Research On Transmission Characteristics And Impedance Matching Of Through-Silicon Vias

With the reduction of the semiconductor manufacturing process feature size,the delay,interference and power caused by huge number of interconnects become more important factors to restrict the performance of the circuit.The use of three-dimensional integrated circuits based on vertical Through Silicon Via(TSV)interconnect technology can significantly reduce the number and length of interconnects in integrated circuits,dramatically improving the overall performance of integrated circuits.However,the significant differences between the structure of the TSV and the plane interconnection line not only led to its electrical characteristics becoming special,but also led to the impedance in signal channel changing.Most of the previous studies focused on the vertical interconnects in the TSV,while less attention was paid to the Redistribution Layer(RDL),which,due to the fact that RDL was a planar interconnect directly connected to TSV,resulting in a certain impact on signal propagation.Therefore,this paper focuses on the transmission characteristics of the whole TSV Signal Channel,which includes TSV and RDL.In this paper,the electromagnetic properties of RDL,TSV and Bump are analyzed respectively.The coupling effect of each part of TSV signal channel is taken into account,and many parasitic parameters such as resistance,inductance,capacitance and conductance(RLCG)are extracted.An equivalent circuit model is proposed base on the three-dimensional model structure of the signal channel.Depending on the RDL interconnect length,different equivalent circuit models can be used separately.The effectiveness of the equivalent circuit model of each part of the TSV signal channel is verified by comparing the S-parameter simulation results of the three-dimensional electromagnetic field solver HFSS and the circuit simulation software ADS.The error of the return loss is less than 1d B and the insertion loss error is 0.01 d B or less.Based on the equivalent circuit model,the signal reflection caused by impedance mismatch between TSV and RDL is analyzed.In order to solve the mismatch of impedance between them,the characteristic impedance calculation formula of TSV and RDL is analyzed,and the variation law of characteristic impedance with geometric dimension is obtained.The scheme of adjusting the characteristic impedance by changing the geometric dimension is proposed.By changing the radius and spacing of TSV,the peak value of the reflected voltage in the TSV signal channel is reduced from 0.189 V to 0.056 V in simulation.And then the other schemes of the impedance matching are proposed,including L network matching section and the gradient transmission line.These two matching programs can significantly reduce the return loss from-30 d B down to-70 d B and-40 d B in the TSV signal channel.Although the L network has a better matching effect,its matching bandwidth is narrow,only about 3GHz,and the gradient transmission line can achieve a good matching effect in the entire 20 GHz simulation range.Finally,the applicability of the proposed three impedance matching schemes is analyzed,and the general selection principle of impedance matching scheme in TSV signal channel is given.