Mofakhami Darius, Seznec Benjamin, Minea Tiberiu, Landfried Romaric, Testé Philippe, Dessante Philippe
Laboratoire de Génie Electrique et Electronique de Paris, Université Paris-Saclay, CentraleSupélec, CNRS, 91192, Gif-sur-Yvette, France.
Laboratoire de Génie Electrique et Electronique de Paris, Sorbonne Université, CNRS, 75252, Paris, France.
Sci Rep. 2021 Jul 26;11(1):15182. doi: 10.1038/s41598-021-94443-7.
The electron emission by micro-protrusions has been studied for over a century, but the complete explanation of the unstable behaviors and their origin remains an open issue. These systems often evolve towards vacuum breakdown, which makes experimental studies of instabilities very difficult. Modeling studies are therefore necessary. In our model, refractory metals have shown the most striking results for discontinuities or jumps recorded on the electron emitted current under high applied voltages. Herein, we provide evidence on the mechanisms responsible for the initiation of a thermal instability during the field emission from refractory metal micro-protrusions. A jump in the emission current at steady state is found beyond a threshold electric field, and it is correlated to a similar jump in temperature. These jumps are related to a transient runaway of the resistive heating that occurs after the Nottingham flux inversion. That causes the hottest region to move beneath the apex, and generates an emerging heat reflux towards the emitting surface. Two additional conditions are required to initiate the runaway. The emitter geometry must ensure a large emission area and the thermal conductivity must be high enough at high temperatures so that the heat reflux can significantly compete with the heat diffusion towards the thermostat. The whole phenomenon, that we propose to call the Nottingham Inversion Instability, can explain unexpected thermal failures and breakdowns observed with field emitters.
微突起的电子发射已经研究了一个多世纪，但对其不稳定行为及其起源的完整解释仍然是一个悬而未决的问题。这些系统往往会演变为真空击穿，这使得对不稳定性的实验研究非常困难。因此，建模研究是必要的。在我们的模型中，难熔金属在高外加电压下记录的发射电流的不连续性或跳变方面显示出了最显著的结果。在此，我们提供了关于难熔金属微突起场发射过程中热不稳定起始机制的证据。发现在稳态下发射电流超过阈值电场时会出现跳变，并且它与温度的类似跳变相关。这些跳变与诺丁汉通量反转后发生的电阻加热的瞬态失控有关。这导致最热区域移动到顶点下方，并产生朝向发射表面的新的热回流。启动失控还需要另外两个条件。发射极几何形状必须确保有较大的发射面积，并且在高温下热导率必须足够高，以便热回流能够显著地与向恒温器的热扩散相竞争。我们提议将整个现象称为诺丁汉反转不稳定性，它可以解释场发射体中观察到的意外热故障和击穿现象。
