Thursday, December 30, 2010

Samsung Proposes SEFET Sensor, Pixart Flips Color Filter and Microlens

Samsung patent application US20100320515 proposes a single-electron JFET-like structure (SEFET) to make small and sensitive pixel:

The photoelectrons are collected in N-doped area and drift close to the p-channel area due to the doping gradient. Then the collected electrons modulate the channel conduction by changing the N-gate potential:


Few different readout schemes are proposed, for example, this one (Vin is N-doped area voltage):

The SEFET pixel is said to be able to achieve a conversion gain of 1-9mV/e, as measured at the N-doped gate. Less than 1um pixel size is claimed to be possible.

One thing I was unable to find in the Samsung application is how the N-doped gate is reset before the integration starts.

Pixart application US20100320552 proposes to place color filter on top of microlens to improve the light passage through the metal stake:

"Compared with the prior art, such arrangement is advantageous in that the micro lens 18 is located much closer to the photo diode 12. As a result, the micro lens 18 has a wider chief ray angle, and the photo diode 12 has a better light collection efficiency."

7 comments:

  1. SEFET = Charge Modulation Device.
    Flip ML/CFA = the color cross talk will be increased and depend on the ray angle.

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  2. Are you sure 1-9mV/e? I think that m = micron here!!!

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  3. In the application it's written meV/e, as the gate is virtual and it talks about the conduction band barrier. The trick here is to have very small area transistor, so the effective gate capacitance is low.

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  4. Millivolts. This is a step towards the jot-based image sensor. We need to be able to detect a single photogenerated carrier.

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  5. 1mV/e => 0.16fF on the detection node. Is this possible? Even in a 4T pixel, the floating diffusion has still 1-2fF.

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  6. have they talked about the thermal noise in this structure please?

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  7. Very similar to DEPFET I guess

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