## 3 Results and Discussion  
### Reset Operation  
The simulated temperature distribution within the mushroom PCM cell at the time of maximum temperature occurrence, that is the end of the RESET pulse, is plotted in Figure 3a, where thermoelectric effects are not considered. Although our model is a three-dimensional finite element simulation, all the results are given in two-dimensions to be able to compare the variation of temperature profiles and phase distributions with and without thermoelectric effects more plainly and clearly. A 2.6 mA, 50 ns input pulse is applied to heat the GST material adjacent to the GST-BE interface above  
Figure 2: (**a**) Electrical conductivity of crystalline and amorphous Ge\({}_{2}\)Sb\({}_{2}\)Te\({}_{5}\) (GST); (**b**) thermal conductivity of GST with phonon and electronic contributions shown; (**c**) heat capacity for GST with a plateau at melting to include latent heat of fusion; (**d**) Seebeck coefficients for GST in amorphous and crystalline phases; (**e**) negative Seebeck coefficient of TiN. its melting temperature, and it subsequently cools into the amorphous phase. The crystallization fraction (f) inside the GST layer is shown in Figure 3b. The GST-BE interface is completely covered by the amorphous GST plug, forming a high-resistance path on readout between the top and bottom electrodes. The corresponding cell resistance increases two orders of magnitude as compared to the original value, and then the RESET operation is accomplished. From the above, the temperature distribution governs the formation of the amorphous region and the resulting cell resistance. Hence, through strongly altering the temperature distribution within the PCM cells, thermoelectric effects can influence the current for successful RESET. Figure 4 shows the temperature profiles within the PCM cells at the end of the pulse with the same current pulses (2.5 mA, 50 ns) for both positive and negative polarities. With the positive polarity current, both the Peltier effect and the Thomson effect can improve the heating efficiency and then expand the volume of the molten region, which is beneficial to form enough amorphous zone for the RESET operation with lower pulse amplitude. Additionally, the cell requires more current because of the cooling induced by the thermoelectric effects under negative current polarity. Because of the different occurrence region, these thermoelectric effects have different influences on the temperature profiles. The Thomson effect mainly occurs in the GST materials, and slightly raises the temperature reached in the GST layer, shown in Figure 4b, similar to the results of the pulse amplitude increasing. The Peltier effect in the cell with the 250 nm width bottom electrode, simulated in this paper, results in a larger change in the thermal profiles compared with the Thomson effect (Figure 4c), because of the greater energy released in the active region and, more importantly, a more critical location at the GST-BE interface. Therefore, the Peltier effect can cause the position of the hot spot to shift towards the GST-BE interface, heat the GST material near the interface more easily, and then, vastly influence the result of the RESET operation. On the contrary, the Peltier effect hinders the RESET operation more seriously with the negative polarity, as plotted in Figure 4f. Figure 4: Temperature profiles within the cells at the end of the pulse (2.5 mA, 50 ns) for positive (**a**–**c**) and negative (**d**–**f**) polarities, including no thermoelectric effects (**a**,**d**), only Thomson (**b**,**e**), and only Peltier heating (**c**,**f**). Figure 3: (**a**) Temperature distribution within the simulated cell at the end of the pulse; (**b**) corresponding phase distribution in the GST layer, with blue and red regions representing the amorphous and crystalline phase, respectively. The cell resistance as a function the RESET current is plotted in Figure 5. The current polarity has no impact on the RESET current (solid squares) when neglecting thermoelectric effects.