We report our results about uncooled La_0.7Sr_0.3MnO₃ (LSMO) bolometers: measurements of the temperature coefficient of the resistance (TCR), low-frequency noise measurements in epitaxial LSMO thin films deposited on buffered Silicon (Si), and SrTiO₃ (STO) substrates, and micromachining techniques for suspended structure fabrication.

A normalized Hooge parameter of 9×10^-31 m³ was measured at 300 K in the case of a 10 μm-wide, 575 μm-long line patterned in the 200-nm-thick film grown on STO substrate. This value is among the lowest reported values for manganites and close to values measured in standard metals and semiconductors. The corresponding noise equivalent temperature (NET) was constant in the 300–340 K range and equal to 6×10^-7 K.Hz^-1/2 at 10 Hz and 0.15 mA for a 10 μm-wide, 575 μm long line patterned in a 200-nm-thick LSMO film [1]. This very low NET value is comparable to the best published results for manganites and was even found to be lower than the NET of other uncooled thermometers such as semiconductors (a-Si, a-Si:H, a-Ge, poly SiGe) and other oxide materials (semiconducting YBCO, VOx, other manganite compounds). The results show that despite a TCR of only 0.017 K^-1 at 300 K, and thanks to a very low-noise level, LSMO thin films are real potential material for uncooled thermometry and bolometry. Optical responses of a LSMO/STO sample at a wavelength of 533 nm in the 300–400 K range has been investigated [2]. We 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. In this case, the thermal conductance G was about 10^-3 W.K^-1.

Further improvements are expected thanks to the fabrication of suspended structures using standard silicon micromachining techniques. Preliminary results showing suspended LSMO bridges of various widths (4 to 10 μm) and lengths (50 to 200 μm) will be presented and their performances as mid-infrared bolometers will be discussed. The effective time response could be less than 1 ms and the electrical sensitivity as well as the thermal conductance could be improved by a factor 1000.

References:

[1] F. Yang, L. Méchin, J.M. Routoure, B. Guillet, R.A. Chakalov, J. Appl. Phys. 99, 024903 (2006)

[2] L. Méchin, J.M. Routoure, B. Guillet, F. Yang, S. Flament, D. Robbes, R.A. Chakalov, Appl. Phys. Lett. 87, 204103 (2005)

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/19309 must be provided.

1. Synthesis of defect-mitigating tunable dielectric materials by MBE
2. Low frequency noise measurements in InN films
3. Structural, 1/f noise and MOKE characterization of vicinal La_0.7Sr_0.3MnO₃ thin films