The UV sensitivity improvement of MPPC

MPPC (Multi-Pixel Photon Counter) is the kind of solid state photon counting device operating in Geiger-mode. The features of the MPPC are the high gain (up to 105∼106), high time resolution and high sensitivity around 400∼500nm. These characteristics are well matched to the general scintillation applications like PET. In recent physics experiment applications, it seems that the liquid scintillator plays an important role to find out new phenomena. We think that the MPPC contributes to fulfill the requirements with its high S/N characteristics. But there were several concerns to recommend the MPPC in this application region. One is the wavelength mismatch between the MPPC sensitive region and the liquid scintillator emission (e.g. 128nm(Liquid Ar), 173nm(Liquid Xe)). The other is the adverse effect of low temperature environment that will cause several kinds of damage to the device package and change characteristics of the MPPC largely. Especially, the rapid increase of the quenching resistor at low temperature region makes the pulse shape lower and longer than at room temperature. We have tried to adjust the peak sensitivity wavelength by AR (Anti-Refractive) coating and optimizing the formation of the active region. We will show that the temperature dependence of the quenching resistor will be reduced by introducing new technology. We are also trying best matching materials (substrate, resin and adhesive) to achieve the high reliability package at low temperature condition.