Dual Gate Insulating Layer for Oxide Semiconductor Threshold Control
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Solution Overview
Problem
Oxide semiconductor transistors face challenges in controlling threshold voltage, particularly in shifting it in the positive direction due to oxygen vacancies and trapped charges, leading to unstable electrical characteristics and normally-on characteristics.
Innovation Solution
A semiconductor device structure is implemented with a gate insulating layer containing nitrogen at 5% or lower and a second gate insulating layer with hafnium oxide, which includes charge trap states to trap electrons and create a negative electric field, stabilizing the threshold voltage and enabling a normally-off switching n-channel transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single gate insulating layer is used with oxide semiconductor, then the structure is simple, but the threshold voltage cannot be controlled in the positive direction and electrical characteristics are unstable
Solution Approach 1:
The gate insulating layer is divided into two separate layers: a first gate insulating layer (silicon oxide) in contact with the oxide semiconductor layer, and a second gate insulating layer (hafnium oxide) above it. This segmentation allows each layer to perform different functions - the first layer provides a stable interface with low nitrogen content, while the second layer introduces charge trap states to control threshold voltage in the positive direction, thereby improving electrical characteristic stability without excessive complexity.
Solution Approach 2:
The patent uses a composite gate insulating layer structure combining silicon oxide and hafnium oxide. The silicon oxide layer provides a stable base interface with controlled nitrogen content, while the hafnium oxide layer contributes charge trap states for threshold voltage control. This composite structure achieves both structural simplicity and electrical stability by leveraging the complementary properties of different materials.
2Ease of manufacture
If nitrogen content in the gate insulating layer is high, then the manufacturing process is easier, but the threshold voltage shifts in the negative direction causing normally-on characteristics
Solution Approach 1:
The patent applies local quality control by specifying that the first gate insulating layer (silicon oxide) in direct contact with the oxide semiconductor must have nitrogen content of 5 at% or lower. This localized nitrogen control at the critical interface prevents negative threshold voltage shifts and normally-on characteristics, while allowing more flexibility in other regions of the device structure.
Solution Approach 2:
The patent changes the nitrogen content parameter of the silicon oxide gate insulating layer to 5 at% or lower. This parameter change is critical for preventing negative threshold voltage shifts caused by trapped charges, thereby achieving proper normally-off transistor characteristics while maintaining manufacturing feasibility.
3Manufacturing precision
If charge trap states are introduced to shift threshold voltage positively, then the threshold voltage control improves, but the trapped charges are unstable and easily recombine
Solution Approach 1:
The patent segments the gate insulating layer into two distinct layers with different functions. The second gate insulating layer (hafnium oxide) contains charge trap states for threshold voltage control, while the first gate insulating layer (silicon oxide) provides a stable base. This segmentation isolates the charge trapping function from the interface stability function, allowing threshold voltage control while maintaining overall system reliability.
Solution Approach 2:
The composite structure of silicon oxide and hafnium oxide layers allows the hafnium oxide to provide charge trap states for positive threshold voltage control, while the silicon oxide layer provides a stable foundation. The combination of these two materials achieves both threshold voltage controllability and charge stability that neither material could achieve alone.
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 proposed structure achieves stable electrical characteristics by suppressing threshold voltage shifts and ensuring a positive threshold voltage, thereby stabilizing the transistor operation and preventing unintended channel formation.
Implementation Method 1
the second gate insulating layer includes charge trap states. It is preferable that electrons be trapped in the charge trap states and thus the second gate insulating layer be negatively charged
Implementation Method 2
the first gate insulating layer includes an oxide in which the nitrogen content is 5 at. % or lower
Data Source
AI summary
A semiconductor device includes a semiconductor layer, a gate electrode overlapping with the semiconductor layer, a first gate insulating layer between the semiconductor layer and the gate electrode, and a second gate insulating layer between the first gate insulating layer and the gate electrode. The first gate insulating layer includes an oxide in which the nitrogen content is lower than or equal to 5 at. %, and the second gate insulating layer includes charge trap states.