Strained Graphene Field-Effect Transistor - Nano-electro-mechanical transistors for low power applications and locally adjustable electronic properties

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For future energy autonomous systems a novel class of switches is needed that provide almost zero stand-by power consumption and that can be operated at very small voltages. In this respect, nano-electro-mechanical systems (NEMS) have attracted a renewed interest: nanoscale relays based on the deflection of nanoscale beams using an electric field are currently being considered as candidates for ultra-low power switches since they exhibit an extremely low off-state leakage and abrupt turn-on characteristics. However, since in NEMS switches a solid beam is forced into mechanical contact with the drain electrode, they are prone to serious reliability issues including beam stiction and contact degradation. Moreover, NEMS switches to-date require very large voltages to provide sufficient electrostatic attraction and exhibit large hysteresis effects. In an alternative NEMS device concept - the suspended gate FET - the beam is capacitively coupled and thus many of the issues related to NEMS relays are avoided. However, the suspended gate FET also exhibits a large hysteresis and substantial gate voltages are required, too. In the current proposal we will fabricate and investigate nano-electro-mechanical switches that combine CMOS reliability, CMOS on-state currents with significantly lower off-state leakage currents compared to conventional CMOS, exploiting the piezo-electric properties of graphene nanoribbons. Field-effect induced actuation and the field-effect itself act on the conduction and valence bands of a graphene nanoribbon employing a moving and a fixed gate electrode resulting in an energetic movement of the conduction/valence bands as in a conventional FET and a modification of the band gap at the same time. As a result, such a device - called nano-electro-mechanical strained graphene FET (NEMSGFET) in the following offers superior switching behavior. Due to the combination of a suspended mechanical gate and a fixed electrostatic gate, in the NEMSGFET (in contrast to the suspended gate FET) the mechanical gate can adjust a certain strain state while the electrostatic gate is used for transistor functionality. This can be used e.g. for analog applications or, if a permanent strain state is achieved due to stiction of the moving gate, several different band gaps can be realized in close proximity on the same chip for e.g. multi-valued logic or in for the realization of nanoscale spectrometers.