Nanodielectric with superparaelectric high-k material

1. Nanodielectric with superparaelectric high-k material

2. Dielectrics Applications – capacitors, gate dielectrics, ultracapacitors, frequency modulation Requirement – high dielectric strength, low leakage current, low hysteresis

3. High-k Dielectrics High-k oxide Sodium β-alumina Ion gel Nanocomposite dielectric

4. Dielectric vs. Ferroelectric Dielectric Electron displacement – lower polar moment No hysteric behavior Ferroelectric Ion displacement – higher polar moment Spontaneous polarization – hysteric behavior

5. Ferroelectric into gate capacitor BaTiO3 NP in PVDF/TrFE Large hysteresis Memory application rather than TFT application

6. Superparaelectric Ferroelectric nanomaterials with their size under superparaelectric limit → Cannot maintain their polarization without external electric field by thermal fluctuation ex) BaTiO3 nanoparticle Superparaelectric Dielectric Large polarization Without hysteresis

7. Superparaelectricity of BaTiO3nanoparticles Tetragonal Cubic Tetragonal Size reduction Higher temperature Cubic Smaller nanoparticle size depresses paraelectric-ferroelectric transition temperature

8. Nanoparticle synthesis Metal alkoxides + C2H5OH or Alcohols Solvothermal 200℃ for 48-96 hrs.

9. Nanoparticle synthesis Nanoparticle size is tunable by arranging alcohol species and concentration Without organic surfactant, nanocrystals show high dispersibility and stability in polar solvents It is likely particles produced have a surface chemistry that is similarly polar

10. Gate dielectric fabrication Spin-coating and 60℃ baking Multiple coating to adjust thickness Intercrystal voids ~20 vol.% A densified film could find higher dielectric constant The absence of alkyl chain ligands enables the low-temperature (T<60℃) processing of the nanoparticlesinto dense purely inorganic films

11. Dielectric property Dielectric constant for a pure BT film ~ 25 A higher dielectric constant is measured in BST ~35 Value for parylene-coated BT film fell to 10 due to the lower dielectric constant of paryleneC (3.15) Parylenecoating limits leakage current density

12. Superparaelectricity BT and BST particles of up to 12nm in size remain superparaelectric (temperature range of 196 to 24℃) Raman spectra indicates no sign of phase transition (Cubic ↔ Tetragonal)

13. Device fabrication The pentacene grains form noncontinuousfilm on bare BaTiO3 and exhibit a large fraction of vertical grains. No measurable transistor behavior is observed Parylenecoating decrease the roughness down to 2~3 nm and provides a favorable surface for the growth of high-quality pentacene.

14. Device characteristic mobility - 0.25 cm2V-1s-1 on/off ratio of 104 effective dielectric constant - 11.3 (200nm BST and 53nm parylene-C) The mobility in linear region: 0.03 cm2V-1s-1in the parylene-control sample 0.35 cm2V-1s-1in BT–parylenesample (attributed to increased concentration of accumulated carriers)

15. Nanodielectric: Advantage in process Normal sol-gel thin-film process: >600℃ for crystallization Nanodielectric process: ~200℃ for Nanocrystal synthesis ~60℃ for Baking after casting

16. Nanodielectric: Advantage in application Low process temperature – favorable to many substrate Withstand well with deformation Enables low-cost, flexible, and high performance electronics

17. vs. Sodium β-alumina Process Temp. 60℃(200℃ for NP synthesis)830℃ Flexibility Good Bad Dielectric constant 11.3 170 Leakage current 9-12nA/cm2 at 5V 1μA at 20V (120μm x 120μm) BaTiO3nanodielectric Sodiumβ-alumina

18. Idea #1 Polyimide/Superparaelectricnanoparticle composite for liquid crystal alignment layer 1. Study about relation of liquid crystal alignment with alignment layer dielectric constant 2. Low-voltage drive liquid crystal device 3. Azimuthal anisotropy of dielectric constant in ferroelectric nanorod/polyimide composite