Fast damaging processes in the TaN thin film absorbers under action of nanosecond electrical pulses

Abstract

Purpose The purpose of this paper is to investigate damaging processes in TaN thin film absorbers under action of high-voltage electrical pulse of nanosecond duration. Despite having mechanical origin of crack opening, estimation based on the readings from oscillograms shows uncharacteristically high velocities of the crack propagation. Design/methodology/approach Microscopic images of damaged absorbers showing the final result of the damaging process provided initial information about its geometrical peculiarities. Then, to clarify the dynamics of the process, the authors create the model of the crack, having elements of self-similarities and multiple stage opening. The influence of heating induced by current concentration at crack tip and of magnetic stress of this concentrated current are both included in the model. Findings Using physical parameters of TaN layers with flowing current and performing calculations the authors define the conditions required to initiate the damaging process and to sustain it. Danger of such damage is relevant for high-Tc superconducting thin films after their switching to normal state which is induced by the high-voltage pulse. Practical implications There were made recommendations to manufactures aiming to improve electrical durability of the absorbers in an effort to prevent the damaging influence of power nanosecond electrical pulses. Originality/value Three stage opening model implies the appearance of zone of high-energy dissipation that can lead to detonation-like destruction of the film and, therefore, explain the high velocities of crack propagation.

S-N border instability, magnetic flux trapping and cumulative effect during pulsed S-N switching of high quality YBaCuO thin films

“…The dissipation causes a crack branching phenomenon when fast crack openings take place [9,10]. YBaCuO materials were shown to be favorable for demonstrating this kind of damage instability [11]. However, these investigations on N-zone propagation did not analyze the microscopic properties of the S-N border, where the S-zone disappears and the N-zone appears.…”

“…These images attract attention due to the specific crack patterns, which are enlighten for the dynamics of the curved cracks openings. Since current influences the propagation of the cracks, analyses of the images of irreversibly damaged films give useful information about the changes of current direction [11]. Thus, the problem of the damage in the high quality films can be clarified.…”