半导体器件与宏微实验室特邀3位专家来校作学术报告，欢迎感兴趣的师生参加。具体信息详见附件如下：

Time： Thursday, 9:30 am ~11:30 am, February 13th, 2025

 Venue：E-Valley Training Camp (电信群楼4号楼1楼E谷训练营)

Title：Development of High-Performance p-type Transistors

Prof. Yong-Young Noh，Namgo Chair Professor，Department of Chemical Engineering，Pohang University of Science and Technology ((POSTECH))

Abstract

Developing high-mobility p-type oxide semiconductors that can be grown using silicon-compatible processes at low temperatures, has remained challenging in the electronics community to integrate complementary electronics with the well-developed n-type counterparts. This presentation will discuss our recent progress in developing high-performance p-type semiconductors as channel materials for thin film transistors. For the first part of my talk, I present an amorphous p-type oxide semiconductor composed of selenium-alloyed tellurium in a tellurium sub-oxide matrix, demonstrating its utility in high-performance, stable p-channel TFTs, and complementary circuits [1]. Theoretical analysis unveils a delocalized valence band from tellurium 5p bands with shallow acceptor states, enabling excess hole doping and transport. Selenium alloying suppresses hole concentrations and facilitates the p orbital connectivity, realizing high-performance p-channel TFTs with an average field-effect hole mobility of ~15 cm2V-1s-1 and on/off current ratios of 106 ~107, along with wafer-scale uniformity and long-term stabilities under bias stress and ambient aging. Tin (Sn2+) halide perovskites emerge as promising p-type candidates but suffer from low crystallisation controllability and high film defect density, which result in uncompetitive device performance. In the second part of my talk, I would like to introduce a general overview and recent progress of our group of p-type Sn-based metal halide perovskites for applying field-effect transistors (FETs). I will mainly address inorganic perovskite thin-film transistors with exceptional performance using high-crystallinity and uniform cesium-tin-triiodide-based semiconducting layers with moderate hole concentrations and superior Hall mobilities, which are enabled by the judicious engineering of film composition and crystallization. The optimized devices exhibit high field-effect hole mobilities of over 50 cm2 V-1s-1, large current modulation greater than 108, and high operational stability and reproducibility [1,2]. Next, I will introduce A-site cation engineering method to achieve high-performance pure-Sn perovskite thin-film transistors (TFTs). We explore triple A-cations of caesium-formamidinium-phenethylammonium to create high-quality cascaded Sn perovskite channel films, especially with low-defect phase-pure perovskite/dielectric interface. As such, the optimized TFTs show record hole mobilities of over cm2 V-1s -1 and on/off current ratios of over 108, comparable to the commercial low-temperature polysilicon technique level [3]. The p-channel perovskite TFTs also show high processability and compatibility with the n-type metal oxides, enabling the integration of high-gain complementary inverters and rail-to-rail logic gates.

References

[1] A. Liu, Y.-Y. Noh et al, Nature, 629, 798–802 (2024)

[2] A. Liu, Y.-Y. Noh et al, Nature Electronics 5, 78-83 (2022).

[3] A. Liu Y.-Y. Noh et al, Nature Electronics 6, 559-571 (2023).

[4] H. H. Zhu, Y.-Y. Noh et al, Nature Electronics 6, 650-657 (2023).

Title: High-k Polymer Dielectrics for Thin-Film Transistor Applications

Prof. Hyun-Suk Kim，School of Energy and Materials Engineering Dongguk University(DGU)

Abstract

Oxide semiconductors have emerged as promising materials for electronic device applications due to their unique combination of electrical, optical, and structural properties. These materials exhibit high mobility, transparency in the visible spectrum, and low leakage current, making them suitable for the active layer in thin-film transistors (TFTs) used in the backplanes of cutting-edge displays.[1] However, the demand for next-generation displays has driven the development of deformable displays using non-traditional substrates rather than rigid ones. Conventional inorganic gate dielectric materials, such as SiOx and AlOx, face integration challenges in flexible devices due to their brittle nature, temperature limitations of deformable substrates, and high costs. Organic materials offer a solution with their flexibility and low processing temperatures.[2]

Organic gate dielectrics are typically fabricated using solution processes like spin coating. However, these methods often compromise film quality due to residual impurities and thermal damage during post-coating baking steps, negatively impacting their electrical and physical properties. Unlike most polymers, poly(chloro para-xylylene) (Parylene) can be deposited via vacuum-based pyrolysis-CVD at low temperatures, resulting in pinhole-free films with excellent step coverage.[3]This method allows for conformal coating and uniform thickness over complex structures, minimizing interface issues encountered with other techniques. Additionally, the properties of the parylene family can be tailored through functionalization.

In this work, parylene-based polymer gate dielectrics were evaluated as alternatives for oxide thin film transistors (TFTs). Three types of conventional parylene (Parylene-C, Parylene-D, and Parylene-AF4) were tested for transistor applications. Additionally, two custom-synthesized parylene types were examined, both showing higher dielectric constants compared to conventional variants. Parylene-Ethynyl achieved more than double the dielectric constant through click chemistry, while Parylene-OH exhibited a significantly higher dielectric constant and UV-reactive nature, enabling UV crosslinking. The intrinsic photo-reactive nature of parylene allows for direct patterning with UV radiation, eliminating the need for additional photoresist. The vacuum-based vapor process ensures excellent interface quality without impurities or voids for both conventional and custom-synthesized variants. Parylene shows promise for a wide range of applications.

References:

[1] K. Nomura et al., Nature 432.7016, p488-492 (2004)

[2] B. Nketia-Yawson, and Y. Noh, Advanced Functional Materials 28.42, 1802201 (2018)

[3] J. Kim et al., ACS Applied Materials & Interfaces 13.36, 43123-43133, (2021)

Title: Bio-Inspired Micro/Nanostructures for Electronic Skin Sensors

Prof. Hyunhyub Ko  School of Energy and Chemical Engineering ，Ulsan National Institute of Science and Technology (UNIST)

Abstract

Electronic skin sensors with high sensitivities have gained great attention in the fields of human-machine interfaces, robotic skins, and healthcare applications. Although various types of wearable soft sensors based on novel materials and sensing mechanisms have been introduced, there remain challenges in their practical applications. To address these challenges, we draw inspiration from biological systems, which have evolved unique micro/nanostructures with excellent sensory capabilities and functions through continued adaptation to environmental changes. Inspired by the structure and function of biological systems, we present several structural design strategies for micro/nanostructured polymer composites as soft sensors with excellent sensing capabilities and their applications in wearable devices and human-machine interfaces. First, inspired by the fingertip skin structure and function, we develop multifunctional electronic skins capable of differentiating various mechanical stimuli (normal, shear, stretching, bending), static and dynamic pressure, and temperature with high sensitivities. Second, inspired by the sound frequency tunability of the cochlea, we demonstrate frequency-selective acoustic and haptic sensors for dual-mode human-machine interfaces (HMIs) based on triboelectric sensors with hierarchical ferroelectric composites. Finally, mimicking stimuli-responsive color changing structures found in biological systems, we present colorimetric tactile sensors that can monitor external forces based on the color change signals.