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Wednesday, 04 February 2015

Negative capacitance detected

Prof Gustau Catalan has published in Nature Materials a “News and Views” commenting the measurement of negative capacitance presented by the teams led by Prof Sayeef Salahuddin and Prof. Ramesh in the same magazine. The study detects the phenomenon in ferroelectrics, a field in which ICN2 treasures significant expertise.

Prof Gustau Catalan, ICREA Research Professor and Group Leader at ICN2, together with Prof David Jimenez from UAB and Prof Alexei Gruverman from University of Nebraska, have released in Nature Materials a News and Views article about the detection of negative capacitance and its uses. The article’s starting point is the research led by Prof Sayeef Salahuddin, from University of Berkeley (USA), where a way to measure the phenomenon is proposed for the first time (Nature Materials).

Prof Catalan’s Oxide Nanoelectronics Group, has ferroelectricity as one of its main research lines. In the article, the three authors make a brief explanation about what negative capacitance is and how Prof Salahuddin’s Group have come to detect it. Negative capacitance in ferroelectric materials had only been predicted theoretically until now. Ferroelectrics switch their polarization when a certain critical voltage is reached. This causes an enormous and sudden accumulation of bound charge at the material’s surface that can momentarily exceed the free charge supplied to the electrodes by a power source. If a resistance is placed between the electrodes and the charge supplied by the external voltage is slowed down, it can be detected for a while a decrease in voltage across the ferroelectric while the charge is still increasing. Consequently, the capacitance (charge divided by voltage) has a negative value.

Catalan, Jimenez and Gruverman discuss the advantages that its use could suppose for designing new electronic devices, and specifically ultra-efficient transistors. However, they also emphasize that there is still a great distance from the (important) proof of concept by Salahuddin et al. and the actual implementation in practical devices, due to the existence of many subtle problems that emerge when ferroelectrics are put in contact with semiconductors.


Article Reference

Catalan G, Jimenez D, Gruverman A. Negative capacitance detected. Nature Materials 14, 137–139 (2015) doi:10.1038/nmat4195