Justin Wong and Sayeef Salahuddin

EECS Department, University of California, Berkeley

Technical Report No. UCB/EECS-2015-57

May 11, 2015

http://www2.eecs.berkeley.edu/Pubs/TechRpts/2015/EECS-2015-57.pdf

A thermodynamic model was constructed to analyze the negative capacitance effect in the presence of piezoelectricity. The model demonstrated that while piezoelectricity can lead to negative capacitance in principle, it is not strong enough in practice due to the unphysical amounts of charge and strain required. The inclusion of higher-order electromechanical coupling such as electrostriction can make the negative capacitance region accessible at a lower amount of charge. However, the required strains are still unphysical on the order of tens of percent. Furthermore, the material must possess a negative electrostriction coefficient, or else the negative capacitance effect will be suppressed by positive electrostriction. Most commonly used oxides, however, possess positive electrostriction coefficients. Finally, piezoelectricity, electrostriction, and ferroelectricity were analyzed together to show that a negative capacitance effect occurs but due to ferroelectricity and not piezoelectricity. The model ultimately demonstrates that for all practical purposes, pure electromechanical coupling is not strong enough to provide a negative capacitance effect.

Advisors: Sayeef Salahuddin

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BibTeX citation:

@mastersthesis{Wong:EECS-2015-57,
    Author= {Wong, Justin and Salahuddin, Sayeef},
    Title= {Piezoelectric Negative Capacitance},
    School= {EECS Department, University of California, Berkeley},
    Year= {2015},
    Month= {May},
    Url= {http://www2.eecs.berkeley.edu/Pubs/TechRpts/2015/EECS-2015-57.html},
    Number= {UCB/EECS-2015-57},
    Abstract= {A thermodynamic model was constructed to analyze the negative capacitance effect in the presence
of piezoelectricity. The model demonstrated that while piezoelectricity can lead to negative
capacitance in principle, it is not strong enough in practice due to the unphysical amounts of charge
and strain required. The inclusion of higher-order electromechanical coupling such as electrostriction
can make the negative capacitance region accessible at a lower amount of charge. However,
the required strains are still unphysical on the order of tens of percent. Furthermore, the material
must possess a negative electrostriction coefficient, or else the negative capacitance effect will be
suppressed by positive electrostriction. Most commonly used oxides, however, possess positive
electrostriction coefficients. Finally, piezoelectricity, electrostriction, and ferroelectricity were analyzed
together to show that a negative capacitance effect occurs but due to ferroelectricity and
not piezoelectricity. The model ultimately demonstrates that for all practical purposes, pure electromechanical
coupling is not strong enough to provide a negative capacitance effect.},
}

EndNote citation:

%0 Thesis
%A Wong, Justin 
%A Salahuddin, Sayeef 
%T Piezoelectric Negative Capacitance
%I EECS Department, University of California, Berkeley
%D 2015
%8 May 11
%@ UCB/EECS-2015-57
%U http://www2.eecs.berkeley.edu/Pubs/TechRpts/2015/EECS-2015-57.html
%F Wong:EECS-2015-57