Quality factor enhancement of CMOS inductor with pyramidal winding of metal turns

In order to exploit the available multilevel interconnects and to reduce the parasitic capacitances, the metal can be traced spirally up and/or down in a pyramidal manner. This paper presents two methods to improve the quality factor (Q) of pyramidically wound inductors. The first method utilizes bulk micromachining to improve the Q. Quality factor improvement of 14.7% and 19.5% and self resonating frequency improvement of 26.5% and 30.6% respectively were observed in 10 nH and 20 nH over conventional micromachined planar inductors. The second method to improve Q is by differential excitation and is illustrated for 8 nH and 23 nH symmetric pyramidal inductors. The performance of the pyramidically wound inductors are characterized using a full wave Electromagnetic simulator for a six metal layer 0.18 mum process.