Solution-Processed Wide-Bandgap Organic Semiconductor For Nonvolatile Organic Field-Effect Transistor Memory

Nonvolatile organic field-effect transistor(OFET)memory devices have attracted extensive attention due to their advantages of simple preparation process,low cost,strong design,nondestructive read-out,easily integrated structure with flexible substrate and multibit storage in a single device.However,the performance(storage density,storage stability)of OFET memories at this stage is still inferior to those of commercial memories,which limited their practical applications.The charge storage layer is a key element in the OFET memory to control storage performance,which directly affects the charge trapping and release process in the OFET memory.Therefore,the design and manufacture of high-efficiency charge storage layer to achieve high-performance OFET memory is of great significance.In recent years,small molecule materials have attracted extensive attention due to the advantages of easy purification,no-batch-batch variation,well-defined molecular and electronic structure,and can be widely concerned according to the needs of electronic structure and energy band design.However,most of the research is based on organic small molecule semiconductors,the storage density is low and the charge leakage is serious.While small-molecule wide-bandgap semiconductors can be well preserved due to their wide-band gap between LUMO and HOMO,so the small-molecule wide-band gap semiconductor is a potential important novel candidate for charge storage layer of OFET memoriesThe first part of this thesis,small-molecule wide-bandgap semiconductors windmill-like grids with different pore size is prepared by Friedel–Crafts reaction,and their charge trapping ability is explored.The device shows a stable ambipolar memory properties with a large memory window as 55 V,excellent retention time more than 104 s with a high ON/OFF current ratio of 102 and 103,respectively,and a stable reversibility.In addition,more charge trapping sites are provided due to the pore structure of the organic windmill-like grids,which can efficiently capture and store the charge.The second part of this thesis,the WG3 were successfully processed into the different size,uniform distribution,large-area and highly ordered nanocolumns by spin-coating the blend solution of WG3/TMP,and studies the effect of nanocolumns structure on the storage performance.The device shows high density,high speed storage properties with a large memory window as 44.8 V,excellent retention time more than 104 s with a high ON/OFF current ratio of 105,and a stable reversibility.In addition,we quantitatively studied the relationship between the storage window and the contact area using matlab simulation method,and found that the storage window is strongly dependent on the contact area.So our research provides a new strategy to achieve high performance nonvolatile OFET memory.The third part of this thesis studies the OFET memory devices based on Si/SiO2/WG3/P13/Pentacene/Cu structure.The device shows a stable ambipolar memory properties with a large storage window about 55.33 V,and stable reversibility over 200 cycles without decay.In addition,we studied the effect of thickness effect on the storage performance of OFET memory devices.As the thickness of P13 decreases,the storage window decreases and the storage stability increases(the electronic storage time and hole storage time can be maintained at more than 5000 seconds with high ON/OFF-current ratio 102).So we have provided a new strategy to achieve high performance nonvolatile heterojunction OFET memory.