Oxide-Polymer Heterojunction Diodes with a Nanoscopic Phase-Separated Insulating Layer

1-Selector 1-Memristor Configuration with Multifunctional a-IGZO Memristive Devices Fabricated at Room Temperature

Serving as neuromorphic hardware accelerators, memristors play a crucial role in large-scale neuromorphic computing. Herein, two-terminal memristors utilizing amorphous indium-gallium-zinc oxide (a-IGZO) are fabricated through room-temperature sputtering. The electrical characteristics of these memristors are effectively modulated by varying the oxygen flow during the deposition process. The optimized a-IGZO memristor, fabricated under 3 sccm oxygen flow, presents a 5 × 103 ratio between its high- and low-resistance states, which can be maintained over 1 × 104 s with minimal degradation. Meanwhile, desirable properties such as electroforming-free and self-compliance, crucial for low-energy consumption, are also obtained in the a-IGZO memristor. Moreover, analog conductance switching is observed, demonstrating an interface-type behavior, as evidenced by its device-size-dependent performance. The coexistence of negative differential resistance with analog switching is attributed to the migration of oxygen vacancies and the trapping/detrapping of charges. Furthermore, the device demonstrates optical storage capabilities by exploiting the optical properties of a-IGZO, which can stably operate for up to 50 sweep cycles. Various synaptic functions have been demonstrated, including paired-pulse facilitation and spike-timing-dependent plasticity. These functionalities contribute to a simulated recognition accuracy of 90% for handwritten digits. Importantly, a one-selector one-memristor (1S1M) architecture is successfully constructed at room temperature by integrating a-IGZO memristor on a TaOx-based selector. This architecture exhibits a 107 on/off ratio, demonstrating its potential to suppress sneak currents among adjacent units in a memristor crossbar.

Phase Separation of P3HT/PMMA Blend Film for Forming Semiconducting and Dielectric Layers in Organic Thin-Film Transistors for High-Sensitivity NO2 Detection

Formation of the semiconductor/dielectric double-layered films via vertical phase separations from polymer blends is an effective method to fabricate organic thin-film transistors (OTFTs). Here, we introduce a simple one-step processing method for the vertical phase separation of poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(methyl methacrylate) (PMMA) blends in OTFTs and their applications for high-performance nitrogen dioxide (NO₂) sensors. Compared to the conventional two-step coated OTFT sensors, one-step processed devices exhibit a great enhancement of the responsivity from 116 to 1481% for 30 ppm NO₂ concentration and a limit of detection of ∼0.7 ppb. Studies of the microstructures of the blend films and the electrical properties of the sensors reveal that the devices formed by the one-step vertical phase separation have better capability for the adsorption of NO₂ molecules. Moreover, a careful adjustment of the blend ratio between P3HT and PMMA can further improve the performance of the NO₂ sensors, ranging from sensitivity to selectivity and to the ability of recovery. This simple one-step processing method demonstrates a potential possibility for developing high-performance, low-cost, and large-area OTFT gas sensors.

Nanoscale Visualization and Multiscale Electrochemical Analysis of Conductive Polymer Electrodes

Conductive polymers are exceptionally promising for modular electrochemical applications including chemical sensors, bioelectronics, redox-flow batteries, and photoelectrochemical systems due to considerable synthetic tunability and ease of processing. Despite well-established structural heterogeneity in these systems, conventional macroscopic electroanalytical methods-specifically cyclic voltammetry-are typically used as the primary tool for structure-property elucidation. This work presents an alternative correlative multimicroscopy strategy. Data from laboratory and synchrotron-based microspectroscopies, including conducting-atomic force microscopy and synchrotron nanoscale infrared spectroscopy, are combined with potentiodynamic movies of electrochemical fluxes from scanning electrochemical cell microscopy (SECCM) to reveal the relationship between electrode structure and activity. A model conductive polymer electrode system of tailored heterogeneity is investigated, consisting of phase-segregated domains of poly(3-hexylthiophene) (P3HT) surrounded by contiguous regions of insulating poly(methyl methacrylate) (PMMA), representing an ultramicroelectrode array. Isolated domains of P3HT are shown to retain bulk-like chemical and electronic structure when blended with PMMA and possess approximately equivalent electron-transfer rate constants compared to pure P3HT electrodes. The nanoscale electrochemical data are used to model and predict multiscale electrochemical behavior, revealing that macroscopic cyclic voltammograms should be much more kinetically facile than observed experimentally. This indicates that parasitic resistances rather than redox kinetics play a dominant role in macroscopic measurements in these conductive polymer systems. SECCM further demonstrates that the ambient degradation of the P3HT electroactivity within P3HT/PMMA blends is spatially heterogeneous. This work serves as a roadmap for benchmarking the quality of conductive polymer films as electrodes, emphasizing the importance of nanoscale electrochemical measurements in understanding macroscopic properties.