Wordline Activation Counting for DRAM Disturbance Prevention
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Solution Overview
Problem
As memory integration increases, the coupling effect between adjacent word lines in memory systems like DRAM leads to word line disturbance, causing data degradation due to excessive activation of certain word lines, necessitating a method to count and detect excessive activations to prevent data damage.
Innovation Solution
A memory system with a first cell array and a second cell array that stores the number of activations for each word line, including an activation number update unit and a memory controller that applies a special refresh mode when the activation count exceeds a reference value, thereby minimizing area usage and preventing data degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the degree of integration of memory is increased to reduce intervals among word lines, then memory capacity and density are improved, but coupling effect between adjacent word lines increases causing word line disturbance and data degradation
Solution Approach 1:
The patent applies preliminary action by counting the number of activations for each word line before data degradation occurs. The memory system monitors activation times and performs refresh operations on adjacent word lines in advance, before the coupling effect causes actual data damage. This preventive approach allows high integration to be maintained while avoiding the harmful effects of word line disturbance.
2Reliability
If the number of activations for each word line is monitored and stored using traditional counter circuits, then word line disturbance can be detected, but circuit area increases significantly
Solution Approach 1:
The patent makes memory cells serve multiple functions: they store both user data and activation count information. By utilizing the existing memory cell structure for dual purposes, the system achieves reliable monitoring of word line activations without adding separate counter circuits, thus maintaining detection capability while minimizing area increase.
Solution Approach 2:
The patent uses a copy of the memory cell structure in a second cell array to store activation count information. Instead of using traditional counter circuits, it creates a parallel memory structure that mirrors the first cell array's organization, allowing activation counts to be stored and retrieved using the same efficient memory cell technology, thereby reducing area overhead.
3Reliability
If refresh operations are performed frequently to prevent data degradation, then data reliability is improved, but memory access time and energy consumption increase
Solution Approach 1:
The patent implements feedback by continuously monitoring the activation count of each word line and using this information to dynamically control refresh operations. Instead of performing frequent periodic refreshes, the system refreshes only when the activation count reaches a threshold, allowing data integrity to be maintained while minimizing unnecessary refresh operations that would increase access time and energy consumption.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively counts and detects excessive word line activations, enabling the special refresh operation to prevent data degradation due to word line disturbance while minimizing circuit area, thus enhancing memory system reliability.
Implementation Method 1
As the intervals among the word lines are reduced, a coupling effect between adjacent word lines is increased. When the word line 'WLL' is activated or deactivated, voltages of the word lines 'WLL−1' and the 'WLL+1' are increased or decreased due to a coupling phenomenon among the word lines
Implementation Method 2
electromagnetic waves, which are generated when the word line is toggled between the activated state and the deactivated state, allow electrons to be introduced into cell capacitors of the memory cells connected to adjacent word lines or to be discharged from the cell capacitor
Data Source
AI summary
A memory includes a first cell array configured to include a plurality of first memory cells connected to a plurality of word lines, a second cell array configured to include a plurality of second memory cells connected to the plurality of word lines, wherein a group of the plurality of second memory cells which are connected to a corresponding word line stores the number of activations for the corresponding word line, and an activation number update unit configured to update a value stored in the corresponding group of the plurality of second memory cells connected to the activated word line of the plurality of word lines.