Untersuchung des epitaktischen Wachstums duenner Pb(Zr_0_,_5_2Ti_0_,_4_8)O_3-Schichten und ihre Anwendung in ferroelektrischen supraleitenden Feldeffektransistoren

The influences of the polarization of ferroelectric Pb(Zr_0_._5_2Ti_0_._4_8)O_3 (PZT) films on the properties of YBa_2Cu_3O_x (YBCO) films were investigated in ferroelectric superconducting field effect transistors (FSuFETs). First the epitaxial growth of PZT films deposited by reactive sputtering in an argon/oxygen atmosphere was investigated. SrTiO_3 single crystals and YBCO thin films proved as suitable substrates. The lead content of the PZT films depended sensitively on the deposition temperature T_s and the gas pressure. By using a high pressure of 0.26 mbar the correct stoichiometry could be achieved up to an maximum T_s of 580 C. Above a minimum T_s of 540 C the ferroelectric perovskite structure grew. In the optimum temperature range between 560 C and 580 C the films grew with a minimum mosaic spread of #DELTA##omega# < 0.3 and a small amount of less than 1% of paraelectric phase. The best ferroelectric properties could be obtained for films with the highest degree of epitaxy and the correct stoichiometry. The maximum remanent polarization amounted P_r = 61 #mu#C/cm"2 and the coercive field E_C was 150 kV/cm at 77 K. The breakdown field was four to five times larger than E_C. Fatigue studies revealed a loss of switchable polarization of 30% after 10"8 cycles at 77 K, whereas loss of retention and the effect of ageing were negligible. During the process of oxidation of the heterostructure at 400 C and an oxygen pressure of 800 mbar a reaction at the PZT/YBCO interface was observed, which lead to a degradation of the transport properties of the superconductor. This reaction could be avoided by a thin SrTiO_3 buffer layer without disturbing the ferroelectric hysteresis essentially120 refs.Available from TIB Hannover: ZA 5141(6226) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman