Preparation Of BST Thin Films And Their Fine-Patterning

Recently, Barium strontium titanate (Ba_xSr_1-xTiO₃) ferroelectric thin films have attracted much attention and become a research focus in the field of ferroelectric thin films, because of its potential application value in many devices such as IC-Capacitors, VLSI-DRAMs, FRAM, uncooled infrared focal plane array fields and so on.. In this paper, BST thin films were prepared successfully on Pt/TiO₂/Si and ITO/Glass substrates by Sol-Gel process, which were characteristic of perovskite square phase structure and had good ferroelectric and dielectric properties. The effect of heat treatment craft parameters, substrate electrode materials, ingredient ratio of Ba, Sr on electrics performance of Ba_xSr_1-xTiO₃ films were discussed. Moreover, the photosensitive solution and gel thin films were fabricated by Sol-Gel technologies with chemical modification. The photosensitive mechanisms of photosensitive solution and gel thin films were studied. A new method of fine-patterned BST thin films was proposed using the photosensitive characteristics of gel thin films. The results are listed as follows:1. When crystallization temperature was above 650℃,the BST thin films prepared on Pt/TiO₂/Si substrates were the integrity square ABO₃ perovskite structure. Increasing the degree of crystallization and grain size were propitious to enhance ferroelectric and dielectric properties of the thin films. BST8/2 thin films annealed at 750℃ for 2h have good ferroelectric and dielectric performance. A remanent polarization Pr was 5.84μC/cm² and a coercive field strength Ec was 38kV/cm.A dielectric constant ε_r was 708 and a dissipation factor tanδ was 0.12 when it was measured at 10kHz.2. The change tendency of electricity performance of BST thin film prepared on ITO/glass substrate is basic same with on Pt/TiO₂/Si substrate along with the crystallization temperature increment. Under the same heat treatment craft condition (annealed at 600℃ for 1h), the ferroelectric and dielectric properties of BST thin film prepared on the Pt substrate, was superior to those which prepared on the ITO substrate.3. The variation range of Ba/Sr ingredient ratio was in 6/4～10/0. The thin films with a composition of 7/3 had the best ferroelectric properties. A dielectric constant ε_r was 778 and a dissipation factor tanδ was 0.1 when it was measured at 10kHz. The thin films with a composition of 8/2 had the best ferroelectric properties. A remanent polarization Pr was 5.33μC/cm² and a coercive field strength Ec was 79kV/cm.4. In the photosensitive BST8/2 sol and its gel thin films prepared by chemical modification with BzAcH, Ti⁴⁺ had the chelaing response with BzAcH, Ba²⁺, Sr²⁺ did not participate in the chelaing the response. After the hydrolisis and polyreaction, finally the sol system with the chela structure was formed. The BST8/2 sol and its gel thin films with the chelaing structure had ultraviolet photosensitive, and they had obvious absorption peak at the wavelength of 358nm. The absorption peak decreased when the gel filmswere irradiated by the ultraviolet light with the relevant wavelength. Fine-patterning of BST thin films which were identical with mask can be obtained by this photosensitive characteristic. The BST8/2 thin films annealed at 600℃ for 1h, had the perovskite phase structure and good the dielectric, the ferroelectric property. This method may realize microfabrication to the BST thin film.