Anjan Chakravorty

In this brief, we present a novel multipath parallel-stacked inductor structure that significantly reduces the current crowding effects. Both the metal layers of the parallel stack are divided into multiple segments and crossovers are provided midway of each turn to steer the current in such a way that all its segments have equal path lengths. Following the multipath architecture, prototype inductor structures are fabricated in a 0.18-μm high-resistivity silicon-on-insulator technology using a dual thick metal stack process. Measurements show >30% improvement in quality factor (Q) with the proposed architecture when compared with a standard parallel-stacked inductor. The Q improvement achieved by the proposed inductor structure is shown to increase with the spiral thickness making them suitable for both radio frequency circuits and DC-DC buck converters without having to use magnetic materials. Via resistance is shown to limit the Q improvement possible with proposed inductor configuration.

In this brief, a novel combination of multilayer up-down series stacking and multipath architecture for equal path length is explored for the first time to improve the performance of on-chip inductors. The up-down series winding reduces the interlayer capacitance, thereby increasing both the peak quality-factor (Q) frequency (Q) and self resonant frequency (SRF). The crossover interconnection architecture ensures equal path length at every pair of spiral turns in the series stack. This architecture lowers skin and proximity effect losses in the spiral, increasing the slope of Q characteristics. Thus, using the proposed architecture, both the ac resistance and capacitance are simultaneously reduced while realizing higher inductance values. Implemented in a 0.18μ high resistivity silicon-on-insulator technology using a dual thick metal stack, the proposed inductor achieves more than 10% improvement in peak-Q value, 50% improvement in f Qmax, and 100% improvement in SRF values when compared with a conventional series stacked multipath inductor.