Technology

15/05/2011

Caeleste aims at providing “Beyond state of the Art” image sensor.

Caeleste’s technology is based on IP that enables the realization of the most challenging optical or radiation detector readout circuits, single pixel, one- and two-dimensional arrays. Here are examples of Caeleste achievements.

Versatile pixel architecture

Pixels which combine CDS (correlated double sampling), full pipelined synchronous shutter and high fill factor (patent pending), both in front- and backside illumination. Caeleste has the IP to design monolithic image sensors with high fill factor, not needing microlenses, and still compatible with regular CMOS technology.The pixel has been first demonstrated on an hyperspectral imager designed for e2v.

 

 

X-rays with “photon counting” accuracy and energy discrimination (color X-ray)

Caeleste developed a family of techniques (patents pending) to realize the holy grail of X-ray imaging: photon counting.  Unlike state-of-the-art X-ray sensors that “integrate” secondary photocharge in classic CMOS or TFT pixels with associated noise and imperfections, photon counting allows true quantum limited imaging.  Quantum limited pixels can also discriminate photon energy, resulting in features as diagnostic “color X-ray”, sharper  and lower dose X-ray images.  Large arrays ≥ 1 dm2 and high yield are now possible.  Photon counting enables unprecedented performance in noise floor, energy discrimination “color X-ray” and sharpness (MTF).  Indirect detection photon counting is demonstrated.  Caeleste’s  91×90 pixel two-color X-ray photon counting demonstrator is soon available.

 

On the diagnostic value of Color X-ray

How Caeleste became involved in proving the mere “medical” diagnostic value of “color X-ray” is a story on its own.  Initially we invented a compact low transistor count photon counting X-ray pixel.  Quickly we noticed that photon counting has the optional feature of energy discrimination.  However, is this a useful feature?  Before investing time and money in the development, we needed the have some proof of value.  Apart from bone densitometry and border control X-ray, which are based on energy discrimination of heavy atoms (Calcium, metals) as compared to light matter, no relevant medical records exits.  Together with the UZB we pioneered multiple exposure color X-ray.  So the added chrominance channels in the images label C-rich (fat) and O-rich (water) tissue, as well as intermediate C/O ratios (proteins, DNA, cancers).

Figs. Color mammography: B&W X-ray absorption and color X-ray images from the same mammary resection specimen (Breast carcinoma specimen “Poorly differentiated invasive duct” type).  In this color X-ray image, hue codes the oxygen/carbon ratio (here blue=carbon-rich, red=oxygen-rich).

Design for radiation tolerance: Highest doses of gamma or particle radiation.

Total dose gamma and heavy particles: ionization damage, charge built-up (X, γ), and displacement damage (e-, H+, ions, hadrons).  Caeleste personnel’s  historical background in radiation tolerant design, and our experience in design X-ray pixels, allowed us to develop pixels that outperform any other published radiation tolerance, Single event hardness (SEE, SEU, SEL).  Caeleste can design image sensors with very high inherent immunity to single events.

 

 

 

Monolithic 3D ranging pixels with noiseless charge level frame accumulation

Using Caeleste’s unique time-gating and time-of-flight pixels in standard CMOS technology (patent US7564022).  With this technology one is able to gate incoming light with sub-nsec accuracy. Applications in fluorescence imaging, TOF ranging, 3D imaging, in-the-pixel demodulation. Although the technique is pure CMOS based, it is superior compared to the established CMOS based techniques as these is absolutely no noise penalty due to the addition of multiple charge packets.

 

 


Visible light photon counting image sensors using APD  / SPAD

Caeleste designs and produces photon counting SPAD (single photo avalanche diode) imagers.  These can be both hybrid and monolithic in standard CMOS technology. Caeleste demonstrated a 150ps time of flight sensor.