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: 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.
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.
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