An Improved Single-Electron-Transistor Model for SPICE Application
You-Lin Wu and Shi-Tin Lin
National Chi-Nan University, TW
Keywords: Single Electron Transistor, SPICE, Coulomb Blockade
Single electron transistors (SETs) have drawn much attention of researchers and scientists because they are considered candidate as one of the elements for future low power, high-density memories and logic circuits. Instead of using Monte Carlo method to calculate the charge states of all the Coulomb islands, Yu el. at. proposed the first SPICE macro model for SETs  according to parameter-based modeling and line-fitting method with the assumption that the interconnection among SETs is large enough so each SET can be treated independently. Although it has been shown that the results obtained from Yu’s model are in good agreement with those from the simulator KOSEC, there’s still a large discrepancy when compared with the results obtained from other simulation tool such as SIMON. An improved SPICE macro model for single electron transistor based on Yu’s model is proposed in this work. Our model correctly describes the I-V characteristics of the single electron transistor both inside and outside the Coulomb blockade regions. The terminal characteristics of the SETs and an SET inverter circuit obtained from our SPICE model are in good agreement with those obtained from the well-known SETs simulator SIMON 2.0. Figure 1 shows our proposed model for single electron transistor. Figure 2 gives the Ids-Vgs characteristics of a SET obtained by using our proposed model, and the Coulomb oscillation can be clearly observed. The Ids-Vgs characteristics obtained from SIMON 2.0, Yu’s model and our proposed model are shown in Fig. 3 for comparison. As can be seen that the result obtained from our model is more consistent with that of SIMON 2.0. An increase of Ids with increasing Vgs is observed for the results of Yu’s model, but no such increase in Ids for both of our model and SIMON 2.0. Figure 4 shows the Ids-Vds characteristics obtained from SIMON 2.0, Yu’s model and our proposed model. Clearly, our result is in good agreement with that in SIMON 2.0 for both the Coulomb blockade region and non-Coulomb blockade region. The transfer characteristics of an inverter will also be shown in this work. The simulation results confirm that our proposed model can give more accurate terminal characteristics of SET and SET’s circuits than Yu’s model.
NSTI Nanotech 2003 Conference Technical Program Abstract