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Dehydration of tin hydroxide and low-temperature, solution-processed zinc tin oxide TFT

Dehydration of tin hydroxide and low-temperature, solution-processed zinc tin oxide TFT. Low-temperature sol-gel oxide. Strategy to low-temperature sol-gel oxide semiconductor. 2008 DA Keszler , JACS. 2010 H . Sirringhaus , Nat. Mat. 2009 M Halik , Adv. Mat. Alkoxides. 1. Deposition.

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Dehydration of tin hydroxide and low-temperature, solution-processed zinc tin oxide TFT

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  1. Dehydration of tin hydroxide and low-temperature, solution-processed zinc tin oxide TFT

  2. Low-temperature sol-gel oxide Strategy to low-temperature sol-gel oxide semiconductor 2008 DA Keszler, JACS 2010 H. Sirringhaus, Nat. Mat. 2009 M Halik, Adv. Mat. Alkoxides 1. Deposition Hydroxides 2. Steam annealing 1. Deposition Oxides 3. Anealing 2. Anealing 1. Deposition (Nanoparticle)

  3. Low-temperature sol-gel oxide Ethoxide Water vapor hydrolysis rate vs. functional group SrBi2Ta2O9 (SBT) sol-gel coating (Ferroelectric material) Water vapor-oxygen flow annealing – less hydrogen, carbon (compared to air annealing) Ethoxide precursor is hydrolized (more H, less C) More than methoxyethoxide precursor Methoxyethoxide

  4. Low-temperature sol-gel oxide Water vapor hydrolysis rate vs. functional group Ethoxide precursor – high hydrolysis rate (less steric effect) Larger grain size after 650ºC annealing Ethoxide Methoxyethoxide

  5. Low-temperature sol-gel oxide Dehydration of metal hydroxides Zinc hydroxide Weight loss from 190ºC from DTA analysis (Generally known to decompose at 125ºC) Indium hydroxide 250 ~ 300ºC : 2In(OH)3 → 2InOOH + 2H2O 305ºC : 2InOOH → In2O3+ H2O

  6. Low-temperature sol-gel oxide Dehydration of metal hydroxides Tin hydroxide Complete dehydration requires very high temperature (600ºC) Hydrogen impurities remain as stannic acid form

  7. Low-temperature sol-gel oxide IZO TFT FE mobility 0.54cm2/Vsat 300ºC

  8. Low-temperature sol-gel oxide IZO TFT FE mobility 0.86cm2/Vsat 300ºC FE mobility 2.12cm2/Vsat 300ºC microwave

  9. Low-temperature sol-gel oxide ZTO TFT Lower mobility at 500ºC (1.1cm2/Vs) TFT characteristic is undetectable at 300ºC

  10. Low-temperature sol-gel oxide ZTO TG-DTA analysis Decomposition was completed at around 500ºC

  11. Low-temperature sol-gel oxide Zr-ZTO TFT Improved mobility at 500ºC (4.02cm2/Vs) and at lower temperature FE mobility 0.028cm2/Vs at 300ºC

  12. Low-temperature sol-gel oxide Zr-ZTO TG-DTA analysis 190-320ºC : Dehydration process Decomposition temperature is reduced by alloying

  13. Zr-ZTO XPS measurement The O 1s peaks 530.1 eV(Oox) - oxygen atoms in the fully oxidized surroundings. 531.2 eV(Ov) - oxygen ions in oxygen deficient regions 532.4 eV(Os) - loosely bound oxygen (H2O and OH groups) Increasing Zr – less hydroxyl

  14. Low-temperature sol-gel oxide ZTO TFT with vacuum annealing Vacuum annealing enabled low-temperature ZTO TFT As-deposition : 5.5 x 10−3cm2/Vs (300ºC 3h : no improvement) 300ºC Vacuum : 3.17 cm2/Vs 300ºC Vacuum-wet : 5.5 cm2/Vs

  15. Low-temperature sol-gel oxide XPS measurement Zn:Sn ratio – maintained 1:1 after the postannealing Cl concentration - significantly reduced after vacuum annealing (0.4 - 2 atom%)

  16. Low-temperature sol-gel oxide XPS measurement The O 1s peaks 530.1 eV(Oox) - oxygen atoms in the fully oxidized surroundings. 531.2 eV(Ov) - oxygen ions in oxygen deficient regions Increased after vacuum annealing 532.4 eV(Os) - loosely bound oxygen (H2O and OH groups) Decreased after vacuum annealing

  17. Low-temperature sol-gel oxide Low-temperature SiO2 Low temperature (<400ºC) grown SiO2 (CVD,PECVD,sol-gel) Poor properties by remaining H2O and OH groups Dehydration of SiO2 requires high temperature over 600ºC FTIR spectra Reduction of H2O and Si-OH signal XeF2 annealing 350ºC annealing with sublimated XeF2

  18. Low-temperature sol-gel oxide TPD spectra H2O desorption is undetectable from XeF2-annealed sample (almost like thermal oxide) Leakage characteristic Dielectric constant: 3.8 Breakdown field strength : 4MV/cm High Si-F bonds Low Si-F bonds

  19. Conclusion • Sol-gel processed ZTO : higher dehydration temperature than IZO • High dehydration temperature is related to tin hydroxide dehydration products • Vacuum annealing effectively improve ZTO TFT’s low temperature characteristics • XeF2 Catalytic dehydration can decrease process temperature

  20. Experiment ZrO2 surface sol-gel dielectric Large leakage current Vg can applied to 1.5V maximum

  21. Experiment ZrO2 surface sol-gel dielectric ~16nm thickness Capacitance ~650 nF/cm2

  22. Experiment Thermal SiO2 ZrO2 surface sol-gel dielectric – leakage current reduced

  23. Experiment Thermal SiO2 ZrO2 surface sol-gel dielectric

  24. Experiment Surface sol-gel SnO2 active layer – 10 cycles thickness

  25. Experiment Surface sol-gel SnO2 active layer – 20 cycles thickness

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