Research On Silicon-based On-chip Inductor And Its Applications In RFIC

Recently, silicon-based on-chip spiral inductor which can be widely used in wireless telecommunication has received more and more international attention as it is a key element to realize monolithic silicon-radio frequency integrated circuit (Si-RFIC). There are many aspects to research on-chip inductor and the research in this paper is on the computation of inductance and optimization of quality factor (Q) of inductor.Based on referring to many papers, we analyze in detail the energy loss mechanism of the inductor by electromagnetic theory and discuss several proposed approaches to optimizing the Q in substrate perspective. To optimize the Q in structure perspective, we put forward a novel inductor with variable width and space after a large amount of simulation by electromagnetic solver HFSS8.0. The proposed optimizing method is relatively easy to implement without any additional process cost. And based on Greenhouse algorithm, we compute the inductance of the novel inductor by physics -based approximation algorithm which calculates the inductance by summing every turn of the inductor and realizes the conversion between electrical parameter and geometrical parameters. The algorithm is efficient and scalable and also provides good accuracy for conventional inductor with errors of about 7%. After the optimization and computation of the on-chip inductor, we design a Butterworth low-pass filter (LPF) to explore the integration performance of the inductor.After a lot of experiments, monolithic on-chip inductors and LC filters are successfully fabricated on silicon with high resistivity in CMOS process. Measurement results indicate that the novel inductor with Q improved by 6.5% performs the same frequency characteristics as the conventional inductor. In addition, the error between the inductance calculated by the proposed physics-based approximation algorithm and measured inductance is within 9.4%, which shows the physics-based approximation algorithm is enough accurate for design. Moreover, the fourth-pole LPF cuts off at 4.7GHz which is close to the designed value at 5GHz.In conclusion, all the experiment results show that the proposed optimizing structure and physics-based approximation algorithm are reasonable and IC designers will benefit from them.