Rohm Develops Cu-In-Ga-Se Image Sensor

Tech-On: Rohm exhibited a thin film multilayer image sensor at CEATEC Japan 2007. The major difference between Rohm's new image sensor and the existing CMOS sensors is that the former has a structure technically identical to that of a Cu-In-Ga-Se (CIGS) solar cell, instead of employing the existing Si photodiode. The CIGS photodiodes formed directly on an LSI chip.

The sensor has 100K pixels, 10um each. Its QE for visible light is said to be approximately twice of that of crystalline Si photodiode. Assuming that good Si photodiode in large pixel approaches to 60-70% QE, I wonder how Rohm doubles that.

The major remaining issue is how to miniaturize the sensor. The pixel in the latest prototype is a 10um. In the technology used for the latest development, grooves between the adjacent elements are made after the formation of CIGS layer. "We need to develop a more sophisticated technique to miniaturize the picture element blocks," Rohm said.