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A comparison of atomic layer deposited Al₂O₃on PVDF-based copolymers in polymer transistors shows a significant improvement in the subthreshold swing for PVDF-HFP devices compared with PVDF-TrFE. Al₂O₃passivates the interfacial traps. 

Abstract Combined with polymer ferroelectric dielectrics, organic field‐effect transistors are promising candidates for both electrical and photonic synapses to emulate important functions of biological synapses. In this work two distinct copolymers of poly (vinylidene fluoride) (PVDF) with trifluoroethylene and hexafluoropropylene, PVDF‐TrFE and PVDF‐HFP, respectively, are utilized as ferroelectric dielectrics due to their polarization control and non‐volatile polarization hysteresis. Using a donor–acceptor copolymer as the semiconductor layer, bottom‐gate, top‐contact transistors are fabricated with externally poled and unpoled films of PVDF‐TrFE and PVDF‐HFP where the operating voltages are less than 10 V. On average, poled PVDF‐TrFE FETs show improved characteristics with carrier mobilities > 1 cm²V⁻¹s⁻¹. The individual transistors are evaluated in a system level network for image recognition. The synaptic response of these devices is quantified using key metrics such as the dynamic range and nonlinearity of the analog channel conductance modulation, which are then employed to simulate the neural network behavior. The accuracy of the network in recognizing a set of handwritten digits is used to assess the effectiveness of these devices in neuromorphic architectures. The results are analyzed in terms of the poling condition of the ferroelectric dielectric, the margin of conductance modulation, and the nonlinear weight updates. 

While electrical poling of organic ferroelectrics has been shown to improve device properties, there are challenges in visualizing accompanying structural changes. We observe poling induced changes in ferroelectric domains by applying differential phase contrast (DPC) imaging in the scanning transmission electron microscope, a method that has been used to observe spatial distributions of electromagnetic fields at the atomic scale. In this work, we obtain DPC images from unpoled and electrically poled polyvinylidene fluoride trifluorethylene films and compare their performance in polymer thin film transistors. The vertically poled films show uniform domains throughout the bulk compared to the unpoled film with a significantly higher magnitude of the overall polarization. Thin film transistors comprising a donor–acceptor copolymer as the active semiconductor layer show improved performance with the vertically poled ferroelectric dielectric film compared with the unpoled ferroelectric dielectric film. A poling field of 80–100 MV/m for the dielectric layer yields the best performing transistors; higher than 100 MV/m is seen to degrade the transistor performance. The results are consistent with a reduction in deleterious charge carrier scattering from ferroelectric domain boundaries or interfacial dipoles arising from electrical poling. 

Abstract Reducing the Schottky barrier height and Fermi level de‐pinning in metal‐organic semiconductor contacts are crucial for enhancing the performance of organic transistors. The reduction of the Schottky barrier height in bottom‐contact top‐gate organic transistors is demonstrated by adding 1 nm thick atomic layer deposited Al₂O₃on the source and drain contacts. By using two different donor‐acceptor copolymers, bothp‐andn‐type transistors are investigated. Temperature‐dependent current–voltage measurements from non‐treated, self‐assembled monolayer treated, and Al₂O₃treated Au source‐drain contact field‐effect transistors with varying channel lengths are carried out. The drain current versus drain voltage near zero gate voltage, which may be described by the thermionic emission model at temperatures above 150 K, allows the estimation of the Schottky barrier height (φ_B). The Al₂O₃contact‐treated transistors show more than 40% lowerφ_Bcompared with the non‐treated contacts in thep‐type transistor. Similarly, an isoindigo‐based transistor, withn‐type transport, shows a reduction inφ_Bwith Al₂O₃treated contacts suggesting that such ultrathin oxide layers provide a universal method for reducing the barrier height.