Stacked Oxide Semiconductor Transistors for Low Off-State Current
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Solution Overview
Problem
Semiconductor devices using silicon suffer from high flow-through current and increased power consumption due to inadequate switching characteristics and high off-state current, which complicates charge retention in memory and liquid crystal display applications.
Innovation Solution
A semiconductor device is designed with a stack of transistors, one using a material other than an oxide semiconductor and the other using an In--Ga--Zn--O based oxide semiconductor, with the oxide semiconductor transistor having a hydrogen concentration of 5×10^19 atoms/cm^3 or less, to reduce off-state current and improve switching characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silicon-based transistors are used, then device complexity is reduced and ease of manufacture is improved, but off-state current increases and power consumption increases
Solution Approach 1:
The patent employs a composite transistor structure where the first transistor uses conventional silicon-based semiconductor material while the second transistor uses oxide semiconductor material. This composite approach allows the device to leverage the manufacturing simplicity of silicon technology while incorporating the low off-state current characteristics of oxide semiconductors, thereby reducing overall power consumption without sacrificing ease of manufacture
Solution Approach 2:
The semiconductor device is divided into two distinct transistor components: a first transistor using silicon-based material and a second transistor using oxide semiconductor material. This segmentation allows each transistor type to perform optimized functions, with the oxide semiconductor transistor specifically targeting leakage current reduction while the silicon transistor handles primary switching operations
2Ease of manufacture
If silicon-based transistors are used, then ease of manufacture is improved, but switching characteristics deteriorate and flow-through current increases
Solution Approach 1:
By combining silicon-based transistors with oxide semiconductor transistors in a single device, the patent achieves both ease of manufacture (from silicon processing) and superior switching characteristics (from oxide semiconductor properties including lower off-state current and improved charge retention)
Solution Approach 2:
The oxide semiconductor material is specifically applied to the second transistor where low off-state current and excellent switching characteristics are most beneficial, while the first transistor uses conventional silicon material optimized for high-current switching operations
3Loss of energy
If oxide semiconductor transistor is added, then off-state current is reduced and power consumption is reduced, but device complexity increases
Solution Approach 1:
The patent merges two transistor technologies into a single integrated device structure, where the first and second transistors are formed in close proximity sharing common elements such as gate electrodes and insulating layers. This merging approach reduces the overall device footprint and interconnection complexity compared to using separate discrete components
4Reliability
If oxide semiconductor transistor is added, then switching characteristics are improved, but device complexity increases
Solution Approach 1:
The dual-transistor structure merges silicon-based and oxide semiconductor technologies in a unified device architecture, achieving superior switching characteristics through the oxide semiconductor component while maintaining reasonable complexity through shared structural elements and integrated fabrication processes
Data Source
AI summary
An objet of the present invention is to provide a semiconductor device with a new structure. Disclosed is a semiconductor device including a first transistor which includes a channel formation region on a substrate containing a semiconductor material, impurity regions formed with the channel formation region interposed therebetween, a first gate insulating layer over the channel formation region, a first gate electrode over the first gate insulating layer, and a first source electrode and a first drain electrode which are electrically connected to the impurity region; and a second transistor which includes a second gate electrode over the substrate containing a semiconductor material, a second gate insulating layer over the second gate electrode, an oxide semiconductor layer over the second gate insulating layer, and a second source electrode and a second drain electrode which are electrically connected to the oxide semiconductor layer.