Monday, December 04, 2017

IEDM Image Sensor Presentations

IEDM Image Sensor session has a nice selection of 6 papers. IEDM publishes figures from two of the presentations:

16.4 Near-infrared Sensitivity Enhancement of a Back-illuminated Complementary Metal Oxide Semiconductor Image Sensor with a Pyramid Surface for Diffraction Structure,
I. Oshiyama, S. Yokogawa, H. Ikeda, Y. Ebiko, T. Hirano, S. Saito, T. Oinoue, Y. Hagimoto, H. Iwamoto, Sony Semiconductor

Boosting Near-Infrared Sensitivity in CMOS Imagers: Backside-illuminated CMOS image sensors are ubiquitous in camera phones, and there is a growing demand for them to be able to handle near-infrared (NIR) light frequencies so that they can be used in iris scanning, facial recognition and motion-sensing applications. However, the NIR-sensitivity of silicon CMOS image sensors has been inadequate. The simplest way to enhance it would be to make the photo-absorption layer thicker, but that would require substantial capital investment in manufacturing equipment like high-energy ion implanters to be able to work with the thicker layer. Instead, Sony researchers developed a way to increase the NIR sensitivity of a 2-megapixel backside imager by building pyramidal light-diffraction structures on its surface. These 400nm structures diffract and trap the light coming to each pixel. The researchers also isolated each 1.12µm pixel from its neighbors by means of a special treatment process and used deep trench isolation to reduce crosstalk. They achieved a 50% increase in NIR sensitivity and a quantum efficiency of 30% at 850nm. Image resolution and levels of dark current (i.e., electrical “noise”) were not compromised.

The image is a photomicrograph of a section of a backside-illuminated CMOS image sensor with a cell size of 1.12µm and pyramid surfaces for diffraction (PSD) and deep-trench isolation (DTI) structures. The PSD pitch was 400 nm.

16.3 Back-side Illuminated GeSn Photodiode Array on Quartz Substrate Fabricated by Laser-induced Liquid-phase Crystallization for Monolithically-integrated NIR Imager Chip,
H. Oka, K. Inoue, T. T. Nguyen*, S. Kuroki*, T. Hosoi, T. Shimura and H. Watanabe, Osaka University, *Hiroshima University

Back-side illuminated single-crystalline GeSn photodiode array has been demonstrated on a quartz substrate for group-IV-based NIR imager chip. Owing to high crystalline quality of GeSn array formed by laser-induced liquid-phase crystallization technique, significantly enhanced NIR photoresponse with high responsivity of 1.3 A/W was achieved operated under back-side illumination.

Record Performance from GeSn Backside Imager: An Osaka University-led team will report on a backside-illuminated germanium-tin (GeSn) photodiode array with a high responsivity of 1.3 A/W at 1550nm, a record high on/off ratio of 5 decades, and low dark current of 10-3 A/cm2. They formed the large-area, tensile-strained and single-crystal GeSn device on a quartz substrate by using laser-induced liquid-phase crystallization. Because quartz has a high transparency to NIR frequencies, and can be combined directly with silicon, this work opens up the possibility to monolithically integrate high-performance GeSn NIR imagers with silicon CMOS circuitry.

In the schematic on the left, (a) is an illustration of lateral liquid-phase crystallization of GeSn wire on a quartz substrate by rapid thermal annealing, while (b) is an in-situ observation of lateral liquid-phase growth of GeSn wire.

At right is a schematic of the fabrication process and an optical image of a single-crystal GeSn n+/p photodiode array on a quartz substrate. P+ implantation was performed to form the n+ regions of the diodes.


  1. Is it me or does Sony always find the most inconvenient units so you can't do off the cuff comparison without converting them to common units? As in if the standard way is to present in e-/s, they would do it in A/cm^2...

    1. You are talking about the 16.3 paper by Osaka and Hiroshima Universities. Sony is not involved there.

    2. When your process is excellent, then you can talk in A/cm2 for dark current.

  2. Interestingly, pyramidal structures etched on top of the photosensitive area have been used for decades in Infrared Quantum Well Photodetectors - QWIPS. These devices were called C-QWIP (Corrugated QWIP) by its inventor, Dr. K.K.Choi from ARL. His group published extensively starting from 1997.

    C-QWIPs operate at wavelengths around 10 um (can work in the range ~3-40um).
    They are not sensitive for normally incident light (light has to have E polarization perpendicular to the quantum wells - i.e. should be propagating parallel to the imager surface), so people have came up with various sorts of diffraction gratings to bend the normally incident light.

    In C-QWIPs, light propagates from the substrate side, and reflects from the pyramids' sidewalls (unlike in Sony's sensors, where light appear to be refracted at the sidewalls).


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