Stretchable Inductor Design

High-quality inductors are difficult to realize in stretchable electronics, since the thick parallel traces needed to minimize resistance also result in a highly rigid structure. Adding periodic waves or kinks to the traces of an inductor coil has been found to result in a more compliant structure that will not permanently deform or break after stretching by tens of percent. In this paper, the effects on electrical performance of creating inductor coils from stretchable wavy traces are investigated. Eight different tortuous trace designs were modeled and experimentally tested in one- and three-turn inductors, as well as an electrical transformer design. Incorporating waves into an inductor was found to result in a negative mutual coupling along the traces, degrading the inductor performance. The incremental self-inductance per resistance of the added length due to the waviness, ~1.2 nH/Q, was similar for all interconnect types tested. This value is less than a third that of using a longer straight conductor of similar cross section (4.4 nH/Q), resulting in a drop in ratio of inductance to resistance and resulting peak quality factor in the measured inductors by as much as a factor of two.