Preparation And Characterization Of Ti-Al-O And BaxSr1-xTiO3 High-k Thin Films

Pt/Ti-Al-O/Si MOS heterostructure were fabricated, respectively, by pulsed laser deposition (PLD) and magnetron sputtering using a Ti3Al alloy target, impacts of laser energy density on the electrical properties of Ti-Al-O films were investigated. It is indicated that the Ti-Al-O films at a laser energy density of 1.25 J/cm2 possesses higher dielectric constant (13) and lower leakage current density (about 2.0×10-6 A/cm2 at a gate voltage of 1 V), although the frequency dispersion is obvious.Ti-Al-O films have been fabricated using PLD method on Pt/Ti/SiO2/Si (001) and Si (001) substrates from a TiO2-Al2O3 (the mole ratio is 2:1) composite oxide target. Pt film was deposited by magnetron sputtering to fabricate Pt/Ti-Al-O/Pt-Si and Pt/Ti-Al-O/Si heterostructures. Thermal stability and dielectric properties of the Pt/Ti-Al-O/Pt capacitor were investigated, it is found that the sample annealed at 800°C is polycrystalline since TiAl2O5(040) peak can be observed from X-ray diffraction measurement. The Pt/Ti-Al-O/Pt capacitor annealed at 750°C shows less dielectric relaxation, and the dielectric constant is about 30 measured at 1MHz. Comparison investigaton of the Pt/Ti-Al-O/Si samples with different annealing atmospheres indicates the sample annealed in O2 atmosphere has higher dielectric costant (about 15) and lower leakage current density (about 9.5×10-8 A/cm2 at a gate voltage of 1 V).Ba0.6Sr0.4TiO3 (BST) thin film was fabricated on Pt/Ti/SiO2/Si (001) substrate by pulsed laser deposition, impacts of low temperature rapid thermal annealing (RTA) in air on the structual and physical properties of the Pt/BST/Pt capacitors were investigated. It is found that the microstructure of BST thin film did not change obviously upon annealing, but the electrical properties of the BST capacitors were enhanced greatly. The dielectric constant and tunability were increased and the dielectric loss of the BST capacitors was reduced from 0.07 to 0.03 upon rapid thermal annealing, the higher negative current of the BST capacitors was significantly lowered by annealing, the symmetric current characteristics at positive and negative bias voltage were obtained, and the leakage current density is 4.3×10-6 A/cm2 at 300 kV/cm.