# Patent: Canon Back Side Illuminated (BSI) DPAF image sensor



## Canon Rumors Guy (Jan 31, 2019)

> Canon continues to work on new sensor designs based on the patents we’ve seen over the last year or so. This patent covers a lot of things, most notably a backside illuminated sensor, or more commonly known as BSI.
> *Canon News writes:*  (USPTO 20190035827)
> Much has been made over Sony’s BSI (back side illuminated) sensors, and I’m sure Canon is certainly researching making their own.  BSI sensors have efficiency gains not found in normal sensors.  They are also much better in mirrorless cameras because the light doesn’t have to penetrate as deep into the sensor, and mirrorless cameras have a higher angle of incidence of light hitting the sensor near the corners.
> We expect some big gains in Canon sensor technology once the next generation of sensors makes...



Continue reading...


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## Josh Leavitt (Jan 31, 2019)

Finally! I was hoping Canon would eventually start looking long and hard at backside illuminated designs. And I'm quite happy they're designing it around DPAF sensor architecture. This will have a huge benefit for low-light performance on high MP sensors.


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## 3kramd5 (Jan 31, 2019)

Josh Leavitt said:


> Finally! I was hoping Canon would eventually start looking long and hard at backside illuminated designs. And I'm quite happy they're designing it around DPAF sensor architecture. This will have a huge benefit for low-light performance on high MP sensors.



Has that low light benefit been demonstrated anywhere? It seems that gapless microlenses render it a bit of a moot point. BSI is required, as far as I know, for stacked architecture, which will help alleviate bandwidth limitations as pixel counts increase and real time image analysis requirements grow. To me that’s the primary advantage.


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## Josh Leavitt (Jan 31, 2019)

3kramd5 said:


> Has that low light benefit been demonstrated anywhere? It seems that gapless microlenses render it a bit of a moot point. BSI is required, as far as I know, for stacked architecture, which will help alleviate bandwidth limitations as pixel counts increase and real time image analysis requirements grow. To me that’s the primary advantage.



Yes, gapless microlenses have helped improve the sensitivity of photodiodes, but the big benefit of BSI is the removal of the transistors from the surface area. That way you maximize the area and volume of the light sensitive region of the photodiode. It provides a bit of a boost to full-well capacity in most cases. But I've heard there's a trade-off in terms of noise performance. What BSI sensor designs tend to gain in light sensitivity and improved photon (shot) noise performance, they end up losing a bit of read noise performance because the transistors are embedded deeper in the silicon where more dark current is generated. And yes, the potential of stacked sensor designs is perhaps the most significant advantage to be had with BSI architectures.


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## Cryve (Jan 31, 2019)

Can someone more experienced chime in and say if it possible that we see this technology in the next cmaeras, like 7d iii?

How has it been in the past? Do those patents get quickly implemented in new products?


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## ThomsA (Jan 31, 2019)

So, should we wait and look out for a BSI-in-IBIS?


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## canonnews (Jan 31, 2019)

Cryve said:


> Can someone more experienced chime in and say if it possible that we see this technology in the next cmaeras, like 7d iii?
> 
> How has it been in the past? Do those patents get quickly implemented in new products?



Canon's been looking at BSI for a while now, including BSI stacked patents. We have found quite a few in the last year or so.

In theory, Canon could implement quickly, it really depends on the complexity of how you actually create a BSI sensor - it's a little tricky. Stacked sensors which Canon has done a ton of patent work on, may be easier to implement and provide nearly the same benefits as BSI, because with a stacked sensor BSI is less important because the transistors and wiring mostly exist in the secondary layer and not the photodiode layer.

Canon's been looking at a ton of different things, from stacked sensors, curved sensors, even curved stacked sensors (a real unicorn), BSI sensors .. you name it Canon's been researching it.

just doing a quick search on our site, i see 17 stacked sensor patents, 5 BSI patents, and 5 curved patents. this in a little over a year since we've been online.


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## 3kramd5 (Feb 1, 2019)

Josh Leavitt said:


> Yes, gapless microlenses have helped improve the sensitivity of photodiodes, but the big benefit of BSI is the removal of the transistors from the surface area. That way you maximize the area and volume of the light sensitive region of the photodiode. It provides a bit of a boost to full-well capacity in most cases. But I've heard there's a trade-off in terms of noise performance. What BSI sensor designs tend to gain in light sensitivity and improved photon (shot) noise performance, they end up losing a bit of read noise performance because the transistors are embedded deeper in the silicon where more dark current is generated. And yes, the potential of stacked sensor designs is perhaps the most significant advantage to be had with BSI architectures.


But have those gains been demonstrated, even in a lab? I’ve looked for quantitative apples to apples comparisons of BSI to FSI, and haven’t found anything (not that I’ve looked particularly hard).


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## Mt Spokane Photography (Feb 1, 2019)

The patent is not about BSI, but a manufacturing method for the Pixels in a DPAF or Quad Pixel or even other split multi pixel sensor. It shows different examples, and while examples 1- thr 8 are conventional Front side wiring, it shows in example 9 how BSI sensors would make use of the manufacturing method.

The issue they are trying to solve is isolation performance between a plurality of photoelectric conversion portions(dual pixels or quad pixels for example) where some wavelengths of light are not isolated as well as desired.

So, yes, it mentions BSI in passing, but its not about BSI at all.


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## yungfat (Feb 1, 2019)

I remember there is a collaboration between Canon & Sony quite some times ago as both of them agreed to ex-change their technology to photography equipment. 

Canon is exchanging their DPAF with Sony sensor technology. Of course both of them won’t handouts everything they have. 

Thus we can see the great improvement of Sony AF and now Canon is about to improve their sensor performance. 

Good for the consumer. 

Thanks.


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## 3kramd5 (Feb 1, 2019)

yungfat said:


> I remember there is a collaboration between Canon & Sony quite some times ago as both of them agreed to ex-change their technology to photography equipment.
> 
> Canon is exchanging their DPAF with Sony sensor technology. Of course both of them won’t handouts everything they have.
> 
> ...



There was some speculation that Canon and Samsung had some sharing. Indeed Samsung has DPAF products. Sony does not.


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## Stuart (Feb 1, 2019)

"We expect some big gains in Canon sensor technology once the next generation of sensors makes it to consumer products. "
Might this just be for their commercial focus on monitoring systems.
With Focusing down to -6eV (with the right lens) then sensors do need to work harder.


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## djack41 (Feb 1, 2019)

This is good news but Canon needs to move quickly. Given the CEO's gloom market forecast, is Canon truly devoted to the task?


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## Josh Leavitt (Feb 1, 2019)

3kramd5 said:


> But have those gains been demonstrated, even in a lab? I’ve looked for quantitative apples to apples comparisons of BSI to FSI, and haven’t found anything (not that I’ve looked particularly hard).



IEEE is probably the best resource for looking into differences between CMOS architecture for active pixel sensors. This whitepaper in particular is a brief overview of differences in fill-factor and peak QE between FSI and BSI designs (but there are plenty more): https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=8334288

In practice the gains of BSI are realized with very small pixel sizes - usually between 1-3 micrometers per side. That's why almost every smartphone sensor (1/2.3" or smaller) and most premium compacts have all adopted BSI designs.


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## melgross (Feb 1, 2019)

It wasn’t all that long ago that we were being told that this is only useful for small sensors. What’s changed?


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## melgross (Feb 1, 2019)

Josh Leavitt said:


> IEEE is probably the best resource for looking into differences between CMOS architecture for active pixel sensors. This whitepaper in particular is a brief overview of differences in fill-factor and peak QE between FSI and BSI designs (but there are plenty more): https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=8334288
> 
> In practice the gains of BSI are realized with very small pixel sizes - usually between 1-3 micrometers per side. That's why almost every smartphone sensor (1/2.3" or smaller) and most premium compacts have all adopted BSI designs.


Youre repeating that old information I just posted about, having not seen your post first. Sensor manufacturers are now using this on larger sensors, so thoughts about this must have changed.


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## criscokkat (Feb 1, 2019)

melgross said:


> It wasn’t all that long ago that we were being told that this is only useful for small sensors. What’s changed?


I think the number of steps required in each layer that laid down have been greatly reduced. I think the only reason why it was only used in phone sensors before was that it was only economical if you were making thousands of sensors per wafer. (for example at $15 per phone sensor you'd be looking at 10,000+ as a full frame sensor). The sensor used to be one of the most expensive parts of a top end phone. These days they are cheap enough they can put 6-7 on them phone.


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## mclaren777 (Feb 1, 2019)

As long as they don't step backwards on DPAF, I'm fine with this.


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## nchoh (Feb 1, 2019)

djack41 said:


> This is good news but Canon needs to move quickly. Given the CEO's gloom market forecast, is Canon truly devoted to the task?



Looking at Canon core business and competencies, the obvious answer is yes. Looking at the number of patents... that is, a proxy for research, the answer would also be yes.


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## nchoh (Feb 1, 2019)

mclaren777 said:


> As long as they don't step backwards on DPAF, I'm fine with this.



As with all focusing systems, there are pros and cons.


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## Mt Spokane Photography (Feb 2, 2019)

melgross said:


> It wasn’t all that long ago that we were being told that this is only useful for small sensors. What’s changed?



Video has changed it (faster readout speed due to a better ground plane, as has the ability to put more complex circuitry on the sensor. Multi layer sensors as in the Sony A9 are the next step as far as faster sensor readout, but very expensive. Photosites on sensors are about as good as they can get as far as low light, some sort of tech breakthru would be needed to have a big boost, so small gains from BSI are now the best low cost way to improve. We see lots of claims of new tech, but most of them are really just fishing expeditions looking for more R&D money.


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## dak723 (Feb 2, 2019)

Yes, sensors are about as good as they can get, and there has been very little improvement for years now.

But "gear-heads" need to believe that technology can be improved endlessly. And they will continually flock to those companies that give them "new" - even if "new" is no better than old. Thus Sony is wildly popular while Canon is continually bashed. Even though the photos are essentially indistinguishable for most photographers (not counting differences in color, which of course have nothing to do with being "new" and thus doesn't count).


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## 3kramd5 (Feb 2, 2019)

Mt Spokane Photography said:


> Video has changed it (faster readout speed due to a better ground plane, as has the ability to put more complex circuitry on the sensor. Multi layer sensors as in the Sony A9 are the next step as far as faster sensor readout, but very expensive. Photosites on sensors are about as good as they can get as far as low light, some sort of tech breakthru would be needed to have a big boost, so small gains from BSI are now the best low cost way to improve. We see lots of claims of new tech, but most of them are really just fishing expeditions looking for more R&D money.


Can you elaborate on how a better ground plane improves readout speed? Also, ground plane in the semiconductor or in the circuit card?


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## jd7 (Feb 2, 2019)

dak723 said:


> Yes, sensors are about as good as they can get, and there has been very little improvement for years now.
> 
> But "gear-heads" need to believe that technology can be improved endlessly. And they will continually flock to those companies that give them "new" - even if "new" is no better than old. Thus Sony is wildly popular while Canon is continually bashed. Even though the photos are essentially indistinguishable for most photographers (not counting differences in color, which of course have nothing to do with being "new" and thus doesn't count).


Sony is wildly popular and Canon is bashed in some (many?) online forums ... but it's the other way around in the market. My guess is the market generally agrees that new isn't necessarily better here, even if the gear head segment struggles with that.


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## juststeve (Feb 2, 2019)

This patent actually makes for fascinating reading. Yes, I lead a boring life.

But the majority of the patent is not so much about back side illuminated sensors, although there is BSI stuff there, it is about introducing impurities like boron and arsenic to the light sensitive silicon layer(s) in different concentrations and depths to create signal amplification and isolation. The patent even talks about sensitivities changing to varying wave lengths at varying depths of the light sensitive layer. That sounds a bit Foveon-like.

An important clue is the n and n+ layers of the top photo sensitive layer. Apparently, the impurities to the silicon are injected and then layered here as the n and n+ layers.

Other parts of the patent mention things like on sensor memory and on sensor noise reduction. Sounds like Canon may be getting ready to give Sony's A9 sensor a run for the money, like by the 2020 Olympics, perhaps.

The caveat here is that I am neither an engineer or a patent lawyer, so I could be full of poo.


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## Mt Spokane Photography (Feb 2, 2019)

juststeve said:


> This patent actually makes for fascinating reading. Yes, I lead a boring life.
> 
> But the majority of the patent is not so much about back side illuminated sensors, although there is BSI stuff there, it is about introducing impurities like boron and arsenic to the light sensitive silicon layer(s) in different concentrations and depths to create signal amplification and isolation. The patent even talks about sensitivities changing to varying wave lengths at varying depths of the light sensitive layer. That sounds a bit Foveon-like.
> 
> ...




At last, someone else who has actually read the patent. It is pretty difficult to wade thru, I had to print it out and mark the various claims versus the numbers on the drawings. 

BTW, all CMOS sensors have noise reduction built in to the sensor, even Canon's first CMOS sensor has it.Its nothing like a foveon Sensor, Canon has patents for those as well. The issue with front side wiring is that there is no room for more complex noise reduction and amplification, BSI allows that, and layered sensors are better yet. 

Its about improving the pixels for dual or quad pixel sensors by tweaking the manufacturing process.


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## MrToes (Feb 2, 2019)

ABOUT FREAKING TIME CANON!


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## drob (Feb 3, 2019)

I can't pretend to know about the pluses and minuses of BSI sensors...I do own a 3-4 year old Samsung NX50 with a BSI 28MP sensor...so Canon hasn't looked into this when Samsung was doing this years ago? I find it hard to believe. I'll give them my NX50 so they can tear it apart and backward engineer newer sensors. I'm still a little bitter about Samsung exiting the camera market...especially after their "Ditch the DSLR" campaign.


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## Mr Majestyk (Feb 3, 2019)

Canon cannot be taken seriously in mirrorless without all new sensor tech (for them that is). The whole myriad of issues with the EOS R stem from the not-designed-for-mirrorless sensor from the 5D4 being used in the first place. Read speed is king in mirrorless, a new Sony class sensor would transform the EOS R series in AF, eye-AF, video, DR, VF lag etc. If they can deliver then I may just stand by them for a lot longer to come. I want to like the EOS R, they have some basics right, nice size, weight and ergonomics but this is almost Rebel class in most ways.


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## Kit. (Feb 3, 2019)

Mr Majestyk said:


> Canon cannot be taken seriously in mirrorless without all new sensor tech (for them that is).


You cannot be taken seriously with the first sentence like this. Doesn't Canon dominate the mirrorless market with their current sensor tech?


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## chik0240 (Feb 4, 2019)

I just hope they can get me a 5D mk V with a sensor of better shadow noise which I once a while would prefer and that’s all I would want


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## melgross (Feb 4, 2019)

Mt Spokane Photography said:


> Video has changed it (faster readout speed due to a better ground plane, as has the ability to put more complex circuitry on the sensor. Multi layer sensors as in the Sony A9 are the next step as far as faster sensor readout, but very expensive. Photosites on sensors are about as good as they can get as far as low light, some sort of tech breakthru would be needed to have a big boost, so small gains from BSI are now the best low cost way to improve. We see lots of claims of new tech, but most of them are really just fishing expeditions looking for more R&D money.



Well, yeah, it was mostly an observation. I know about the advances. I just find it interesting that just a few years ago “experts” were insisting that it was useless for serious photography, and yet, here it is!


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## Mt Spokane Photography (Feb 5, 2019)

melgross said:


> Well, yeah, it was mostly an observation. I know about the advances. I just find it interesting that just a few years ago “experts” were insisting that it was useless for serious photography, and yet, here it is!


What I heard (long before video in DSLR's) was that there were diminishing returns on the % increase in sensor space as sensors got larger. It was said that the first sensors to use it would be cell phones where there is a large advantage, with larger sensors well off in the future because its expensive and difficult to do with large sensors. That's still true, but now we have video which we did not have then, and we have users demanding more FPS, so Sony has introduced them. I think that Canon is a ways off because dual pixel sensors will be much more difficult to do. They may even go straight to multi layer bonded sensors.


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## YuengLinger (Feb 5, 2019)

Even if this approach leads nowhere, at least Canon is covering its backside!


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## 3kramd5 (Feb 6, 2019)

YuengLinger said:


> Even if this approach leads nowhere, at least Canon is covering its backside!


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## blackcoffee17 (Feb 6, 2019)

Kit. said:


> You cannot be taken seriously with the first sentence like this. Doesn't Canon dominate the mirrorless market with their current sensor tech?



Dominating the market with the M series is one thing, but they are behind in sensor tech. And i don't mind if the DR is 0.5 stops less than the competition but now they don't have a separate AF and metering sensor like in the DSLR's, everything has to be done by the main sensor.

The EOS R has very slow burst rate with AF-C, cropped and soft 4K video and this is likely because they have a bottleneck in sensor readout speed or processing. In AF-C the the camera sometimes drops to 1-2 FPS, that is not good enough.


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## Kit. (Feb 6, 2019)

blackcoffee17 said:


> Dominating the market with the M series is one thing,


Dominating the market cannot be taken seriously? By whom?



blackcoffee17 said:


> but they are behind in sensor tech. And i don't mind if the DR is 0.5 stops less than the competition but now they don't have a separate AF and metering sensor like in the DSLR's, everything has to be done by the main sensor.
> 
> The EOS R has very slow burst rate with AF-C, cropped and soft 4K video and this is likely because they have a bottleneck in sensor readout speed or processing. In AF-C the the camera sometimes drops to 1-2 FPS, that is not good enough.


The EOS R has best in class low light autofocus performance and best in class video autofocus performance. All thanks to Canon's sensor tech.

Yes, one needs to pay for that by reading twice as much pixels per frame.


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## Diko (Feb 11, 2019)

dak723 said:


> Yes, sensors are about as good as they can get, and there has been very little improvement for years now.
> 
> But "gear-heads" need to believe that technology can be improved endlessly. And they will continually flock to those companies that give them "new" - even if "new" is no better than old. Thus Sony is wildly popular while Canon is continually bashed. Even though the photos are essentially indistinguishable for most photographers (not counting differences in color, which of course have nothing to do with being "new" and thus doesn't count).


This is not quite the case. 

Low light photos a few years ago prior to 5D4 was somewhat behind compared to the back then trendy SONYKON & SONY devices. Talking from personal experiences. It was not nice to see results from similiar lenses but different vendor bodies resulting mostly from lack of enough DR


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## Diko (Feb 11, 2019)

Mr Majestyk said:


> ...The whole myriad of issues with the EOS R stem from the not-designed-for-mirrorless sensor from the 5D4 being used in the first place...


Could you please elaborate on that part?


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## Ozarker (Feb 11, 2019)

dak723 said:


> Yes, sensors are about as good as they can get, and there has been very little improvement for years now.
> 
> But "gear-heads" need to believe that technology can be improved endlessly. And they will continually flock to those companies that give them "new" - even if "new" is no better than old. Thus Sony is wildly popular while Canon is continually bashed. Even though the photos are essentially indistinguishable for most photographers (not counting differences in color, which of course have nothing to do with being "new" and thus doesn't count).


Sony is only wildly popular on this website, and mostly brand new account holders.


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## sdz (Sep 27, 2019)

juststeve said:


> snip/
> 
> The caveat here is that I am neither an engineer or a patent lawyer, _so I could be full of poo_.



That's the only qualification you need to post here!


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