Voltage Switch Circuit for Negative Word-Line Transfer in NAND Flash
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Solution Overview
Problem
Conventional NAND type flash memory devices are limited in controlling threshold voltage distributions due to the inability to transfer negative voltages to memory cell arrays, reducing the margins between threshold voltage distributions and affecting multi-level cell performance.
Innovation Solution
A voltage switch circuit utilizing a triple well high voltage transistor to supply both positive and negative voltages to the word lines of a selected memory cell block, enabling precise control of threshold voltage distributions through a positive voltage supply circuit, negative voltage supply circuit, and switch circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional block selection circuit is used, then the circuit structure is simple, but the circuit can only transfer positive voltage and not negative voltage to the memory cell array
Solution Approach 1:
The block selection circuit is divided into separate positive voltage supply circuit and negative voltage supply circuit, each with independent control. This segmentation allows the circuit to handle both positive and negative voltages while maintaining clear control logic and manageable complexity.
Solution Approach 2:
The block selection circuit is designed to perform multiple functions: transferring positive voltage, transferring negative voltage, and selectively enabling/disabling each voltage type through control signals. This multi-functionality resolves the contradiction by expanding voltage transfer capability without requiring completely separate circuits.
2Reliability
If only positive voltage is used for word lines, then the circuit design is simple, but the margins between threshold voltage distributions are reduced
Solution Approach 1:
The circuit introduces negative voltage as a new parameter for word line control, changing the voltage parameter from solely positive to include negative values. This parameter change enables better threshold voltage distribution control and improved margins while maintaining reasonable circuit complexity through shared circuit structures.
3Adaptability or versatility
If a voltage switch circuit with triple well high voltage transistor is used, then negative voltage can be transferred to word lines, but the circuit complexity increases
Solution Approach 1:
The triple well high voltage transistor acts as an intermediary component that enables negative voltage transfer while isolating the negative voltage path from other circuit portions. This intermediary approach allows negative voltage capability to be added without proportionally increasing overall circuit complexity.
Solution Approach 2:
The positive voltage supply circuit and negative voltage supply circuit share common control signal generation logic and block selection mechanisms. By merging these functions, the circuit achieves negative voltage transfer capability while avoiding duplicate circuitry, thus limiting the increase in overall complexity.
Data Source
AI summary
A voltage switch circuit includes a positive voltage supply circuit configured to supply a positive voltage to a control node in response to an enable signal, a negative voltage supply circuit configured to supply a negative voltage to the control node in response to a negative voltage enable signal, a control signal generation circuit configured to generate the negative voltage enable signal in response to the enable signal, and a switch circuit configured to transfer an input voltage with a positive potential or a negative potential to an output node in response to a potential of the control node.