Analysis of Physical Degradation Mechanisms of Charge Coupled Device Image Sensor

Charge coupled device (CCD) image sensors are important building blocks for high-responsivity, low noise optical cameras. It plays a critical role in applications including astronomical observation, environmental monitoring, and microscopic study. To achieve overall robust system reliability, good knowledge of reliability physics is indispensable. In this paper, we focus on the physical mechanisms of CCD degradation. Firstly, the functional architecture and implementation of CCD are introduced. The CCD consists of three functional domains which are photosensitive array, readout shift register and on-chip amplifier. Metal-Insulator-Semiconductor (MIS) is the basic structure of both photosensitive array and readout shift register. The on-chip amplifier is a multi-stage source-follower structure which consists of metal oxide semiconductor field effect transistors (MOSFETs). Secondly, the physical mechanisms of CCD degradation are studied. The high electric field in the gate insulator of the photosensitive array and readout shift register imposes a reliability concern of dielectric breakdown. For the on-chip amplifier, hot carrier effect would lead to the characteristic parameters degradation. Finally, reliability evaluation methods of CCD are proposed based on the degradation mechanisms and the stress under application condition.