• Back
• Next

日本語

When measuring specific molecules in the breath and blood as an index for identifying the existence and degree of progression of various illnesses, there are several methods to choose from. Amongst these methods, non-invasive measuring by breath testing has emerged as a promising and patient-friendly option. It has been identified that volatile organic compounds found in exhaled breath will increase in concentration in cases of diabetes, renal failure, lung cancer, and other illnesses. Consequently it can be reasonably be expected that these laboratory markers will be measured for use in patient screenings.

Up to now semiconductor gas sensors have generally worked by using a film formed on a sensor whose electrical resistance and capacitance change in reaction to a gas. Measurements are then made by heating the film to several hundred degree Celsius. However, in order to reduce the resulting temperature increases in the peripheral circuits, it becomes necessary to house them in a separate structure. This in turn creates issues arising from the increased complexity of the manufacturing processes and the decrease of the integration per unit area due to the isolation of elements. In addition, the increase in power consumption caused by heating poses a problem for applications in IoT devices.

To counteract these problems, the research team developed a new type of sensor that forms a polymer material which expands and contracts when gas molecules are absorbed onto a thin, flexibly deformable nanosheet. It then measures the amount of the target gas absorbed in terms of the amount of deformation of the sheet. The proposed sensor uses the interferometric property of light intensification through a narrow gap to determine gas adsorption in terms of color change. As a result of this technology, it is now possible to create a testing chip that can measure gas at room temperature without a heating mechanism.

Also, this sensor can increase sensitivity without increasing area because of the formation of a narrow, sub-micron air gap of up to a few hundred nanometers between the thin flexible nanosheet and the semiconductor substrate. However, it was very difficult to merge the thin nanosheet above the sub-micron air gap while forming the gap, and it was necessary to develop a new manufacturing process to achieve the structure.

Therefore, the team focused on the strong adhesive properties of the thin nanosheet when heat and pressure are applied. A new manufacturing process was introduced where two different silicon substrates are adhered, and then the substrate on one side is removed to create a sensor structure with a sub-micron air gap of about 400 nanometers. In comparison to traditional sensor structures formed with a gap of a few micrometers, the sensor response was demonstrated to have improved by 11 times, and it was possible to determine the deformation of the thin nanosheet due to gas adsorption in terms of color change.

Additionally, it was demonstrated that the testing chip that was developed can detect ethanol gas, a typical volatile organic compound, in ppm level concentrations. The lower concentration detection limit is equivalent in performance to the most sensitive semiconductor sensors that can measure at room temperature, and compared to sensors that use the same detection method, the detection performance improved by 40 times, while the area per single element was reduced to 1/150. These properties make it likely that this sensor can be used in future as part of a small, portable breath testing device.

The research team plans to demonstrate the possibility of using the semiconductor sensor they developed to detect various volatile gasses related to illnesses. Also, they aim to construct a small, portable sensor system for breath monitoring that consumes less power than traditional IoT gas sensors.