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Growth Mechanism and Infrared Detection of High-temperature Superconducting and Colossal Magnetoresistance Films

by Hong, Meng-Tsong

Abstract (Summary)
Growth Mechanism and Infrared Detection of High-temperature Superconducting and Colossal Magnetoresistance Films Department of Electrical Engineering, National Sun Yat-Sen University Meng-Tsong Hong* Ying-Chung Chen**, Hsiung Chou** -------------------------------------------------- Abstract---- The growth mechanism of YBa2Cu3O7-d (YBCO) films grown by RF sputtering has been investigated. When growing films by RF sputtering, the shape of the plasma and the degree of resputtering effect were varied by setting different relative positions of the heater to the gun. As the substrate was near the plasma, the negative oxygen ions resputtered part of the mobile atoms from the surface of film back into the plasma, which caused the composition distortion, delayed the merge of grains and left uncovered holes. Setting a longer relative distance, the resputtering effect was suppressed and the precipitates appeared on the surface of films resulting in a rough surface. At an optimum relative position between heater and gun, the function of resputtering produced a polishing effect on the surface of films. This polishing effect suppressed the growth of precipitates without slowing down the growth of grains, a smooth and precipitate-free YBCO film might obtain. We also found that the film with smooth and precipitate-free morphology exhibited suppressed superconductivity. The most direct way to enhance the photoresponse of a bolometer is by modifying the microbridge from a single straight bridge to a meander or change the thermal coupling configuration between bolometer and heat sink. In the study of high-temperature superconducting (HTSC) bolometers, it is found that the geometry and thermal coupling configuration play very important roles on the behavior of heat conduction, which alter the thermal conversion efficiency, DT/WD. Actually, DT/WD is a matter of the absorption of the AC thermal irradiation and the dissipation of both the irradiation and the DC joule heat generated by the bias current. The competition between the capability of heat dissipation and the thermal generation determined the magnitude of DT/WD. The La0.67Ca0.33MnO3-y (LCMO) thin films with epitaxial structure and smooth surface morphology have been deposited. A LCMO thin-film microbridge was fabricated into a microbridge by conventional photolithography and dry etching for optical detection. The measured photoresponse, DV, of this LCMO thin-film microbridge reveals that it is bolometric in nature. The photoresponse is linearly proportional to the bias current Ib and the power density of irradiation WD, which strongly suggests the applicability of an LCMO thin-film microbridge to a linear optical detector. The ratio of the photoresponse to the irradiated power density, DV/WD, is independent of the incident-light wavelength l from 0.633 to 3.5 mm. The dependence of the photoresponse on modulated frequency f, follows the DV µ f -0.21 relation. Under Ib = 100 mA and f = 5 Hz at an operating temperature Top = 223 K, the responsivity S and noise voltage Vn are 685 V/W and 20 nV¡ÑHz -0.5, respectively, for this LCMO thin-film microbridge. From the measured S and Vn, the noise equivalent power (NEP) and detectivity D* were be calculated to be 2.92´10-11 W¡ÑHz -0.5 and 2.76´109 cm¡ÑHz 0.5¡ÑW -1, respectively, for this LCMO thin-film microbridge. The experimental results from this LCMO thin-film microbridge show the practical applicability of this new detector system compared to other established detectors. *Student **Advisor
Bibliographical Information:

Advisor:Mau-Hsiung Chen; Ying-Chung Chen; Hsiung Chou; Kuang-Chih Huang; Mau-Phone Horng; Yung-Her Wang; Horong-mo, Duh

School:National Sun Yat-Sen University

School Location:China - Taiwan

Source Type:Master's Thesis

Keywords:cmr thermal conduction infrared detection thin film htsc

ISBN:

Date of Publication:07/17/2001

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