Photo-sensitive sol-gel solutions for the low-temperature UV-assisted processing of PbTiO3 based ferroelectric thin films

摘要

Photo-sensitive PbTiO3 solutions were synthesised by a sol-gel process that combines the use of a diol solvent, HO(CH2)(3)OH, and a titanium alkoxide modified with a beta-diketonate, Ti(OC3H7)(2)(CH3COCHCOCH2)(2). O-Nitrobenzyl alcohol (NBA), 1-hydroxy-cyclohexyl-phenyl-ketone (HPK) and acetylacetone (ACACH) were added to the synthesised sols as UV-activators. Solutions with nominal compositions of Pb0.76Ca0.24TiO3 were prepared. These solutions have a maximum of absorption in UV between 200 and 300 nm. Pyrolysis of the solutions was studied by means of thermogravimetry and differential thermal analysis (TGA/DTA). Films were deposited by spin-coating onto TiO2/Pt/TiO2/Ti/SiO2/(100) Si substrates. They were irradiated at 250 degreesC with light of lambda similar to 225 nm and then treated at 550 or 450 degreesC for 420 s with Rapid Thermal Processing (RTP) in air, using a heating rate of similar to30 degreesC s(-1). Crystalline phases and structures developed in the films were studied by X-ray diffraction with the Bragg-Brentano geometry and with grazing incidence (XRD and GIXRD). Films showed the formation of a single perovskite phase. These films have spontaneous pyroelectricity with a maximum value of the pyroelectric coefficient of gamma(s) similar to +12 x 10(-9) C cm(-2) K-1. Non-irradiated films prepared at 550 degreesC did not show a defined ferroelectric response. The ferroelectric properties measured in the films processed at 550 degreesC under UV were similar to those reported for films prepared at higher temperatures without irradiation. Values of the remanent polarisation of P-r similar to 22 muC cm(-2) and of the coercive field of E-c similar to 170 kV cm(-1) were obtained in these irradiated films prepared at 550 degreesC. [References: 41]