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Electrical characteristics of solution-processed IGZO and its effects on contact resistivity

Electrical characteristics of solution-processed IGZO and its effects on contact resistivity. amorphous semiconductor/metal. I-V characteristics : w. channel distance As channel distance is decreased, Total resistance ↓. Linear I-V : ohmic. d. Ti/Au. a-IGZO.

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Electrical characteristics of solution-processed IGZO and its effects on contact resistivity

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  1. Electrical characteristics of solution-processed IGZO and its effects on contact resistivity

  2. amorphous semiconductor/metal I-V characteristics : w. channel distance As channel distance is decreased, Total resistance ↓ Linear I-V : ohmic d Ti/Au a-IGZO

  3. amorphous semiconductor/metal Increased slope As annealing temperature increases, Sheet resistance Contact resistance Lowered intercept

  4. amorphous semiconductor/metal As annealing temperature increases, Carrier concentration ↑

  5. amorphous semiconductor/metal As-deposited film – moderate electron concentration Thermionic emission dominates (kT >> qE00) φ ~ |ФTi(4.33eV) – Фa-IGZO(4.5eV)| = 0.17eV Pt : 5.65eV Au : 5.10eV Contact resistivity Barrier height Carrier concentration

  6. amorphous semiconductor/metal 2. Annealed film – high electron concentration Field emission dominates (kT >> qE00) As carrier concentration is increased, Contact resistance is decreased As carrier concentration is increased, Mobility↑ (by enhanced percolation conduction) Contact resistivity Barrier height Tunneling parameter

  7. amorphous semiconductor/metal Near ohmic contact with Pt Localized bandtail state in amorphous semiconductors Local shallow potential barrier : electron path

  8. amorphous semiconductor/metal As annealing temperature increases, interdiffusion↑ Formation of Ti-O phase Carrier concentration at surface↑ Au diffusion into a-IGZO layer Degraded contact resistance

  9. amorphous semiconductor/metal As annealing temperature is increased, Optical transmittance (2.0 – 3.5 eV) increases (by removal of shallow localized state) Delocalization of electrons → Increased carrier concentration

  10. Structural relaxation Localized bandtail states in amorphous semiconductor 1) Carrier conc. dependency 2) Temperature dependency

  11. Structural relaxation Low Quality a-IGZO (low power PLD) → Deeper tail-like states (20meV) High Quality a-IGZO (high power PLD) → Shallower tail-like states (7meV) → Higher carrier concentration → Higher mobility

  12. Structural relaxation For annealing temp. < 500°C Film is not crystallized but, Hall mobility↑ Crystallization Temp ~ 520°C

  13. Structural relaxation As film is annealed at 400°C Temperature dependency↓ Bandtail becomes shallower → Higher carrier concentration → Higher mobility In-In bond distance (EXAFS) 0.325nm (as-deposited LQ) → 0.320 (400°C annealed)

  14. Solution-processed Effect of chlorine on carrier concentration ClO substitution – donates electron In case of amorphous – incorporation of Cl without bond-breaking (less doping) 1) Sprayed SnO2 2) MOCVD ZnO

  15. Solution-processed Quenching produces peroxide anion, and oxygen vacancies 1) Crystallinity degradation 2) Increased carrier concentration Conventional IGZO 3.922 × 1014/cm3 ↓ Quenched IGZO 1.766 × 1015/cm3

  16. Solution-processed 3) Decreased bandgap 4) Increased FE mobility (Oxygen vacancies reduce bandtail)

  17. Solution-processed Ga-doped IZO is active with lower annealing temperature IZO films have higher threshold energies for structural relaxation structural relaxation in In-rich IGZO films is incomplete at 250°C Solution-processed IZO Solution-processed IGZO

  18. Solution-processed IZO films annealed below 300°C -are composed primarily of hydroxides IGZO – less hydroxyls Oxygen vacancies increases with annealing temperature

  19. Conclusion • In Vacuum-deposited a-IGZO, • In solution-processed a-IGZO Increasing Post-annealing temp. Structural relaxation Increased carrier concentration Reduced contact resistivity Residual impurities (ex. Cl) Solution composition Oxygen vacancy formation Effects on carrier concentration Post annealing condition Structural relaxation

  20. Future works • Experiment – hall measurement of solution-processed IZO • 300°C – inactive (very high sheet resistance) • 400°C – N = 8.49 x 1017~ 1.29 x 1018/cm3 • μ =  7.23 ~ 9.74 cm2/V.s • 3) 500°C – N ~ 2 x 1018/cm3 • μ~ 16 cm2/V.s • Future works • Observation of structural relaxation in solution-processed IZO • (EXAFS, TEM-EELS) • Analysis impurity concentration of carrier concentration • (XPS – hall measurement)

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