Variable Resistance Switch Segmentation for Crossbar Reliability
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Solution Overview
Problem
The existing crossbar switches using two-terminal type variable resistance elements in ULSI suffer from an 'OFF disturbing' problem, where erroneous writing occurs due to logical amplitude of signals, especially when the programming voltage is lowered to match the operating voltage of logic LSI, leading to reliability issues.
Innovation Solution
A semiconductor device comprising a variable resistance first switch and a second switch with intermediate nodes, connected through intersecting wirings and selection switch elements, which apply voltage or current to program the unit element by changing resistive states, ensuring high reliability by preventing erroneous writing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the programming voltage of the variable resistance element is lowered to match the operating voltage of logic LSI, then the compatibility with logic LSI is improved, but the OFF disturbing problem becomes remarkable and reliability deteriorates
Solution Approach 1:
The patent divides a single variable resistance element into two separate elements connected in series, forming a unit element. This segmentation allows each element to withstand lower voltages individually while the series combination can tolerate higher voltages, preventing erroneous writing when compatibility voltage is used. The two-terminal type element is split into a three-terminal type structure with intermediate nodes, enabling better control over voltage distribution.
Solution Approach 2:
The patent introduces intermediate nodes between the variable resistance elements and the signal lines. These intermediate nodes act as mediators that control the application of programming voltages, ensuring that the full programming voltage is only applied when intentionally programmed, while logical signals at lower voltages cannot cause erroneous writing. The selection switch elements connected to intermediate nodes provide controlled access to the variable resistance elements.
2Device complexity
If a two terminal type variable resistance element is used in a crossbar switch, then the device complexity is reduced, but the OFF disturbing problem occurs and reliability deteriorates
Solution Approach 1:
The patent segments the single two-terminal variable resistance element into two separate elements connected in series, creating a three-terminal type structure with an intermediate node. This segmentation increases structural complexity but eliminates the OFF disturbing problem by requiring higher combined voltage to affect either element, thus improving reliability while maintaining reasonable complexity through systematic design.
3Adaptability or versatility
If the programming voltage is lowered for compatibility, then the adaptability to logic LSI operating voltage is improved, but the logical amplitude of signals causes erroneous writing more easily
Solution Approach 1:
The patent introduces intermediate nodes with selection switch elements that mediate between the signal lines and the variable resistance elements. These intermediaries ensure that only controlled programming voltages applied through the selection switches can affect the resistance state, while logical signals at lower amplitudes are blocked from causing erroneous writing, even when the overall programming voltage level is reduced for compatibility.
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 effectively prevents the 'OFF disturbing' problem, enhancing the reliability of the semiconductor device by accurately controlling the resistive states of the switches, thereby improving area efficiency and reducing power consumption.
Implementation Method 1
a variable resistance element which uses the movement of a metal ion in a solid (ion conductor) in which an ion can freely move when an electric field or the like is applied and the electrochemical reaction
Implementation Method 2
the metal ion is supplied from the first electrode to the ion conduction layer and the metal ion is not supplied from the second electrode to the ion conduction layer
Data Source
AI summary
This semiconductor device is provided with: a variable resistance first switch (103), which has a first terminal and a second terminal, and which has the resistance value thereof varied when an applied voltage exceeds a reference value; a variable resistance second switch (104), which has a third terminal and a fourth terminal, and which forms an intermediate node (105) by having the third terminal connected to the second terminal, and has the resistance state thereof varied when an applied voltage exceeds a reference value; first wiring (101) connected to the first terminal; second wiring (102), which is connected to the fourth terminal, and which extends in the direction intersecting the first wiring (101) in a planar view; a first selection switch element (106) connected to the first wiring (101); and a second selection switch element (107) connected to the second wiring (102).