Influence of porous silicon as thermal insulation layer on the structural, optical, electrical and temperature responsive properties of Mn-Co-Ni-O NTC thin films

The temperature response rapid of Mn-Co-Ni-O (MCNO) thin film within excellent NTC charters is limited by the heat transfer between the film and its substrate. To settle the bottleneck, the porous silicon (PS) as thermal insulation layer was brought forward. Although both MCNO/SiO2/Si and MCNO/SiO2/PS/Si films exhibited typical polycrystalline spinel structure, the (220) and (400) XRD peak strength as well as Raman active mode (around ca. 290 cm(-1)) changed represent the tensile stress appearing on the surface of the PS layer. From spectroscopic ellipsometer spectroscopy, it was found that the maximal refractive index of the MCNO thin film was more than twice as to the value of films with PS layer. However, it had little influence on the electrical properties as thermal constants (3515 and 3469 K) were similar even the high-frequency vibration experiments employed. The FEA simulation result showed that the PS layer forms a high interface thermal resistance due to the low thermal conductivity of the air in the pores of PS. The MCNO/SiO2/PS/Si composite film captured faster response time (11 ms) compared to the MCNO films on SiO2/Si substrates (345 ms). It will open a way to design an ultra-fast response NTC film thermistor by substrate modification.