D. Y. Kaufman

Anomalous leakage current characteristics of Pt/(Ba0.75,Sr0.25)Ti1+yO3+z/Pt thin films grown by metalorganic chemical vapor deposition

The leakage and dielectric properties of a thickness series (90–480 nm) of {100} fiber-textured metalorganic chemical vapor deposited (Ba0.75Sr0.25)Ti1+yO3+z (BST) thin films on Pt/SiO2/Si were investigated. The permittivity demonstrated a suppressed temperature and electric field response that transitioned to a more bulk-like response with increasing thickness, consistent with earlier observations. At low fields the leakage currents showed a weak-field dependence and a monotonic increase with increasing temperature. In contrast, a positive temperature coefficient of resistance (PTCR) was observed in the leakage current behavior at high-field. The PTCR behavior was more pronounced for thicker BST films. The observed effect is contrasted with PTCR behavior in bulk BaTiO3 ceramics.

MOCVD (BaxSr1−x)Ti1+yO3+z (BST) thin films for high frequency tunable devices

Abstract We have investigated the structural and electrical characteristics of (BaxSr1−x)Ti1+yO3+z (BST) thin films synthesized at 650°C on Pt/SiO2/Si substrates using a large area, vertical metalorganic chemical vapor deposition (MOCVD) reactor equipped with a liquid delivery system. Films with a Ba/Sr ratio of 70/30 were studied, as determined using X-ray fluorescence spectroscopy (XRF) and Rutherford backscattering spectrometry (RBS). A substantial reduction of the dielectric loss was achieved when annealing the entire capacitor structure in air at 700°C. Dielectric tunability as high as 2.3:1 was measured for BST capacitors with the currently optimized processing conditions.

Strategy for the Integration of PLZT Thin Films on Base-Metal Foils for High Voltage Embedded Passives

Evolution of electronic devices towards higher performance and smaller size requires the passive components to be embedded within a printed wire board (PWB). A “film-on-foil” approach is the most viable fabrication method. A high permittivity of lead lanthanum zirconate titanate (PLZT) thin film was coated on nickel foil by chemical solution deposition. Such a prefabricated capacitor sheet can be embedded into a PWB. However, formation of a parasitic low-permittivity interfacial layer of nickel oxide during thermal processing of the PLZT films considerably reduces the capacitance density. To eliminate this parasitic effect, conductive buffer layer of lanthanum nickel oxide (LNO) was coated by chemical solution deposition on nickel foil. We produced PLZT film-on-foil capacitors with capacitance densities as high as 1.5 μF/cm 2 and breakdown field strength >1.4 MV/cm. With the desirable volumetric character, PLZT film-on-foil capacitors hold particular promise for use in high voltage embedded passives.

Chemical solution deposition of PLZT films on base metal foils.

In an effort to develop cost effective, volumetrically efficient, high charge density and high energy density capacitors, Pb(Zr,Ti)O 3 and La-doped Pb(Zr,Ti)O 3 films were deposited by chemical solution deposition on nickel and alloy foils. PZT films deposited on bare foils exhibited lower permittivity and more electric field hysteresis compared to films deposited on platinized silicon substrates, due to the formation of low capacitance interfacial layers and/or diffusion of foil elements into the PZT. However, an ultimate dielectric breakdown strength of approximately 1.35 MV/cm was obtained for a film thickness of 1.8 μm, corresponding to a withstand voltage of 245 V. A reduced temperature dependence of capacitance was observed with decreasing film thickness. In order to improve the dielectric response, barrier layers of LaNiO 3 , Ru, or Ir were deposited on top of the metal foils used as substrates. The barrier improved relative permittivity and reduced hysteresis in relative permittivity as a function of dc bias.

Positive Temperature Coefficient of Resistance in MOCVD (Ba 0.75 Sr 0.25 )Ti 1+y O 3+z Films

The leakage and dielectric properties of a thickness series (90–480 nm) of {100} fiber-textured MOCVD (Ba 0.75 Sr 0.25 )Ti 1+y O 3+z (BST) thin films on Pt/SiO 2 /Si were investigated. The temperature and voltage dependence of the permittivity were consistent with previous observations, where thinner films demonstrated a suppressed temperature and electric field response that transitioned to a more bulk-like response with increasing film thickness. The current-voltage characteristics showed two distinct regimes. At low fields the current displayed weak field dependence and a monotonic increase with increasing temperature. In contrast, positive temperature coefficient of resistance (PTCR) was observed in the high-field leakage current behavior. The PTCR behavior was more pronounced for thicker BST films. Factors contributing to the observed PTCR effect are outlined and contrasted with the description for bulk BaTiO 3 ceramics.