Research On The Integration Of P-channel Metal Oxide Thin Film Transistors

Metal oxide semiconductors have become the key components in flat-panel displays due to their high carrier mobility,excellent optical transparency,and electrical stability.Most of the metal oxide semiconductors reported to date were n-type oxide,however,few p-type oxide semiconductors have been reported.This limited the application of p-type metal oxide semiconductors in thin film transistors?TFTs?.In this study,one-step synthetic method was employed to fabricate Cu₂O thin films at low temperature and the Cu₂O/SiO₂ TFTs with excellent electrical performance were fabricated futher.The characteristics of the thin films as a function of annealing temperature were investigated.The analysis indicates that the phase evolution of Cu₂O to CuO occurred at high temperatures and the pure CuO phase was achieved at 250 ^oC.The average grain size and surface morphology of the Cu_xO thin films were found to increase as the annealing temperature was increased.To explore the possible applications of the obtained Cu₂O films as semiconducting channel components,bottom-gated TFTs based on SiO₂ gate dielectrics were constructed.The optimized Cu_xO TFTs were achieved at 250 ^oC and the devices exhibited a hole mobility of 0.32 cm² V^-1 s^-1,a large on/off current ratio of5×10⁴,and a subthreshold swing of 1.1 V dec^-1.Until now,the reports on p-type oxide TFTs were mainly focused on binary oxide?Cu_xO?NiO?SnO,etc.?TFTs.In this work,ternary p-type CuCrO₂ semiconductor thin films were fabricated by using a solution process and the characteristics of the CuCrO₂thin films as a function of annealing temperature were investigated.Two-phase structures composed of CuO and CuCr₂O₄ were observed for the thin films annealed at 500 ^oC and600 ^oC.As the annealing temperature was increased to 700 ^oC,the phase conversion from a mixture of CuO and CuCr₂O₄ to pure CuCrO₂ was achieved.By using SiO₂ as the dielectric layer,we further investigate the effect of annealing temperature on the electrical properties of CuCrO₂/SiO₂ TFTs in a nitrogen environment.The result indicates that the electrical performance of the CuCr_xO_y TFTs is improved with increasing annealing temperature from 500 ^oC to 800 ^oC.The optimized TFT exhibits high field-effect mobility(?=0.59 cm² V^-1 s^-1)and large on/off current ratio(I_on/I_off¹0⁵).However,the further increase of annealing temperature up to 900 ^oC leads to the degraded electrical performance,which could be attributed to the decreased carriers generated from copper vacancies and/or oxygen interstitials at an excessively high annealing temperature.To clarify the gate-bias-stability of the device,both positive bias stress and negative bias stress?PBS and NBS?measurements were carried out on the optimized CuCrO₂ TFT by applying a gate voltage of±60 V.A maximum threshold voltage shift of 0.84 and 3.28 V were recorded after PBS and NBS measurements for 2000 s.As we know,this work demonstrates the ternary p-type Cu Cr O₂ TFTs fabricated via a low-cost solution process for the first time,which represents an important advancement towards the development of CMOS logic circuits.