Image Sensors and Cameras Based on Colloidal Quantum Dots for Defense Applications

Colloidal quantum dot (CQD) -based image sensors accomplish several advantageous and unique features such as tailorable wavelength response via selection of dot size and material system, monolithic integration by processing directly onto the CMOS wafer surface thus avoiding hybridization cost and complexity, and scalability in pixel dimensions and density, whereby the limitations are primarily set by the resolution of the underlying CMOS process. Major efforts and successes have been reported in recent years by several academic groups and industrial entities in the research and development of CQD image sensors and their monolithic integration on CMOS platforms. To achieve uniform and defect-free imagers performing at high speed with low read-out noise, the entire system from ROIC front-end to wafer surface planarization to pixel stack structure, must be optimized as a whole; this is the approach Emberion has pursued with our in-house ROIC design and end-to-end fabrication process development.

This article reports on the image sensor technology and the VS20 camera product developed at Emberion. The article does this by describing the image sensor design comprising the sensor stack based on a p-i-n photodiode implementation with PbS QDs sandwiched between thin-film hole transport (HTL) and electron transport (ETL) layers as well as the CMOS ROIC architecture and pixel front-end interfacing the photodiode stack. Further on, the functionalities of the camera are described at hardware (HW) and software (SW) level including a brief introduction of the image processing pipeline (IPP) implementation. Next, we outline the image sensor fabrication process involving wafer planarization steps and photosensor stack processing including CQD deposition and ligand exchange steps.