Effect of Y-Doping on the Dielectric Properties of BatiO 3 Films Deposited in Reducing Atmospheres Using Pulsed Laser De
- PDF / 1,243,874 Bytes
- 6 Pages / 417.6 x 639 pts Page_size
- 50 Downloads / 227 Views
Barium titanate based dielectrics are commonly used in the production of ceramic multilayer capacitors (MLCC). The requirements of higher capacitance and further miniaturization in MLCC are driven by the down-sizing trend in electronics. Structurally this has meant the reduction of layer thickness and an increase in the number of layers. Manufacturers of MLCC traditionally employed precious metals such as platinum, palladium, silver and their alloys for inner electrodes [1,2]. For cost reduction, the expensive noble metals are now beginning to be replaced by nickel. However Ni electrodes are easily oxidized during the firing process. Consequently, low oxygen partial pressure during firing is indispensable. In reducing atmospheres, BaTiO 3 ceramics form large numbers of ionized oxygen vacancies (Vý') and conduction electrons which give rise to poor insulation resistance. However, in practice, the conduction electrons can be effectively trapped by acceptor doping in the perovskite lattice. Capacitors based on acceptor doped BaTiO 3 dielectrics show satisfactory resistivity values [3]. However a residual ionic conductivity is retained, because of electromigration of the ionized oxygen vacancies. This leads to long-term degradation under dc fields [4]. To avoid such electrical degradation due to oxygen vacancies (Vý*), amphoteric dopants such as Y, Ho and Dy have been used [5-6].
487 Mat. Res. Soc. Symp. Proc. Vol. 596 © 2000 Materials Research Society
Pulsed laser deposition (PLD) is a thin film fabrication method which is reasonably good in transporting the target stoichiometry to the film. Consequently, many researchers have used PLD to fabricate multicomponent thin films [7-9]. In this paper, PLD was used to prepare undoped and Y-doped BaTiO 3 thin films to investigate the effects of Y-doping on dielectric properties of BaTiO 3 thin films grown in reducing atmospheres. EXPERIMENTAL PROCEDURE BaTiO 3 films with and without Y-doping were prepared in reducing atmospheres by pulsed laser deposition (PLD). Both types of films were prepared from ceramic targets containing MnO 2 and a small amount of Si0 2 . The slight Ba excess in the starting targets encourages B-site occupancy for the Y. The SiO 2 is added as a sintering aid. The specific deposition parameters are given in Table 1. All films were grown in pure (99.99%) N2 atmospheres. Films were deposited2
onto Pt/Ti/SiOJ/Si substrates using a 5-10Hz laser repetition rate, an energy density of 4.2J/cm
and a working pressure of 100mtorr. Growth temperatures of 700°C were achieved by adhering the substrates to a stainless steel block-style heater with silver paint. A Lambda Physik Compex 102 excimer laser operating at 248nm was used. 0.3mm diameter platinum top electrodes were sputtered through a shadow mask to complete the device structure. Samples were then thermally annealed at 370°C for 5min. Table 1. Pulsed laser deposition parameters for film growth
Targets
Y-free
BaTiO 3 Ceramics (BaITi = 50.1/49.9) (MnO 2 -0.2wt%, Si0 2-0. I wt%)
Y-doped
BaTiO 3 Ceramics
Data Loading...
