Microwave design of multi-layer interposers for the packaging of photonic integrated circuits

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Jezzini, Moises A.
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University College Cork
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The increasing growth of data traffic on the Internet is supported by innovations in high-speed photonic devices. Some of this novel photonic devices are photonic integrated circuits (PICs) that use higher speeds, have higher circuit density and integrate more heterogeneous devices. A new generation of photonic packaging is also required to handle the increasing device density and data rate of the PICs. An important element to package the PICs is the carrier board which also serves as an interposer between the PIC and the package. The usual interposer material for PICs is a single-layer aluminium nitride (AlN) substrate due to its high thermal conductivity and good microwave performance. In contrast, other high-speed and high-density applications use multi-layer substrates as carrier boards. The typical multi-layer technologies for high-speed interposers is low-temperature co-fired ceramic (LTCC). The motivation of this research is the need of multi-layer interposers suitable for the packaging of high-speed and high-density PICs. A key element to enable this multi-layer interposer is the high-speed channels. The task of this research was the microwave design of these high-speed channels for a multi-layer interposer and carrier board suitable for PICs. The main findings of this research can be divided into three areas. First, improvements to the microwave theory. A novel impedance profile reconstruction algorithm based on time-domain reflectometry (TDR) was developed. Additionally, a novel set of equations to calculate the characteristic impedance and the complex propagation constant from the vector network analyser (VNA) measurements of long lines was found and tested with positive results. Also, a novel single impedance thru-only de-embedding algorithm was completed. Second, the design of a novel rotatable vertical transition. The vertical transition has a 3 dB bandwidth around 35 GHz and small penalties on the eye diagram at 40 Gbit s−1 . Third, positive measured results of these designs in co-fired AlN. The measurements of the co-fired AlN board show similar results than in an LTCC board proving that co-fired AlN is an attractive option for PICs where the thermal management is important. The main conclusion from these findings is that the designed transmission lines and vertical transitions are suitable for the use of LTCC or of co-fired AlN as multi-layer interposers for the packaging of high-speed PICs Future work include improvements to the novel microwave algorithms, the development of equation-based models for the transmission lines. Also, the vertical transition has a resonance around 35 GHz that could be compensated using stubs or other elements. Finally, the transmission line designs and vertical transition designs need to be used for real applications of high-speed PICs using LTCC or co-fired AlN.
Photonics packaging , Low Temperature Co-fired Ceramics , Microwave design , System on a Package (SoP) , Microwave vertical transition , Aluminium nitride (AlN)
Jezzini, M. A. (2018) Microwave design of multi-layer interposers for the packaging of photonic integrated circuits. PhD Thesis, University College Cork.