Semiconductor Gate Electrode Work Function Shift for Leakage Reduction
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Solution Overview
Problem
Tunnel field effect transistors (TFETs) face a significant challenge due to the large difference in work function between the source diffusion layer and the gate electrode, leading to a redundant electric field and increased leakage current in the gate insulation film.
Innovation Solution
The work function of the gate electrode is shifted towards the source region's conductivity type, reducing the electric field applied to the gate insulation film and minimizing leakage current by adjusting the impurity introduction and metal film composition in the gate electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the work function difference between source diffusion layer and gate electrode is large, then the tunnel transistor achieves low power consumption and sub-threshold slope exceeding MOSFET limit, but a redundant electric field occurs in the gate insulation film and leakage current is generated between source and gate
Solution Approach 1:
The gate electrode is divided into two regions with different work functions: a first region above the source diffusion layer with work function closer to the source, and a second region above the channel with work function optimized for tunneling. This local differentiation reduces the electric field in the gate insulation film over the source while maintaining the tunneling effect in the channel, thereby reducing leakage current without sacrificing power efficiency.
Solution Approach 2:
The work function of the gate electrode is modified by changing its material composition or structure. Specifically, the gate electrode uses a first metal film with a work function closer to the source diffusion layer in the region above the source, which reduces the potential difference and consequently the electric field strength in the gate insulation film, preventing leakage current generation.
2Object-generated harmful factors
If the work function of gate electrode is adjusted to reduce leakage current, then gate insulation film electric field is reduced, but the threshold voltage control may be affected
Solution Approach 1:
The gate electrode employs spatially varying work function characteristics: the first region above the source has one work function value to minimize leakage, while the second region above the channel has a different work function value to maintain proper threshold voltage and tunneling characteristics. This local quality differentiation allows simultaneous optimization of both leakage reduction and threshold voltage control.
Solution Approach 2:
The gate electrode is segmented into functionally distinct regions: a first region aligned with the source diffusion layer and a second region aligned with the channel. Each segment is optimized for its specific function - the first segment minimizes electric field and leakage, while the second segment maintains threshold voltage control and enables tunneling operation.
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 approach effectively reduces gate leakage current and allows for a lower threshold voltage in tunnel transistors, enhancing their performance and efficiency.
Implementation Method 1
The work function of a first region (111) on the source region side within the gate electrode is shifted toward the first conductivity type as compared to the work function of a second region (112) on the drain region side within the gate electrode
Implementation Method 2
reducing the electric field applied to the gate insulation film and minimizing leakage current
Data Source
AI summary
According to one embodiment, a semiconductor device includes a gate electrode formed on a substrate with a gate insulation film interposed therebetween, and a source region of a first conductivity type and a drain region of a second conductivity type reverse to the first conductivity type, which are formed so as to hold the gate electrode therebetween within the substrate. The work function of a first region on the source region side within the gate electrode is shifted toward the first conductivity type as compared to the work function of a second region on the drain region side within the gate electrode.