A device includes a flexible substrate, N coiled conductors, and a plurality of folding regions. The N coiled conductors are deposited on the flexible substrate and connected in series by conductive interconnects. N is greater than 1. Each of the folding regions is defined by a separation distance between adjacent ones of the N coiled conductors. The conductive interconnects traverse the folding regions between the N coiled conductors to connect the N coiled conductors in series. The flexible substrate is folded such that the N coiled conductors form a stack of N coiled conductors.