Oxide Semiconductor Stacked-Layer Transistor for Threshold Voltage Control
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Solution Overview
Problem
Existing transistors using oxide semiconductors face challenges in achieving positive threshold voltage, leading to normally-off type switching elements, while also requiring improved on-state characteristics for high-speed operation and low off-state current for low power consumption.
Innovation Solution
A transistor structure and manufacturing method utilizing an oxide semiconductor stacked layer with multiple layers having different energy gaps, where the energy gap of one layer is larger than or equal to 3 eV and the other is smaller than 3 eV, to adjust electrical characteristics and achieve desired threshold voltage and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single oxide semiconductor layer is used, then the structure is simple, but the electrical characteristics cannot be precisely adjusted to achieve positive threshold voltage
Solution Approach 1:
The semiconductor layer is divided into multiple oxide semiconductor sub-layers, each with different energy gaps (≥3 eV and <3 eV). This segmentation allows independent control of electrical characteristics for each sub-layer, enabling precise adjustment of threshold voltage to achieve positive values for normally-off transistor operation.
Solution Approach 2:
The patent employs a composite structure of multiple oxide semiconductor materials with different energy gap characteristics. By combining materials with energy gaps ≥3 eV and <3 eV in a stacked configuration, the invention achieves synergistic effects that enable precise threshold voltage control while maintaining the benefits of oxide semiconductor technology.
2Ease of operation
If the threshold voltage is negative, then the transistor is normally-on type with easy conduction, but it is difficult to control and不适合 for integrated circuits
Solution Approach 1:
The invention changes the energy gap parameters of the oxide semiconductor layers to achieve positive threshold voltage. By selecting materials with specific energy gaps (≥3 eV and <3 eV) and configuring them in a stacked structure, the threshold voltage is shifted from negative to positive values, enabling normally-off operation with improved circuit control while maintaining conduction characteristics.
3Speed
If the on-state characteristics are improved for high-speed operation, then the field-effect mobility increases, but the off-state current may increase leading to higher power consumption
Solution Approach 1:
Different regions of the semiconductor structure (different oxide semiconductor sub-layers) are assigned different energy gap qualities. The sub-layer with energy gap ≥3 eV provides low off-state current and low power consumption, while the sub-layer with energy gap <3 eV provides high field-effect mobility and high-speed operation. This local differentiation of material properties enables simultaneous optimization of both speed and power characteristics.
Data Source
AI summary
Provided are a transistor which has electrical characteristics requisite for its purpose and uses an oxide semiconductor layer and a semiconductor device including the transistor. In the bottom-gate transistor in which at least a gate electrode layer, a gate insulating film, and the semiconductor layer are stacked in this order, an oxide semiconductor stacked layer including at least two oxide semiconductor layers whose energy gaps are different from each other is used as the semiconductor layer. Oxygen and/or a dopant may be added to the oxide semiconductor stacked layer.