Graphene-Based Image Sensor To Enhance Low-Light Photography

cylonlover writes "A team of scientists at Nanyang Technological University (NTU) in Singapore has developed a new image sensor from graphene that promises to improve the quality of images captured in low light conditions. In tests, it has proved to be 1,000 times more sensitive to light than existing complementary metal-oxide-semiconductor (CMOS) or charge-coupled device (CCD) camera sensors in addition to operating at much lower voltages, consequently using 10 times less energy."

Comments

1000 times better?

[thesupraman]

They claim 1000 times better sensitivity than CMOS, which people seem to be swallowing hook line
and sinker, however since there are plenty of current CMOS sensors with a Quantum Sensitiviy (QE)
of 60% to 80% for visible light, how exactly will the convert 1000 times more efficiently than that?
1000 times less loss would take them from 80% to 99.99%, that thats only actually 20% better...

I would imagine they are measuring at an extreme wavelength that existing CMOS sensors do not target,
hardly an advantage for the applications being discussed in the article (normal cameras).

Even quite boring consumer cameras have a QE of 20% to 40%..

Re: 1000 times better?

[Bender_]

Some people do not seem to understand the term "quantum efficiency" (QE).

The quantum efficiciency measures the fraction of photons that are actually detected by the camera.
An external quantum efficiency of 50% means that 50% of all incident photons are converted into electron-hole pairs and can be detected.
There are, however, loss mechanisms that prevent all e-h pairs to be collected. But this is not off by a factor of 1000x from the theoretical limit.

As already stated by the original poster. This figure is probebably for some other wavelengths, like far infrared, where silicon is "blind" due to its band gap.
Since humans are very blind to this wavelengths as well, the relevance in the cameras is questionable.

Re:1000 times better?

[asvravi]

First off, if we cut through the usual dismal quality of scientific reporting, what they made is a photodetector, not an image sensor. It detects single events rather than capture an image. The sensitivity of the detector is not the same as quantum efficiency. The sensitivity they mention here includes a "photogain" by virtue of the detector operating more or less as a light-controlled amplifier. It takes electrical input energy and simply amplifies it based on incident light. That can create a flow of many more electrons than incident photons. The same thing can possibly be also done by introducing a gain in the conventional image sensor electronics too, but having this photogain right inside the sensor should theoretically lead to better noise performance. So we would expect the paper to quantify the noise characteristics, but it is woefully sparse on the noise details - which leads me to suspect this is yet another "invention" that is never going to see the light of day.

Re: 1000 times better?

[thegarbz]

This figure is probebably for some other wavelengths, like far infrared, where silicon is "blind" due to its band gap.
Since humans are very blind to this wavelengths as well, the relevance in the cameras is questionable.

From TFA: "The new sensor is able to detect broad spectrum light, from the visible to mid-infrared, with great sensitivity. This will make it ideal for use in all types of cameras, including infrared cameras, traffic safety cameras, satellite imaging, and more."

Certainly doesn't sound too different to CMOS based applications, though they do mention mid-IR and most CMOS sensors drop off towards the end of the near-IR spectrum.

Re:quantum efficiency

[BronsCon]

That's 50% of visible light, as in 50% of the minimum level of light in the visible spectrum required to be seen by the naked eye. If this sensor can "see" light that is 1/500th the intensity required to be seen by the naked eye, whereas current sensors can only "see" light that is 2x the intensity required to be seen by the naked eye, then the new sensor is 1000x more sensitive. It's not rocket science; hell, it's not even physics or optical science, just plain ol' algebra.

The three orders of magnitude...

[Mr. Chow]

According to the paper, "Through this scheme, we have demonstrated a high photoresponsivity of 8.61A/W, which are about three orders of magnitude higher than those in previous reports from pure monolayer graphene photodetectors.". So it is 1000x better than previous iterations of a particular variety of detector, not the detectors we actually use.

Re:quantum efficiency

[thegarbz]

With some basic maths that's how. Double the efficiency of 50% means that half of the photons that previously weren't converted will now be converted, i.e. 75% QE. Quadruple the sensitivity and a quarter of the photons that weren't converted will now be converted, i.e. 87.5% QE

So from that if you make the sensor 1000x times more sensitive you go from a QE of 50% to a QE of 99.95%

Re:Can someone explain?

[femtobyte]

Despite the poorly written article, this sensor tech is very *insensitive* compared to what you currently have for visible light technology. It's a 1000x improvement compared to previous wide-band graphene detectors, which can sense light from the visible out to 10um mid infrared (your camera can't do that). So no, this won't help your camera photograph at higher ISOs. And current camera sensors are within spitting distance of the theoretical physical limits on low light performance: while they've improved tremendously over the past couple decades, the noisiness of low-light pictures with the best current generation sensors is close to what you'll always be stuck with --- its the result of there being a finite number of photons, with sqrt(N) counting statistics fluctuations, available for even a "perfect" camera to see.

Re:New type of "bio" imaging ?

[femtobyte]

No, this is not 1000x better than CMOS/CCD; it's 1000x better than previous graphene detectors --- which are far worse in the visible range than CMOS/CCD, but can sense out to the 10um mid-infrared band, which other sensors can't.

Re:New type of "bio" imaging ?

[femtobyte]

^^^ This. The Nature Communications article is very clear, right from the abstract, that this sensor is 1000x more sensitive than previous *graphene* sensors. *Nowhere* in the journal article is the performance compared directly against CCD/CMOS sensors, but it's trivial to tell (from the numbers given) that this sensor isn't remotely "competitive" in the visible light region. Fortunately, that's not the interesting use of the sensor --- the journal article does compare and cite advantages against other infrared sensing technologies. The researchers might have meant to say that these graphene sensors could be useful for cheap, low-power (but not high sensitivity) visible light applications --- not what the journalists have twisted this into.