Imec’s thin-film pinned photodiode boosts IR-sensing

Imec has successfully integrated a pinned photodiode structure in thin-film image sensors with comparable noise performance to a standard silicon pinned photodiode pixel. The device enables the superior absorption qualities of thin-film imagers – beyond one micrometer wavelength – to be exploited.

Detecting wavelengths beyond visible light, for instance infrared light, offers clear advantages. Applications include cameras in autonomous vehicles to ‘see’ through smoke or fog and cameras to unlock your smartphone via face recognition. Whilst visible light can be detected via silicon-based imagers, other semiconductors are necessary for longer wavelengths, such as short-wave infrared (SWIR).

Use of III-V materials can overcome this detection limitation. However, manufacturing these absorbers is expensive, limiting their use. In contrast, sensors using thin-film absorbers (such as quantum dots) have recently emerged as a promising alternative. They have superior absorption characteristics and potential for integration with conventional CMOS readout circuits. Nonetheless, such infrared sensors have an inferior noise performance, which leads to poorer image quality.