Concave-Suspended High-$Q$ Solenoid Inductors With an RFIC-Compatible Bulk-Micromachining Technology

Presented in this brief is a concave-suspended solenoid inductor that can be post-CMOS integrated into a low-resistivity silicon substrate using a novel radio frequency integrated circuit (RFIC)-compatible micromachining technology. The three-mask processes include photoresist spray coating, XeF
₂
gaseous etching and copper electroplating, etc. The fabricated 11.5-turn inductor is measured with 2.96-nH inductance at 5.35 GHz, where the peak Q-factor is as high as about 45. Even with a compact layout (50% area occupation saved), the 8.5-turn inductor is still measured with 2.78 nH and peak Q of about 28 at 4.90 GHz. Both finite element simulation and shock testing results show that the suspended inductor is almost free of influence from environmental vibration and shock. Featuring high-Q performance and robust properties, the RFIC-compatible inductors are promising for high-performance RFIC applications