Design and Fabrication of Integrated Power Inductor Based on Silicon Molding Technology

Abstract

This paper reports a new fabrication process that can be used to integrate high-power-density and low-loss inductors with silicon-based power ICs to realize monolithic integration of power converters for portable electronics applications. In this new process, copper is electroplated into through-wafer silicon trenches, resulting in thick copper windings (200~500 µm) and thus low winding resistance. The magnetic cores are electroplated on both sides of the silicon substrate to cover the copper windings, and through-wafer magnetic vias are used to close the magnetic path. Powder permalloy with relatively high resistivity (400 µ ·cm) and low permeability (40) are used to reduce the loss of large magnetic cores. The powder permalloy can be fabricated by using high-current-density electroplating without mixing or high temperature sintering. A pot-core inductor has been designed and fabricated. The inductance and saturation current of the designed inductor are 179 nH and 5 A, respectively. The measured winding resistance of the 200 µm thick copper winding is 23 m .

A Technology Overview of the PowerChip Development Program

“…Similar inductors and transformers have also been successfully electroplated in copper on Pyrex substrates [49], [50]. Thick spiral inductors [51] and toroidal inductors [52], [53] have also been embedded in silicon and other substrates.…”

A novel integrated power inductor in silicon substrate for ultra-compact power supplies

“…The copper winding is formed inside the silicon substrate by electroplating. The electroplating molds are created by deep reactive ion etch (DRIE) of silicon [16]. Silicon DRIE offers high aspect ratios, typically about 20:1.…”

“…PSoC, on the other hand, employs CMOS technology and/or microfabrication technology to fabricate power inductors directly on IC chips. Several PSoC power inductors have been reported, such as spiral air core inductors [9,10], sputtered magnetic inductors [11,12], electroplated magnetic inductors [2,[13][14][15][16][17] and ferrite magnetic inductors [18,19]. These inductors are typically fabricated on the top of CMOS substrates.…”

Design and fabrication of micro-coils for NMR micro probes

“…Table 2.2 summarizes the most relevant planar micro-coils realized through copper electroplating inside trenches of different substrates. It can be seen from Table 2.2 that micro-coils embedded in a silicon substrate have been reported by [33][34][35][36][37] and they employ Cu electroplating to achieve thick copper depositions in the Si substrate. Similarly, planar micro-coils embedded inside other polymer based materials such as SU8 [40,43], parylene [42], polymide [39] and even inside trenches defined by photoresist [41] have also been reported.…”

“…A Si substrate also gives a highly planar top surface which allows realizing polymer-based microfluidics or other structures fabricated by subsequent post-processing. But the greatest advantage of realizing micro-coils in Si is that it is IC-compatible process [36]. It can start with silicon wafers with ICs already built by commercial IC foundry.…”