Composite Oxide Semiconductor CAC Structure for Threshold Voltage Control
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Solution Overview
Problem
Existing transistors using In-Ga-Zn-based metal oxides exhibit high field-effect mobility but have large 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 developed, comprising regions with varying elemental distributions, including In, Zn, and additional elements like Al, Ga, Si, B, Y, Ti, Fe, Ni, Ge, Zr, Mo, La, Ce, Nd, Hf, Ta, W, Mg, V, Be, and Cu, with specific micrograin sizes and concentrations, enhancing electrical characteristics and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a two-layer stack of In-Zn oxide and In-Ga-Zn oxide is used as the active layer, then field-effect mobility is improved (μ=62 cm²V⁻¹s⁻¹), but the subthreshold swing becomes large (S=0.41 V/decade) and the transistor exhibits normally-on characteristic (Vth=-2.9 V)
Solution Approach 1:
The patent applies local quality by creating distinct regions within the metal oxide semiconductor layer with different elemental compositions. Specifically, it forms regions enriched with Ga elements and regions enriched with In elements, where each region has optimized local properties: Ga-enriched regions provide appropriate threshold voltage and switching characteristics, while In-enriched regions contribute to high field-effect mobility. This spatial differentiation of composition resolves the contradiction between mobility and electrical characteristics.
Solution Approach 2:
The patent employs composite materials by combining multiple metal elements (In, Ga, Zn) in specific ratios and distributions within the semiconductor layer. The composite oxide semiconductor contains In-Ga-Zn-O with controlled atomic ratios (In: 20-40 at%, Ga: 10-30 at%, Zn: 20-40 at%), creating a material that integrates the beneficial properties of different metal oxides to achieve both high mobility and proper switching characteristics simultaneously.
2Speed
If In-Ga-Zn-based metal oxide is used to achieve high field-effect mobility, then transistor speed is improved, but electrical performance and reliability deteriorate due to large S value and Vth
Solution Approach 1:
The patent creates spatial variation in elemental distribution within the metal oxide semiconductor. By forming Ga-enriched regions and In-enriched regions with different local compositions, it achieves local optimization: Ga regions control threshold voltage and switching behavior for reliability, while In regions enhance carrier mobility for speed, resolving the performance-reliability contradiction.
Solution Approach 2:
The patent modifies key parameters including elemental composition ratios (In: 20-40 at%, Ga: 10-30 at%, Zn: 20-40 at%), oxygen content (40-60 at%), and micrograin size (0.5-3 nm). These parameter adjustments optimize the balance between mobility and electrical characteristics, enabling high-speed operation with reliable switching behavior.
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.