Buried Oxide Semiconductor Transistor Stack for Stable Threshold Voltage
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Solution Overview
Problem
Transistors with oxide semiconductor channels face issues with increased off-state current and threshold voltage variations due to oxygen vacancies and impurity entry, leading to unreliable semiconductor devices with poor on-state characteristics.
Innovation Solution
A semiconductor device structure is developed with a buried channel structure using oxide layers without impurity elements like silicon, where the oxide semiconductor layer is sandwiched between two oxide layers with higher electron affinity, reducing interface scattering and trap levels, and an oxide insulating layer with excess oxygen supplies oxygen to fill vacancies, stabilizing the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oxygen is released from the oxide semiconductor layer, then a carrier is generated, but off-state current increases and reliability deteriorates
Solution Approach 1:
The patent applies preliminary action by forming an oxide insulating layer containing excess oxygen before transistor operation. This layer pre-stores oxygen that will be supplied to fill oxygen vacancies in the oxide semiconductor layer during heat treatment, preventing carrier generation and off-state current increase before they occur
Solution Approach 2:
The oxide insulating layer acts as an intermediary that mediates oxygen supply to the oxide semiconductor layer. It serves as an oxygen reservoir that releases oxygen during heat treatment to fill vacancies in the channel formation region, preventing direct oxygen loss from the semiconductor and maintaining device reliability
2Reliability
If impurity elements such as silicon or hydrogen enter the oxide semiconductor layer, then carriers are generated, but threshold voltage variations increase and reliability deteriorates
Solution Approach 1:
The patent extracts harmful impurity elements (silicon, hydrogen) from the system by using an oxide insulating layer that does not contain these impurities. This layer is specifically designed to be free from impurity elements that would otherwise enter and contaminate the oxide semiconductor layer, thereby preventing threshold voltage variations and maintaining reliability
Solution Approach 2:
The oxide insulating layer creates an inert environment barrier between the oxide semiconductor layer and external sources of impurities. By using materials that do not contain silicon or hydrogen, it prevents these impurity elements from entering the channel formation region during device fabrication and operation
3Speed
If the oxide semiconductor layer is used for high-speed operation, then on-state characteristics must be improved, but interface scattering and trap levels reduce performance
Solution Approach 1:
The patent changes the oxygen concentration parameter in the oxide semiconductor layer by supplying oxygen from the oxide insulating layer during heat treatment. This fills oxygen vacancies, reduces trap levels at interfaces, and improves carrier mobility, enabling both high-speed operation and good on-state characteristics
Solution Approach 2:
The patent converts the potential harm of oxygen vacancies (which cause trap levels and reduce mobility) into a benefit by using the oxide insulating layer as an oxygen source. The controlled oxygen supply during heat treatment fills vacancies, transforms defective regions into high-quality channel regions, and improves on-state characteristics for high-speed 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 configuration enhances the on-state characteristics, reduces off-state current, and improves the reliability of semiconductor devices by preventing impurity entry and stabilizing electrical characteristics.
Implementation Method 1
oxygen released from a silicon oxide film containing excessive oxygen is supplied to the oxide semiconductor layer to fill the oxygen vacancy in the oxide semiconductor layer
Data Source
AI summary
The on-state characteristics of a transistor are improved and thus, a semiconductor device capable of high-speed response and high-speed operation is provided. A highly reliable semiconductor device showing stable electric characteristics is made. The semiconductor device includes a transistor including a first oxide layer; an oxide semiconductor layer over the first oxide layer; a source electrode layer and a drain electrode layer in contact with the oxide semiconductor layer; a second oxide layer over the oxide semiconductor layer; a gate insulating layer over the second oxide layer; and a gate electrode layer over the gate insulating layer. An end portion of the second oxide layer and an end portion of the gate insulating layer overlap with the source electrode layer and the drain electrode layer.