CAM Cell Threshold Voltage Stabilization in Semiconductor Memory
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Solution Overview
Problem
Semiconductor memory devices experience errors due to shifts in threshold voltages of Code Address Memory (CAM) cells, which can result in incorrect operation setting information, leading to unstable memory cell states and potential failures during read, program, and test operations.
Innovation Solution
A semiconductor memory device and method that includes a memory array with CAM cells for storing operation setting data, an operation circuit to detect unstable CAM cells by performing test operations with specific read voltages, and a controller to adjust threshold voltages based on the detection results to ensure the difference between threshold and read voltages exceeds a permitted limit, thereby preventing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If read voltage and pass voltage are supplied to CAM cells during CAM read operation, then the CAM read operation can be performed, but the threshold voltage of the CAM cell is shifted by interference phenomenon
Solution Approach 1:
The patent applies preliminary action by performing a test operation before the actual CAM read operation to detect unstable CAM cells. The controller identifies CAM cells with threshold voltages close to the read voltage and prevents them from being read, thereby preventing threshold voltage shifts before they occur during normal operation.
Solution Approach 2:
The patent implements feedback by using the results of test operations to adjust and control subsequent CAM read operations. The controller receives feedback about unstable CAM cells from the test operation and uses this information to modify the read operation, preventing errors caused by threshold voltage shifts.
2Ease of operation
If the threshold voltage of CAM cell is greatly shifted, then the CAM cell may be misread, but this results in error in operation setting information
Solution Approach 1:
The patent performs a test operation as a preliminary step before the actual CAM read operation to identify unstable CAM cells. By detecting CAM cells with threshold voltages close to the read voltage in advance, the system prevents misreading and loss of operation setting information during normal operation.
Solution Approach 2:
The controller uses feedback from the test operation results to control the subsequent CAM read operation. When unstable CAM cells are detected, the controller adjusts the operation to avoid reading from these cells, thereby preventing information loss and ensuring accurate retrieval of operation setting information.
3Reliability
If test operation is performed to detect unstable CAM cells, then reliable operation can be ensured, but this requires additional time and complexity
Solution Approach 1:
The patent applies universality by designing the test operation circuit to perform multiple functions. The same circuitry is used for both detecting unstable CAM cells during test operations and for controlling the actual CAM read operations, thereby ensuring reliability without requiring entirely separate complex circuits.
Solution Approach 2:
The controller performs the test operation and uses the results to automatically adjust and control subsequent CAM read operations. The system serves itself by using its own resources (controller and test operation circuit) to ensure reliable operation without requiring external intervention or additional complex control mechanisms.
Data Source
AI summary
A semiconductor memory device includes a memory array configured to include memory cells for storing input data and Code Address Memory (CAM) cells for storing setting data used to set an operation condition; an operation circuit configured to perform a CAM read operation by supplying a read voltage to the CAM cells, perform a test operation for detecting unstable CAM cells in each of which a difference between a threshold voltage and the read voltage is smaller than a permitted limit, from among the CAM cells, and perform an erase operation or a program operation for the unstable CAM cells; and a controller configured to control the operation circuit so that the program operation for storing the setting data in the unstable CAM cells is performed if the number of unstable CAM cells detected in the test operation is greater than a permitted value.