A new sensor technology promises to make cellphone cameras good enough to use for wedding photos.
InVisage Technologies, a Menlo Park, California, company, has developed an image sensor using quantum dots instead of silicon. The company claims its technology increases sensor performance by more than four times.
“We have all heard ‘Gee, I wish the camera on my iPhone was better,’” says InVisage’s President and CEO Jess Lee. “But the heart of the problem is in the heart of the camera, which is the sensor.”
Most cameras today used either a CCD (charged-couple device) sensor or a CMOS (complementary metal-oxide-semiconductor)-based sensor. The silicon in current image sensors has a light-absorbing efficiency of only about 50 percent, says Lee.
Reducing efficiency still further are the layers of copper or aluminum circuitry laid on top of the silicon. The metal blocks the light, so only a fraction of a sensor’s silicon is exposed to light.
Replacing silicon with quantum dots could change all that. A quantum dot is a nanocrystal made of a special class of semiconductors. It allows manufacturers to have a very high degree of control over its conductive properties, and is about 90 percent efficient at absorbing light, according to Lee.
The quantum dots are usually suspended in fluid. InVisage takes a vial of these and spins it onto a layer of silicon, then adds the required metal circuitry to create a new type of sensor that it is calling QuantumFilm.
In addition to the increased sensitivity, InVisage’s technology allows the metal circuits to be placed underneath the quantum film, where they don’t block the light.
“This is entirely different from the type of image sensors that we have right now,” says Tom Hausken, director with market research firm Strategies Unlimited. “Usually you see incremental improvements in sensor design, but these guys have made a significant change in the process.”
Quantum dots can be made from silicon, tellurides or sulphides. InVisage won’t reveal exactly which material it is using.
As opposed to silicon’s indirect band gap, quantum dots have a direct band gap. Lee says Invisage can tune the Dots’ band gap much more efficiently than silicon so it is more sensitive to visible light, ultraviolet and even infrared waves.
In the last few years, manufacturers have been touting megapixels as the measure of a camera’s prowess. But the true measure of picture quality is not as much in the megapixels but in the size of the sensor used in the device.
To capture the light, imaging sensors need to have as much area as possible. Powerful DSLR cameras have an imaging sensor that’s about a third of the size of a business card, while camera phones sport sensors that are only about a quarter inch wide (see top photo). Smaller sensors mean less light sensitivity for each pixel on the sensor, and that translates into lower-quality images.
Quantum dot-based sensors won’t be more expensive than traditional CMOS-based sensors, promises Lee. InVisage says it will have samples ready for phone manufacturers by the end of the year and the sensors could be in phones by mid next-year.
Though quantum dots are commercially produced by other manufacturers, they have never been used on image sensors before, says Hausken.
“Mostly people have looked to use it in displays, solar cells and as identification markers,” he says. “So we will have to see how effective and reliable it is as a sensor.”
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Photo: CCD senor (Divine Harvester/Flickr)
Photo: Jonathan Snyder / Wired.com
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