Image Sensors on ISSCC 2008

ISSCC 2008 published an advance program. It contains quite a lot image sensor related stuff.

First, there is Imager Design Forum, almost entirely devoted to high dynamic range solutions.

Image sensors technology session has 10 papers. Probably the most interesting among them is one written by Keith Fife:

A 3MPixel Multi-Aperture Image Sensor with 0.7μm Pixels in 0.11μm CMOS

K. Fife, A. El Gamal, H-S. Wong
Stanford University, Stanford, CA

A multi-aperture imager sensor is designed to reduce lens requirements, produce 3D maps and improve pixel-defect tolerance. It comprises a 166×76 array of 16×16 0.7μm full-frame transfer CCD sub-arrays, a CMOS readout circuit and per-column 10b ADCs fabricated in a 0.11μm CMOS process. Snap-shot image acquisition with CDS is performed at up to 15fps. The array has 0.15V/lx·s sensitivity, 3500e- full-well capacity, 5e- read noise, 25e-/s dark signal, 57dB DR and 35dB peak SNR.

The most surprising one comes from Toshiba:

A White-RGB CFA-Patterned CMOS Image Sensor with Wide Dynamic Range

E. Yoshitaka
Toshiba, Yokohama, Japan

A 2Mpixel CIS for mobile imaging applications has a pixel pitch of 2.2μm and is fabricated in a 0.13μm CMOS technology. The sensor uses a white-RGB color filter array instead of the regular Bayer pattern to improve the low-light SNR by about 3dB. The array also achieves a wide dynamic range by using charge skimming and multiple acquisitions. The dynamic range can be expanded by 8 while maintaining the improved SNR.

I bet nobody expected that Toshiba would follow Kodak path in exploiting the modified Bayer pattern with white pixels. In the meantime Kodak presents a hole-based photodiode:

Low-Crosstalk and Low-Dark-Current CMOS Image-Sensor Technology Using a Hole-Based Detector

E. Stevens(1), H. Komori(2), H. Doan(1), H. Fujita(1), J. Kyan(1), C. Parks(1), G. Shi(1), J. Wu(1)
(1) Eastman Kodak, Rochester, NY, (2) Eastman Kodak, Yokohama, Japan

A CIS with a hole-based pinned photodiode is presented. The detector reduces crosstalk by 3× and dark current up to 5× compared with an equivalent electron-based pinned photodiode detector. This technology is capable of full-well capacities of 60kh, 11kh and 4kh for 4.3μm, 1.75μm and 1.4μm pixels, respectively. A red-into-green pixel crosstalk of 7% is achieved at 650nm for a 4.3μm pixel, and the measured dark-current density is 25pA/cm2 at 60°C.

Another noteworthy paper comes from Matsushita on high DR sensor:

A 140dB-Dynamic-Range MOS Image Sensor with In-Pixel Multiple-Exposure Synthesis

T. Yamada, S. Kasuga, T. Murata, Y. Kato
Matsushita Electric Industrial, Takatsuki, Japan

A wide dynamic range 177×144pixel CMOS image sensor that can simultaneously capture both dark and bright objects in one synthesized frame has an analog accumulator within each 8μm pixel to synthesize a wide dynamic range image from multiple exposures. The sensor is capable of acquiring a 140dB dynamic range image at 15fps without external frame buffers.

Another hot topic is random telegraph noise and ways to reduce it:

A CMOS Image Sensor with a Buried-Channel Source Follower

X. Wang(1), M. Snoeij(1,2), P. Rao(1), A. Mierop(3), A. Theuwissen(1,4)
(1) Delft University of Technology, Delft, Netherlands, (2) Texas Instruments, Erlangen, Germany, (3) DALSA Semiconductor, Eindhoven, Netherlands, (4) Harvest Imaging, Bree, Belgium

A CIS fabricated in a 0.18μm process with a 4T pinned-photodiode pixel and a buried channel source follower (BSF) is presented. Measurements confirm that the BSF reduces the dark random noise by more than 50% and improves the output swing by almost 100% when compared with a surface-channel NMOS source follower. Moreover, the BSF reduces the variance of the dark random noise distribution by minimizing the number of pixels that have RTS noise.

Life sciences session has a paper on eye-implantable image sensor for blind people:

CMOS Imager Technologies for Biomedical Applications

J. Burghartz, T. Engelhardt, H-G. Graf, C. Harendt, H. Richter, C. Scherjon, K. Warkentin
IMS CHIPS, Stuttgart, Germany

Two CMOS imager chips are described. The first is a sub-retinal implant, being the only imager chip ever implanted into a human eye that partially restores vision to a blind patient. The second is a miniature imager chip, based on a thin-film-on-CMOS (TFC) pixel technology provides an optimum trade-off between sensitivity and pixel size.