Design And Synthesis Of Single-Component Organic Charge Trapping Molecules And High-Performance Organic Filed-Effect Transistor Memory Study

The non-volatile memory based on the organic field effect transistor?OFET?structure not only has the characteristics of single-transistor realization,nondestructive reading,fast writing speed and large memory capacity,but also has the advantages of low cost,large area solution processing,and high compatibility with flexible substrates and current CMOS circuits.It is expected to become a mainstream alternative to next-generation memory,and show broad application prospects in memory chips,flexible integrated circuits,artificial intelligence,etc.The charge trapping materials of OFET memory can effectively trap and stabilize charge with a simple device fabrication,which have became the mainstream of the field effect transistor device research.However,the relationship between molecular structure,condensed state,device performance parameters and storage mechanism are not clear.It is still a challenge to develop a new single-component small-molecule charge trapping element?CTE?to improve storage density and stability.Therefore,it is of great significance to design a model system to study the molecular structure and the photoelectric characteristics of organic thin film condensed matter,and deeply study the structure-activity relationship between molecules and device performance.This dissertation focus on the single-component organic small-molecule CTEs,detail study the molecular design of single-component small-molecule CTEs in tunneling dielectric layer?TDL?-free device structure.The main research contents are as follows:1.To achieve efficient small-molecule CTEs,three diazafluorene derivatives TPA?PDAF?_n?n=1,2,3?serving as CTEs were designed and synthesized.With highly nonplanar topological configuration,TPA?PDAF?₃ showed weaker intermolecular interaction in the solid state and thus exhibited single nano-molecular behavior.Furthermore,diazafluorene derivatives process completely separate of HOMO/LUMO which offer ideal hole and electron trapping sites.As CTE,triphenylamine groups provide the hole trapping sites,while diazafluorene units not only provide the electron trapping sites but also act as hole blocking group to restrain the leakage of stored hole trapped in triphenylamine.The pentacene-based OFET memory device based on TPA?PDAF?₃ showed a high charge trapping density(4.55×10¹² cm^-2),a fast saturation programming speed?<20 ms?,a large memory window?89 V?,and a tunable ambipolar memory behavior.Optimized device?10 wt%blend with polystyrene?showed a large ON/OFF ratio?2.85×10⁷?,good charge retention?>10⁴ s?and reliable endurance property.The novel CTEs design of trapping core attached with diazafluorene is a promising candidate for high performance OFET memory.2.The grid-effect of conjugated small molecules was proposed,and a series of small-molecule materials based on diarylfluorene were designed and synthesized.The closed-loop nanogrid exhibits rigid molecular conformation and nano-scale pore structure with good solubility and film formation.Combined with theoretical calculations,the optical,electrical and thermal properties,film morphology and energy band engineering of the molecules were systematically studied.Grid has better thermal,electrochemical and morphological stability than its uncyclized counterparts.Grid maintained a wide bandgap and separated HOMO/LUMO levels,and showed weaker intermolecular interaction in solid state and thus exhibited discrete molecular trapping centers for charge stored and restained.3.The nanogrid based TDL-free OFET memory was fabricated by using the processability and excellent photoelectric properties of grid.And the structure-activity relationship between molecular structure and device performance was successfully explained.Owning to the unique closured and 3-dimensional topological structure,remarkable memory performances including 8-level?3 bit?memory capacity,fast writing speed?down to ns?and ultrastable non-volatility?up to 100 years?can be realized simultaneously in a 20 nm ultrathin grid film but without additional tunneling layer.The new CTE combines high capacity,fast programming,long-term non-volatility and significant scalability,providing research ideas for the rational design of emerging organic storage media.4.In order to explain the charge trapping mechanism of grid memory,we studied the dielectric properties of material films from the perspective of physical mechanism,and revealed the basic principles of memory window and memory efficiency.The charge trapping kinetics of the films was studied by Kelvin probe force microscopy.The charge confinement ability of the memory film was studied,and the the long-term stability of the stored charge in grid film was explained.The frontier molecular orbitals,electrostatic potential,ionization potential,electron affinity,dipole moment and molecular cohesive energy density were studied by theoretical calculations.The location and high stability of charge storage in the molecule were explained from the perspective of molecular structure and energy.A reasonable charge storage mechanism based on grid memory is proposed.Furthermore,we applied grid to flexible memory devices,which proved that the grid based flexible memory has excellent mechanical durability against bending strain and maintains good performance after 1500bending cycles.Finally,the thermal stability of the device at 120°C was verified.Grid memory finds a balance between high memory capacity,fast writing speed and non-volatility,solving the problem of fast writing and stable retention in OFET memory.5.The modular synthesis of grid can realize the introduction of functional groups and the precise regulation of the nano-pore size.Two kinds of D-A type nanogrids were designed and synthesized by introducing benzothiadiazole?BT?groups into nanogrids to adjust the energetics of the HOMO/LUMO levels to match the electronics.The photosensitive OFET memory based on the D-A type nanogrids realized the control of the memory switch by electricity and light independently,and the device obtained large memory windows and fast response speed,stable retention time and endurance.The D-A type nanogrid based two-terminal memristor successfully realizes conventional learning processes,synaptic potentiation,and depression plasticity,which are essential for neuromorphic computation.