| Flexible thin film transistors?TFTs?are important parts in flexible electronic devices,and the flexible oxide thin film transistors?MOTFTs?with high mobility,good transparency,good flexibility,good stability,are the most widely-studied.This paper mainly studies the room-temperature techniques for the fabrication of flexible MOTFTs by adopting sputtering methods,designs of new device structures,optimal deposition techiques and new materials.The flexible MOTFTs with high performance,high stability and good flexibility were achieved to meet the needs of flexible electronic devices.Firstly,we systematically studied the low temperature or room temperature preparation for different high-k oxide insulation materials?HfO2,Al2O3?.Among them,the dielectric constant of 200?-annealed HfO2 insulating layer can reach 28.5 with good dielectric properties.The Al2O3 insulator fabricated at room temperature already showed excellent film qualities and insulating properties,whose dielectric constant is 8.6,exhibiting good thermal stability and mechanical performance,which can guarantee the proper functioning of the flexible MOTFTs.Then,we also designed a series of room-temperature multilayered active layer structures,which can control the carriers forming quasi two-dimensional electronic transmission along the near-channel region of semiconductor layer by field effect.By inserting an Al2O3 layer between the S/D electrodes and semiconductor layer,the scattering or charge trapping by the defects on the back-channel surface can be avoided,improving the on-state current of devices;At the same time,the tunneling effect through Al2O3 layer is used to reduce the generation of channel leakage current,which also reduces the off-state current of device,thereby improving the mobility and Ion/Ioff ratio of the device.In addition,this paper presents a new method to improve the components and properties of the semiconductor thin films and their electrical properties by using the pulse-DC sputtering technology modulated by voltage waveforms.By modulating the frequency and duty ratio of sputtering waveforms,we can reduce the difference of deposition rate between each target element and promote the M-O-M bonds formed by the combination of the metal ions and oxygen,optimizing the electrical properties of the corresponding MOTFT devices at room temperature.Finally,based on the above researches,the mobility of flexible a-IGZO TFT based on low-temperature HfO2 insulation layer prepared on PI substrate can reach 10.3 cm2 V-1 s-1,the Ion/Ioffff ratio is 4.3×107,the SS value is 0.28 V dec-1,and Vth is 1.1 V.Moreover,the mobility of the flexible a-IGZO TFT based on room-temperature Al2O3 insulation layer on the PI substrate is as high as 20.9 cm2 V-1 s-1,the Ion/Ioff ratio was 2.3×107,the SS value is 0.32 V dec-1,and the Von is-0.1 V.In addition,the mobility of the all-sputtered flexible a-IGZO TFT,based on the room-temperature Al2O3 insulating layer on the PEN substrate,can reach 18.3 cm2 V-1 s-1,the Ion/Ioff ratio can reach107,the SS value is 0.33 V dec-1,and the Von is 1.3 V.All the above devices show good stabilities under both electrical bias and bending stress,which demonstrates their great prospect in flexible electronic device applications. |
PDF Full Text Request