DRAM Word-Line Protection Using Randomized Refresh Counters
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Solution Overview
Problem
Dynamic random access memory (DRAM) systems are vulnerable to the 'row hammer' effect, where memory cells adjacent to frequently accessed rows experience charge leakage, potentially altering their content, which can be exploited maliciously.
Innovation Solution
A memory device with a protection circuit that includes a random number generator and counter to randomly select and protect vulnerable word lines by generating a random number based on the last accessed word line and the last refreshed word line, ensuring these lines are refreshed in subsequent cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard refresh cycles are used to maintain memory data, then data retention is improved, but adjacent word lines are vulnerable to charge leakage from frequently accessed rows
Solution Approach 1:
The protection circuit performs preliminary actions by refreshing adjacent word lines before charge leakage can occur. The circuit identifies word lines adjacent to frequently accessed rows and proactively refreshes them during refresh cycles, preventing charge leakage from affecting data integrity.
Solution Approach 2:
The protection circuit acts as an intermediary between the standard refresh mechanism and the vulnerable word lines. It selectively targets adjacent word lines for additional refreshing, mediating the interaction between frequently accessed rows and their neighbors to prevent harmful charge leakage effects.
2Reliability
If all word lines are refreshed during each refresh cycle, then data retention is improved, but the complexity of the refresh control logic increases
Solution Approach 1:
Instead of uniformly refreshing all word lines, the protection circuit applies local quality by selectively refreshing only adjacent word lines that are vulnerable to charge leakage. This targeted approach maintains data retention where needed while reducing unnecessary refresh operations elsewhere in the memory array.
Solution Approach 2:
The refresh control logic is segmented into different functions: standard refresh for all word lines and protection refresh for adjacent word lines. The protection circuit identifies and separates the vulnerable word lines, applying additional refresh only to those specific segments, thereby managing complexity through functional decomposition.
3Reliability
If frequently accessed word lines are protected from charge leakage, then security against row hammer is improved, but the frequency of refresh operations increases
Solution Approach 1:
The protection circuit applies local quality by focusing refresh operations only on adjacent word lines that are vulnerable to row hammer attacks. This targeted protection reduces the overall refresh frequency compared to refreshing all word lines uniformly, while still providing security where it is most needed.
Solution Approach 2:
The protection circuit uses partial action by refreshing only the necessary adjacent word lines rather than all word lines. This partial refresh approach provides sufficient protection against row hammer while minimizing unnecessary refresh operations that would increase overall frequency and reduce productivity.
Data Source
AI summary
A memory device and a method for protecting the same are provided. The memory device includes a controller configured to refresh a first word line and a first protected word line during a first refresh cycle in response to a refresh signal, a random number generator configured to receive an address of the first word line and an address of the first protected word line to generate a first number, a counter electrically coupled to the random number generator. The counter is configured to receive the first number as an initial value of the counter, and configured to be turned on in response to the refresh signal. The controller is configured to obtain an address of a second accessed word line being accessed when the counter counts down to zero, and refresh a second protected word line, adjacent to the second accessed word line, during a second refresh cycle.