Design of CMOS Photodiode for Gamma Camera Application Nur_ Sultan SALAHUDDIN Gunadarma University Indonesia sultan@staff.gunadarma.ac.id Michel PAINDAVOINE LE2I Laboratory UMR CNRS 5158, University of Burgundy, France paindav@u-bourgogne.fr Abstract We designed new photodiodes sensors including current mirror amplifiers. These photodiodes have been fabricated using a CMOS 0.6 micrometers process from Austria Micro System (AMS). The Photodiode areas are respectiveley 1mm x 1mm and 0.4mm x 0.4mm with fill factor 98 % and total chip area is 2 square millimetres. The sensor pixels show a logarithmic response in illumination and are capable of detecting very low blue light (less than 0.5 lux) . These results allow to use our sensor in new Gamma Camera solid-state concept. 1. Introduction In recent years [1] there has been a growing interest in developing compact gamma cameras to improve nuclear medicine imaging. Conventional full-size gamma cameras using a NaI (TI) scintillator block coupled to a bulky array of PMT are, by nature of their large size, preclude from use in more clinic situation. The compact scintillation camera uses an array of discrete scintillator crystals and a matching array of photodiodes to detect the scintillation light that result when a gamma-ray is absorbed [3] . This scheme thus replaces the bulky PMT photodectectors used in conventional scintillation cameras with small photodiodes, greatly reducing the camera size as shown in figure 1 Figure 1. Module of discrete scintillation camera. In this context we designed a new CMOS image sensor array that we present in this article. We introduce in the second section CMOS photodiode design. In the third and fourth sections we describe model and simulation of our CMOS Photodiode in VHDL-AMS. In the fifth section we present fabrication and test results about this new sensor. 2. Pixel Design Description In a standard CMOS process several parasitic junction can be used as photodiode aither p-well or n-well [15] . two pixels different structure as shown in figure 2 have been realized using a photodiode formed partly hollowed n+ diffusion in n-well (vertical photodiode) and partly hollowed n+ and p+ diffusion in n-well (lateral photodiode). The photodiode is forward biased, and when incoming photons are absorbed, a photocurrent proportional to the intensity of light flows through the photodiode. This current is converted to output voltage value using current mirroring integration readout circuits [16] .