This article describes new imaging capabilities and technologies developed for infrared focal plane arrays (FPAs) at SCD. One of the new technologies is the patterning of the back surface of the FPA, whose front surface is bonded to a silicon readout integrated circuit (ROIC). Another is the hybridization of a spectral filter to the same back surface.
Increased image resolution has been achieved by using an opaque mask on the backside of the FPA with small central apertures. The reduced fill factor of the sensor leads to lower crosstalk between neighboring pixels and a higher Nyquist frequency. A highly detailed multi-mega pixel image is obtained when the sensor is micro-scanned relative to the imaging optics.
Spectral filtering was achieved by hybridization of a designated filter to the backside of the FPA. The filter was glued to the FPA with high accuracy achieving single pixel resolution. System implementation of these SWIR sensor cameras has been demonstrated at imec and is reported in this paper.
First results are reported for a continuously varying monolithic filter deposited onto the FPA, which has a high spectral dispersion. We report electro-optical measurements on several different sensors and describe some of their key parameters.
SWIR (Short Wave Infrared) imaging can be of great use in precision agriculture, food processing and recycling industry, among other fields. However, hyperspectral SWIR cameras are costly and bulky, preventing their widespread deployment on the field. To answer the market need for compact and cost-efficient hyperspectral cameras covering the SWIR range, imec and SCD have joined efforts to develop a novel integration approach combining imec know-how in pixel level patterned thin film spectral filter technology, with SCD’s InGaAs technology. The here presented line-scan SWIR hyperspectral camera covers the 1.1-1.65 μm range with 100+ bands and a spectral resolution better than 10 nm. This imager uses a set of patterned Fabry-Pérot interferometers processed using semiconductor grade thin-film technology. The optical filters are then integrated directly on top of the sensing side of the InGaAs detector with high accuracy and with a minimum gap between filters and Focal Plane Array to limit cross-talk. The resulting line-scan camera, measuring only 70x62x60 mm and with a weight below 0.5kg, is the lightest and most compact SWIR hyperspectral camera on the market. Full sensor readout can be performed at up to 350 fps. An imecpatented SnapScan system with internal scanning was also developed, capable of acquiring data cubes of 640x512x128 pixels in a second. Maximum cube size is 1200x640x128. By selecting a subset of contiguous spectral bands and a reduced spatial resolution the sensor could be operated @ +1000 fps, for example enabling cube acquisitions of 320x512x64 in less than 300 ms.
Imec has developed a process for the monolithic integration of optical filters on top of CMOS image sensors, leading to compact, cost-efficient and faster hyperspectral cameras. Different prototype sensors are available, most notably a 600- 1000 nm line-scan imager, and two mosaic sensors: a 4x4 VIS (470-620 nm range) and a 5x5 VNIR (600-1000 nm). In response to the users’ demand for a single sensor able to cover both the VIS and NIR ranges, further developments have been made to enable more demanding applications. As a result, this paper presents the latest addition to imec’s family of monolithically-integrated hyperspectral sensors: a line scan sensor covering the range 470-900 nm. This new prototype sensor can acquire hyperspectral image cubes of 2048 pixels over 192 bands (128 bands for the 600- 900 nm range, and 64 bands for the 470-620 nm range) at 340 cubes per second for normal machine vision illumination levels.
Spectral imaging can reveal a lot of hidden details about the world around us, but is currently confined to laboratory environments due to the need for complex, costly and bulky cameras. Imec has developed a unique spectral sensor concept in which the spectral unit is monolithically integrated on top of a standard CMOS image sensor at wafer level, hence enabling the design of compact, low cost and high acquisition speed spectral cameras with a high design flexibility. This flexibility has previously been demonstrated by imec in the form of three spectral camera architectures: firstly a high spatial and spectral resolution scanning camera, secondly a multichannel snapshot multispectral camera and thirdly a per-pixel mosaic snapshot spectral camera. These snapshot spectral cameras sense an entire multispectral data cube at one discrete point in time, extending the domain of spectral imaging towards dynamic, video-rate applications. This paper describes the integration of our per-pixel mosaic snapshot spectral sensors inside a tiny, portable and extremely user-friendly camera. Our prototype demonstrator cameras can acquire multispectral image cubes, either of 272x512 pixels over 16 bands in the VIS (470-620nm) or of 217x409 pixels over 25 bands in the VNIR (600-900nm) at 170 cubes per second for normal machine vision illumination levels. The cameras themselves are extremely compact based on Ximea xiQ cameras, measuring only 26x26x30mm, and can be operated from a laptop-based USB3 connection, making them easily deployable in very diverse environments.