Two-layer electroplated microcoils with a PECVD silicon dioxide interlayer dielectric

This paper covers the design, fabrication, and characterization of two-layer microcoils wherein an unannealed plasma-enhanced CVD Si[O.sub.2] functions as the insulator between silicon-and photoresist-molded copper coils. This design overcomes the thermal limitations placed upon coils that are embedded within polymer molds and thereby enables higher current carrying capability. The fabrication process is compatible with deep reactive-ion etching and may be used to integrate coils with flexures/compliant mechanisms. Thermal and mechanical limitations were determined experimentally and used to create design rules that limit the coil design space. The breakdown strength of the unannealed Si[O.sub.2] was measured at 4.6 MV/cm. Experiments show that coils with 40-[micro]m pitch, 30 x 30-[micro][m.sup.2] winding cross section, and Si[O.sub.2] thickness of 1 [micro]m may carry more than 1 A (larger than [10.sup.9] A/[m.sup.2]) with less than 10[degrees]C temperature change. These characteristics make the coils useful in small-scale actuators and power systems. [2008-0170] Index Terms--Copper damascene, electroplating, magnetic microactuator, microcoil, microelectromechanical devices, silicon dioxide.