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 SiO₂ 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 SiO₂ was measured at 4.6 MV/cm. Experiments show that coils with 40-mum pitch, 30 times 30-mum² winding cross section, and SiO₂ thickness of 1 mum may carry more than 1 A (larger than 10⁹ A/m²) with less than 10degC temperature change. These characteristics make the coils useful in small-scale actuators and power systems.