Mn-Co-Ni-O (MCNO) flexible thermistors are fabricated on polyethylene terephthalate or polyimide sheets by RF magnetron sputtering method at room temperature. The whole fabricating processes is completed at room temperature. The temperature coefficient of resistance (TCR) is -3.1% and resistivity as low as 110Ωcm at 295K. The bendingstraightening cycle test indicates the flexible MCNO sheet is stable. The temperature sensing test shows the thermistors respond to temperature change rapidly and sensitively. Due to the heat-treat free process, high TCR and moderate resistivity features, the technique we provide here allows a convenient and low cost industrial manufacture of high performance flexible thermistors and wide band infrared detectors.
Mn-Co-Ni-O spinel oxide materials, with the prototype of AB<sub>2</sub>O<sub>4</sub>, are excelled in uncooled thermal sensing and infrared detection due to its high absolute NTC value and moderate resistivity at room temperature. In this work, Mn<sub>1.56</sub>Co<sub>0.96</sub>Ni<sub>0.48</sub>O<sub>4</sub> film (MCN-CSD) and Mn<sub>1.40</sub>Co<sub>1.00</sub>Ni<sub>0.60</sub>O<sub>4</sub> (MCN-RF) film are fabricated on amorphous sapphire substrate with chemical solution method (CSD) and radio frequency deposition method (RF), respectively. Morphological characteristics are revealed by SEM graphs. And the result shows that MCN films acquire better crystalline properties and compactness than MCN bulk materials. To verify the excellent features for infrared detection, detectors sized 1mm<sup>2</sup> × 0.17 μm and 1 mm<sup>2</sup> × 0.33 μm are fabricated based on MCN-RF and MCN-CSD films, respectively. The excess noise at 11 Hz for each detector has been tested and the Hooge's parameters have been calculated. The MCN films obtained by RF deposition and CSD method both show γ/n value of about 2×10<sup>-21</sup> cm<sup>3</sup>, an order lower than bulk MCN and amorphous silicon, which indicates great potentials in integrated infrared detection.
ZnO:Al (AZO) films have potential applications in ultraviolet detecting devices. The structural and optical properties of
the AZO films are presented. Highly <i>c</i> axis oriented wurtzite phase AZO films are prepared on quartz substrate by rf
sputtering method. The optical constants and the thickness of the AZO films are determined by fitting the measured
transmission spectra with Tauc-Lorentz (TL) model. The refractive index <i>n</i> increases as the photon energy increases, and
reaches the maximum of 2.50 at 3.66 eV, beyond which the refractive index <i>n</i> decreases with further increasing of
photon energy. The peak of the refractive index <i>n</i> corresponds to the optical band gap of the AZO films, which is
associated with interband transition between the valence and conduction bands. The extinction coefficient <i>k</i> also
increases with the enhancement of the photon energy, and a strong absorption peak with maximum of 1.10 is prominent.
The absorption peak due to an electronic transition accords with the peak transition energy <i>E<sub>0</sub></i> (3.79 eV) is obtained by
TL model. The energy <i>E<sub>0</sub></i> of this model corresponds to the Penn gap, where the strong absorption of the material took
place. By fitting the absorption coefficient, the optical band gap 3.62 eV of the film is evaluated. Based on the Tauc's
power law, the optical band gap of the films is proved as a direct interband transition between the valence and
conduction bands. This enhanced band gap compared with ZnO (3.37 eV) correlates to the Burstein-Moss band filling
effect due to Al doping.