Sunday, March 30, 2008

Sharp 1.75um Pixel Sensor Reverse Engineering

Chipworks published a reverse engineering report of Sharp 1.75um pixel sensor. The 3.2MP C13P22 sensor is said to have "evidence to suggest that the device is fabricated by Dongbu".

The part uses 4 levels of Al in the logic areas, and 3 levels of Al in the pixel array. Based on a single preliminary cross section, it was manufactured using a 0.18 µm process. This makes the sensor quite unique, as most of other manufacturers use 0.11-0.13um process for that pixel size. The pixel layout at poly and diffusion level is below:

Poly to poly spacing looks much smaller than a standard 0.18um process would allow. Probably Sharp pushed DRs to make this.
While making 1.75um pixel in 0.18um process is quite an achievement, the fill factor at the diffusion level looks a bit low, less than 20-25% to my eye. Also, the difference between two green colors in Bayer pattern is probably high and needs some ISP correction.

The sensor was found in the Aquos SH905iTV phone from Sharp, available through NTT DoCoMo in Japan.

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