Indium oxide transistors fabricated via atomic layer deposition

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master_Lambrou_Ion_2025.pdf (5.23 MB)

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School of Chemical Engineering | Master's thesis
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Date

2025-09-12

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Functional Materials

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Degree programme

Master's Programme in Chemical, Biochemical and Materials Engineering

Language

en

Pages

89

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Abstract

Indium oxide (In2O3) has attracted a lot of attention as a channel layer material in complementary metal oxide (CMOS) back end of line (BEOL) compatible thin film transistors (TFTs) due to its high mobility and low off-state current even at sub-nanometre level thicknesses. The capability of atomic layer deposition (ALD) to deposit smooth and conformal In2O3 films with atomic level thickness control across complex geometries at low temperatures enables the In2O3 to become a key material in next generation logic and memory components that require monolithic 3D integration. This thesis presents the fabrication and characterisation of TFTs with ALD deposited In2O3 channel layers. The work focuses on developing and optimising the ALD process for In2O3, designing and fabricating transistors and lastly characterising both the material properties of the films and the electrical performance of the transistors. Films were deposited at two different temperatures (150 °C and 120 °C) resulting in 5 samples with different thicknesses ranging between ~2-5 nm. For each film sample, transistors with channel lengths ranging between 1 μm and 20 μm were fabricated. It was examined how the deposition temperature, In2O3 thickness and channel length affect the performance of the transistors and quality of the films. The fabricated TFTs had amorphous In2O3 channels that were slightly carbon doped and exhibited mobility values as high as 25.7 cm2/V·s. The TFT with the overall best performance had a 3.2 nm In2O3 layer and displayed a mobility of 11.7 cm2/V·s, threshold voltage of -37 V and an Ion/off ratio in the range of 105 for a channel length of 1 µm. These results indicate the feasibility of fabricating functional TFTs with ALD deposited In2O3 and relatively high mobility at a low fabrication temperature of 150 °C.

Description

Supervisor

Miikkulainen, Ville

Thesis advisor

Kilpi, Olli-Pekka
Eskelinen, Patrik

Keywords

ALD, atomic layer deposition, indium oxide, In2O3, transistor, TFT, microfabrication

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https://urn.fi/URN:NBN:fi:aalto-202510228517

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[dipl] Kemian tekniikan korkeakoulu / CHEM