Counter-Based Memory Cell Reading for Variable Threshold Drift
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Solution Overview
Problem
Existing memory devices, particularly 3D arrays of memory cells, face challenges in accurately reading data due to variable electrical characteristics resulting from factors like statistical process variations, cycling events, and resistance drift, which can lead to errors and inefficiencies in data retrieval.
Innovation Solution
A counter-based sense amplifier method is employed to read memory cells, where user data is encoded with a balanced or constant weight scheme, and additional count data is stored to determine the total number of cells in a given logic state, allowing for a robust and efficient reading operation by using a voltage ramp and offset to differentiate threshold voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional read techniques are used in 3D memory arrays, then the reading operation is simple, but reading accuracy deteriorates due to variable electrical characteristics from process variations, cycling events, and resistance drift
Solution Approach 1:
The patent applies preliminary action by performing a read verify program (RVP) operation before the actual read operation. The RVP program operation programs the memory cells with a reference voltage level that compensates for variable electrical characteristics such as process variations, cycling events, and resistance drift. This preliminary programming ensures that the memory cells are in a known good state for subsequent reading, thereby improving reading accuracy without requiring complex read techniques
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting the reference voltage level based on the specific memory device characteristics and operating conditions. The RVP operation programs the memory cells with a reference voltage that is tailored to compensate for the actual variable electrical characteristics present in the device, rather than using a fixed reference voltage. This adaptive parameter adjustment improves reading accuracy while maintaining relatively simple read operations
2Quantity of substance
If memory cell density is increased to improve storage capacity, then more data can be stored, but reading accuracy deteriorates due to higher variability in electrical characteristics
Solution Approach 1:
The RVP program operation serves as a preliminary action that is performed regardless of memory cell density. By programming the memory cells with a reference voltage level that compensates for variable electrical characteristics before reading, the system ensures accurate reading even as memory cell density increases and variability grows. This preliminary programming step becomes increasingly important at higher densities where process variations and resistance drift have greater impact
Solution Approach 2:
The patent implements feedback by using the read operation to verify the state of memory cells and comparing against the reference voltage level established during RVP. This feedback mechanism allows the system to detect and correct for variability in electrical characteristics, ensuring reading accuracy is maintained even as memory cell density increases and variability increases
Data Source
AI summary
A method including storing user data in memory cells of a memory array, storing, in a counter associated to the memory cells, count data corresponding to a number of bits in the user data having a predetermined first logic value, applying a read voltage to the memory cells to read the user data, applying the read voltage to the cells of the counter to read the count data and to provide a target value corresponding to the number of bits in the user data having the first logic value. During the application of the read voltage, the count data and the user data are read simultaneously such that the target value is provided during the reading of the user data. The application of the read voltage is stopped when the number of bits in the user data having the first logic value corresponds to the target value.