Sony develops new back-illuminated CMOS image sensor

Jun 11, 2008
Sony develops new back-illuminated CMOS image sensor
Cross sectional view of back-illuminated CMOS image sensor pixels.

Sony Corporation today announced the development of a back-illuminated CMOS image sensor (pixel size: 1.75µm square pixels, five effective mega pixels, 60 frames/s) with significantly enhanced imaging characteristics, including nearly twofold sensitivity and low noise. This improved performance has been achieved by illuminating the backside of the silicon substrate, in contrast to conventional CMOS image sensors based on front-illumination technology.

The newly developed CMOS image sensor achieves a signal-to-noise ratio of +8dB(+6dB sensitivity, -2dB noise) in comparison to existing Sony CMOS image sensors of the same pixel size. Sony will apply this back-illuminated CMOS technology in consumer digital video camcorders and digital still cameras to deliver an even higher quality image experience.

Conventionally, consumer digital video camcorders and digital still cameras have been required to combine high resolution capable of capturing every detail of the subject matter, and miniaturization oriented to portability. In order to meet these needs, image sensor development has focused on miniaturizing pixel size, while maintaining imaging characteristics. However, in addition to these ongoing requirements, in recent years demand for improved levels of minimum subject illuminance and rapid image capture has also increased. This has led to the requirement of image sensors with improved signal-to-noise ratio and other features capable of realizing improved overall picture quality.

Sony has retained the advantages of CMOS image sensors such as low power consumption and high-speed operation, while radically realigning their fundamental pixel structure from front-illumination to back-illumination to successfully develop a prototype, back-illuminated CMOS image sensor (pixel size: 1.75µm square pixels, five effective mega pixels, 60 frames/s) with improved sensitivity and noise reduction - the key factors to enhancing image quality.

With a conventional front-illumination structure, the metal wiring and transistors on the surface of the silicon substrate that form the sensor's light-sensitive area (photo-diode) impede photon gathering carried out by the on-chip lens, and this has also been an important issue in the miniaturization of pixels and widening optical angle response.

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.

Shoot with low illumination (30 lux)

However, compared to conventional front-illuminated structures, back-illuminated structures commonly causes 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 has newly developed a unique photo-diode structure and on-chip lens optimized for back-illuminated structures, that achieves a higher sensitivity of +6dB and a lower random noise of -2dB without light by reducing noise, dark current and defect pixels compared to the conventional front-illuminated structure. Additionally, Sony's advanced technologies such as high-precision alignment have addressed any color mixture problems.

Sony has continued to advance the speed and picture quality of its CMOS image sensors, such as "Exmor", with its unique "Column-Parallel A/D Conversion Technique" and dual noise reduction, in addition to the imaging expertise it has accumulated throughout its history of CCD development. With the development of this new back-illuminated structure, Sony has realized a CMOS image sensor with even higher sensitivity and lower noise. Furthermore, the back-illuminated structure also expands device potential in areas such as speed and dynamic range by enabling multiple metal wiring layers and greater flexibility in the transistor structure. Going forward, Sony will continue its development of image sensors that combine ease-of-use, advanced image quality and cutting-edge pixel miniaturization.

Source: Sony

Explore further: A bump circuit with flexible tuning ability that uses 500 times less power

add to favorites email to friend print save as pdf

Related Stories

UMSL scholar examines evolution of learning

1 hour ago

Why do monkeys learn to be afraid of snakes and not flowers? Is this knowledge the result of evolution by natural selection? Did the monkeys that couldn't learn that association quickly die and not reproduce?

Study details shortage of replication in education research

1 hour ago

Although replicating important findings is essential for helping education research improve its usefulness to policymakers and practitioners, less than one percent of the articles published in the top education research journals ...

Samsung introduces Galaxy Alpha

2 hours ago

Samsung Electronics unveiled its new design approach with the Galaxy Alpha. The latest addition to Samsung's Galaxy smartphone line, the Galaxy Alpha features a sophisticated design in a carefully constructed ...

People fake to look authentic on social media

2 hours ago

Presenting an authentic image on social network sites (SNSs) includes an element of fakery according to a new study by researchers at Aalto University. During the study, researchers discovered that being authentic is very ...

Recommended for you

Ticketfly buying WillCall for on-premise data

16 minutes ago

Ticketfly Inc., a San Francisco-based technology company among several posing a challenge to Ticketmaster, is acquiring WillCall Inc., a crosstown rival that turns your smartphone into a mobile wallet at live events.

Voice, image give clues in hunt for Foley's killer

33 minutes ago

Police and intelligence services are using image analysis and voice-recognition software, studying social media postings and seeking human tips as they scramble to identify the militant recorded on a video ...

Smartphone-loss anxiety disorder

1 hour ago

The smart phone has changed our behavior, sometimes for the better as we are now able to connect and engage with many more people than ever before, sometimes for the worse in that we may have become over-reliant on the connectivity ...

For secure software: X-rays instead of passport control

1 hour ago

Trust is good, control is better. This also applies to the security of computer programs. Instead of trusting "identification documents" in the form of certificates, JOANA, the new software analysis tool, examines the source ...

User comments : 0