CMOS image sensors are widely used on Earth and are becoming increasingly favourable for use in space. Advantages, such as low power consumption, and ever-improving imaging peformance make CMOS an attractive option. The ability to integrate camera functions on-chip, such as biasing and sequencing, simplifies designing with CMOS sensors and can improve system reliability. One potential disadvantage to the use of CMOS is the possibility of single event effects, such as single event latchup (SEL), which can cause malfunctions or even permanent destruction of the sensor. These single event effects occur in the space environment due to the high levels of radiation incident on the sensor. This work investigates the ocurrence of SEL in CMOS image sensors subjected to heavy-ion irradiation. Three devices are investigated, two of which have triple-well doping implants. The resulting latchup cross-sections are presented. It is shown that using a deep p well on 18 μm epitaxial silicon increases the radiation hardness of the sensor against latchup. The linear energy transfer (LET) threshold for latchup is increased when using this configuration. Our findings suggest deep p wells can be used to increase the radiation tolerance of CMOS image sensors for use in future space missions.
Time Delay and Integration (TDI) is used to increase the Signal to Noise Ratio (SNR) in image sensors when imaging fast moving objects. One important TDI application is in Earth observation from space. In order to operate in the space radiation environment, the effect that radiation damage has on the performance of the image sensors must be understood.
This work looks at prototype TDI sensor pixel designs, produced by e2v technologies. The sensor is a CCD-like charge transfer device, allowing in-pixel charge summation, produced on a CMOS process. The use of a CMOS process allows potential advantages such as lower power consumption, smaller pixels, higher line rate and extra on-chip functionality which can simplify system design. CMOS also allows a dedicated output amplifier per column allowing fewer charge transfers and helping to facilitate higher line rates than CCDs.
In this work the effect on the pixels of radiation damage from high energy protons, at doses relevant to a low Earth orbit mission, is presented. This includes the resulting changes in Charge Transfer inefficiency (CTI) and dark signal.
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