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.
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