F55: F55 global shutter and BSI sensor

marvinhello

marvinhello

Well-known member
I've been wondering, since global shutter circuitry on F55 sensor reduces the fill factor of the photosites, does this mean the sensor is not back-side illuminated? or the specifically the global shutter circuitry has to be placed on the photo sensitive layer?

On F65, Sony claims that the use of copper interconnect (Cu BEOL) reduces the wiring layer by 40% and results in improved sensitivity, does this also mean that the wiring layer is in front of the photodiode?
 
Here's my theory but of course have nothing to back it up with.

With the F55 something is taking up space on the photo sensitive side, or otherwise each photosite itself would be larger and at least the same size as it is found on the F5 and hence would have a similar or identical native ISO of 2000. In the case of the F65, which packs even more photosites in the same surface area, it would undoubtedly make sense that the F65 sensor employs some type of wiring that does not take up as much or even any space on the photo sensitive side.

Its not to say that the F55 sensor isn't "double sided" but perhaps it was just cheaper to put the gate switches on the photo side and avoid the technology that was used for the F65.
 
marvinhello said:
I've been wondering, since global shutter circuitry on F55 sensor reduces the fill factor of the photosites, does this mean the sensor is not back-side illuminated? or the specifically the global shutter circuitry has to be placed on the photo sensitive layer?

On F65, Sony claims that the use of copper interconnect (Cu BEOL) reduces the wiring layer by 40% and results in improved sensitivity, does this also mean that the wiring layer is in front of the photodiode?
Click to expand...

It's a complicated topic - and I may butcher this a bit. the nature of CMOS photosites essentially means they're always collecting voltage, unless they're flushed. This is why you get rolling shutter - because no a/d converter and dsp can read all the photosite voltages at the same exact moment in time. So with the F55 the clever trick is they flush the voltage and store it next to the photosite on the chip until it can be read. But that takes up space.

The F65 doesn't do this. The F65 sensor is actually going to produce rolling shutter. Sony gets around this by using a mechanical shutter, and timing the collection of photosite values to occur while the sensor is not receiving light (due to the mechanical rotary shutter being closed) - the photosites are trying to collect light - but there's none present.
 
Thanks for the reponses guys, but Sony's BSI technology (Exmor R sensor) moves the wiring and circuitry layer below the photosensitive layer, there shouldn't be any reduction in fill factor with global shutter if this is true.

FYI F65 has a fill factor of 94%
 
Ah yes James, what an oversight on my part. The F65 doesn't need the space for gate switches since of course it uses a mechanical based shutter.
 
OK so here's what I got from a sony engineer, only F65 sensor is BSI, the others are standard Exmor sensor (FSI)
 
marvinhello said:
Thanks for the reponses guys, but Sony's BSI technology (Exmor R sensor) moves the wiring and circuitry layer below the photosensitive layer, there shouldn't be any reduction in fill factor with global shutter if this is true.

FYI F65 has a fill factor of 94%
Click to expand...

Exactly where are you reading that the F55 sensor is back-side illuminated or that it's an Exmor R sensor? I've never heard or seen that stated anywhere. The Sony PMW-F55 product page simply says "S35mm 4K/Wide Color Bayer CMOS".

Everything I've previously read on the subject suggests that the F55s lower light sensitivity is due to the space for the voltage gates that make the global shutter possible. Sony being Sony really doesn't answer a lot of questions about technical things like this, but it makes sense.

So perhaps the answer to your original question is "the PMW-F55 does not appear to be back side illuminated, or at least not fully backside illuminated"

The F65 is a rolling shutter, and therefore doesn't have to make space for the voltage gates present on the F55.
 
Viddovation said:
Exactly where are you reading that the F55 sensor is back-side illuminated or that it's an Exmor R sensor? I've never heard or seen that stated anywhere. The Sony PMW-F55 product page simply says "S35mm 4K/Wide Color Bayer CMOS".

Everything I've previously read on the subject suggests that the F55s lower light sensitivity is due to the space for the voltage gates that make the global shutter possible. Sony being Sony really doesn't answer a lot of questions about technical things like this, but it makes sense.

So perhaps the answer to your original question is "the PMW-F55 does not appear to be back side illuminated, or at least not fully backside illuminated"

The F65 is a rolling shutter, and therefore doesn't have to make space for the voltage gates present on the F55.
Click to expand...

yes FS700/FS7/F5/F55 are all Fron-side Illuminated, because the pixel pitch is relatively large and BSI would not bring much benefits.

F65 uses BSI as far as I know, the pixel pitch is 4 microns and would suffer in lowlight if there are readout wiring in the way of the light path.
 
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