Converting NAND Flash to One-Time Programmable Memory via Cell Degradation
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Solution Overview
Problem
Existing one-time programmable (OTP) memory technologies are expensive and less dense compared to read/writeable memories like NAND flash, and attempts to convert NAND flash to OTP memory face reliability and security issues such as semi-invasive attacks and data retention problems.
Innovation Solution
Converting multiple programmable memory, like NAND flash, into OTP memory by inducing accelerated degradation of select memory cells through repetitive program and erase operations, which permanently changes their performance characteristics to encode data values, ensuring that the encoded data cannot be changed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If NAND flash memory is converted to OTP memory by disabling erase and re-writing options, then cost and density benefits are achieved, but security and reliability are compromised due to semi-invasive attacks and data retention issues
Solution Approach 1:
The patent applies parameter changes by repeatedly stressing memory cells through program-erase cycles to permanently alter their physical characteristics. This degradation changes the electrical parameters of selected cells, making them distinguishable from non-stressed cells and creating a permanent, tamper-resistant state that cannot be reverted or attacked through semi-invasive methods.
Solution Approach 2:
The patent converts the harmful effect of memory cell degradation, which is normally a reliability issue, into a beneficial security feature. By intentionally degrading selected memory cells through repeated stress operations, the patent creates permanent, irreversible changes that prevent both semi-invasive attacks and ensure data retention, thus turning a potential harm into a security advantage.
2Reliability
If traditional OTP memory technologies are used, then security and reliability are improved, but cost and density are worsened compared to read/writeable memory
Solution Approach 1:
The patent applies universality by using standard NAND flash memory technology to achieve OTP functionality. Instead of requiring specialized OTP hardware, the patent makes regular flash memory perform the additional function of secure, permanent storage through software-controlled stress operations, thus eliminating the need for separate OTP memory components and achieving both high density and reliability.
Solution Approach 2:
The patent changes the physical parameters of memory cells through repeated program-erase cycling to create permanent degradation. This parameter change transforms the memory cells into a permanent storage state, achieving OTP reliability while maintaining the high density characteristics of NAND flash memory, thereby resolving the contradiction between reliability and density.
3Reliability
If memory cells are repeatedly programmed and erased to induce degradation, then permanent encoding is achieved, but manufacturing complexity and process time increase
Solution Approach 1:
The patent applies preliminary action by performing the memory cell degradation process during the manufacturing stage before the product is deployed. By completing the OTP encoding process during production, the patent ensures permanent encoding reliability without adding time to the end-user experience, as the degradation cycles are executed once during fabrication rather than requiring repeated operations during product usage.
Data Source
AI summary
A memory system is configured to convert multiple programmable memory or a portion thereof to one-time programmable (OTP) memory. The system is configured to repetitively perform memory operations (such as program and erase procedures) on a portion of memory in order to induce accelerated degradation (aging) of select memory cells, thereby permanently changing the select cells, such that a pattern of the cells with degraded performance indicate a data value that has been permanently encoded into the memory.