Resistance Change Memory Device Constant-Voltage Write Control
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Solution Overview
Problem
Existing memory devices with integrated resistance change memory elements, such as magnetoresistive elements, face challenges in reliably switching between low-resistance and high-resistance states during write operations, particularly due to the potential adverse effects of constant-current writes on the magnetoresistive elements and the need for large-scale circuits to manage voltage drops and delays.
Innovation Solution
The memory device employs a configuration with a first and second transistor, along with a voltage holding section, to perform a constant-voltage write operation, where the voltage applied to the gate of the first transistor during a first write period is held and applied to the second transistor during a second write period, allowing the magnetoresistive element to switch between resistance states without increasing voltage, thus reducing adverse effects and enabling high-speed, reliable writes without requiring large-scale circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If constant-current write operation is used, then write speed can be improved, but it causes adverse effects on magnetoresistive elements and requires large-scale circuits to manage voltage drops and delays
Solution Approach 1:
The patent changes the write operation mode from constant-current to constant-voltage. Specifically, the control circuit applies a constant voltage to the gate of the selection transistor during the write period, rather than maintaining constant current. This parameter change eliminates the adverse effects on magnetoresistive elements while maintaining high write speed, as the constant voltage ensures stable electric field application without the harmful current fluctuations associated with constant-current operation.
2Productivity
If constant-current write operation is used, then write speed can be improved, but it requires large-scale circuits to manage voltage drops and delays
Solution Approach 1:
The patent simplifies the circuit by changing from constant-current to constant-voltage operation. The control circuit generates a constant voltage signal for the selection transistor gate, which inherently compensates for voltage drops and delays in the bit line without requiring additional complex compensation circuits. This reduces device complexity while maintaining high write speed performance.
3Reliability
If voltage is increased during write operation, then switching reliability between resistance states can be improved, but it increases the risk of damaging the magnetoresistive elements
Solution Approach 1:
The patent changes the control parameter from current to voltage. By applying constant voltage to the selection transistor gate during write operations, the electric field across the magnetoresistive element is stabilized, ensuring reliable switching between resistance states. The constant voltage prevents excessive current spikes that could damage the elements, thus achieving both high switching reliability and element protection simultaneously.
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 allows for reliable and efficient switching between low-resistance and high-resistance states in magnetoresistive elements, reducing the risk of damaging the elements and enabling high-speed, low-latency write operations while maintaining a small circuit scale, thereby improving the overall performance and reliability of the memory device.
Implementation Method 1
a first resistance change memory element to which one of a first low-resistance state and a first high-resistance state is allowed to be set in accordance with a write current
Implementation Method 2
a voltage holding section holding a first voltage applied to the first gate in the first write period
Data Source
AI summary
According to one embodiment, a memory device includes a resistance change memory element to which one of a low-resistance state and a high-resistance state is allowed to be set in accordance with a write current, a first transistor including a first gate, and causing a current to flow through the resistance change memory element in a first write period, a voltage holding section holding a first voltage applied to the first gate in the first write period, and a second transistor including a second gate, in which the first voltage held in the voltage holding section is applied to the second gate, thereby causing a current to flow through the resistance change memory element in a second write period after the first write period.