[ISSCC] Samsung's CMOS Sensor Takes Range, RGB Images at Same Time (page 2)

Feb 25, 2012
Tomonori Shindo, Nikkei Electronics

The Z pixel measures 2.25 x 9.0μm and has an area that is four times larger than that of a red, green or blue pixel. The Z pixel is adjacent to RGB pixels and located below them.

Two column CDS circuits were formed on the upper and lower sides of the pixel area for the RGB pixels and the Z pixel, respectively. A part of the RGB pixels' information that is missing due to the existence of the Z pixel is interpolated by an image processing algorithm.

The operating frequency of the ToF is 20MHz. The integral time of the Z pixel is 10ms per one phase (out of four phases). The margin of error in range measurement is 1m or less for a distance of 1-5m when the output of the LED for the ToF is 0.92W. And it is 1% or less in all the measurable areas when the output of the LED is 1.35W.

Z pixel located below RGB pixels

To develop the new CMOS sensor, Samsung made some improvements so that the effective size of the Z pixel becomes three times as large as its actual size. Specifically, a potential barrier was formed in the layer below the RGB pixels so that photoelectrons generated by the near-infrared light for the ToF do not go to the RGB pixels.

The PD of the Z pixel was formed even in an area deeper than the potential barrier. Also, an epitaxial layer is used to increase quantum efficiency.

The sensor was manufactured by using 0.13μm CMOS image sensor technology. This time, Samsung used a process for FSI. But if BSI (back-side illuminated) technology is applied, it is possible to double the quantum efficiency, the company said. It is because the cross-talk to the RGB pixels by the near-infrared light for the ToF can be more easily prevented.