We present a near-infrared (NIR) imager based on high-performance organic photodiode in terms of dark current, specific detectivity and response time. A carefully designed interfacial layer is introduced in the thin-film organic photodiode stack to reduce trap assisted carrier emission leading to sub-nA/cm2 dark current and external quantum efficiency above 50% in the NIR range. The developed imager chip benefits from this improved dark current-voltage characteristic (high light signal to dark noise ratio) and enables high-resolution, monolithic NIR image sensors.
Hyperspectral and multispectral imaging enable augmented reality experience by collecting spectral information of a scene and mapping it onto a 2D image. This imaging method is especially powerful if done in short-wave infrared (SWIR) because of the unique spectral fingerprints of many molecules found in this region of the spectrum. Despite its high potential, this technology has not been widely adopted due to the high price of standard SWIR cameras. Recently, image sensors based on colloidal quantum dot thin films have gained a lot of attention due to their potential to enable affordable and high-resolution SWIR imaging. In this work, we present the latest results of our efforts to leverage imec's thin-film SWIR imaging platform for spectral imaging. We present the measurement results of our multispectral photodetectors, as well as the results of optical simulations demonstrating new concepts for light filtering in the SWIR region, compatible with the thin-film technology.
In this work, we present a photodetector based on PbS colloidal quantum dots which can be used for low-cost, high-resolution multispectral imaging in the short-wavelength infrared range. Using versatile solution-based processing of thin films, we fabricated a switchable, dual-channel, two-terminal photodetector that can be monolithically integrated with small-pitch CMOS readout arrays. Its vertically stacked structure provides higher spatial resolution compared to conventional snapshot multispectral image sensors. We show the results of the optical simulations based on the transfer matrix method, which allowed us to achieve a wavelength-tunable narrowband response. We demonstrate the operation of the photodetector and its facile tunability by showing an EQE of more than 25% at different bands in the wavelength range of 1-1.5 μm. This work demonstrates the potential of the emerging thin-film technology for multispectral imaging.
In this paper, we present short-wave infrared (SWIR) image sensors with high pixel density. Quantum dot (QD) photodiode stack is monolithically integrated on custom, 130 nm node CMOS readout circuit. State-of-the-art pixel pitch of 1.82 μm is demonstrated in focal plane arrays sensitive at eye-safe region above 1400 nm wavelength. Thin-film photodiode (TFPD) technology will facilitate realization of ultra-compact SWIR sensors for future XR applications, including eye-safe tracking systems and enhanced vision.
CMOS image sensors for visible wavelength range have been receiving much attention over the last two decades, offering ultra-low power and camera-on-chip integration. Imagers are now able to extract additional information from the scene thanks to infrared sensing for recognition or Time-of-Flight for 3D imaging. Such capabilities enable an unlimited amount of applications in several businesses, i.e. automotive, industrial, life science, security, agricultural or consumer. Imec has been continuously developing advanced technologies together with innovative pixel and circuit architectures to realize prototypes for various scientific applications. Thanks to state-of-the-art IIIV and thin-film (organics or quantum dots) material integration experience combined with imager design and manufacturing, imec is proposing a set of research activities which ambition is to innovate in the field of low cost and high resolution NIR/SWIR uncooled sensors as well as 3D sensing in NIR with Silicon-based Time-of-Flight pixels. This work will present the recent integration achievements with demonstration examples as well as development prospects in this research framework.
Colloidal quantum dots (QDs) based on lead sulfide (PbS) have acquired scientific interest for infrared optoelectronic devices with potential bandgap tunability and ease of fabrication on arbitrary substrates. In this work, we show how device analysis data feed back into process optimization, towards the realization of high performance QD NIR photodetectors. Using the combination of transient PL, carrier transport and CV measurements we obtain the carrier density, lifetime and diffusion length in the layers. From the measured short diffusion length of the minority carriers, we deduce the need to achieve a wide depletion region to minimize recombination and thus enhance the carrier harvesting. Process optimization lead to a depletion region of more than 150 nm, resulting in high photon to carrier conversion. Furthermore, the complex index of refraction of all layers is characterized using ellipsometry and reflection/transmission, and these values are used as input for a transfer matrix method. Using the first interference peak, we show that a maximum EQE of 25% can be expected from optical modeling, a value that we almost reach experimentally (20%). Combining all of the above, we demonstrate 1450-nm photodetectors with dark current in the range of μA and specific detectivity (D*) of 10^11 Jones.
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