Already quite a bit of words are spent on the organic conductive sensors presented in the Panasonic papers. Nevertheless, here is some more info.
Kazuko Nishimura presented the paper on the large HDR sensor with a low noise level. A few remarks about this sensor :
– HDR is obtained by two light sensitive areas within one pixel : one with low and one with high sensitivity. This is a very similar method as proposed long time ago by Fuji in their SuperCCD,
– The pixels do suffer from kTC noise, but by means of a cleaver circuit/feedback, they are able to reduce the remaining kTC noise to 1.2 e– reset noise and to 5.4 e– overall. In combination with a full well of 600 ke–, it creates a gorgeous dynamic range,
– The process used to fabricate the sensor is 65 nm CMOS, 1P3Cu1Al,
– The results mentioned are overall not bad, but there was no information provided about dark current, about quantum efficiency, about uniformity and about reliability of the material. So this suggests (to me) that there are still some issues to solve.
Sanshiro Shishido presented the paper on the global shutter version of the organic photoconductor sensor. The topplate of the photoconductor is made out of ITO and needs to be biased to larger voltages. But the overall light sensitivity of the organic photoconductor depends strongly on the exact voltage on the ITO gate. A lower voltage on the ITO gate lowers the light sensitivity and actually 0 V on the gate makes the sensor even blind. In this way one can create a global shutter functionality to the sensor. Moreover, one has the possibility to modulate the sensitivity during the exposure time, for instance, the exposure time can be split in parts in which the sensor will be sensitive and in parts in which the sensor will be insensitive. Even one has the option to modulate the sensitivity during the periods the sensor is sensitive by means of adapting the high voltage set to the ITO gate. Overall a nice technology !
The third paper of Panasonic, presented by Yoshihisa Kato had nothing to do with the organic conductive layer, but the sensor presented was provided with an EM-function. The latter is built in the vertical direction of the silicon. This is new and is never shown before in an imager (to my knowledge). The EM-functionality can be switched on and off by means of the voltage biasing the substrate (around 23 V). Amazing images were shown (shot at extremely low light levels). From the data shown, it looks like the EM is very strongly depending on the exact voltage on the substrate. In comparison to the well-known EM-CCD and EM-CMOS devices (which are on the market), the EM-multiplication in the latter is done with very small gain steps, but by doing multiple EM-steps finally a large gain can be reached. In the case of the Panasonic paper, the EM is done only once, so all the gain needs to be created in one step. Has this way of working advantages or disadvantages compared to EM-CCD and EM-CMOS ?
Albert, 04-02-2016.
Seems pixel sensitivity is very sensitive to the voltage of ITO. The voltage can be homogeneous across entire pixel array? won’t create non-uniformity?