RF inductors with sputtered nanomagnetic films on glass substrates

Abstract

Inductors utilize spiral or helical designs to enhance magnetic flux and inductance. Spiral inductors require large footprint while solenoid inductors require thick substrates to achieve adequate flux coupling. As such, both these designs impose trade offs in inductance density, Q, and frequency stability. Nanomagnetic films with stable and high permeability can enhance inductance density and correspondingly the Q factor. However, nanomagnetic films suffer from two disadvantages. They have high losses beyond 1.0 GHz. They are also sputter-deposited as thin films that are less than five microns. Therefore, the benefits of nanomagnetic films in RF inductors are not clear. Performance improvements and trade-offs in RF inductors with nanomagnetic films are analyzed through material and component-level modeling. In the first part of the paper, nanomagnetic films and properties are modeled. The inductance density and Q trade-offs with nanomagnetic films are simulated after imposing their constraints: frequency dependence and thickness of five microns. Both helical and spiral inductors are considered with and without the nanomagnetic films. The simulations show enhancement in inductance by 5× with mild degradation in Q for spiral inductors. However, the Q degraded more with solenoid inductors. Higher resistivity and ferromagnetic resonance frequency are critical to improve the performance of nanomagnetic film inductors.