Novel machine vision cameras featuring CQD sensors for high resolution, lower-cost SWIR imaging By George Wildeman and Ethan Klem, SWIR Vision Systems
Imaging of fill levels in plastic pharmaceutical vials: colour image (left) and SWIR CQD camera image S
WIR Vision Systems is introducing a new class of cameras featuring a 400nm to 1,700nm broadband image sensor
technology based on colloidal quantum dot (CQD) thin film photodiodes fabricated monolithically on silicon readout wafers. Tese sensors have the potential to achieve for SWIR imaging, what CMOS image sensors and micro-bolometer arrays have achieved for visible and longwave infrared imaging respectively. Namely, to leverage the scale and cost structure of the silicon integrated circuit industry, moving SWIR imaging from a specialised niche into broad commercial markets. Te current SWIR imaging market is dominated
by indium gallium arsenide (InGaAs) sensors, a compound semiconductor grown epitaxially on lattice-matched indium phosphide (InP) substrates. Te fabrication method imposes limitations on pixel size, pixel spacing and sensor resolution; commercially practical InGaAs SWIR cameras are limited to VGA resolution, and even these are too costly for most machine vision uses. Conversely, SWIR Vision Systems’ CQD
sensor technology uses a monolithic integration approach, in which the quantum dot-based sensor is fabricated directly onto CMOS readout integrated circuits (ROICs) using well-established, low-cost semiconductor deposition techniques. Te process requires no hybridisation, no epitaxial growth or exotic substrate materials, no pixel-level sensor patterning, and can be easily scaled to wafer-level fabrication. Te approach also employs low-cost, solution-processed lead sulphide (PbS) colloidal quantum dots to form as small as 3µm pitch p-n photodiode arrays sensitive in SWIR and visible spectral bands. Te relative crystalline disorder of colloidal quantum dots currently results in lower quantum
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efficiency when compared to InGaAs cameras, which may make these cameras less suitable for photon-starved uses. But, in the majority of machine vision applications a CQD sensor-based camera can be paired with relatively inexpensive active illumination, resulting in near InGaAs equivalent performance with a significant reduction in overall system cost. To demonstrate applicability to imaging
applications, SWIR Vision Systems has fabricated 2D arrays of quantum dot-based photodiodes on numerous commercial-off-the-shelf silicon CMOS
CQD sensor technology uses a monolithic integration approach
ROICs and integrated them with corresponding camera electronics. It is releasing the production Acuros camera family featuring: InGaAs equivalent noise, pixel operability greater than 99 per cent, 15µm pixel pitch, and three different pixel array sensor formats (640 x 512, 1,280 x 1,024, and 1,920 x 1,080). Tey are capable of up to 380fps via GenICam-compliant GigE Vision and USB3 Vision interfaces. CQD camera sensors made with low-cost
materials and CMOS-compatible techniques are a major advance to accessible high definition SWIR imaging. SWIR Vision Systems expects the camera’s lower cost and its non-ITAR, EAR99 export classification to drive higher adoption rates, broadening the market for SWIR camera technology. Tis technology will open up applications InGaAs cameras cannot yet reach due to constraints on image resolution, or higher cost.
www.swirvisionsystems.com
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