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8/7/2019 MgO-doped compositionally graded multilayer barium strontium titanate films
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Presented by : Md. Mehedi Hasan
St. Id.- 0611039
8/7/2019 MgO-doped compositionally graded multilayer barium strontium titanate films
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Purpose
y tunable dielectric materials for voltage controlled,frequency-agile phase shifters and filters
y Doping of BST with MgO to reduce dielectric losses inmonolithic BST films
y dielectric constant, loss tangent, and tunability at 237
kV/cm of BST 60/40 and 5 mol % MgO doped BST60/40 thin films were reported as 720, 0.1, and 28%and 334, 0.007, and 17.2%
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Experimental
y BST thin films were grown via metal organic solutiondeposition MOSD on Pt-coated Si substrate
y Viscosity and surface tension were adjusted by varying
the 2-methoxyethanol content
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Experimentaly compositional layers of 220
nm total thickness withcompositionscorresponding toBST60/40, BST75/25, andBST90/10
y sample was pyrolyzed at
350 C for 10 min and,subsequently,postdeposition annealed at750 C for 1 h in flowing O2
Schematic configuration of multilayeredheterostructure BST thin film sandwichedbetween metallic electrodes
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Observation: XRDy all of the samples prepared
were polycrystalline and single
phasey (110) peak of multilayered BST
film was shifted to lowerangles i.e., an increase in
lattice spacingy further increase in lattice
parameter was observed uponMgO doped multilayered film
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Fractured cross section of the MgO-doped multilayered BST films revealthat the films are dense, crack-free,and the substrate/film contact iswell-developed, i.e., it is free fromvoids, amorphous material, and
secondary phases
In multilayered samples, nostructural delineation was visible
FESEM cross-sectional image of MgO-
doped multilayered BST thin film
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Observation : AFM & RBS
y average grain size of undoped anddoped multilayered samples were
estimated as 72 and 60 nmy Surface roughness of doped films 3.101
nm was less than that of undopedfilms 3.479 nm, which is in accordance
with smaller grain size of doped filmsy RBS analysis confirmed that no
interdiffusion had occurred betweenthese layers AFM micrograph showing the
plane-view surface morphology
of the MgO-doped multilayeredBST thin film
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8/7/2019 MgO-doped compositionally graded multilayer barium strontium titanate films
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Tuna
bility VS
Temp.
y A slight increase intunability was observed
with increasing temperatureat low electric fieldstrengths, i.e., around 250kV/cm
y tunability of dopedmultilayered films was lowerthan both undoped and
uniform BST thin films
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Applications
y for phase shifters, one would require a large tunability:
undoped multilayered
y for frequency-agile filters operating in the microwaveregime, low dielectric losses are a premium: doped
multilayered