Proton irradiation of the CIS115 for the JUICE mission

Abstract

The CIS115 is one of the latest CMOS Imaging Sensors designed by e2v technologies, with 1504x2000 pixels on a 7 µm pitch. Each pixel in the array is a pinned photodiode with a 4T architecture, achieving an average dark current of 22 electrons pixel -1 s -1 at 21°C measured in a front-faced device. The sensor aims for high optical sensitivity by utilising e2v's back-thinning and processing capabilities, providing a sensitive silicon thickness approximately 9 µm to 12 µm thick with a tuned anti-reflective coating.The sensor operates in a rolling shutter mode incorporating reset level subtraction resulting in a mean pixel readout noise of 4.25 electrons rms. The full well has been measured to be 34000 electrons in a previous study, resulting in a dynamic range of up to 8000. These performance characteristics have led to the CIS115 being chosen for JANUS, the highresolution and wide-angle optical camera on the JUpiter ICy moon Explorer (JUICE).The three year science phase of JUICE is in the harsh radiation environment of the Jovian magnetosphere, primarily studying Jupiter and its icy moons. Analysis of the expected radiation environment and shielding levels from the spacecraft and instrument design predict the End Of Life (EOL) displacement and ionising damage for the CIS115 to be equivalent to 10 10 10 MeV protons cm -2 and 100 krad(Si) respectively. Dark current and image lag characterisation results following initial proton irradiations are presented, detailing the initial phase of space qualification of the CIS115. Results are compared to the pre-irradiation performance and the instrument specifications and further qualification plans are outlined.

Thermal annealing response following irradiation of a CMOS imager for the JUICE JANUS instrument

“…It also documents that the recovery of pre radiation dark current following a thermal anneal has a near identical relative effectiveness, highlighting the anneal characteristics are independent of the proton fluence. Moreover, furthering on from the work of [13], figure 2 shows that following a thermal anneal the mean value of dark current (in electrons) is decreased for each of the irradiated devices. Creating a fit between the mean dark current values at EOL proton fluence and the temperature of the device in kelvin using the exponential relationship from (3.1), similar to the ones presented in [15], dark current response of the CIS115 at a range of temperatures can be inferred.…”

“…It also documents that the recovery of pre radiation dark current following a thermal anneal has a near identical relative effectiveness, highlighting the anneal characteristics are independent of the proton fluence. Moreover, furthering on from the work of [12], Figure 2 shows that following a thermal anneal the mean value of dark current is decreased for each of the irradiated devices.…”

“…Previous studies of the CIS115 have shown an increase in the dark signal in the device following displacement damage in the detector [13]. The pixel-by-pixel dark current distributions, as measured at 40 • C, are shown in figure 1.…”

Development of a photon-counting near-fano-limited x-ray CMOS image sensor for THESEUS' SXI

“…In radiation studies of Teledyne-e2v CIS for other missions, such as the CIS115 for JANUS, 8 the BOL dark current and Total Ionising Dose (TID)-induced dark current has been insignificant compared to the increase in bright pixel defects induced by the TNID radiation environment. 9,10 The increased pitch and depleted volume in the CIS221-X (when compared to the partially depleted 7 µm pixel of the CIS115) will increase the dark current defect density per pixel, and therefore it is even more critical to understand the effect of TNID-induced dark current defects on the overall imager performance. The detailed analysis of the TNID-induced CIS115 bright pixel defect has been utilised to build a model for the THESEUS pixel and radiation environment.…”

Electro-optic and radiation damage performance of the CIS115, an imaging sensor for the JANUS optical camera onboard JUICE

“…The CIS115 is undergoing radiation qualification to identify and quantify any changes in performance parameters that can be expected during the mission lifetime and confirm that it meets specifications for camera performance throughout the mission. A study on displacement damage in the CIS115 has been reported [5] showing good device performance following exposure to an EOL equivalent fluence of protons. An ionising radiation damage campaign has been undertaken which will be presented here.…”