RESUMEN
Second harmonic generation (SHG) and frequency mixing of electrical signals are fundamental for a wide range of radiofrequency applications. Recently, ferroelectric field-effect transistors (FeFETs), made from ferroelectric hafnium oxide (HfO2), have demonstrated promising SHG capabilities because of their unique symmetric transfer curves. In this paper, we illustrate how this symmetry is highly sensitive to material properties by varying the thickness of the ferroelectric layer and the doping of the silicon substrate. We show that the SHG conversion gain and the spectral purity are greatly increased (up to 96%) by precisely tuning the ferroelectric polarization reversal and the quantum tunneling currents. Based on this, we propose and experimentally demonstrate the generation of the difference and of the sum of two input frequencies (frequency mixing) with a single FeFET, which we attribute to the inherently strong quadratic component of the symmetric transfer characteristics. Because of the reversible and continuous ferroelectric switching in HfO2, our approach allows for an electrical control of the energy distribution of spectral components, thus opening up new and very promising paths for frequency manipulations with simple ferroelectric devices.
RESUMEN
The microstructure of ferroelectric hafnium oxide plays a vital role for its application, e.g., non-volatile memories. In this study, transmission Kikuchi diffraction and scanning transmission electron microscopy STEM techniques are used to compare the crystallographic phase and orientation of Si and Zr doped HfO2 thin films as well as integrated in a 22 nm fully-depleted silicon-on-insulator (FDSOI) ferroelectric field effect transistor (FeFET). Both HfO2 films showed a predominately orthorhombic phase in accordance with electrical measurements and X-ray diffraction XRD data. Furthermore, a stronger texture is found for the microstructure of the Si doped HfO2 (HSO) thin film, which is attributed to stress conditions inside the film stack during crystallization. For the HSO thin film fabricated in a metal-oxide-semiconductor (MOS) like structure, a different microstructure, with no apparent texture as well as a different fraction of orthorhombic phase is observed. The 22 nm FDSOI FeFET showed an orthorhombic phase for the HSO layer, as well as an out-of-plane texture of the [111]-axis, which is preferable for the application as non-volatile memory.
RESUMEN
The interaction between oxygen vacancies and La atoms in the La doped HfO(2) dielectric were studied using first principles total energy calculations. La dopants in the vicinity of a neutral oxygen vacancy (V(O)) show lower formation energy compared to the La defects far from V(O) centres. La doping in HfO(2) leads to the shift of the defect states of oxygen vacancies towards the conduction band edge. A statistical average of this shift over several possible configurations of La atoms and V(O) shows that the incorporation of La effectively passivates the V(O) induced defect states leading to the reduction of the gate leakage current and improvement of the device reliability.