Friday, October 05, 2018

Assorted News

Science Magazine publishes a paper on wideband light sensing device "Ultrabroadband photosensitivity from visible to terahertz at room temperature" by Dong Wu, Yongchang Ma, Yingying Niu, Qiaomei Liu, Tao Dong, Sijie Zhang, Jiasen Niu, Huibin Zhou, Jian Wei, Yingxin Wang, Ziran Zhao, and Nanlin Wang from Peking University, Tianjin University of Technology, and Tsinghua University, China.

"Charge density wave (CDW) is one of the most fundamental quantum phenomena in solids. Different from ordinary metals in which only single-particle excitations exist, CDW also has collective excitations and can carry electric current in a collective fashion. Manipulating this collective condensation for applications has long been a goal in the condensed matter and materials community. We show that the CDW system of 1T-TaS2 is highly sensitive to light directly from visible down to terahertz, with current responsivities on the order of ~1 AW−1 at room temperature. Our findings open a new avenue for realizing uncooled, ultrabroadband, and sensitive photoelectronics continuously down to the terahertz spectral range."

Everything is great about the new photodetection mechanism, except the dark current, which is about 15 orders of magnitude higher than in Si photodiode: reports that Columbia University team managed to create a very thin wide IR-band lens made of metamaterials and accepted paper in Nature:

"The Columbia Engineering researchers have created the first flat lens capable of correctly focusing a large range of wavelengths of any polarization to the same focal point without the need for any additional elements. At just 1┬Ám thick, their revolutionary "flat" lens offers performance comparable to top-of-the-line compound lens systems.

The team’s next challenge is to improve these lenses' efficiency. The flat lenses currently are not optimal because a small fraction of the incident optical power is either reflected by the flat lens, or scattered into unwanted directions. The team is optimistic that the issue of efficiency is not fundamental, and they are busy inventing new design strategies to address the efficiency problem.

Globenewswire: Atomera licenses its Mears Silicon Technology (MST) technology to ST. MST is an additional non-silicon implant that reduces transistors variability at a given processing node. Also, 1/f noise is reduced due to the elimination of halo implant (also called pocket implant by some fabs).

Why is this relevant for image sensors? First, if Sony pixel-parallel ADC presented at ISSCC 2018 gets the market traction, the reduction of mismatch between transistors might become more important to reduce pixel-level FPN coming from multiple ADCs. Second, reduction of SF gain variations across the pixel array might reduce PRNU in the regular image sensors. Although 1/f noise reduction might not directly affect pixel transistors that do not have halo implant anyway, for the most part, other parts of the image sensor still might benefit from it.

Atomera's seminar at IEDM 2017 explains their proposal:


  1. Your link to the "paper in Nature" is another interesting article by several research groups in China and in Taiwan, not the Columbia University paper.

    1. Sorry, indeed, I put a wrong link. Will look for the correct one.

    2. Looks like the paper has been accepted but not published yet. So, I've changed the link to the early preview version.


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