Perhaps the key improvements in semiconductor fabrication that have made possible this giant imaging chip are the quality of materials used and the cleanliness of fabrication facilities. If the “clean” rooms aren’t sufficiently clean, dust and other particulate matter can contaminate the chemical layers used to build the CCD, says Barry Burke, a senior staff member at MIT’s Lincoln Laboratory. Not only can defects create defunct pixels – ones that are permanently white or black, he says, they can also create electrical shorts in the circuitry, rendering portions, if not all of the device, defective. “To get a perfect device of that size is a major challenge,” he says. Hence, advances in air-filtering technology in clean rooms have enabled larger defect-free devices, Burke says.
Design considerations are also important in making such a large chip, says Bredthauer. The pixels of a CCD collect photons that are instantly converted to an electrical charge proportional to the intensity of light. In order for the charge to actually produce an image, it is passed through the chip to circuitry lying on the periphery of the device, where it is amplified and converted into a voltage that’s used to record the final image. A large CCD runs the risk of producing “traffic jams,” where the electric charge can’t quickly and effectively make it to the output circuitry. To solve this problem, Bredthauer designed the output ports to simultaneously extract charge from different regions of the chip, thereby keeping the charge flowing smoothly and allowing for quick image rendering.
Currently, these mega-chips are priced at a breath-taking $80,000-100,000 each, and are custom manufactured for each specific (mostly astronomical) application. The steep cost is one reason such CCDs are not likely to show up in consumer products soon. And, for the average image-taker, current resolutions in the tens of megapixels is sufficient. “From the consumer’s point of view, it seems like there’s almost enough pixels to do what people want to do – to look at pictures and share them,” says Michael Cohen, senior researcher in Microsoft’s interactive visual media group and graphics group.
However, the chance to take extremely high-quality digital pictures, which can produce three-foot by three-foot posters without losing quality, is alluring to photography buffs outside scientific and surveillance fields. Since the announcement of their record-breaking chip, Bredthauer says the photography blogging community has been writing about using the chips in professional cameras that traditionally use film that’s four inches by five inches. He’s received inquiries about their 100-megapixel chip from private parties. “That’s high-end photography,” he says.