Three-Dimensional Solenoids Realized via High-Density Deep Coil Stacking for MEMS Application

Three-dimensional solenoids have been developed and demonstrated for the first time in stacking of through-silicon via chips. High-density microcoils (width, space, and depth with 24 turns) were completely filled with Cu. Eight high-density microcoil chips were stacked using a conductive adhesive. The inductance of the eight stacked high-density microcoil chips is measured to be at 0.9 MHz, and the maximum magnetic field reaches to 0.67 mT, as characterized by a magnetic field detector 2 mm above the cavity center of the coils. The eight stacked high-density microcoil chips achieved 66-h operation under continuous current (0.2 A) stress testing without failure. Two microcoil chips stacked using solder also completed 1000 thermal cycles (to 125) successfully with merely 3.7% resistance change.