P. K. Baumann

Composition-control of magnetron-sputter-deposited (BaxSr1 - X)Ti1 + yO3 + z thin films for voltage tunable devices

Precise control of composition and microstructure is critical for the production of (BaxSr1−x)Ti1+yO3+z (BST) dielectric thin films with the large dependence of permittivity on electric field, low losses, and high electrical breakdown fields that are required for successful integration of BST into tunable high-frequency devices. Here, we present results on composition-microstructure-electrical property relationships for polycrystalline BST films produced by magnetron-sputter deposition, that are appropriate for microwave and millimeter-wave applications such as varactors and frequency triplers. Films with controlled compositions were grown from a stoichiometric Ba0.5Sr0.5TiO3 target by control of the background processing gas pressure. It was determined that the (Ba+Sr)/Ti ratios of these BST films could be adjusted from 0.73 to 0.98 by changing the total (Ar+O2) process pressure, while the O2/Ar ratio did not strongly affect the metal ion composition. Film crystalline structure and dielectric properties ...

Epitaxial Pb(Mg1/3Nb2/3)O3 thin films synthesized by metal-organic chemical vapor deposition

Metal-organic chemical vapor deposition was used to prepare Pb(Mg1/3Nb2/3)O3 (PMN) thin films on (001) SrTiO3 and SrRuO3/SrTiO3 substrates, using solid Mg β-diketonate as the Mg precursor. Parameters including the precursor ratio in the vapor phase, growth temperature, growth rate, and reaction pressure in the reactor chamber were varied in order to determine suitable growth conditions for producing phase-pure, epitaxial PMN films. A cube-on-cube orientation relationship between the thin film and the SrTiO3 substrate was found, with a (001) rocking curve width of 0.1°, and in-plane rocking-curve width of 0.8°. The root-mean-square surface roughness of a 200-nm-thick film on SrTiO3 was 2 to 3 nm as measured by scanning probe microscopy. The zero-bias dielectric constant and loss measured at room temperature and 10 kHz for a 200-nm-thick film on SrRuO3/SrTiO3 were approximately 1100 and 2%, respectively. The remnant polarization for this film was 16 μC/cm2.

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.

Epitaxial Pb(Mg1/3Nb2/3)O3-PbTiO3 thin films grown by MOCVD

Abstract Epitaxial Pb(Mg1/3Nb2/3)O3 (PMN) and (l-x)(Pb(Mg1/3Nb2/3)O3)-x(PbTiO3) (PMN-PT) thin films have been deposited by metalorganic chemical vapor deposition at 700 – 780°C on (100) SrTiO3 and SrRuO3/SrTiO3 substrates. Room temperature values of 900 and 1.5%, were measured for the zero-bias permittivity and loss respectively, at 10 kHz for 220 nm thick pure PMN films. For PMN-PT films, the small-signal permittivity ranged from 1000 to 1500 depending on deposition conditions and Ti content; correspondingly low values for the zero-bias dielectric loss between 1 and 5% were determined for all samples. For PMN-PT with x of approximately 0.30–0.35, polarization hysteresis with Prμ18μC/cm2 was obtained. Initial piezoresponse results are discussed.

Magnetron sputter-deposited multilayer (BaxSr1x)Ti1+yO3+z thin films for passive and active devices

Abstract High permittivity (BaxSr1−x)Ti1+yO3+z(BST) thin films are being investigated for integration into charge storage dielectrics and electric-field tunable elements for high frequency devices. For the latter application, it is desirable to have BST capacitors with high tunability and low losses. Therefore, we investigated the use of multilayer BST thin films consisting of very low dielectric loss BST/electrode interfacial layers ((Ba+Sr)/Ti = 0.73) sandwiching a high tunability, high permittivity primary BST layer ((Ba+Sr)/Ti = 0.9). BST capacitors with multiple layers of controlled composition can be effectively produced insitu by magnetron sputter deposition, using a single stoichiometric target and controlling the layer composition by changing the total process gas (Ar+O<2) pressure. The layered BST film capacitors exhibit simultaneous low loss (tan Δ = 0.005), high tunability (76%), high charge storage energy density (34 J/cm3), low leakage, and high dielectric breakdown (>2.8 MV/cm).

Ferroelectric and Piezoelectric Properties of MOCVD Pb(Mg1/3Nb2/3)O3-PbTiO3 Epitaxial Thin Films

We have grown epitaxial Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) and (1-x)(Pb(Mg 1/3 Nb 2/3 )O 3 )- x(PbTiO 3 ) (PMN-PT) thin films by metalorganic chemical vapor deposition at 700 - 780°C on (100) SrTiO 3 and SrRuO 3 /SrTiO 3 substrates. The zero-bias permittivity and loss measured at room temperature and 10 kHz for 220 nm thick pure PMN films were 900 and 1.5%, respectively. For PMN-PT films, the small-signal permittivity ranged from 1000 to 1500 depending on deposition conditions and Ti content; correspondingly low values for the zero-bias dielectric loss between 1 and 5% were determined for all specimens. For PMN-PT with x of approximately 0.30–0.35, polarization hysteresis with P r ,≈18μC/cm 2 was obtained. Initial piezoresponse data are discussed.