Low Temperature Dielectric Properties of BST/ZrO 2 Multilayer Films
- PDF / 115,410 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 56 Downloads / 272 Views
C3.7.1
Low Temperature Dielectric Properties of BST/ZrO2 Multilayer Films Santosh K. Sahoo1, D. C. Agrawal1, S. B. Majumder2, R. S. Katiyar2 and Y. N. Mohapatra1 1
Materials Science Programme, IIT Kanpur 208016, India
2
Department of Physics, University of Puerto Rico, San Juan, PR
ABSTRACT Thin films of Ba1-x SrxTiO3 (BST) are being actively investigated for applications in dynamic random access memories (DRAM) because of their properties such as high dielectric constant, low leakage current, and low fatigue. Several approaches have been used to improve the properties of thin films such as doping with aliovalent dopants, graded compositions, and layered structures. We have found that interposing layers of an electronic insulator such as ZrO2 in between BST layers results in a significant reduction in the leakage current. In this paper the low temperature electrical properties of these multilayer structures are reported. The structures consist of alternate layers of Ba0.8Sr0.2TiO3 and ZrO2 deposited by a sol-gel process on platinized Si substrates. The thickness and the number of layers are varied while keeping the total thickness of the film constant. Multiple peaks in the dielectric constant vs temperature plots at all frequencies are observed in the multilayered films. The properties of the multilayer films are a complex function of the number of layers and their thicknesses. A structure with several thin layers of ZrO2 interposed between the BST layers produces smoother plots than a single layer of ZrO2 of same total thickness. This is attributed to more uniform distribution, as determined by XPS, of ZrO2 in the multilayer structure due to smaller diffusion distances. INTRODUCTION Barium-strontium-titanate (BaxSr1-xTiO3, BST) thin films are of interest for application in the capacitors of DRAM cells because of their high dielectric constant, low leakage current and low fatigue [1]. In the paraelectric state their dielectric constant can be changed by application of low voltages, making them useful for tunable microwave devices. Several approaches such as doping, graded compositions and layered structures have been used to improve the properties of thin films. Use of multilayers with BST as the major component appears to be an attractive approach to tailor the properties of the films for a given application. Investigations on the multilayers of several systems have been reported in literature [2- 4]. In the present study, with a view to reduce the leakage current in BST thin films, we have explored the use of BST-ZrO2 multilayers. In this paper we describe the low temperature dielectric properties of these multilayer films.
C3.7.2
EXPERIMENTAL Ba0.8Sr0.2TiO3 thin films and Ba0.8Sr0.2TiO3/ZrO2 multilayer thin films are prepared on Pt/Ti/SiO2/Si substrates by a sol-gel method. Barium acetate, strontium acetate and titanium butoxide are used as starting materials and acetic acid, 2-methoxy ethanol and acetyl acetone are used as solvents/chelating agents for the preparation of Ba0.8Sr0.2TiO3 sol [5]. The sol
Data Loading...
