News and discussions about image sensors
Many of these are very drole. And it is good to see such a list.The definition of photogate is incorrect. A gate refers to the control gate of a field effect device and a photogate is a field effect device gate that controls a photonic effect. In CCDs it was initially an MOS gate (the "M" in MOS makes this an oxymoron but we all understand what this means). The photonic effect is the collection and integration of optically generated carriers. Replacing the "M" with semi-transparent polysilicon or with ITO improved CCD sensitivity. Blue response was sitll a problem. Thanks to Jerry Hynecek and his virtual gate device, the CCD photogate became more of a junction field effect device gate with good blue response. With Nobu Ternishi's subsequent "pinned photodiode" ILT CCD (essentially a more useful version of the virtual gate) the photogate was now a junction field effect device whose gate was tied to substrate. Peter Noble had also proposed a buried photodiode device around 1968 but Teranishi's device had the ability to transfer charge for complete charge transfer and the consequent avoidance of lag and kTC noise. Teranishi's device is of course a key element in both CCDs and CMOS APS devices. It was first applied to CIS devices in a joint invention and technology development effort between Kodak and JPL as reported publicly in 1995.So while the term "photogate" is most closely associated with a poly MOS gate a better definition would include both MOS and junction-type photogates, of which the pinned photodiode is a specific case.
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