Pulsed Laser Deposition of BaxSr1−xTiO3 Films on MgO, LaAlO3 and SrTiO3 for Tunable Microwave Applications

AbstractSingle phase BaxSr1−xTiO3 (BST) films (∼0.5-7 μm thick) have been deposited onto single crystal substrates (MgO, LaAlO3, SrTiO3) by pulsed laser deposition. Silver interdigitated electrodes were deposited on top of the ferroelectric film. The room temperature capacitance and dielectric Q (1/tanδ) of the film have been measured as a function of electric field (≤80 kV/cm) at 1 - 20 GHz. The dielectric properties of the film are observed to strongly depend on substrate type and post-deposition processing. After annealing (≤1000° C), it was observed that the dielectric constant and % tuning decreased and the dielectric Q increased for films deposited onto MgO, and the opposite effect was observed for films deposited onto LaA1O3. Presumably, this change in dielectric properties is due to the changes in film stress. Very thin (∼50 Å) amorphous BST films were successfully used as a stress-relief layer for the subsequently deposited crystalline BST (∼5000 Å) films to maximize % tuning and dielectric Q. Films have been deposited from stoichiometric targets and targets that have excess Ba and Sr. The additional Ba and Sr has been added to the target to compensate for deficiencies in Ba and Sr observed in the deposited BST (x=0.5) films. Films deposited from compensated targets have higher dielectric constants than films deposited from stoichiometric targets. Donor/acceptor dopants have also been added to the BST target (Mn, W, Fe ≤4 mol.%) to further improve the dielectric properties. The relationship between the dielectric constant, the dielectric Q, the change in dielectric constant with electric field is discussed.

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Comparison of Microwave Dielectric Properties of between (001) and (011) Ferroelectric Ba1-xSrxTiO3 Thin Films grown by Pulsed Laser Deposition

MRS Proceedings ◽

10.1557/proc-720-h3.9 ◽

2002 ◽

Vol 720 ◽

Author(s):

Seung Eon Moon ◽

Eun-Kyoung Kim ◽

Su-Jae Lee ◽

Seok-Kil Han ◽

Kwang-Yong Kang ◽

...

Keyword(s):

Dielectric Properties ◽

Pulsed Laser Deposition ◽

Phase Shifter ◽

Metal Layer ◽

Pulsed Laser ◽

Dielectric Constants ◽

Laser Deposition ◽

Diffraction Measurement ◽

Differential Phase Shift ◽

Bst Films

AbstractThe effects of anisotropic dielectric properties of ferroelectric Ba1-xSrxTiO3 (BST) films on the characteristics of phase shifter have been studied in microwave regions at room temperature. Ferroelectric BST films with (001) and (011) orientation were epitaxially grown on (001) and (011) MgO substrates, respectively, by pulsed laser deposition method. The structures of BST films were investigated using x-ray diffraction measurement. The microwave properties of orientation engineered BST films were investigated using coplanar waveguide transmission lines that were fabricated on BST films using a thick metal layer by photolithography and etching process. The measured differential phase shift and insertion loss (S21) for (011) BST films are larger than those for (001) BST films. Dielectric constants of the ferroelectric BST films are calculated from the measured S21 using a modified conformal-mapping model.

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Pulsed Laser Deposition of BaxSr1-xTiO3 Thin Films for Frequency Agile Microwave Electronics

MRS Proceedings ◽

10.1557/proc-526-205 ◽

1998 ◽

Vol 526 ◽

Cited By ~ 5

Author(s):

W. Chang ◽

J. S. Horwitz ◽

J. M. Pond ◽

S. W. Kirchoefer ◽

D B. Chrisey

Keyword(s):

Thin Films ◽

Pulsed Laser Deposition ◽

Lattice Mismatch ◽

Pulsed Laser ◽

Dielectric Behavior ◽

Laser Deposition ◽

Film Stress ◽

Bst Films ◽

The Difference ◽

Film Substrate

AbstractOriented, single phase thin films (~5000Å thick) of BaxSr1-xTiO3 (BST) have been deposited on to (100) MgO and LaAlO3 (LAO) single crystal substrates using pulsed laser deposition (PLD). A strong correlation is observed between the microstructure of the deposited film and the dielectric tuning and loss at microwave frequencies. Microstructural defects observed in as deposited films include strain, due to film substrate lattice mismatch and oxygen and cation vacancies. Compensation of the ablation target with excess Ba and Sr is observed to increase the dielectric constant and to reduce the dielectric loss. Post-deposition, bomb annealing of films at high temperatures (1250°C) is observed to fill oxygen vacancies and increase grain size. The difference in the dielectric behavior for as-deposited and low temperature annealed BST films on MgO and BST films on LAO is observed and may be attributed to the differences in film stress. A further improvement in the dielectric behavior is observed by the addition of donor/acceptor dopants such as Mn. The data shows that ferroelectric thin films can be used to build tunable microwave circuits that offer significant performance advantages over devices made from conventional semiconducting materials.

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Frequency Agile Microwave Applications Using (Ba,Sr)TiO3/Y3Fe5O12 Multilayer Grown by Pulsed Laser Deposition

MRS Proceedings ◽

10.1557/proc-603-123 ◽

1999 ◽

Vol 603 ◽

Cited By ~ 3

Author(s):

W.J. Kim ◽

W. Chang ◽

S.B. Qadri ◽

H.D. Wu ◽

J.M. Pond ◽

...

Keyword(s):

Dielectric Constant ◽

Phase Shift ◽

Pulsed Laser Deposition ◽

Pulsed Laser ◽

Bias Field ◽

Laser Deposition ◽

Differential Phase Shift ◽

Differential Phase ◽

Bst Films ◽

Dc Bias

Abstract(Ba,Sr)TiO3 (BST) thin films have been deposited by pulsed laser deposition (PLD) onto single crystal Y3Fe5O12 (YIG) substrates with/without an MgO buffer layer. The structure and microwave properties of BST films have been investigated as function of substrate orientation and O2 deposition pressures (5-800m Torr). The orientation of BST film is varies with the deposition conditions. The dielectric constant, loss tangent, and change in dielectric constant with an applied electric field have been measured at room temperature using interdigitated capacitors at 0.1 – 20 GHz. Polycrystalline BST films have a high tunability (∼40%) with a dc bias field of 67kV/cm and a dielectric Q (=l/tanδ) between 30 and 40, while (001) oriented BST films have a lower tunability (∼20%) but higher dielectric Q (∼50). A coplanar waveguide transmission line was fabricated from a (001) oriented BST film on (111)YIG which exhibited a 17° differential phase shift with an applied dc bias of 21 kV/cm. An equivalent differential phase shift was achieved with a magnetic field of 160Guass.

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Microstructural and Electrical Characterization of Barium Strontium Titanatebased Solid Solution Thin Films Deposited on Ceramic Substrates by Pulsed Laser Deposition

MRS Proceedings ◽

10.1557/proc-720-h2.4 ◽

2002 ◽

Vol 720 ◽

Author(s):

Costas G. Fountzoulas ◽

Daniel M. Potrepka ◽

Steven C. Tidrow

Keyword(s):

Thin Films ◽

Dielectric Constant ◽

Pulsed Laser Deposition ◽

Pulsed Laser ◽

Electrical Characterization ◽

Field Variable ◽

Laser Deposition ◽

X Ray Diffraction ◽

Ceramic Substrates ◽

Nominal Thickness

AbstractFerroelectrics are multicomponent materials with a wealth of interesting and useful properties, such as piezoelectricity. The dielectric constant of the BSTO ferroelectrics can be changed by applying an electric field. Variable dielectric constant results in a change in phase velocity in the device allowing it to be tuned in real time for a particular application. The microstructure of the film influences the electronic properties which in turn influences the performance of the film. Ba0.6Sr0.4Ti1-y(A 3+, B5+)yO3 thin films, of nominal thickness of 0.65 μm, were synthesized initially at substrate temperatures of 400°C, and subsequently annealed to 750°C, on LaAlO3 (100) substrates, previously coated with LaSrCoO conductive buffer layer, using the pulsed laser deposition technique. The microstructural and physical characteristics of the postannealed thin films have been studied using x-ray diffraction, scanning electron microscopy, and nano indentation and are reported. Results of capacitance measurements are used to obtain dielectric constant and tunability in the paraelectric (T>Tc) regime.

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