C. Wasshuber, H. Kosina and S. Selberherr: Single-Electron Device and Circuit Simulation
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Next: References Up: Abstract Previous: 3 Simulating Co-tunneling

4 Application - Electron Trap

An electron trap with a read-out circuit as shown in Fig. 6 is simulated.

 figure9
Figure 6: Electron trap with read-out circuit.

A voltage pulse on Vin transports one elementary charge onto the 'storage node'. This stored charge influences via C2 the read-out circuit which is a single-electron transistor. The current through the read-out transistor depends on the charge which is stored in the trap. We are interested in the leakage current I or which is equivalent, in the lifetime of a stored electron. The lifetime t and leakage current are related by


where e is the charge of an electron. The leakage current is partly due to thermal fluctuations and partly due to co-tunneling. Our interest is in which simulation algorithm gives better results. Hence we simulated the same circuit with a plain MC method and with our new MC-ME method. The following figures show the leakage current as a function of Vin.

 
Figure 7: Leakage current versus input voltage, simulated with our new MC-ME algorithm

  
Figure 8: Leakage current versus input voltage, simulated with a plain MC algorithm

 
Figure 9: Leakage current versus input voltage, simulated with a plain MC algorithm

It can be clearly seen form Fig. 7, that our new MC-ME algorithm produces in a short simulation time much better results than the plain MC method (Fig. 8). One has to simulate with a plain MC method many more tunnel events to achieve a similar accuracy (Fig. 9). The reason for this is that the read-out circuit consumes many tunnel events which do not contribute to the accuracy of the leakage current. In bigger and more complicated circuits this problem can be much more pronounced and render a plain MC method useless for co-tunneling simulations.


C. Wasshuber, H. Kosina and S. Selberherr: Single-Electron Device and Circuit Simulation