Role of the Electrode Morphology, Thickness and Orientation in the Ferroelectric Performance of Epitaxial Pb(Zr,Ti)O 3 T
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Role of the Electrode Morphology, Thickness and Orientation in the Ferroelectric Performance of Epitaxial Pb(Zr,Ti)O3 Thin Films Cesar Guerrero, Florencio Sánchez, José Roldán, Frank Güell1, María V. García-Cuenca, Cesar Ferrater and Manuel Varela Universitat de Barcelona, Departament de Física Aplicada i Òptica, Av. Diagonal 647, E-08028 Barcelona, SPAIN 1 Universitat Rovira i Virgili, Lab. Física Aplicada i Cristal·lografia, E-43005 Tarragona, SPAIN
ABSTRACT A comparison of pulsed laser deposited PbZr0.53Ti0.47O3 (PZT) thin film capacitors with SrRuO3 (SRO) and LaNiO3 (LNO) electrodes on (001) yttria-stabilized zirconia (YSZ) and lattice matched (001) LaAlO3 substrates is presented. Both electrode materials allow for the formation of ferroelectric capacitors with large remnant polarization (20-30 C/cm²) and negligible fatigue, although slight differences arise regarding the promotion of either the rhombohedral or tetragonal phases of PZT. Far more crucial seems to be the tendency of SrRuO3 to develop a rougher surface at either small (100 nm), and on YSZ substrates. In those cases a highly defective and possibly low dielectric interface forms between the electrode and the ferroelectric layer, resulting in greatly degraded ferroelectric performance. LaNiO3 is free from these limitations except for the cracks forming at very large thickness (>300 nm), and therefore appears as a more versatile electrode material.
INTRODUCTION Ferroelectric thin films are of great interest for a wide range of applications such as pyroelectric and piezoelectric sensors, microwave devices, microactuators, and most remarkably, non-volatile randomaccess memories (NVRAMs) [1]. One of the most popular ferroelectric materials is PbZrxTi1-xO3 (PZT) in the vicinity of the morphotropic phase boundary (x≈0.53), where the bulk ceramics show a maximum in the remnant polarization to coercive field ratio [2]. Early efforts on the fabrication of PZT capacitors with platinum electrodes ultimately showed that fatigue degradation -i.e. loss of remnant polarization with cumulative switching- is practically impossible to overcome. The origins and mechanisms of fatigue are still controversial, thought it seems related to accumulation of oxygen vacancies at the electrode/ferroelectric interface, as was first suggested by the discovery that epitaxial capacitors with superconducting YBa2Cu3O7 electrodes do not show significant fatigue [3]. It is commonly acknowledged now that oxide electrodes are indispensable to obtain fatigue-free PbZrxTi1-xO3 capacitors. Simple oxides like RuO2 and IrO2 are desirable from the point of view of device fabrication, but they are not particularly well suited for the fabrication of pure perovskite PZT. Therefore, growing attention has been paid to a few conductive oxides of the perovskite family, chiefly La0.5Sr0.5CoO3 [4] and to a lesser extent SrRuO3 [5] and LaNiO3 [6]. All these materials show electrical resistivities of a few hundred µ Ω··cm and have been used to fabricate fatigue-free PZT thin film capacitors. However, c
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