Electrical Characteristics of BaxSr1-xTiO3(BST) Capacitors Implemented with Ti-Al Electrodes
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Electrical Characteristics of BaxSr1-xTiO3(BST) Capacitors Implemented with TiAl Electrodes Thottam S Kalkur1, Jeff Whitescarver2, and Nick Cramer2 1 Electrical and Computer Engineering, University of Colorado at Colorado Springs, Colorado Springs, 80933-7150 2 University of Colorado at Colorado Springs, Colorado Springs, 80933-7150 Abstract: Ti-Al was used as the electrode for RF magnetron sputtered BST film at a substrate temperature of 450 oC for decoupling capacitor applications. X-ray diffraction analysis shows that the deposited film BST film is amorphous. Electrical characterizations of the devices performed by capacitance versus voltage measurements show a dielectric constant of about 55. With increase in annealing temperature above 450 oC, the capacitance was found to decrease significantly.
Introduction: High dielectric constant ferroelectric thin film capacitors such as BST and BCTZ are finding increasing importance for a variety of applications such as tunable varactors for high-frequency circuits, on-chip decoupling capacitors, storage capacitors for highdensity dynamic random access memories and a variety of sensing applications [1,5]. Platinum and Iridium oxide are most widely studied electrode materials for BST[6]. Recently, Nickel films were also used as electrodes for high-K materials such as Barium Calcium Titanium Zirconate (BCTZ)[7]. Of late, Ti-Al alloys have attracted the attention of many investigators as barriers for ferroelectric thin film capacitors based on lead zirconate titanate (PZT) [8,9]. This paper reports the results of BST films deposited on Ti/Al electrodes by RF magnetron sputtering at a substrate temperature of 450 oC. The deposition of BST at low temperatures allows us to integrate BST decoupling capacitors after the completion of interconnect process for silicon VLSI. Advantages of using Ti/Al instead of platinum as electrodes includes ease of etching and low cost. Sample Preparation: The starting wafer is 4” (100) silicon with 0.5 micron silicon dioxide grown on it by wet thermal oxidation at 1100 oC Bulk Titanium/aluminum alloy(TiAl::30:70) was formed by melting aluminum and titanium pellets by electron beam heating. Ti/Al was deposited by electron beam evaporation and the thickness of the film deposited was approximately 150nm. BST film of thickness 50nm to 100 nm was deposited by RF magnetron sputtering from BST target (Ba0.5Sr0.5TiO3) with Argon as the sputtering gas. The substrate temperature was maintained at 450 oC. Top electrode Ti-Al was also deposited by vacuum evaporation. The electrodes were patterned by standard photolithographic technique and ion-milling. Figure 1 shows the structure of the fabricated BST parallel plate capacitors.
RF magnetron deposited BST film
Ti/Al Top Electrode Ti/Al bottom electrode
Figure 1 Structure of BST capacitor fabricated by RF magnetron sputtering
Results and discussion:
Figure 2 X-ray diffraction spectra of BST on Ti-Al electrode. Figure 2 shows the x-ray diffraction (XRD) spectra of BST on Ti-Al electrodes.
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