Composite Oxide Semiconductor CAC Structure for Stable TFT Switching
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Solution Overview
Problem
Existing transistors using In—Ga—Zn-based metal oxides suffer from high subthreshold swing (S value) and threshold voltage (Vth), leading to a normally-on characteristic, which affects their electrical performance and reliability.
Innovation Solution
A composite oxide semiconductor with a cloud-aligned composite (CAC) structure is introduced, comprising regions with varying elemental distributions, including In, Zn, and additional elements like Al, Ga, Si, etc., forming a mosaic pattern with distinct band gaps, enhancing field-effect mobility and switching characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a two-layer stack of indium zinc oxide and IGZO is used as the active layer, then field-effect mobility is improved (μ=62 cm²V⁻¹s⁻¹), but subthreshold swing becomes large (S=0.41 V/decade) and threshold voltage becomes negative (Vth=-2.9 V)
Solution Approach 1:
The active layer is divided into three distinct layers: a first insulating layer (In-Zn-O), a semiconductor layer (In-Ga-Zn-O), and a second insulating layer (In-Al-Zn-O). This segmentation allows each layer to perform its specific function - the semiconductor layer provides high mobility while the insulating layers control the threshold voltage and improve subthreshold characteristics, resolving the contradiction between mobility and reliability.
Solution Approach 2:
Different regions of the active layer are assigned different material compositions and properties. The first insulating layer has high insulation properties to prevent carrier generation, the semiconductor layer has high mobility for fast switching, and the second insulating layer provides additional insulation. This local differentiation allows the structure to achieve both high mobility and reliable switching characteristics simultaneously.
2Ease of manufacture
If In-Ga-Zn-based metal oxide is used for the transistor, then manufacturing is simplified, but electrical performance deteriorates due to high S value and normally-on characteristic
Solution Approach 1:
The invention uses a composite structure combining three different metal oxide materials (In-Zn-O, In-Ga-Zn-O, and In-Al-Zn-O) in a stacked configuration. This composite approach maintains the ease of manufacturing oxide-based transistors while achieving superior electrical characteristics through the synergistic combination of materials with different properties, resolving the contradiction between manufacturing simplicity and electrical performance.
Data Source
AI summary
A novel material and a transistor including the novel material are provided. One embodiment of the present invention is a composite oxide including at least two regions. One of the regions includes In, Zn and an element M1 (the element M1 is one or more of Al, Ga, Si, B, Y, Ti, Fe, Ni, Ge, Zr, Mo, La, Ce, Nd, Hf, Ta, W, Mg, V, Be, and Cu) and the other of the regions includes In, Zn, and an element M2 (the element M2 is one or more of Al, Ga, Si, B, Y, Ti, Fe, Ni, Ge, Zr, Mo, La, Ce, Nd, Hf, Ta, W, Mg, V, Be, and Cu). In an analysis of the composite oxide by energy dispersive X-ray spectroscopy, the detected concentration of the element M1 in a first region is less than the detected concentration of the element M2 in a second region, and a surrounding portion of the first region is unclear in an observed mapping image of the energy dispersive X-ray spectroscopy.