CMOS imagers, now considered as a valuable alternative to CCD in many application fields, still suffer from higher optical crosstalk and lower quantum efficiency. Therefore investigations have to be done in order to characterize these parameters and model them. This paper describes photodiode test structures implemented on two different standard technologies, a 0.7 micrometers lightly doped substrate CMOS SLP/DLM and a 0.5 micrometers EPI on heavily doped substrate CMOS processes from Alcatel-Microelectronics. Both dedicated in-line 20 micrometers square photodiodes and 20 micrometers pitch APS photodiode pixels are implemented. Quantum efficiency and optical crosstalk were measured for several wavelengths. The spotscan measurement setup that makes use of a dedicated halogen optical source coupled to a thin core optical fiber and a microscope objective is described and results illustrating charge collection and diffusion mechanism phenomena are given. For each technology, analytical modeling and physical 2D device simulations (ISE-TCAD) have been performed to evaluate charge collection efficiency. They are taken into account in the comparison with experimental results regarding both quantum efficiency and optical crosstalk. As a summary, the behavior of these two technology types will be compared and perspectives related to processes evolution will be drawn.
Pierre Magnan, Anne Gautrand, Yavuz Degerli, Cecile Marques, Francis Lavernhe, Cyril Cavadore, Franck Corbiere, Jean Farre, Olivier Saint-Pe, Michel Tulet, Robert Davancens
This paper describes a 128 X 128 pixels prototype array organized as sub-arrays of 32 X 32 pixels each, with 21 micrometers pixel pitch. The sub-arrays, photodiode or photogate based, are implemented using a standard 0.7 micrometers CMOS process. Various topologies of the photosensitive area have been implemented and some of them have an optical metal shield over the so-called non-sensitive area to evaluate the contribution of the active electronic area to the responsivity of the sensor. A synthesis of the measurements carried out by CIMI-SUPAERO and MMS, addressing darkness parameters, noise, photometric and radiometric performances, are presented with emphasis on the photogate type pixels. Results of spot-scan analysis and crosstalk measurements performed on selected topologies are also reported. Several samples were irradiated at different proton doses and their related behavior is discussed. From these results, a new 512 X 512 pixels array has been designed for space applications. The main features of this APS device are presented here.
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