This study systematically investigates the failure mechanisms of silicone encapsulants in high-power light-emitting diode (LED) packages under thermal stress. The silicone material before and after thermal aging was characterized by scanning electron microscopy (SEM) for morphology observation and elemental analysis, combined with thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The results indicate that thermo-oxidatively aged encapsulants exhibited brittleness, cracking, and other failure phenomena. Compared with unaged samples, the aged encapsulant displayed a significantly rougher surface with particulate precipitation. Elemental analysis revealed substantially higher silicon mass fraction in aged/cracked regions than in intact areas. FTIR characterization further confirmed pronounced oxidative degradation of side chains in failed specimens. TGA and DSC curves further revealed that silicone undergoes simultaneous degradation and cross-linking under thermo-oxidative stress. It is concluded that the failure mechanisms of silicone materials under thermo-oxidative stress mainly involve two chemical pathways: oxidative cross-linking of side groups and cyclization depolymerization of the main Si−O chain.
This study presents a comprehensive investigation on the properties of negative capacitance field-effect transistors (NCFETs) based on the metal-ferroelectric-insulator-semiconductor (MFIS) structure with HfxZr1−xO2 (HZO, 0.5≤x≤0.9) thin film. The results indicate that the NCFETs exhibit excellent subthreshold swing (SS) values, consistently below 60 mV·decade−1, which is the theoretical physical limit of conventional Si-based field-effect transistors (FETs). The ferroelectric HZO composition significantly influences the longitudinal electric field, electron concentration, and hole concentration within the channel, thereby directly affecting the SS and saturation current. Notably, the MFIS NCFET incorporating an Hf0.5Zr0.5O2 ferroelectric layer exhibited the lowest SS. Moreover, by modifying the dielectric material and channel length, variations in the trends of SS and saturation current were observed. The device with ZrO2 dielectric layer, characterized by the highest dielectric constant, demonstrated the lowest SS of 47.49 mV·decade−1. Furthermore, the SS decreased as the channel length increased from 50 nm to 1000 nm. This research provides theoretical support for the performance optimization of low-power NCFETs and negative capacitance capacitors.
