ReRAM NVM Shines, Even in In High-Rad Applications
June 22, 2023
Saying that non-volatile memory (NVM) is ubiquitous is an understatement. From our consumer devices to industrial and medical/healthcare applications, even in our cars, NVM is omnipresent. It’s used to store the operating system, the program files, our pictures, videos, and other data. In environments with high levels of radiation, such as aerospace and medical devices, selecting the right NVM can be a key consideration since radiation can impact the operation of many technologies.
However, flash memory has its limitations in terms of speed, power, cost, and endurance, meaning that there are both economic and technical challenges designers face when embedding flash memory into SoCs. Hence, designers continue to be on the lookout for NVM alternatives, particularly for SoCs in high-radiation applications, where embedding flash memory requires added complexity and redundancy.
Flash memory is highly sensitive to radiation due to its reliance on electrical charge storage. Radiation can affect flash memory through cumulative exposure, displacement damage, or single event effects. The damage caused can range from state flipping to permanent alteration of atomic structure. This issue worsens with smaller process geometries.
Further complicating matters, using flash memory in high-radiation environments complicates the design process, as designers need to incorporate error correction code (ECC) and redundancy to ensure continued operation, leading to increased size, cost, and latency.
Help Is Here
New memory technologies, such as ReRAM, are helping to overcome some of these challenges, including sensitivity to radiation. ReRAM, which stands for Resistive Random Access Memory, is not affected by ionizing radiation, because there is no direct interaction between radiation and the storage mechanism. ReRAM is just starting to become a mainstream technology, offering radiation tolerant alternatives to conventional flash memory.
Shown is the Weebit Nano ReRAM module embedded into a RISC-V-based SoC.
Weebit Nano, a developer of advanced semiconductor memory technology, and the Nino Research Group (NRG) in the University of Florida’s Department of Materials Science and Engineering are studying the effects of radiation on Weebit Nano’s ReRAM technology under various conditions. Results confirm that the ReRAM arrays are tolerant to high levels of radiation and can retain data integrity and memory functionality after being subjected to high doses of gamma irradiation.
Without going into painstaking detail here, the results of the study conclusively show that all the distribution properties in both the high resistive state (HRS) and the low resistive state (LRS) were preserved. Thus, the researchers confirmed that after irradiation at high doses, the Weebit Nano ReRAM technology was able to preserve the information and can be fully reprogrammed.
For this study, only 16-kbit arrays were characterized. In the next round, the researchers will extend the irradiation experiments to include the type of radiation sources that cover the entire spectrum of radiation environments that may be encountered in typical medical and aerospace applications.
These initial studies are just the starting point for investigations into the radiation tolerance of Weebit Nano’s ReRAM. The Weebit Nano ReRAM modules will also be included in future irradiation experiments, allowing an extensive characterization of the company’s technology for rad-hard applications. Following that, an in-situ test set-up will be built at the University of Florida Training Reactor (UFTR) facility. The goal of this latter phase is to gain a deeper understanding of the memory behavior when operating under radiation environments in real time.
*Note that the full study is explained in detail in the whitepaper Design Considerations for Embedded NVM in High- Radiation Applications.