Study On Copper Alloy Electrode Of Oxide Thin Film Transistor

With the development of normal display technology,the demand of high-performance display panel characterized by large size,high resolution,high refresh rate and flexibility in commercial and consumer fields is increasingly strong.The above technical features require that the electrode of the display driving device should not only reduce the characteristic line width,reduce the characteristic size,but also improve the conductivity and reduce the signal delay.The traditional electrodes represented by aluminum(Al)and molybdenum(Mo)are gradually showing fatigue in terms of performance improvement,and the marginal benefit is diminishing,which can no longer meet the requirements of metallized wiring for high-performance display.Pure copper(Cu)electrodes have excellent electrical conductivity but poor adhesion.In order to improve the bonding ability with the substrate,it is necessary to develop new copper alloy electrode materials.Amorphous oxide semiconductor(AOS)is a relatively ideal active layer material for high performance display due to its low cost,high mobility,high uniformity and flexibility.Therefore,developing copper alloy films with high conductivity and high bonding strength as the electrode and wiring materials of high mobility AOS thin film transistor(TFT)as well as reducing the RC delay in charge transfer have great significance.Therefore,this paper focused on the copper alloy electrode and flexible application of oxide thin film transistor.The main results are as follows.1.The composition,phase structure and component transport law of Cu alloy target with Cr and Zr as ultra-low solid solubility co-doped alloy elements under magnetron sputtering were studied,and Cu-Cr-Zr ternary copper alloy target for AOS-TFT electrode was developed.By increasing the types of alloying elements and adjusting the ratio of alloying elements,the benign interaction of Cr and Zr alloying elements makes the precipitation phase in the copper alloy target change from granular to uniform network,which solves the problems of nodulation on the sputtering surface of the target material and unstable film-forming composition of the Cu-Cr and Cu-Zr binary copper alloy targets due to solid solution precipitation and precipitation.Finally,the composition of Cu-0.12 wt.%Cr-0.08 wt.%Zr(CCZ)copper alloy target is uniformly transferred under high power sputtering,which ensures the stability and controllability of the composition of copper alloy film.2.The composition of copper alloy films was precisely adjusted by multi-cathode target magnetron co-sputtering system,and the effects of doping alloy elements on the conductivity,bonding strength and residual stress of copper films were studied.It is found that when Cr and Zr coexist in Cu matrix,it is better to maintain the high conductivity of Cu films than any single element.And realized that the Cu(220)texture of CCZ films is the same as that of pure Cu films.According to the above rules,CCZ monolayer and CCZ/Cu laminated structure electrodes were prepared,while maintaining the bonding strength as high as 4B-5B,the resistivity was close to that of pure copper film.It effectively solves the contradiction that the conventional binary copper alloy electrode is difficult to have both high bonding strength and high conductivity.3.A high-performance flexible TFT device with CCZ gate electrode was developed.The new CCZ ternary alloy was used to fabricate the bottom gate top contact TFT.The compatibility with the Si N_x/Si O_x gate insulating layer deposited by plasma enhanced chemical vapor deposition(PECVD)and the Al₂O₃ high-k gate insulating layer deposited by physical vapor deposition(PVD)was verified.It was found that the latter is more conducive to improving the performance of TFT.Finally,CCZ gate was applied to Nd IZO-TFT device on PI flexible substrate.The saturation mobility(?_sat)is 27.1 cm²·V^-1·s^-1,the switching ratio(I_on/I_off)is2.87×10⁷,the subthreshold swing(SS)is 0.28 V/decade,and the threshold voltage(V_th)is 0.09V.After 10000 times bending with 1 mm curvature radius,V_th drifts only 0.19 V,and the change rate of?_sat is only 0.37%.4.In order to further reduce the power consumption and RC delay,the CCZ material was used in the source and drain electrodes of TFT,which can adjust the channel carrier transport behavior with higher conductivity,and the high mobility and threshold voltage compensation can be realized.The results show that?_sat is 32.1 cm²·V^-1·s^-1,I_on/I_off is 4.10×10⁷,SS is 0.16V/decade and V_th is 0.42 V.The TFT with CCZ electrodes shows excellent electrical stability and bending reliability:after 5400 s±1 m V/cm gate bias,the V_th drift is-0.28 V/+2.46 V;with2.5 mm static bending,the V_th drift is-0.32 V;after 10000 dynamic bending with 4 mm radius,the V_th drift is-0.29 V.