Wednesday, March 10, 2021

Image Sensor Technologies at CEA-Leti

i-Micronews publishes an interview with Agnès Arnaud, head of the Optics and Photonics Department at CEA-Leti "CEA-Leti’s involvement in the CMOS Image Sensor ecosystem." Few quotes:

"CEA-Leti has been involved in CIS development since the mid-1990s. In the early 2000s, CEA-Leti had patents on CIS, including Analog-to-Digital Converters (ADCs), demoisaicing architectures and compression schemes. Some of these technologies have been transferred to the imaging division of STMicroelectronics. STMicroelectronics and CEA-Leti have cooperated for several years on technologies, leading to a boom in imaging applications for mobile telephones. CEA-Leti provided STMicroelectronics with a Through-Silicon-Via (TSV) technology block and processes to make thinner imagers, boost photon collection efficiency and develop innovative architectures. In 2012, a first scientific publication on a Global Shutter Pixel triggered a long-term collaboration on pixel technologies with the imaging division of STMicroelectronics. The cooperation is still on going on advanced concepts, from technologies like dense 3D interconnect announced at IEDM in 2019 to architectures like autonomous imagers announced at VLSI 2020.

Leti has been developing bolometric imagers since 1992 and transferred the technology to start-up Ulis in 2002. Ulis, now Lynred, is a world leading bolometer manufacturer.

You must keep in mind that many innovations require 15 to 20 years before one can find them in a commercial product. Our PhD students are currently working on innovations which may show up in a product in 2040.

Detection in the short wave IR (SWIR) band is very attractive for various applications, such as military, security, telecommunications and medical diagnostics. The SWIR light presents many advantages compared to visible light. It is invisible to the human eye and is less sensitive to extreme weather conditions such as fog and dust. The use of  germanium (Ge) as an active layer in the PiN photodiodes presents many advantages such as its good absorption and its compatibility with the mass-production processes used in the silicon (Si) microelectronics industry. At CEA-Leti, Ge/Si vertical PiN devices have been developed, fabricated, and characterized at room temperature with promising performances such as a low dark current density and good external responsivities. The segmentation of the NIR/SWIR market will ultimately depend on the evolution of InGaAs costs and the improvement of Ge or organic performance. Ge and organic photodiodes are compatible with 300mm diameter silicon wafer production lines. Ge and organic photodiodes are low-cost solutions. Compliance with IC manufacturing make them attractive candidates for consumer products. Yet their intrinsic performance, especially in terms of dark current, is still below InGaAs detectors. And as you know, CEA-Leti is also involved in InGaAs developments. It is CEA-Leti’s mission to investigate the ultimate potential of Ge or organic detectors to offer a reasoned set of technologies.

At CES 2019, CEA-Leti demonstrated a new bioinspired technology for visible image sensors, IR sensors and microdisplays that replicates the curve of the human retina.

This curved image sensor technology breakthrough, called Pixcurve, has several advantages compared to traditional flat image sensors. The form factor of a digital camera module can be reduced by 60% thanks to the reduction of the number of lens elements.

The overall length of the optical system is also shorter. Curved image sensors reduce the cost of the camera module. A lot of markets could be targeted by Pixcurve approach, such as high-end photography, automotive, consumers application or medical."

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