Solution-Processed Zinc Oxide Field-Effect Transistors Based on Self-Assembly of Colloidal Nanorods EE C235 Tim Bakhishev

Why Solution Processing? Flexible Substrates - Displays, Packaging, Solar Cells Low Cost Low Temperature Environmentally Friendly

Process Step 1 – Preparation of ZnO Nano-Spheres and Nano-Rods Zinc Acetate [Zn(Ac)2] Methanol [CH3OH] Potassium Hydroxide [KOH] Water, Temp, Time Nano-Spheres or Nano-Rods

Process Step 2 – Post-Deposition Growth (i) Spin-Cast Nano-Spheres/Rods Anneal (230 ºC) (ii) Submerge in Aqueous Solution of: - Zinc Nitrate - Ethyldiamine (iii) Growth at 90 ºC (iv) N2/H2 Anneal (200 ºC)

Without Post-Deposition Results Without Post-Deposition Nano-Spheres Ion/Ioff = 5 x 103 μ.sat= 4.6 x 10-4 cm2/V-s (b) Nano-Rods Ion/Ioff = 1.1 x 105 μ.sat= 0.023 cm2/V-s

Results Effects of Post-Deposition (a) As-Deposited Ion/Ioff = 1.1 x 105 μ.sat= 0.023 cm2/V-s (b) After Post-Deposition Ion/Ioff = 3 x 105 μ.sat= 0.6 cm2/V-s Post-Deposition Effects: Vt shift Increased Leakage (higher intrinsic conductivity) Only Marginal Improvement for Nano-Spheres Kink ???

Results Effects of Post-Deposition (a) Nano-Rods (b) Nano-Spheres The film is “well packed” as-deposited No structural benefit of Post-Dep Orientation is Preserved Nano-Rods Fuse

Conclusion Low temperature ZnO FET process is demonstrated Questions: - Size Effects - Post-Deposition effects Carrier concentration, conduction mechanism, electrostatics, defect density