CMOS Breakthrough Announced

A new CMOS image sensor could become the platform of choice for scientific photonics applications such as live cell microscopy, particle imaging velocimetry, adaptive optics, machine vision, and solar astronomy, according to scientists from Andor Technology (Belfast, Northern Ireland), Fairchild Imaging (Milpitas, Calif.) and PCO imaging (Kelheim, Germany), who unveiled the technology Tuesday during Laser World of Photonics 2009.

Fairchild Imaging, Andor Technology and PCO imaging held a press conference Tuesday during Laser World of Photonics 2009 in Munich to announce their sCMOS technology, which they are calling a breakthrough for high-performance imaging. Pictured are (l-r): Dr. Emil Ott, president and head of development dept., PCO; Dr. Gerhard Holst, head of science, research and marketing dept., PCO; Colin Earle, vice president, sales and marketing, Fairchild Imaging; Boyd Fowler, CTO, Fairchild Imaging; Donal Denvir, technical director, Andor Technology; and Dr. Colin Coates, market development manager, Imaging, Andor Technology. (Photonics Media photo by Melinda Rose)

Called scientific CMOS, or sCMOS, the technology doesn't have to make the tradeoffs in key performance parameters such as sensitivity, speed, dynamic range, resolution and field of view that today's other imaging detectors do, said Dr. Colin Coates, market development manager, Imaging, for Andor Technology. Instead of having to pick and choose among the features it can provide, sCMOS is capable of simultaneous providing them all.

CMOS image sensors, like CCD sensors, are semiconductor devices with photosensitive areas in each pixel that convert incident photons into electrons. While CMOS was developed in the 1960s, CCDs have dominated the image sensor market since the early 1970s. Over the past five to six years, some development work has gone into creating hybrid CCD/CMOS devices to match the high fidelity imaging performance of CCDs with the readout speed capabilities of CMOS, but such hybrids have been expensive to design and fabricate, with noise limitation issues (as noise increases, it becomes more difficult to see dim objects during microscopy).

The 5.5 megapixel sCMOS sensor developed by Andor Technology, Fairchild Imaging and PCO and announced at Laser World of Photonics 2009.

During a press conference Tuesday that brought together research, marketing and development heads of the three companies, Coates presented some key performance highlights of the sensor, which is the result of an 18-month collaboration between the three companies. The sensor format is 5.5 mp, with a read noise of less than 2 electrons rms @30 fps, and less than 3 electrons rms @100 fps.

Fig 8: Comparative low light images taken with sCMOS (1.5 electrons read noise @ 400 MHz) vs interline CCD (5 electrons read noise @ 20 MHz vs back-illuminated EMCCD (<1 e- read noise), under extremely low light conditions ('LED 1' setting). sCMOS and interline CCD were 2x2 binned in order to have the same effective pixel pitch (and light collection area per pixel) as the 13-µm pixel of the EMCCD sensor.

Coates compared many of the sCMOS' characteristics to one of the most popular, high-performance, low-cost front-illuminated scientific CCD technologies on the market today, the interline CCD, and also to the electron multiplying CCD (EMCCD), which was introduced to the market in 2000 and represented a significant step forward in addressing the CCD's inability to provide both high speed and low noise.

Coates said the sCMOS has rolling and global snapshot shutter modes that are user selectable, which is not typical of other CMOS sensors currently on the market.

Rolling shutter means that the different lines of the array are exposed at different times as the read out "wave" sweeps down through the sensor, a method suited to the majority of scientific applications. Global shutter mode, which operates like a "snapshot" exposure mode, means that all pixels of the array are exposed simultaneously. This method is suited to applications such as machine vision.

Global mode disadvantages include that it halves the frame rate that can be achieved in rolling mode, and also increases the RMS read noise by a factor of 1.41 over the rolling readout. The downside of the rolling shutter is spatial distortion, which is more apparent in devices such as CMOS camcorders, where rapid panning of the camera can be done at a rate that the image readout can't match.

Field of view comparison of two technologies, x60 magnification, 1.25 NA, 5.5 megapixel sCMOS vs 1.3 megapixel interline CCD (each have ~6.5 µm pixel pitch). sCMOS is capable of offering this larger field of view @ 100 frames per second with <3 electron read noise.

The read noise of the Sony interline CCD is between 4 and 8 electrons, more than double sCMOS's 2 or 3, while the back-illuminated EMCCD's is less than 1 electron. Coates said EMCCDs still have an advantage over sCMOS in low light situations (less than 1 photon per pixel). But its harder for EMCCD to bigger faster or improve its field of view. The Sony's sensor format is 1.3 MP, while the EMCCD offers a maximum of 1 MP. The sCMOS sensor format is 5.5 MP, which gives it the ability to get a whole cell into the field of view, as compared to just a small piece with the EMCCD.

Each of the three companies is building its own camera to house the sensor, which was developed at Fairchild Imaging. Andor said their sCMOS product will be available early in 2010. PCO said it also will have its first product beginning next year. Fairchild said the sensors will be available in the third quarter of this year to its partners and its camera by the first part of 2010.

Other potential applications for sCMOS include: single molecule detection, superresolution microscopy, luminescence, fluorescence spectroscopy, bio- and chemolumninescence, genome sequencing, photovoltaic inspection, x-ray tomography, laser induced breakdown spectroscopy and biochip reading, among others.

This in the beginning of these kind of sensors, and they're going to get better," said Donal Denvir, technical director of Andor Technology. "This is just the start of it."

The sCMOS "leverages where the technology is going, from the semiconductor point of view," said Boyd Fowler, chief technology officer of Fairchild, adding that the ability to take advantage of the research and development work done by larger companies adds value for the customer.

For more information, visit: www.scmos.com

Melinda Rose
Senior Editor
melinda.rose@laurin.com