XPS depth profiling and leakage properties of anodized titania dielectrics and their application in high-density capacitors

The chemical structure and electrical properties of anodized titania are investigated for their application as conformal ultra-thin dielectrics on high surface area titanium electrodes. The chemical structure is studied by XPS depth profiling for the first time along with the role of anodization conditions on dielectric thickness, leakage current, and capacitance densities. Different leakage current models were used to identify the defect mechanisms in the titania film formed at different voltages. EDS and structural SEM studies were performed to investigate the morphology and structure of the titania films. This research also demonstrates the fabrication and characterization of high-density capacitors using high surface area titanium metal electrodes, conformal high K, and thin-film dielectric of titania. High-permittivity and thin-film titania dielectric was grown on high surface area titanium anodes using anodization, while conducting polymer was used as the cathode. The fabricated capacitor showed 7.15 lF cm at 100 kHz which corresponded to 7.5X enhancement in surface area compared to planar thin-film capacitors. This is the first demonstration of high-density capacitors using high surface area titanium anodes along with high-permittivity and thin-film titania as the dielectric. Introduction Capacitors used in the electronics industry generally fall into two categories—traditional discretes (surface mounted to board) and thin-film layers using substrate compatible processes. Tantalum capacitors [1], multilayered co-fired ceramic capacitors (MLCC) [2], and integrated passive devices (IPDs) fall under the first category. They provide high volumetric capacitance density at low cost, tested and ready for board-level assembly using standard surface mount technologies (SMT). However, they are manufactured and assembled as thick components, limiting their use in emerging high performance and miniaturized applications. The second class of capacitors comprises those that are directly deposited as thin-film layers, providing proximity advantages to active devices, while resulting in simultaneous miniaturization. These thin-film layers are deposited on the surface of the package substrate to form thin-film capacitors that can be within 30–40 lm from the active devices, while the capacitors themselves may range from 1 to 50 lm in thickness. However, these types of capacitors have other limitations. These include defects that form in the capacitor process, thus affecting not only the yield of the capacitor but also of the entire substrate. As a result, they tend to be expensive and are not scaled up to high-volume manufacturing. In addition, there is another challenge related to achieving very high capacitance density with substrate compatible materials and processes. The second type of capacitors is of more interest to emerging high performance and miniaturized electronic systems, and is the key focus of this paper. The capacitance of any capacitor is given by C 1⁄4 Aeeo t ; ð1Þ & Himani Sharma [email protected] 1 Packaging Research Center, Georgia Institute of Technology, 813 Ferst Dr, Atlanta, GA 30332, USA 2 Material Science and Engineering, Georgia Institute of Technology, Atlanta, GA, USA 123 J Mater Sci (2015) 50:7600–7609 DOI 10.1007/s10853-015-9320-6