Asymmetric Variable Resistive Memory Cell With Load Circuit
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Solution Overview
Problem
Conventional nonvolatile semiconductor memory devices using variable resistive elements face challenges in achieving stable and high-speed switching operations due to complex circuit configurations and high power consumption, particularly in bipolar and unipolar switching methods, which limit their scalability and competitiveness with flash memory devices.
Innovation Solution
A nonvolatile semiconductor memory device with a variable resistive element having asymmetric characteristics, where the threshold voltages for switching between resistance states are manipulated using a load circuit and voltage generation circuit to apply voltages of either polarity without varying pulse duration, allowing for stable switching operations without the need for selection transistors and reducing sneak path currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bipolar or unipolar switching methods are used in conventional nonvolatile semiconductor memory devices, then switching operations can be achieved, but the circuit configuration becomes complex and power consumption increases
Solution Approach 1:
The patent applies asymmetry by designing the variable resistive element with different threshold voltages for positive and negative polarity voltages. The first threshold voltage (for switching from low to high resistance state) differs from the second threshold voltage (for switching from high to low resistance state). This asymmetric characteristic simplifies the circuit configuration by eliminating the need for selection transistors and reduces power consumption while maintaining stable switching operations.
2Productivity
If conventional variable resistive elements are used, then resistance change can be achieved, but sneak path currents occur and switching stability is poor
Solution Approach 1:
The asymmetric threshold voltage design ensures that the variable resistive element only switches states when the applied voltage exceeds the appropriate threshold, preventing unintended switching caused by sneak path currents. This improves switching stability while maintaining high-speed operation.
Solution Approach 2:
The patent introduces a voltage generation circuit as an intermediary that applies controlled voltages to the variable resistive element. This circuit mediates between the data input and the resistive element, ensuring that voltages are applied only when they exceed the threshold values, thereby preventing sneak path current effects and improving switching reliability.
3Reliability
If selection transistors are added to each memory cell, then sneak path currents can be prevented, but the memory cell area increases and scalability is reduced
Solution Approach 1:
The asymmetric threshold voltage characteristic of the variable resistive element inherently prevents sneak path currents without requiring additional selection transistors. The element only responds to voltages exceeding its threshold, automatically blocking sneak path currents while maintaining small memory cell area and good scalability.
4Ease of operation
If voltage pulse duration is varied to control switching, then switching between resistance states can be achieved, but the operation becomes complex and power consumption increases
Solution Approach 1:
The patent changes the parameter of threshold voltage asymmetry to simplify switching control. Instead of varying pulse duration, the system uses the asymmetric threshold voltages to naturally control switching behavior. This simplifies the operation and reduces power consumption by eliminating the need for complex pulse duration control 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
This configuration enables efficient, high-speed switching operations with reduced power consumption and simplified circuit designs, enhancing the scalability and performance of nonvolatile semiconductor memory devices.
Implementation Method 1
a variable resistive element whose resistive characteristics vary in accordance with application of voltage
Data Source
AI summary
A nonvolatile semiconductor memory device include: a two terminal structured variable resistive element, wherein resistive characteristics defined by current-voltage characteristics at both ends transit between low and high resistance states stably by applying a voltage satisfying predetermined conditions to the both ends. A transition from the low resistance state to the high resistance state occurs by applying a voltage of a first polarity whose absolute value is at or higher than first threshold voltage, and the reverse transition occurs by applying a voltage of a second polarity whose absolute value is at or higher than a second threshold voltage. A load circuit is connected to the variable resistive element in series having an adjustable load resistance. A voltage generation circuit applies a voltage to both ends of a serial circuit. The variable resistive element can transit between the states by adjusting a resistance of the load circuit.