Research On Optimization Core Architecture And Improvement Performance Of Organic Field-Effect Transistor Memory

Organic field-effect transistors?OFETs?based nonvolatile memories?NVMs?have attractive great attention of semiconductor industry for their many advantages in low-cost,non-destructive reading-out,ultra-high density information storage,good processing compatibility with integrated circuits,large area preparation,and potential application in flexible and wearable electronics.In this work,we focus on two types OFET-NVMs:charge trapping-type OFET-NVMs and polarization-type OFET-NVMs,in which core architecture is closely interrelated to the performances of memories.The research goal is to optimize the core architecture of the memories for improving their quality by material selection,structure design,fabrication process,interface control,operating principle and so on.The results not only show new ideas and methods for improving the quality of memories,but also provide important strategies for practical application.The main research contents and achievements are as follows:1.We synthesized a series of polarizable polymers NPx and used them as the gate dielectrics to build OFET-NVMs.Furthermore,several groups of OFET-NVMs with a double-or multi-layer gate dielectric structure were fabricated to verify the mechanism of the data storage and to improve the retention capability.The memory mechanism originated from the reversible polarization effect of-OH groups in the polymers NPx.More-OH groups in the polymers induced larger reversible remnant polarization,and therefore resulted in larger memory window and higher memory on/off ratio.The problem,that short retention time observed in the OFET-NVMs with a pure NPx gate dielectric,was prominently improved by inserting cross-linked poly?4-vinyl phenol??PVP?and poly?methyl methacrylate??PMMA?blocking layers on both sides of the polymer NPx films to prevent the charge injection and trapping in the polymers NPx at the reading state.High memory performances were achieved in the optimized OFET-NVM with large memory window??V_T?of 33.7 V and memory on/off ratio of1.1×10⁴ on average,good retention capability with clearly distinguishable binary states over 10000 s,and reliable programming/erasing switching endurance over 200 cycles.Our research proposed good strategies for the design on the polarizable polymers as the functional gate dielectrics and the improvement on the performances of OFET-NVM devices.2.We proposed a strategy to fabricate floating-gate based organic field-effect transistor?FG-OFET?nonvolatile memory?NVM?with an integrated floating-gate/tunneling?I-FG/T?layer by synchronously evaporating small molecular semiconductor C₆₀ and long-chain alkane molecule tetratetracontane?TTC?,in which C₆₀ nanoparticles?NPs?were embedded in TTC acting as the floating-gate and the tunneling layer,respectively.The results showed that during their synchronously thermal deposition,C₆₀ and TTC were uniformly mixed and the number of the trapped charges in the floating gate directly depended on the density of C₆₀.After optimizing the thickness and the component of the I-FG/T layer,a high-performance FG-OFET NVM was achieved with a large?V_T of 8.0V on average,stable retention capability over 10 years,and reliable switching endurance over 100 cycles,owing to that the TTC layer prevented the lateral and vertical leakage of the trapped charges between C₆₀ NPs each other and between C₆₀ NPs and the pentacene channel.The device structure breaked the traditional structure design with double gate stack of floating-gate/tunneling layers and simplified the fabrication process of FG-OFET NVMs.3.We reported flexible FG-OFET NVMs based on an I-FG/T layer and a pn-heterojunction organic semiconductor channel layer.By spin-coating,polymer semiconductor poly?9,9-dioctylfluorene-co-benzothiadiazole??F8BT?NPs with a uniform size were uniformly distributed in the insulating polymer polystyrene?PS?to build the I-FG/T layer.The dependence of the memory performances on the structure of I-FG/T layer was researched.For achieving a large charge storage capacity,the pn-heterojunctionchannel,consistingof2,9-didecyldinaphtho[2,3-b:20,30-f]thieno[3,2-b]thiophene(C₁₀-DNTT)and F₁₆CuPc,was fabricated to provide both electrons and holes for injecting and trapping in the floating gate by overwriting the stored charges with an opposite polarity at the programming and erasing voltages,respectively.As an optimal result,a high performance flexible FG-OFET NVM was achieved,with a large?V_T of 21.6 V on average,a highly stable charge storage retention capability up to 10 years,and a highly reliable programming/erasing switching endurance over 200 cycles.The FG-OFET NVM also exhibited an excellent mechanical bending durability with the memory performances maintaining well over 6000 bending cycles at a bending radius of 5.9mm.The research results provided theoretical basis and technical support for further improving the performance of FG-OFET NVMs and developing new flexible memories technology.4.We demonstrated FG-OFET NVMs with an I-FG/T layer consisting of F8BT and PS.The photoelectric effect of organic/polymer semiconductors was used to improve the controllability on the polarity and amount of the charges stored in the floating-gate.The FG-OFET NVMs integrated light sensitivity and nonvolatile information storage functions.By selecting reasonable optical and electrical programming/erasing conditions,ternary storage states were achieved and freely switched each other.The memory mechanism and the dependence of the memory performances on the F8BT contents in I-FG/T layer were investigated.As a result,good memory performances,with mobility larger than 1.0 cm²/Vs,reliable ternary switching endurance over 100 cycles and stable ternary retention capability over 10years,were achieved in our memory.Furthermore,an imaging system with a nonvolatile information storage function was demonstrated in a 16×5 array of FG-OFET NVMs.Our research work was expected to develop a new type of photosensitive sensor array with information storage function or information storage unit with optical sensing function.