Research On Preparation Of PVA Substrate Transient Thin-film Transistors

Transient electronics is an emerging research hotspot.Transient electronic equipment can run stably for a certain period of time,and finally make each component of the device completely or partially disappear into the surrounding environment through a specific trigger,such as physical dissolution,biodegradation,photothermal cracking,etc.It has a wide range of potential applications in military reconnaissance and surveillance,information security storage,biomedical implant equipment,environmental sensors,electronic waste control and so on.The Thin Film Transistor（TFT）is the basic component of electronic displays and programmable logic circuits.With the development of technology,the traditional silicon-based thin film transistor has failed to meet the needs of these special fields.Polyvinyl alcohol（PVA）is a biocompatible,environmentally friendly and degradable polymer material.Compared with polylactic glycolic acid（PLGA）,polyvinylpyrrolidone（PVP）,polylactic acid（PLA）and other common transient degradable materials,polyvinyl alcohol（PVA）has better thermal stability.By AFM test,the surface roughness of PVA substrate is low,which has the potential to prepare high-performance transient thin film transistors.This paper mainly studies the preparation process of PVA base transient device,device film using green non-toxic materials,and then optimized the preparation conditions of active layer and insulating layer of transient device,to achieve the goal of low cost,simple process,rapid batch to make high performance transient thin film transistor.In this paper,transient devices are prepared by vacuum mask deposition,aluminum（Al）is evaporated by electron beam evaporation equipment（EB）as the gate,hafnium oxide（Hf O₂）is deposited by magnetron sputtering equipment（PVD）as the insulation layer,and aluminum zinc oxide（AZO）is deposited by magnetron sputtering equipment（PVD）as the active layer.Finally,100 nm aluminum（Al）was vaporized by electron beam evaporation equipment（EB）as the source drain,and the field effect characteristics of the transient device were realized.The current switching ratio of the device was 42,the mobility was 5.95×10^-2cm²·V^-1·s^-1,the threshold voltage was 3.1 V,and the subthreshold swing was 3.18 V?dec^-1.Finally,the transient degradability of PVA substrate thin film transistor is realized.In the environment of normal temperature deionized water,the film material on the substrate can be completely cracked within half an hour.In 80℃ionized water,the whole device is completely cracked in a few minutes.In order to improve the electrical performance of the device,the optimal preparation conditions of the active layer and the structure of the insulation layer are studied.The main contents are as follows.The optimal aluminum doping amount of active layer AZO in PVD was studied,and the glass substrate and Amorphous silicon AZO-TFT were set as PVA substrate transient devices.The results show that when the doping power of Al is 7.5 W,the electrical performance of all three groups of different substrate TFT is the best,among which the current switching ratio of PVA substrate transient TFT is 6.1×10³,the subthreshold swing is as low as 0.99 V?dec^-1,the threshold voltage is only 3.3 V,and the carrier mobility is as high as 1.74 cm²·V^-1·s^-1.The optimal oxygen content of AZO in active layer was studied by PVD method,and amorphous silicon based Azo-TFT was set as the comparison group of transient devices on PVA base.The results show that although the high dielectric constant insulating layer Hf O2 can improve the carrier mobility of the device,the large leakage current affects the electrical performance of the device.The leakage current was reduced by optimizing the insulation layer preparation parameters,when the argon oxygen ratio of the growing atmosphere is 90:10,the electrical properties of the PVA base TFT and silicon base TFT are the best.The switching ratio of the transient TFT of the PVA base is 6.8×10⁵,the threshold voltage is 7.0 V,and the subthreshold swing is 0.83 V?dec^-1.Carrier mobility 4.14×10^-2cm²·V^-1·s^-1.The effects of different laminated insulation layer structures on the performance of the transient device were studied.Two kinds of high dielectric constant materials,hafnium oxide（Hf O₂）and alumina（Al₂O₃）,were used to construct the laminated structure.The experimental results show that different Hf O2 and Al2O3 stacked structures can reduce the leakage current,can withstand higher gate voltage,improve the performance of the device,in which the thin film transistor with 40 nm Al₂O₃/80nm Hf O₂/40 nm Al₂O₃"sandwich"structure insulation layer achieves the optimal performance,the off-state current is as low as 5.71×10^-12A,and the subthreshold swing is as low as 0.53 V?dec^-1.The switching ratio can reach 2.5×10⁶and the threshold voltage is 10.6 V.It is proved that the performance of PVA based transient devices deposited with green film materials by low temperature vacuum mask is as good as that of traditional silicon based TFT.The electrical performance of transient devices approach those of conventional hard substrate thin film transistors.