Quantum Tunneling And The Semiconductors’ Struggle in the Miniaturization Race

7 min readJun 2, 2023

Introduction:

In the ever-evolving landscape of technology, the demand for smaller and faster computing devices continues to grow. However, as we push the boundaries of miniaturization, an unavoidable challenge emerges:
‘the phenomenon of quantum tunneling’.

This article dives into the basics of quantum computing and sheds light on the persistent issue that semiconductor-based devices have in handling electron transfers at such minuscule scales.

What's a semiconductor?

Simply put a semiconductor is a special material that can control the flow of electricity. It is used in electronic devices to process and store information. Examples of these semiconductors include ‘transistors’ and ‘integrated circuits’ (IC’s).

Transistors are essential semiconductor devices that play a vital role in modern electronics. They serve as electronic switches or amplifiers, controlling the flow of current within a circuit.

The semiconductor material used in transistors can be doped to create different types: P-type and N-type. Doping involves intentionally introducing impurities for the purpose of modulating its electrical, optical and structural properties (it’s crystal structure).

In a N-type semiconductor, the majority of charge carriers are ‘free electrons’ whereas the ‘holes’ are in the minority.

N-type semiconductors provide regions where negative charge carriers (electrons) can move.

In a P-type semiconductor, the majority of charge carriers are ‘holes’ whereas the ‘free electrons’ are in the minority.

P-type semiconductors have ‘holes’ that can be filled by electrons.

By combining N-type and P-type materials, we can control the flow of electric current in electronic devices like transistors and diodes.

Understanding the issue:

To first understand where the issue lies, we first need to know the premise of ‘Moore’s Law’.

Moore’s Law, is the prediction of the exponential increase in the number of transistors on a chip doubling approximately every two years.

For instance in 1970, transistors were approximately 12,000 nm wide. However, with advancements in semiconductor technology, the size of transistors has steadily decreased.
In 2022, IBM unveiled the world’s first chip built on a 2nm process node.
This is a substantial reduction in transistor size.

Judging by the graph and considering that Moore’s Law is a prediction, we see it’s reaching a plateau. The ability to shrink half its size on the 2 year increment is getting smaller and smaller. We see this by the cluster of plots at the top of the graph.

Some engineers and scientists argue that Moore’s Law is slowly becoming irrelevant due to this, however, we can still logically suspect that semiconductors will shrink past the 1nm range. I will expand on this idea further on in the article…

As transistors and other semiconductor devices continue to shrink to sizes of atoms, we enter the realm of the quantum world. Here, we encounter an increasingly significant phenomenon known as “quantum tunneling”.

What is quantum tunneling?

Imagine you have a ball, and there’s a wall in front of you. In classical physics, if you throw the ball towards the wall, it will either bounce back or stop at the wall because it doesn’t have enough energy to go over it. This is what we would expect to happen in our everyday experience.

In scientific terminology. If the ball doesn’t have enough kinetic energy to get over the potential energy of the hill, it will never get over. Ever.

However, at the quantum level, things work differently. In quantum mechanics, particles like electrons can behave like waves.

This is due to the ‘wave-particle duality’ principle. It explains that every particle (in our case electron’s) may be described as either a particle or a wave.
At the quantum level, the exact location of a particle becomes indeterminable. To account for this, we employ a wave-like representation to determine its probabilistic whereabouts. This representation is known as a ‘wavefunction’, a mathematical entity that describes the probability distribution of finding the particle in various states or locations.

In it’s wave-like nature these electrons can do something called “tunneling”. This means that they can pass through barriers that, classically, they wouldn’t have enough energy to overcome.

Quantum tunneling occurs when a particle’s wavefunction, described by the Schrödinger equation, is not required to be zero inside a barrier, allowing it to pass through the barrier.

What does this all mean for Transistor’s?

Earlier I mentioned I would be referring to transistors for the duration of this article…

‘Transistors’ are miniature semiconductor like switches that control the flow of electricity. They use the presence or absence of electrons to represent and manipulate information in electronic circuits.

This means electrons can just pass through the transistor thus bypassing it’s switch-like nature.

The increasing prominence of quantum tunneling introduces unwanted current leakage.

What is leakage?

In semiconductor devices, leakage refers to the phenomenon where charge carriers (electrons or holes) pass through an insulating region, which is influenced by quantum tunneling. As the insulating region becomes thinner, leakage increases exponentially. Tunneling leakage can also happen at semiconductor junctions between heavily doped P-type and N-type semiconductors.

Additionally, carriers can leak between the source and drain terminals of a Metal Oxide Semiconductor (MOS) transistor, known as ‘subthreshold’ conduction. The main cause of leakage occurs within transistors, but electrons can also leak between interconnects.

Leakage results in higher power consumption and potential circuit failure.

Mitigation. Enter Quantum Computing:

While there are many developing mitigation possibilities like ‘Tunnel Diodes’.

For this post I want to shed light on the ever-more present alternative computing technologies being explored beyond the traditional semiconductor-based devices…

Quantum computers leverage the inherent properties of quantum particles, such as quantum tunneling, superposition and entanglement, to perform computations.
Quantum computers have the potential to overcome the limitations posed by quantum tunneling and offer new possibilities for computing power and efficiency.

With new heightened levels, I believe in the potential for techniques like…

Quantum Error Correction, ensuring the reliability and stability of quantum computations.
There is a lot of research done by Google, D-Wave and IBM on error correction and the race to develop the most autonomous error detection systems are being developed here!
I aim to write more on Quantum Error Correction in thorough detail at a later date.

(Note, as of June 2023: I understand there is many more organisations and research centers than the listed above that research in quantum computing, however according to my research as of the June, the listed organisations/companies/institutions have the most public documented reports in this specific field)

Quantum Sensing, can provide more accurate measurements of important properties in semiconductor devices, such as current flow, charge density, and electric fields.
Quantum Simulation, by modeling the quantum state of electrons and the semiconductor structure, we can simulate and study the tunneling process. This helps us analyze its impact on device performance.

If your interested in the intricate details of mitigation for leakage in this niche. Google Quantum AI have a very informative and in detailed video that can be found here.

Moore’s Law no more?, welcome, Rose’s Law:

So should we see semiconductors become even smaller?, yes.
However it will be slow, for now.

Affluent to ‘Moore’s Law’, I want to introduce…

‘Rose’s Law’, the prediction of the doubling of qubits every two years.
‘Qubits’, or quantum bits, are the fundamental units of information in quantum computing. Unlike classical bits that can represent either 0 or 1, qubits can exist in a superposition of both states simultaneously. (I will not be explaining on this for my sanity)

All this newly developed research point towards the highly anticipated growth of quantum computing. As we see the semiconductor shrink, we should suspect that error detection should play a crucial part in the mitigation of the leakage phenomenon.

Conclusion

As semiconductor devices continue to shrink in size, the challenges posed by quantum tunneling become more and more pronounced. We see the issue of current leakage influence and reduce the reliability of the semiconductor’s performance thus resulting in poor-performing or none-performing chips.

Ongoing research and development efforts are focused on mitigating these effects through quantum computing technologies, would be very interesting and points towards suitable reliability testing.
Addressing the impact of quantum tunneling is crucial for the continued advancement of semiconductor-based technologies and the realization of more powerful and efficient electronic devices.

Personal Note:

I am still a novice in this very fascinating and world changing field, I thought writing down small articles documenting my research can help me personally learn and understand this fascinating topic.

This is my first public article written on Medium and article written documenting my learning journey in the world of engineering and science. I appreciate anyone who took time out of there day to read my article on this very interesting phenomenon and it’s exciting future.