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HOME > No.25, May 2021 > Semiconductor chip that detects exhaled gas with high sensitivity at room temperature

Semiconductor chip that detects exhaled gas with high sensitivity at room temperature

Toward the realization of IoT chemical sensors capable of diagnose diseases through breath testing By Toshiaki Takahashi
Toshiaki Takahashi

Doctoral student Toshiaki Takahashi, associate professor Kazuhiro Takahashi, and their research team of the Department of Electrical and Electronic Information Engineering at Toyohashi University of Technology developed a testing chip using semiconductor micro-machining that can detect volatile gasses in exhaled breath at the ppm level at room temperature. A polymer that expands and contracts when gas is absorbed is formed on a flexibly deformable nanosheet, and the amount of deformation that occurs when a target gas is absorbed is measured, allowing gas to be detected at high sensitivity. The testing chip which is no more than a few square millimeters in area thanks to semiconductor micro-machining technology, is expected to contribute to telehealth as an IoT gas sensor that can easily be used in the home for breath tests.

*The authors' affiliation and title is at the time this research was conducted.

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.

IoT chemical sensor that detects minute quantities of gas molecules adsorbed on the surface of the thin nanosheet
IoT chemical sensor that detects minute quantities of gas molecules adsorbed on the surface of the thin nanosheet

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.


Toshiaki Takahashi, Yong-Joon Choi, Kazuaki Sawada, and Kazuhiro Takahashi, A ppm Ethanol Sensor Based on Fabry–Perot Interferometric Surface Stress Transducer at Room Temperature, Sensors.


By 高橋 利昌

豊橋技術科学大学 電気・電子情報工学専攻博士後期課程 高橋利昌、電気・電子情報工学系 髙橋一浩准教授らは、半導体マイクロマシン技術を用いて作製したチップ上で、室温環境下において呼気に含まれる揮発性ガスをppm程度の濃度で検出可能な検査チップを開発しました。ガスを吸収した際に膨張・収縮する特性を持ったポリマーをフレキシブルに変形するナノシート上に形成し、標的ガスの吸収に伴う変形量を計測することにより、ガスの高感度検出が可能となります。半導体技術により数ミリ角のサイズで形成した検査チップは、IoTガスセンサとして、家庭において簡易的な呼気検査を行うことで、遠隔医療への貢献が期待されます。




そこで、研究チームは、ガス分子の吸収により膨張・収縮する特性を持ったポリマー材料 をフレキシブルに変形するナノ薄膜上に成膜し、標的ガスの吸収量を膜の変形量として計測するセンサを開発しました。提案センサは,光が狭い隙間で強め合う干渉特性を利用して,ガスの吸着を色の変化としてとらえることができます。この技術により,加熱機構を搭載せずに室温環境下でガスの計測が可能な検査チップが実現できました。





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Researcher Profile

Toshiaki Takahashi
Name Toshiaki Takahashi
Affiliation Micron Memory Japan, G.K.
Title ADTJ PI Engineer
Fields of Research Micromechanics, Semiconductor devices, Gas sensors, Bio sensors
Degree Ph.D. (Engineering), Toyohashi University of Technology
National Institute of Technology,
Asahikawa College