On-chip Crosstalk-suppressing Differential Interconnect Structure Design And Analysis

With the development of Moore’s Law, digital integrated circuits has reached into ultra-deep submicron process node. The size and spacing of the interconnects slowly decrease, but the operating frequency of a chip gradually increase. The crosstalk induced by the coupling of electromagnetic fields between interconnects has become a bottleneck which restricting a chips’ performance. Crosstalk can make the signal timing and logic of a chip disorder, which affect the normal function of the chips. So, as one of the core problem of signal integrity(SI) on chips, crosstalk has drawn widespread concern. Compared with the general interconnect line, differential transmission line(DTL) has a faster signal propagation speed and greater ability to suppress crosstalk. So it has been widely researched and used on chips. But differential transmission lines also have crosstalk problem with the lines around it, which can affect the signal transmission in some serious conditions. Thus how to effectively suppress the crosstalk of differential transmission line has become the key point of current research. In this paper, we do the following work to solve the problem of crosstalk in differential transmission line on VLSI at 65 nm CMOS process:1. With the basic theory of crosstalk, we extract the parasitic parameters which include resistance, capacitance(to ground capacitance and coupling capacitance), and inductance(self inductance and mutual inductance) of chipa at 65 nm process. This parasitic parameters take account into skin effect and inductance. It has a higher accuracy and more suitable for high-frequency transmission line.2. We modeling the equivalent RLC circuit of plane four-wire differential transmission line based on crosstalk theory. The model considers the electromagnetic coupling between adjacent lines an non-adjacent lines. By research and analysis, we can conclude that the adjacent lines need to take into account both electric and magnetic coupling, while non-adjacent lines just need to consider magnetic field coupling. Then by the S-parameter co-simulation of four-wire differential transmission line between three dimensional physical model in HFSS and equivalent circuit model in ADS, we do the extracted S-parameter curve fitting. The result shows that the frequency within 0 ~ 20 GHz, the S-parameter curve can be a good fit. The average error of S parameter does not exceed 8.31%.3. We propose the concept of equivalent impedance, which equivalent the electromagnetic coupling between transmission lines to an impedance. We can can calculate the equivalent impedance by equivalent circuit model. The equivalent impedance can make it more convenient to analysis crosstalk. Then we study the crosstalk characteristics of differential transmission lines by HFSS three-dimensional model simulation and obtain crosstalk condition under different physical configuration, including length, spacing, floor height, via and corner. And analysis the structure’s effect to crosstalk in mechanism by equivalent impedance. Finally we obtaine the design rule guidance to suppress crosstalk of differential transmission line.4. We realized the signal time domain simulation of differential transmission line in different structures in ADS by the Touch Stone file(S parameter netlist) that extracted from HFSS. In the frequency of 10 GHz, by analysis of the coupling voltage and signal eye diagram simulated by ADS, we present two crosstalk-suppressing differential transmission line structure, that is the 3x width of the interconnection spacing(3W) in plane differential line structure and 2x width of the interconnection spacing(2W) in diagonal differential line structure. This structure can ensure the high quality signal transmission of differential transmission line with the minimum use of routing resource.