Indium Oxide FET with i-Type Layer for Normally Off Operation
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Solution Overview
Problem
Field effect transistors (FETs) using oxide semiconductors with indium as a main component face challenges in achieving high mobility while maintaining a normally off characteristic, as they tend to be normally on due to high carrier concentrations, which is exacerbated by oxygen deficiency and the difficulty in setting carrier concentration below 1×10^18/cm^3.
Innovation Solution
The FET design incorporates a first oxide semiconductor with indium as a main component and a second i-type oxide semiconductor with a wider bandgap, where the energy difference between the vacuum level and the Fermi level of the second oxide semiconductor is greater than that of the first, forming a junction that reduces electron concentration near the interface, allowing for a normally off characteristic by creating a quasi-i-type region with high field effect mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an oxide semiconductor with indium as a main component is used to achieve high field effect mobility, then the field effect mobility increases to 50 cm2/Vs or higher, but the device exhibits normally on characteristic due to high carrier concentration caused by oxygen deficiency
Solution Approach 1:
The semiconductor layer is divided into two distinct regions: a first region containing an oxide semiconductor with indium as main component for high mobility, and a second region containing an i-type oxide semiconductor with wider bandgap for carrier concentration control. This segmentation allows each region to fulfill its specific function without compromising the other.
Solution Approach 2:
Different regions of the semiconductor layer are assigned different material compositions and properties. The first region uses indium-rich oxide semiconductor for high mobility, while the second region uses i-type oxide semiconductor for low carrier concentration, creating local quality variations that solve the contradiction between mobility and normally off characteristic.
2Reliability
If the carrier concentration is reduced to achieve normally off characteristic, then the normally off characteristic improves, but the field effect mobility decreases below 50 cm2/Vs
Solution Approach 1:
The semiconductor layer is divided into two distinct regions: a first region containing an oxide semiconductor with indium as main component for high mobility, and a second region containing an i-type oxide semiconductor with wider bandgap for carrier concentration control. This segmentation allows each region to fulfill its specific function without compromising the other.
Solution Approach 2:
Different regions of the semiconductor layer are assigned different material compositions and properties. The first region uses indium-rich oxide semiconductor for high mobility, while the second region uses i-type oxide semiconductor for low carrier concentration, creating local quality variations that solve the contradiction between mobility and normally off characteristic.
3Device complexity
If a single oxide semiconductor layer is used to simplify device structure, then the device complexity is reduced, but it is impossible to simultaneously achieve high mobility and normally off characteristic
Solution Approach 1:
The semiconductor layer is divided into two distinct regions: a first region containing an oxide semiconductor with indium as main component for high mobility, and a second region containing an i-type oxide semiconductor with wider bandgap for carrier concentration control. This segmentation allows each region to fulfill its specific function without compromising the other.
Solution Approach 2:
The semiconductor layer is formed as a composite structure combining two different oxide semiconductor materials: indium-rich oxide semiconductor and i-type oxide semiconductor with wider bandgap. This composite material approach enables simultaneous achievement of high mobility and normally off characteristic within a single integrated layer.
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 achieves a high field effect mobility and a normally off characteristic by reducing electron concentration and maintaining the high mobility of the first oxide semiconductor, while ensuring a sufficiently high threshold voltage and low off-state current.
Implementation Method 1
an energy difference between a vacuum level of the second oxide semiconductor and a Fermi level of the second oxide semiconductor is larger than an energy difference between a vacuum level of the first oxide semiconductor and a Fermi level of the first oxide semiconductor
Data Source
AI summary
An insulating film is provided over one surface of a first semiconductor layer including a first oxide semiconductor including indium as a main component, and a second semiconductor layer including an i-type second oxide semiconductor is provided in contact with the other surface. The energy difference between a vacuum level and a Fermi level in the second oxide semiconductor is larger than that in the first oxide semiconductor. In the first semiconductor layer, a region in the vicinity of the junction surface with the second oxide semiconductor which satisfies the above condition is a region having an extremely low carrier concentration (a quasi-i-type region). By using the region as a channel, the off-state current can be reduced. Further, a drain current of the FET flows through the first oxide semiconductor having a high mobility; accordingly, a large amount of current can be extracted.