Young-Chan Kim

7.1 A 1/4-inch 8Mpixel CMOS image sensor with 3D backside-illuminated 1.12μm pixel with front-side deep-trench isolation and vertical transfer gate

According to the trend towards high-resolution CMOS image sensors, pixel sizes are continuously shrinking, towards and below 1.0μm, and sizes are now reaching a technological limit to meet required SNR performance [1-2]. SNR at low-light conditions, which is a key performance metric, is determined by the sensitivity and crosstalk in pixels. To improve sensitivity, pixel technology has migrated from frontside illumination (FSI) to backside illumiation (BSI) as pixel size shrinks down. In BSI technology, it is very difficult to further increase the sensitivity in a pixel of near-1.0μm size because there are no structural obstacles for incident light from micro-lens to photodiode. Therefore the only way to improve low-light SNR is to reduce crosstalk, which makes the non-diagonal elements of the color-correction matrix (CCM) close to zero and thus reduces color noise [3]. The best way to improve crosstalk is to introduce a complete physical isolation between neighboring pixels, e.g., using deep-trench isolation (DTI). So far, a few attempts using DTI have been made to suppress silicon crosstalk. A backside DTI in as small as 1.12μm-pixel, which is formed in the BSI process, is reported in [4], but it is just an intermediate step in the DTI-related technology because it cannot completely prevent silicon crosstalk, especially for long wavelengths of light. On the other hand, front-side DTIs for FSI pixels [5] and BSI pixels [6] are reported. In [5], however, DTI is present not only along the periphery of each pixel, but also invades into the pixel so that it is inefficient in terms of gathering incident light and providing sufficient amount of photodiode area. In [6], the pixel size is as large as 2.0μm and it is hard to scale down with this technology for near 1.0μm pitch because DTI width imposes a critical limit on the sufficient amount of photodiode area for full-well capacity. Thus, a new technological advance is necessary to realize the ideal front DTI in a small size pixel near 1.0μm.

46.1: Directivity Enhanced BLU for Edge-type Local Dimming

In this paper, we suggest an elegant and cost-effective Backlight Unit which is slim and has locally confined light needed for 1-dimensional local dimming and scanning. We fabricated LGP with micro-structures patterned by CO2 Laser. Lights from LGP are well distributed and uniform with density control of micro-patterns because they are continuous over the whole region of LGP. With one dimensional local dimming, we obtained 43% power-saving effect and contrast ratio of 11400:1 without any hot spot and the artifact.

P‐76: Highly Efficient Backlight Unit with a Polarization‐Separating Anisotropic Layer

We have developed a highly efficient backlight unit (BLU) with a polarization-separating anisotropic layer on which asymmetric microstructures were embossed. Our BLU provides the polarized light along the direction normal to the anisotropic layer and has over 30% higher luminance than a BLU adopting a reflective polarizer.

Design of a Highly Efficient Lightguide Plate Using an Anisotropic Layer with Polarization-Separating Microstructures

We developed a highly efficient lightguide plate (LGP) using an anisotropic layer (AL) with polarization-separating microstructures. The microstructures were fabricated on a uniaxially stretched polymeric AL through a hot embossing process. Our LGP with asymmetric saw-tooth bistructures produces highly efficient polarized light along the direction normal to the AL by reducing the stray light propagating at large inclination angles. The backlight unit (BLU) with a newly designed LGP has about 30% higher luminance and integrated intensity than the conventional BLU with a reflective polarizer.