Summary:
The present diploma thesis aims to study and understand the electrical properties of yttrium oxide (Y2O3) and titanium oxide (TiO2) as MIM-type gate dielectrics under the influence of different conditions. Initially, a brief overview is presented of the solid state device models and analysis techniques of such models.
In the second chapter there is an extensive reference to the basic concepts of dielectric theory such as polarization and relaxation time. In particular, the various polarization mechanisms that appear in dielectrics are analyzed.Furthermore, the main conduction mechanisms in which the dielectrics obey are studied in the present work.Finally, reference is made to the computational method of measuring the transient polarization and depolarization currents used in the measurements that were carried out.
In the third chapter are presented the materials studied in the work. Specifically, their basic characteristics and crystalline structure are presented. The main properties of the particular oxides are then analyzed, and finally the most important electronic applications in which these materials are used is being noted.
The following chapter presents and analyzes the experimental results for yttrium oxide. Initially the technical characteristics and structure of the sample, as well as the experimental setup used to obtain the measurements, are described. The electrical properties of the yttrium oxide were examined for various conditions, both in terms of time and temperature. The increase in electric field strength was found to increase vector trapping resulting in long rehabilitation times in both charging and discharge. In addition, from current-voltage measurements to the temperature range of 300K to 440K, it appears that the dominant conduction mechanisms at Y2O3 are highly dependent on the temperature. Specifically, for the range of 300K to 340K, the mechanism the Hopping mechanism is predominant. For the 350K to 370K and low fields up to 0.5 MV / cm the Hopping mechanism dominates, while for high fields the Poole-Frenkel mechanism predominates. Finally, for the range of 380K to 420K and for low fields the Schottky mechanism dominates, while the Hopping mechanism appears in the intermediate field values. For high fields, Poole-Frenkel also dominates these temperatures.
A similar analysis is made in the last chapter for the titanium dioxide. The measurements made for positive and negative polarity verify the memristive behavior of TiO2. Regarding the RS phenomenon in this case, it is observed that the set and reset process takes place in different polarities, so the process is characterized as Bipolar Resistance Switching (BRS). From the results obtained from the current-voltage measurements as a function of the temperature for the range of 300K to 440K, it’s resulted that for the 300K-380K range the dominant mechanisms are the Hopping mechanism for low elecric fields and the Schottky mechanism for high electric fields. For the intermediate field intensity values a coexistence of these two mechanisms could be said, without excluding the existence of a thied mechanism. For the 400K-440K range, the mechanism that dominates the low is that of Hopping. However, in the high fields the mechanism that appears to dominate is that of Space-Charge-Limited-Conduction, which starts to appear in 400K with the ohmic region and at 440K the SCLC appears in full display with three distinct regions.
Keywords:
Εlectrical characterization, metal oxides, conduction mechanisms, polarization mechanisms, charge and discharge carrier transient.
