Semiconductors and Devices

Developing eco-friendly and highly efficient devices is one of the emerging interests in materials engineering. From fundamental functional materials such as 2D materials, thin films, and ferroelectrics to next-generation devices such as triboelectric nanogenerators, 2D material-based devices, and ferroelectric-based devices, our research aims to understand the basic chemical and physical properties of those materials in their as-synthesized forms and to apply them for diverse device systems with improved performance and stability.

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Ferroelectric Materials

Ferroelectric HfO2 films have gained great attention due to their large polarization & coercive field, scalability down to sub-10 nm scale, and their compatibility with conventional silicon-based devices. HfO2 films are known to exhibit ferroelectricity at nanometer-scale thicknesses, but questions about size, structure, distribution of ferroelectric domains within the film, and characteristics of grain boundaries that govern the overall ferroelectric properties of the HfO2 film are yet to be answered. In particular, the stabilization mechanisms of the ferroelectric phase in HfO2 are of our interest. We analyze the HfO2 films with various electron microscopy methods such as cross-sectional (S)TEM, in-plane (S)TEM, iDPC-STEM to determine the relationship between physical properties and crystal structure. In addition, we are developing next-generation ferroelectric devices with fabrication techniques.

Devices Based on 2D Materials

Atomically thin 2D materials have unique physical properties in terms of electrical and thermal conductivity, mechanical flexibility, and optical transparency, which are different from their bulk counterparts. Industry-level device application of the 2D materials must be preceded by the development of large-scale 2D material growth with uniformly controlled size, thickness, and chemical composition. However, the controlled growth of 2D materials has been limited by challenges in stable and ratio-controlled supply of monomers onto the target substrate. We develop a uniform and controlled growth process for transition metal dichalcogenides (TMDs) monolayers by using conversion reaction of nanoparticles. We also develop the large-scale fabrication of ultrathin flexible field-effect transistors (FETs), logic gates, and phototransistors with reliable performances by using the uniform TMD monolayers grown by the nanoparticle precursors.

Device Fabrication Based On Nanoparticles

In our research, we utilize engineered NPs as a functional filler in a polymer matrix to develop practical applications, such as chemical/biochemical sensors and energy devices. We investigate engineering methods such as synthesis process control, functionalization, and structure control, to develop NPs with amplified functionalities that can form and improve the device’s capabilities.