Samsung Galaxy S5’s ISOCELL image sensor explained

February 24, 2014

samsung camera module

[Update - The Galaxy S5 contains Samsung's revolutionary new ISOCELL technology. Check it out below, and more on this to come soon!]

Megapixels make for an easy number to compare, which is why so many manufacturers love to brag about it, selling higher MP counts like the panacea of all problems of smartphone photography. But there are a lot of other important features that make up a high quality image sensor, which is important to keep in mind when talking about ISOCELL.

Camera aficionados have probably heard about Samsung’s ISOCELL image sensor, which is reportedly making an appearance in the Galaxy S5. This new technology promises increased light sensitivity and higher color fidelity even in poor lighting conditions, and Samsung bills it as the next step in the evolution of backside-illuminated (BSI) sensors.

We will all be hearing a lot more about ISOCELL technology over the next several months. But ISOCELL is not just a buzzword, so it’s important to understand what the technology is and how it works. Using information from a recent technology presentation we attended, we’re going to take a closer look at exactly how Samsung wants to change smartphone cameras.

camera sensor

Designing a high quality image sensor 

One of the biggest factors in determining the overall quality of an image sensor is the amount of light that it can capture in each pixel. It’s a very simple premise — the more of the light in a scene that an image sensor can capture, the more accurate the picture is reproduced. This means that having larger individual pixels is beneficial for image quality, because each pixel can capture more light.

However, when you have large pixels, you can cram fewer of them on the surface of the camera sensor, which results in a smaller resolution and less detailed images.

Typically, smartphone makers have been more interested in packing more small pixels on the sensor to increase resolution, than in having more sensitive pixels.

Good resolution vs Good light sensitivity

A notable exception is HTC, who attempted to buck the trend of ever-shrinking pixels with its UltraPixel technology. UltraPixels are essentially larger pixels, and that’s why HTC had to reduce the resolution of the One’s camera to just 4MP. On the flip side, thanks to this the One can take nice images even in lighting conditions that would make other cameras struggle.

However, not everyone is willing to follow HTC’s path, so sensor makers have poured billions into developing sensors that offer both high resolution and good light sensitivity, all within the constraints of a smartphone-friendly footprint.

In an attempt to capture more light even on minuscule pixels, manufacturers have gone to great lengths to improve sensor efficiency, from removing gaps between pixels to switching over to backside illumination, which increases efficiency by moving the metal wiring that connects each pixel below it, so it doesn’t occlude any light. This illustration shows how a BSI sensor captures more photons, compared to the FSI sensor, where the metal wiring reflects some of them.

6641-sony_cmos_diagram

Source: Tested

But BSI technology only goes so far at maximizing sensor efficiency. One other big stumbling block for mobile image sensors is crosstalk, and this is where ISOCELL comes into play.

What issues does ISOCELL solve?

One issue that Samsung is trying to solve with ISOCELL is that, as a pixel shrinks, its well capacity, (the charge an individual pixel can hold before saturating) decreases, meaning that the pixel has a smaller dynamic range. By dynamic range with regard to imaging, we mean the difference in intensity between the lightest and darkest parts of the image.

There’s also another big issue with increasingly smaller pixel sizes, whereby photodiodes are incorrectly sensing the color and amount of light due to a phenomenon called crosstalk. Photodiodes are the tiny detectors that turn light into a current, which the sensor’s chip processes and turns into an usable image.

Crosstalk happens when some of the light that should hit a specific photodiode “leaks” to neighboring photodiodes, causing faint currents to form where there shouldn’t be any.

Crosstalk occurs for a number of reasons, but the most likely cause is light bouncing around inside the diode, which is called light crosstalk. Also, when a pixel receives more light that it can handle (light exceeds saturation levels), electronic crosstalk occurs, which is the creation of currents in incorrect photodiodes due to the leakage of electrical signals transmitting data from the diodes.

Image sensor crosstalk

An example of crosstalk leakage, both light and electronic, between individual color pixels.

Put in other words, if we were to shine a light at a green pixel, some photons may leak into the blue and red ones and cause a small current in these photodiodes, even though there’s no red or blue in the scene. As you can imagine, this leads to a slight distortion of the original picture when you attempt to look back at it, manifested in blooming and noise. Crosstalk is unavoidable, but it can be mitigated with some clever manufacturing techniques.

To sum up, an ideal image sensor can capture enough light to accurately reproduce the original image, both in terms of a wide spectrum and large dynamic range, and should consist of accurate sensors which avoid as much crosstalk as possible.

How does ISOCELL work?

ISOCELL is essentially an evolution of existing technologies and aims to address the problems highlighted above.

First off, ISOCELL attempts to fix the problem of crosstalk by isolating each pixel with a physical barrier, hence the “iso” part of the name. These barriers ensure that the correct photons remain trapped in their desired cells and are therefore more likely to be absorbed into the correct pixel’s photodiode.

Here’s how Samsung explains ISOCELL in a video:

Compared to conventional BSI pixels, ISOCELL is expected to decrease crosstalk and increase the sensor’s full well capacity by approximately 30 percent, due to the way each color pixel is isolated. That doesn’t mean that the image quality is going to improve by 30 percent, but it will result in higher color fidelity, which will be noticed as a slight improvement to sharpness and richness.

samsung 16mp isocell sensor 2

Tech details

ISOCELL is actually the commercial name of what Samsung calls 3D-Backside Illuminated Pixel with Front-Side Deep-Trench Isolation (F-DTI) and Vertical Transfer Gate (VTG).

The problem with insulating photodiodes (F-DTI) is that it actually reduces the surface of the photodiode that captures light, and therefore the full well capacity. To solve this issue, Samsung changed the design of photodiodes to use a component called Vertical Transfer Gate (VTG), instead of the horizontal type normally found on BSI sensors. Using VTG enabled Samsung to isolate photodiodes, but still have a large well capacity and therefore good light sensitivity.

Thanks to this technology, Samsung managed to reduce crosstalk from 19 percent, in the case of a regular BSI sensor, to 12.5 percent for ISOCELL. The new technology enables an excellent luminance signal to noise (YSNR =10) ratio of 105 lux, compared to the 150 lux in the case of BSI; full well capacity was increased to 6,200 e- compared to 5,000 e- on a similar BSI sensor.

ISOCELL also enables a wider view angle by capturing more of the light coming obliquely. This allows the use of lower F-number lenses, for better quality pics in less well lit environments. Finally, ISOCELL gives manufacturers more freedom to lower the height of the module or to increase the surface of the pixel array. Sensors will be able to fit into even smaller packages, potentially saving on manufacturing costs later down the line.

ISOCELL CRA

What this means for smartphones

Clearly ISOCELL is promising improvements to general image quality, in the form of improved sharpness, a wider dynamic range, and more accurate image capture. Here’s a little taste of the sorts of improvements we’re talking about.

BSI ICOCELL Comparison

BSI vs ISOCELL, outdoors. Click to enlarge

isocell sample

BSI vs ISOCELL, indoors sample. Click to enlarge

As well as image quality improvements, ISOCELL is likely to have an effect on the cost and future development of smartphone cameras. As a new technology involving a more complicated manufacturing process, ISOCELL cameras will likely start out as a bit more expensive than the current crop, so it’s probably only destined for premium level devices for now.

Although the first Samsung image sensor to adopt this technology will consist of 8 megapixels, each pixel will be sized at under 1.12 microns each, which could certainly see Samsung eventually match the number of megapixels in the current high-end sensors, without sacrificing as much image quality to noise and crosstalk. Remember that a 16 megapixel version is already rumored for the Samsung Galaxy S5. The smallest this technology can be scaled down to, at the moment, is 0.9 microns, meaning that Samsung will be able to squeeze in even more pixels in the future. 

Shrinking down the size of the camera module means that the consumer could also benefit from smaller and potentially cheaper components, or designers could decide to use the extra space for improvements to other bits of camera technology, such as better lenses and optical image stabilization systems. Shrinking camera modules could make room for thinner designs or bigger batteries.

ISOCELL is a promising new technology that looks like it could consolidate Samsung’s status as a top dog in the mobile industry. Samsung itself has said that ISOCELL will be arriving in “top tier tech on modern mobile devices in 2014″, which suggests that the Galaxy S5 or Note 4 could be the first inline to benefit from this new technology.

Comments

  • MasterMuffin

    I don’t believe that this is going to be in S5, but maybe is a later version of it (Samsung likes doing lots of versions :D)

    • http://www.AndroidAuthority.com/ Darcy Alexander LaCouvee

      MasterMuffin, in the webinar, I met with their lead researcher and others and they told me it is actively shipping in ‘key products to hit the market soon’ so it’s a reasonable assumption on our part.

      • MasterMuffin

        well see ;)

        • Mel

          you forget the apostrophe ( we’ll ) mister grammar police ;)

          • MasterMuffin

            Corrected :)

          • http://www.AndroidAuthority.com/ Darcy Alexander LaCouvee

            Told you it would be in the Galaxy S5 :)

          • MasterMuffin

            :'(

            :D

      • MasterMuffin

        Just here to admit that I was wrong :))

    • jeff

      Wrong muffdaddy

  • bungadudu

    Great article!

    Let there be more of this!

    • http://www.AndroidAuthority.com/ Darcy Alexander LaCouvee

      Thanks, Bungadudu. Took a surprising amount of work. What matters to people? Build quality, display, camera ability, software efficiency, and the like. We are going to dig deep in 2014 to uncover all the gold to serve guys just like you. Please let us know what you want us to pay attention to. Thanks for being a fan!

      • Mystery Man

        want you to drop test it

        • butofcourse

          but of course :D

          • http://www.AndroidAuthority.com/ Darcy Alexander LaCouvee

            You guys are hilarious. Samsung told us they do extensive drop tests, and that the S5 represents a big step forward. Stay tuned for the drop!

          • Castor

            it should be with the new bezel they have. i don’t want to say they copied sony’s bezel design of having the glass slightly sunk in to prevent direct impact upon dropping. the xperias hardly break when dropped because their glasses are protected by the metal rim that slightly protrudes to avoid direct impact on the glass.

          • das

            to be fair ,the s5 looks like the s2 again with its slightly raised edging around the front

        • No Mystery, man

          What no blend, nor crysis !

  • Celc

    This better be integrated in the G5 software…even if chances are slim

    • Shark Bait

      software??? this is a hardware feature

  • Anirudh

    At one time i thought i am on anandtech.com

    • happytech

      naah, if it were anandtech, they’d have ended with “however, this is no iphone” :P

  • Frank

    Wow it is the greatest sensor i’ve ever seen before lol. Im very expected!!

  • http://digigato.dyndns.org/ DigiGato

    But since is not an iCamera stuff people (that loves Apple) will say: Meh! It looks better with my iPhone 5 camera…
    Hopefully in the Galaxy Note 4 this camera will be included (praying!) :D

    • jeff

      Gato…you be on wrong page. Dis is androit

      • Castor

        jeff you misunderstood his post.

      • http://digigato.dyndns.org/ DigiGato

        Yup, I am in the right page, perhaps next time I’ll add some tags :D ;)

  • Bone

    Fantastic article!

    I don’t think ISOCELL will arrive with the Galaxy S5 though, I’d expect pretty low yield for such technology at first, and the 16MP & 20MP rumors (there was one alleged 16:9 photo that suggested the latter) point to Sony’s trusted Exmor RS. Simply put, I see no way Sammy has 25 million ~20MP ISOCELL units ready that’s required for the S5’s global launch, they’ll most likely debut it with the premium P series.

    • blahblahblah

      I dont think so

    • xhozt

      care to rethink that ;-)

  • On a Clear Day

    Really informative article Robert. It had to have taken “forever” to pull all of this info together and organize it and make it comprehensible.

    One of Samsung’s truly great advantages is that, rather than being a manufacturer of devices that are pieced together from other manufacturer’s best components – as in the case of some companies that buy a little bit of this from Sony and then a bit of that from Samsung and then season it with a dash of fairy dust – so they can then say “Now it’s I believe I can fly” time”

    Samsung is involved in the actual creation OF the new technologies they perceive are most pressing to address at the moment – thus we see ISOCELL and its related underlying developments.

    The question – re cameras in phones though – that all of this bodes is, when is good – good enough? I realize everyone who makes devices wants to be able to have every little bit of added differentiating factors added to their side of scale so people favor theirs.

    But, at some point, we have to realize that we are talking about a device where the ability to take nice, quality pictures is obviously a convenient adjunct to its functionality – taking pictures is NOT its main function. I think we are fast approaching the point of diminishing returns re both perceivable picture quality differentiation as well as using it as marketing value/hype/bragging rights. If I want a REAL picture, I sure as hell won’t use a cell phone for it, but I will use a cellphone/device for all the myriad lovely functions we all couldn’t dream of living without – now that we have become accustomed to them.

    Darcy asked for what we thought would be important in 2014 to us? One must be careful what one asks for.

    The bloom is off the rose; the honeymoon is over – and the reality of marriage and the, “You mean we actually have to talk too” phase – so to speak – has begun to set in in the device firmament. We have or are at least well into entering the stage where at the higher end what is going to impress – is/are devices that are lovely to look at, beautiful to behold and yet have the ability to kick ass and keep on ticking while providing us with higher and higher functionality and ease of use allowing us to do the jobs we need them to do.

    I will be buying based on my primary anticipated uses of a device – not on whether it can take another picture that I will forget I ever have; no one will ever see and even I in two days won’t care about.

    If I were a manufacturer, I would be feeling the chill cool winds of reality and practicality beginning to make their way across the landscape of devicedom and face the fact that it might just be a good time to focus more on making sure I have the basics really, f—ing well covered so that when the dust that the spin mavens settles I am the one left standing.

    • LogicMaster

      I think Canon controls most if not all the tech it uses in cameras and most of the manufacturing segments also. But give Samsung kudos, they are a major player in today’s market and have risen to the top quickly.

      I have the Samsung 64 inch 3D plasma HD tv set and is the best TV I have ever viewed. I am hoping they do get better camera tech, I will then get a Galaxy s5 or whatever the current smart phone model will be at that time as they work together well.

  • http://www.brosix.com/ Brosix

    Tech explained beautifully in the Article. But I still believe the iPhone 5s has a better camera

    • das

      TROLL

  • john

    TL;DR

  • http://www.multicorechina.com/ Multicorechina.com

    Yup! Keep them coming! Nice article

  • Der Astar

    Well phone looks good but i`m waited more from Samsung, well if we look carefully LG G2 is same as S5 only 2.5Ghz and a +3mp camera, heart sensor? look samsung, not many guy need it and i think it can`t be usefull, still it has no OIS and no 4K recfording and still plastic back… shame really even G Pro 2 has metalic back -_- LG is making it better (even LG SUCKS with software updates)

    • Abi Lingam

      S5 can record 4K video for 5min each video.

  • Amine Elouakil
  • Danny switcher

    Look closely at the photo to the left side above the table isn’t that thing half in HDR off and is complete in HDR ON?
    I found this on their official site http://www.samsung.com/global/microsite/galaxys5/mobile/features(DOT)html

  • http://www.Physicsism.com/ Elias Fazel

    The Most Useful, helpful article ever.
    please do same research for all special hardware.

    almost post in tech-sites are just about news without any technical explanation.

    u can be educational +Android Authority

    GeeksEmpire

  • CHOPZZ

    great stuff!

  • Rohit Naik
  • Rohit Naik
  • jazz

    duhh, those pictures are so average

  • Android ftw

    Sounds quite similar to Sony’s Triluminous technology with regards to color isolation and gamut.

    • Tralala

      That’s for displays.

  • Pandemonium_ctp

    I’d love to see this compared to the 1020, 808, or even the N8. Sensors matter greatly, but so does the lens. ;)

  • xd feng

    This rigid flex circuits is a small bendable and foldable cable attaching to the circuit. Beside, it has very good heat resistance, heat dissipation and great capability of transmisson.