Properties of Lead Zirconate Titanate Thin Films Prepared Using a Triol Sol–Gel Route

Abstract

Microstructure and phase development during the thermal decomposition of sol–gel precursor coatings of PbZr0.53Ti0.47O3 on platinized silicon substrates have been investigated for a triol sol–gel route. The single‐layer, 0.4 μm PZT films were heated from below the substrate, over the temperature range 350–600°C, using a calibrated hot plate. The first crystalline phase to appear was a PbPt3 intermetallic phase at the Pt/PZT interface. Although perovskite PZT formed at ca. 500°C, heating at higher temperatures, for example 550°C for 30 min, was required to develop ferroelectric hysteresis loops. However, the rather low value of remanent polarization, Pr= 11 μC·cm−2, was consistent with incomplete crystallization at 550°C. The values of remanent polarization increased with increasing processing temperatures, reaching 21 μC·cm−2 for samples heated at 600°C, with a corresponding Ec value of 57 kV·cm−1. Distinctive spherical precipitates up to ca. 50 nm in size have been identified by TEM in the lower portions of otherwise amorphous coatings, after heating at around 350–400°C. Although their precise composition could not be identified, they were mostly Pb‐rich, and it is speculated that they form due to reduction of some of the lead(II) acetate starting reagent, to atomic Pb during the early stages of thermal decomposition of the organic components of the gel; it is possible that subsequent reactions occur to form lead oxides or carbonates. High levels of porosity were present in many of the fully crystallized films. The possible reasons for this are discussed.

Fundamental Issues in the Synthesis of Ferroelectric Na0.5K0.5NbO3 Thin Films by Sol−Gel Processing

“…This plot may be compared to the thermal analysis plots of the dried NKN sol (Figures −). The triol based route for PZT is a well established process that has been reported to produce very high-quality PZT films with excellent structural and electrical properties. , …”

“…In addition, the DTA data indicate a single crystallization event in PZT, immediately following the carbonate decomposition. Hence, PZT single-phase ferroelectric films, free from residual carbonate phases, may be produced by heating at 600−700 °C. , In the future, it would be useful to investigate the possibility of developing alternative Na, K, and Nb precursors, including long chain carboxylates which are less liable to decompose to release CO 2 and generate intermediate carbonates; such compounds have been developed for other ferroelectric ceramics. − …”

Crystallization of Ferroelectric Lead Zirconate Titanate Thin Films by Microwave Annealing at Low Temperatures

“…L ead zirconate titanate (Pb(Zr x Ti 1− x )O 3 : PZT) thin films have attracted great interest for their potential applications in nonvolatile ferroelectric random access memories 1,2 and microelectro–mechanical systems, 3,4 such as atomic force microscopy cantilevers 5 and microscanning mirror devices 6 . Many fabrication techniques have been used for PZT film deposition, such as sputtering, 7 pulsed laser deposition, 8 metalorganic chemical vapor deposition, 9 the sol–gel method, 10 and hybrid process 11,12 comprising the sol–gel method and laser ablation. In most cases, deposited PZT films are amorphous so that postdeposition annealing is necessary to crystallize the PZT films into the ferroelectric perovskite structure.…”

Compaction of lead zirconate titanate sol–gel coatings

“…It has been shown that by moving from the hydrolysis-condensation gelation mechanism involving Ti and Zr isopropoxides, which underpinned the early PZT sol-gel routes, to gelation by molecular bridging using a bi-functional alcohol, 1,3 propanediol, it was possible to produce films with a single-layer, crack-free thickness of ~ 1 µm [7,8]. Later a triol route was developed which could also produce ~1 µm single-layers [9,10]. The diol route has been demonstrated for multi-layer films up to 10 µm, and the triol route for films up to 3 µm [11,12], both requiring many fewer repetitions than for sols based on hydrolysis of metal alkoxides.…”

“…The diol route has been demonstrated for multi-layer films up to 10 µm, and the triol route for films up to 3 µm [11,12], both requiring many fewer repetitions than for sols based on hydrolysis of metal alkoxides. Although surface and fracture sections appeared to be dense by scanning electron microscopy (SEM), subsequently transmission electron microscopy revealed that the films possessed nanoscale porosity, with most pores falling in the range 20-30 nm [10,13].…”