[EN]To manufacture faster electron devices, the industry has entered into the nanoscale dimensions and
Terahertz (THz) working frequencies. The discrete nature of the few electrons present simultaneously
in the active region of ultra-small devices generate unavoidable fluctuations of the current at THz
frequencies. The consequences of this noise remain unnoticed in the scientific community because its
accurate understanding requires dealing with consecutive multi-time quantum measurements. Here,
a modeling of the quantum measurement of the current at THz frequencies is introduced in terms
of quantum (Bohmian) trajectories. With this new understanding, we develop an analytic model for
THz noise as a function of the electron transit time and the sampling integration time, which finally
determine the maximum device working frequency for digital applications. The model is confirmed
by either semi-classical or full- quantum time-dependent Monte Carlo simulations. All these results
show that intrinsic THz noise increases unlimitedly when the volume of the active region decreases.
All attempts to minimize the low signal-to-noise ratio of these ultra-small devices to get effective THz
working frequencies are incompatible with the basic elements of the scaling strategy. One can develop
THz electron devices, but they cannot have ultra-small dimensions. Or, one can fabricate ultra-small
electron devices, but they cannot be used for THz working frequencies.
