Tailoring NTC thermistor performance in high-entropy spinel oxide films via sputtering power optimization

(CoCrFeMnNi)3O4 high-entropy oxide thin films were prepared by magnetron sputtering at different powers to study their structure and electrical properties. Films deposited at 20 W showed a single-phase cubic spinel structure, fine grains, high grain boundary density, and maintained stoichiometry, leading to excellent negative temperature coefficient (NTC) thermistor performance with a high B20/50 value of 3629.70 K. In contrast, 40 W deposition caused element-specific sputtering yield differences, favoring the deposition of Cr and Mn. This resulted in compositional deviation and impurity phase formation during annealing, degrading electrical properties. Resistance-temperature analysis confirmed that the improved performance in low-power films stems from ideal stoichiometry and phase purity, with grain boundary scattering further enhancing resistance and the B value. This study directly links sputtering-induced elemental segregation and microstructure to NTC behavior, underscoring the importance of optimizing sputtering parameters to reduce yield disparities and stabilize entropy-driven phase formation. The findings offer a strategy for designing high-performance high-entropy thermistors through controlled deposition and composition, promoting their use in high-sensitivity infrared sensing and precision thermal management.