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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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Presentation Transcript
slide1

Dehydration of tin hydroxide and

low-temperature, solution-processed zinc tin oxide TFT

slide2

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)

slide3

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

slide4

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

slide5

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

slide6

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

slide7

Low-temperature sol-gel oxide

IZO TFT

FE mobility 0.54cm2/Vsat 300ºC

slide8

Low-temperature sol-gel oxide

IZO TFT

FE mobility 0.86cm2/Vsat 300ºC

FE mobility 2.12cm2/Vsat 300ºC microwave

slide9

Low-temperature sol-gel oxide

ZTO TFT

Lower mobility at 500ºC (1.1cm2/Vs)

TFT characteristic is undetectable at 300ºC

slide10

Low-temperature sol-gel oxide

ZTO TG-DTA analysis

Decomposition was completed at around 500ºC

slide11

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

slide12

Low-temperature sol-gel oxide

Zr-ZTO TG-DTA analysis

190-320ºC : Dehydration process

Decomposition temperature is reduced by alloying

slide13

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

slide14

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

slide15

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%)

slide16

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

slide17

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

slide18

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

slide19

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
slide20

Experiment

ZrO2 surface sol-gel dielectric

Large leakage current

Vg can applied to 1.5V maximum

slide21

Experiment

ZrO2 surface sol-gel dielectric

~16nm thickness

Capacitance ~650 nF/cm2

slide22

Experiment

Thermal SiO2

ZrO2 surface sol-gel dielectric – leakage current reduced

slide23

Experiment

Thermal SiO2

ZrO2 surface sol-gel dielectric

slide24

Experiment

Surface sol-gel SnO2 active layer – 10 cycles thickness

slide25

Experiment

Surface sol-gel SnO2 active layer – 20 cycles thickness