Thursday, December 01, 2005

Metal as Microlens in Agilent Sensors

An interesting idea is exploited by Agilent guys in their camera-phone sensor (EETAsia).

"According to Agilent product line manager Sanjeev Chandrashekher, the story began in a series of research experiments. Agilent researchers had observed that in 1Mpixel sensors small enough to be embedded in a handset camera module, the individual pixels were so small that the optical aperture above each pixel was approaching an untenable threshold. Designers throw up their hands when the aperture gets below about 25m.
The research team created a series of pixel architectures based on a trapezoidal well shape in which they moved the metal lines around to measure the effect of the interconnect metal lines obscuring the edges of the aperture. To their surprise, they found that when the metal lines covered up a certain portion of the edges of the well, the charge generation in the well increased. Further work determined that the metal lines manipulated the electric field in the optical path, i.e. they behaved as a tertiary lens, gathering in light that would have fallen outside the well and focusing it toward the phototransistor. The researchers learned that the effect could be optimized to improve the sensitivity of the CMOS sensor pixel.
That unexpected result was combined with engineering projects that were exploring new geometries for the dopant well and the array layout. Those resulted in lower dark current, lower temporal noise and the ability to flush the charge more quickly from the well, thus reducing the image lag effects that harm image quality during high-repetition-rate image capture, such as in video applications."

I eager to see how this new Agilent sensor performs in the real world.

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