Sensors Unlimited Inc. (SUI), a Raytheon Company, continues to expand its sensor portfolio through the development of time-of-flight (TOF) capable technologies. The utility of SWIR for active TOF solutions is of particular interest due to its inherent eye safety characteristic. SUI is developing TOF technologies both at the detector and readout integrated circuit (ROIC) layers of the focal plane array (FPA). In this work, SUI will offer updates to the internal development efforts comprising both areas as it pertains to the time-of-flight technologies.
In this work, SUI presents an update on PIN Photodiode Array (PDA) developments and the advancements in Avalanche Photodetectors (APD) Array development. SUI continue to push the PIN based SWIR photodetector performance by reducing the dark current, increasing the quantum efficiency in broad spectral wavelength range from 400nm to 1700nm and extending the wavelength to 2.6μm. We will also present APD technology advancements specifically related to low temperature performance from room temperature to 260K and Geiger Mode operation. In addition, we will discuss the requirements of Readout Integrated Circuits (ROIC) for APD based sensor development for synchronous and asynchronous pulse detection and active and passive quenching mechanisms. We will also discuss 2-D and 3-D TCAD simulation results at low temperature and compare them with measured performance results. Finally, recent results related to the advanced development of Geiger Mode Avalanche Photodetectors (GMAPD) and the results using passive and active quenching circuits are presented.
Recent short-wave infrared (SWIR) sensors have demonstrated in-pixel multimode capabilities. One of the additional modes is range finding. High resolution range finding is increasingly becoming vital functionality in high precision targeting and imaging systems. Highly precise and accurate range-to-target information is essential for many modern commercial and military applications. With the recent advances in LiDAR (Light Detection and Ranging) technology, range measurement accuracies as low as a centimeter at kilometer ranges. Sensors Unlimited Inc. (SUI), a Raytheon Technologies (RTX) Company, has been developing these multimode sensors using traditional PIN-based InGaAs detector technology. However, the capability of these sensors has been extended through the introduction of Avalanche Photodetector (APD) InGaAs sensors. This APD technology has been developed onshore to better serve the onshore community requiring simultaneous laser tracking, ranging, and imaging applications. In this work, SUI offers an update on previously presented, PDA-specific development, most specifically related to the advancement of Geiger Mode Avalanche Photodetectors (GMAPD). SUI’s APD technology is in direct response to the challenging SWaP and NEI performance requirements of active imaging and tracking applications. This update includes 2D and 3D TCAD simulation results with a comparison with measured performance results. Finally, initial results related to the advanced development of Geiger Mode Avalanche Photodetectors (GMAPD) themselves as well as supporting electronics is given. The revitalization of SUI’s APD development is a direct response to the challenging SWaP and longer-range with higher accuracy performance requirements of active imaging applications. SUI’s most recent APD design improvements facilitates greater signal to noise ratio at the pixel, which subsequently enables a supporting ROIC pixel design with improved performance.
KEYWORDS: Aerospace engineering, Photodetectors, Diffusion, Modulation transfer functions, Avalanche photodetectors, Readout integrated circuits, Personal digital assistants, Metals, Short wave infrared radiation, Scanning electron microscopy
Increasing shortwave infrared (SWIR) sensor performance requirements have pushed traditional HOT detector technologies to their limits. Collins Aerospace Princeton, a Raytheon Technologies (RTX) Company, has answered this call by looking beyond dark current reduction, and leveraging its onshore foundry capabilities to develop unprecedented, high performance photodetector array (PDA) technologies to better serve both passive and active imaging applications. In this work, Collins Aerospace Princeton offers an update on several previously presented, PDA-specific development fronts as well as offering introductions into other novel efforts. In addition to presenting current state-ofthe-art (SOA) InGaAs dark current performance, results related to mesa-structure PDAs for modulation transfer function (MTF) improvement and hybridization capacitance reduction for active imaging noise equivalent irradiance (NEI) improvement are offered. Additionally, focal plane array (FPA) interconnection improvement techniques and results for yield improvement and cost reduction are presented. Finally, results related to the three most advanced and nascent development tracks, avalanche photodiode (APD), PDA metallization and single side bumped FPA, are introduced. Collins Aerospace Princeton’s APD technology is in direct response to the challenging size, weight, and power (SWaP) and NEI performance requirements of active imaging applications. Similarly, Collins Aerospace Princeton’s PDA metallization technology, inspired by silicon-based brethren, facilitates greater integration capability on the PDA itself, which subsequently allows for greater functionality and performance at every pixel location. The most recently developed single side bumped FPA will dramatically improve operability with reduced cost. Overall, these PDA-specific developments represent the most innovative SWIR technology portfolio known to date.
KEYWORDS: Sensors, Short wave infrared radiation, Personal digital assistants, Photodiodes, Modulation transfer functions, Sensor technology, Detector arrays, Capacitance
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.
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.
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.
Two-dimensional photo detector arrays with a cutoff wavelength of 2.5 μm were fabricated on InP/InGaAs
epitaxial wafers with graded buffer layers in a 320x256 geometry on a 12.5μm pitch. Novel growth and fabrication
techniques were employed to fabricate these arrays and optimize the performance. The dark current of the detector was
investigated for a wide range of temperatures. The fabricated detector array was mated with a ROIC and packaged with a
multi-stage TEC and investigated further at the FPA level. The effect of the graded buffer layers on the sensor
performance was investigated and the results were compared to other methods used to develop and fabricate 2D image
sensors on extended wavelength materials.
Under the DARPA Photon Counting Arrays (PCAR) program we have investigated technologies to reduce the overall noise level in InGaAs based imagers for identifying a man at 100m under low-light level imaging conditions. We report the results of our experiments comprising of 15 InGaAs wafers that were utilized to investigate lowering dark current in photodiode arrays. As a result of these experiments, we have achieved an ultra low dark current of 2nA/cm2 through technological advances in InGaAs detector design, epitaxial growth, and processing at a temperature of +12.3°C. The InGaAs photodiode array was hybridized to a low noise readout integrated circuit, also developed under this program. The focal plane array (FPA) achieves very high sensitivity in the shortwave infrared bands in addition to the visible response added via substrate removal process post hybridization. Based on our current room-temperature stabilized SWIR camera platform, these imagers enable a full day-night imaging capability and are responsive to currently fielded covert laser designators, illuminators, and rangefinders. In addition, improved haze penetration in the SWIR compared to the visible provides enhanced clarity in the imagery of a scene. In this paper we show the results of our dark current studies as well as FPA characterization of the camera built under this program.
Hyperspectral imaging has been receiving much attention for its potential for high-resolution imaging and target recognition, chemical analysis and spectroscopy. In target recognition, identifying targets in cluttered and partially obscured environments requires the analysis of spectral content of the scenery. Spectroscopy type of applications can benefit from the real-time data collection of spatial and spectral content in a single image capture. We report on the design, simulation and fabrication of integrating MEMs tunable Fabry-Perot etalon filters with 2 dimensional InGaAs focal plane arrays for simultaneous spectral and spatial imaging. By tuning the transmission wavelength of the MEMs based filter, the spectral information is provided at each pixel of the photodiode array. The MEMs device is based on two InP/air-gap DBR reflectors, and a single wavelength air cavity that separates them. The selective etching of InGaAs forms the air gaps that suspend the quarter wavelength InP reflector layers. The top mirror reflectivity as well as the cavity air-gap is tuned by deflecting the suspended InP layer through a reverse biased p-i-n junction. Due to the high refractive index contrast of InP and air, the spectral width of the DBR reflectors is wide enough to block transmitted light from 1000nm to 1700nm, allowing the InGaAs absorber layer to detect only the MEMs filtered spectral content. A theoretical study on wide tuning range designs and the expected FWHM will be presented.
KEYWORDS: Avalanche photodetectors, Signal to noise ratio, Avalanche photodiodes, Receivers, Sensors, Indium gallium arsenide, Staring arrays, LIDAR, Capacitance, Chemical elements
We report on recent progress in developing 2-dimensional arrays of InGaAs/InP avalanche photodiodes. Advances in compound semiconductor epitaxy and device processing technologies enable large (128x128) element focal plane arrays with breakdown voltage standard deviations < 0.3%. The uniformity in breakdown voltage simplifies readout integrated circuit designs, in that a single bias voltage may be used for all elements in the array. Each element in the array achieves responsivities greater than 10 A/W at a wavelength of 1550 nm, while maintaining dark currents less than 20 nA. The APD arrays stand to enable new cameras for such applications as three-dimensional imaging, and various other laser radar and communications systems. In particular, the improved responsivity of avalanche photodiodes over their pin photodiode counterparts can improve sensitivities by as much as 6 - 10 dB depending upon the readout integrated circuit bandwidth. So-called "flash" laser radar systems wherein a single high energy laser pulse is used to image a target require the extra sensitivity afforded by avalanche photodiodes due to the low return photon count from distant targets.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.