Effect of seed layers on the performance of planar spiral microinductors

This paper reports on the effect of the electrical performance related to magnetic seed layers used within planar power microinductors. These studies involve structural and magnetic characterisation of Ni80Fe20 films electro-deposited on non-magnetic and magnetic seed layers (i.e. copper and nickel respectively). Microelectronic mechanical test structures and xray analysis have been used to characterise the stress levels and structural properties of Ni80Fe20 films electro-deposited on both copper and nickel seed layers. In addition, planar spiral micro-inductors, with patterned magnetic cores, have been fabricated in order to confirm the improvement in the electrical performance from magnetic seed layers, as a result of enhanced magnetic and resistive contribution.

I. Introduction

Micro-inductors fabricated using MEMS-based processes are widely reported in the literature [1]–[3]. These processes typically involve a number of electro-deposition steps that require conductive ‘seed’ layers. It has been postulated that the use of magnetic seed layers, within the magnetic core, should improve electrical performance. However, detailed systematic experimental studies on any such improvement have not been documented in the literature. This paper quantifies the advantages of implementing magnetic seed layers for the electro-deposition of magnetic cores.