Properties of Zr-Substituted (Ba, Sr)TiO 3 Thin Films for Integrated Capacitors

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ABSTRACT There has been significant interest recently in use of BaSrTiO 3 (BST) thin films for integrated capacitors; these devices have benefits for high frequency operations, particularly when high levels of charge or energy storage are required. We discuss the electrical properties of BST thin films grown by metalorganic chemical vapor deposition (MOCVD) which make them suitable for these applications, as well as the impact of processing conditions such as growth temperature on specific film properties. We have also examined addition of Zr in amounts ranging up to 20% to the BST films. X-Ray diffraction indicates that the Zr is incorporated into the BST lattice. Voltage withstanding capability, leakage and dielectric constant of the thin films have been measured as functions of deposition temperature and Zr content. Addition of Zr to BST films increases breakdown voltages by as much as a factor of two, to approximately 2 MV/cm, raising their energy storage density values to levels approaching 30 J/cc. Charge storage densities of above 60 fF/ jm 2 were also obtained. INTRODUCTION The market for personal communications devices such as cellular phones and computer notepads with built-in faxes and modems is expected to undergo explosive growth over the next decade. Circuits in these devices typically have many bypass and decoupling capacitors which operate at low voltages and that must occupy very little space. Due to the high cost of chip area for Si and GaAs active devices, an improvement over the charge storage density achievable with Si0 2 dielectrics is needed. BaxSr(,.X)TiO 3 (BST) offers this possibility. Although DRAM applications have been examined for this material, integrated capacitors in communications devices add several new challenges. The devices must operate at high frequencies (100 MHz to several GHz) and often at high temperatures, due to close packing of circuit components. Several options are available to improve the basic properties of BST, including process modification, electrode modification (metals vs. conductive oxides) and doping or substitution. There have been reports that Zr addition can reduce relaxation and leakage currents in chemical solution deposited (CSD) thin films of BaTiO 3 .[1] In this work we have investigated the effect of adding Zr as a substitutional cation on the B-site of the perovskite lattice, examining electrical properties in these thin films. Significant improvements in breakdown voltage, leakage properties, high temperature performance and storage density due to Zr incorporation were seen in metalorganic chemical vapor deposited (MOCVD) films in this work, and we will discuss applicability of the substituted films to charge storage and energy storage capacitors. To the best of our knowledge, this is the first systematic examination of which we are aware of Zr addition to BST thin films made by MOCVD.

131 Mat. Res. Soc. Symp. Proc. Vol. 603 ©2000 Materials Research Society

EXPERIMENT Barium bis(2,2,6,6-tetramethyl-3,5-heptanedionate) (abbreviated (thd)) with Le

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