High-Temperature (100 °C) Operating Multi-Bit β-Ga₂O₃ Non-Volatile Memory with InSb Quantum Dots Floating Gate

The rapid development of flash memory technology has significantly advanced data storage systems, addressing the growing demand for higher memory density and faster access times. However, conventional flash memory suffers from critical limitations in high-temperature environments, leading to performance degradation and reduced reliability. This highlights the need for more robust, high-temperature-capable multi-bit memory devices. β-Ga₂O₃ has emerged as a promising candidate for such applications due to its unique properties. With an ultrawide bandgap of approximately 4.9 eV, β-Ga₂O₃ exhibits excellent thermal and chemical stability, making it well-suited for operation in harsh environments. In this work, we present a high-temperature-operating multi-bit non-volatile memory (NVM) device incorporating an InSb colloidal quantum dots (CQDs) floating gate, utilizing the high-temperature resilience of β-Ga₂O₃ and the charge storage capability of In CQDs.
The β-Ga₂O₃ NVM was fabricated by mechanically exfoliating β-Ga₂O₃ flakes and dry-transferring them onto a silicon substrate. Source and drain electrodes were defined using e-beam lithography, followed by Ti/Au deposition. To improve Ohmic contact, the device was annealed at 470 °C for 1 minute. A 10 nm-thick Al₂O₃ tunneling layer was deposited via atomic layer deposition. InSb CQDs were then spin-coated onto the tunneling layer, and hexagonal boron nitride (hBN) was transferred as the gate dielectric. Finally, Ti/Au control gate was deposited.
Flash memory operates through programming and erasing mechanisms, where charge carriers are injected into or removed from the floating gate, leading to changes in the threshold voltage, which defines the stored state. During programming, a positive gate pulse is applied through the control gate, causing electrons from the channel of the β-Ga₂O₃ to tunnel through a thin tunneling oxide layer and accumulate in the floating gate, increasing the threshold voltage. Conversely, erasing involves applying a negative gate pulse, which causes the electrons to move back from the floating gate to the channel, restoring the original threshold voltage.
The resulting β-Ga₂O₃ NVM exhibits a high switching ratio of approximately 10^8, significantly enhancing its potential for multi-bit memory. The adjustable threshold voltage, demonstrated by control gate voltages ranging from 25 V to 50 V, results in a threshold voltage shift from -7.54 V to 16.08 V across 26 discrete steps. This precise control allows the realization of a multi-bit memory capable of storing three bits in a single flash memory cell. To mitigate noise-induced errors commonly observed in multi-bit flash memory devices, 8 distinct states were selected to ensure sufficient separation between states. The triple-level cell (TLC) exhibited excellent retention, maintaining data for up to 5000 seconds. Furthermore, linear extrapolation of the retention characteristics indicates that data can be retained for over 10 years, with each state maintaining at least 20% of its original value. The device also demonstrated strong endurance, withstanding up to 150 program-erase cycles. These excellent memory stability These excellent retention and strong endurance characteristics were further confirmed at 100 °C, underscoring its reliability for high-temperature operation. In addition to electrical pulses, the memory can be erased through infrared light, offering a flexible, non-contact method for memory resetting.
This study presents a β-Ga₂O₃-based NVM device capable of operating at high temperatures with exceptional stability. The device achieves a switching ratio of 10^8, stores three bits per memory cell, and retains data for over 10 years while maintaining at least 20% of its state values. Withstanding up to 150 program-erase cycles and reliable performance at 100°C, this NVM device represents a significant advancement in multi-bit memory technology, particularly for use in extreme environmental conditions.