Dielectric Properties of (Ba,Sr)TiO 3 Thin Film Capacitors Fabricated on Alumina Substrates
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Dielectric Properties of (Ba,Sr)TiO3 Thin Film Capacitors Fabricated on Alumina Substrates I.P. Koutsaroff, A. Kassam, M. Zelner, P. Woo, L. McNeil, T. Bernacki, A. Cervin-Lawry, and A. Patel Gennum Corporation, 970 Fraser Drive, Burlington, Ontario L7L 5P5 Canada ABSTRACT Double layer (DL) Ba0.7Sr0.3TiO3 (BST) capacitors with Pt electrodes have been fabricated with similar growth conditions on different substrates. The substrates used in the present study were r-plane sapphire, polycrystalline alumina Al2O3 (99.6% and 96%), and glazed polycrystalline alumina. BST films were grown by metal-organic decomposition (MOD) method. By varying the annealing conditions which affects the formation of the crystalline structure, significant changes in the dielectric properties of the BST films have been observed. BST films were characterized by Field Emission Scanning Electron Microscopy (FE-SEM) and Powder Xray Diffractometer (PXRD). These observations showed that BST films grown at lower temperatures on alumina substrates exhibited the smallest grain size. BST films of the same thickness prepared under the same thermal processing conditions showed higher capacitance when grown on all types of alumina-based substrates compared to those deposited on control SiO2/Si. The higher capacitance on alumina was always associated with larger dissipation factor, and lower or similar leakage current density. The final tuning, of the dielectric properties of BST DL capacitors on non-silicon substrates, was correlated to the initial film formation temperature and post-annealing conditions of the BST films. The leakage current density, of DL BST capacitors fabricated on glazed alumina, becomes smallest when the BST processing temperature was lowered by 100 oC compared to the control SiO2/Si. The typical achieved leakage current density for 1500x1500 µm2 DL capacitors on glazed alumina was 3.8x10-9 A/cm2 at 250 kV/cm (36.5 fF/µm2), about 3 times lower than on SiO2/Si substrates (1.1x10-8 A/cm2 at 250 kV/cm, 31 fF/µm2).
INTRODUCTION BST and other ceramic oxides are important materials used in integrated passive devices, multi-chip modules (MCM), high-density interconnect (HDI), and chip-scale packaging. A variety of techniques have been employed to manufacture BST thin films, e.g.: Metal-organic decomposition (MOD), reactive sputtering, sol-gel, metal-organic chemical vapor deposition (MOCVD), ion beam assisted deposition (IBAD) and pulsed laser deposition (PLD) [1]. BST-based multi-level capacitors (MLC) are widely used for decoupling purposes and can be fabricated with high yield, reproducibility and high capacitance per unit area (e.g., 120 fF/µ m2) on Si substrates [2] or other single crystal substrates (e.g., sapphire). The stability at high temperatures and low dissipation factors at high frequencies (5-20 GHz) of polycrystalline alumina and sapphire are significant advantages over more economical polymer (“flex”) substrates. However, the cost of sapphire substrates is still very high. Therefore, recent focus of suitable substra
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