Weak Erase Prior to Read for 3D Memory Cell Sensing
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Solution Overview
Problem
In 3D memory devices, the issue of word line voltage creep-up leads to residual electrons being trapped in shallow interface traps, altering the threshold voltage of memory cells, which can result in inaccurate sensing operations unless the system waits for the voltage to settle, causing delays.
Innovation Solution
Implementing a strategy to discharge the read pass voltage in a manner that purges residual electrons from the memory string channel or a portion thereof after a sensing operation, either by providing a path for electrons to leave the channel or using a weak erase operation to remove trapped electrons, thereby preventing the impact of word line voltage creep-up on threshold voltage accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the system waits for the word line voltage to settle after a sensing operation, then the threshold voltage reading accuracy is improved, but the operation time increases
Solution Approach 1:
The patent applies preliminary action by performing a weak erase operation immediately after the sensing operation to remove trapped electrons before they can cause significant voltage creep-up. This proactive approach eliminates the need to wait for voltage settlement, thereby maintaining measurement precision while reducing operation time.
Solution Approach 2:
The weak erase operation serves as a preliminary anti-action by counteracting the harmful effect of electron trapping in shallow interface traps before it can significantly alter the threshold voltage. By applying this counter-measure immediately, the system prevents the voltage creep-up problem rather than waiting for it to resolve naturally.
2Measurement precision
If a weak erase operation is performed to remove trapped electrons, then the threshold voltage accuracy is maintained, but additional operations are required
Solution Approach 1:
The patent merges the weak erase operation with the existing sensing operation sequence, combining two functions into a unified process flow. By integrating the electron removal step immediately following the sensing operation, the system maintains threshold voltage accuracy while minimizing the increase in operational complexity through efficient sequencing.
Data Source
AI summary
Techniques are disclosed for accurately sensing memory cells without having to wait for a voltage that creeps up on word line after a sensing operation to die down. The word line creep up could cause electrons to trap in shallow interface traps of a memory cell, hence impacting its threshold voltage. In one aspect, trapped electrons are removed (e.g., de-trapped) from shallow interface traps of a memory cell using a weak erase operation. Therefore, problems associated with word line voltage creep up are reduced or prevented. Thus, the memory cell can be sensed without waiting, while still providing an accurate result. The weak erase could be part of a sensing operation, but that is not required. For example, the weak erase could be incorporated into the beginning part of a read operation, which provides for a very efficient solution.