The Olden Days
Previously, light production in semiconductors suffered
from several problems, including:
Inability of standard silicon-based processes to produce
light directly. The vast majority of chips that are
produced today use standard silicon technology and
suffer from the lack of light emitting devices.
Functional light emitting devices in production use
exotic and non-silicon materials to produce light. These
materials are not compatible with the production of
highly integrated devices -- such as microprocessors --
due to cost and yield issues that cannot be cost
effectively eliminated.
What’s the future hold?
The production of light in a standard CMOS process is a
fundamentally disruptive force in the semiconductor
industry. Light emission technologies will transform the
current semiconductor integrated circuit market for
decades to come. By bridging the growing gap between the
massive computing power of leading-edge microprocessors
and the ability to quickly move data on and off chip,
Advanced Plasmonics’ technology will support both current
and future generations of integrated circuits.
With speeds more then a thousand times faster than
conventional on-chip wiring, Advanced Plasmonics’
optical-based technology will support data rates
substantially higher than those achieved by current
copper interconnect technologies used in today’s
integrated circuits. Advanced Plasmonics’ technology
enables these massive data rates through light emission
devices that are directly interfaced to and between
integrated circuits, printed circuit boards, and local
area networks. This massive increase in available
bandwidth will create new and unprecedented applications
by bringing optics-based data communications to the chip
and “desk-top”. In addition, there is also the potential
to use light for future intra-chip transport of signals
and clocks within a single CMOS silicon integrated
circuit. This can possibly “tame” one of the most
demanding aspects of modern chip design – clock skew.
Enter Advanced Plasmonics. Advanced Plasmonics’ technology is a departure from other
nano-technologies. Standard large volume production CMOS
lithography is used to manufacture active CMOS circuits
and nano-structures on a single silicon substrate..
Advanced Plasmonics’ technology generates light using
nano-antennas that radiate photons.
Unlike LEDs (light emitting diodes) primarily used for
displays and/or illumination, PEDs (Plasmon Enabled
Devices) are easier to manufacture and are more
efficient.
Surface Plasmons
Ok, so what is a plasmon? Plasmons are a physics
phenomenon based on the optical properties of metals;
they are represented by the energy associated with
charge density waves propagating in matter through the
motions of large numbers of electrons. Electrons, in a
metal, screen an electric field. Light of a frequency
below the plasma frequency is reflected. Electrons
cannot respond fast enough to screen above the plasma
frequency, and so such light is transmitted. Most metals
tend to be shiny in the visible range, because their
plasma frequency is in the ultraviolet. Metals such as
copper have their distinctive color because their plasma
frequency is in the visible range. The plasma frequency
of doped semiconductors is generally in the infrared
range.
Those plasmons that are confined to surfaces and which
interact strongly with light are known as surface
plasmons. The interface between a conductor and an
insulator is where surface plasmons propagate; bound to
the surface between the two, they exponentially decay
into both media.
Plasmons have a variety of potential uses. Plasmon wires
can be much thinner than conventional wires, and could
support much higher frequencies, so plasmons have been
considered as a means of transmitting information on
computer chips. The extremely small wavelengths of
plasmons mean that they could be utilized in high
resolution lithography and microscopy. Surface-plasmon-based
sensors find uses in gas sensing, biological
environments such as immuno-sensing and electrochemical
studies; they are currently commercially available in
some of these applications.
Metallic nano-particles exhibit strong colors due to
plasmon resonance, which is the phenomenon that gives
stained glass its color. The strong pure colors of
medieval stained glass windows are sometimes ascribed to
the impurities of the glass. However, metals or metallic
oxides are what actually give glass color: gold gives a
deep ruby red; copper gives blue or green, iron gives
green or brown, and so forth. Plasmons on the surface of
the gold nano-particles (i.e. at the interface with the
glass) move such that they absorb blue and yellow light
but reflect the longer wavelength red to give the glass
a characteristic ruby color; the same is true of the
other metals/ metal oxides, insofar that they
selectively absorb some wavelengths, but reflect others.
Building Plasmon Enabled Devices
In addition to the fundamental plasmon breakthroughs,
Advanced Plasmonics has accomplished significant
technical milestones relating to its light emitting
technologies.
Emitter Devices:
- Designed, fabricated, and tested light-emitting plasmon
devices.
- Shown that different and multiple modes can be achieved
in one device at the same time.
- Built multiple frequency devices on one chip at the same
time, and in the same layer
- Showed that devices can be built that emit
selective frequencies of light
- Tested emitter switching speeds at 130MHzMEM, limited
only by readily available, commercial, detectors.
- Developed a comprehensive understanding of
theory/design/test/fabrication for its light emitting
devices
- Developed frequency-related design rules for
development, design, and manufacturing of its light
emitting technologies
Summary
The production of light emission technologies in a
standard CMOS process offers the promise to transform
the semiconductor integrated circuit market for decades
to come. Advanced Plasmonics technology will support both
current and future generations of microprocessors and
will reduce the growing gap between the ever-increasing
computing power of leading-edge microprocessors and the
inability to quickly move data on and off chip.
Appendix: Brief Overview of Light Generation
In addition to incandescent lights, where the light is
produced by electrical heating of a tungsten filament,
there are other sources of light. Fluorescent lights
contain low pressure mercury vapor in a glass tube which
has electrodes at each end. When a current is Advanced
across the electrodes, the electrons collide with and
ionize the mercury vapor. The ionized mercury vapor
emits some light in both visible and ultraviolet ranges.
The visible light is emitted directly, while the
ultraviolet light is absorbed by the phosphor and
re-emitted as visible light. Because a greater fraction
of the energy is consumed by light production rather
than heating, fluorescent lights are more efficient than
incandescent lights. The inside of the glass is coated
with a phosphor, a material that is fluorescent.
Phosphors absorb high-energy photons, and emit the
light as lower energy photons; i.e., they absorb light
in the ultraviolet range, and re-emit it as visible
light. This can be explained by the fact that some of
the electrons of the phosphor do not immediately drop
all the way to their ground state, but drop to an
intermediate state before dropping to ground state.
The second type of light is a sodium or neon-type light.
These are filled with a particular gas at low pressures.
Electric current passed through the gas causes electrons
of the individual gaseous molecules to jump to higher
energy states. They then decay to their normal state,
emitting light of a characteristic wavelength: sodium
lights are yellow, neon is red, and so on. Some
elements, like sodium, give a single, very intense line
when the light is passed through a prism to separate the
colors (sodium lamps are 6-8x more efficient than
incandescent lamps, because their light is a single
frequency rather than the mixture found in incandescent
lamps). Other elements, such as helium or neon, give a
series of lines when the light is passed through a
prism, some of which are in the ultraviolet region; the
characteristic color of these gases is determined by the
combination of the relative intensities of the various
bands.
LED (light emitting diode) technology has made recent
gains beyond basic display applications to achieve use
in low-end illumination applications (flashlights,
automobile tail lights, etc.), but with great
improvement in reliability over prior filament-based
lamps. Economies of scale have continued to make the
technology increasingly affordable. The basic mechanism
of light emission in LEDs is the combination of
electrons and holes to generate a photon. Because
electrons must move through the semiconductor material,
energy is lost as electrons collide with the bulk of the
material.
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