# Microheater Topology for Advanced Gas Sensor Applications with Carbyne-Enriched Nanomaterials
## 3 Results  
Before testing the sensor structure in heating mode, the piezoelectric properties of the LiNbO\({}_{3}\) substrate were evaluated in the temperature range from room temperature to the maximum heating temperature of 80 \({}^{\circ}\)C, provided by the heaters. Understanding the impact of temperature on the piezoelectric properties of the substrate is particularly important because it directly influences the sensor's sensitivity and response characteristics. The results are presented in Figure 3. It can be seen that at higher temperatures, the piezoelectric coefficient also increased. This is ascribed to the increased lattice spacing, which allows for greater freedom of movement for the charged particles within the crystal  
Figure 2: Test setup for the sensor samples: (**a**) measurement of the samples’ impedance and contact parameters before and after heating; (**b**) measurement of the sensor’s response characteristics at different ethanol concentrations [23]. lattice, thus resulting in an enhanced piezoelectric response [24]. Due to the high thermal stability of the LiNbO\({}_{3}\), the contribution of this variation is with a factor of 0.12 for a temperature range of \(\Delta\)T = 55 \({}^{\circ}\)C.  
Figure 4a compares the contact resistance and interface capacitance formed between the carbyne-enriched sensing layer, the electrodes, and the substrate before (Rs, Cs) and after heating (Rsh, Csh). As can be seen, the contact resistance deviates by approximately \(\pm\)0.6 M\(\Omega\) from the average value of this quantity, no matter the delivered heat flow from any of the microheaters. Given the excellent thermal stability of the carbyne [25], this is expected behavior and can be interpreted as a lack of change in the sensing layer's microstructure. This is also supported by the change in the sensing layer resistance over the time graph for several hours exposed to the maximal temperature of the microheaters without analyte loading (Figure 4b), which is in the same range and close in values. The carbyne film resistance remains relatively constant over the 10 h duration exposed to the maximum temperature of the microheaters. The slight difference in the resistance can be ascribed to the thermal activation of defects, which are stimulated according to the power of the microheaters. Thus, the most powerful microheater (dense rectangular) activates deep and shallow traps, which, escaping the defect states, contribute to the conductivity of the film and reduce its overall resistance. On the contrary, the small meander activates only shallow traps, caused by impurities, due to its low power. Thus, the carbyne resistance, in this case, is almost unchanged compared to the film without heat exposure. Regarding the time dependence, it is visible that there is a trend for the initial release of the trapped charges during the first few hours. Afterwards, the resistances reach saturation and constant values are established. An exception can be noted for the small meander microheater, which is inert and needs more time to release even the small quantities of shallow traps. However, it can be noted that the interface capacitance increases gradually with the increase in the active area of the microheater--the lowest value of 6.5 pF was measured for the small meander, 8.65 pF was measured for the large meander, and the highest value of 12.5 was obtained for the dense rectangular shape, giving the fastest heating concentrated in the middle spot of the sensor between the two transducers. This behavior can be ascribed to thermally stimulated charges that were probably trapped in defect formations in the carbyne-enriched layer. These charges, together with the additional charges of the piezoelectric substrate produced after temperature increase (Figure 3), contribute to the higher capacitance. Therefore, the most prolonged time delay in the output signal is expected to be generated for the sensor with the dense rectangular microheater due to the time needed for the charge and discharge of the high-value capacitance.