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BASIC KNOWLEDGE - SILICON Semiconductor materials: What is silicon?

From Simon Morrison

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The use of silicon as a semiconductor revolutionized the electronics industry and ushered in the digital age. However, many people are still unaware of the properties and uses of this all-important material. We take a close look at silicon, what it is, how it is manufactured, what it is used for, and what might lie ahead for the silicon industry.

Silicon wafers are used in almost all computers and electronic devices on the market today and are produced using a highly complex manufacturing process.
Silicon wafers are used in almost all computers and electronic devices on the market today and are produced using a highly complex manufacturing process.
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You may not be aware of it, but silicon (Si) plays a crucial role in our everyday lives. As one of the most common materials used in the manufacturing of power electronics, silicon can be found in everything from smartphones to laptop computers to microwaves and LED lights. It is no exaggeration to say that without silicon, the modern digital world as we know it would not exist.

Despite the ubiquitous nature of silicon, many people are unaware of this miraculous substance. What is silicon exactly, and why is it so important for the electronics industry? What are the pros and cons of using silicon? Are there any alternatives to silicon? How big is the silicon market and what might the future hold for silicon production and development? You will find the answers in this article!

What is silicon (Si)?

Silicon is a chemical element that is designated by the symbol Si. Sitting between metals and non-metals on the Periodic Table, silicon is a metalloid that belongs to the carbon family. Silicon has the atomic number 14, with an atomic weight of 28.086u. The melting point of silicon is 1,410 °C and it has a boiling point of 3,265 °C.

Pure silicon is highly reactive and does not exist naturally in a free state. However, silicon is most commonly found as an oxide in almost all rocks as well as, clay, sand, and soil. Oxidized silicon in the form of silicon dioxide and silicates is found in high concentrations in the earth’s crust, making up 27.7% of the crust. In fact, silicon is the second most abundant element in the crust after oxygen. Silicon compounds are found in water, in plants, and throughout the atmosphere, and are often found in the fluids, tissues, and skeletons of animals.

Silicon’s name is derived from the Latin words ‘silex’ and ‘silicis’, which mean ‘hard stone’ or ‘flint’. People have been using silica and silicates for centuries. The ancient Egyptians made glass, beads, and other items from at least 1500BC. Silicates have been found in the mortar used for construction purposes by our earliest ancestors.
The modern use of silicon began in 1824, when the Swedish chemist Jöns Jacob Berzelius was able to isolate elemental silicon, doing so in 1824. Impure silicon had already been obtained in 1811. It was not until 1854 that crystalline elemental silicon was able to be produced by using electrolysis.

Silicon was used as an alloying agent throughout the late 1800s and into the 20th century. During this time, researchers discovered that silicon was a highly effective semiconductor and had insulating properties. They found that electrical current flowed more easily in one direction between electrodes that were attached to silicon. This discovery put scientists on the path to developing semiconductor rectifiers that could convert alternating current into direct current.

However, it was not until 1954 when Morris Tanenbaum a chemist at Bell Labs was able to produce the first silicon transistor. His work was based on discoveries made by Nobel prize winners William Shockley, John Bardeen, and Walter Brattain, who first invented the transistor in 1947. The use of silicon as a semiconductor by these scientists marked the dawn of the electronic age.

The very first computer microprocessor, the Intel 4004, was developed by Intel in 1971 using innovative silicon-gate technology. This invention led to the hyper-connected digital world of today.

How is silicon manufactured?

Silicon wafers are used in almost all computers and electronic devices on the market today and are produced using a highly complex manufacturing process. Pure silicon, also known as polysilicon, is produced by first making metallurgical silicon using an electric furnace to force a reaction between quartz and coke. The metallurgical silicon is converted to trichlorosilane (TCS) using fluidized bed reactors. Hydrogen is used to purify and then decompose the TCS. The result is a poly-silicon rod. The poly-silicon rod is then crystallized which results in the production of silicon crystals or ingots. These ingots are then cut into wafers which can be used in power electronics.

It must be pointed out that the manufacturing process does result in a large number of waste materials and many toxic substances are used and produced in the manufacturing of pure silicon.

What are the unique properties of silicon?

The pure form of silicon has an atomic structure that makes it highly effective as a semiconductor. This means it has the conductive properties of metal as well as being an insulator, so silicon can conduct and block electricity. This ability makes silicon ideal as a switching mechanism. Pure silicon is highly stable, resists water, steam, and acid, and can be used to form alloys, oxides, and nitrides.

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When compared to Germanium, silicon has more stable and results in less current leakage. This is because silicon has an energy band gap of 1.12eV at 0 K. Adding impurities to pure silicon, a process that is known as ‘doping’, can further enhance its semiconducting properties.

Despite the complicated process involved in producing pure silicon, the abundance of silicon makes it an attractive material for producers of power electronics. Silicon’s highly efficient semiconducting properties and its inherent strength and stability make it a hugely versatile material.

How is silicon used?

Silicon is crucial to the power electronics industry. It is used by engineers to build switches, circuits, and gates. The many applications of purified silicon include computer chips, transistors, integrated circuits, liquid crystal displays, diodes, and much more. Silicon is also the major component of solar cells and is vital to the renewable energy industry.

Silicon in a less purified form is used to alloy metals such as steel, brass, aluminum, and bronze. Silica contained in sand and clay is used to make bricks and concrete and is often utilized as an industrial abrasive, for instance, in glass production. Silicates are used to produce glass and fabricate pottery and enamels. Polymers containing silicon are found in cosmetics and hair products. Silicone rubber is used as a sealant in the aviation and automotive industries. Silicon can be found in non-stick kitchenware, paints, and coatings, as well as a range of clothing and sporting goods.

How big is the worldwide silicon market?

According to recent reports, the global silicon market was valued at USD 6.05 billion in 2019. The market is expected to continue to grow at a compound annual growth rate (CAGR) of 4.6 % during the next decade. The global silicon market is projected to reach a value of USD 11.46 billion by 2027.

China is by far the world’s biggest producer of silicon, with over 6,000 metric tons produced in 2021. In comparison, the next two biggest producers are Russia with 580 metric tons and Brazil with 390 metric tons of silicon produced during the same period.

What is the future of silicon?

Although silicon has long been the preferred material for the power electronic industry, it is not the only substance that is suitable for semiconductors. There are alternatives being developed that could see silicon displayed as the king of semiconductors.

Silicon carbide (SiC) has been shown to be able to withstand much higher temperatures than regular silicon. SiC is a mixture of silicon and carbon and is currently being used to manufacture smaller batteries for electric vehicles. SiC has faster switching capabilities and is much more efficient in terms of energy loss than regular silicon. It is now viewed as a viable alternative to silicon. However, SiC currently has a much higher manufacturing cost when compared to silicon.

Gallium Nitride (GaN) is also touted as a replacement material for pure silicon. GaN is crated via a metal-organic chemical vapor deposition (MOCVD) process which combines gallium and nitrogen. Electrons move over GaN semiconductors incredibly quickly. It has a bandgap of 3.4 eV, Regular silicon has a value of 1.12 eV. GaN semiconductors can withstand higher temperatures and higher voltages than silicon semiconductors. The drawback to GaN semiconductors is that at present the manufacturing process is still more expensive than regular silicon semiconductors and not yet as versatile.

For now, silicon still reigns as the number one semiconductor. If better manufacturing techniques can be attained, however, the future could see materials such as SiC and GaN replacing silicon as the preferred semiconductor for the power electronics industry.

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