Characterization of symmetrical spiral inductor in 0.35 μm CMOS technology for RF application

Integrated Circuit and System Laboratory, Institute of Microelectronics, 11 Science Park Road, Singapore Science Park II, Singapore 117685, Singapore; School of Electrical and Electronics Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore
Solid-State Electronics (Impact Factor: 1.48). 09/2004; DOI: 10.1016/j.sse.2004.04.004

ABSTRACT Characteristics of symmetrical spiral inductor in differential mode is studied and optimized in this work. The characteristics of interest include inductor value, quality factor, peak frequency and self-resonance frequency. Both single-layer and double-layer inductor using top metals are characterized. Inductor excited in differential mode and single-ended mode are characterized for comparison. The optimized symmetrical spiral inductors are fabricated in standard digital 0.35 μm CMOS process. Experimental results show 60–100% improvement of quality factor and peak frequency, meanwhile 10–20% improvement of self-resonance frequency by exciting the symmetrical spiral inductors in differential mode compared with single-ended mode. To further validate the characterized inductor, the differential spiral inductors are adopted in optimizing low power and low phase noise fully integrated 2.4 GHz voltage-controlled oscillator (VCO). The designed VCO achieved phase noise of more than −105 dBc/Hz at 100 kHz offset with approximately 4.5 mA at 3.0 V supply.

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    ABSTRACT: This paper presents the design of a multilevel pyramidically wound symmetric (MPS) inductor structure. Being multilevel, the MPS inductor achieves high inductance to area ratio and hence occupies smaller silicon area. The symmetric inductor is realized by winding the metal trace of the spiral coil down and up in a pyramidal manner exploiting the multilevel VLSI interconnects technology. Closed form expressions are also developed to estimate the self resonating frequency (f res ) of the MPS inductor and results are compared to two layer conventional symmetric and asymmetric stack. The estimation is also validated with full wave electromagnetic simulation. The performance of various MPS inductors of different metal width, metal offsets and outer diameter is demonstrated. For an inductance of 8nH, the MPS inductor reduces the area by 65–95% over conventional planar symmetric inductors and 71–94% over its equivalent pair of asymmetric planar inductors. The performance is also compared to other symmetric inductors reported in literature. With MPS inductor, the cost and size of RF IC’s will be reduced significantly. KeywordsMultilevel symmetric spiral-Integrated-Inductance-Lumped model-Passive-Quality factor-Differential inductor-Inductance to area ratio
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