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Ferroelectric Superlattices for Use in Non-linear Transmission Lines

Ferroelectric Superlattices for Use in Non-linear Transmission Lines. Robert James Sleezer Research Proposal Defense 16 December 2008. Acknowledgements. Gregg Salamo , Advisor Jerzy Krasinski , Masters Advisor and Committee Member Laurent Bellaiche , Committee Member

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Ferroelectric Superlattices for Use in Non-linear Transmission Lines

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  1. Ferroelectric Superlattices for Use in Non-linear Transmission Lines Robert James Sleezer Research Proposal Defense 16 December 2008

  2. Acknowledgements Gregg Salamo, Advisor JerzyKrasinski, Masters Advisor and Committee Member Laurent Bellaiche, Committee Member Jacques Chakhalian, Committee Member Ken Vickers, Committee Member Morgan Ware, Mentor VasylKunets, Mentor Zhao-QuanZeng, Mentor National Science Foundation G-K12 Progam MRI #0421099 (Red Diamond) and MRI #072265 (Star of Arkansas) from the National Science Foundation

  3. Non-linear Transmission Line Motivation Shock wave generation Voltage gain Creation of harmonics Soliton propagation

  4. Overview • Dielectric Background • Ferroelectric Material Properties • Strain and Thickness Effects • Material Growth • Prior Non-linear Transmission Line Results • Discrete Lines • Bulk Results • Thin Film Expectations and Results • Transmission Line Model • Finite Element Model • Preliminary Results • Proposed Research • Expected Deliverables • Research Plan • Intellectual Property Expected to Result From Research

  5. Dielectric Backgroud • Ferroelectric Material Properties • Hysteresis • Dielectric Constant • Curie Temperature • Strain and Thickness Effects • Strain and Ferroelectric Films • Thin Film Effects • Superlattices • Material Growth • Shuttered RHEED MBE • Soluble Substrates

  6. E Ferroelectric Material Properties P : of or relating to crystalline substances having spontaneous electric polarization reversible by an electric field E Definition According to Mirriam-Webster Non-linear Relationship Between Polarization and Electric Field Dielectric Constant Depends On Electric Field

  7. Ferroelectric Material Properties • Curie Temperature • Temperature of Phase Change • Below Tc the Material is Ferroelectric • Above Tc the Material is Paraelectric • The Dielectric Constant, a Function of Temperature, Peaks at Tc

  8. Strain Effects orthorhombic rhombohedral tetragonal Strain Imposed by Lattice Mismatch With Substrate or Neighboring Layers Phase is a Function of Strain Strain May Effect Tc in a Thin Film Ferroelectric

  9. Thickness Effects Satellites in the diffraction pattern of PTO are an indication of ferroelectric stripe domains. The sample with four unit cells remains ferroelectric through at least 644K, the three unit cell sample looses it’s ferroelectricity between 463K and 549K, and the thinner samples remain paraelectric at all temperatures. An Atom in an Ultrathin Film Does Not Experience the Same Environment as an Atom in Bulk Material Slightly Thicker Films Also Show Material Property Variation

  10. Ferroelectric Superlattices Layered Thin Film Materials Can Create Local Environments Unlike Bulk Environments Thicker Films Can Create Strain Throughout the Sample

  11. Oxide Growth By MBE TiO2 Surface SrO Surface • Shuttered RHEED Growth • Beam Flux Calibration Done With Shuttered RHEED • Requires Extra Substrate • Time Consuming • Addition of Quartz Microbalance Planned

  12. Soluble Substrates • Use of Soluble Substrates Allows • Freestanding Thin Films • Eliminate Strain Contribution of Substrate • Study the Backside of the Material • Metal Contact to Top and Bottom of Thin Film • Novel Devices • Substrate of Choice is LiF • Good Lattice Match • Moderately Soluble • Relatively Inexpensive • Surface Quality May Be a Problem

  13. Current State of the Art Non-linear Transmission Lines • Discrete Lines • Varactor Based • Ferroelectric Capacitor Based • Bulk Lines • Thin Film Lines • Previous Results • Expectations

  14. Varactor Based Non-linear Transmission Lines tr = 80ns tr = 40ns Transmission Line Constructed From Discrete Inductors and Varactors Shock Wave With Ringing Related to Unit Cell Resonant Frequency is Developed

  15. Bulk Ferroelectric Lines Lines 2m Were Fabricated and Tested Probes Were Placed at Different Locations Along the Line Output Was Studied as a Function of Input

  16. Ferroelectric Thin Film Transmission Lines • Coplanar Transmission Lines Fabricated on BST • 400 nm of BST on LaAlO3 • 1.0um Thick Silver Conductors • Center Conductor Width of 53um • Line Length of 10.52mm • The Third Harmonic Increased with Increasing Input Power • Only Known Study Using Thin Film Ferroelectric Transmission Lines

  17. Transmission Line Modeling • Finite Element Model • Unit Cell • Derivation of Differential Equation • Implementation • Preliminary Results • Initial Parameters • Pulse Propagation • Ringing and Filtering • Rise Time and Gain Analysis

  18. Model Unit Cell

  19. Differential Equation Resulting From Unit Cell

  20. High Level Pseudo Code Analysis • Nt = t/dt • Nn = x/dx • Loop on Nt • Loop on Nn • Solve Differential Equation • End • End • O(Nt*Nn) • Nt is about 10^7 and Nn is about 10^5

  21. Simulation Parameters for Preliminary Results

  22. Ringing and Filtering Unfiltered Simulation Results Show Significant Ringing at Unit Cell Resonant Frequency Application of a Band Reject Filter Removes Unwanted Ringing Smaller Unit Cells Have Higher Frequency Ringing Adjustments to Rc to Account For Frequency Dependant Loss Tangent

  23. Proposed Research • Expected Deliverables • Material Research • Property Variation With Strain • Dielectric Constant • Loss Tangent • Curie Temperature • Hysteresis Curve • Comparison to Previously Developed Model • Transmission Line Behavior • Rise Time as a Function of Propagation Distance • Gain as a Function of Propagation Distance • Comparison to Model • Research Plan

  24. Proposed Material Structure Layer A: Ba0.5-xSrx+0.5O3 Layer A: Bax+0.5Sr0.5-xO3

  25. A Study of Material Property Variation With Strain

  26. Transmission Line Study

  27. Unproposed Research • Extensions • Modification of Transmission Line Structure • Creation of Artificial Unit Cell • Modification of Structure for Optimal Voltage Gain • Study of Thickness Contribution Above Critical Thickness • Future Directions • Study of Thickness Below Critical Thickness • Use of Additional Materials

  28. Research Plan

  29. Intellectual Property Issues Freestanding Thin Films Cold-welded Thin Films Non-linear Transmission Line

  30. Ferroelectric Superlattices for Use in Non-linear Transmission Lines Robert James Sleezer Research Proposal Defense 16 December 2008

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