Just as photographic film was mostly replaced by silicon image chips, now the new “Quantum Flm” threats to replace the conventional 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 film can image scenes with more pixel resolution, according to their inventors, InVisage Inc., offering four-times better sensitivity for ultra-high resolution sensors that are cheaper to manufacture.
“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 (Mountain View, Calif.) “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, vice president of strategic technologies at Semico Research Corp. (Phoenix), 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.”
Essentially, the technology works by adding a new finely tuned light-sensitive layer on top of the silicon chip, Lee said. That layer is more efficient at converting incoming light into electrical signals, and the light isn’t partially blocked by a microprocessor’s metallic layers, either.
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-sulfide 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 photodetectors 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 chip. With a tiny smartphone 3-megapixel sensor, we could make that a 12-megapixel sensor, or we could quadruple its sensitivity and ISO. That’s the net benefit here.”
The company also has plans to move beyond today’s era of separate pixels for detecting red, blue, and green light. That approach, called the Bayer pattern, divides the grid of pixels into a checkerboard pattern, and through a process called demosaicing, the camera has to make its best guess to fill in the missing data so each pixel has values for red, green, and blue.
InVisage believes it can stack three layers of QuantumFilm–blue on top, then green, then red at the bottom–to capture all three values of light at each pixel location. Another possibility is to pattern its quantum dots specifically into a color array. Either approach gets rid of the color filter array atop today’s image sensors, letting more light through to the sensor.