A limiting amplifier module using wafer level package for 10Gbps optical transmission system

Abstract

A 10 Gb/s limiting amplifier IC with the emitter area of 1.5xlOpn1~ for optical transmission system was designed and fabricated with a AIGaAs/GaAs HBTs technology. In this study. we evaluated fme pitch bump using WL-CSP (Wafer This paper describes the design and fabrication of lOGbps limiting amplifier using AIGaAdGaAs HBTs for the optical transmission system and the development of fme pitch WL-CSP process. Finally the frequency response and eye diagram of the limiting amplifier package module are discussed. Level-Chip Scale Packag-ing) instead of conventional wire bonding for interconnection. To study the effect of WL-CSP, electrical performance was measured and analyzed in wafer and package module using WL-CSP. In a package module, clear and wide eye diagram openings were observed and the rise/fall times were about 9@s, and the output voltage swing was limited to 65OmV,, with input voltage ranging from 50 to 50OmV. The Small signal gains in wafer and package module were 16.25dB and 14.86dB respectively. It was found that the difference of small signal gain in wafer and package module was less then 1.5dB up to 1OGHz. But, the characteristics of return loss was improved in package module. This is due to the short interconnection length by WL-CSP. In this study, we developed fine pitch bump with the 4 0 p m diameter and 100 p m pitch using WL-CSP process. So, WL-CSP process can be used for millimeter wave GaAs MMIC with the fme pitch pad.