# Using Negative Capacitance and Ferroelectrics to Follow Moore’s Law

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Transistors have decreased in size over the years. Image courtesy of Benedikt Seidl

Moore’s Law, which states that the number of transistors on an integrated circuit will double about every two years, has held true since Intel’s co-founder Gordon Moore explained it in 1965. How does this affect your computer? Well, when your laptop or netbook overheats, it’s because the numerous transistors crammed in there are tiny, but still require a minimum amount of electricity to operate. All that electricity means heat, and it’s difficult to cool those components down efficiently. Basically, until we’re able to reduce the amount of electricity needed for the transistors, we’re stuck with toasty keyboards.

Luckily, Sayeef Salahuddin, assistant professor of electrical engineering and computer sciences at UC Berkeley, may have hit upon a solution. He and his team have proven that negative capacitance could hold the answers to this problem, and demonstrated the proof of principle in the September 12 issue of Applied Physics Letters.

## What are Ferroelectrics, Negative Capacitance, and Proof of Principle?

These complex-sounding terms are not as complicated as they may seem:

• What are ferroelectrics? These materials are able to hold a positive or a negative electric charge, even with no additional voltage applied. Ferroelectrics can also switch polarity, from positive to negative, when an external electric field is applied.
• What is negative capacitance? A capacitor stores energy – the amount of energy the capacitor can store is called the capacitance of the device. Negative capacitance refers to the power boost provided by combining a ferroelecric material with an insulator in the capacitor.
• What is proof of principle? Proof of principle is an important step in research. It basically means that the scientist has demonstrated that the principle in question is correct, even on a very small scale.

Professor Saleef Salahuddin

Professor Salahuddin has agreed to answer some questions about the project for Decoded Science:

Decoded Science: You’ve been working since 2008 to improve transistor efficiency – when did you first come to believe that the use of ferroelectric material held the answers?

S. Salahuddin: During my PhD, I had been working on magnets. It turns out that one can switch a magnet with low energy. I wrote a paper on this topic in 2007 (Applied Physics Letters, vol. 90, 093503, 2007)but magnets are not compatible with computing technologies. I recognized ferroelectric are analogous to magnets in terms of switching energy but are directly compatible to computers. Thus the work began on Ferroelectrics and in 2008 I published a paper predicting negative capacitance in ferroelectric materials (Nanoletters, vol. 8, No. 2, 2008).

Decoded Science: What was the first thing that went through your mind when you saw that you had achieved ‘proof of concept?’

S. Salahuddin: The proof of concept gave the confidence that the negative capacitance is more than a mere theoretical construct and could potentially find its place in modern computers. This gives us a lot of inspiration to focus our energy to the development and optimization of appropriate material systems.

Decoded Science: Can you estimate the amount of time that will pass before the benefits of your research reach consumers, whether through cooler computers or other applications?

S. Salahuddin: It is always hard to estimate such possibilities as history says that these estimates are more often than not incorrect. We are hopeful that we shall know about the critical design issues in terms of materials optimization and semiconductor integration within the next 2-3 years. However, to be ready for everyday use many other factors may become important much of which are non-scientific, e.g., the cost of introducing new materials in today’s production line, cost of the materials themselves etc. I believe that only time itself can answer this question.

Thank you to Professor Salahuddin for taking the time to share his insight!

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