3D NAND Search Circuit Using Conduction-State Matching
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Solution Overview
Problem
Existing in-memory-searching technologies in 3D flash memory face inaccuracies in judgment criteria due to variations in output current intensity, leading to inconsistent searching results over time.
Innovation Solution
A 3D memory array with NAND strings that encode storage data and searching inputs using bit values of '0', '1', wildcard, and invalid bits, determining search results based on the on/off state of NAND strings rather than current intensity, with transistors having specific threshold voltages and driving voltages to control conduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the searching result is determined by judging the output current intensity of an NAND string, then the searching function can be implemented, but the judgment criteria become inconsistent and searching accuracy deteriorates due to current intensity variations
Solution Approach 1:
The patent changes the judgment parameter from continuous current intensity to discrete conduction state (on/off). By encoding data and search keys with specific bit patterns and using threshold voltage comparisons, the system transforms the analog current measurement problem into a digital state detection problem, eliminating sensitivity to current intensity variations
Solution Approach 2:
The patent introduces threshold voltages as an intermediary layer between the data storage and search comparison. The threshold voltage acts as a reference standard that mediates the comparison process, allowing consistent judgment criteria independent of current intensity fluctuations. The sensing circuit uses this threshold as a stable reference to determine conduction states
2Productivity
If the output current intensity is used for searching judgment, then the searching process can be completed, but the current intensity varies after long-term use leading to inaccurate results
Solution Approach 1:
The patent performs preliminary encoding of both stored data and search keys into specific bit patterns before the search operation. By pre-configuring the data bits and key bits with defined values (0 or 1) and their complements, the system establishes a deterministic comparison framework that is independent of subsequent current intensity variations during operation
Solution Approach 2:
The patent implements a feedback mechanism where the conduction state of each NAND string is sensed and used to determine the search result. The sensing circuit continuously monitors the conduction state and provides feedback to the control logic, which then determines whether a match is found, creating a closed-loop system that compensates for drift
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 enhances searching accuracy by eliminating errors from current intensity variations, ensuring precise judgment through NAND string conduction status, thereby improving the reliability of memory searching engines.
Implementation Method 1
each of the plurality of memory cells comprises a first transistor and a second transistor connected in series along a current direction of the output current, and each of the first transistor and the second transistor has a first threshold voltage or a second threshold voltage
Data Source
AI summary
A three-dimensional memory array comprising a plurality of NAND strings. Each NAND string is configured to store a storage data having multiple bits and receive a searching input having multiple bits. Each bit of the storage data and the searching input is of a bit value “0”, a bit value “1”, a wildcard bit or an invalid bit. At least one bit of the storage data is configured as data bit(s), at least bit of the searching input is configured as search bit(s). All of the data bit(s) and the search bit(s) are of bit value “0” or bit value “1”. When the position of the data bit(s) in the storage data overlaps with the position of the search bit(s) in the searching input, the NAND string that stores the storage data is turned off; otherwise, the NAND string that stores the storage data generates an output current.