Effect of Thermal Annealing on Charge Trapping Characteristics and Synaptic Plasticity in Sol-Gel AlO_x-Based Floating Gate Devices

The advancement of high-performance organic floating gate memory and synaptic devices represents a significant breakthrough in the field of electronics. These devices hold considerable promise for transforming data storage and processing, especially in applications that require low power consumption and flexibility with various substrates. Realizing such high performance necessitates an efficient charge-trapping medium that can effectively capture and retain charge carriers, which is crucial for information storage and processing. Multiple candidates have been proposed for the charge-trapping layer.<br/>Our investigation employed a simple, cost-effective solution-processed sol-gel aluminum oxide (AlO_x) as the charge trap layer. We analyzed the properties of sol-gel AlO_x thin films at different annealing conditions (Pristine, 100 °C, 200 °C, 300 °C, 400 °C, 500 °C) utilizing X-ray diffraction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). With the increase in annealing temperatures, it becomes apparent that the sol-gel AlO_x thin film undergoes the decomposition of organic residues and nitrate groups and the transformation of aluminum hydroxide into aluminum oxide.^[1] At lower annealing temperatures, the organic floating gate device exhibited a wider hysteresis window (ΔV_th) and charge trap density (<i>n</i>), which became negligible at elevated temperatures, suggesting that the hysteresis window is influenced by hydroxyl groups.<br/>Furthermore, we examined the potential of enhancing the synaptic behavior of the device by employing a solution-processed sol-gel AlO_x-based floating gate transistor. The synaptic weight stored in the channel conductance of the floating gate transistor is modulated by the positive and negative electrical pulse stimuli and the annealing temperature of the sol-gel AlO_x thin film layer. We examined essential characteristics of long-term potentiation (LTP) and long-term depression (LTD), including dynamic range (DR) and nonlinearity (NL), which play a significant role in the adaptive learning and decision-making capabilities of synaptic devices. ^[2] Devices annealed at 200 °C demonstrated favorable nonlinearity (NL) and dynamic range (DR) compared to those annealed at other temperatures.