Thin-film inductors

Thin-film inductors offer many practical advantages over air wound cores (though of course they can not achieve the same Q factors). Thin-film inductors are easier to pick and place in a SMT process than air core inductors. They can easily be processed in the IR, vapor phase and wave processes typically used in today’s assembly. Further, they will maintain value through those processes, as well as through handling and through high-vibration environments. Though they can not be tuned in circuit like air cores can, thin-film inductors can be used to replace air cores once an exact inductance value is determined for proper circuit function (assuming the Q factor is acceptable).

As in the case of thin-film capacitors, ESR and loss are dramatically reduced due to line width control and dielectric laydown quality/accuracy. This results in an end product which can be as small as an 0402 package with virtually any inductance value imaginable plus tolerance accuracy as close as 0.05 nH. Further, consistent metalization allows relatively high-current-carrying capability in thin-film inductors – up to 1,000 mA depending on device selected.

Other thin-film structures:

A variety of other structures have been created with the knowledge and process capability gained in manufacturing thin-film capacitors and inductors. Among these are couplers and harmonic low pass filters.

Miniature SMT couplers are a welcome addition to the designer’s toolbox. These devices provide high directivity, repeatable coupling with low insertion loss. They handle large amounts of power in a PCB footprint as small as 0402 with low profiles. As in the case with other thin-film components their electrical response and consistency on a lot-to-lot and inter lot basis is unmatched.

An example of thin-film inductor implementation might be in frequency compensation on broadband amplifiers. Previously, a resistor/inductor combination was used. As in the case of thin-film capacitors, the use of a thin-film inductor can reduce the number of components used in the circuit thereby saving size, weight, assembly and cost as well as improving reliability.

Just as thin-film capacitors, thin-film inductors are limited in maximum value.

In particular, a thin-film inductor provides designers with a good solution at extremely high frequencies. A common example is in multi-gigahertz oscillators. At high frequencies, wire-wound inductors may simply not be available, due to the absence of cost effective manufacturing techniques to build such low value wire-wounds.

At this point the designer is left with the choice of creating a low value inductor with serpentine PC board trace designs or choosing a miniature SMT thin-film inductor.

Though a PCB-based solution can be considered low cost, it uses valuable board space, and can vary based upon the PCB supplier. The thin-film inductor will have the same extremely repeatable and consistent frequency response on a lot-to-lot basis and on an inter lot basis as that of thin-film capacitors.