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PIN photodiode bandwidth optimization in integrated CMOS process

Silicon photodiode integrated with CMOS has been in extensive study for the past ten years due to its wide use in applications such as short-distance communication, VCD players, ambient light sensors and many other intelligent systems. In recent years, high speed blue-ray DVD is replacing conventional DVD due to its larger storage capacity and higher speed. In this work, the photodiode optimized for blue ray is fully integrated with standard 0.35um CMOS process and the bandwidth dependency upon thermal process and epitaxial material is investigated. It was found that the additional substrate thermal process can improve bandwidth for blue and red light but reduce bandwidth for infra-red. It is also found that higher level p-type epi doping does not impact bandwidth for blue light but reduces bandwidth for red and infra-red. The various mechanisms of bandwidth were discussed based on the experimental results. It indicated that the bandwidth of photodiodes depends on photo carriers travel time which can be explained by simple model of drift transport and diffusion transport. The design of photodiode should optimize the depletion region and reduce the carrier travel time.