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Register a new userA critical analysis of models and experimental evidence of negative capacitance stabilization in a ferroelectric by capacitance matching to an adjacent dielectric layer
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We present a thorough analysis of the foundations of models of stabilization of negative capacitance (NC) in a ferroelectric (FE) layer by capacitance matching to a dielectric layer, which claim that the FE is stabilized in a low polarization state without FE polarization switching (non-switching), showing that the concept is fundamentally flawed and unphysical. We also analyze experimental evidence concluding that there is no data supporting the need to invoke such stabilization; rather, conventional models of ferroelectric polarization switching suffice to account for the effects observed. We analyze experimental evidence that at least in some of the model systems for which this effect has been claimed, categorically rule out stabilized non-switching NC. Microscopic measurements recently published as supporting non-switching stabilized NC actually rule them out, since the ferroelectric in a stack sandwiched between two dielectric layers was found to be in a mixed domain state (high polarizations within each domain) rather than in the low polarization state predicted by non-switching stabilized NC models. Nonetheless, since stabilized NC (corresponding to a minimum in free energy) is not physically impossible, it would be useful to move the research efforts to investigating scenarios and systems in which this effect is possible and expected and assess whether they are useful and practical for low power electronics.
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The pressing quest for overcoming Boltzmann tyranny in low-power nanoscale electronics revived the thoughts of engineers of early 1930-s on the possibility of negative circuit constants. The concept of the ferroelectric-based negative capacitance (NC) devices triggered explosive activity in the field. However, most of the research addressed transient NC, leaving the basic question of the existence of the steady-state NC unresolved. Here we demonstrate that the ferroelectric nanodot capacitor hosts a stable two-domain state realizing the static reversible NC device thus opening routes for the extensive use of the NC in domain wall-based nanoelectronics.
It is well known that one needs an external source of energy to provide voltage amplification. Because of this, conventional circuit elements such as resistors, inductors or capacitors cannot provide amplification all by themselves. Here, we demonstrate that a ferroelectric can cause a differential amplification without needing such an external energy source. As the ferroelectric switches from one polarization state to the other, a transfer of energy takes place from the ferroelectric to the dielectric, determined by the ratio of their capacitances, which, in turn, leads to the differential amplification. {This amplification is very different in nature from conventional inductor-capacitor based circuits where an oscillatory amplification can be observed. The demonstration of differential voltage amplification from completely passive capacitor elements only, has fundamental ramifications for next generation electronics.
Negative capacitance (NC) in ferroelectrics, which stems from the imperfect screening of polarization, is considered a viable approach to lower voltage operation in the field-effect transistors (FETs) used in logic switches. In this paper, we discuss the implications of the transient nature of negative capacitance for its practical application. It is suggested that the NC effect needs to be characterized at the proper time scale to identify the type of circuits where functional NC-FETs can be used effectively.
Integrating negative capacitance (NC) into the field-effect transistors promises to break fundamental limits of power dissipation known as Boltzmann tyranny. However, realization of the stable static negative capacitance in the non-transient regime without hysteresis remains a daunting task. Here we show that the failure to implement the NC stems from the lack of understanding that its origin is fundamentally related with the inevitable emergence of the domain state. We put forth an ingenious design for the ferroelectric domain-based field-effect transistor with the stable reversible static negative capacitance. Using dielectric coating of the ferroelectric capacitor enables the tunability of the negative capacitance improving tremendously the performance of the field-effect transistors.
The unique capabilities of capacitance measurements in bilayer graphene enable probing of layer-specific properties that are normally out of reach in transport measurements. Furthermore, capacitance measurements in the top-gate and penetration field geometries are sensitive to different physical quantities: the penetration field capacitance probes the two layers equally, whereas the top gate capacitance preferentially samples the near layer, resulting in the near-layer capacitance enhancement effect observed in recent top-gate capacitance measurements. We present a detailed theoretical description of this effect and show that capacitance can be used to determine the equilibrium layer polarization, a potentially useful tool in the study of broken symmetry states in graphene.
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