When the term "traceable calibration standards" gets mentioned, it's
not likely to trigger a giddy rush of excitement among most
professionals in the semiconductor, flat-panel display, and related
micro/nano industries. But without such measurement-accuracy-enhancing
tools, process and metrology engineers would be comparing apples to
oranges far too frequently, with no way to be absolutely certain that
one piece of equipment's critical dimension readout matches another's,
or that the film thickness and resistivity numbers they see on an
instrument are consistent with those of every other similar system.
The photovoltaics industry has its own calibration standards needs,
especially when it comes to measuring those all-important solar-cell
and module conversion efficiencies. By properly and consistently
monitoring and calibrating the solar simulators used to determine those
efficiencies, the quality and accuracy of the measurements can be
drastically improved, which has enhanced revenue and
performance-reliability ramifications all the way up the PV system
validation value chain.
company that's synonymous in the chip-, panel-, and hard disc-making
sectors with the tools and services required for the heady world of
NIST-traceable measurements, announced last week that it's entered the
PV manufacturing fray, opening the doors of an accredited solar
calibration lab at its San Jose HQ as well as offering a couple of
versions of an NREL-traceable solar reference cell product.
VLSI Standards' Tortonese seeks solar-cell measurement accuracy.
I've known VLSI's Marc Helvey for years, as much for his dogged
determination in marketing and selling his company's products and
services around the globe as for his lifelong loyalty to the San
Francisco Giants and his glee in giving me grief about my baseball team
and archrivals of the Giants, the Los Angeles Dodgers. After I saw the
press release announcement, I emailed Marc and his boss, Marco
Tortonese, president of the company, with a list of follow-up questions
about VLSI's new solar side.
Here are most of my Q's and Marco's A's:
How long have you been working on the solar products and service, and what are the reasons for launching now?
About two years ago, we realized that we were selling our existing
semiconductor products into the photovoltaics industry. I am referring
to our traditional step-height standards, which are used to calibrate
the profilometers that control the texturization of solar cells; film
thickness standards, used to calibrate the ellipsometers that control
antireflective coatings; and resistivity standards, used to calibrate
the machines that measure doping.
We made a conscious decision to focus our efforts on solar about a
year ago when we made a capital investment with the addition of a
photovoltaic calibration lab. Our first product introduction was a
certification service for Solar Reference Cells, which was released in
conjunction with our own reference cell in order to provide a turnkey
solution for manufacturers who do not want to build their own. A
reference cell is used to calibrate the solar simulators that measure
the efficiency of solar cells or panels at the end of a production
This product makes a lot of sense for us. VLSI Standards' mission
is to make a positive impact in the world by improving the quality of
industrial production through accuracy in measurement. We found that we
can have a big impact on the solar industry by helping our customers
measure the efficiency of solar cells with accuracy. Efficiency is the
single most important measurement in the photovoltaic energy market, as
it ties directly to the economic value of the product throughout its
supply chain, from cell to panel to final installation. Therefore, it
is critical to measure cell efficiency accurately and early on in the
manufacturing process, in the solar-cell manufacturing plant, before
errors propagate all the way through a completed installation.
When did you actually begin offering the products and the
service, and what has been the response so far? Which do you expect to
be more popular, the service or the cells?
We officially entered the market on July 15, the first day of
Semicon West. The market has responded enthusiastically. The industry
had been relying on national laboratories or research institutes to
provide these calibration services, and was really waiting for a
commercially viable and accredited laboratory to step up to the plate
and provide this calibration service on a reliable commercial basis.
We are engaged with some of the major manufacturers of solar
simulators. They are interested both in our Solar Reference Cell and in
our calibration services. We expect that some of our customers will
build their own reference cells and will [want] to have us certify
them. Others will prefer a turnkey solution, where we provide both the
cell and the certification. We have chosen to offer the reference cell
and the certification service as two separate products, providing
customers the maximum flexibility in managing their supply chain.
What are some of the main differences you've learned about,
between the calibration and certification needs in the solar and
semiconductor industries as well as the infrastructure in general?
The use case for calibration is remarkably similar between solar
and semi, and probably any other manufacturing industry for that
matter. If you measure a critical parameter in a production process,
that metrology tool must be calibrated to give accurate readings,
whether it is the critical dimension of a 25-nm transistor gate or the
efficiency of a solar cell. Even more so if the measurement is directly
related to a final product specification, and the purchase price of the
product is tied to that specification, as is the case for efficiency
measurements of solar cells and panels. From a business model
perspective, we have observed that solar production facilities tend to
purchase turnkey factories more than their semi counterparts. That
makes it more important for us to partner with OEMs and system
What are the most important requirements for a
certification product in solar? Can you explain how the
certification/calibration process works?
Calibrating a solar reference cell is not an easy task. It requires
competencies in a variety of metrological areas, from radiometry to
spectral photometry, electrical measurements, thermometry, and
dimensional measurements. All of those parameters have an effect on the
final certified values. Each of the measurements we perform must be
traceable to the International System of Units through an unbroken
chain of measurement comparisons to fundamental standards, and
measurement errors in each of these comparisons must be propagated
rigorously. In particular, the fundamental radiometric standard for the
photovoltaic industry is maintained by an international body that
performs extensive direct black body radiation measurements from the
sun in Davos, Switzerland. We were able to tie to those standards
through the National Renewable Energy Laboratory in Colorado.
In practice, we have created a solar simulator that is traceable to
those same measurements in Davos. For us to calibrate a reference cell
we must first perform all the checks and balances on our solar
simulator to ensure that it matches the standard test condition for
spectral emission and intensity, then we measure the output of the cell
in a traceable way under those controlled conditions.
Do you manufacture the reference cells or outsource that?
We have a dual-manufacturing strategy. We can manufacture our own, but we also outsource.
What special manufacturing requirements are involved?
The most typical special manufacturing requirement that we have
encountered for reference cells is that the cell should be a fairly
close match to the cells being measured in the manufacturing plant. For
example, you cannot use a single-crystal reference cell to calibrate a
solar simulator that is then used to measure efficiency of amorphous
silicon cells. This is because single crystal and amorphous silicon
have different spectral responses. Therefore, we have to simulate the
material properties, for instance, using appropriate color filters to
obtain a good spectral match to our customers' products.
Alternatively, we can use our customer's own special materials and
create reference cells for them. This will allow us to provide
calibrated reference cells for all kinds of conventional and new exotic
materials, from crystalline to thin films, from organic to
multijunction devices, provided we use the correct approach.
In a typical cell or module factory, how would the
manufacturer use the reference cells? How many would be needed for a
typical volume line?
A manufacturer would put the reference cell under a solar simulator
and adjust the intensity of the light until the current output of the
reference cell matches the value that we certify. At that point the
manufacturer is assured that the solar simulator reproduces the
irradiance of the standard test conditions, which are defined as 1000
watts per square meter, or one sun in common solar terminology.
Typically this process is automated by the manufacturer of the solar
simulator and frequently the reference cell is integrated with the
simulator. In this case, there needs to be a reference cell for every
solar simulator in the plant.
What kind of impact will the use of these cells have on conversion efficiencies, traceability, and other solar metrics?
The benefits to the industry and to the consumers from using
accurate and consistent efficiency measurements should be pervasive.
For example, within a factory, it is important to match the efficiency
measurements of all the simulators used by the different production
lines. A common ruler for efficiency will be important in addressing
disputes between buyers and vendors of photovoltaic products. We have
purchased solar cells that did not meet their efficiency
specifications, while on the other hand I have friends who have been
pleasantly surprised with their rooftop installations supplying more
electricity than they had contracted for. Overall I believe everyone
will benefit from the use of a common ruler, and that is what we are
here to provide.
What role did NREL play in development of the products and service?
We have worked very closely with both NREL and NIST [National
Institute of Standards and Technologies] in our product development.
NREL has provided a traceability path to the international radiometric
standards. NIST has provided us with an accreditation to the ISO/IEC
17025 standard, which is pretty much a requirement for any calibration
laboratory to play the game. To our knowledge, we are the only U.S.
commercial laboratory to have achieved this accreditation for