ON THE IMPOSSIBILITY OF A STABLE NEGATIVE CAPACITANCE REALIZATION IN MOSFET TRANSISTORS WITH INSULATORS BASED ON THIN LAYERS OF DIELECTRIC AND FERROELECTRIC

We consider a silicon MOSFET, in which the gate insulator is formed from thin layersof a dielectric SiO2 and a weak ferroelectric HfO2. We study the possibility of implementing a stablenegative capacitance of the insulator in such a system, which would open the principal possibility toreduce the subthreshold swing to the values below the threshold, 60 mV/decade at room temperature,and supply voltage to the values below the fundamental Boltzmann limit, 0.5 V, which would bean important step towards further miniaturization of MOSFETs. It is shown theoretically that it ispossible to achieve a transient negative capacitance of a ferroelectric in the situation when the chargeat the capacitor plates increases more slowly than the ferroelectric polarization. Note that the negativecapacity is fundamentally transient. Its temporal stabilization in thin dielectric and ferroelectric layersrequires stable positive free energy and capacity of the whole system. Therefore, the effect of thenegative capacitance of a ferroelectric itself cannot be manifested “outside” the ferroelectric, includingthe transistor applications.