Sony’s Back-Illuminated CMOS Sensor Promises Better Camcorder Performance
New sensor achieves a signal-to-noise ratio of +8 dB
Sony said it has retained the advantages of CMOS image sensors, such as low power consumption and high-speed operation, while radically realigning the fundamental pixel structure to back-illumination. The company has developed a prototype, back-illuminated CMOS image sensor (pixel size: 1.75 µm square pixels, five effective mega pixels, 60 frames/sec) with improved sensitivity and noise reduction-the key factors to enhancing image quality.
A back-illuminated structure minimizes the degradation of sensitivity to optical angle response, while also increasing the amount of light that enters each pixel due to the lack of obstacles, such as metal wiring and transistors that have been moved to the reverse of the silicon substrate.
Back-illuminated structures commonly cause problems such as noise, dark current, defective pixels and color mixture that lead to image degradation and also cause a decrease in the signal-to-noise ratio. To overcome this, Sony developed a photo-diode structure and on-chip lens optimized for back-illuminated structures that achieves a higher sensitivity of +6 dB and a lower random noise of -2 dB without light by reducing noise, dark current and defect pixels compared to the conventional front-illuminated structure.
The company did not say when camcorders using the new technology would be available.