Tuesday, January 13, 2015

Latest Jot Pixel Paper

Open-access IEEE Journal of the Electron Devices Society publishes an early-access paper "A Pump-gate Jot Device with High Conversion Gain for a Quanta Image Sensor" by Jiaju Ma and Eric Fossum. The new jot sensor uses BSI pixel with charge stored under TG:


A special precaution has been made to reduce the FD capacitance by spacing it away from TG and making RST gate of trapezoidal shape:


The simulated CG of the jot is 380uV/e for a 1.4um pixel in 65nm process (FD capacitance of 0.4fF). The work was sponsored by Rambus.

4 comments:

  1. Wondering why so many papers are published with just simulations and with the claim that the chip is in the foundry. I understand those who don't plan to fabricate it for time reasons or lack of funding. Isn't it better to wait few more months and publish a paper with experimental results and at an even better journal? It is not a critics towards this work, I think this is a nice paper, just trying to understand the publication policies of universities..

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    1. Thank you for the nice comment. I can't speak for other universities, but in our case we think that the idea of the pump gate, distal FD, and other features, may be of interest for "regular" CIS devices. I think the risk of the device not working is small since TCAD is pretty good these days, but it might require several fab iterations for implant adjustments. You know that a new pixel probably costs a million dollars or more to fully develop. We just don't have that much of a budget. So, we share our ideas with the community, and we are taking a stab at fabbing it, thanks to our sponsor Rambus and the cooperation of TSMC. It will require a split from the regular process due to different implant conditions (same masks) and who knows when/if we will ever get a chip, much less a working chip, back. But we will keep our fingers crossed and if works well enough, we will write a follow up paper.
      By the way, one of the "products" of a research university is new knowledge and ideas. So, when I feel we have something worth sharing, we publish it. Most of this work was done by Jiaju Ma. (Nice job JJ!)

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  2. Why does the VB's potential change ? It's not under TX gate ... Thanks !

    -yang ni

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    Replies
    1. Yang Ni - it is just a fringing-field effect from TG being turned on. You can see this better in Fig 9, I think.

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