Variable Resistance Memory with Selector Transistor for Multi-Level Storage
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Solution Overview
Problem
Current methods for achieving multi levels in resistance change type nonvolatile memory using current compliance control are hindered by parasitic capacitance, making it difficult to accurately control resistance values and resulting in unreliable operations, which complicates the miniaturization and high-capacity requirements of these memory devices.
Innovation Solution
The proposed solution involves an information recording device with a variable resistance layer composed of high-resistance material and low-resistance nano-particles between electrodes, where the resistance is controlled by short-circuiting the electrodes with the nano-particles, allowing for precise resistance value changes through controlled voltage or current application, enabling accurate multi-level storage without the need for additional transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current compliance control method is used to achieve multi levels, then resistance values can be changed on multi levels, but parasitic capacitance greatly affects reliability and makes highly accurate control of resistance values difficult
Solution Approach 1:
The patent introduces a selector transistor as an intermediary component between the word line and the memory element. This selector transistor controls the current flow through the memory element, enabling precise resistance value control for multi-level storage while isolating the memory element from the effects of parasitic capacitance in the word line. The selector transistor acts as a gatekeeper that allows controlled current entry, thereby improving both measurement precision and operational reliability.
2Reliability
If one transistor is added to one memory element to carry out highly reliable operation, then operation reliability is improved, but size of memory cell increases
Solution Approach 1:
The patent segments the memory cell structure by introducing a selector transistor that divides the current path into controlled segments. This segmentation allows the memory element to be controlled more efficiently, achieving high reliability without requiring an additional transistor per memory element. The selector transistor creates distinct functional zones within the memory cell, enabling reliable operation while maintaining compact cell size.
3Productivity
If memory cell size is reduced to achieve high capacity, then capacity is improved, but it becomes more difficult to achieve reliable multi-level operation with current compliance control
Solution Approach 1:
The patent changes the control parameter from direct current compliance control to voltage-controlled current regulation through the selector transistor. By using the selector transistor as a voltage-controlled switch, the system can achieve precise current control for multi-level resistance changes even in miniaturized memory cells. This parameter change enables reliable multi-level operation in smaller memory cells, thereby improving capacity while maintaining reliability.
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 allows for highly accurate control of resistance levels, enhancing the reliability and capacity of resistance change type nonvolatile memory by eliminating the limitations imposed by parasitic capacitance and enabling efficient multi-level data storage.
Implementation Method 1
when the memory element is a variable resistance element consisting of, e.g., TiO2, a resistance value of the memory element varies depending on a state that oxygen ions in the variable resistance element move and oxygen defects are thereby continuous between electrodes and a state that the oxygen ions are again arranged in these oxygen defects
Implementation Method 2
as the ReRAM, one which is of a type whose resistance varies by precipitating a metal filament in a high-resistance layer between electrodes is known. For example, an ReRAM using Cu2S for the high-resistance layer corresponds to this type
Implementation Method 3
when the memory element consists of a gallium-antimony-tellurium (GST) compound, a resistance value of the memory element varies depending on a crystalline state and an amorphous state
Data Source
AI summary
According to one embodiment, an information recording device includes first and second electrodes, a variable resistance layer between the first and second electrodes, and a control circuit which controls the variable resistance layer to n (n is a natural number except 1) kinds of resistance. The variable resistance layer comprises a material filled between the first and second electrodes, and particles arranged in a first direction from the first electrode to the second electrode in the material, and each of the particles has a resistance lower than that of the material. A resistance of the variable resistance layer is decided by a short between the first electrode and at least one of the particles.