UV Photodetection Based On Organic Field-Effect Transistors

Recently,photodetectors based on OFET structure have attracted considerable attention.Normally,we utilize photoactive layer to realize photodetection.Compared with commercial photodiodes,detectors based on OFET structure have their unique properties,such as low cost,light weight,compatible with flexible substrates,effectively modulating the light-dark current ratio.In addition,photodetectors based on OFET structure also have many potential photoelectric applications,such as photo switch,image sensor and UV radiation exposure dosimeter.In the field of memory,OFET nonvolatile memory will be extremely important components of future integrated circuits owing to its merits of nondestructive reading,reliable data storage and compatibility with logic circuits.Combining the advantages of photodetection and nonvolatile memory storage of OFET,we integrate them into a single device and fabricate the devices equipped with virtues above for application of dosimeter and image sensor in the future.Meanwhile,we have also realized multibit memory with light-assisted programing,and main contents include two parts:Firstly:Study on solar-blind UV photodetection.It refers to be sensitive to the spectra from 200 nm to 280 nm,has a wide range of applications in diverse fields of civil and military,including missile warning,environmental monitoring,chemical/biological analysis and UV astronomy.Because long time solar-blind UV radiation exposure is harmful to personal health,UV dose monitoring is of great importance as well,as it is not only helpful for monitoring ozone depletion but.also provide important information for personal UV radiation protection and health risk prevention.In this work,we fabricated the pentacene-based phototransistor which utilizing the heavily-doped Si wafer with 100 nm thick SiO2 as substrate and PVN as charge storage layer.It is evident that there is no memory effect when the OFET works in dark,and upon illumination of either visible light or the UV light of 365 nm.In contrast,interestingly,upon illumination of the UV light of 254 nm,a large memory window emerges.On the other hand,similar device behaviors are present for the PTCDI-C13H27-based phototransistor.Generally in photodetectors,the photocurrent recovers after turning off the incident light.However,we found the photocurrent can be maintained after removing the light source.To verify the nonvolatile memory effect of the devices,we test the retention characteristics of both P-type and N-type OFET devices.The results show both of them possess excellent retention capability over 10000 s and stable programming/reading/erasing/reading(P/R/E/R)endurance over 100 cycles.In addition,we also research the relationship between trapped charge and UV exposure energy.In order to clarify the phenomenon that the devices are selectively sensitive to 254 nm UV light,we modulate the gate bias and change the light intensity and proposed a potential model about interfacial excitation.Furthermore,due to its good compatibility with flexible substrate,we also successfully fabricated the P-type flexible solar-blind UV detector.Secondly:Study on multi-bit memory.In this paper,we utilize the OFET structure where PVN is used as charge storage layer and pentacene is used as photoactive layer.By controlling the 254 nm UV illumination pulse time at a certain gate bias to modulate the number of injection electrons,different memory states were obtained.Meanwhile,we test the retention and programming/reading/erasing/reading(P/R/E/R)endurance,the result showed all state can possess the excellent retention and programming/reading/erasing/reading(P/R/E/R)endurance.Notably,switch between different states can be controllable.This paper figures out the mechanism of selectively sensing for solar-blind UV detector based on organic field-effect transistor,and we have realized the prototype devices of UV dosimeter and multi-bit memory.Its experimental results can provide important information for applications of high-performance flexible UV dosimeter and multibit memory in the future.