Semiconductor Memory Transistor Drain Electrode Melting Prevention
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Solution Overview
Problem
Conventional memory transistors face reliability issues due to melting of metal electrodes during writing, leading to damage and disconnection of current paths, especially when using metals with low melting points like aluminum and copper.
Innovation Solution
The semiconductor device incorporates a drain electrode with a multilayer structure, where a high-melting-point metal forms the first layer that overlaps the gate and metal oxide layer, while a low-melting-point metal forms the second layer that does not overlap, preventing melting and maintaining electrical connectivity during writing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a metal electrode with low melting point (aluminum or copper) is used in the drain electrode, then the ease of manufacture is improved, but the reliability deteriorates due to melting during writing operation
Solution Approach 1:
The drain electrode is divided into two separate metal layers: a first metal layer (high melting point) and a second metal layer (low melting point). This segmentation allows each layer to fulfill different functions - the first layer provides thermal stability during writing while the second layer maintains electrical conductivity and ease of manufacture.
Solution Approach 2:
Different regions of the drain electrode have different material compositions. The first metal layer (e.g., tungsten, molybdenum, or titanium) is positioned to overlap with the gate electrode and metal oxide layer to provide local thermal resistance where heat is generated during writing, while the second metal layer (e.g., aluminum or copper) is positioned in regions where electrical conductivity is prioritized.
2Productivity
If the writing duration is shortened to improve productivity, then the productivity is improved, but the reliability deteriorates due to insufficient heat dissipation causing metal melting
Solution Approach 1:
The first metal layer with high melting point is pre-configured in the drain electrode structure before writing operation. This preliminary arrangement of thermal management materials ensures that when writing occurs, the heat is immediately dissipated or contained, preventing melting even during ultra-short writing durations.
Solution Approach 2:
The patent changes the thermal parameters of the drain electrode by introducing materials with different melting points and thermal conductivities. This allows the electrode to withstand the extreme thermal conditions generated during ultra-short writing operations while maintaining electrical functionality.
3Reliability
If a multilayer structure with high-melting-point metal is used in the drain electrode, then the reliability is improved by preventing melting, but the device complexity increases
Solution Approach 1:
The first metal layer with high melting point serves multiple functions simultaneously: it acts as a thermal barrier to prevent melting during writing, provides structural support to the drain electrode, and maintains electrical conductivity. This multi-functionality reduces the need for additional separate components.
Solution Approach 2:
The drain electrode is constructed as a composite structure combining two different metal materials with complementary properties. The first metal (high melting point) and second metal (high conductivity) work together to achieve both thermal stability and electrical performance, eliminating the need for more complex cooling systems or thermal management structures.
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 shorter writing durations while enhancing the reliability of the memory transistor by preventing damage from heat-induced melting, ensuring stable operation and data retention.
Implementation Method 1
Joule heat produced by the drain current
Implementation Method 2
melting of the drain electrode due to heat produced during writing
Data Source
AI summary
A semiconductor device includes a memory transistor (10A) which is capable of being irreversibly changed from a semiconductor state where drain current Ids depends on gate voltage Vg to a resistor state where drain current Ids does not depend on gate voltage Vg. The memory transistor (10A) includes a gate electrode (3), a metal oxide layer (7), a gate insulating film (5), and source and drain electrodes. The drain electrode (9d) has a multilayer structure which includes a first drain metal layer (9d1) and a second drain metal layer (9d2), the first drain metal layer (9d1) being made of a first metal whose melting point is not less than 1200° C., the second drain metal layer (9d2) being made of a second metal whose melting point is lower than that of the first metal. Part P of the drain electrode 9d extends over both the metal oxide layer (7) and the gate electrode (3) when viewed in a direction normal to a surface of the substrate. The part (P) of the drain electrode (9d) includes the first drain metal layer (9d1) and does not include the second drain metal layer (9d2).