HY
H. Ye
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With the rapid development of science and technology, the Internet of Things and big data have become important forces driving the progress of modern technology. The evolution of these technologies has spurred the widespread application of smart devices and services, bringing revolutionary changes to various industries. In this context, flexible sensors have become a key bridge between the physical and digital worlds because of their unique bendability and high adaptability. They not only provide real-time data collection and transmission, but also serve a crucial role in health monitoring and environmental detection due to their lightweight and flexible characteristics. As fabrication technologies continue to innovate, flexible sensors are evolving towards miniaturization, integration, and customization. Although flexible sensors based on a variety of micro- and nanostructures and innovative materials have made significant progress in recent years, challenges still exist in terms of sensor performance, integration capability, and fabrication efficiency. To address these challenges, we utilized ultraviolet (UV) laser direct writing technology to efficiently achieve the microstructure fabrication and material modification required for the sensing capabilities of flexible sensors by precisely controlling the time, space, and energy of the laser. Correspondingly, we developed innovative fabrication technologies based on UV laser direct writing for different types of flexible sensors, including pressure sensors, strain sensors, gas sensors, and temperature sensors. The application of these technologies not only improves the fabrication efficiency but also enhances the sensor performance to meet the demands for customization and miniaturization.
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With the rapid development of science and technology, the Internet of Things and big data have become important forces driving the progress of modern technology. The evolution of these technologies has spurred the widespread application of smart devices and services, bringing revolutionary changes to various industries. In this context, flexible sensors have become a key bridge between the physical and digital worlds because of their unique bendability and high adaptability. They not only provide real-time data collection and transmission, but also serve a crucial role in health monitoring and environmental detection due to their lightweight and flexible characteristics. As fabrication technologies continue to innovate, flexible sensors are evolving towards miniaturization, integration, and customization. Although flexible sensors based on a variety of micro- and nanostructures and innovative materials have made significant progress in recent years, challenges still exist in terms of sensor performance, integration capability, and fabrication efficiency. To address these challenges, we utilized ultraviolet (UV) laser direct writing technology to efficiently achieve the microstructure fabrication and material modification required for the sensing capabilities of flexible sensors by precisely controlling the time, space, and energy of the laser. Correspondingly, we developed innovative fabrication technologies based on UV laser direct writing for different types of flexible sensors, including pressure sensors, strain sensors, gas sensors, and temperature sensors. The application of these technologies not only improves the fabrication efficiency but also enhances the sensor performance to meet the demands for customization and miniaturization.
This dissertation investigates copper sintering as a high-temperature die-attach technology for wide bandgap (WBG) power semiconductors such as SiC and GaN. WBG devices require advanced packaging solutions to maintain performance under high power, fast switching, and elevated temperatures. The study first employs molecular dynamics simulations to elucidate sintering mechanisms, microstructure evolution, and particle size effects, showing that applied pressure promotes plastic flow, densification, and pore reduction, while substrate pinning may induce residual stresses. Next, a self-developed Cu paste was fabricated and sintered under various temperature, pressure, and time conditions. Thermal and electrical conductivity, die shear strength, and microstructural evolution were evaluated, identifying 250°C, 3 min, and 20 MPa as an optimal processing window. Mechanical characterization including indentation hardness, elastic modulus, and creep behavior demonstrates the effect of process parameters on room-temperature properties and long-term reliability. Finally, pressure-assisted Cu sintering was applied to SiC power modules and compared with Ag-sintered modules. Both static and dynamic tests, including thermal cycling and high-temperature storage, confirm that Cu-sintered modules achieve equivalent performance and reliability at lower cost. The work establishes a systematic understanding of copper sintering processes, linking simulations, materials, processing, and application, providing a robust methodology for WBG power electronics packaging.
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This dissertation investigates copper sintering as a high-temperature die-attach technology for wide bandgap (WBG) power semiconductors such as SiC and GaN. WBG devices require advanced packaging solutions to maintain performance under high power, fast switching, and elevated temperatures. The study first employs molecular dynamics simulations to elucidate sintering mechanisms, microstructure evolution, and particle size effects, showing that applied pressure promotes plastic flow, densification, and pore reduction, while substrate pinning may induce residual stresses. Next, a self-developed Cu paste was fabricated and sintered under various temperature, pressure, and time conditions. Thermal and electrical conductivity, die shear strength, and microstructural evolution were evaluated, identifying 250°C, 3 min, and 20 MPa as an optimal processing window. Mechanical characterization including indentation hardness, elastic modulus, and creep behavior demonstrates the effect of process parameters on room-temperature properties and long-term reliability. Finally, pressure-assisted Cu sintering was applied to SiC power modules and compared with Ag-sintered modules. Both static and dynamic tests, including thermal cycling and high-temperature storage, confirm that Cu-sintered modules achieve equivalent performance and reliability at lower cost. The work establishes a systematic understanding of copper sintering processes, linking simulations, materials, processing, and application, providing a robust methodology for WBG power electronics packaging.