download Primer on eXcelon technology

Until recently, researchers whose applications require low-light broadband photon detection had to choose between cameras that utilize either standard (i.e., thinned) back-illuminated or back-illuminated deep-depletion technologies. Although both of these options are capable of delivering extremely high sensitivity, their performance is nonetheless compromised to a certain extent by the limitations described in the preceding section. Recently, Princeton Instruments has worked with e2v, a leading CCD/EMCCD manufacturer, to develop a new generation of sensors (and associated cameras) that will minimize and even eliminate some of these hindrances. While the precise details regarding the new technology are beyond the scope of this primer and cannot be revealed for intellectual property reasons, the benefits of eXcelon can be explained via comparative measurements. New eXcelon sensors are based on a standard backilluminated architecture and provide three significant advantages over the other technologies under discussion:

• Higher sensitivity across broader wavelength range (than standard back-illuminated CCDs)
  
• Lower etaloning (than standard back-illuminated CCDs)
  
• Lower dark current (than back-illuminated deepdepletion CCDs)

Etaloning in the NIR
Standard (i.e., thinned) back-illuminated CCDs are solid-state imaging devices that have been etched to 10-15µm thickness in order to collect light through the back surface. As a result of this modification, no light is lost via absorption and reflection by the polysilicon gate structure; these CCDs have more than twice the QE of their front-illuminated counterparts. An unfortunate side effect of this process is that the devices become semi-transparent in the NIR. Reflections between the parallel front and back surfaces of these CCDs cause them to act as partial etalons. This etalon-like behavior leads to unwanted fringes of constructive and destructive interference, which artificially modulate a spectrum. The extent of modulation can be significant (more than 20%) and the spectral spacing of fringes (typically 5 nm) is close enough to make them troublesome for almost all NIR spectroscopy.  

New eXcelon technology
Until recently, researchers whose applications require low-light broadband photon detection had to choose between cameras that utilize either standard (i.e., thinned) back-illuminated or back-illuminated deep-depletion technologies. Although both of these options are capable of delivering extremely high sensitivity, their performance is nonetheless compromised to a certain extent by the limitations described in the preceding section. Recently, Princeton Instruments has worked with e2v, a leading CCD/EMCCD manufacturer, to develop a new generation of sensors (and associated cameras) that will minimize nd even eliminate some of these hindrances.While the precise details regarding the new technology are beyond the scope of this primer and cannot be revealed for intellectual property reasons, the benefts of eXcelon can be explained via comparative measurements.

Conclusions
Developed jointly by Princeton Instruments and e2v, new eXcelon back-illuminated sensor technology provides higher sensitivity (over a broad wavelength range) as well as lower etaloning than standard back-illuminated sensor technology. For most applications in which standard backilluminated sensors are commonly utilized, eXcelon now offers researchers superior performance. For applications that require extremely high sensitivity and the lowest etaloning in the NIR, back-illuminated deep-depletion sensors are still the best choice. Front-illuminated sensors, meanwhile, remain a highly cost-effective option, as long as substantially lower QE is acceptable to the user.