Dielectric and Pyroelectric Characteristics of PLZT (9.5/65/35) Relaxor Thin Films
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PLZT (9.5/65/35)
RELAXOR THIN FILMS
K. K. DEB U.S. Army Research Laboratory Infrared/Optics Technology Office, Fort Belvoir, VA 22060, [email protected]
ABSTRACT Ferroelectric relaxor thin films of lead lanthanide zirconate titanate (PLZT) (9.5/ 65/35) have been deposited by the laser ablation technique onto metallized silicon and lanthanum aluminate substrates. The dielectric and pyroelectric properties of PLZT films and their temperature dependencies have been investigated in some detail in an evaluation of their potential as prospective pyroelectric infrared (IR) detector materials. The temperature at which the dielectric constant of a PLZT film reaches its peak is different from that for the peak pyroelectric coefficient. A lower dielectric constant at which the pyroelectric peak appears contributes to a high figure of merit for PLZT films, so that it is competitive with its ceramic counterpart, as well as with Pb(Mg1 /3Nb2/ 3)0 3 (PMN) relaxor ferroelectric ceramic. INTRODUCTION
Conventional pyroelectric detectors are traditionally prepared from bulk materials such as lead zirconate titanate (PZT), lanthanum-doped PZT (PLZT), or barium strontium titanate (BST). These bulk materials are normally sliced to a thickness of 5 to 10 pm, and then they are bonded to either silicon or gallium arsenide integrated circuits with solder bump technology. If they are fabricated in thin-film forms, they offer the potential for integration of these functions directly onto semiconducting substrates to attain the greatest performance gain. PZT and PLZT are useful for a wide range of electronic applications, such as piezoelectric, pyroelectric, and electro-optic devices, as well as high-value capacitors and memories. Recently, B. Rod and I studied the pyroelectric characteristics of PLZT (9.5/65/35) as a function of a selected electric bias field [1,2]. The results showed that the charge-coupled device (CCD) figure of merit is competitive with the existing ferroelectric materials, such as lead magnesium niobate (PMN) and lead scandium tantalate (PST) [3]. It would be interesting to compare the structural and electrical properties of PLZT (9.5/65/35) films on compatible substrates and compare their electrical properties with the bulk material. In this work I applied the excimer laser ablation method to the formation of thin films of PLZT (9.5/65/35) on substrates of platinum-coated silicon (Pt/Si) and lanthanum strontium cobalt oxide coated lanthanum aluminate (LSCO/LaAlO 3). Polycrystalline films with a pseudocubic structure were obtained without substrate heating followed by a post-deposition thermal treatment. The resultant thin films were characterized with respect to their dielectric and pyroelectric properties, and compared with bulk ceramic data. Their potential for pyroelectric detector applications is discussed. The laser deposition technique presents, I believe, a very important route for the preparation of good-quality ferroelectric thin films. 603 Mat. Res. Soc. Symp. Proc. Vol. 403 01996 Materials Research Society
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