Accurate monitoring of CO₂ concentration in exhaled breath is of great significance for disease diagnosis, and with the growth of personal medical and health needs, CO₂ infrared gas sensors have gradually become a research hotspot in the field of wearable respiratory monitoring. However, temperature changes can have a significant impact on the performance of the sensor, so effective temperature monitoring is required to ensure proper operation. The addition of NTC bare chips to CO₂ infrared gas sensors helps to improve the measurement stability of the sensor due to its fast temperature feedback.

The main working principle of CO₂ infrared gas sensors is that when CO₂ molecules enter the optical chamber, they absorb infrared radiation of a specific wavelength and convert that part of the energy into heat. This temperature change is then captured by a thermopile-type infrared detector located at the other end and converted into an electrical signal output. By comparing the baseline signal in the absence of CO₂ with the actual measured data, the specific concentration of CO₂ exhaled by the subject in the wearable breath monitoring device can be calculated.

In this process, the heat generated by the surrounding environment and internal components may interfere with the working state of the CO₂ infrared gas sensor, and engineers usually bond and solder the NTC bare chip on the substrate to monitor the temperature of the sensor in real time. The bare chip provides real-time temperature feedback to the temperature control unit, which helps the CO₂ infrared gas sensor to accurately adjust the temperature, which helps to reduce the influence of the light source on it and improve the sensitivity and accuracy of its own gas measurement. In addition, in order to ensure the stable light source output of the CO₂ infrared gas sensor and the stable performance under different temperature conditions, the NTC bare chip is used for efficient temperature compensation to eliminate the influence of temperature fluctuations on the measurement results, which plays an important role in maintaining the high accuracy measurement of the CO₂ infrared gas sensor.

Due to the limitations of wearable respiratory monitoring devices on the installation location of CO₂ infrared gas sensors, the size of the NTC bare chip and internal components is also put forward strict requirements. The double-sided Ag+Au termination NTC bare chip developed and mass-produced by EXSENSE Electronics Technology Co., Ltd. can adapt to the installation requirements of CO₂ infrared gas sensors with its small size, providing more assembly space for other components. Secondly, the high accuracy of the NTC bare chip can effectively reduce the deviation of the temperature measurement of the CO₂ infrared gas sensor. In addition, the double-sided Ag+Au NTC bare chip has a gold termination on the upper surface (better bonding effect) and a silver termination on the lower surface (better silver glue soldering effect), which is cost-effective and maximizes the cost-effectiveness of CO₂ infrared gas sensor.