Crystals and electronics

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From an electric guitar to the axial tomograph in the hospital, from the personal computer to video consoles, all current electronic devices work thanks to the properties of crystals. You’ll find semiconductor crystals in chips; piezoelectric crystals in electronic watches, microphones and loudspeakers; pyroelectric crystals in thermographs and alarm systems; and liquid crystals in the displays of mobile phones and televisions. And you’ll find crystals such as graphene or quasicrystals in the materials of the future.

Do you know what crystalline properties are used for this technology? Can you guess how many products that you use every day work thanks to crystals? Would you like to learn how crystals are obtained in industry?

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Silicon chip inside a microprocessor. Monocrystalline silicon wafer with etched electronic chips.

Inside every one of the small chips that make our electronic devices work is a tiny sheet of semiconductor crystal with minute circuits etched on the nanoscale that integrate between several hundred and several million electronic components. The crystalline properties of semiconductors in crystalline state make their functioning possible.

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It is highly likely that your mobile phone is equipped with an LCD screen. The acronym stands for “Liquid Crystal Display” and its working is indeed based on the light modulation properties that liquid crystals, being crystals, possess. Another screen technology is LED (“Light Emitting Diode”). In this case the image is formed by the light emitted by each pixel, which is a tiny diode of semiconductor crystal. LEDs are more and more present in everyday life, and not only in television screens and mobile phones, but also in advertising boards and even the lamps in our homes.

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Telephones are increasingly equipped with sensors that make them “smarter”. They are commonly equipped with compasses, gyroscopes or accelerometers that enable them to know their orientation and movements. In time, other sensors (temperature, humidity, pressure…) will be incorporated. The technology of MEMS allows micro-manufacturing upon crystalline bases of mechanical, thermal, optical and fluidic structures, together with the electronics necessary for its operation.

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All digital electronic devices (including the mobile phone) use one or more clocks to set the pace of the electronic circuitry and synchronise their operations. This clock is typically a resonance circuit based on the piezoelectric effect of a quartz crystal. In fact, the corresponding electronic component is colloquially called “crystal” and is the same found in wristwatches, computers, radios and a near-infinity of other electronic devices. The same phenomenon of piezoelectricity is also used to make other devices work, such as microphones and telephone speakers, pickups for musical instruments, sonar and medical ultrasounds.

As well as electronic and mechanical, other properties of crystals are at the basis of current technologies, such as the laser or the components of non-linear optics that enable us to generate or manipulate beams of light.

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Solar energy uses silicon crystals, among other materials, and its future depends in large part on finding the cheapest way to produce compound III-V crystals.

Did you know that…

  • The silicon we build our electronic circuits with is the seventh element in the universe and the second most abundant on the Earth. Approximately a quarter of the Earth’s crust is silicon.
  • As might be expected, the semiconductor manufacturing industry is very broad and competitive. In 2013, global sales exceeded 300 billion dollars.
  • In an LCD, the electric current is used to transform segments of liquid crystal from a transparent phase to an opaque one. These segments, typically in the form of dots or pixels, are individually modified to block or let through the polarised light, generating light or dark points on the screen.
  • In all LCDs, the liquid crystals are confined between two pieces of transparent glass or plastic, but not any plastic will do. If the glass or plastic has too much sodium or other alkaline ions, they will move to the surface, where any humidity will modify the pattern of the electric field and therefore the alignment of the liquid crystal. To prevent this, LCD manufacturers use borosilicate glass or apply a coating of silicon dioxide to the glass or plastic.
  • The dimensions of MEMS devices vary from less than a micron to a few millimetres. The types of MEMS also vary a lot, from relatively simple structures without moving parts to complex electromechanical systems with multiple moving parts controlled by integrated microelectronics.
  • Many MEMS microsensors have shown superior performance to traditional devices with the same function. The miniaturised version of a pressure sensor, for example, is normally more sensitive than the best macroscopic versions of comparable sensors.
  • The structure of an optical crystal used to amplify laser emission determines its optical properties and its resistance to damage by radiation. Therefore the development of lasers with specific applications depends critically on the definition of this structure and on the methods needed to grow crystals with this structure.

To find out more

  • You can learn more about nanocrystals on Wikipedia. There are also several videos on the subject on YouTube, such as “A Journey to the Nanoworld”.
  • The electronic chips that make all our electronic devices work are based on semiconductor crystals. On Wikipedia you can find out more about semiconductors. If you are interested in how semiconductor crystals are manufactured and how the chips are made on these crystals, you can find plenty of mini-documentaries on YouTube, such as “How do they make Silicon Wafers and Computer Chips?
  • Wikipedia also contains abundant additional information on liquid crystals. A quicker introduction is the YouTube video: Liquid Crystals – Chalk Talk.
  • The clocks of the vast majority of electronic devices are based on piezoelectric crystals. On Wikipedia you can learn more about piezoelectricity.

 

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