Abstract
In this letter, we report the design and measurement of a 3D solenoid inductor that is embedded in a Si substrate and can integrate an iron core. Various inductor designs were fabricated with good structural integrity and repeatability via a CMOS-compatible MEMS fabrication process. The average inductance and quality factor peak-to-peak variation of the inductors was below 10%, which indicates that the fabrication process is repeatable. Among the inductors without iron cores, the highest quality factor (37.6 at 21 MHz) was found in a 5-turn inductor, and the highest inductance and inductance density (respectively, 86.6 nH and 21.7 nH/mm2) were found in a 20-turn inductor. Among the iron-core inductors, the 15-turn inductor had an inductance of 1063 nH and an inductance density of 354.3 nH/mm2, nearly 18 times higher than the same design without an iron core, which is the highest inductance density for a MEMS microinductor to the best of our knowledge. This type of inductor is an important component in RF MEMS and electromagnetic power MEMS devices and can improve their performance and efficiency.
Highlights
T HE inductor is the most basic component of electromagnetic devices and the fundamental building block of electronic devices
To examine the solid structure of the inductor solenoid more clearly, the silicon substrate of a 10-turn inductor was removed by etching in 25% tetramethyl ammonium hydroxide (TMAH) solution at 75 ◦C
We reported the design of a 3D solenoid inductor that is embedded in the substrate and can integrate an iron core
Summary
T HE inductor is the most basic component of electromagnetic devices and the fundamental building block of electronic devices. Power MEMS devices, such as transformers [5], [6], energy harvesters [7], and electromagnetic motors [8], usually require inductors with high inductance for power density and a high quality factor for efficiency. As MEMS devices are becoming increasingly compact, they require inductors with high current capacity but compact physical dimensions. These demands can be fulfilled by integrating all power electronic components into one chip [9], [10]; higher integration will lower cost, reduce the space needed, and increase power density.
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