Retention time in multiple-tunnel junction memory device

A computationally inexpensive approximation is obtained for the retention time of charges stored on a memory node of a multiple-tunnel junction (MTJ) memory device, based on previous simplifying assumptions by Jensen and Martinis. The approximation takes into account both thermally assisted single electron tunneling and higher order processes, or cotunneling and is in good agreement with a full master equation simulation of the device up to a temperature T approximate to T-0/10, where T-0 = e(2)/k(B)C. For the case of a memory device formed within a delta-doped layer in GaAs, it is predicted that leakage due to single tunneling starts to dominate over cotunneling at temperatures above T approximate to T-0/60, and that a sharp reduction in retention time occurs above T approximate to T-0/100. Our analysis also shows that with the typical dimensions of present devices, a memory lifetime of a year requires the stringent condition of an 11-junction MTJ operated at below 1 K. (C) 1999 American Institute of Physics. [S0021-8979(99)07902-5].