With the widespread adoption of the Internet of Things, artificial intelligence, and big data analytics technologies, modern information systems are experiencing an exponential increase in demand for data storage capacity and processing speed. To address the "memory wall" problem caused by the data transfer bottleneck between the central processing unit and volatile main memory, the industry has proposed innovative architectures such as near-memory computing and in-memory computing, which impose more stringent requirements for high speed and low power consumption in non-volatile memory technologies. Due to the significant latency gap between existing volatile main memory and traditional non-volatile storage media, not only is system response speed limited, but considerable energy waste also occurs. Therefore, developing a novel memory solution that achieves nanosecond-scale read/write speeds, exhibits excellent reliability, and is deeply compatible with complementary metal-oxide-semiconductor processes has become a research focus in the semiconductor field.

Although various emerging non-volatile memory technologies are under active research, they still face performance bottlenecks and technical challenges that are difficult to overcome simultaneously in practical applications. Magnetoresistive random-access memory is limited by the power consumption and scaling difficulties associated with high write currents. Ferroelectric random-access memory suffers from destructive readout and insufficient endurance. Phase-change memory requires extremely high currents to melt the material during state switching, while redox-based resistive random-access memory typically relies on complex forming processes and suffers from poor read/write consistency due to the randomness of conductive filament formation. Even more problematic is that these mainstream emerging memory technologies generally experience severe performance degradation under extreme environments such as high temperatures, severely limiting their application prospects in high-standard scenarios such as industrial control and aerospace.

To address the above issues, a team from the National University of Singapore, Zhejiang University, and other institutions conducted systematic research using ZEPTOOLS' in-situ TEM measurement system. By utilizing electric-field-induced reversible phase transition between wurtzite and rocksalt structures in aluminum scandium nitride thin films, they successfully developed a novel non-volatile memory featuring nanosecond switching speed, ultra-low operating voltage, and excellent high-temperature stability.

Title: A nitride-based non-volatile memory enabled by electric-field-induced phase transition
Journal: Nature Materials
URL: doi.org/10.1038/s41563-024

This study developed an electric-field-induced phase transition memory based on aluminum scandium nitride material, termed EPTRAM, providing a new pathway to overcome the power consumption and endurance bottlenecks of traditional non-volatile memories. The researchers discovered that by precisely adjusting the scandium doping ratio in aluminum scandium nitride alloys, a reversible transition from the high-resistance wurtzite phase to the high-conductivity rocksalt phase can be achieved in nanoscale thin films. This novel mechanism does not rely on the random and unstable conductive filaments in conventional resistive random-access memories, nor does it require the high-current Joule heating needed for phase-change memory, thereby fundamentally avoiding the reliability issues associated with structural fluctuations and laying a solid physical foundation for constructing high-uniformity memory arrays.

In electrical performance evaluation, this device exhibited outstanding comprehensive metrics, particularly achieving significant breakthroughs in ultra-low voltage operation and extreme environmental adaptability. Experimental data show that the memory can switch states at an ultra-low voltage below 0.3 V, with a write speed of less than 3 nanoseconds and extremely low energy consumption per bit, outperforming the vast majority of reported similar technologies. Even more groundbreaking, the device operates stably at high temperatures up to 583 K, with a write endurance exceeding 100 million cycles—a figure two orders of magnitude higher than that of current mainstream emerging non-volatile memories. This fully demonstrates its tremendous application potential in harsh environments such as aerospace and industrial electronics.

To analyze this physical process at the atomic scale, the research team used in-situ scanning transmission electron microscopy to observe the phase transition region in real time. During this process, the in-situ sample holder developed and manufactured by ZEPTOOLS played a key role, providing stable electrical excitation to the nanoscale thin film while synchronously collecting high-precision current-voltage data inside the transmission electron microscope. With the precise control enabled by this instrument, the researchers directly observed the dynamic evolution of the wurtzite-to-rocksalt phase transition under electric field driving, ruling out the dominant influence of Joule heating or mechanical stress, and confirming that nitrogen ion migration-induced phase transition is the core scientific principle enabling non-volatile memory. This provides new evidence for understanding the physical properties of group-III nitrides.

Addressing the practical requirements for future large-scale integration, this study further explored the scaling effect of the device and its compatibility with mainstream semiconductor processes. Through finite element simulations and experimental validation, the study showed that when the device feature size is reduced to the nanometer scale, the enhancement of the local electric field actually improves the phase transition efficiency, indicating excellent scaling potential. Furthermore, the team successfully constructed a CMOS-compatible one-transistor-one-resistor (1T1R) architecture, effectively addressing the sneak current issue in memory arrays, and providing a practical technology roadmap for translating this electric-field-induced phase transition technology into a high-performance, high-density universal memory system.

ZEPTOOLS, as a Chinese high-end precision instrument company, is a leading supplier of in-situ electron microscopy characterization solutions. The PicoFemto series of in-situ transmission electron microscopy characterization solutions have successively provided technical support for major research achievements of users both domestically and internationally. The figure below shows the ZEPTOOLS in-situ TEM sample holder product used in this research achievement: