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QD-Si Image Sensors- beating InGaAs and SiGe in the NIR and SWIR regions with 1.62-2.2um pixel pitch

It took roughly 20 years of R&D to commercialize colloidal quantum dots (CQD) image sensors, which are the first commercial products in the marketplace to use CQDs in electro-active devices in contrast to all of the other current products that use CQDs in photoluminescence mode.

First, why quantum dots? The particle size of PbS QDs can be tuned to absorb thoughout the SWIR region spanning from 1000nm to 2500nm. This is shown in slide below, showing also that these QDs can also absorb in the NIR, visible, and UV regions at the same time.

Second, why quantum dots + silicon? Obviously the most advanced imaging technology is based on silicon. However, silicon is not sensitive to NIR and SWIR. As such, InGaAs and SiGe sensors have taken hold of this market. However, they are often expensive and their heterogenous integration with silicon read-out circuity (ROIC) can add to complexity and limit pixel sizes/pitches although advances in Cu-Cu bonding may change this.

As shown in the slide below, The QDs can be spin coated atop a 300mm silicon wafer. Single PbS QDs are formed into thin QD films with a ligand matrix. Out of this, a QF (quantum film) photodiode if formed with top and bottom electrodes (which must be transparent to a broad light spectrum). These QD photodiodes are formed atop the BEOL of a top-side illuminated image sensor. Cu vias are then used to connect the QD layer to the image sensor.

In addition to bringing silicon image sensor technology to the NIR/SWIR spectrum, the QD technology can also enable 100% fill factor and help shrink a complex global shutter pixel (which otherwise would need a larger space for the photodiode)

In this study, to be presented at TechBlick's Quantum Dot and microLED conference on 30Nov-1Dec, Jonathan Steckel from ST will outline the state-of-the-art, showing how 1.62-2.2um pixel pitches have been demonstrated on 300mm wafers. The quantum efficiency (QE) is >60% (940-1400nm)

To learn more join Jonathan and many other world-class speakers on 30Nov-1Dec online in TechBlick's interactive and engagement platform vist here

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