Progress on Mn-Co-Ni-O infrared thin films and detectors

High quality Mn-Co-Ni-O (MCN) spinel films are prepared on Al₂O₃ substrate by RF magnetron sputtering (RF) and chemical solution deposition (CSD). The microstructural characterizations reveal the films present excellent crystallization and compact surface. The variable temperature electrical results show the films have temperature coefficient of resistance (TCR) of -3.8 %/K at 295 K. Based on the electrical results of CSD-MCN films in 130∼304 K, we find that the hopping exponent p of small polaron hopping conduction shows a clear variation from a value of 0.46 in the paramagnetic to 0.91 in the ferromagnetic phase at around 200 K. The mid-infrared optical properties of the films are obtained by fitting the measured ellipsometric parameter data using the classical infrared model. MCN film detectors are fabricated by photolithography follow by wet etching process to evaluate the applications for infrared detection. It exhibits a noise equivalent temperature difference as low as 2.1×10^-7 K/Hz^1/2, responsivity of 330 V/W, and detectivity of 0.6×10⁸ cmHz^1/2/W at 30 Hz. The 8×1 element MCN detector array is also successfully fabricated, and the response uniformity is about 5.9 %.