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Originally the exciting features of sCMOS cameras were the low noise (typically 10 times lower) and the faster read-out speeds than a CCD (up to 10 times faster). Additionally, sCMOS detectors have a multi-gain architecture on the pixels, which expands the dynamic range.
1. High Quantum Efficiency (QE)
One of the more recent developments for sCMOS is back illumination. The difference between back and front illuminated sensors is covered in our article What is a CCD Detector? The quantum efficiency of these back-illuminated sCMOS detectors can approach as high as 95%. This means that almost all of the signal can be captured and thus allows for exceptionally high sensitivity and improved detection.
Andor provide both back- and front-illuminated cameras because the latest generation of front illuminated sensors are lower cost- yet still offer high QE of up to 82%, which is only slightly lower than back illuminated sensors. Additionally, at low signal levels it is read noise that sets the ultimate noise floor of the camera. Front illuminated sCMOS cameras like the ZL41 Cell offer a high performance at a lower price point. Back illuminated sCMOS such as the Sona-6 provide a higher QE and similar read noise for when the highest sensitivity is required.
We have a range of sCMOS detectors available - back and front illuminated - so you can tailor the camera specification to your experimental and budget needs. Our specification sheets give full details of individual cameras and some suitable applications.
2. sCMOS as X-Ray Detectors
There is a breadth of applications that our cameras are used for. We added a fibreoptic end onto our sCMOS sensors to give a version of our camera which could be adapted easily for applications such as X-ray tomography - used for imaging cross-sections of the body.
High energy X-rays are also formed by vast underground machines which produce synchrotron radiation - particle accelerators. Examples of these are at Daresbury in north-west England and CERN in Geneva. At these facilities, the most sensitive detectors in the world are needed to make discoveries about the tiniest subatomic particles, and to learn about the nature of distant galaxies in the universe.
Our semiconductor sCMOS detectors are used at these facilities and many others doing the most challenging experiments.
3. Very Fast Readout Time, High Resolution Images in Astronomy - details at distances never seen before.
Continuing with Astronomy, we recently launched a camera called the Balor, a very large area, sCMOS detector. This takes advantage of the large, multiplexed read-out of the sCMOS that is not found on a CCD. It offers a large high-resolution array, with fast readout and low noise. Previously a high-resolution CCD, used in astronomy to image a large area of sky, for a fixed exposure time, would have typically about 45 seconds read-out time. This compares to only 40 milliseconds with a sCMOS for a similar, 17-megapixel array, that's a thousand-fold difference in read-out time.
Therefore, the throughput of measurements is increased, enabling the study of dynamic processes, or even extending the exposure times, increasing the signal-to-noise. Very fast read-out, high-resolution images are ground-breaking for astronomy.
EMCCDs or electron-multiplying CCDs, are still a very valid technology. Prior to the introduction of sCMOS, EMCCDs were the solution to overcome high read noise and allow fast read out. EMCCDs are essentially CCDs with an additional technology on board for amplifying the signal before the read out process. This circumvents the noise floor that occurs normally from reading a CCD out fast - or an sCMOS. But the key difference about EMCCDs is, because you can apply an amplification factor to the incoming signal, and the amplification factor can be quite large, EMCCDs are truly single-photon-sensitive in a way that even the latest low noise sCMOS cannot be. And they are also back-illuminated and feature large pixels to maximise signal collection under light starved conditions.
EMCCDs can be used for photon counting, for example, for untangled photon quantum experiments. So they still are the most sensitive technology available. There are lots of applications that benefit across the life sciences and physical sciences. For applications like single-molecule detection, in life sciences, where you can watch two-single biomolecules interact with each other in real time. EMCCD is still an invaluable technology for ultra-sensitive techniques. View our EMCCDs vs sCMOS article for more.
Here are four examples of future development areas for sCMOS.
1. SCMOS sensors have higher dark current than CCDs. While this is not important for fast fluorescence-based imaging where each frame may be only 50-500 milliseconds exposure. Some applications however require long exposure applications lasting seconds or even many minutes. For example, 40-second images for a long astronomy acquisition, or 20 minutes required for some luminescence imaging for in animal in vivo or plant imaging studies. The dark current for sCMOS will be a couple of orders of magnitude higher than CCD and typically not suitable for imaging when exposures are 5-10 seconds or longer. Deep cooled CCD therefore remain the best solution for luminescence and other imaging with such long exposures.
2. sCMOS detectors don't yet do true pixel binning, whereas CCDs do. With sCMOS, if we wish to do 2x2 pixel binning to create a superpixel of four times the area; compromising the resolution but gathering more photons in very low-light conditions. On a sCMOS, we would collect 4 times the signal, but the read noise would also double. This is because each row of the sCMOS sensor is read out at a time before binning is performed. On a CCD, the read noise remains unimpacted, yet the signal would be increased by a factor of 4 - making binning a very effective way to greatly boost sensitivity. It’s a development which would be well-appreciated by many with sCMOS detectors.
3. Moving forward with Andor's Balor large-area sensor, we can anticipate even larger sensors for Astronomy to see as much of the sky as possible.
4. In microscopy applications we can expect development of even smaller pixels. A lot of sensors today are standardised on a 6.5 μm pixel size as this provides a good compromise between signal collection and resolution. With smaller pixels we can expect to be able to use lower magnification objectives and therefore obtain high-resolution imaging of larger and larger samples. However, while there are many standard grade CMOS sensors with small pixels there are a lack of scientific grade sCMOS sensors with small pixels.
From this discussion you can see the importance of our ongoing development of scientific camera technologies. And the importance of our research and products in furthering your scientific discoveries.
Date: January 2023
Author: Dr. Jo Walters, Dr. Aleks Marsh, Colin Coates & Alan Mullan
Category: Technical Article