Design And Fabrication Of High Voltage A-IGZO Power Device

Metal oxide semiconductor devices represented by amorphous indium gallium zinc oxide thin film transistors（a-IGZO TFT）have the advantages of high mobility,low subthreshold swing,low off-state current,excellent ductility,low fabrication temperature and large-area manufacturing.a-IGZO TFTs have great application prospects in many fields,including information display,artificial intelligence,medicine and so on,and have received extensive attention from researchers at home and abroad.Due to its excellent electrical characteristics,a-IGZO TFTs technology has been successfully applied to the active-matrix display terminal.The information storage and processing system based on a-IGZO TFTs has also been studied and developed rapidly.The power management system,where power devices play a key role,is the"heart"of electronic products.However,the lack of a-IGZO-based power devices limits the realization of the a-IGZO-based full integration chip.The breakdown voltage is determined by the thickness of the gate dielectric and is difficult to be improved because of the breakdown weak point in the overlay between the gate and drain for the conventional TFT.In addition,there are few reports on high-voltage（HV）a-IGZO devices in the academic field.Therefore,the research and fabrication of high-performance HV a-IGZO devices is the key to expanding the application of a-IGZO in power management chips.This paper’s research content is to improve the device breakdown voltage and optimize the on-resistance.Through the investigation of gate-dielectric and drift region breakdown mechanisms,novel structure design,and process optimization,three kinds of HV a-IGZO TFTs have been proposed and fabricated,which lays the foundation for the realization of a-IGZO-based high-low voltage integrated process,flexible power management chip,and fully flexible electronic products.The main research contents are as follows:（1）The HV a-IGZO device with an asymmetric stair gate dielectric was proposed and fabricated.The thickness of the gate dielectric layer at the drain side is increased locally to improve the breakdown voltage between the gate and the drain.20 nm-thick Al₂O₃ high-k gate-dielectric layer is used in the channel region to increase the channel carrier concentration to reduce the on-resistance.Based on TCAD simulation,the exponential dependence of on-resistance and gate-dielectric thickness is established for the proposed device and the device structure is further improved.Compared with the conventional device,the breakdown voltage increases to 50 V,3times the conventional device with 20 nm-thick gate-dielectric,and the on-resistance increases only0.7 times.（2）The HV a-IGZO device with a symmetric stair gate dielectric was proposed and fabricated.Increase the thickness of the gate dielectric layer at the source and drain sides to improve the breakdown voltage between the source and gate and between the source and gate to achieve high operation voltage.Compared with conventional devices.The on-resistance of the channel in and out of stair regions is extracted via the Gate-Four-Probe test technique,revealing the linear dependence between the channel resistance and the length of the stair region.Compared with the conventional device with 20 nm-thick gate-dielectric,both the drain and source breakdown voltages increase from 17 V to 60 V and the on-resistance increases only 0.3 times.（3）The HV a-IGZO device with a drift region doped by hydrogen was proposed and fabricated.The drift region and some channels are doped by a local hydrogen plasma treatment process to reduce the drift region resistance.The measurements show that the breakdown voltage is 406 V,8times the conventional devices.The specific on-resistance is 6240 mΩ·cm²,only 0.54 times the conventional device with 100 nm-thick gate-dielectric.The threshold shift is negative 0.66V under3600s stress,which exhibits excellent reliability for the proposed device.