Temperature Sensors Based on Negative Temperature Coefficient of ZnO Thin Films

Based on the experimental discovery about the negative temperature coefficient (NTC) of ZnO, we fabricated a low-temperature sensor with ZnO thin film. Oxygen plasma and annealing treatment were carried out to manipulate the related defects and explore the negative temperature response, while a series of microstructural and optical properties were also characterized and compared for the cases before and after treatment. It demonstrated that zinc interstitials (Zni) played an important role in NTC response process. Moreover, we simulated the application conditions of cell cryopreservation and conducted relevant tests in the common temperature range of −120 °C–0 °C. The ZnO NTC sensor was applied for actual real-time temperature monitoring in a commercial low-temperature system. The sensor presented a nice sensitivity of 3.51
$\times \,\,10^{{4}}\,\,\Omega \cdot \text{K}^{-{1}}$
at 90 K, a good repeatability, recoverability, and a fast response speed. The results showed a great potential of ZnO NTC sensor for biomedical cryogenics applications.