Cross Point Memory Read Stability via Constant Current Control
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Solution Overview
Problem
Cross point variable resistance nonvolatile memory devices face challenges in maintaining a stable read margin due to voltage variations and electromagnetic noise caused by current changes through unselected word lines, which affects the accuracy and efficiency of data reading.
Innovation Solution
A cross point variable resistance nonvolatile memory device configuration that includes a cross point memory cell array with variable resistance elements and bidirectional current steering elements, a decoder circuit, a read circuit, and a control circuit that applies a constant current to unselected word lines instead of a constant voltage, enhancing read stability and reducing electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a voltage is applied to unselected word lines to reduce leakage current, then the read margin is improved, but the actual read margin is reduced due to significant current variation with voltage changes
Solution Approach 1:
The patent changes the control parameter from voltage to constant current for unselected word lines. By supplying a constant current instead of applying a voltage, the system eliminates the problem of current variation with voltage changes, thereby maintaining both read margin and reading stability simultaneously
Solution Approach 2:
The control circuit monitors and adjusts the current supplied to unselected word lines to maintain a constant current level. This feedback mechanism ensures that regardless of voltage fluctuations or array size changes, the leakage current remains controlled and stable, preserving read margin while improving reading stability
2Measurement precision
If voltage is applied to unselected word lines to reduce leakage current, then read margin is improved, but electromagnetic noise is generated due to current changes
Solution Approach 1:
The patent changes the control parameter from voltage to constant current for unselected word lines. By supplying a constant current instead of applying a voltage, the system eliminates the problem of current variation with voltage changes, thereby maintaining both read margin and reading stability simultaneously
Solution Approach 2:
The patent converts the harmful effect of voltage-induced current variations into a beneficial constant current supply. By using a constant current source for unselected word lines, the system turns what would be a source of electromagnetic noise into a stable, noise-free operation, while still achieving leakage current reduction
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 configuration increases the actual read margin and stabilizes the reading process by minimizing current variations and electromagnetic noise, allowing for more reliable data reading despite voltage fluctuations.
Implementation Method 1
a variable resistance element reversibly changing between at least two states including a low resistance state and a high resistance state when voltages of different polarities are applied to the variable resistance element
Implementation Method 2
the bidirectional current steering element being connected in series with the variable resistance element and having nonlinear current-voltage characteristics
Data Source
AI summary
A cross point variable resistance nonvolatile memory device including: a cross point memory cell array having memory cells each of which is placed at a different one of cross points of bit lines and word lines; a word line decoder circuit that selects at least one of the memory cells from the memory cell array; a read circuit that reads data from the selected memory cell; an unselected word line current source that supplies a first constant current; and a control circuit that controls the reading of the data from the selected memory cell, wherein the control circuit controls the word line decoder circuit, the read circuit, and the unselected word line current source so that when the read circuit reads data, the first constant current is supplied to an unselected word line.