MgO-doped compositionally graded multilayer barium strontium titanate films

8/7/2019 MgO-doped compositionally graded multilayer barium strontium titanate films

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Presented by : Md. Mehedi Hasan

St. Id.- 0611039


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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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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

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MgO-doped compositionally graded multilayer barium strontium titanate films