Ferroelectric differential capacitance affected by stresses and strains and implications for use in electronic devices

Abstract

There has been a continuing interest in finding ways to shrink the dimensions of electronic devices, especially active devices like transistors, down to become compatible with the ever decreasing size scales, using fabrication processes such as at Intel, with the trend toward 10 nm. Eventual gate length in MOSFETs is roughly half this dimension. This had been one of the (not the only one) of interests in using ferroelectric (FE) materials in the gate of FETs, for example, when the FE material displays a negative polarization effect. Such ideas as escaping the Boltzmann tyranny have loomed large, regarding the subthreshold voltage, and have motivated this interest. It is generally understood that for stable, steady state operation of devices typical of microwave and millimeter wave electronics, no negative differential capacitance is possible with conventional thinking. However, it may be possible, perhaps in transient regions of the hysteretic curve, with strain engineering of materials, to obtain some if not all elements of the differential capacitance tensor which are negative. The analysis is based upon analyzing the physics using thermodynamic phenomenological free energy.