Systems and methods for improving radiation tolerance of memory
Inventors
Ray, Biswajit • Milenkovic, Aleksandar
Assignees
University of Alabama in Huntsville
Publication Number
US-11762563-B1
Publication Date
2023-09-19
Expiration Date
2041-08-04
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Abstract
A system for improving radiation tolerance of memory senses an amount of radiation exposure and, based on the sensed amount of radiation exposure, determines whether to perform one or more techniques for mitigating the effects of the radiation exposure. As an example, the system may perform a data refresh operation by re-writing data that has been corrupted by radiation, or the system may adjust the reference voltage used to read memory cells. In another example, the system may perform a fault repair operation by re-programming cells that have erroneously transitioned from a program state to an erase state. The system may selectively perform different radiation-mitigation techniques in a tiered approach based on the sensed amount of radiation in order to limit the adverse effects of the more invasive techniques.
Core Innovation
The invention provides systems and methods for improving the radiation tolerance of memory, particularly flash memory. A memory controller determines an amount of radiation exposure and, based on this sensed amount, selectively performs one or more techniques to mitigate the effects of radiation-induced charge leakage in memory cells. These techniques may include a data refresh operation (re-writing previously stored data to restore charge levels), adjusting the reference read voltage to account for charge loss, and performing fault repair operations that re-program cells experiencing bit flips due to radiation.
The background describes the problem that flash memory, which operates by storing charge in cells, is highly susceptible to errors from ionizing radiation that induces charge leakage. Existing solutions like shielding are often inadequate, costly, or bulky. Thus, there is a need for techniques that increase memory resiliency to radiation without significantly increasing cost. The invention aims to address this by providing dynamic, sensor-informed approaches to mitigate radiation effects through targeted interventions at the memory controller level.
Distinctively, the system employs a tiered approach where different mitigation methods are selected based on the detected range of radiation exposure. For example, less invasive actions like adjusting read voltage may be used at lower radiation levels, while more invasive actions such as data refresh or fault repair are reserved for higher detected radiation events. In 3D memory architectures, the controller uses knowledge of spatial radiation effects to vary error correction strength and prioritization of data placement, thereby optimizing resource allocation for improved overall radiation tolerance.
Claims Coverage
The patent claims cover multiple inventive features relating to improving the radiation tolerance of flash memory, particularly in how a memory controller detects, quantifies, and mitigates the effects of radiation-induced charge leakage.
Memory controller selection of compensation operations based on sensed radiation value
The memory controller is configured to determine a value indicative of the amount of radiation exposure and, based on this value, perform at least one operation that compensates for charge leakage in the memory cells induced by radiation. The controller chooses different compensation operations depending on whether the value is within a first or second range.
Control of operation duration based on sensed radiation value
The memory controller can adjust the duration of compensation operations in response to the amount of sensed radiation, tailoring the operation to the severity of charge leakage.
Adjustment of read voltage as a mitigation strategy
The controller, in response to the sensed value, can adjust (reduce) the read voltage for one or more memory cells, with the flash memory chip determining stored data based on whether the cell's charge exceeds the adjusted threshold.
Data refresh operation to mitigate radiation-induced errors
A data refresh operation is performed by reading data from memory cells, correcting detected errors, and writing the corrected data to an erased area of memory, thereby restoring charge levels and minimizing error propagation.
Fault repair by reprogramming cells that have transitioned to erroneous states
The controller can force additional charge into one or more memory cells associated with data errors, transitioning them from an erase state back to a program state, usually using a partial program operation tailored to the sensed radiation.
Region-specific radiation sensing and mitigation in 3D memory structures
For 3D memory structures, the controller associates radiation measurements with specific areas and may perform different compensation operations in different regions of the memory based on localized radiation sensing.
In summary, the claims focus on a memory controller capable of dynamically detecting radiation exposure and deploying a selection of tiered, adaptive mitigation techniques—including region-specific strategies in 3D memory—to compensate for radiation-induced charge leakage and maintain memory fidelity.
Stated Advantages
Increases memory system resilience to radiation exposure without significantly increasing cost or relying on bulky shielding.
Extends useful life of memory by limiting the use of invasive refresh operations to periods of significant radiation.
Enhances data integrity through targeted error correction and selective application of mitigation techniques based on real-time radiation sensing.
Efficiently allocates error correction resources by varying ECC strength across different regions depending on susceptibility to radiation.
Reduces likelihood of over-programming or accumulation of charge errors by using partial programming during fault repair.
Better protects critical or high-priority data by storing it in memory areas less susceptible to radiation effects.
Documented Applications
Use in memory systems within electronic devices where exposure to ionizing radiation is likely, such as vehicles or satellites operating in outer space.
Application in electronic devices including but not limited to smartphones, mobile devices, tablets, personal computers, game consoles, game cartridges, memory cards, USB flash drives, and solid-state drives.
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