Physical device simulation in a shrinking world

The effect of shrinking device dimensions from micrometers to nanometers on the validity of device simulators is examined. It is shown that the assumptions underlying the drift-diffusion equation weaken when applied to small devices. Using the Monte Carlo method to simulate the microscopic motion of several thousand carriers as they travel through a device, an alternative approach that is beginning to find wide application in device engineering is discussed. Because the Monte Carlo method directly mimics carrier motion at a microscopic level, it provides highly accurate, detailed, realistic simulations of carrier transport in devices. However, it imposes a heavy computational burden, and the noise associated with the use of a relatively small sample-a few thousand electrons-sometimes limits its application. Nevertheless, its advantages continue to grow as device dimensions shrink. As the devices shrink to dimensions below 100 nm, the wave nature of electrons will play an increasingly important role, and even semiclassical Monte Carlo techniques are inadequate. Quantum approaches for use in that regime are considered.<>