Anjan Chakravorty

The on-chip planar spiral inductors having variable width (W) and spacing (S) across their turns are known to exhibit higher quality factors (Q). In this paper, we present an efficient parameterized cell (pcell) design in cadence using SKILL scripts for automatic layout generation of these complex, high-Q, variable W&S spiral inductors comprising of single ended and symmetric structures with rectangular, hexagonal, octagonal and circular spirals. Electromagnetic simulations are performed on the inductor layouts generated using the developed pcells. The constant W&S and variable W&S spiral inductor structures are fabricated in a 0.18 μm silicon on insulator process. Measurements show ∼25% improvement in the quality factor of variable W%S spiral inductors compared to their constant W&S counterparts and also validates the proper operation of the developed inductor parameterized cells. The presented variable W&S inductor pcell significantly reduces the layout design time of RF circuit designers and also helps in the design automation of these complex inductor structures to boost their own performance and the RF circuits as well.

Conical inductors and metal-oxide-metal (MOM) capacitors are shown to have higher quality factor ( ${Q}$ ) characteristics at millimeter wave (mm-wave) frequencies over conventional inductors and nitride MIM capacitors. In this work, Physics-based analytical models are developed for conical inductors and MOM capacitors usable at mm-wave frequencies. The linear voltage profile along the turns of the conical inductor is taken into account for capacitance calculation which is critical in accurately predicting ${Q}$ -values. Two RL networks coupled by capacitors are proposed to capture the frequency-dependent characteristics of the MOM capacitor. The lumped elements in both these device models are frequency independent and can be calculated using layout and process parameters. The proposed models for conical inductors and MOM capacitors are verified with electromagnetic (EM) simulations till 100 GHz. A prototype 60-GHz bandpass filter (BPF) is fabricated using $0.18~\mu \text{m}$ RF-silicon on insulator (SOI) technology to validate the accuracy of the developed compact models. BPF simulation results using the proposed models are shown to be in excellent agreement with those produced with EM simulations and silicon measurements.

In this brief, a novel combination of multilayer up-down series stacking and multipath architecture for equal path length is explored for the first time to improve the performance of on-chip inductors. The up-down series winding reduces the interlayer capacitance, thereby increasing both the peak quality-factor (Q) frequency (Q) and self resonant frequency (SRF). The crossover interconnection architecture ensures equal path length at every pair of spiral turns in the series stack. This architecture lowers skin and proximity effect losses in the spiral, increasing the slope of Q characteristics. Thus, using the proposed architecture, both the ac resistance and capacitance are simultaneously reduced while realizing higher inductance values. Implemented in a 0.18μ high resistivity silicon-on-insulator technology using a dual thick metal stack, the proposed inductor achieves more than 10% improvement in peak-Q value, 50% improvement in f Qmax, and 100% improvement in SRF values when compared with a conventional series stacked multipath inductor.

This brief proposes a technique to increase the performance of spiral inductors through appropriate selection of excitation port, especially in the case of variable width spirals. In this brief, forward excitation refers to applying ac voltage at the outer or upper terminal of the inductor with the inner or lower terminal grounded, while in reverse excitation, the inner or lower terminal is connected to the signal. Performance improvement with reverse excitation is explained using the voltage profile of the spiral. While tapered layout increased the peak-Q from 15.9 to 22.8, reverse excitation increased it further to 26.7. Moreover, reverse excitation also resulted in an increased peak-Q frequency from 5 to 8 GHz and self resonant frequency from 12 to 14.6 GHz in these tapered inductors. On the other hand, a similar approach is shown to be detrimental in the case of series stacked inductors, while symmetric inductors remain unaffected. © 2014 IEEE.

This letter presents a technique to accurately predict the proximity effect losses in spiral inductors with variable width and spacing (taper) across the turns. The change in magnetic flux in a spiral turn due to the nearby non-uniformly spaced traces is considered while developing expression that captures proximity effect. A broadband, scalable, and frequency-independent compact model is developed for tapered inductors using the proposed technique. Resistance, inductance, and quality factor plots are shown for spiral inductors with different values of taper. Excellent agreement between model and EM simulated/measured data demonstrates the scalability of the proposed model. The proposed model can be used to accurately predict the high possible with tapered inductors.

A high density symmetric inductor using a novel combination of solenoidal wound series stacked spirals is proposed in this paper. Series stacking in the individual sections increases overall inductance density, while solenoidal winding pushes the quality factors (Q) to higher frequencies. The proposed inductor achieves more than 65% improvement in peak-Q value and 100% higher peak-Q frequency and self resonance frequency, while occupying 20% lesser area when compared with a standard symmetric inductor with crossovers. Implemented in a high resistivity 0.18 μm CMOS silicon-on-insulator process with dual-thick metal stack, the proposed inductor achieves 70-nH inductance and a Q of 11.3 operating at 1.6 GHz within 250 × 250 μm2 area. This translates to a record figure-of-merit of 12.2, which is highest in air core symmetric inductor literature. Further, the proposed inductor configuration is extended to realize a planar transformer with very high turns ratio of 9.25 using only two metals. © 1963-2012 IEEE.

In this brief, closed-form analytical expressions are obtained to accurately calculate the oxide and substrate (both lateral/vertical) capacitances of the π-equivalent circuit model for on-chip tapered spiral inductors. A lateral RC substrate network using the above-mentioned expressions is shown to significantly improve the model accuracy, especially with lower substrate resistivities. Furthermore, improvement in Qmax with reverse excitation in tapered spirals is also accurately predicted by the proposed model. The accuracy of the proposed model is validated till 15 GHz using several inductor geometries across process parameters suitable for the design of RF circuits. Excellent agreement is observed between the model, electromagnetic simulations, and measurements.