Investigation of High-k Dielectrics for Terahertz Rectenna

Abstract

This thesis gives contribution to the field of sustainable energy harvesting. To tap into terahertz energy region of 30-300 THz, being received on earth from the sun, considerable research has been dedicated to the study of near-zero-biased Metal-Insulator-Metal (MIM) based rectifying antenna (rectenna) devices. These devices are to be engineered to rectify extremely high frequency signals, operate without requiring an external voltage, and convert the high frequency signals into usable direct current (DC) electricity. Several MIM diode configurations have been fabricated and examined in this thesis, utilizing thermal evaporation for depositing metals and radio frequency sputtering for depositing oxides. Additionally, variable angle spectroscopic ellipsometry (VASE), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and DC electrical measurements have been utilized to examine and ascertain rectification performance of the experimental devices. The performance of Sc2O3-based MIM diodes has been investigated for use in a 28.3 THz rectenna. The diodes were fabricated using sputtering to deposit thin films of Sc2O3 (~3-5 nm) and thermal evaporation to deposit metal electrodes such as aluminium and gold. The choice of Ti/Au and Al/Mo dissimilar electrodes is done to investigate the effect of work function difference of 1.0 eV and 0.1 eV respectively, on diode non-linearity. The figures of merit, such as asymmetry, responsivity, non-linearity, and dynamic resistance, of fabricated MIM devices were ascertained using electrical measurements. Furthermore, Mo/ 33.2 nm Sc2O3/ Si and Al/ 4.5nm Sc2O3/Al capacitors were fabricated. The capacitance voltage (C-V) measurements are carried out in order to determine the static permittivity (κ) of Sc2O3 film. Temperature-dependent current-voltage (I-V) characteristics also, were used to study the conduction mechanisms in an Al/Sc2O3/Al diode. The results indicate that Fowler-Nordheim tunnelling (FNT) and Schottky emission are two of the conduction mechanisms that govern electron transport in this device. Sc2O3 film permittivity was measured to be κ =13.2 from associated C-V plots, while the barrier heights for Ti/Sc2O3 and Al/Sc2O3 interfaces were determined from FNT plots to be 1.86  0.2 eV and 1.92  0.2 eV, respectively. Additionally, the band gap and electron affinity of Sc2O3 were ascertained using XPS O 1s and secondary electron cut-off spectra. The key results of the XPS measurements are found to be a band gap of Sc2O3 of 5.78  0.2 eV and electron affinity of 1.95  0.2 eV. The band alignment experimental findings were used in the simulation of MIM devices’ I-V characteristics, which showed a good agreement between the experimental and fitted curves. A comparison of rectification parameters of similar