Polycrystalline PbSe technology is today an emerging technology thanks to the method for processing monolithic
detectors based on a Vapor Phase Deposition (VPD) technique developed at CIDA. The first monolithic device was
successfully processed in 2007 (16x16 FPA, 200 μm pitch and Digital Pixel Sensor (DPS) concept). Remarkable
progress has been made improving some technological steps and developing tools for processing high signal rates. In this
work, low resolution IR images taken up to 20 Kfps with a real uncooled device are shown. These results represent an
important milestone and allocate the VPD PbSe technology among the major players within the domain of uncooled IR
detectors. It is a photonic detector suitable for being used in low cost IR imagers sensitive in the MWIR band and with
frame rates above 10,000 Hz. The number of applications is therefore huge, some of them specific, such as sensor for
Active Protection Systems or low cost seekers.
Paradoxically more than 50 years after being used in WWII, polycrystalline PbSe technology has turned today into an
emerging technology. Without any doubt one of the main facts responsible for the PbSe resurgence is a new method for
processing detectors based on a Vapour Phase Deposition (VPD) technique developed at CIDA. Using this method, the
first low density 2D PbSe Focal Plane Array (FPA), an x-y addressed type device, was processed on silicon. Even
though the last advances have been important they are not yet enough to consider this technology as a real alternative to
other uncooled technologies. To reach technical relevance and commercial interest it is obligated to integrate
monolithically or hybridize the sensors with their corresponding read out electronics (ROIC). Aiming to process
monolithic devices, a proper CMOS read out electronics were designed. In parallel, enabled technologies were
developed for adapting the material peculiarities to the CMOS substrates. In this work, the first monolithic device of
VPD PbSe is presented. Even though it is a modest 16x16 FPA with a pitch of 200 μm, it represents an important
milestone, allocating polycrystalline PbSe among the major players in the short list of uncooled IR detectors. Unlike
microbolometers and ferroelectrics, it is a photonic detector suitable for being used as a detector in low cost IR imagers
sensitive to the MWIR band and with frame rates as high as 1000 fps. The number of applications is therefore huge,
some of them specific, unique and highly demanded in the military and security fields such as sensors applied to fast
imagers, Active Protection Systems or low cost seekers.
The existing technology for uncooled MWIR photon detectors, based on polycrystalline lead salts, is stigmatized for being a 50-year-old technology, and it has been traditionally relegated to single-element detectors and relatively small linear arrays due to the chemical deposition techniques used on the manufacturing process. Along the last 10 years, it has been developed an innovative technology based on thermal evaporation of polycrystalline PbSe in vacuum at CIDA. In this work a new 32x32 format FPA is presented. These devices, processed on 4" silicon wafers, have a pitch of 200 μm and a filling factor of 80 %. It is a remarkable fact that the manufacturing process has been optimized and adapted to high volume requirements, allowing a considerable unitary cost reduction. Preliminary calculus based on experimental processing yields show that now, as it, is possible to deliver devices with a price per unit around 1000 $. This photonic detector is sensitive to MWIR radiation with a value of detectivity around one order of magnitude higher than that of the best thermal detector, and also much faster. Taking that into account, it can be asserted without any doubt that there is a new player in the domain of very low cost IR devices.
Although IR detectors are old and well known devices, at present they have not reached the status of a mass-market product. The main reason is directly related to their lack of affordability. Fifteen years ago the latest generation of thermal infrared (IR) detectors, as large format focal plane arrays (FPA), appeared with very promising expectation. They have been called low cost detectors because they do not need cooling and, as a consequence, prices are sensitively lower. However, they are currently still not affordable. Issues related to packaging and processing are limiting the potential affordability of these type of devices. Meanwhile, the technology of uncooled photonic detectors such as polycrystalline lead salt detectors are evolving fast and now they are a real alternative in the field of cheap detectors. CIDA owns an innovative technology for processing low density polycrystalline PbSe FPAs. This technology presents some advantages compared to the standard technology, mainly for processing more complex devices, such as 2D arrays or multicolor detectors. Mass production and prices decrease depend strongly on the monolithic integration between detectors and read out electronics. The method developed makes possible to process monolithic devices without any fundamental limitation. This work presents the latest results obtained during a study of monolithic integration viability carried out in our laboratories. A complementary metal oxide semiconductor (CMOS) test circuitry was designed, processed and submitted to all PbSe processing with promising results. The next phase will consist of designing a proper CMOS circuitry and process sensors on top.
This work reports on progress on development of polycrystalline PbSe infrared detectors at the Centro de Investigación y Desarrollo de la Armada (CIDA). Since mid nineties, the CIDA owns an innovative technology for processing uncooled MWIR detectors of polycrystalline PbSe. Based on this technology, some applications have been developed. However, future applications demand smarter, more complex, faster yet cheaper detectors. Aiming to open new perspectives to polycrystalline PbSe detectors, we are currently working on different directions: 1) Processing of 2D arrays: a) Designing and processing low density x-y addressed arrays with 16x16 and 32x32 elements, as an extension of our standard technology. b) Trying to make compatible standard CMOS and polycrystalline PbSe technologies in order to process monolithic large format arrays. 2) Adding new features to the detector such as monolithically integrated spectral discrimination.
A technology to process uncooled polycrystalline PbSe IR detectors on interference filters has been developed. Thus, the lead salt natural spectral response can be modified as required. PbSe is deposited, processed and sensitized, following a unique method, on an interference filter made up of a sapphire or silicon substrate and a Ge/SiO multilayer structure. Unlike standard polycrystalline PbSe processing methods, we deposit PbSe by sublimation in vacuum. As-deposited, PbSe is not sensitive to infrared light. In order to turn it photosensitive it is necessary to expose the films to specific thermal treatments. We have developed a very efficient sensitization process during which substrates are submitted to temperatures as high as 450 ºC. In this work we demonstrate that we are able to process a PbSe detector directly on top of an interference filter. Also, we present preliminary results regarding the compatibility of our technology with standard photolithography and dry etch techniques. Results obtained pave the way for the development of uncooled multicolor medium-wave infrared detectors.
A technology for processing low density uncooled focal plane arrays (FPAs) of polycrystalline PbSe has been developed. PbSe is deposited, processed and sensitized on a silicon substrate with two levels of metal separated by a thin dielectric layer of SiO<sub>2</sub>. An x-y addressed type read out permits a reduced number of leads and high filling factors. Unlike standard polycrystalline PbSe processing method we deposit PbSe by sublimation in vacuum. As-deposited, PbSe is not sensitive to IR light. In order to turn it photosensitive it is necessary to expose the films to specific thermal treatments. We have developed a very efficient sensitization process during which substrates withstand temperatures as high as 450°C. As a technology demonstrator, a low density (8x8 elements) PbSe FPA has been processed. Room temperature detectivities typically yield values of Dλ* (500 K, 300 Hz, 1.2 Hz) approximately 3 x 10<sup>9</sup> cm Hz<sup>1/2</sup>/W. The technological capabilities developed can be easily extended to more dense arrays.