La0.7Sr0.3MnO3 thin films for uncooled bolometers

Bruno Guillet 1Shuang Liu 1Cédric Fur 1Sheng Wu 1Jean-Marc Routoure 1Carolina Adamo 2Darrell G. Schlom 2Laurence Mechin 1

1. GREYC, CNRS-ENSICAEN-Université de Caen Basse Normandie, 6 Bd Maréchal Juin, Caen 14050, France
2. Cornell University, Department of Materials Science and Engineering, Ithaca, NY 14853-1501, United States

Abstract

We report our results about uncooled La0.7Sr0.3MnO3 (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)

 

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Presentation: Oral at E-MRS Fall Meeting 2009, Symposium D, by Jean-Marc Routoure
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-25 23:48
Revised:   2009-09-04 14:01