Analysis of Excitation Pulsed Signal Propagation for Atom Probe Tomography System
The purpose of this paper is on the behavioural modelling of surge voltage pulses used in Atom Probe Tomography. After brief description of the atom probe functioning principle, we examine the excitation electrical pulse signal integrity along the electric pulser (E-pulser) feeding line modelling with respect to the IEC1733/04 standard. This feeding electric line is ended by cylindrical via ground to control the ion emission. By using the transmission line (TL) ultra-broadband RLCG model, the propagating pulsed signals degradation is predicted. The signal propagation was analysed in both frequency and time domains by taking into account the substrate dispersion. The wideband frequency behaviours of the surge signal along the feeding line were examined from DC-to-2 GHz. In addition, by considering pulse surge signals with pulse-width and rise-/fall-time parameters (T1=9 ns, tr1=tf1=1.6 ns) and (T2=30 ns, tr2=4 ns/tf2=18 ns), the transient responses from 5 cm to -20 cm length TL are characterized. It was shown that the excitation pulse was significantly distorted. It was emphasized that the operated signal delay varies from 0.3 ns-to-1.5 ns in function of the via capacitor value. The time-dependent radiated E-field on the performance of the atom probe system which enables to characterize the nature of tested materials (ions or atoms) is discussed. The presented analysis approach is particularly useful for E-pulser integrated in measurement scientific instruments as Atom Probe Tomography time of flight optimisation, a nano-analysing technique that uses ultra-sharp high vacuum pulse to induce controlled erosion of samples. In this application, the excitation voltage pulse integrity during the propagation is required in order to improve the measurement instrument performances.