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Key Technologies and Innovative Applications of Next-Generation Nanodevices: The Smart Gas Sensor Chip

On July 31, 2014, a propylene gas explosion unexpectedly occurred in Kaohsiung City in southern Taiwan. The explosion overturned cars, destroyed roads, and sparked a massive inferno causing severe damage, including numerous deaths and injuries.

This tragedy could have been prevented by installing smart gas sensors near the explosion site to detect the extensive leakage of high-risk volatile organic substances. However, gas sensors currently available on the market are large-sized and can only be installed at fixed locations or be operated manually.

To prevent future explosions and protect people's lives and properties, the National Nano Device Laboratories (NDL) of National Applied Research Laboratories (NARLabs) is developing smart gas sensor chips that can be directly installed in portable devices (e.g., smartphones or watches) to supplement fixed environmental sensors and vastly increase the sensing range. Smart sensor chips that can detect volatile organic compounds, carbon monoxide, carbon dioxide, and formaldehyde have already been successfully developed by NDL.

Flaws in Existing Gas Sensors
According to an estimate by the International Data Corporation, the market size of Internet-of-things (IoT) applications will reach US$1.7 trillion by 2020. In particular, wearable and portable devices play a crucial role in the IoT market. It's predicted that the gas sensors employed for breath analysis (e.g., sobriety tests) and air pollution detection is most likely to be applied for use in wearable and portable products. According to Yole Development, a French market research agency, the number of gas sensors in use will expand to 350 million units in 2021, reaching almost 300 times the 1.2 million units reported to be in use in 2014. This will result in an output value of more than US$2 billion.

Available gas sensors that can accurately detect gas flow volumes and types are generally large-sized. By contrast, the recently introduced semiconductor gas sensor prototype is no larger than 1cm; however, it remains too large for portable devices. Moreover, this prototype consumes a considerable amount of energy and cannot be integrated with smartphones or watch chips, thus cannot accurately identify the presence of gas.

The Portable Smart Gas Sensor Chip Developed by NARLabs
Through their accumulated microelectromechanical system manufacturing experiences, as well as integrated optical and electrical technology collaboration with Lite-On Technology, NDL has developed a smart gas sensor chip over a period of approximately 2 years. The resultant sensor is an IoT chip that can be applied to environmental gas detection.

The smart gas sensor chip incorporates a metal oxide semiconductor material as its gas sensor film. Through oxidation and reduction reactions among various metal oxides and gases at a specific temperature, as well as the electron capturing and releasing processes of the film, the resistance of the film is altered to detect different types and concentrations of gases.

The smart gas sensor chip exhibits the following two technological characteristics: (1) The gas sensor film was created using unique nanoparticle and nanopore technology to increase the surface area and enhance the reaction sensitivity. In addition, through the characteristics of different incorporated metallic nanoparticles, the film can detect different types of gas through its improved specificity in recognizing certain gas types. (2) A special low-stress dielectric layer was developed to enhance the insulation effect of the chip by markedly reducing the area of the high-temperature region of the gas sensor film (250 °C), thereby reducing the volume of the chip and preventing potential damage to the non-heat-resistant components from such high temperatures.

By applying the aforementioned two technological characteristics, NDL developed a 3x2.35x1mm smart gas sensor chip that is miniaturized, consuming little power, can be integrated into smartphones and watches, and can accurately identify various gases, thus developing a portable gas sensor for various applications.

Promoting Sensor Technology Development in Taiwan to Prevent Future Gas Explosion Incidents
NDL has successfully created the first gas sensor chip for smart devices and global technological industries. Thus, a human-centered monitoring approach has been applied to the existing spatial environment monitoring technology. When all gas sensor data are instantly uploaded to cloud-based storage, government agencies can directly monitor the environmental quality of each region. In Taiwan, if another leakage of volatile organic compounds such as propylene occurs, the police, fire, and environmental agencies can utilize this new gas sensor chip to preemptively alert residents and resolve the leakage, thus preventing another gas explosion, or at the very least, minimizing the resultant casualties.

Recently, there has been an increase in the application of various sensors implemented in personal IoT applications or wearable devices in various domains such as consumer electronics, smart homes, security monitoring, health care, transportation, retail sales, and emergency rescue. NDL has succeeded in developing smart gas sensor chips that detect carbon monoxide, carbon dioxide, formaldehyde, and volatile organic compounds. NDL plans to continue developing new types of gas sensor chips and research composite gas sensors for industrial use and personal body care.

NDL also plans to establish an open manufacturing technology service platform for Taiwanese industrial and academic research teams to integrate systems required for IoT chips, thereby further promoting the sensor technology development required for IoT-wearable products in Taiwan.

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