Improving insulating property of sol-gel processed gate dielectrics

DISPLAY & PLASMA RESEARCH LABORATORY Ta doping on ZrO 2 gate dielectric 10 2 times lower leakage current Surface sol-gel ZrO 2 dielectric As applied electric field is increased, Effectiveness of Ta-doping in decreased

DISPLAY & PLASMA RESEARCH LABORATORY Rough surface increases leakage current Surface sol-gel film has relatively larger RMS (compared with ALD film) Surface sol-gel ZrO 2 dielectric

DISPLAY & PLASMA RESEARCH LABORATORY Successful TFT fabrication with SSG dielectric Using bilayer dielectric (HfO 2 /Polystyrene) 10 3 times lower leakage current by improved rms High-k/polymer bilayer dielectric

DISPLAY & PLASMA RESEARCH LABORATORY Decreased capacitance value 21.1nm PS has very low capacitance (k = 2.6) High-k/polymer bilayer dielectric

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

DISPLAY & PLASMA RESEARCH LABORATORY High-k/polymer bilayer dielectric Bilayer organic/inorganic gate dielectric Low RMS value: 0.3nm ALD HfO 2 film is very smooth RMS is slightly increased after organic coating

DISPLAY & PLASMA RESEARCH LABORATORY 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 (I g < ) Limitations: Low-k value of polymer layer Cannot endure active layer sol-gel coating process (high temp. annealing)

DISPLAY & PLASMA RESEARCH LABORATORY 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 Inorganic smoothing layer

DISPLAY & PLASMA RESEARCH LABORATORY Thin, smooth coating of inorganic thin film 1.8nm ultrathin film from 3g ZrCl 4 /l RMS – 0.3nm after 500ºC annealing Si Wafer 1.8nm ZrO 2 Inorganic smoothing layer

DISPLAY & PLASMA RESEARCH LABORATORY Chemical solution deposition of ZrO 2 Zr(C 3 H 7 O) 4 : hydrolysis in water Hydroxide precipitation in citric acid and H 2 O 2 Hydroxide re-dissolved by NH 4 OH addition Thin film <5nm easily achieved by spin-coating (very fine particle in colloid solution) Citric acid:Zr Inorganic smoothing layer

DISPLAY & PLASMA RESEARCH LABORATORY Inorganic smoothing layer Chemical solution deposition of ZrO 2 Smooth film – RMS < 0.5nm Not very dependent to precursor concentration and citric acid concentration

DISPLAY & PLASMA RESEARCH LABORATORY 10nm 20nm 40nm Inorganic smoothing layer Chemical solution deposition of ZrO 2 Smooth film – RMS < 0.5nm Thicker film tends to crystallize Ultrathin film maintained low RMS after annealing 3nm

DISPLAY & PLASMA RESEARCH LABORATORY Inorganic smoothing layer Chemical solution deposition of ZrO 2 High k~20, not dependent to citric acid concentration Relatively higher leakage current (compared with SSG dielectric)

DISPLAY & PLASMA RESEARCH LABORATORY Plasma treatment Improved insulating property of HfO 2 dielectric film Gate leakage suppression

DISPLAY & PLASMA RESEARCH LABORATORY Gate leakage suppression Plasma treatment HfCl 4 precursor and 250ºC annealing Removal of residual alkoxides and hydroxyl groups Hf 4f 7/2 and Hf 4f 5/2 energy levels: Binding energies of the Hf–O bonds Increased binding energy: Advancement of the O-Hf-O bonds Plasma treatment completes oxidation

DISPLAY & PLASMA RESEARCH LABORATORY Gate leakage suppression Plasma treatment Treatment was more effective than HfO 2 case Plasma annealing was effective But annealing plasma was not

DISPLAY & PLASMA RESEARCH LABORATORY 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) SnO 2 active layer (New precursor: Tin tert-butoxide) Ta-doped SnO 2 active layer (Sol-gel on chip) Equipment setup (Revised paper) Transmittance/Sheet resistance data of WAW electrode, Band diagram, Ti electrode Conclusion & Future work