SRAM Gate Work Function Layout for Low Leakage Current
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Static random access memory (SRAM) suffers from high leakage current, which is related to the threshold voltage (Vt) of its transistors, and existing methods of improving Vt through ion doping have limited effectiveness.
Innovation Solution
Incorporating a P type work function metal layer into the gate structures of SRAM transistors to increase the threshold voltage, thereby reducing leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If ion doping is used to improve the threshold voltage of transistors, then the leakage current is reduced to some extent, but the reduction effect is limited and not significant enough
Solution Approach 1:
The patent changes the work function parameter of the gate electrode by selecting specific metal materials (TiN, TaN, WN for P-type; TiAl, Pt, Ir for N-type) to directly adjust the threshold voltage of transistors. This material parameter change achieves a more significant reduction in leakage current compared to conventional ion doping methods, as it fundamentally alters the electrical characteristics of the gate rather than relying on gradual doping concentration changes.
Solution Approach 2:
The patent employs composite gate electrode structures combining multiple metal layers with different work functions. By creating a composite material system where P-type work function metals are used in pull-up transistors and N-type work function metals are used in pull-down transistors, the invention achieves optimized threshold voltage control and significant leakage current reduction that surpasses single-material or ion-doping approaches.
2Loss of energy
If the threshold voltage of transistors is increased to reduce leakage current, then energy loss decreases, but the transistor performance and switching characteristics may be affected
Solution Approach 1:
The patent applies different work function metal materials to different transistor types within the SRAM circuit. P-type work function metals (TiN, TaN, WN) are specifically applied to pull-up transistors to increase their threshold voltage and reduce leakage, while N-type work function metals (TiAl, Pt, Ir) are applied to pull-down transistors to maintain appropriate threshold characteristics. This localized material assignment optimizes each transistor's performance for its specific function, achieving overall leakage reduction without compromising circuit-speed performance.
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 addition of a P type work function metal layer significantly enhances the threshold voltage, resulting in an approximately 80% reduction in leakage current compared to methods using ion doping alone.
Implementation Method 1
the gate structures of the first pull-down transistor (PD1), the second pull-down transistor (PD2), the first access transistor (PG1) and the second access transistor (PG2) each include a P type work function metal layer
Data Source
AI summary
The invention provides a static random access memory, which comprises at least a first pull-up transistor (PU1), a first pull-down transistor (PD1), a second pull-up transistor (PU2), a second pull-down transistor (PD2), a first access transistor (PG1), a second access transistor (PG2), a first read port transistor (RPD) and a second read port transistor (RPD). The gate structures of the first pull-down transistor (PD1), the second pull-down transistor (PD2), the first access transistor (PG1) and the second access transistor (PG2) each include a P type work function metal layer, and an N type work function metal layer is located on the P type work function metal layer. The invention provides a static random access memory with low leakage current.