Oxide Semiconductor Stack Transistor for Low Power Control
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Solution Overview
Problem
Existing semiconductor transistors face challenges in achieving desired electric characteristics, particularly in controlling threshold voltage and power consumption, due to limitations in material properties and manufacturing conditions, which affect their suitability for high-performance and low-power applications.
Innovation Solution
A semiconductor device structure utilizing an oxide semiconductor stack with multiple layers of different energy gaps, where the energy gaps of the oxide semiconductor layers are strategically chosen to optimize on-state and off-state characteristics, allowing for precise control of electric properties and reduced parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single oxide semiconductor layer is used, then the manufacturing process is simple, but the electric characteristics cannot be precisely controlled
Solution Approach 1:
The semiconductor layer is divided into multiple oxide semiconductor layers with different energy gaps. Each layer contributes differently to the transistor characteristics, allowing independent optimization of on-state current and threshold voltage. The first oxide semiconductor layer provides high on-state current, while the second layer controls threshold voltage, achieving precise electric characteristic control through layered segmentation.
Solution Approach 2:
The invention uses a composite structure of multiple oxide semiconductor materials with different energy gaps. By combining materials with complementary properties (one with smaller energy gap for high on-state current, another with larger energy gap for threshold voltage control), the transistor achieves optimized electric characteristics that cannot be obtained with a single material.
2Productivity
If the threshold voltage is negative, then the transistor is in normally-on state with high current flow, but power consumption increases and circuit control becomes difficult
Solution Approach 1:
The invention changes the threshold voltage parameter from negative to positive by utilizing the specific energy band alignment of the multi-layer oxide semiconductor structure. The second oxide semiconductor layer with larger energy gap creates a potential barrier that prevents channel formation at zero gate voltage, thereby achieving positive threshold voltage and normally-off characteristics while maintaining high on-state current capability.
3Use of energy by stationary object
If the threshold voltage is positive, then the transistor achieves normally-off characteristics with low power consumption, but on-state current and field-effect mobility may be reduced
Solution Approach 1:
The semiconductor layer is segmented into two distinct oxide semiconductor layers where the first layer (in contact with source and drain) is optimized for high on-state current and field-effect mobility, while the second layer (between first layer and gate insulating film) is optimized for threshold voltage control. This functional segmentation allows both high productivity and low power consumption to be achieved simultaneously.
Solution Approach 2:
Different regions of the semiconductor structure are assigned different material properties: the first oxide semiconductor layer has smaller energy gap for high carrier mobility and on-state current, while the second layer has larger energy gap for effective threshold voltage control. This local differentiation of material quality enables optimization of both on-state performance and off-state power consumption.
Data Source
AI summary
A transistor which is formed using an oxide semiconductor layer and has electric characteristics needed for the intended use, and a semiconductor device including the transistor are provided. The transistor is formed using an oxide semiconductor stack including at least a first oxide semiconductor layer in contact with a source electrode layer and a drain electrode layer and a second oxide semiconductor layer which is provided over the first oxide semiconductor layer and has an energy gap different from that of the first oxide semiconductor layer. There is no limitation on the stacking order of the first oxide semiconductor layer and the second oxide semiconductor layer as long as their energy gaps are different from each other.