Hybrid Sensors Offer High Performance
THE
JET PROPULSION LABORATORY (JPL) IN Pasadena, California, is making
major strides in hybrid imaging technology (HIT)—the next generation
of high-performance image sensors—to apply to low-power cameras
in spaceborne scientific instruments. HIT can also be used in virtually
any situation requiring very high imaging quality and low power
dissipation, such as remote surveillance cameras, portable video
equipment and portable digital still cameras.
HIT is the name of a discipline in which the advancement of electronic
image sensors is pursued via the hybridization of charged coupled
devices (CCDs) and complementary metal oxide/semiconductor (CMOS)
circuitry. JPL's approach melds the exceptional quantum efficiencies,
broad spectral responses and low noise levels of CCDs with the low-power
levels, system integration capabilities and cost efficiency of CMOS-based
active-pixel sensors.
Previous attempts to unite CCD and CMOS circuitry at the device-fabrication
level have been expensive and yielded devices with high noise and
poor image quality. In JPL's approach, the CCD and CMOS components
are fabricated separately. Matching bump-bond pads are formed on
the CCD imager and CMOS chips during their respective fabrication
processes. Indium bumps are deposited on the pads, and the chips
are joined by standard bump-bonding techniques.
This element of HIT makes it possible to avoid costly process
development. This approach also makes it possible to optimize the
CCD and CMOS parts independently, in such a way as to maximize the
overall performance of the resulting image sensor in a highly miniaturized
format. The lack of optimization has been caused by a basic incompatibility
between CCD and CMOS processes as they relate to processing temperatures
and to required oxide thicknesses for CMOS transistors.
Another advantage of HIT is that it enables the reuse of CCD imaging
devices and CMOS readout circuitry without the need for costly refabrication.
A supply of unhybridized components can be maintained so that combinations
of components can be selected to satisfy requirements in specific
applications.
The imager integrated-circuit chip of a HIT image sensor is essentially
a CCD chip, except that the on-chip amplifier usually found in such
a device has been replaced by either a floating diffusion or a floating
gate output node. The companion CMOS chip must contain a charge-to-voltage
conversion amplifier similar to an operational amplifier configured
as a charge integrator. Depending on the application, the CMOS chip
could also contain additional circuitry to perform such functions
as correlated double sampling and analog-to-digital conversion.
For more information, contact the Technology Commercialization
Office at the Jet Propulsion Laboratory. Call: 818/354-2577, E-mail:
Merle.Mckenzie@ccmail.jpl.nasa.gov Please mention you read
about it in Innovation.
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ROBOT-ASSISTED
SPACE MISSIONS POSSIBLE
Scientists
at NASA's Ames Research Center, Moffett Field, California,
are developing an autonomous robot to support future space
missions after recently completing a key test of the robot's
components. About the size of a softball, the Personal Satellite
Assistant (PSA) will be equipped with a variety of sensors
to monitor environmental conditions in a spacecraft, such
as the amount of oxygen, carbon dioxide and other gases in
the air, the amount of bacteria growth, air temperature and
air pressure. The robot will also have a camera for videoconferencing,
navigation sensors, wireless network connections and even
its own propulsion components, enabling it to operate autonomously
throughout the spacecraft.
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| Principal
Ames researcher Yuri Gawdiak is working on developing
a softball-sized robot with its own propulsion components
for autonomous operation in a spacecraft to monitor environmental
conditions such as the amount of gases, bacterial growth,
air temperature and air pressure. The robot will also
have a camera for videoconferencing, navigation sensors
and wireless network connections. |
"We're
developing an intelligent robot that essentially can serve
as another set of eyes, ears, and nose for the crew and ground
support personnel," said NASA Ames researcher Yuri Gawdiak,
the project's principal investigator. "Our research objective
is to test intelligent autonomous systems that use advanced
sensors and monitoring technologies for supporting current
and future spacecraft operations."
The design
approach of the little round robot has several key advantages.
Besides data assistant capabilities to the onboard crew, payload
scientists and mission controllers on the ground, the PSA
would be able to remotely monitor their payloads, especially
when onboard crewmembers are not available. Another key benefit
of the design would be the ability to have several PSAs conduct
collaborative environmental troubleshooting activities. To
accomplish this complicated task, at least three PSAs would
use formation-flying techniques to zero in on the location
of an environmental problem, such a pressure leak, temperature
spike, off-gassing and so forth.
The PSA
is also being designed to handle more mundane housekeeping
chores, such as independent environmental sensor calibration
checks and inventory monitoring, to free the crew to focus
on their research activities. Beyond crew support operations
aboard the Space Shuttle in about two years and the International
Space Station in about three years, the long-term future goals
of the PSA are to support remote diagnostic operations and
to substitute, as necessary, for damaged or nonfunctioning
sensors on future spacecraft.
For more
information, visit http://ic.arc.nasa.gov/ic/psa
Or contact Michael Mewhinney at Ames Research Center. Call:
650/604-3937, Fax: 650/604-9000, E-mail: mmewhinney@mail.arc.nasa.gov
Please mention you read about it in Innovation.
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