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Quantum films : Next tech for digicams

Posted: 25 Mar 2010     Print Version  Bookmark and Share

Keywords:quantum film  CMOS  image sensor  silicon image chip 

Will CMOS sensors be elbowed out by quantum films?

Just as photographic film was mostly displaced by silicon image chips, quantum films are claimed to replace the conventional CMOS image sensors in digital cameras. Made from materials similar to conventional film—a polymer with embedded particles—instead of silver grains like photographic film, the embedded particles are quantum dots. Quantum films can image scenes with more pixel resolution offering 4x better sensitivity for ultra high-resolution sensors that are cheaper to manufacture, according to their inventors, InVisage Inc.

"Many innovations are said to be revolutionary, but are really incremental changes. InVisage's quantum film, on the other hand, really is revolutionary," said Tom Hausken, director of photonics and compound semiconductors at Strategies Unlimited. "Quantum dots have been a solution looking for a problem for several years, and InVisage has found a very significant problem they can solve."

According to Morry Marshall, VP of strategic technologies at Semico Research Corp., InVisage could have the next-generation image sensor. "It gathers more light so you can either make a smaller image sensor for a less expensive cell phone camera, or you make a higher resolution sensor for high-end digital cameras," Marshall said. "It's a huge step forward and the market is also huge, so they will also need to overcome the problems facing any small company when trying to penetrate a large market."

The new semiconducting material was invented by University of Toronto professor Ted Sargent, who is now chief technology officer at InVisage. Sargent perfected a method of suspending lead-sulphide nanoparticles in a polymer matrix to form a new class of semiconducting polymer that InVisage has spent the last three years integrating into a standard CMOS process. Now it can paint quantum film atop a low-cost wafer that has the electrode array for super-dense high-pixel-count images, but without any of the expensive CMOS photo detectors that make up the bulk of conventional digital camera sensors.

"Our quantum film replaces the silicon used for image capture, but what we have really created here is a new semiconductor material," said Jess Lee, InVisage president and CEO. "Our quantum film even looks like photographic film—an opaque black material that we deposit right on the top layer of our image chips."

Unlike tradition semiconductors, which have a fixed band gap, the band gap of InVisage's quantum film can be adjusted by changing the size of the embedded quantum dots. The film can also be painted-on at room temperature, obviating the need for expensive high-temperature fabrication techniques required by conventional sensors.

"We can paint our quantum-dot film onto any surface," said Lee. "Right now we are painting them on silicon wafers for our first product—an ultra low cost image sensor that obsoletes CMOS sensors."

Traditional CMOS sensors require that light filter down past several microns of metallisation to reach the photo detectors on a silicon wafer, but InVisage's quantum film is on the top layer for 100 per cent exposure to incident light.

"Traditional CMOS sensors require light to travel down through four or five microns of metal before reaching the photo detector, whereas our quantum film captures all the incident light in a layer just 500 nanometres thick," said Michael Hepp, director of marketing at InVisage.

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