Research On The Mechanism And Application Of Low-Voltage Organic Phototransistor Memory Based On Gate Dielectric Ta₂O₅

Organic phototransistor memory?OPTM?integrates field-effect,photosensitivity and memory effect into one single device.Owing to the advantages of easily integrated structure and the fabrication of flexible,multibit and high-density devices,OPTM has attracted growing interest.However,the understanding of the mechanism,the improvement of OPTM performances and the exploration of the application are essential.Therefore,we occupied tantalum pentaoxide?Ta₂O₅?as the gate dielectric layer since its high dielectric constent was favorable for low operating voltage.The Ta₂O₅ film processed by reactive sputtering was not stoichiometric.Adjusting the proportion of O and Ta in the dielectric film could enhance the performance of OPTM.Based on the OPTM with the best performance,we researched on the key issure – what the charge transport process was at the interface between dielectric layer and organic semiconductor,and explored some applications.The main contents and efforts were as follows:1.Increasing the oxygen content from 10% to 30 then to 50% during the reactive sputtering process,the OPTM performances were improved.On one hand,due to the increasing grain size of pentacene and the decrease of the contact resistance between pentacene and the source and drain electrodes,the carrier density in the conduct channel increased.On the other hand,the results of ionization energy of the dielectric layer,the interface states and the interface potential difference demonstrated that the increase of the ratio of O and Ta lead to the increase of charge traps.The change of the crystal structure of the dielectric layer gave rise to the increased charge traps,and the dangling bonds and Ta-OH were charge traps at the interface between the dielectric layer and pentacene.2.Energy level alignment between dielectric layer and organic semiconductor was utilized to tune the charge transport process at the interface.The lowest unoccupied molecular orbital?LUMO?energy of PVP matched much better with that of pentacene than that of PMMA with pentacene,facilitating the electron injection process from pentacene to Ta₂O₅.As a result,the performance of the PVP modified device is better than the PMMA modified device.Furthermore,the additional electric field made the energy level of the interface modification layer lower and thinner,which made it possible for charge transport.By tuning the additional electric field and the thickness of the modified layer,the charge transport at the interface between the dielectric layer and pentacene could be successfully adjusted.3.Ta 4f peaks of XPS depth profile of Ta₂O₅ film treated by UV/ozone demonstrate that UV/ozone treatment changed the oxidation state of Ta in the 1.8 nm ultrathin film.The charge transport process could be tuned because the radicals,dangling bonds and Ta-OH could be cured by UV/ozone treatment.Moreover,the trap density could be enhanced when the Ta floating gate was introduced in the OPTM device.As a result,the charge transport process could be adjusted.The control of charge transport at the interface enhanced the device performances.And the highest mobility,photoresponsivity and retention time could reach 0.47 cm2 V-1 s-1,3.52 A W-1 and 2 × 105 s,respectively.4.The stability of OPTM devices was studied.And we explored three kinds of applications.The first is applying OPTM in organic opto-coupler.The second is using OPTM to automatically tune the brightness of OLED.And the third is using OPTM to drive OLED.OPTM has a wide application prospect since it combines light with electronic.