminate the unwanted smells that are trapped in the sensor and that interfere in our smell analysis.

For the development of this odour sensor, we have explored many microheater geometries, studying what is the impact in their thermal characteristics and temperature uniformity. These studies are performed experimentally and via simulations, and allowed us to select the most suitable design. Additionally, we have provided a detailed overview on the fundamental physics of the transistors, compared two device designs to select the optimal one, and demonstrated that their behaviour can be modelled using a simulation tool not typically applied in this field. Furthermore, we have experimented with a novel approach to integrate the metal-organic framework.

The performance of our sensor is studied intensively for the detection of methanol and include the analysis of the many different parameters that are important in transistors. Compared to other sensors, we have demonstrated a very strong response, although is limited at low concentrations. We have identified an interesting behaviour of the transistor that arises when the smell molecules are trapped. Additionally, we have proved that brief temperature pulses can be beneficial to remove interferents and improve the sensor readings. This sensor was tested for other types of gases, including ethanol, 2-propanol and water, but it provides the best response towards methanol. Although the results are promising, there are some limitations coming from the selected materials that need to be overcome in future investigations.