Non-Volatile Memory Cell Programming Window Expansion
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Solution Overview
Problem
Existing flash memory technologies face challenges in effectively utilizing the full range of a programming window for non-volatile multilevel memory cells, particularly in determining threshold voltages, which limits memory density and increases circuit complexity and power consumption due to the need for negative voltages during read and verify operations.
Innovation Solution
The method involves applying a read voltage to a selected cell while applying a pass voltage to unselected cells, a boost voltage to the source line, and a voltage greater than the boost voltage to the bit line, allowing for the detection of current variations to determine threshold voltages, thereby expanding the programming window to include both positive and negative voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If negative voltages are applied to word lines to read and verify Vt levels of cells programmed to negative Vt levels, then the full range of the programming window can be utilized, but circuit complexity and power consumption increase
Solution Approach 1:
The patent introduces a source line as an intermediary element to apply negative voltages. Instead of applying negative voltages directly to word lines through complex word line drivers, the negative voltage is applied to the source line, which then serves as the reference for reading cells with negative Vt levels. This simplifies the circuit architecture by using the source line as a mediator.
Solution Approach 2:
The patent changes the voltage parameter of the source line from a conventional positive or ground reference to a negative voltage. This parameter change allows the programming window to be expanded to include negative Vt levels while avoiding the need for complex negative voltage generation circuits on the word line side.
2Adaptability or versatility
If negative voltages are applied to word lines to read and verify Vt levels of cells programmed to negative Vt levels, then the full range of the programming window can be utilized, but power consumption increases
Solution Approach 1:
The source line acts as an intermediary that carries the negative voltage, eliminating the need for power-consuming negative voltage generation circuits in the word line drivers. By moving the negative voltage application point to the source line, power consumption is reduced while maintaining the ability to read negative Vt levels.
3Quantity of substance
If the number of Vt distributions within a programming window is increased to represent more bits per cell, then memory density increases, but the Vt distributions must be sufficiently spaced apart which limits the number of states
Solution Approach 1:
The patent extends the voltage dimension from positive only to include negative values. By allowing Vt distributions in the negative voltage range, the programming window is effectively doubled in size, enabling more Vt distributions to be packed within the available window while maintaining sufficient spacing between them for reliable reading.
Data Source
AI summary
Embodiments of the present disclosure provide methods, devices, modules, and systems for utilizing an expanded programming window for non-volatile multilevel memory cells. One method includes associating a different logical state with each of a number of different threshold voltage (Vt) distributions. In various embodiments, at least two Vt distributions include negative Vt levels. The method includes applying a read voltage to a word line of a selected cell while applying a pass voltage to word lines of unselected cells, applying a boost voltage to a source line coupled to the selected cell, applying a voltage greater than the boost voltage to a bit line of the selected cell, and sensing a current variation of the bit line in response to the selected cell changing from a non-conducting state to a conducting state.