The sensor is made of stacked organic films and the sensitivity of the layers and pixels can be controlled by applying a voltage. This allows the sensor to switch between color imaging and NIR imaging on a frame-by-frame basis without a mechanical IR cut filter required for conventional image sensors. The extinction ratio of NIR sensitivity at 800 nm was -28dB.
The technology also enables global shutter operation making such a sensor suited to applications in machine vision and inspection and recognition.
In the organic CMOS image sensor, photoelectric conversion is executed by an organic film while signal charge accumulation and the signal readout are executed in silicon circuits beneath the organic film.
Panasonic has stacked two organic layers, one of which can absorb visible light and the other of which can absorb NIR light and which have a high resistance ratio. In this structure a relatively low voltage is applied to one organic layer while relatively high voltage is applied to the other layer using the same voltage source. Both layers are subject to a voltage threshold for operation. By altering the voltage, it is possible to create two modes of operation. One where the sensor is sensitive only to visible light and a NIR imaging mode, in which the sensor is sensitive to visible light and NIR light.
Next: Subtract one from the other
In many applications, including night vision, sensitivity to both visible and NIR is acceptable while it is theoretically possible in alternate frames to capture images in both modes and subtract one from the other to obtain the NIR-only image.
Many multispectral sensors are created by using optical filtering having NIR as a fourth pixel after RGB. This has the limitation in loss of resolution and sensitivity compared with Panasonic’s stacked arrangement.
Panasonic was due to present papers on parts of these technologies at International Solid-State Circuit Conference held in San Francisco on Feb 5 to 9, 2017.
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