Abstract
We report a fabrication technology for 3D air-core inductors for small footprint and very-high-frequency power conversions. Our process is scalable and highly generic for fabricating inductors with a wide range of geometries and core shapes. We demonstrate spiral, solenoid, and toroidal inductors, a toroidal transformer and inductor with advanced geometries that cannot be produced by wire winding technology. The inductors are embedded in a silicon substrate and consist of through-silicon vias and suspended windings. The inductors fabricated with 20 and 25 turns and 280-350 μm heights on 4-16 mm2 footprints have an inductance from 34.2 to 44.6 nH and a quality factor from 10 to 13 at frequencies ranging from 30 to 72 MHz. The air-core inductors show threefold lower parasitic capacitance and up to a 140% higher-quality factor and a 230% higher-operation frequency than silicon-core inductors. A 33 MHz boost converter mounted with an air-core toroidal inductor achieves an efficiency of 68.2%, which is better than converters mounted with a Si-core inductor (64.1%). Our inductors show good thermal cycling stability, and they are mechanically stable after vibration and 2-m-drop tests.
Highlights
Inductors and transformers are the fundamental building blocks of electronics, and they are found in every electronic device
We focus on the atomic layer deposition (ALD) of Al2O3, deep reactive ion etching (DRIE) for through-silicon vias (TSV) etching, Cu electroplating for TSVs and inductor windings, photoresist spray coating for buffered hydrofluoric acid (BHF) etching of Al2O3 and SiO2, and isotropic inductively coupled plasma (ICP) etching of the Si core
Compared with prior art on toroid inductors, we demonstrated a fourfold larger inductance density while keeping a good-quality factor and operation frequency
Summary
Inductors and transformers are the fundamental building blocks of electronics, and they are found in every electronic device. The PwrSoC vision is to integrate all power electronics components on one chip. One of the most important inductor requirements for PwrSoC technology is the CMOS compatibility for on-chip integration. Switching at very high frequencies (VHF, 30– 300 MHz) is one route toward PwrSiP and PwrSoC11,12. In the VHF range, inductors with an air core or non-magnetic core are preferred, as suitable magnetic materials working at these frequencies are limited and the core implementation is very challenging[13]. At 50 MHz, NiZn and CoNiZn have low magnetic saturation fluxes and cause detrimental core heating in high-flux power electronics applications[14]. VHF converters require inductance values of 10 s of nH, which is in the inductance range of air-core inductors, thereby lending themselves to a promising solution[15]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
