InGaAs based long-wavelength near infrared detector arrays are very important for high dynamic
range imaging operations seamlessly from daylight environments to dark environments. These
detector devices are usually made by open-hole diffusion technique which has the advantage of
lower leakage current and higher reliability. The diffusion process is usually done in a sealed
quartz ampoule with dopant compounds like ZnP2, ZnAs3, CdP2 etc. side by side with
semiconductor samples. The ampoule needs to be prepared and sealing process needs to be done
in very clean environment and each time can have variations. In this work we demonstrated
using MOCVD growth chamber to perform the diffusion process. The advantages of such a
process are that the tool is constantly kept in ultra clean environment and can reproducibly
provide clean processes without introducing unexpected defects. We can independently control
the temperature and flow rate of the dopant - they are not linked as in the ampoule diffusion case.
The process can be done on full wafers with good uniformity through substrate rotation, which is
good for large detector array fabrications. We have fabricated different types of InGaAs/InP
detector arrays using dimethyl zinc as the dopant source and PH3 or AsH3 for surface protection.
Pre-studies of Zn-diffusion profiles in InGaAs and InP at different temperatures, flow rates,
diffusion times and followed annealing times were conducted to obtain good control of the
process. Grown samples were measured by C-V profilometer to evaluate the diffusion depth and
doping concentration. The dependence of the diffusion profile with temperature, dopant partial
pressures, and annealing temperature and time and some of the fabricated device characteristics
are reported.
It has been known since the early 1960s that hexagonal sampling is the optimal sampling approach for isotropically
band-limited images, providing a 13.4% improvement in sampling efficiency over rectangular sampling. Despite
this fact and other significant advantages of hexagonal sampling, rectangular sampling is still used for virtually
all modern digital image processing systems. This is arguably due to the lack of an efficient addressing system for
hexagonal grids. Array set addressing (ASA) is a recent advance in addressing hexagonal grids that allows image
processing techniques to be performed efficiently on hexagonally sampled images. This paper will describe ASA
and discuss its advantages. With ASA, a renewed interest in sensors that sample hexagonally is occurring. We
will describe a new visible imager that simultaneously samples both hexagonally and rectangularly. This novel
research tool has the ability to provide real imagery that can be used to quantitatively compare the performance
of an image processing operation on both hexagonally sampled and rectangularly sampled images. We will also
describe current efforts and plans for future visible sensors that sample hexagonally. The advantages of hexagonal
sampling are not limited to the visible domain and should be equally realizable in the infrared domain. This
paper will discuss considerations for developing infrared sensors that sample hexagonally. On-focal plane array
(FPA) processing, readout architectures, detector materials, and bump-bonding are among the topics to be
discussed.
KEYWORDS: Sensors, Micro unmanned aerial vehicles, Optical testing, Head, Microcontrollers, Analog electronics, Visualization, Very large scale integration, Digital electronics, Signal processing
NRL is developing compact optic flow sensors for use in a variety of small-scale navigation and collision avoidance tasks. These sensors are being developed for use in micro air vehicles (MAVs), which are autonomous aircraft whose maximum dimension is on the order of 15 cm. To achieve desired weight specifications of 1 - 2 grams, mixed-signal VLSI circuitry is being used to develop compact focal plane sensors that directly compute optic flow. As an interim proof of principle, we have constructed a sensor comprising a focal plane sensor head with on-chip processing and a back-end PIC microcontroller. This interim sensors weighs approximately 25 grams and is able to measure optic flow with real-world and low-contrast textures. Variations of this sensor have been used to control the flight of a glider in real-time to avoid collisions with walls.
Conference Committee Involvement (1)
Bioengineered and Bioinspired Systems
19 May 2003 | Maspalomas, Gran Canaria, Canary Islands, Spain
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