Colossal magnetoresistive thin films for uncooled bolometer

Pulsed laser deposition technique has been employed to fabricate a continuous series of solid solutions with basic composition of La-0.7(Pb1-xSrx)(0.3)MnO3. which undergo metal-to-insulator transition near the room temperature. These films exhibit colossal magnetoresistivity (CMR) and strong temperature dependence of resistivity in the vicinity of phase transition. Temperature coefficient of resistivity (TCR) has been tailored by precise compositional control to get maximum value closer to room temperature. Film with TCR as high as 7.4 %K-1 at 295 K and magnetoresistance of 30% at 7 kOe has been used to make uncooled bolometer demonstrator. The responsivity as high as 0.6 V/W, noise equivalent power of 3 . 10(-8) W/root Hz, detectivity of 9 . 10(6) cm root Hz/W, and noise equivalent temperature difference as low as 120 nK/root Hz at 30 Hz frame frequency have been achieved for non-optimized bolometer based on 0.45-mum-thick film grown on 2.5x5x 0.5 mm(3) LaAlO3 (001) substrate. Measurements of optical responsivity in frequency and time domains yield substrate-to-thermostat thermal conductance G = 3 . 10(-3) W/K and three relaxation times responsible for heal transfer from film thermistor to substrate, from substrate to thermostat, and heat exchange via leads to be 0.5 s, 1.9 ms and 90 mus correspondingly. Improving bolometer design by micromachining technique, one can expect that reducing of thermal conductance G down to 10(-6) W/K for bolometer with resistance of 500 Omega, should result in the increasing of responsivities to 3.9 A/W and 2.8 . 10(3) V/W and detectivities to 3.5 . 10(8) cm root Hz/W and 9.3 . 10(8) cm root Hz/W at 30 Hz in voltage and current biasing regime correspondingly.