Variable Resistance Nonvolatile Storage Device Stabilizing Low Resistance State
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Solution Overview
Problem
Variable resistance nonvolatile storage devices face variations in resistance values, particularly in the low resistance state, leading to instability and reduced reading speed and operating margin due to variations in the variable resistance element characteristics and threshold voltages of selection transistors.
Innovation Solution
A variable resistance nonvolatile storage device with a memory cell array including a selection circuit, a high-resistance-state write circuit, and a low-resistance-state write circuit, where the low-resistance-state write circuit has specific driving circuits that control voltage and current to stabilize the resistance change, reducing variations in the resistance value of the variable resistance element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If variable resistance elements are used in memory cells, then nonvolatile data storage is achieved, but variations in resistance values occur leading to instability
Solution Approach 1:
The patent applies parameter changes by carefully controlling the oxygen-to-metal ratio in the variable resistance layer within the range of 0.4 to 0.7. This specific compositional parameter control reduces resistance value variations in the low resistance state while maintaining the nonvolatile storage function, directly resolving the contradiction between reliability and manufacturing precision
Solution Approach 2:
The patent uses composite materials by combining the variable resistance layer made of oxygen-deficient transition metal oxide with specific electrode materials. This composite structure stabilizes the resistance characteristics and reduces variations, addressing both the reliability requirement for stable data storage and the manufacturing precision requirement for consistent resistance values
2Speed
If variable resistance elements with low resistance state are used, then reading speed increases, but variations in resistance value decrease operating margin
Solution Approach 1:
The patent optimizes the oxygen-to-metal ratio parameter within 0.4 to 0.7 to achieve a balance where the low resistance state provides fast reading speed while the controlled composition minimizes resistance variations, thereby maintaining sufficient operating margin for reliable operation
Solution Approach 2:
The patent creates a variable resistance layer that is oxygen-deficient but within a controlled range, providing enough oxygen deficiency to achieve low resistance state for fast reading, while avoiding excessive oxygen deficiency that would cause excessive variations and reduce operating margin
3Ease of operation
If selection transistors are used for memory cell access, then memory cell selection is enabled, but variations in threshold voltage affect resistance change stability
Solution Approach 1:
The patent controls the composition parameter of the variable resistance layer (oxygen-to-metal ratio) to reduce sensitivity to threshold voltage variations of selection transistors, ensuring stable resistance change during write operations while maintaining ease of memory cell access through standard transistor selection mechanisms
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
The solution stabilizes the resistance change state of the variable resistance element, enhancing reading speed and improving yield by minimizing variations in the low resistance state and maximizing the resistance change window between high and low resistance states.
Implementation Method 1
the variable resistance element including (i) a first electrode, (ii) a second electrode, and (iii) a nonvolatile variable resistance layer disposed between the first electrode and the second electrode, the nonvolatile variable resistance layer having a resistance state that reversibly changes between a high resistance state and a low resistance state according to a polarity of a voltage to be applied between the first electrode and the second electrode
Data Source
AI summary
The variable resistance nonvolatile storage device reduces variations in a resistance value of a variable resistance element (100) in the low resistance state, performs stable operations, and includes an LR write circuit (500) (i) applying a voltage to a memory cell (102) so that a resistance state of the variable resistance element included in the memory cell is changed from high to low, and (ii) including a first driving circuit (510) and a second driving circuit (520) which apply voltages to the memory cell and which have connected output terminals. When applying a voltage to the memory cell, the first driving circuit supplies a first current, and the second driving circuit (i) supplies a second current when a voltage at the output terminal of the first driving circuit is higher than a reference voltage VREF, and (ii) is in a high impedance state when the voltage is lower than the VREF.