sCMOS
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Fairchild imaging sCMOS Scientific CMOS Technology A High-Performance Imaging Breakthrough sCMOS - 1.5 e noise White Paper : chnology Dr. Boyd Fowler, Fairchild Imaging Dr. Gerhard Holst, PCO AG 16 June 2009 www.scmos.com

Introduction Since its inception, CMOS image sensor (CIS) technology has held great potential to become the detector platform of choice for many scientific imaging applications. These demanding fields require a unique combination of sensitivity, speed, dynamic range, resolution, and field of view. Although CIS technology has steadily improved it has not fully realized its potential, with CCD, and more recently EMCCD, detectors remaining the platforms of choice for the majority of high-end scientific imaging applications. In this paper we present sCMOS, a breakthrough technology based on...

1.1 - CCDs and EMCCDs Many scientific imaging applications demand multi-megapixel focal plane sensors that can operate with very high sensitivity and wide dynamic range. Furthermore, it is often desirable that these sensors are capable of delivering rapid frame rates in order to capture dynamic events with high temporal resolution. Often there is a strong element of mutual exclusivity in these demands. For example, it is feasible for CCDs to achieve less than 3 electrons RMS readout noise, but due to the serial readout nature of conventional CCDs, this performance comes at the expense of...

This effectively increases the RMS shot noise of the signal by a factor of 1.41, which is manifested in the imagery as an increase in the pixel to pixel and frame to frame variability of low light signals. The net effect of multiplicative noise is that the acquired image has a diminished signal-to-noise ratio, to an extent that the QE of the sensor can be thought to have been effectively reduced by a factor of two. For example, a QE-enhanced backilluminated EMCCD with 90% QE has effectively 45% QE when the effects of multiplicative noise are considered. Dynamic range limitations of EMCCDs...

1.2 - CMOS Imaging Sensors (CIS) CMOS image sensors are similar to CCD sensors, in so far as they are semiconductor devices with photosensitive areas in each pixel that convert incident photons into electrons. Although CMOS image sensor technology was developed in the 1960’s, CCDs have dominated the image sensor market since the early 1970’s. It was not until the mid-90s that serious attention has once again focused on CMOS image sensor development. This work was fuelled largely by the increasingly sophisticated imaging demands of high-volume consumer markets such as camcorders, digital...

2.1 - sCMOS - A new breed of scientific CIS Recently, we have pioneered a breakthrough imaging sensor technology that is based on a new generation of CMOS design and process technology. This device type carries an advanced set of performance features that renders it entirely suitable to high fidelity, quantitative scientific measurement. Scientific CMOS (sCMOS) can be considered unique in its ability to simultaneously deliver on many key performance parameters, overcoming the ‘mutual exclusivity’ that was earlier discussed in relation to current scientific imaging technology standards,...

2.3 - Insight into the sCMOS architecture While the primary technical advancements that underlie this innovation must remain proprietary, some of the architectural detail can be disclosed in the interests of further understanding. The sensor features a split readout scheme in which the top and bottom halves of the sensor are read out independently. Each column within each half of the sensor is equipped with dual column level amplifiers and dual analog-to-digital converters (ADC), represented as a block diagram in Figure 3. This architecture was designed to minimize read noise and maximize...

Figure 5: Comparative low light images taken with sCMOS (1.5 electrons read noise @ 400MHz) vs interline CCD (5 electrons read noise @ 20MHz), under the two weakest LED intensities. Figure 6: Intensity line profiles derived from LED images captured by sCMOS and interline CCD technology, for a range of LED intensities.

2.4 - Rolling vs Global (Snapshot) shutter modes CMOS imagers read out in either Rolling Shutter or Global Shutter mode. Rolling shutter essentially means that different lines of the array are exposed at different times as the read out ‘wave’ sweeps down through the sensor. Global shutter mode, which can also be thought of as a ‘snapshot’ exposure mode, means that all pixels of the array are exposed simultaneously. With sCMOS technology has come the capability to offer both readout modes from the same sensor, such that the most appropriate mode can be selected dependent on...

Figures 5 to 11 show the results of head to head comparisons, pitching a prototype 5.5 Megapixel sCMOS camera against a 1.3 megapixel interline CCD device, and also against 1 Megapixel back-illuminated EMCCD. The sCMOS was set up to image at 400MHz, at this readout speed achieving 70 full frames/s, with only 1.5 electrons read noise. The interline CCD camera, an Andor ‘Clara’, was read out at 20MHz, achieving 11 frames/s with 5 electrons read noise (representing extreme optimization of this sensor at this speed). The EMCCD camera, an Andor iXonEM+ 888, was read out at 10MHz with x300 EM...

Figure 9: 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 frame/s with < 3 e- read noise.

5.5 Megapixel sCMOS 1.3 Megapixel Interline CCD Figure 10: Field of view and resolution comparison of two technologies; x100 magnification; 1.45 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 frame/s with < 3 e- read noise.

Figure 11: Comparative low light fluorescence microscopy images taken with sCMOS vs interline CCD under conditions typical of those employed in dynamic live cell imaging. ND filters on a widefield fluorescence microscope were used to reduce light levels relative to the read noise floor. Note that sCMOS can deliver this improved field of view and SNR ratio at ~ 70 frames/s under the conditions used (400MHz pixel readout), vs 11 frames/s of the interline CCD. At low photon fluxes however, typified in figure 11, the higher read noise of the interline device results in greater sacrifice in...