Leakage current of Al- or Nb-doped Ba 0.5 Sr 0.5 TiO 3 thin films by rf magnetron sputtering
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Leakage current of Al- or Nb-doped Ba0.5 Sr0.5 TiO3 thin films by rf magnetron sputtering Tae-Gyoung In and Sunggi Baika) Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), 790-784 Pohang, South Korea
Sangsub Kim Department of Materials Science and Metallurgical Engineering, Sunchon National University, 540-742, Sunchon, South Korea (Received 21 September 1997; accepted 1 November 1997)
The effects of Al and Nb doping on the leakage current behaviors were studied for the Ba0.5 Sr0.5 TiO3 (BST) thin films deposited on PtyTiySiO2ySi(100) substrate by rf magnetron sputtering. Al and Nb were selected as acceptor and donor dopants, respectively, because they have been known to replace Ti-sites of the BST perovskite. The BST thin films prepared in situ at elevated temperatures showed relatively high leakage current density and low breakdown voltage. However, the BST thin films deposited at room temperature and annealed subsequently in air showed improved electrical properties. In particular, the leakage current density of the Al-doped BST thin film was measured to be around 1028 Aycm2 at 125 kVycm, which is much lower than those of the undoped or Nb-doped thin films. The results suggest that the Schottky barriers at grain boundaries in the film interior could determine the leakage behavior in the BST thin films.
I. INTRODUCTION
Barium strontium titanate (Bax Sr12x TiO3 ) has received great interest as a new dielectric material for the capacitors applicable to next-generation ultralarge scale integrated dynamic random access memories (ULSI DRAM’s) of 1 Gbit and beyond due to its relatively high dielectric constant, low leakage current density, high dielectric breakdown strength, and low dissipation factor. Particularly in the case of x , 0.7 Ba0.5 Sr0.5 TiO3 (BST) remains paraelectric at room temperature showing no aging or fatigue behaviors. A number of deposition methods have been also employed to prepare the BST thin films.1–5 In particular, many studies have been carried out intensively focusing on achieving the low leakage current density and identifying the leakage current mechanism since the level of leakage current density determines the reliability of data storage in a DRAM cell and refresh time.6–10 Nevertheless, it is still unclear what determines the leakage current. The parameters that have been identified to affect the leakage currents include the type of electrode,10 grain boundaries,6 annealing conditions,9 microstructures,7 and their correlations. Also, it has been reported that the addition of dopants seriously influences the electrical properties of BST thin film capacitators.8 a)
Address correspondence to this author. e-mail: sgbaik@postech. ac.kr
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http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 4, Apr 1998
Downloaded: 12 Apr 2015
In this work, we focus on the effects of acceptor and donor doping on the leakage current of BST thin films. The addition of alivalent ions produces elect
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