The Development Of Model And Model Library For RF-CMOS On-chip Spiral Inductors

With the rapid development of silicon-based integrated circuits technology and wireless communication market, the radio frequency integrated circuits (RFICs) are applied widely for the advantages of low cost and low power. As a critical component of RFIC function cells such as LNA, VCO, Mixer, Filter, and PA, the design and optimization of on-chip spiral inductors are essential in circuits design. In addition, the performance of the devices and circuits on silicon substrate is degrading due to various losses in which the substrate loss is especially significant as frequency increased. Nowadays, advances in nano-scale CMOS technology even have made it feasible to implement W-Band circuits in CMOS. In this case, the parasitic effects such as the skin and proximity effects in the conductor and the eddy current effect in the substrate will become more serious, which increases the difficulty in device modeling. Thus, an accurate equivalent circuit model with robust parameter extraction methodology is indispensable for inductor characterization and circuit simulation for CMOS mixed-signal/RF SoC and millimeter-wave circuit designs. In this thesis, the analysis, Electro-magnetic (EM) simulation and modeling of on-chip spiral inductor are discussed.Firstly, the fundamentals of on-chip spiral inductors such as layout structures, performance parameters, loss mechanisms and modeling methods are discussed. The losses of metal and substrate which are two types of major loss mechanisms are discussed in detail. Subsequently, the major modeling methods of on-chip spiral inductor are presented including EM simulation, segmental equivalent circuit model and compact lumped-element model.Two new equivalent-circuit models are proposed in this paper, which are single-πand double-πmodels. The new single-πmodel has better wideband prediction capability than traditional single-πorΤ-models. The eddy current in substrate is represented by an R-L-C network coupled with DC inductance. A new substrate network, consisting of R/L/C, is proposed to model the broadband loss mechanisms in the silicon substrate. In the new double-πmodel, the skin and proximity effects are represented by a parallel network, consisting of several R-L series branches and mutual inductors. As the skin and proximity effects are frequency-dependent, the number of branches varies with the frequency of interest, and more branches are needed with increasing frequency. The substrate network in the new single-πmodel is also proved to be suitable for this double-πmodel.Lastly, three inductor model libraries are developed based on the proposed double-πmodel and two reported models. These model libraries can be categorized into two types: (1) The empirical scalable models based on the reported single-πand double-πmodels. Performing the parameter-extraction procedure on a series of inductors, then the values of equivalent-circuit elements are expressed by a set of functions related to the geometry parameters of inductors. (2) The physical scalable model based on the new double-πmodel. The scalable expressions are determined by physical meanings, geometry parameters and process parameters.A series of inductors with different geometries are fabricated in standard SMIC 0.18-μm 1P6M RF CMOS process to verify the new equivalent-circuit models and inductor libraries. Excellent agreements have been obtained between the modeled and measured data up to 40 GHz.