Sensors Unlimited Inc. (SUI), a Raytheon Technologies Company, has long been the vanguard of low-noise InGaAs/InP PiN back-side illuminated (BSI) planar-type photodiode technology. In addition to focusing on dark current reduction efforts, SUI has also initiated other photodiode detector array (PDA) improvement efforts to better serve its broad portfolio of sensor technology. In previous years, SUI has presented results related to mesa-structure PDAs for modulation transfer function (MTF) improvement and hybridization capacitance reduction for NEI improvement. An update to these technologies is offered. Additionally, SUI has more recently engaged in more advanced PDA development to better satisfy active imaging applications. Results of these efforts are also presented.
Sensors Unlimited Inc. (SUI), a Collins Aerospace Company, has developed a large-area, high-speed, short-wave infrared (SWIR) focal plane array (FPA) to meet the field-of-view (FOV) and bandwidth requirements of LiDAR applications. Modifications to SUI’s standard InGaAs photodiode array (PDA), include junction shape, dielectric thickness, and contact metallization. These changes allow for a reduction in the effective capacitance seen by the hybridized FPA’s readout integrated circuit (ROIC) while preserving the epitaxial structure that ensures the company’s industry-leading dark current. Compared to SUI’s standard device, significant capacitance reductions have been demonstrated. Enhancements of laser pulse detection performance arising from the capacitance improvement, and suitability of the resulting device for implementation in LiDAR systems, will be discussed.
Next-generation multi-mode tracking (MMT) technology developed by Sensors Unlimited Inc. (SUI), a Collins Aerospace Company, is presented. The technology provides focal plane arays (FPAs) with pulse detection capability in addition to traditional passive imaging, enabling more compact electro-optical (EO) systems with significantly lower power consumption. SUI’s latest MMT device is a short wave infrared (SWIR) FPA that features low-noise imaging, asynchronous laser pulse detection (ALPD), and time-of-arrival (TOA) capability in every pixel in the 12 μm pitch, 1280 x 1024 array. Simulated and measured results from the new FPA’s readout integrated circuit (ROIC), the 1280MMT, are given along with a comparison to SUI’s first multi-mode tracking ROIC, the 640MMT.
Sensors Unlimited Inc. (SUI), a Collins Aerospace company, has developed a short wave infrared (SWIR) photodetector device structure using isolated mesa pixels to improve the detector modulation transfer function (MTF), an important parameter in determining the overall image quality of a camera system. A combination of device fabrication and simulation has been used to evaluate the design and manufacturability of various mesa morphologies. Because mesa formation entails both the removal of some portion of the active region of the photodetector and the introduction of non- planar surfaces, any MTF improvement must be balanced against a loss of quantum efficiency (QE) and potentially higher dark current. Focal plane arrays (FPAs) based on the optimal mesa morphology have been fabricated and compared for MTF and QE performance at the camera level to FPAs built using SUI’s standard pixel structure. The mesa structure described herein is implemented on the front side of the photodetector and could also be implemented across all of SUI’s backside-illuminated (i.e., VIS/SWIR, NIR/SWIR, SWIR) structures for applications where a premium is placed on MTF performance.
For ultra-fine pixel pitch focal plane array (FPA) applications, flip-chip hybridization has advantages including high I/O density and short distance between the photodiode array (PDA) and the readout integrated circuit (ROIC). Indium has become the primary interconnect material because of its high ductility at low temperature. Successful mating of large format die becomes increasingly difficult, however, for finer pitch applications where bumps are shorter, as tolerance for bowing is low. Simultaneously, the epoxy filling process for large image format, hybridized focal planes becomes more challenging. These constraints call for tall indium bumps with high aspect ratio to accommodate die bowing and provide larger openings for the flow of fill epoxy. A process for the fabrication of highly uniform, high aspect ratio (height:diameter) indium bumps has been developed by Sensors Unlimited Inc. (SUI), a Collins Aerospace Company. The grain size of the deposited indium metal is minimized by optimizing process parameters as well as introducing intermediate metal layers underneath the indium bumps. Anisotropic deposition has been achieved by optimizing deposition rate and controlling substrate parameters. Indium bumps with aspect ratios over 2:1 and flat bump heads have been achieved. The developed bump process has been successfully applied to the fabrication of high resolution indium gallium arsenide (InGaAs) FPAs. Key control parameters for bump formation will be discussed in this paper.
Unattended ground monitoring that combines seismic and acoustic information can be a highly valuable tool in
intelligence gathering; however there are several prerequisites for this approach to be viable. The first is high
sensitivity as well as the ability to discriminate real threats from noise and other spurious signals. By combining
ground sensing with acoustic and image monitoring this requirement may be achieved. Moreover, the DS Sentry®provides innate spurious signal rejection by the "active-filtering" technique employed as well as embedding some
basic statistical analysis. Another primary requirement is spatial and temporal coverage. The ideal is
uninterrupted, long-term monitoring of an area. Therefore, sensors should be densely deployed and consume very
little power. Furthermore, sensors must be inexpensive and easily deployed to allow dense placements in critical
areas. The ADVIS DS Sentry®, which is a fully-custom integrated circuit that enables smart, micro-power
monitoring of dynamic signals, is the foundation of the proposed system. The core premise behind this technology
is the use of an ultra-low power front-end for active monitoring of dynamic signals in conjunction with a highresolution,
Σ Δ-based analog-to-digital converter, which utilizes a novel noise rejection technique and is only
employed when a potential threat has been detected. The DS Sentry® can be integrated with seismic accelerometers
and microphones and user-programmed to continuously monitor for signals with specific signatures such as impacts,
footsteps, excavation noise, vehicle-induced ground vibrations, or speech, while consuming only microwatts of
power. This will enable up to several years of continuous monitoring on a single small battery while concurrently
mitigating false threats.