Study On The Organic Field-effect Transistor Memory Enhanced By The N-type Semiconductor Interlayer

Organic electronic devices show great prospects in various fields such as integrated electronics,flexible displays,and organic sensors,owning to the advantages of light weight,flexible and large-area fabrication.In order to promote the practical application of the organic field effect transistors（OFETs）,great efforts have been made in developing OFETs,and a lot of progresses have been achieved in the OFET memory devices.However,the present performance of pentacene OFET memory devices is still far from reaching the industrial requirements of commercial application.In this thesis,we focus on the fabrication of high performance OFET memory devices to provide our solutions to the related issues,and design several OFET memory structures in which n-type semiconductor layer was introduced as an interlayer,and the electrical characteristics of the OFET memory devices were also studied.The main achievements are as followed:1.The positively charged defects in pentacene film at the interface between pentacene and polymer result in unacceptable high programming/erasing（P/E）gate voltages in pentacene OFET memory devices.In view of this,we propose an OFET memory structure with an n-type organic semiconductor layer at pentacene/polymer interface.In this structure,electrons are induced on the surface of n-type organic layer near the interface due to the electrostatic field of the positively charged insulator,and partly compensate the local positive charges at the interface,leading to the reduction of the height of hole-barrier formed at the interface.On the other hand,the positive space charges will be induced in an extended region in n-type organic layer due to the limited density of ionized donors,blocking the back transfer of holes to pentacene as a result of the thicker positively charged layer.This idea is implemented in an OFET structure Cu/pentacene/PTCDI-C₁₃/PVN/SiO₂/Si（p⁺）,in which the greatly reduced P/E gate voltages(±35 V/10^-3 s),reliable P/E endurance of more than 10⁴ cycles,and excellent retention time of more than 10⁴ s with an I_ON/I_OFF of more than 10⁴ under a set of P/E pulses with low amplitudes and short pulses were achieved in air.2.To increase the the low field-effect mobility caused by the high surface roughness of the n-type organic semiconductor film,we report a pentacene OFET in which an n-type semiconductor layer was intercalated between polymer and the blocking insulator.In this structure the hole-barrier caused by the defect layer can be adjusted by the thickness and charge-carrier density of n-type semiconductor interlayer based on the electrostatic induction theory.At the same time,this structure enables pentacene to grow on the polymer directly,which ensures the field-effect mobility of the device.This idea was implemented in an OFET structure Cu/pentacene/PVN/ZnO/SiO₂/Si（p⁺）,which shows low P/E gate voltages(±30 V/5×10^-4 s),large field-effect mobility(0.73 cm² V^-1s^-1),and long retention time in air.3.Due to the fact that pentacene OFET also suffers from the thicker blocking layer,which results in the high operation gate-voltage,we fabricateed a pentacene OFET with a structure of Cu/pentacene/PS/Al₂O₃/ZnTe/Al₂O₃/Si(n⁺⁺),in which high-k dielectric Al₂O₃ and n-type semiconductor ZnTe serve as the blocking layer and interlayer,respectively.The electrical measurements as measured indicated the further reduced operation voltage for the OFET,which shows a memory window of 10 V at an applied sweeping gate-voltage of±15 V,a high I_ON/I_OFF ratio of more than 10⁶,and a good retention property with a high I_ON/I_OFF ratio of 6×10⁵ after 10⁴ s.