Princeton
University Invention # 09-2523
Quantum
Cascade (QC) wafer quality testing requires intensive processing and
characterization. Conventional techniques used for wafer quality testing include
photoluminescence, x-ray diffraction, Hall effect measurements, high resolution
x-ray diffraction, transmission electron microscopy and secondary ion mass
spectrometry, all of which are useful but are time consuming and highly
invasive.
More
importantly, none of these methods are complete in that they do not give the
necessary QC information, such as turn-on voltage, maximum operating current
density, and the peak wavelength and full¿width at half-maximum (FWHM)
value of the electroluminescence (EL) spectra. Testing QC devices under the
appropriate operating bias typically entails elaborate fabrication steps,
including dicing of the wafer, which destroys the integrity of the wafer and
precludes further wafer scale processing.
Researchers
in the Department of Electrical Engineering and the MIRTHE Research Center,
Princeton University have developed a rapid and minimally invasive technique
which can be applied at the wafer level and from which rapid feedback on the
optical and electrical properties of a QC laser can be obtained. In this
technique a single mesa, covering a total area of 0.28mm² is fabricated on a QC
wafer, and its electrical and optical properties are measured. This method has
been validated by comparing the results from the mesas with those of QC lasers
fabricated from the same wafer. Results from the two types of QC devices show
excellent agreement, differing by less than ~10 percent.
The
new technique saves time and processing cost when compared to the otherwise
required full laser testing as significantly fewer processing steps are
involved; e.g. 1 metallization steps instead of 2, 2 lithography steps instead
of 3, no side-wall passivation and patterning steps. Overall, the number of
processing steps is halved, and the processing time is shortened at least by
about that amount as well. Cost-savings result from the time savings and
also from the fact that the wafer integrity is kept intact, such that the same
wafer can be used for follow-on wafer-scale QC laser processing.
MIRTHE is a
National Science Foundation Engineering Research Center headquartered at
Princeton University, with partners City College New York, Johns Hopkins
University, Rice, Texas A&M, and the University of Maryland Baltimore
County. The center encompasses a world-class team of engineers, chemists,
physicists, environmental and bio-engineers, and clinicians. MIRTHE's goal is to
develop Mid-Infrared (~ 3-30 µm) optical trace gas sensing systems based on new
technologies such as quantum cascade lasers or quartz enhanced photo-acoustic
spectroscopy, with the ability to detect minute amounts of chemicals found in
the environment or atmosphere, emitted from spills, combustion, or natural
sources, or exhaled.
Princeton
is currently seeking commercial partners for the further development and
commercialization of this opportunity. Patent protection is pending.
Publications:
Bentil EN,
Toor F, Hoffman AJ, Escarra MD, Gmachl C, Rapid and Minimally Invasive Quantum
Testing Cascade Wafer Testing, IEEE Photonics Technology Letters, Vol 21,
No.8, April 15,2009
For more
information on Princeton University invention # 09-2523 please
contact:
Laurie Tzodikov
Office of Technology Licensing and Intellectual Property
Princeton University
4 New South Building
Princeton, NJ 08544-0036
(609) 258-7256
(609) 258-1159 fax
tzodikov@princeton.edu