Inspired by the human brain, neuromorphic computing and artificial synaptic devices offer significant advantages including low power consumption, high speed, and in-memory computing. However, conventional oxide-based resistive switching memories face severe stability challenges under extreme conditions such as high temperatures. Diamond, with its ultra-wide bandgap, exceptional thermal conductivity, and outstanding chemical stability, is recognized as an ideal semiconductor material for developing extreme-environment electronics. Current explorations of diamond-based synaptic devices primarily rely on photoelectric effects, heterojunction barrier modulation, or doping modification strategies to achieve resistive switching characteristics.

However, the inherently high chemical stability and difficulty in modulating the electrical conductivity of diamond greatly limit the realization of its purely electrically driven resistive switching behavior. Currently reported diamond devices generally suffer from bottlenecks such as low resistive switching on/off ratios, limited endurance, and insufficient long-term retention characteristics. How to construct reliable conductive pathways and achieve efficient non-volatile electrical resistive switching modulation without sacrificing the material's intrinsic stability has become a core challenge restricting the practical application of diamond-based memristors.

To address the above issues, a joint team led by Zhengzhou University and others conducted in-depth research using ZEPTOOLS' in situ TEM measurement system. The team innovatively utilized metal-diamond interfacial reactions at grain boundaries to construct vertical ion migration channels, successfully developing a high-performance non-volatile diamond memristor that operates stably over a wide temperature range from -150°C to 600°C, and achieving simulations of artificial synaptic and biological pain perception functions.

Title: Grain Boundary Enabled Diamond Memristor 
Journal: Advanced Materials 
URL: http://dx.doi.org/10.1002/adma.74418

To address the inherent bottleneck that the electrical conductivity of diamond is extremely difficult to directly modulate via electrical bias, the research team proposed a material design strategy based on grain boundary engineering to construct vertical ion migration channels. The researchers employed chemical vapor deposition to grow polycrystalline diamond films rich in grain boundaries on silicon substrates, and utilized the catalytic reaction characteristics of transition metal nickel at diamond interfaces at elevated temperatures to induce selective etching at grain boundary defects through metal deposition and thermal treatment. After removing the residual catalytic metal, vertical nanochannels penetrating along the grain boundaries were successfully constructed inside the diamond film, providing low-resistance pathways for directional migration of active metal ions while fully preserving the diamond crystal framework and thermal properties.

In the critical step of elucidating the microscopic physical mechanism of the device's electrically induced resistive switching, the research team utilized ZEPTOOLS' transmission electron microscope in situ sample holder to conduct systematic and in-depth in situ studies. By applying electrical stimulation in real time within the microscope system and synchronously recording the microstructural evolution, the researchers directly captured the dynamic structural changes of the device during the set and reset processes. Microscopic morphology and elemental energy spectrum analysis clearly confirmed that the non-volatile switching characteristics of this diamond memristor originate from the reversible migration of silver electrode ions along the pre-fabricated grain boundary channels—namely, the periodic formation and rupture of silver conductive filaments—thereby conclusively verifying the conductive mechanism of the resistive switching channels at the microscale.

Based on this grain boundary ion channel architecture, the fabricated diamond memristor devices demonstrated excellent electrical performance and groundbreaking wide-temperature-range operational capability. The devices exhibited a high resistive switching on/off ratio of approximately 10⁴, highly concentrated operating voltage distributions, and excellent batch-to-batch consistency. Particularly notably, the devices maintained robust non-volatile bipolar resistive switching characteristics across a harsh wide temperature range from -150°C to 600°C. After 10⁴ seconds of data retention testing and 5,000 consecutive pulsed write/erase cycles at 600°C, they still maintained a memory window exceeding 10³, significantly advancing the reliability boundaries of memristor devices in extreme high-temperature environments.

Leveraging the controllability of conductive filament dynamics, this diamond memristor successfully achieved hardware-level functional emulation of biological neural synaptic plasticity and nociceptor behavior. The device not only accurately reproduced typical synaptic learning mechanisms including paired-pulse facilitation, long-term potentiation and depression, and spike-timing-dependent plasticity, but also realistically simulated the threshold response, non-adaptation characteristics, and pathological states such as tactile allodynia and hyperalgesia resulting from tissue damage in biological pain systems. This work fully validates the potential of diamond-based memristors for in-memory computing and intelligent sensing under complex extreme operating conditions, laying a device foundation for extreme-environment-resistant neuromorphic computing systems targeting frontier applications such as deep-earth drilling and aerospace.

ZEPTOOLS, as a Chinese domestic high-end precision instrument company, is a first-class supplier of in situ electron microscopy characterization solutions. Its PicoFemto series of in situ transmission electron microscopy characterization solutions have successively provided technical support for significant research outcomes of both domestic and international users. The following image shows the ZEPTOOLS in situ TEM sample holder product used in this research: