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Research Alert: Dec. 3, 2013

Imec integrates CCD and CMOS technology to improve performance of CMOS imagers

Imec, the Belgian nanoelectronics research center, will present at this week’s ‘CMOS Image Sensors for High Performance Applications’ workshop in Toulouse (France) a prototype of a high-performance, time-delay-integration (TDI) image sensor. The image sensor is based on imec’s proprietary embedded charge-coupled device (CCD) in CMOS technology. Imec developed and fabricated the sensor for the French Space Agency, CNES, which plans to utilize the technology for space-based earth observation.

The prototype image sensor combines a light-sensitive, CCD-based TDI pixel array with peripheral CMOS readout electronics. By integrating CCD with CMOS technology, imec combined the best of both worlds. The CCD pixel structure delivers low-noise TDI performance in the charge domain, while CMOS technology enables low-power, on-chip integration of fast and complex circuitry readouts.

A TDI imager is a linear device that utilizes a clever synchronization of the linear motion of the scene with multiple samplings of the same image, thereby increasing the signal to noise ratio. CCDs fit extremely well with the TDI application since they operate in the charge domain, enabling the movement of charges without creating excess noise. By combining the TDI pixels array with CMOS readout circuitry on the same die, imec produced a camera-on-a-chip or system-on-a-chip (SOC) imager, which reduces the overall system complexity and cost. The CMOS technology enables on-chip readout electronics, such as clock drivers and analog-to-digital convertors (ADCs), operating at higher speeds and lower power consumption not possible with traditional CCD technology.

The prototypes were fabricated using imec’s 130nm process with an additional CCD process module. An excellent charge transfer efficiency of 99.9987 % has been measured ensuring almost lossless transport of charges in the TDI array, and guaranteeing high image quality. Imec’s specialty imaging platform combines custom design (i.e., specialized pixels, high-performance readout circuits and chip architectures) with optimized silicon processing, such as dedicated implants and backside thinning, to achieve high-end specialized imagers.

New thermoelectronic generator

Through a process known as thermionic conversion, heat energy — such as light from the sun or heat from burned fossil fuels — can be converted into electricity with very high efficiency. Because of its promise, researchers have been trying for more than half a century to develop a practical thermionic generator, with little luck. That luck may soon change, thanks to a new design — dubbed a thermoelectronic generator — described in AIP Publishing’s Journal of Renewable and Sustainable Energy (JRSE).

Thermionic generators use the temperature difference between a hot and a cold metallic plate to create electricity. “Electrons are evaporated or kicked out by light from the hot plate, then driven to the cold plate, where they condense,” explained experimental solid-state physicist Jochen Mannhart of the Max Planck Institute for Solid State Research in Stuttgart, Germany, the lead author of the JRSE paper. The resulting charge difference between the two plates yields a voltage that, in turn, drives an electric current, “without moving mechanical parts,” he said.

Nanoscale coating improves stability and efficiency of devices for renewable fuel generation

Splitting water into its components, two parts hydrogen and one part oxygen, is an important first step in achieving carbon-neutral fuels to power our transportation infrastructure – including automobiles and planes.

Now, North Carolina State University researchers and colleagues from the University of North Carolina at Chapel Hill have shown that a specialized coating technique can make certain water-splitting devices more stable and more efficient.

Atomic layer deposition, or “ALD,” coats three-dimensional structures with a precise, ultra-thin layer of material. “An ALD coating is sort of like the chocolate glaze on the outside of a Klondike bar – just much, much thinner,” explains Dr. Mark Losego, research assistant professor of chemical and biomolecular engineering at NC State and a co-author on the work. “In this case, the layers are less than one nanometer thick – or almost a million times thinner than a human hair.”

A graphic representation of how atomic layer deposition can aid renewable hydrogen fuel generation. Two papers published in Proceedings of the National Academy of Sciences show how atomic layer deposition can make water-splitting devices more stable and more efficient.

Although extremely thin, these coatings improve the attachment and performance of surface-bound molecular catalysts used for water-splitting reactions in hydrogen-fuel-producing devices.

In the first paper, “Solar water splitting in a molecular photoelectrochemical cell,” the researchers used ALD coatings on nanostructured water-splitting cells to improve the efficiency of electrical current flow from the molecular catalyst to the device. The findings significantly improved the hydrogen generating capacity of these molecular-based solar water-splitting cells.

In the second paper, “Crossing the divide between homogeneous and heterogeneous catalysis in water oxidation,” the researchers used ALD to “glue” molecular catalysts to the surface of water-splitting electrodes in order to make them more impervious to detachment in non-acidic water solutions. This improved stability at high pH enabled a new chemical pathway to water splitting that is one million times faster than the route that had been previously identified in acidic, or low pH, environments. These findings could have implications in stabilizing a number of other molecular catalysts for other renewable energy pathways, including the conversion of carbon dioxide to hydrocarbon fuels.

“In these reports, we’ve shown that nanoscale coatings applied by ALD can serve multiple purposes in water-splitting technology, including increasing hydrogen production efficiency and extending device lifetimes,” Losego said. “In the future, we would like to build devices that integrate both of these advantages and move us toward other fuels of interest, including methanol production.”

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