We report measurements of the optical responses of a La2/3Sr1/3MnO3 (LSMO) sample at a wavelength of 533 nm in the 300 -400 K range. The 200 nm thick film was grown by pulsed laser deposition on (100) SrTiO3 substrate and showed remarkably low noise. At 335 K the temperature coefficient of the resistance of a 100 µm wide 300 µm long LSMO line was 0.017 K -1 and the normalized Hooge parameter was 9×10 -30 m 3 , which is among the lowest reported values. We then measured an optical sensitivity at I = 5 mA of 10.4 V.W -1 and corresponding noise equivalent power (NEP) values of 8.1×10 -10 W.Hz -1/2 and 3.3×10 -10 W.Hz -1/2 at 30 Hz and above 1 kHz, respectively. Simple considerations on bias current conditions and thermal conductance G are finally given for further sensitivity improvements using LSMO films.The performances were indeed demonstrated on bulk substrates with G of 10 -3 W.K -1 . One could expect a NEP reduction by three orders of magnitude if a membrane-type geometry was used, which makes this LSMO device competitive against commercially available uncooled bolometers.Submitted to Appl. Phys. Lett.
1The remarkable electronic and magnetic properties of rare-earth manganite oxides have raised lot of interests for applications [1]. In addition to the widely studied magnetoresistive sensors and spin electronics, uncooled bolometers using the large resistance change at the metal-to-insulator transition are among the most promising. Indeed uncooled technologies open new opportunities for infrared detection for both military and commercial applications [2]. Actual materials used for the fabrication of uncooled resistive bolometers are amorphous semiconductors, polycrystalline SiGe, semiconducting YBa2Cu3O7 (YBCO), VO2 and VOx. Around 300 K they present typical maximum temperature coefficient of the resistance (TCR), defined as the relative resistance derivative (1/R)×(dR/dT), of 0.02 to 0.06 K -1 [3, 4], -0.007 K -1 [5], -0.029 K -1 [6], -0.017 K -1 [7, 8] and -0.033 K -1 [9], respectively.Rajeswari et al. [10] showed that the optical response of La0.67Ca0.33MnO3 was of thermal nature, but the maximum of the resistance derivative (corresponding to TCR = 0.079 K -1 ) was obtained at 260 K. Goyal et al. [11] mentioned the high TCR values of several compositions of manganites. The highest values (0.2 K -1 ) were obtained in Nd0.7Sr0.3MnO3 well below room temperature (235 K). Only La0.7Sr0.3MnO3 and La0.7Ba0.3MnO3 that showed TCR of 0.02 K -1 and 0.04 K -1 , respectively, were suitable for uncooled operation. Other manganite compositions such as La2/3(Ca,Pb)1/3MnO3 [12] and (La0.6Pr0.4)0.67Ca0.33MnO3 [13] even showed TCR as high as 0.1 K -1 at 300 K. However no noise data are available for the first material and preliminary measurements showing a high low frequency noise level are reported for the second one. In comparison TCR of La0.5Ba0.5MnO3 and La0.5Sr0.5MnO3 were lower (about 0.015-0.02 K -1 ) but with a much lower noise level at 30 Hz, which makes them potentially more suitable for uncooled bolometer fabricati...