Sub-nH Inductor Modeling and Design in 90-nm CMOS Technology for Millimeter-Wave Applications

Inductor design is an important issue in millimeter-wave CMOS circuits. In these frequencies the required inductance is very small and hence special structure is required for inductors. The quality factor is the most important design parameter for these inductors, especially in CMOS process. To incorporate these inductors in circuit simulation, a simple lumped model is necessary. This work proposes a simple and accurate model, developed for design and optimization of such inductors. This model is based on quasi-transverse-electromagnetic-mode assumption. To increase the model accuracy we have separately modeled the short-end section of the inductor. Model parameters are calculated using reported analytic equations and some new empirical equations. Using this model we have designed and optimized a 250-pH inductor with different shield layers, for STMicroelectronics 90-nm digital CMOS process. The accuracy of the model parameters and the evaluation of the model has been carried out using 2-D and method-of-momentss electromagnetic solvers in Advanced Design System, with the substrate modeled using foundry design kit data.