## 3 Results and Discussion
### Electrical Properties of STO Planar Capacitive Structures  
The electrical properties of STO films were studied on the samples that demonstrated the best structural characteristics. Figures 6 and 7 show the normalized capacitance, response time parameter, and quality factors of planar capacitors formed on the base of STO films on silicon carbide, depending on the control field strength. For comparison, the figures also show the characteristics of the capacitors based on the STO film deposited at T\({}_{\text{s}}\) = 650 \({}^{\circ}\)C and which had a significantly worse structure. The graphs show that the nonlinearity and microwave losses of the capacitors correlate with the structural quality of the films under study. Capacitors formed on the basis of films deposited at P = 10 Pa and having a minimum number of structural defects and internal stresses exhibit a tunability of 36% at a quality factor of 120-105, while capacitive structures on films deposited at 3 Pa--32.7% at a quality factor of 85-115. Noteworthy are the dynamics of decreasing capacitance with increasing control field strength and the absence of a flat section of the C-V characteristic at a field strength of more than 30 V/\(\upmu\)m. This indicates that the tunability of the studied capacitors is far from saturation and that the nonlinearity of the structures can be increased by increasing the level of control action. The best combination of tunability and losses of capacitive elements can be determined based on the commutation quality factor CQF. According to [1], for effective use in microwaves, a capacitive element should demonstrate a CQF of at least 1000. Table 1 shows the comparative electrical characteristics of the studied capacitors--capacitance, quality factor, tunability, and the CQF calculated on their basis. A CQF value of more than 2500 allows us to expect the promising characteristics of controlled microwave elements based on STO/SiC films. Figure 5: AFM image of a STO film surface on a SiC substrate. Figure 6: Normalized capacitance and response time parameters of capacitors obtained at different working gas pressures. Figure 7: Quality factor of capacitors obtained at different working gas pressures. One of the most important parameters of microwave device operation is its response speed, i.e., the reaction rate of the permittivity to the application and removal of the control action. For tunable elements based on FE films in the paraelectric state (in the absence of spontaneous polarization), a decrease in \(\varepsilon\) under the action of the control field occurs in times of the order of \(10^{-9}\) s [57], which is due to the fundamental properties of ferroelectrics. However, when the control voltage is removed, a slow relaxation of the capacitance to the initial value can be observed in FE capacitive elements. This relaxation is associated with the formation and redistribution of space charge, which significantly reduces the response speed of FE devices and can be an obstacle to pulse control of the FE element. The main reason for the formation of space charge in a film in the paraelectric phase is considered to be the injection of charge carriers from the electrodes and their capture by defects in the volume of the film [57]. Figure 6 shows the response time parameter \(\Delta\)C/C0 of the studied STO capacitors, which reflects the capacitance 100 ms after the control voltage is removed. It is evident that the tunability of 36% is accompanied by the non-return of the capacitance by a value not exceeding 7.5%, which is a promising result for use in devices with fast switching. Regarding the response time characteristics of strontium titanate, two important points should be noted. Firstly, until now, the response time of capacitors based on STO films has been estimated only at cryogenic temperatures and only for elements on Al\({}_{2}\)O\({}_{3}\) and GaNdO\({}_{3}\) substrates [58; 59].