RF Magnetron Sputtered Ba 0.96 Ca 0.04 Ti 0.84 Zr 0.16 O 3 Thin Films For High Frequency Applications
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RF Magnetron Sputtered Ba0.96Ca0.04Ti0.84Zr0.16O3 Thin Films For High Frequency Applications Ali Mahmud, T.S. Kalkur and N. Cramer1 Dept. of Electrical and Computer Engineering, 1420 Austin Bluffs Parkway, Colorado Springs, CO 80918 1 Applied Ceramics Research, 1420 Owl Ridge Road, Colorado Springs, CO 80918 ABSTRACT Perovskite ferroelectric thin films in the paraelectric state exhibit outstanding dielectric properties, even at high frequencies (>1 GHz). The tunable dielectric constant of ferroelectric thin films can be used to design frequency and phase agile components. High dielectric constant thin film ferroelectric materials in the paraelectric state have received enormous attention due to their feasibility in applications such as decoupling capacitors and tunable microwave capacitors; the latter application has been fueled by the recent explosion in wireless and satellite communications. This paper reportsBa0.96Ca 0.04Ti0.84Zr0.16O3 (BCTZ) thin films that were deposited on Pt electrodes using radio frequency magnetron sputtering at a low (450 ºC) substrate temperature. Sputtered thin film BCTZ at low substrate temperature is compatible with conventional integrated circuit technology. The structural characterization of the deposited films was performed by x-ray diffraction. The electrical characterization of the films was achieved by capacitance-voltage, current-voltage, and S-parameter (via vector network analyzer) measurements. In addition, the effect of post annealing on the deposited films was investigated. A detailed understanding of both their processing and material properties is discussed for successful implementation in high frequency applications. INTRODUCTION High-K ferroelectric materials continue to be of great interest for a wide variety of on-chip applications. In studies of thin film ferroelectrics in the paraelectric state, the most widely studied material is Ba1-xSrxTiO3 (BST) on Pt electrodes. Ba1-xCaxTi1-yZryO3 (BCTZ) has been widely studied and applied as a thick film formed by sintering for multi-layer chip capacitors (MLCCs) [1] and has recently been studied in thin film form [2,3]. BCTZ has been widely used in the discrete capacitor industry due to its high dielectric constant and low leakage current— qualities shared with BST. In contrast, BCTZ is routinely processed in reducing atmospheres such as forming gas, while the dielectric properties of BST are known to degrade sharply with exposure to reducing anneals [4,5]. This resistance of BCTZ to reducing environments has lead to the development of an rf magnetron sputtering process that does not require oxygen in the sputter gas and does not require annealing in oxygen after deposition [3]. In terms of qualities valuable for microwave applications, such as tunability of the dielectric constant, BCTZ performs similar to BST and therefore should be of interest for microwave devices such as varactors. In this paper, the effect of anneal temperature and anneal gas content is reported for BCTZ films on Pt that were deposited using a p
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