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Consumer Electronics Topic Type Semiconductors Interview


FOR BETTER AR CAMERAS, SWAP PLASTIC LENSES FOR SILICON CHIPS

METALENZ ADDS THE POWER OF POLARIZATION TO ITS INNOVATIVE POLAREYES CHIPS


Tekla S. Perry
20 Jan 2022
5 min read
2


Metalenz uses standard semiconductor manufacturing processes to build
metasurfaces comprising nanostructures that control light, with one chip
replacing multiple traditional camera lenses.

Metalenz
augmented reality lenses cameras metalenz nanopillars face recognition
metasurfaces nanotechnology


This week, startup Metalenz announced that it has created a silicon chip that,
paired with an image sensor, can distinguish objects by the way they polarize
light. The company says its “PolarEyes” will be able to make facial
authentication less vulnerable to spoofing, improve 3D imaging for augmented and
virtual reality, aid in telehealth by distinguishing different types of skin
cells, and enhance driving safety by spotting black ice and other hard-to-see
road hazards.

The company, founded in 2017 and exiting stealth a year ago, previously
announced that it was commercializing waveguides composed of silicon
nanostructures as an alternative to traditional optics for use in mobile
devices.

Metalenz recently began a partnership with ST Microelectronics to move its
technology into mass production and expects to be shipping imaging packages
sometime in the second quarter of this year, according to CEO Robert Devlin.

IEEE Spectrum spoke with Devlin last week to find more about the company’s
technology and what it will be able to do when it gets into consumer hands.

Before we talk about your new polarization optics, briefly help us understand
how your basic technology works.

Robert Devlin: We use standard semiconductor lithography on 12-inch wafers to
create nanostructures in the form of little pillars. These structures are
smaller than the wavelength of light, so by changing the radius of the pillars,
we can use them to control the length of the optical path of the light passing
through. For the first generation of this technology, we are working with
near-infrared wavelengths, which transmits through silicon, rather than
reflecting as visible light would do.



What’s the advantage of using nanostructures over traditional lenses?

Devlin: Our technology is flat, for one. When you are using a curved lens to put
an image on a flat sensor, you have to make all sorts of corrections using
multiple lenses and finely controlling the spacing between the lenses to make it
work; we don’t have to do that. We also can bring the functions of multiple
traditional lenses onto one chip . And we can manufacture these lenses in the
same semiconductor foundries as the image sensors and electronics used in camera
modules.

The iPhone face ID system, for example, has three lenses: one diffractive lens,
for splitting infrared light being projected onto your face into a grid of dots,
and two refractive, for collimating the lasers to project onto the face. Some of
these modules have an optical path that’s folded by mirrors, because otherwise
they would be too thick to fit into compact spaces required for consumer
devices. With the single-chip flat optics, we can shrink the overall thickness,
and don’t need folded optical paths or mirrors in even the most
space-constrained applications.

3D mapping is another infrared imaging application that uses multiple lenses
today. Augmented reality systems need to create a 3D map of the world around
them in real time, in order to know where to place the virtual objects. Today,
these use a time-of-flight system—again, working in the infrared part of the
spectrum—which sends out pulses of light and times how long they take to get
back to the image sensor. This system requires several refractive lenses to
focus the outgoing light and a diffractive lens to multiply the light to a grid
of points. They also require multiple lenses on the imaging side to collect the
light from the scene. Some of the lenses are needed to correct for the curvature
of the lenses themselves, some are needed to make sure the image is crisp across
the entire field of view. Using nanostructures, we can put all of these
functions onto one chip.

So that’s what the chips you announced do?

Devlin: Yes, and the first product to use our technology, shipping in the second
quarter of this year, will be a module for use in 3D imaging.

Initially for mobile phones?

Devlin: For consumer devices generally but also for mobile phones.

What about AR?

Devlin: Of course, everyone is eagerly waiting for AR glasses, and the form
factor remains a problem. I think what we are doing—simplifying the optics—will
help solve the form-factor problem. People get suspicious if they see a big
camera sitting on someone’s face. Ours can be very small, and, for this
application, infrared imaging is appropriate. It allows the system to understand
the world around it in order to meld the virtual world with it. And it isn’t
affected by changes in lighting conditions.



Okay, let’s talk about what you’re announcing now, the polarization technology,
your PolarEyes.

Devlin: When we spoke a year ago, I talked about Metalenz wanting to not just
simplify existing mobile-camera modules, but to take imaging systems that have
been locked away in scientific laboratories because they are too expensive,
complex, or big, and combine their optics into a single layer that would be
small enough and cheap enough for consumer devices.

One of those imaging systems involves the polarization of light. Polarization is
used in industrial and medical labs; it can be used to see where cancerous cells
start and end, it can in many cases tell what material something is made of. In
industry, it can be used to detect features of black objects, the shape of
transparent objects, or even scratches on transparent objects. Today, complete
polarization cameras measure around 100 by 80 by 80 millimeters, with optics
that can cost hundreds of dollars.

The PolarEyes chip from Metalenz sorts light by its polarization, allowing the
pixels of images captured to be color-coded by polarization. In this case, the
difference in polarization between materials makes it obvious when a mask
obstructs skin.Metalenz

Using metasurface technology, we can bring the size down to 3 by 6 by 10 mm and
the price down to [US] $2 to $3. And unlike many typical systems today, which
take multiple views at different polarizations sequentially and use them to
build up an image, we can use one of our chips to take those multiple views
simultaneously, in real time. We take four views—that turns out to be the number
we need to combine into a normal image or to create a full map of the scene
color-coded to indicate the complete polarization at each pixel.

Besides the medical and industrial uses you mentioned, why else are polarized
images useful?

Devlin: When you get these into mobile devices, we will likely find all sorts of
applications we haven’t thought of yet, and that’s really exciting. But we do
have an initial application that we think will help get the technology
adopted—that’s in facial recognition. Today’s facial recognition systems are
foiled by masks. That’s not because they couldn’t get enough information from
above the mask to recognize the user. They use a high-res 2D image that provides
enough data to the algorithms to do that. But they also use a 3D imaging system
that is very low resolution. It’s meant to make sure that you’re not trying to
spoof the system with a mask or photograph, and that’s what makes facial
recognition fail when you are wearing a mask. A polarization imaging module
could easily distinguish between skin and mask and solve that problem.

From Your Site Articles
 * Inside the Development of Light, the Tiny Digital Camera That ... ›
 * Metasurface Optics for Better Cellphone Cameras and 3-D Displays ... ›
 * Can Silicon Nanostructures Knock Plastic Lenses Out of Cell Phone ... ›

Related Articles Around the Web
 * STMicroelectronics and Metalenz Partner to Transform ›
 * Metalenz: Homepage ›


augmented reality lenses cameras metalenz nanopillars face recognition
metasurfaces nanotechnology

Tekla S. Perry

Tekla S. Perry is a senior editor at IEEE Spectrum. Based in Palo Alto, Calif.,
she's been covering the people, companies, and technology that make Silicon
Valley a special place for more than 40 years. An IEEE member, she holds a
bachelor's degree in journalism from Michigan State University.

The Conversation (1)
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FB TS21 Jan, 2022
INDV

IMHO one of the best applications for lensless flat surface digital cameras
could be both ground & space telescopes!

Imagine being able to create telescopes of any size by simply joining together
flat panels!

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HOW NANOTECH CAN FOIL COUNTERFEITERS


THESE TINY MECHANICAL ID TAGS ARE UNCLONABLE, CHEAP, AND INVISIBLE


Roozbeh Tabrizian

Swarup Bhunia
28 May 2021
10 min read
2

Horizontal

University of Florida
DarkGray

What's the largest criminal enterprise in the world? Narcotics? Gambling? Human
trafficking?

Nope. The biggest racket is the production and trade of counterfeit goods, which
is expected to exceed US $1 trillion next year. You've probably suffered from it
more than once yourself, purchasing on Amazon or eBay what you thought was a
brand-name item only to discover that it was an inferior-quality counterfeit.



It's an all-too-common ploy, and legitimate manufacturing companies and
distributors suffer mightily as a result of it. But the danger runs much deeper
than getting ripped off when you were seeking a bargain. When purchasing
pharmaceuticals, for example, you'd be putting your health in jeopardy if you
didn't receive the bona fide medicine that was prescribed. Yet for much of the
world, getting duped in this way when purchasing medicine is sadly the norm.
Even people in developed nations are susceptible to being treated with fake or
substandard medicines.

Tiny mechanical resonators produced the same way microchips are made (bottom)
can serve to authenticate various goods. Being less than 1 micrometer across and
transparent, these tags are essentially invisible. University of Florida

Counterfeit electronics are also a threat, because they can reduce the
reliability of safety-critical systems and can make even ordinary consumer
electronics dangerous. Cellphones and e-cigarettes, for example, have been known
to blow up in the user's face because of the counterfeit batteries inside them.

It would be no exaggeration to liken the proliferation of counterfeit goods to
an infection of the global economy system—a pandemic of a different sort, one
that has grown 100 fold over the past two decades, according to the
International AntiCounterfeiting Coalition. So it's no wonder that many people
in industry have long been working on ways to battle this scourge.





The traditional strategy to thwart counterfeiters is to apply some sort of
authentication marker to the genuine article. These efforts include the display
of Universal Product Codes (UPC) and Quick Response (QR) patterns, and sometimes
the inclusion of radio-frequency identification (RFID) tags. But UPC and QR
codes must be apparent so that they are accessible for optical scanning. This
makes them susceptible to removal, cloning, and reapplication to counterfeit
products. RFID tags aren't as easy to clone, but they typically require
relatively large antennas, which makes it hard to label an item imperceptibly
with them. And depending on what they are used for, they can be too costly.

We've come up with a different solution, one based on radio-frequency (RF)
nanoelectromechanical systems (NEMS). Like RFID tags, our RF NEMS devices don't
have to be visible to be scanned. That, their tiny size, and the nature of their
constituents, make these tags largely immune to physical tampering or cloning.
And they cost just a few pennies each at most.

Unseen NEMS tags could become a powerful weapon in the global battle against
counterfeit products, even counterfeit bills. Intrigued? Here's a description of
the physical principles on which these devices are based and a brief overview of
what would be involved in their production and operation.

You can think of an RF NEMS tag as a tiny sandwich. The slices of bread are two
50-nanometer-thick conductive layers of indium tin oxide, a material commonly
used to make transparent electrodes, such as those for the touch screen on your
phone. The filling is a 100-nm-thick piezoelectric film composed of a
scandium-doped aluminum nitride, which is similarly transparent. With
lithographic techniques similar to those used to fabricate integrated circuits,
we etch a pattern in the sandwich that includes a ring in the middle suspended
by four slender arms. That design leaves the circular surface free to vibrate.

The material making up the piezoelectric film is, of course, subject to the
piezoelectric effect: When mechanically deformed, the material generates an
electric voltage across it. More important here is that such materials also
experience what is known as the converse piezoelectric effect—an applied voltage
induces mechanical deformation. We take advantage of that phenomenon to induce
oscillations in the flexible part of the tag.

To accomplish this, we use lithography to fabricate a coil on the perimeter of
the tag. This coil is connected at one end to the top conductive layer and on
the other end to the bottom conductive layer. Subjecting the tag to an
oscillating magnetic field creates an oscillating voltage across the
piezoelectric layer, as dictated by Faraday's law of electromagnetic induction.
The resulting mechanical deformation of the piezo film in turn causes the
flexible parts of the tag to vibrate.



This vibration will become most intense when the frequency of excitation matches
the natural frequency of the tiny mechanical oscillator. This is simple
resonance, the phenomenon that allows an opera singer's voice to shatter a wine
glass when the right note is hit (and if the singer tries really, really hard).
It's also what famously triggered the collapse of the Broughton suspension
bridge near Manchester, England, in 1831, when 74 members of the 60th Rifle
Corps marched across it with their footsteps landing in time with the natural
mechanical resonance of the bridge. (After that incident, British soldiers were
instructed to break step when they marched across bridges!) In our case, the
relevant excitation is the oscillation of the magnetic field applied by a
scanner, which induces the highest amplitude vibration when it matches the
frequency of mechanical resonance of the flexible part of the tag.


SHAPE SHIFTERS









These electron micrographs show some of the tags the authors have fabricated,
which can take various forms. The preferred geometry (top) is a circular tag
containing a piezoelectric ring suspended by four beams. It includes a coil
(lighter shade), which connects with electrode layers on the top and bottom of
the ring. Voltages induced in this coil by an external scanner set up mechanical
oscillations in the ring. University of Florida

In truth, the situation is more complicated than this. The flexible portion of
the tag doesn't have just one resonant frequency—it has many. It's like the
membrane on a drum, which can oscillate in various ways. The left side might go
up as the right side goes down, and vice versa. Or the middle might be rising as
the perimeter shifts downward. Indeed, there are all sorts of ways that the
membrane of a drum deforms when it is struck. And each of those oscillation
patterns has its own resonant frequency.

We designed our nanometer-scale tags to vibrate like tiny drumheads, with many
possible modes of oscillation. The tags are so tiny—just a few micrometers
across—that their vibrations take place at radio frequencies in the range of 80
to 90 megahertz. At this scale, more than the geometry of the tag matters: the
vagaries of manufacturing also come into play.

For example, the thickness of the sandwich, which is nominally around 200 nm,
will vary slightly from place to place. The diameter or the circularity of the
ring-shaped portion is also not going to be identical from sample to sample.
These subtle manufacturing variations will affect the mechanical properties of
the device, including its resonant frequencies.

In addition, at this scale the materials used to make the device are not
perfectly homogeneous. In particular, in the piezoelectric layer there are
intrinsic variations in the crystal structure. Because of the ample amount of
scandium doping, conical clusters of cubic crystals form randomly within the
matrix of hexagonal crystals that make up the aluminum nitride grains. The
random positioning of those tiny cones creates significant differences in the
resonances that arise in seemingly identical tags.

Random variations like these can give rise to troublesome defects in the
manufacture of some microelectronic devices. Here, though, random variation is
not a bug—it's a feature! It allows each tag that is fabricated to serve as a
unique marker. That is, while the resonances exhibited by a tag are controlled
in a general way by its geometry, the exact frequencies, amplitudes, and
sharpness of each of its resonances are the result of random variations. That
makes each of these items unique and prevents a tag from being cloned,
counterfeited, or otherwise manufactured in a way that would reproduce all the
properties of the resonances seen in the original.

An RF NEMS tag is an example of what security experts call a physical unclonable
function. For discretely labeling something like a batch of medicine to document
its provenance and prove its authenticity, it's just what the doctor ordered.

You might be wondering at this point how we can detect and characterize the
unique characteristics of the oscillations taking place within these tiny tags.
One way, in principle, would be to put the device under a vibrometer microscope
and look at it move. While that's possible—and we've done it in the course of
our laboratory studies—this strategy wouldn't be practical or effective in
commercial applications.

But it turns out that measuring the resonances of these tags isn't at all
difficult. That's because the electronic scanner that excites vibrations in the
tag has to supply the energy that maintains those vibrations. And it's
straightforward for the electronic scanner to determine the frequencies at which
energy is being sapped in this way.


CATCH THE WAVE

The authors directly measured the surface topography of a tag using a digital
holographic microscope, which is able to scan reflective surfaces and precisely
measure their heights (top). The authors also modeled various modes of
oscillation of the flexible parts of such a tag (bottom). Each mode has a
characteristic resonant frequency, which varies with both the geometry of the
tag and its physical composition. University of Florida; Bottom: James Provost

The scanner we are using at the moment is just a standard piece of electronic
test equipment called a network analyzer. (The word network here refers to the
network of electrical components—resistors, and capacitors, and inductors—in the
circuit being tested, not to a computer network like the Internet.) The sensor
we attach to the network analyzer is just a tiny coil, which is positioned
within a couple of millimeters of the tag.

With this gear, we can readily measure the unique resonances of an individual
tag. We record that signature by measuring how much the various
resonant-frequency peaks are offset from those of an ideal tag of the relevant
geometry. We translate each of those frequency offsets into a binary number and
string all those bits together to construct a digital signature unique to each
tag. The scheme that we are currently using produces 31-bit-long identifiers,
which means that more than 2 billion different binary signatures are
possible—enough to uniquely tag just about any product you can think of that
might need to be authenticated.

Relying on subtle physical properties of a tag to define its unique signature
prevents cloning but it does raise a different concern: Those properties could
change.

For example, in a humid environment, a tag might adsorb some moisture from the
air, which would change the properties of its resonances. That possibility is
easy enough to protect against by covering the tag with a thin protective layer,
say of some transparent polymer, which can be done without interfering with the
tag's vibrations.

But we also need to recognize that the frequencies of its resonances will vary
as the tag changes temperature. We can get around that complication, though.
Instead of characterizing a tag according to the absolute frequency of its
oscillation modes, we instead measure the relationships between the frequencies
of different resonances, which all shift in frequency by similar relative
amounts when the temperature of the tag changes. This procedure ensures that the
measured characteristics will translate to the same 31-bit number, whether the
tag is hot or cold. We've tested this strategy over quite a large temperature
range (from 0 to 200 °C.) and have found it to be quite robust.

A tag is characterized by the differences between its measured resonant
frequencies (dips in red line) and the corresponding frequencies for an ideal
tag (dips in black line). These differences are encoded as short binary strings,
padded to a standard length, with one bit signifying whether the frequency
offset of positive or negative (right). Concatenated, these strings provide a
unique digital fingerprint for the tag (bottom) University of Florida

The RF network analyzer we're using as a scanner is a pricey piece of equipment,
and the tiny coil sensor attached to it needs to be placed right up against the
tag. While in some applications the location of the tag on the product could be
standardized (say, for authenticating credit cards), in other situations the
person scanning a product might have no idea where on the item the tag is
positioned. So we are working now to create a smaller, cheaper scanning unit,
one with a sensor that doesn't have to be positioned right on top of the tag.

We are also exploring the feasibility of modifying the resonances of a tag after
it is fabricated. That possibility arises from a bit of serendipity in our
research. You see, the material we chose for the piezoelectric layer in our tags
is kind of unusual. Piezoelectric devices, like some of the filters in our
cellphones, are commonly made from aluminum nitride. But the material we adopted
includes large amounts of scandium dopant, which enhances its piezoelectric
properties.

Unknown to us when we decided to use this more exotic formulation was a second
quality it imparts: It makes the material into a ferroelectric, meaning that it
can be electrically polarized by applying a voltage to it, and that polarization
remains even after the applied voltage is removed. That's relevant to our
application, because the polarization of the material influences its electrical
and mechanical properties. Imparting a particular polarization pattern on a tag,
which could be done after it is manufactured, would alter the frequencies of its
resonances and their relative amplitudes. This approach offers a strategy by
which low-volume manufacturers, or even end users, could “burn" a signature into
these tags.

Our research on RF NEMS tags has been funded in part by Discover Financial
Services, the company behind the popular Discover credit card. But the
applications of the tiny tags we've been working on will surely be of interest
to many other types of companies as well. Even governments might one day adopt
nanomechanical tags to authenticate paper money.

Just how broadly useful these tags will be depends, of course, on how successful
we are in engineering a handheld scanner—which might even be a simple add-on for
a smartphone—and whether our surmise is correct that these tags can be
customized after manufacture. But we are certainly excited to be exploring all
these possibilities as we take our first tentative steps toward
commercialization of a technology that might one day help to stymie the world's
most widespread form of criminal activity.

This article appears in the June 2021 print issue as “The Hidden
Authenticators."

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