1. Solution processible Inorganic Nanocrystal based Thin-film Transistor Hongki Kang EE235 April 27 2009

2. Flexible Electronics Polymer Vision: Readius

3. Printed Electronics Deposit FilmPhotoresistLithographyDevelopEtchingRemove PR Print

4. Flexible & Printed Electronics - Printable (=solution processible) semiconductor material - Organic semiconductor - Unstable (H 2 O, O 2 etc) - Low performance (≈ amorphous Si, mobility 1cm 2 /Vs)

5. Inorganic Semiconductor

6. Nano particle Sintering large surface-to-volume ratio

7. Nano particle Sintering

8. HgTe/HgSe inorganic nanoparticle based TFTs

9. Process Flow (1) - Nanocrystal Synthesis HgTe, HgSe -High mobility (µ HgTe,p : 320cm 2 /Vs, µ HgSe,n : 15,000cm 2 /Vs @300K) -Low melting point (T m,HgTe : 670°C, T m,HgSe : 799°C) NC synthesis (diameter ~5nm) -synthesized in an aqueous solution by a colloidal method Solution A: Hg(ClO 4 ) 2 + 1-thioglycerol in DI water with NaOH in N 2 Gas B: H 2 Te gas (generated Al 2 Te 3 + H 2 SO 4 under N 2 ) Under stirring, Gas B was passed through Solution A The precipitate containing thioglycerol-capped HgTe particles was separated by centrifugation.

10. - Single-crystalline - Transparent - sintering temperature ↑ => conductivity ↑ optimized condition: @150 °C for 15 min Process Flow (1) - Nanocrystal Synthesis

11. Process Flow (2) - Device Fabrication 65° Prohibiting the water vapor from penetrating the bare poly-ether-sulfone (PES) Minimizing the damage of the PVP layers occurring during photo-resist development and lift-off processes Cross-linked poly-4-vinylphenol (C-PVP) buffer layer on PES substrate (spin coating) Patterning (photolithography) HgTE/HgSe nanocrystal channel layer (spin coating) Lift-off process Changing the layers into hydrophilic easily and rapidly (a) Before UV/ozone treatment Gold gate electrode (thermal evaporator) Al 2 O 3 insulator (atomic layer deposition) UV/ozone treatment (b) After UV/ozone treatment Sintering process at 150 o C for 15 minutes Source/drain electrodes HgSe nanocrystal-based thin film transistor (TFT) SDG HgSe Nanocrystals A HgSe nanocrystal-based flexible TFT

12. Device Characteristic

13. Result NCHgTeHgSe TypeP-typeN-type Sintered NC grain size (nm) 1315 Mobility ( cm 2 /Vs) 4.14.0 I ON /I OFF ratio10 3 10 2 Sintering temp (°C) 150 Flexibility negligible characteristic variation under the 0.2% of tensile or compressive strain  Mobility: better than organic semiconductor, a-Si  Thermal budget: compatible with plastic substrate  Stability: Air stable  I ON /I OFF ratio : low

14. Conclusion Inorganic Nanoparticle High performance Chemical stability Plastic substrate compatibility  Optimization  Printability  More material research  Material Compatibility

15. Conclusion Thanks, Questions?