Thursday, January 31, 2008

Weekly Patent Review

ST Micro continues to churn out backside illuminated sensor applications. US20080017893 application solves the diffusion crosstalk problem. The solution is a retrograde doping of the substrate to form an electric field in vertical direction, so photoelectrons in the substrate are pulled toward the photodiode directly above them (or below them in backside illuminated pixels). The application shows that ST bumpes into the same problems like all the industry and uses the same approaches trying to solve them. I'm not sure this application will be granted, but at least it reveals that ST has a good team devoted to backside illumination.

Another ST's application US20080017946 talks about reducing thermal gradients in back-lit sensors. The proposed solution is to use through-silicon vias to conduct heat to the bottom side of the sensor and then use thermaly conductive layer to spread heat equally over the sensor area. It's a popular solution used by many packaging designers, I doubt this patent would be ever granted. Well, may be in combination with backside illuminated sensor they can cut something.

Application US20080018662 filed by Avago, now it probably belongs to Micron. To reduce crosstalk between pixels it proposes to put a shading elements in between them. That's it. One more thing, the shading is symmetrical to avoid artifacts. The application was filed in mid-2006, published just now. What I can say about it? First, I do not believe it will be granted, but if it will, I do not believe anybody can be sued for its infringement.

Application US20080018762 comes from Micron and talks about reset transistor charge injection suppression. How it works? Very simple: when the reset transistor is turned off, its gate goes to some sufficiently low voltage, which is higher than the prior art ground. So, the charge injection becomes smaller. Many companies use similar solutions for various reasons, I don't think Micron invented anything here.

Samsung US20080018765 application talks about hexagonal pixels with 2-way sharing. Very interesting read, just to learn what wild ideas these guys are trying! It gives example pixels layouts and how they plan to squeeze all the transistors in between. I'm unable to say anything about its novelty, buy I enjoyed reading this application. I don't think this is practical though.

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