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Quantum Film Might Replace CMOS Sensors
An anonymous reader writes "Quantum film could replace conventional CMOS image sensors in digital cameras and are four times more sensitive than photographic film. The film, which uses embedded quantum dots instead of silver grains like photographic film, can image scenes at higher pixel resolutions. While the technology has potential for use in mobile phones, conventional digital cameras would also gain much higher resolution sensors by using quantum film material." The original (note: obnoxious interstitial ad) article at EE Times adds slightly more detail.
There seems to be a sensationalist mix-up with the two terms... is this technology going to bring about more sensitive pixels (i.e. higher ISO capabilities) or just more pixels on the sensor? or both?
Can the speed be adjusted like ISO 100-400 etc?
Right now night vision goggles give a very grainy tinged image. Clarifying that could have millions of applications.
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Aldous Huxley
I want the pixels that I have on iso 50 and with F1 over a 700mm objective please. Make it smaller and less 'noticeable' then the L-glass I have to carry with me these days and I might buy myself a new body and some glass... Oh, this one is really important. Make it cheaper please. I know you know that we (photographers) will just give you all that we have for a decent setup, but it would be so cool if a real good objective, would cost less than a real good car.
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I don't know too much about the physics of photography, but it seems to me that the real problem in the picture quality of tiny cameras is that the lenses are terrible. Improving the sensors just means that we'll get very accurate digital representations of blurry images, produced by tiny, dirty lenses with minuscule, fixed focal lengths. Even as things stand now, a older camera with good optics and a 5MP sensor produces much better images than a new camera with cheap optics and a 12MP sensor. It seems to me that sensor isn't the bottleneck anymore.
"This is either a picture of your Aunt Mavis... or not."
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I read a story about this in a recent issue of The Economist. The article focuses more on the other direction -- how quantum dots can be used to enhance LEDs to create more pleasing/efficient/versatile lighting. But it also mentions how they can be used to read light, too; for example, to make better solar panels.
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According to the articles, both.
In particular:
- It replaces the in-chip photodetector with an on-top-of-chip detector, allowing all the real estate on the chip be used for the REST of the system rather than reserving most of it for light sensors. That means you can use bigger features (and cheaper processes) - and/or get more pixels by shrinking the features back down a bit.
- It gives about a 4x sensitivity improvement. (2x because the quantum dots are more sensitive, another 2x because they get to be on top (so the light isn't attenuated by chip structures) and cover the whole pixel rather than part of it.) You can use that to make 4x more sensitive pixels of the same size, 4 times more pixels of the same sensitivity, or some other tradeoff.
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I dunno about quantum photography, it's neither here nor there.
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If the sensor gets small enough, the lens can be something other that a refractive solid. Perhaps a drop of liquid in some sort of electrostatic suspension, where problems with the material are far less, and the lens can be focused by reshaping rather than moving.
As an engineer who does astronomical optics rather than a photographer, I can say with certainty with absolute certainty that all else being equal (i.e. diffraction limited case) a larger aperture is sharper. This is simply a matter of physics. The resolution is inversely proportional to diameter of the aperture due to the wave-like nature of light.
Now, if by 'crisper' you don't mean sharper, but rather a fuzzy measure of how you think it looks, its not surprising because smaller lenses of good quality are easier to make, and will thus approach the ideal diffraction limit. But this isn't a case of all other things being equal, and won't be as capable.
That's the trouble with it - you can know its sensitivity or its resolution, but not both, and the act of measuring one changes the other.
If you point any of those cameras toward the sun, you will see flare. This is carefully explained in the video. To suppress flare, you need to stop reflections. On the glass, you can multilayer coatings. On the sensor, you can't do that. So you have to live with the reflection. If you have a concave lens element facing toward the camera body, you have a little concave mirror just waiting to reflect the specular reflection of the sun back onto your sensor. If the new sensors are black, they are not going to reflect much - so less flare.
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> Where do I get my Quantum film developed at ?
You put it in a box with a certain cat.
> I thought photography was getting away from film . . .
Well, it is and it isn't.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
Image quality is limited by several factors. The sensitivity of the detector is only one, and is the only one that quantum dots can address. In this instance, the sensitivity increases only by a moderate amount, so the improvement in signal level (or reduction in pixel size preserving signal level) is also moderate.
Increasing the signal level will improve the S/N ratio for readout noise, assuming the readout is comparable to that available in today's cameras. Readout noise has been aggressively tacked by camera manufacturers, and is already very low. The principal source of noise in conventional images is shot noise (photon noise), and this is unrelated to the detector sensitivity. Shot noise depends ONLY on the number of photons arriving at each pixel, and is the reason that darker areas of digital images tend to be noisier, or require information-destroying denoising operations in postprocessing. Other forms of noise, such as dark current and dark noise, are relevant only in special applications, such as astrophotography.
Shot noise is intrinsic in the statistics of photon fluxes. The number of photons arriving at a pixel from a radiance which is "uniform" in time and space is Poissonian: the standard deviation is the square root of the mean. The signal to noise ratio is the mean divided by its square root, which is the square root of the number of photons which arrived in that sampling interval (exposure). If 10,000 photons are expected to arrive at a pixel in a given exposure time, then the shot noise will be about 1% when comparing multiple "identical" exposures of that pixel. Changing the detector sensitivity raises or lowers the readout signal level, but does not change the signal to noise ratio in the signal from shot noise.
Reducing the shot noise requires more photons arriving at each pixel. Getting more photons per pixel requires either (i) bigger pixels on the detector, (ii) better illumination of the subject, or (iii) better optics. This is why professional cameras have larger pixels than prosumer cameras, which tend to have larger pixels than pocket cameras, phone cameras, etc. Better lenses also help (but large apertures also affect depth of field). For given lighting conditions and optics, bigger pixels result in lower image noise, unless the readout circuitry really sucks.
So, quantum dots will result in a higher signal level than conventional CCD/CMOS/CID detectors under similar imaging circumstances. The improvement is probably limited to improving the ratio of signal to readout noise, which is already pretty good. Quantum dots will not magically increase the number of photons arriving at the detector, and if used to reduce pixel size, will result in worse signal to noise ratio for the shot noise (biggest noise problem in most photography). Result: not a dramatic improvement, although detectors giving horribly noisy images (needing heavy destructive denoising) may get even smaller.
Just send the bums some money, so they'll shut up. The potential of quantum dots in imaging sensors has been known for years.
Those who can make you believe absurdities can make you commit atrocities. - Voltaire
This material has a tunable band-gap by using different combinations and ratios of S, Pb, Cu, Ti, Cd, Hg, Te, Ag, etc. Silicon sensors and their exotic equivalents have fixed, and very limited band-gaps. Additionally silicon based sensors have a rather limited quantum efficiency which is about 40% to 50% efficient under idea configurations. CMOS imagers are anything but idea configurations.
OmniVision's innovation of using BSI didn't increase their efficiency to 80%, it reduced the number of photons absorbed by interfering metalization. area over front-side illuminated solutions... under ideal conditions. This is where the 40% - 50% efficiency numbers come from, and they cannot say so with a straight face because the trenching around the sensor's pixels reduced the coverage over the array... increasing the gaps between pixels.
With this new material they get increased conversion efficiency from the material and increased active area within the pixel with the first-surface configuration. (the metal area is hidden under the photo-sensitve layer, with no trenching. With the tunable band-gap they also get to target IR solutions with sensitivity to wave lengths >1000nm. Si can't do that at all. With other tunings they get improved visible light sensitivity.
While the material is far more toxic than silicon-only solutions, it is a lot cheaper to deposit. Don't eat the film and you should be fine :)