Ferroelectric Thin Films and Their Applications
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ABSTRACT Ferroelectric morphotropic phase boundary (MPB) materials based on Pb 2+ - containing compositions are potentially important for optical and electronic applications because they exhibit high switchable polarization near this boundary with superior electro-optic and piezoelectric properties. In this paper we discuss these MPB materials, substrate issues, and the growth of MPB film compositions based on the PZT and PSKNN systems.
INTRODUCTION Guided-wave electro-optic devices are widely used with optical fibers for applications in communications, signal processing, sensing and spatial light modulators [ 1,2]. The realization of low-loss single mode optical waveguides is critical to the practical implementation of these devices, and it is desirable to use materials with large electro-optic coefficients to achieve low voltage performance. Ferroelectric oxide crystals have generally been a popular material choice for this technology. The most widely used among these have been LiNbO 3 and LiTaO 3 crystals or films in the ilmenite family, primarily because of their commercial availability and established methods for fabricating optical waveguides in each case [3-6]. Significant interest, however, lies in producing optical waveguide devices in other ferroelectric materials with higher electro-optic coefficients which could be used for making compact, low-voltage electro-optic modulators and switches, as well as tunable wide-band filters. Recently, Taylor and Eknoyan (7-10) did extensive work on the tungsten bronze materials and reported that these ferroelectrics (SBN, BSTN, BSKNN, KLN, BNN) provide an attractive choice for such needs because their linear electro-optic coefficient (r33) is generally much greater in magnitude than that in LiNbO 3 and LiTaO 3. At Rockwell, we have identified several morphotropic phase boundary (MPB) materials based on Pb 2 +-containing systems in which polarization is exceptionally large near such regions, thus giving large electro-optic (rij) and piezoelectric (dij) coefficients. Although 2 the single crystal growth work on these materials has been frustrated due to the loss of Pb + during the growth, we have been successful in fabricating good quality films with high optical figures-of-merit. In this paper, we describe our thin film work on perovskite PZT and tungsten 165 Mat. Res. Soc. Symp. Proc. Vol. 392 ©1995 Materials Research Society
bronze Pb 2 _xSrxKl-yNayNb 5O0 5 (PSKNN), with emphasis on
current useful substrate
materials.
EXPERIMENTAL PROCEDURE PZT and PSKNN thin films were fabricated using the sputtering and sol-gel techniques. The sputtering targets employed were a mixture of PZT or tungsten bronze PSKNN and PbO. Approximately 5 mole% excess PbO was added in the targets to control the Pb2 + concentration in the films. The targets were prepared using ceramic sintering; well-mixed powders were cold pressed and then sintered at 1000 'C after ball-milling. The sputtered PZT and PSKNN thin films were deposited with an MRC rf sputtering instrument; the sputtering condi
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