Caeleste was granted two new patents in the field of Xray and Xcolor Xray detection. Caeleste has a strong focus on CMOS and scintillation based Xray detection is a key know-how at Caeleste and we are pleased to make these circuits available to our partners.
Combined pulse and integration detection
Full text available for download.
Counting pixel with good dynamic range properties
Full text available for download.
You can find all our papers and patents in our pages.
Caeleste successfully designed and tested a SPAD (single photon avalanche diode) photon counting image sensor. After a first successful demonstration with hybrid avalanche photodiode, Caeleste introduces integrated, compact pixels with avalanche photodiodes, allowing large resolution image sensor with single photon detection capabilities in the visible spectrum range. The demonstrated array has 32×32 pixels on a 30µm pitch, in TSMC 0.18µm technology. Several SPAD pixel variants are optimized for QE, dark count and afterpulsing.
to know more about this technology, do not hesitate to contact us.
Caeleste published this week its first measurement results of a 0.5 e- noise RMS CMOS image sensor at the occasion of the CNES Workshop on High performance CMOS image sensors in Toulouse, France. starting from a 2 e- RMS baseline obtained with in-pixel CTIA amplifier, the noise is further reduced by oversampling of uncorrelated pixel data. decorelation is achieved by 1/f noise “reseting function”. The presentation is available for download as pdf here.
A second generation of the ZPS technology is under process at the moment with a dedicated column structure aiming at performing most of the operation on-chip with a further reduction of noise expected to be below 0.3 e-.
This 4T pixel, in a 0.18µm CMOS technology, has high fill factor and is compatible with frontside and backside illumination. The pixel has a very high charge to voltage conversion. In the present configuration we now demonstrate less than 0.5 electronsRMS read noise in the dark.
We will disclose more details on this proprietary technology at upcoming scientific conferences. We invite interested groups willing to provide independent confirmation of our results to contact us. Applications are in low noise and/or low light imaging, i.e. in virtually all imaging domains.
For more informations on this technology, do not hesitate to contact us.
The “LAP2010A” pixels array are primarily designed for and used in in medical X-ray. Four samples of the LAP2010A prototype pixel arrays were irradiated with 0, 100, 200 and 500Gy, in a qualified 60CO facility, 25°C, 128Gy/h, no bias applied. Dark currents are recorded and normalized to pixel size 10µm. Measurement results are shown below, all at RT, in e-/s.
We observe no significant dark current increase for these pixels. This is an exceptional achievement as for the first time, pixels that have not measureable dark current increase?
Comparison with state of the art
The plot superimposes our LAP results with the few published[,,] gamma TID (total ionizing dose) results in relevant other CMOS imagers. The compilation has to be interpreted with a margin of error, as radiation conditions, measurement conditions, bias conditions etc. all differ. For some cases we had to make assumptions on the actual conversion factor mV/s to e-/s.
this Figure compilation of relevant literature on Gamma TID, dark current [e-/s] versus TID [kGy], pixel size normalized to 10µm. Remark: the point “0.0” is added on the logarithmic X-axis to indicate time 0 or beginning of life (BOL).
In the plot, the “LAP default” is the actual pixel being used in the medical X-ray applications. It is a classic 5 T charge integrating pixel. LAP DS, LAP DX and LAPXS are variants of the default LAP pixel. Of these especially the LAP XS is relevant. It has due to its specific design a dark current that is 5 times lower than the default pixel, and can maintain that low level virtually unchanged even after 500 Gy (50kRad).
Other forms of radiation tolerance
We demonstrated exceptional gamma (and X-ray) TID tolerance. However, Caeleste pixels and arrays are tolerant for other forms of radiation too:
Proton and heavy ion total dose damage susceptibility
This form of radiation damage is generally understood as an inherent bulk Si property, creating isolated localized defects in the diode’s sensitive volume. As the photosensitive volume is quite constant across technologies and pixels design, even from CCD to CMOS, so is the damage effect.
Single event or single event upsets (SE, SEU) and Single event latchup (SEL)
SE(U) is the temporary failure of the circuit due to the localized deposition of a large charge packet due to a heavy particle absorption. Such large charge packet can “upset” analog or digital circuitry. Ideally circuits should be insensitive. If not, the imager should recover in maximally one frame period. Caeleste can design its imager with the highest possible SE tolerance. A specific case of SE is Single Event Latchup (SEL). The triggering of CMOS latchup can be prevented by proper choice of technology options and circuit design style.
 J.Bogaerts, B.Dierickx, C.Van Hoof, “Radiation effects in CMOS Active Pixel Sensors”, RADECS, ESTEC Noordwijk, 2000
 B.Dierickx, J.Bogaerts, “STAR250 Radiation-Tolerant APS for Star Tracker Applications”, CNES Atelier, Toulouse, 2002 (same data also in later publications)
 M.Innocent, “A radiation tolerant 4T pixel for space applications”, IISW, Bergen, 2009