Electromagnetic Characteristic Analysis of Microbump Structures Under Standard Integrated Circuit Processes

To evaluate microbump antenna performance for high-frequency communications, this study utilizes 3D electromagnetic simulations comparing solder-ball and copper-pillar structures across three feeding schemes. The simulation results show that the copper-pillar type exhibits a lower resonant frequency and more stable relative bandwidth (with a fluctuation of only 0.63%) under the same feeding condition, while the bandwidth fluctuation of the solder-ball type reaches 13.17%. Regarding gain characteristics, the absolute differences between the two structures across all feeding methods remain negligible (within 0.03–0.06 dBi). Both antenna types exhibit the highest realized gain among the investigated schemes under microstrip feeding, yielding 5.54 dBi for solder-ball and 5.48 dBi for copper-pillar configurations, while coaxial center feeding results in the minimum gain. Given the extreme difficulty of sub-THz measurements, a measurement-compatible GSG-fed copper-pillar-type model resonating at 477.9 GHz was designed and subsequently enlarged by a factor of 46 according to the electromagnetic similarity principle. It should be emphasized that the fabricated and measured prototype is the scaled 10.4–10.5 GHz model rather than the original sub-THz microbump antenna. Based on the electromagnetic similarity principle, the measured resonant frequency and gain of the antenna are 10.5 GHz and 7.1 dBi, respectively. The measured S parameters are generally consistent with the simulated ones in trend. Therefore, under the same conditions considered in this work, the copper-pillar-type microbump antenna can achieve a lower resonant frequency and more stable relative bandwidth; while microstrip feeding provides the highest realized gain among the three investigated feeding schemes. The conclusions provide data support for the antenna-in-package design and performance optimization of microbump antennas.