Wafer-Level Fabricated Double-Helix Rf-Mems Transformers with Coupling-Factor of 0.93@100Mhz For High-Efficiency Isolated Power/Signal Transmission

This paper presents silicon-chip-based 3D embedded double-helix RF transformers (EDHTs) that are wafer-level micromachined using the rapid molten-alloy MEMS-casting technique. With tightly coupled metal double-helix structure and ZnAl-alloy MEMS-casting process in silicon wafers, one EDHT with the tiny footprint of 1mm*2mm can be fabricated in batches. Isolation is achieved by the silicon dioxide layer formed by thermal oxidation between the coils. The EDHT is showing low enough DC resistance (0.8Ω) and 121.4nH inductance value which is several times higher inductance integration density than those planar spiral devices and measured to exhibit ultra-high coupling-factor (>0.90) and maximum transformer efficiency (>81%) in the wide frequency range of 30MHz~200MHz, being proved to significantly improve the efficiency and the integration-density in isolated power/signal transmission applications.