Vasupradha Ramachandran
Semiconductors are materials that conduct electricity between conductors such as metal and non-conductors or insulators such as glass and ceramic. The advent of semiconductors that started in 1950 has completely downsized computing technology into smartphones and other devices by reducing the size of the electronic device in every aspect. The most commonly used semiconductor material is silicon (Si).
Being the second most abundant element and comparatively cheaper as opposed to other semiconductor materials, silicon is being prominently used semiconductor material.
Silicon’s applications
Robert Noyce, the founder of Intel alongside Geroge Moore (co-founder), invented integrated chips. Integrated chips (ICs) are single-chip made of silicon to which many transistors are etched. These ICs have made a tremendous impact in the field of electronics by paving the way for microprocessors in computers in today’s modern world.
Until lately, the size of the microscopic transistors was being reduced down to half each year. At present, the size of a transistor is 14 nanometers wide, which is 14 times wider than a DNA molecule. Given the modern digital age with fast-developing technologies like the internet of things (IoT), artificial intelligence (AI), robotics, self-driving cars and ever-developing telecommunications and the physical limitations of silicon-based ICs, what would be the future of silicon?
Moore’s law
Geroge Moore, in 1965 came up with a law that states about the performance of the computer (“The speed of capacity of the computers can be expected to double every two years, as a result of an increase in the number of transistors a microchip can contain.”) Now the estimated time of 24 months came down to 18 months and it is expected to be gradually decreasing only.
What is after silicon?
Stephen Doran, the CEO of compound semiconductor applications catapult anticipates that silicon has reached its limit for performance in several applications that require increased speed, reduced latency and light detection. According to Statista, it is found that 17,600 million square inches of silicon will be shipped globally between 2021 and 2025. This report makes it evident that Moore’s law could hold up its potential until at least 2025. But it is also important to find a suitable alternative to replace silicon.
With technologies like artificial intelligence, the machine will be capable of learning and adapting itself in the future. This makes it essential for the computational processes to be more powerful and more agile. It is more likely that chip manufacturing would create a new revolution in the era of computing. Below are some of the potential replacements for silicon chips that can increase the performance of computing capabilities.
Compound semiconductors
Compound semiconductors are semiconductors that are made from two or more elements. The next generation of compound semiconductors will be a combination of two elements whose combined properties could make it more faster and efficient than silicon.
Though silicon has various advantages like in terms of availability, good physical properties and stable oxide (SiO2), which is a good insulator, silicon has its own drawbacks.
Combining more transistors into a single chip will enable an IC to process information faster. This increase in the speed with an increase in the number of transistors depends on how easily the electrons can move within the semiconductor material. This motion of electrons within the semiconductor material is known as electron mobility. The electron mobility is fairly high in silicon but not as high as other semiconductor materials like gallium arsenide and indium antimonide.
In terms of conducting properties of electrons, it is not simply based on electron mobility but also the movement of electron holes. Modern integrated chips are based on a technique called complementary metal-oxide-semiconductor (CMOS) which uses a couple of transistors. Here, one transistor uses electrons while the other uses electron holes.
The mobility of electron holes in silicon is very poor and acts as a barrier to increase the performance of an IC. This challenge can be addressed by doping germanium with silicon.
The most important drawback of silicon is that its performance decreases so much at high temperatures. Today’s computers with high-performance capabilities are known for generating a considerable amount of heat to an extent that there are several cooling methods involved. In scenarios like this, silicon semiconductors can be replaced with gallium nitride (GaN) and silicon carbide (SiC).
The use of compound semiconductors can increase the speed, performance and efficiency of IC chips. One of the most well-known types of compound semiconductors is an III-V compound semiconductor that contains indium in the form of indium arsenide and indium antimonide. Compound semiconductors are already being used in lasers, LED lights and displays and solar panels where silicon failed to function efficiently.
Quantum computers
Quantum computers are computers that perform calculations based on quantum mechanics (the behavior of particles at subatomic levels) like quantum entanglement and superposition principle.
Today’s computers manipulate data in binary format, that is, as 0s and 1s. Whilst, quantum computers are not confined within the limitations of binary states. These quantum computers can manipulate data in the form of qubits or quantum bits that exist in superposition, the state where the data is in neither of the binary states (0 and 1). These qubits can be atoms, photons or electrons in their respective devices that can act as computer memory and processor. This superposition of qubits provides inherent parallelism to quantum computers where the quantum computer can work on numerous (millions) calculations at the same time while ordinary computers can perform one calculation at a time. These qubits are massively faster and powerful than silicon transistors. Hence they can be used in place of silicon transistors where huge amounts of data have to be manipulated frequently.
Graphene
Graphene, a material based on carbon, has been discovered in 2004. The two-dimensional layer of graphite in the perfect hexagonal layout is called graphene. This immensely strong material possesses both thermal and electrical properties. Though graphene is highly abundant in nature, it will take many years for it to come out to the market for commercial applications.
One of the biggest drawbacks of graphene is that it cannot act as a switch while silicon-based semiconductors can be switched on or off by passing electric current through. This means that graphene-based computers can never be turned off. Graphene and carbon nanotubes are still pretty new to this field, while silicon-based semiconductors have been used for a few decades now.
If graphene potentially replaces silicon in the future, then new methods have to be developed to overcome the challenges associated with graphene-based semiconductors.
Compound semiconductors, quantum computers and graphene are potential replacements for silicon but with their own merits and demerits. Despite the physical limitations, silicon-based electronics have proved to be much more adaptable and available at lower costs. It is impossible to completely replace silicon, at least for a while. But if it has to be replaced, then, there are no clear ideas as to how it can address the challenges of each potential replacement of silicon yet.
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