Nonvolatile Memory Device Using Bi-directional Diode for Circuit Simplification
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Solution Overview
Problem
Bipolar type resistive memory devices require complex voltage pulse generating circuits to switch between high and low resistance states, leading to increased peripheral circuit area and reduced integration levels in semiconductor memory devices.
Innovation Solution
A nonvolatile semiconductor memory device with a bi-directional diode and variable resistor at crossing points of lines, utilizing a voltage control circuit to apply voltage pulses and charge/discharge a capacitor to change resistance states, simplifying circuit configuration and reducing area requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If bipolar type resistive memory uses voltage pulses with switching polarity for setting and resetting operations, then data write and erase operations can be performed, but voltage pulse generating circuits with large area are required
Solution Approach 1:
Instead of using separate positive and negative voltage pulse generating circuits for setting and resetting operations, the patent inverts the approach by using a single voltage pulse generating circuit that generates only positive voltage pulses. The bi-directional diode's inherent characteristics allow the same positive pulse to perform both setting and resetting functions through different application methods, eliminating the need for complex dual-polarity voltage generation circuitry.
Solution Approach 2:
The single voltage pulse generating circuit is designed to perform multiple functions: it can generate voltage pulses for both setting operations (changing variable resistor from high to low resistance state) and resetting operations (changing variable resistor from low to high resistance state). This multi-functional approach eliminates the need for separate voltage pulse generating circuits for each operation, significantly reducing the peripheral circuit area.
2Reliability
If bipolar type resistive memory uses separate voltage pulse generating circuits for setting and resetting, then proper voltage polarity can be applied, but peripheral circuit area increases
Solution Approach 1:
The patent inverts the conventional approach by eliminating the need for separate positive and negative voltage pulse generating circuits. Instead, a single voltage pulse generating circuit generates only positive voltage pulses, and the bi-directional diode's unique characteristics enable the system to achieve both setting and resetting functions using this single circuit, thereby reducing peripheral circuit area while maintaining reliable voltage polarity control.
Solution Approach 2:
The bi-directional diode serves multiple functions: it acts as a rectifier during setting operations and as a voltage inversion element during resetting operations. This self-service capability allows the diode to enable both setting and resetting functions without requiring external dual-polarity voltage generation circuitry, significantly reducing the peripheral circuit area while maintaining proper voltage polarity control.
3Device complexity
If bipolar type resistive memory uses unipolar voltage pulses, then circuit area is reduced, but resistance state switching cannot be achieved
Solution Approach 1:
The patent utilizes parameter changes in the bi-directional diode's voltage-current characteristics to achieve both setting and resetting operations with a single unipolar voltage pulse generating circuit. By exploiting the diode's non-linear characteristics and its ability to conduct in both directions with different voltage thresholds, the system can switch resistance states without requiring separate positive and negative voltage pulse generation circuitry.
Solution Approach 2:
The bi-directional diode acts as an intermediary element that enables the single voltage pulse generating circuit to control both setting and resetting operations. The diode's unique property of allowing current flow in both directions with different voltage characteristics serves as a mediator, translating a single unipolar voltage pulse into the appropriate current flow patterns for both setting and resetting the variable resistor.
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 solution allows for efficient data write/erase operations with reduced circuit complexity and area, enhancing integration levels in memory devices by eliminating the need for dual polarity voltage pulse generation.
Implementation Method 1
a variable resistor R and a bi-directional diode D connected in series... the variable resistor being configured to change its resistance value depending on a polarity of a voltage applied thereto
Implementation Method 2
the voltage control circuit being configured to apply a voltage pulse to the selected one of the first lines and to connect a capacitor of a certain capacitance to one end of the selected one of the second lines
Data Source
AI summary
A nonvolatile semiconductor memory device comprises: a plurality of first lines; a plurality of second lines; a plurality of memory cells each disposed at each of crossing-points of the first lines and the second lines and each comprising a variable resistor and a bi-directional diode; and a voltage control circuit configured to control a voltage of selected one of the first lines, unselected ones of the first lines, selected one of the second lines, and unselected ones of the second lines, respectively. The variable resistor is configured to change its resistance value depending on a polarity of a voltage applied thereto. The voltage control circuit is configured to apply a voltage pulse to the selected one of the first lines and to connect a capacitor of a certain capacitance to one end of the selected one of the second lines.