Lead zirconate titanate thin film capacitors on electroless nickel coated copper foils for embedded passive applications

• Published in: Thin solid films 2007-06, Vol.515 (18), p.7331-7336
• Main Authors: Kim, Taeyun, Kingon, Angus I., Maria, Jon-Paul, Croswell, Robert T.
• Format: Article
• Language: English
• Subjects: Composition and phase identification; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Electroless nickel; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport phenomena in thin films and low-dimensional structures; Embedded passive; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Lead zirconate titanate; Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids); Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Physics; Printed wiring board; Solid-solid transitions; Specific phase transitions; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2007.02.085

Lead zirconate titanate (PZT, 52/48) thin film capacitors were prepared on electroless Ni coated Cu foil by chemical solution deposition for printed wiring board embedded capacitor applications. Phase development, dielectric properties, and leakage characteristics of capacitors were investigated, in particular as a function of the process temperature. Dielectric properties of the capacitors were dependent on the crystallization temperature, and capacitance densities of more than 350 nF/cm 2 and loss tangent of less than 0.03 were measured for capacitors crystallized below 600 °C. Lowest leakage current densities (around 2 × 10 − 7  A/cm 2 at 10 V direct current (DC)) and highest breakdown fields could be obtained for capacitors crystallized at 650 °C. Capacitors with different thickness and a two-layer capacitor model were used in analyzing the interface layer between PZT and the underlying electroless Ni. From the capacitance and leakage measurements, it is suggested that the interface reaction layer has low permittivity (K around 30) and high defect concentration, which has an important effect on the electrical properties of capacitors. This interface is from the reaction of the electroless nickel layer with the adjacent PZT, and may specifically be moderated by the nickel phosphide (Ni–P) phase, transformed from amorphous Ni during the annealing step. The results have significant implications for embedded capacitors in printed wiring boards. They demonstrate that the process can be tuned to produce either voltage independent capacitors with low leakage and high breakdown fields (above 30 V DC), or the more usual hysteretic, switching, ferroelectric capacitors with higher capacitance densities.