Silicon MOS Pixel Based on the Deep Trapping Gate Principle: Design and Material Science Challenges

Abstract

The deep trapping gate pixel device was described recently as an alternative to CMOS 3T pixel. The feasibilty of this device was studied with technological and transport simulations used in classical electron devices and process design. A buried gate containing localized deep level centers (Deep Trapping Gate or DTG) is the key for the operation of this field effect pixel detector. This can be made with deep levels or a quantum box. This buried gate can modulates the drain-source current, the same way the upper gate does. This principle was evaluated with realistic simulations physical parameters and this shows that the signal magnitude is sufficient for an energy deposition of a Minimum Ionizing Particle within a limited silicon thickness (a few microns). We will study here the potential techniques usable for the fabrication of the device with their drawbacks, advantages and limits. The first technique introduced is impurity implantation, followed by annealing. The problems related to the control of the defects in the DTG will be examined in the light of recent work on ion implantation. As an alternative recent work on quantum dots opens the possibility to the use Ge dots as a DTG. Ion implantation can again be used with some limitations. As an alternative to ion implantation an epitaxial DTG could be fabricated using standard techniques. The first conclusion of this study is that all the established techniques necessary for the development of the DTG pixel can reasonably be successful because the related bottlenecks may be overcome. The deep levels concentration in the DTG (above 10^18 cm-3) is higher than the concentration of radiation induced defects for integrated fluences lower than 1x10^16 cm-3.