Chipworks recently released an article analysing the CMOS Image Sensor (CIS) processes from a variety of manufacturers, including Nikon, Sony, and Canon. Historically, Canon has used a 0.5 micron (500nm) process for all of their FF sensors since the original 1Ds. In the Canon analysis, they noted that Canon has a 0.18 micron (180 nanometer) fabrication process (possibly what they used for the 120mp APS-H?) that they may begin using for future FF sensors:
[quote author=Chipworks]Canon does have a 0.18 µm generation CIS wafer fab process, featuring a specialized Cu back end of line (BEOL) including light pipes (shown below). It is possible to speculate that Canon may be preparing to refresh its FF CIS line to supply devices for a new FF camera system.[/quote]
A move from their 0.5um process to a 0.18um process for FF CIS manufacture would be a fairly significant move for Canon. The accompanying image figure also seems to indicate a double microlens layer...one above the CFA and one below...which could lead to higher Q.E. The article also mentions the use of "Light Pipes", a term I had not heard before. According to a few papers I've read, lightpipes in CMOS sensor design make use of high refractive index materials and a reflective wall in the optical stack the to improve transmission of light from the color filter/microlens to the photodiode, which exists at the end of a narrow tube where all the readout wiring exists (in a frontside-illuminated design). Seems like a lightpipe is an alternative to using a backside-illuminated design that aims to improve Q.E while avoiding some of the complexities and issues with BSI designs. Additionally, the use of copper interconnects should improve efficiency, allowing lower power usage, and hopefully leading to a lower level of electronic noise (the great bane of Canon these days.)
Seems Canon is most definitely not out of the CMOS Image Sensor design game yet. They seem to have some new tricks up their sleeves, and hopefully they will see the light of day in their next FF camera. Ah, competition is good!
[quote author=Chipworks]Canon does have a 0.18 µm generation CIS wafer fab process, featuring a specialized Cu back end of line (BEOL) including light pipes (shown below). It is possible to speculate that Canon may be preparing to refresh its FF CIS line to supply devices for a new FF camera system.[/quote]
A move from their 0.5um process to a 0.18um process for FF CIS manufacture would be a fairly significant move for Canon. The accompanying image figure also seems to indicate a double microlens layer...one above the CFA and one below...which could lead to higher Q.E. The article also mentions the use of "Light Pipes", a term I had not heard before. According to a few papers I've read, lightpipes in CMOS sensor design make use of high refractive index materials and a reflective wall in the optical stack the to improve transmission of light from the color filter/microlens to the photodiode, which exists at the end of a narrow tube where all the readout wiring exists (in a frontside-illuminated design). Seems like a lightpipe is an alternative to using a backside-illuminated design that aims to improve Q.E while avoiding some of the complexities and issues with BSI designs. Additionally, the use of copper interconnects should improve efficiency, allowing lower power usage, and hopefully leading to a lower level of electronic noise (the great bane of Canon these days.)
Seems Canon is most definitely not out of the CMOS Image Sensor design game yet. They seem to have some new tricks up their sleeves, and hopefully they will see the light of day in their next FF camera. Ah, competition is good!