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The existence of the Coulomb blockade is clearly visible in the [[current–voltage characteristic]] of a SET (a graph showing how the drain current depends on the gate voltage). At low gate voltages (in absolute value), the drain current will be zero, and when the voltage increases above the threshold, the transitions behave like an ohmic resistance (both transitions have the same permeability) and the current increases linearly. It should be noted here that the background charge in a dielectric can not only reduce, but completely block the Coulomb blockade. <math>q_0 = \pm (0.5 + m) e.</math>
In the case where the permeability of the tunnel barriers is very different <math>(R_{T1} \gg R_{T2} = R_T),</math> a stepwise I-V characteristic of the SET arises. An electron tunnels to the island through the first transition and is retained on it, due to the high tunnel resistance of the second transition. After a certain period of time, the electron tunnels through the second transition, however, this process causes a second electron to tunnel to the island through the first transition. Therefore, most of the time the island is charged in excess of one charge. For the case with the inverse dependence of permeability <math>(R_{T1} \ll R_{T2} = R_T),</math> the island will be unpopulated and its charge will decrease stepwise.
<math>q = -ne + q_0 + C_{\rm G}(V_{\rm G} - V_{2}).</math>
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