Size Dependence of the Read Voltage and Electrical Diameter of STT MRAM Cells

We present an experimental study of the size-dependent tunnelling magnetoresistance ratio (TMR) and voltage read signal in perpendicular spin transfer torque magnetoresistive random access (STT-MRAM) memory cells, which shows that the maximum read signal is mostly independent of the size, while TMR decreases with decreasing size. Our analysis shows that this is due to a size-dependent parasitic resistance specific to the nanofabrication process and that the intrinsic ΔRA of the cells is size-independent. As a consequence, we show that the electrical diameter of an MRAM cell can be reliably extracted down to sub-20 nm assuming that ΔRA does not depend on the cell size.