Quantum bits: This camera sensor chip contains a layer of quantum dots that absorbs light before it reaches the silicon.
InVisage
A layer of light-absorbing particles boosts digital image quality.
Cell phone cameras are famous for taking grainy, low-resolution pictures. Part of the problem is the lens, which is usually cheaply made and has limited resolution and ability to collect light. But another problem is the light sensor: a silicon chip containing photodetectors. When shrunk to fit in a phone, these chips are limited in the amount of light they can capture.
Now, InVisage, a Menlo Park, CA-based startup, is demonstrating a way to improve the quality of pictures, at least on the sensor side, without adding size, significant complexity, or cost. At the DEMO conference in Palm Springs, CA, today, the company's executives announced a new technology called QuantumFilm that lets small camera sensors, like those in cell phones, capture more light than ever before. QuantumFilm is simply a layer of quantum dots--tiny crystals that efficiently absorb light and emit either photons or electrons--in a top layer of the sensor. The electrons emitted by QuantumFilm are collected and sorted the chip's circuitry.
The result is a sensor that collects twice the light of the standard chip, converts it to electricity twice as efficiently, and is just as cheap to make, says Ted Sargent, chief technology officer of InVisage and professor of electrical and computer engineering and the University of Toronto, where the early research for QuantumFilm began. "Silicon image sensors have a really severe problem in that they just throw away photons left right and center," says Sargent. Quantum dots, he says, provide a "fundamental solution to the problem."
In today's digital cameras, a silicon sensor does double duty. It serves as a photodetector that absorbs incoming light and converts it to an electrical signal. But it also acts as the foundation for the electronics that store the signal from the photodetector and route it away from the chip, where it is processed by separate electronics. The problem is that the photodetector part of the silicon often sits below layers of transistors, metal wires, and a color filter. Because of these obstructions, only about half the original light reaches the photodetector.
There are some commercial technologies that try to tackle the problem of the obstructed photodetector. For instance, manufacturers have added microlenses that focus the light into a tiny space. But even with a bigger photodetector area, silicon still isn't the best light collector: it registers less than half of the photons that hit it.
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Guest (aarontco)
increased resolution for high end cameras?
Shouldn't this improve the resolution for high end, silicon based cameras? Normally resolution is improved by created more, smaller light receptors. But doubling the sensitivity of the receptor to detect light would also seem to have an effect upon potential resolution or an image that otherwise might be too dim to register on normal silicon. Is there a term other than resolution that is more appropriate?
Re: increased resolution for high end cameras?
I am not sure about resolution, but an increase in color bit depth sure seems possible. There are already sensors that act as both CCD and photomultiplier, but they are for high end scientific applications, and not very flexible. It seems that this might be able to get beyond the bit depth issues that have made scientific imaging with standard digital cameras less than ideal.
Re: increased resolution for high end cameras? - Yes
Designing a QD with a photo-multiplier stack is possible. This would help in low-photon count scenarios.
Resolution is an interesting question with respect to 3D video systems where mass and dynamic oscillation of the camera platform can become critical. The larger the CCD - the higher the resolution - but also the larger the risk of visible alignment errors between the two imaging detectors and the more cooling required to operate the camera.
Currently, high-end digital cinema projection systems are at a 4k pixel-wide 16x9 frame size. On the other hand, 3.5k pixel-wide CCD detectors are standard in studio production cameras - which deliver a 2k pixel-wide image - after over-sampling.
Compared to film, the 3.5k detectors can cause detectable digital artifacts on 4k projection system displaying on a 60-foot diagonal screen.
And, Japan is already testing 10k projection systems.
In 3D, with two detectors requiring critical alignment, there is a chance that the artifacting will disrupt pin-striped textures with Moire patterns. This can be very noticeable near the frame edges of digital camera shot productions.
Because the QD detectors are 3x times more efficient at light collection, their actual detector area sizes can be smaller and more compact than traditional CCD. This then reduces the weight and area error risk of lens systems. QD detectors have the potential of reducing detector alignment errors in 3D digital cinema production, while further reducing the mass and cooling requirements of current day production 3D digital cinema cameras.
Consumer 3D digital video cameras could be deliverable with QD technology at a cost and quality level not achievable with CCD detectors. Then, we can truly say that the Star Trek "tricorder" has arrived.
absorption is great, but charge extraction?
What is the quantum efficiency of this quantum dot film - i.e. how many of the almost 100% absorbed photons are extracted as current?
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Edenseeker
5 Comments
PV cells
Is there any applicability to PV cells?
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rboblee
8 Comments
Re: PV cells - Certainement!
Quantum dots could be used for photo-voltaics - certainly. In manufacture, it doesn't take much to align a quantum dot, so a slurry of QD's could be applied, and then the individual particles could be aligned and evaporation fixed to contact sites by designing "electrostatic wells". QD's that don't find sites would be washed off with a post-fix pass of the carrier liquid and then recycled.
An appropriately designed metafabric - say with woven carbon nanotubes - could efficiently carry the photo-voltaic current to distribution terminals.
An interesting thought experiment is to consider a biological system providing the conductor matrix: Imagine a hair dye system consisting of a mix of quantum dots as photo-voltaic cells for power and light-emitting diodes for color, because human hair fiber is an interesting insulator and current conductor. The color displayed by a QD could be an RGB or CYMK mix and rendered as a response to dynamic "message-passing" through the QD matrix deposited on a human hair's collagen fibers. What's really interesting is that it could be a dynamic multi-color display - which could be coordinated by cellphones and WiFi networks - for really large advertising banners at, say, football and soccer games. And that would be an opportunity Google would love to trade for advertising sales.
Integrated to a mood display cellphone app, or through integration with normal skin potentials, this could help mediate social situations more effectively by codifying social interactions with dynamic color displays driven by neural activity.
Then again, there is that Ben Franklin uncontrolled discharge problem with electrostatic hairdos. I guess that's where the voltage regulating QD's come in to enable peer-to-peer WiFi power distribution.
A rock concert's electrified audience will then actually be quantifiable in produced kilowatts.
In any case, photo-voltaic QDs are in the realm of possibility.
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