Improving insulating property of sol-gel processed gate dielectrics

1. Improving insulating property of sol-gel processed gate dielectrics

2. Surface sol-gel ZrO2 dielectric Ta doping on ZrO2 gate dielectric 102 times lower leakage current As applied electric field is increased, Effectiveness of Ta-doping in decreased

3. Surface sol-gel ZrO2 dielectric Rough surface increases leakage current Surface sol-gel film has relatively larger RMS (compared with ALD film)

4. High-k/polymer bilayer dielectric Successful TFT fabrication with SSG dielectric Using bilayer dielectric (HfO2/Polystyrene) → 103 times lower leakage current by improved rms

5. High-k/polymer bilayer dielectric Decreased capacitance value 21.1nm PS has very low capacitance (k = 2.6)

6. High-k/polymer bilayer dielectric Bilayer organic/inorganic gate dielectric Thinner polymer layer – less capacitance degradation Using UV epoxy layer as polymer dielectric (Thickness is decreased during cross-linking)

7. High-k/polymer bilayer dielectric Bilayer organic/inorganic gate dielectric Low RMS value: 0.3nm ALD HfO2 film is very smooth RMS is slightly increased after organic coating

8. High-k/polymer bilayer dielectric • Bilayer organic/inorganic gate dielectric • As polymer layer is thin (10nm), capacitance degradation is minimized. • Insulating property is also good (Ig < 10-7) • Limitations: • Low-k value of polymer layer • Cannot endure active layer sol-gel coating process (high temp. annealing)

9. Inorganic smoothing layer Thin, smooth coating of inorganic thin film General sol-gel spin-coating Gelation in acid-catalyzed condition Decreasing precursor conc. Decreasing hydrolysis rate Decreasing acidity

10. Inorganic smoothing layer Thin, smooth coating of inorganic thin film 1.8nm ultrathin film from 3g ZrCl4/l RMS – 0.3nm after 500ºC annealing Si Wafer 1.8nm ZrO2

11. Inorganic smoothing layer Chemical solution deposition of ZrO2 Zr(C3H7O)4 : hydrolysis in water Hydroxide precipitation in citric acid and H2O2 Hydroxide re-dissolved by NH4OH addition Thin film <5nm easily achieved by spin-coating (very fine particle in colloid solution) Citric acid:Zr

12. Inorganic smoothing layer Chemical solution deposition of ZrO2 Smooth film – RMS < 0.5nm Not very dependent to precursor concentration and citric acid concentration

13. Inorganic smoothing layer 10nm Chemical solution deposition of ZrO2 Smooth film – RMS < 0.5nm Thicker film tends to crystallize Ultrathin film maintained low RMS after annealing 20nm 40nm 3nm

14. Inorganic smoothing layer Chemical solution deposition of ZrO2 High k~20, not dependent to citric acid concentration Relatively higher leakage current (compared with SSG dielectric)

15. Gate leakage suppression Plasma treatment Improved insulating property of HfO2 dielectric film

16. Gate leakage suppression • Plasma treatment • HfCl4 precursor and 250ºC annealing • Removal of residual alkoxides and hydroxyl groups • Hf 4f7/2 and Hf 4f5/2energy levels: • Binding energies of the Hf–O bonds • Increased binding energy: • Advancement of the O-Hf-O bonds • Plasma treatment completes oxidation

17. Gate leakage suppression Plasma treatment Treatment was more effective than HfO2 case Plasma → annealing was effective But annealing → plasma was not

18. Conclusion & Future work • Conclusion • Bilayer dielectric is effective for reducing gate leakage current density • Plasma treatment is effective for reducing gate leakage current density • Future work • (Gate Dielectric) • Increasing thickness of SSG dielectric : 20 cycles → 30,40 cycles • Adopt sol-gel smoothing layer • Oxygen plasma treatment • (Active layer) • SnO2 active layer (New precursor: Tin tert-butoxide) • Ta-doped SnO2 active layer • (Sol-gel on chip) • Equipment setup • (Revised paper) • Transmittance/Sheet resistance data of WAW electrode, Band diagram, Ti electrode