5.2.4 Power Consumption

  Because of the minuteness of capacitances and the low number of electrons involved in charging and discharging, the power consumption of SET memories is orders of magnitudes smaller than that of conventional memories. However, high integration densities and high switching speed may lead to unacceptable power dissipation of $\sim 3$ kW/cm² [78]. Especially a design which merely replaces FETs with SET transistors has a high power consumption since a constant static current is flowing. The energy dissipation of a single tunneled electron is of the order of the Coulomb energy, e²/2C. With a tunnel rate of $\sim 1/eR_T$ the power dissipation of one SET transistor becomes $\sim e/2R_TC$, which is for characteristic parameters about 0.1 $\mu$W. Therefore integration densities of 10¹⁰/cm² and more demand heat removal rates of kilowatts per square centimeter. Much better in this respect is SET logic, where a small number of electrons represent a logic state. No static current is flowing. Here again, one transferred electron dissipates roughly the Coulomb energy, e²/2C, but this time the switching rate of gates is much lower than the intrinsic tunnel rate. With a switching time of 1 ns, the power consumption of one logic gate is about 10^-10 W. Assuming the same integration density as before results in an acceptable power dissipation of $\sim$ 1 W/cm² (see also D. Averin and K. Likharev [9]).