CCDs are slabs of silicon like photovoltaic cells. Gate structures are added to the top (usually polysilicon or indium tin oxide) so a charge can be applied to corral electrons where they were created (in order to get an image). These gate structures block incoming light and reduce the quantum efficiency (QE). One way to improve QE is to flip the CCD over so that the gates are on the bottom, then grind down CCD until it is about 15 microns thick. The gates are still close enough to the front surface that charge is captured where it is created. Back-illuminated or thinned CCDs have very high quantum efficiencies, but typically cost much more than front-illuminated CCDs.

IDEX Health & Science offers both. Color CCDs are great for applications with plenty of light (bright field microscopy) or applications requiring simultaneous exposure of all colors. For low-light scientific applications where the image is acquired through external filters (e.g. emission filters), a monochrome CCD is the best choice.

A color CCD has a fixed set of filters, typically in a Bayer pattern (red-green-green-blue). If you use a blue filter (e.g. DAPI) in front of a color CCD, only one of every 4 pixels will see any significant amount of light. An 8 megapixel color sensor is not delivering 8 megapixels of red, and 8 megapixels of green, and 8 megapixels of blue. A monochrome sensor acquiring sequential red, green, and blue images using a filter wheel or filter cubes acquires the full 8 megapixels of each.

Lower noise and improved cosmetics. CCDs create charge from incoming light but also from thermal energy. For very short exposures with plenty of light (bright field microscopy), you don’t notice the thermal part of the image. But for low light applications like fluorescence, you want to minimize thermally generated charge to get a better signal-to-noise ratio in the light-generated charge. Cooling also minimizes dark current from hot pixels.

IDEX Health & Science uses Peltier devices, which are thermoelectric coolers that get cold on one side and hot on the other when electricity is applied. Designing a CCD chamber than can keep a seal for many years is part of the engineering; efficiently dissipating the heat generated by the cooling is another part. Typically the temperature sensor for a camera is installed in a copper block that links the CCD to the Peltier cooler. If there is a problem with contact between the copper block and the sensor, the block may be cold but the sensor may not be fully cooled. In this case, you can see dark current values that are inconsistent with reported temperature of the camera.

IDEX Health & Science supports a variety of CCDs and scientific CMOS sensors. For our current offerings, please review this chart.

Yes. Binning is the process of adding pixels together on the CCD itself to increase the signal to noise ratio. Binning 2×2 adds together 4 pixels, but does not increase readout speed by a factor of 4; rather, by a factor of about 2 (because vertical shift time is not affected).

For panning and rough focus, yes; for fine focus, no. Binning increases the size of the pixels, which makes it harder to see if you are in focus. For fine focus, use sub-array readout to increase frame rate.

Yes. IDEX Health & Science cameras provide sub-array readout and binning; cameras with interline transfer sensors have simultaneous readout and exposure. The actual frame rate depends on resolution of the sensor, the number of pixels being read out, and the binning factor selected.

C-mount is a small aperture (1-inch / 25.4 mm) developed for small format sensors.

AIMO = Advanced Inverted Mode Operation. NIMO = non-IMO. Some e2v CCDs, such as deep depletion devices, cannot be operated in inverted mode. As a result, dark current is 100-200X higher than AIMO CCDs. Instead of 0.1 electron per pixel per second (eps) of dark current, for example, expect 10 eps. AIMO vs NIMO is not a choice made by a camera manufacturer like FLI. The CCD is manufactured by e2v either as AIMO, IMO, or NIMO.

Residual bulk image. CCDs are normally 500 microns thick. The gate structures are at the top, and create wells that extend 10 or 15 microns into the CCD. But near IR light can penetrate into the CCD far beyond the reach of the wells created by the gates. This charge gradually leaves the CCD (over hours or days), creating a ghost image in subsequent images. If the CCD is warmed up, the charge will leave the CCD. However, it is not practical to warm up the CCD between images. Alternatively, some cameras provide a pre-flash that uniformly illuminates the CCD, leaving no place for such charge to accumulate below the epitaxial layer. This preflash does slightly lower the full well capacity of the sensor.

Near infrared light can penetrate 200 or more microns into CCDs. As a result, when CCDs are thinned to 15 microns thick, NIR (especially beyond 800 nm) can penetrate to the back of the CCD and reflect off the back (and again off the front, and again off the back, etc), creating a ring of halos around a bright point source. Deep depletion CCDs have high QE in the NIR, but they also have etaloning. Front-illuminated CCDs have less QE in this region but do not suffer from etaloning.

Interline CCDs use part of each pixel to collect light, and part of each pixel to store and move charge. The storage area has a metal mask to prevent corruption of the image during readout. New CCDs have a microlens over each pixel to focus incoming light onto the photodiode portion of the pixel so that light is not lost landing on the metal masks. Because only part of the pixel is used to collect light, the full well capacity of interline CCDs is typically lower than comparably sized full frame pixels. Interline transfer CCDs shutter the image by moving the charge from the photodiode to the storage diode side of the pixel. As a result, interline exposures can potentially be very short. For FLI cameras, interline exposure times can be as low as 30 microseconds (as opposed to about 30 milliseconds for an electromechanical shutter). Usually interline CCDs are used without electromechanical shutters. However, it is complicated to take a dark image without a shutter unless you have some way of keeping the camera in a 100% dark environment. Full frame sensors use 100% of each pixel to collect, store, and transfer charge. They require an electromechanical shutter unless the camera is going to be used in a 100% dark environment. Full frame devices typically have higher full well capacities and higher quantum efficiencies than interline sensors.