Parasitic Effects Analysis and Equivalent Circuit Modeling of Tapered Serpentine Interconnects of On-chip FBAR up to 67GHz

As an important part of the 5G communication system, millimeter-wave on-chip circuits and systems have become a hot research area in recent years. With the rapid development of silicon-based processes, film bulk acoustic resonators (FBAR) and filters can be designed under advanced silicon-based substrates. In order to reduce the size of the circuit area, serpentine interconnects have become more and more popular. However, with the increase of working frequency, parasitic effects can become much more obvious, especially in the region of the millimeter wave bandwidth. Currently, the circuit models provided by chip manufacturers cannot reach such high frequency regions. Therefore, this paper has first analyzed the parasitic effects of two types of tapered serpentine interconnects in the on-chip FBARs, such as the skin effects, coupling effects, eddy currents and energy loss. Then, based on these effects, two equivalent circuit models have been established. An RL ladder network is used to model the skin effect. Also, an extra capacitor and inductor are used to model the coupling effects between the inner structures of the tapered serpentine lines. A weak self-resonance phenomenon can also be observed. The values of the components are extracted and optimized. To verify the accuracy of the proposed circuit models, the simulated S-parameter results are compared with the measured ones. It can be observed the simulated S-parameters of the proposed circuit models are in good agreement with the measured one in both magnitude and phase properties starting from 0.1GHz up to 67GHz. Since the speed of circuit simulation is much faster than that of full-wave simulation during circuit design process, the proposed circuit models can be used for on-chip FBAR fast circuit design in the 5G millimeter wave region.