PSD9: The 9th International Conference on Position Sensitive Detectors

Performance Comparison of CMOS-based Photodiodes for High Resolution and High Sensitivity Digital Mammography

14 Sept 2011, 09:00

1h

Board: 16

Poster Presentation Poster Session

Speakers

Mr Bo Kyung Cha (KERI)Mr Dae Hee Lee (KAIST)Mr Dong-uk Kang (KAIST)Mr Hyunjun Yoo (KAIST)Mr Jun Hyung Bae (KAIST)Mr Minsik Cho (KAIST)

Description

Recently, CMOS Image Sensors (CIS’s) are becoming candidate solution for digital mammography (DM) systems due to relatively low cost, high speed and possibility to integrate signal processing electronics. Therefore, it is very important to optimize the performance of the CMOS-based photodiode combined with the scintillator for DM. In this research, we compared the performance of four different photodiodes fabricated using 0.18 μm CMOS process which is specialized in image sensor technology. All photodiodes have 50 μm pitch and the same pixel structure, 3-transistor active pixel. Moreover, the same readout architectures are connected to each photodiode so that the comparison can be focused only on the photodiode itself. The four photodiodes are n-well/p-epi, p+/n-well/p-epi, n+/p-epi and n-/p-epi. The flexibility of the process to fabricate photodiodes allows a lightly doped (n-) implant layer and shallow trench isolation (STI) blocked n-well region, as well as an epitaxial wafer necessary for widely depleted photodiodes. The active pixel for each photodiode was designed in the form of a 40 x 40 array for statistical analysis of noise, dark current rate, charge-to-voltage conversion gain and uniformity. In addition, thallium doped cesium iodide (CsI:Tl) scintillator, which is usually used in the DM system, was directly deposited on the test chip so as to investigate the photodiode’s sensitivity to X-rays.

Preferred medium (Oral/poster)

poster

Presentation materials

Poster

PSD2011_(Poster)J.H._Bae.pdf