Memory Pre-Programming for Reflow Voltage Shift Compensation
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Solution Overview
Problem
The reflow process for memory devices causes a shift in threshold voltage, leading to data retention issues due to heat-induced charge loss or redistribution, resulting in read errors and reduced reliability.
Innovation Solution
A memory sub-system that estimates the threshold voltage shift during the reflow process and pre-compensates by updating the verify reference voltage, applying multiple programming pulses at consistent or incrementally higher voltage levels to suppress charge losses and maintain intended logic states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the memory device undergoes a reflow process, then the memory device can be soldered to the circuit board, but the threshold voltage shifts due to heat-induced charge loss or redistribution
Solution Approach 1:
The patent applies preliminary action by performing a pre-programming operation before the reflow process. The memory device is pre-programmed with data at a first voltage level before soldering, and then undergoes a reflow process. After reflow, a read operation is performed to detect if data integrity is maintained. This preliminary programming allows the device to be prepared in advance for the thermal stress of soldering.
Solution Approach 2:
The patent utilizes parameter changes by varying the voltage level applied during programming. A first voltage level is applied during pre-programming before reflow, and a second voltage level (different from the first) is applied during a second programming operation after reflow. This parameter change compensates for the threshold voltage shift caused by the reflow process, maintaining data integrity despite the thermal exposure.
2Reliability
If multiple programming pulses are applied at higher voltage levels, then charge losses are suppressed and data integrity is maintained, but the complexity of the programming process increases
Solution Approach 1:
The patent applies segmentation by dividing the programming process into distinct stages: a first programming operation before reflow and a second programming operation after reflow. Each programming operation uses different voltage levels tailored to the specific conditions at that stage. This segmentation allows optimization of each stage independently, maintaining data integrity while managing process complexity through structured phases.
Solution Approach 2:
The patent implements feedback by performing a read operation after the reflow process to detect whether data integrity is maintained. Based on the read result, a second programming operation is conditionally applied with a second voltage level. This feedback mechanism ensures that programming parameters are adjusted according to the actual state of the memory device after thermal stress, improving reliability while avoiding unnecessary complex operations when data integrity is already maintained.
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
This approach ensures data integrity and reduces read error rates, enhancing the reliability of memory devices by maintaining threshold voltages within the target range post-reflow.
Implementation Method 1
The reflow process for memory devices causes a shift in threshold voltage, leading to data retention issues due to heat-induced charge loss or redistribution
Data Source
AI summary
A system includes a memory device and a processing device, operatively coupled with the memory device. The processing device is configured to perform operations that include determining a verify reference voltage associated with a logic state of a memory cell of the memory device, the verify reference voltage defining a target voltage level of a threshold voltage associated with the logic state; determining an amount of voltage compensation based on a thermal profile associated with a heat to be applied to the memory device, the thermal profile comprising a temperature associated with the heat and a period of time the heat is to be applied to the memory device; and updating the verify reference voltage using the amount of voltage compensation for an expected shift in the threshold voltage of the memory cell after the heat is applied to the memory device.