This thesis reports the analysis, design, and fabrication of planar micro-inductors on silicon substrate by using the conventional semiconductor process. A small and thin planar type micro-inductor is proposed for low-power and low-voltage CMOS DC-DC converters where low resistance(＜ 1 Ω) and high inductance(＞600 nH) are required. This micro-inductor consists of spiral type Cu coils and NiFe permalloy magnetic cores.
To design the spiral type micro-inductor, computer simulations have been performed for various design parameters such as coil width, coil spacing, core gap, and core overlap over the coil edge, etc. From simulations a few key parameters have been determined for optimum design. Cu coils and NiFe cores are formed by using electroplating process. PI2556 polyimide is used for insulation layers. All the unit processes are carried at low temperatures below 300℃, so that this inductor can be fabricated on the top of on-chip integrated circuits as post IC processes.
A planar spiral type micro-inductor with a single core located under the coils has been fabricated. The coil width is 100㎛ and 200㎛, the coil thickness is 10㎛, and the core thickness is 8㎛, respectively. This inductor shows about 45% increase in inductance over the air core inductor. This increase over the air core inductor decreases as the frequency goes higher. The maximum Q-value is measured about 6 at 10MHz. Magnetic saturation current is estimated about 1.6 A and 0.8 A for the 200um-wide and 100um-wide coils, respectively, which are both higher than the required average d.c. current(300 mA) for CMOS DC-DC converters.
