Comparison of small cross inductors and rectangular inductors designed in 0.35um CMOS technology

This paper describes the design, and experimental characterization of cross inductors in a 0.35μm CMOS technology. The Sonnet tools were used to simulate and evaluate the performance of the new inductor structure, whose core has perpendicular crossed segments at the two highest layers available of the technology. Due to this arrangement, the positive as well as the negative mutual inductance are almost null. To make a fair comparison, the new structure and conventional rectangular inductor were designed to get similar inductance value, and with the same segment width and spacing fixed at 10μm. The proposed cross structure occupied an area of 160x140μm 2 while the square planar inductor presents an area of 180x180μm 2 . Thus, the last one occupies 45% more area than the cross inductor. Some deembedding structures were fabricated and used to subtract the effect of the test-fixture in the on-wafer measurements. The main experimental results are: for cross inductor an inductance value of 2.1nH and Q of 3.3 at 5.2GHz and for the square one an inductance of 1.9nH and Q of 5.5 at 5.5GHz. Although, for similar inductance value, the quality factor of the cross inductor is lower than for the rectangular inductor one, the new cross inductor structure shows to be useful at RF circuits where the inductors are largely used and the most area consuming components.