Heterostructures on Si. A. M. GRISHIN,1 S. I. KHARTSEV,1 J.-H. KIM,1 and JUN LU2. 1Condensed Matter Physics, Royal Institute of Technology,. SE-164 40 ...
Integrated Ferroelectrics, 67: 69–76, 2004 C Taylor & Francis Inc. Copyright ISSN: 1058-4587 print/ 1607-8489 online DOI: 10.1080/10584580490898470
Epitaxial Colossal Magnetoresistive/Ferroelectric Heterostructures on Si A. M. GRISHIN,1 S. I. KHARTSEV,1 J.-H. KIM,1 and JUN LU2 1
Condensed Matter Physics, Royal Institute of Technology, SE-164 40 Stockholm-Kista, SWEDEN 2 ˚ Angstr¨om Microstructure Laboratory, Uppsala University, SE-751 21 Uppsala, SWEDEN (Received in final form May 1, 2004) We report on processing and properties of La0.67 (Sr,Ca)0.33 MnO3 (LSCMO) films grown by pulsed laser deposition technique on Si(001) substrates buffered with Bi4 Ti3 O12 /CeO2 /YSZ heteroepitaxial layers. X-ray diffraction shows cube-on-cube growth of epitaxial Bi4 Ti3 O12 /CeO2 /YSZ/Si heterostructure whereas the LSCMO layer grows in the “diagonal-on-side” manner onto the Bi4 Ti3 O12 (BTO) template. High resolution TEM images demonstrate sharp interfaces between the buffer layers and LSCMO film as well as rare misfit dislocations on the CeO2 /YSZ interface. LSCMO film processing conditions have been optimized to get maximum temperature coefficient of resistivity TCR = 4.4% K−1 and colossal magnetoresistance (CMR) ρ/ρ ∼ 2.9% kOe−1 @ 294 K. Almost ultimate CMR performance at room temperature has been achieved due to successive improvement of c-axis orientation of layers: full widths at half-maximum (FWHM) = 0.65, 0.58, 0.65, 1.13 and 0.18 degrees in LSCMO/BTO/CeO2 /YSZ/Si stack, respectively. Characterization of electrical noise in CMR √ film yields Noise Equivalent Temperature Difference (NETD) as low as 1.2 µK/ Hz @ 30 Hz and 294 K.
INTRODUCTION +2 Perovskite metal-oxide manganites with the formula La+3 1−x Ax MnO3 +2 (A = Ca, Sr, Ba, Pb) attract much attention due to their potential applications for various devices. Such a potential arises from very strong dependence of the resistivity of manganites on magnetic field and temperature (Colossal Magnetoresistance effect, CMR). These occur in close vicinity of semiconductor-to-metal (para-to-ferromagnetic) phase transition temperature Tc . High temperature coefficient of resistivity (TCR), combined with
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rather low electric excess noise achieved in thin epitaxial films, promise manganites to be the material of choice for uncooled infrared (IR) bolometers [1]. Real progress in industrial environment requires the integration of IR detector array with CMOS readout architecture on the same Si wafer. So far, only few high performance CMR films were grown on the Si [2–5]. In this paper we report on processing and characterization of epitaxial manganite films grown on Si substrates with a Tc tailored to room temperature (RT). To get phase transition at RT we make alloying and fabricated a continuous series of solid solutions La0.67 (Sr1−x Cax )0.33 MnO3 . Two ceramics: La0.67 Ca0.33 MnO3 (LCMO) and La0.67 Sr0.33 MnO3 (LSMO) were chosen as the ends of La0.67 (Sr1−x Cax )0.33 MnO3 series of alloys. To possess high TCR, manganite film should be grown in epitaxial quality. This means a Si substrate should be coated with the buffer layer(s) to meet the following requirements: (i) to minimize film-substrate lattice mismatch, (ii) to match film-substrate thermal expansion coefficients, (iii) to eliminate the chemical reaction between substrate and deposited film. We chose yttrium stabilized zirconia (YSZ), CeO2 and Bi4 Ti3 O12 (BTO) to serve as buffer multilayers between Si and manganite film. YSZ is widely used for protective buffering between Si and manganite/HTSC films [6], while BTO is found to be perfect [2] for highly oriented growth due to its elongated c-axis (32.8 ˚ At the same time, there is a perfect in-plane “side-to-diagonal” match of A). BTO-to-LCMO(LSMO) unit cells. Finally, we used CeO2 in-between YSZ and BTO to improve the crystalline quality of BTO layer. Moreover, this additional buffer layer makes multilayered structure very resistive against the thermal stresses.
EXPERIMENTALS To grow films we used excimer 248-nm laser Compex-102. Five highdensity ceramic targets of stoichiometric compositions were charged in PC-controlled multitarget carousel. The p-type Si(001) substrates were degreased in acetone and etched in 1:10 mixture of H2 O and HF. To avoid the reoxidation of Si substrates they were heated in the chamber just after the ultimate base pressure
