Preparation and ferroelectric properties of sol-gel-derived (Pb, Ca)TiO3 thin films

Abstract

PbTiO3 is a perovskite-type compound having remarkable ferroelectric, pyroelectric and piezoelectric properties. Bulk PbTiO 3 ceramics have been used[ as both pyroelectric infrared detectors and piezoelectric transducers. Although cut and polished thick plates of dense PbTiO3 have been used for tlhe former application, the latter application involves the use of a thin deposited film of the material. In recent critical device applications it has become increasingly necessary to consider the requirements of the low operating voltage of the device in addition to the large component area and connection to many circuit elements. Many of these critical requirements have been met by breakthroughs in thin-film techniques such as r.f. sputtering [1, 2], ion plating and chemical vapour deposition [3]. Substantial progress has been achieved, especially in films deposited by r.f. sputtering: Recently it has been shown that calcium-or lanthanum-modified PbTiO3 pyroelectric films [4,5] prepared by r.f. sputtering have higher sensitivity than pure PbTiO3 films. However, there are some problems, such as the higher capital equipment costs and difficulty in achieving stoichiometry, which is due to pre, ferential sputtering of one element over the other and the different vapour pressures of the constituents.The sol-gel processing technique has the following advantages: (1) it is a simple non-vacuum chemical technique which is inexpensive; (2) it can be used for the uniform deposition of several polycomponent oxide films; and (3) the films can be deposited over a large surface area. Several ferroelectric thin films such as BaTiO3 [6], PbTiO3 [7][8][9], PZT [10] and PLZT [11] have been prepared by this process. However, the preparation of the sol-gel-derived (Pb,Ca)TiO3 system for infrared detector applications has not been reported.In this study the structural and ferroelectric properties of (Pbl_xCax)TiO 3 (0.0 ~< x ~< 0.35) films prepared by the sol-gel method were investigated. For the sample preparation, titanium isopropoxide, trihydrated lead acetate and calcium metal were used as the starting materials. Titanium isopropoxide was first diluted with 2-methoxyethanol. Trihydrated lead acetate was dissolved at 85 °C in 2-methoxyethanol and the solution was subsequently boiled to remover water. The dehydrated solution was cooled to room temperature. Calcium alkoxide solution, ]however, was prepared by the direct reaction of calcium metal with dry ethanol. The 0261-8028/9'1 $03.00 + .12 ©1991 Chapman and Hall Ltd. mixed solutions with the desired composition were refluxed at 120 °C in flowing nitrogen to promote complexation, and the by-products (e.g. alkylacetates) of the reaction were removed by subsequent distillation. The Pb-Ca-Ti precursor solutions were then concentrated to 0.25 to 0.4 moll -1 by vacuum distillation. Inductively coupled plasma (ICP) emission spectrochemical analysis was used to confirm that the deviation from stoichiometry was within + 1 mol %.Thin films were deposited on fused silica and platinum substrates b...

METALLO-ORGANIC DECOMPOSITION SYNTHESIS AND CHARACTERIZATION OF FERROELECTRIC (PB1 −XCAX)TIO3 Thin Films

“…At places these grains coalesce to form continuous granular morphology. When compared with round shape grains in pure PbTiO 3 films reported earlier by Tsuzuki et al [25], structure evolution of PCT10 film may be attributed to the addition of Ca. Although granular nature of PCT films with different Ca concentration is generally similar, significant differences in the spatial distribution and size of grain as well as surface roughness were seen.…”

“…Dielectric dispersion measurements were made in the metal-film-metal capacitor configuration using a Solartron analytical 1260 Impedance/gain-phase analyzer over the frequency range of 1 KHz to 1. 25 MHz. An array of several capacitors each of area ∼3 × 10 −4 cm 2 were formed by sputter deposition of Pt dot top film electrode of 800-1000Å thickness through a shadow mask.…”

Effects of the Sol-Gel Processing and Sol Aging on the Properties of the High-Ca Modified PbTiO3Derived Films

“…Different sol-gel methods have been employed in the literature to prepare precursor solutions of (Pb 1−x Ca x )TiO 3 [12][13][14][15][16]. However, difficulties arise for high Ca 2+ concentrations in the system (>30%) due to the low solubility of the calcium compounds in the typical CSD solvents.…”

Enhanced piezoelectric properties of Pb0.8Ca0.2TiO3 thin films prepared at low temperature by a sol–gel process

“…Among these materials, calcium modified lead titanate, Pb 0.8 Ca 0.2 TiO 3 (PCT), thin film has attracted particular interest [1][2][3][4].…”