Bandwidth improvement of ceramic feedthrough in hermetic packaging

The protection of opto-electronics for telecom requires hermetic packaging. With such protection, the operation of the component remains stable in aggressive environment (chocks, vibration, thermal and chemical stress) for many years. The engineers rely on metal and ceramic packages with two interconnections technologies: the Glass To Metal Seal (GTMS) and the High Temperature Cofired Ceramic (HTCC) which ease the electrical access between the PC hoard where the package is attached and the opto-electronic function inside. In the following we depict three different types of ceramic interconnects - also named feedthrough - with their modeled and measured RF performance: first a T shape feedthrough with S_ll -20 dB and S_ll-0.6 dB up to IS GHz, then a 0.7 mm vertical transition with SI,< -14 dB and -0.5 dB up to 15 GHz, finally a reduced sue coplanar feedthrough with SS_ll -10 dB and S₂₁,>. -1.8 dB up to 40 GHz. We modeled this performance with Ansoft HFSS´ and found good correlation with the measurement. Also described is the quality of the grounding and, because of the interest for increased circuit density, an insight on the aspect of isolation is given: for the vertical transition, two grounding vias are sufficient at 10 Gh/s transmission rate, four grounding vias minimum are requested at 40 Gb/s. For signal integrity, we estimate that -30 dB between two adjacent RF channels limits the impact of cross talk on the transmission. Considering the bandwidth improvement beyond 50 GHz, HTCC can achieve it by reducing the design cross section in the area of high effective permittivity, a technique similar to coaxial propagation. Inder terms - HTCC, ceramic, wide hand, hermetic package, Ansoft HFSS´ modeling, 10Gb/s and 40 Gb/s, flex.