University of Twente Student Theses


The theory of the Negative-Capacitance-FETs gate-stack.

Wigchering, R. (2017) The theory of the Negative-Capacitance-FETs gate-stack.

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Abstract:In society, portable electronics are getting more and more important. Not only the technology in mobile communication devices, but also in sensing in construction or the human body, for example. An important parameter in portable electronics is the energy consumption. In some applications battery-lifetimes of several years may be needed and this calls for low power electronics. For years, engineers reduced the size of transistors, the building blocks of modern technology, allowing for a lower supply voltage of processors or microcontrollers and therefore, reducing the energy consumption. However, improving the energy efficiency by size reduction has reached a limit and new infinitive ways have to be found. A ferroelectric material can in certain conditions show negative capacitance. This effect can be used to amplify a voltage, for example the gate voltage of a transistor. If the voltage inside a transistor can be amplified, it can be driven with a lower supply voltage, reaching the goal of energy consumption. But before ferroelectric based transistors can be made, its parameters as, voltage amplification, capacitances, stability conditions and work functions have to be analyzed. In this study, a 1-D analysis is done on Metal-Insulator-Metal (MIM) and Metal-InsulatorMetal-Insulator-Metal (MIMIM) structures, where the insulator is a ferroelectric or a conventional dielectric. This is done mostly analytical but at some point a numerical tool has to be used. It is all based on theory and is aimed at giving basic insight into the operation of ferroelectrics. It is shown that a negative capacitance ferroelectric capacitor can be stabilized by placing a smaller conventional capacitor in series. This results in a higher total capacitance and voltage amplification between the two capacitors. It is shown that in a Metal-FerroelectricMetal-Oxide-Semiconductor-Field-Effect-Transistor (MFEMOSFET) the work function of the second metal has no influence in the operation of the transistor and can therefore be chosen to what suits best to the technology. Furthermore, to have voltage amplification inside the channel the capacitance of the oxide has to be larger than the capacitance of the ferroelectric. This may give rise to stability problems and therefore, a recommendation for another design is made.
Item Type:Essay (Bachelor)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:53 electrotechnology
Programme:Electrical Engineering BSc (56953)
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