Schematic comparing flexoelectric actuation and piezoelectric bimorph actuation in nanoscale actuators.
They have found that, at the nanoscale, the desirable attributes of flexoelectricity are maintained, while the figure of merit (bending curvature divided by electric field applied) of their first prototype is already comparable to that of the state of the art piezoelectric bimorph cantilevers. Additionally, the universality of flexoelectricity implies that all high-k dielectric materials used currently in transistor technology should also be flexoelectric, thus providing an elegant route to integrating “intelligent” electromechanical functionalities within already existing transistor technology.
The information revolution is synonymous with the traditional quest to pack more chips and increase computing power. This quest is embodied by the famous “Moore’s law,” which predicts that the number of transistors/ chip doubles every couple of years and has held true for a remarkably long time. However, as Moore´s law approaches its limit, a parallel quest is becoming increasingly important: nick-named “more than Moore,”. It aims to add new functionalities (not just transistors) within each chip by integrating smart materials on top of the ubiquitous and still indispensable silicon base.
Experimental design.
Among these so-called smart materials piezoelectrics stand out for their ability to convert a mechanical deformation into a voltage or, conversely, generate a deformation when a voltage is applied to them (which can be used, for example, in piezoelectric fans for cooling down the circuit). However, the integration of piezoelectricity with silicon technology is extremely challenging. The range of piezoelectric materials to choose from is limited, and the best piezo electrics are all lead based ferroelectric materials, and their toxicity poses serious concerns. Moreover, their piezoelectric properties are strongly temperature-dependent, making them difficult to implement in the hot environment of a typical computer processor, whose junction temperature can reach up to 150C.
There exists, however, another form of electromechanical coupling that allows a material to polarize in response to a mechanical bending moment, and, conversely, to bend in response to an electric field. This property is called “flexoelectricity,”. At the nanoscale at least, flexoelectricity can be as big as or bigger than piezoelectricity; this is easy to understand if we consider that bending something thick is very difficult, but bending something thin is very easy. In addition, flexoelectricity offers many desirable properties: it is a universal property of all dielectrics, ie one needs not use toxic lead-based materials, and flexoelectricity is more linear and temperature-independent than the piezoelectricity of a ferroelectric http://www.alphagalileo.org/ViewItem.aspx?ItemId=158527&CultureCode=en http://dx.doi.org/10.1038/nnano.2015.260
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