Using a custom built contact testing system, direct current micro contact damage under hot-switching conditions was explored in ruthenium-on-ruthenium contacts operated at a contact force of approximately 400 μN. For the first time, contact damage on making and breaking contact under bias (leading and trailing edge hot switching) is compared. Trailing-edge hot switching leads to significantly higher adhesion (1.5-4 times higher) than leading-edge hot switching. The high-voltage tests (3.5 V) lead to polarity-dependent material transfer, with material moving in the direction of the electric field. The amount of material transfer does not depend strongly on the current limit from 0.78 to 380 mA. The low voltage (0.71 V) tests result in much less damage, and the material transfer does not have a clear directionality. However, the amount of damage does increase significantly as the current limit is increased from 16 to 78 mA. Also observed for the first time is a new type of high-current, short duration current spike associated with hot switching events at voltages above 1.5 V. The fact that these spikes occur at the higher voltage but not at the lower voltage suggests (but does not prove) that they are associated with the polarity dependent material transfer.
Using an AFM-based test setup, experiments were performed on Ru microcontacts under a variety of leading and trailing edge hot switching conditions, including different voltages, different currents, different polarities (including bipolar and ac up to 20 MHz), and different approach and separation rates. It was found that hot switching damage is a complex phenomenon for microcontacts. It consists of a number of different mechanisms occurring simultaneously to different degrees depending on the hot switching conditions. It was determined through a combination of experiments and models that the mechanisms leading to contact erosion operate when the electrodes are separated by less than a few Å or are barely touching. For leading edge hot switching, i.e. hot switching when the contacts are closing, the main damage mechanism was found to be associated with currents less than 0.15 mA. Pre-contact currents were observed on uncleaned contacts and were not found to contribute to contact damage. Despite the damage caused by hot switching, it was found that unless the contact material is almost or completely eroded, hot switching does not lead to high contact resistance or high adhesion on Ru contacts. Under bipolar hot switching conditions, microcontacts with a 400 μN contact force maintained a contact resistance of less than 1 Ω and a pull-off force less than 60 μN for more than 100 million cycles.
This paper presents a finite element approach for modeling a thermal-electrical-mechanical coupled-field contact comprised of an elastic hemisphere pressed against an elastic half-space. The goal of this investigation is to develop a fundamental understanding of the behavior of this multiphysics contact, with a particular interest on the contact area through which current flows. The results from the model illustrate a distinct difference in contact behavior between force control and displacement control in the presence of an applied electrical potential/current. It is shown that, while Hertz contact theory can be used to accurately predict the behavior of the contact under force control, a new relationship is established to accurately predict the behavior of the contact under displacement control.
Although metal-to-metal direct contact MEMS switches are a promising alternative to solid state switches in RF communication systems, the reliability of their electrical contacts has proven to be a barrier to entry to the market. Hot switching is known to have the most damaging effect on the contacts although an understanding of all the mechanisms leading to this damage is a work-in-progress. In this investigation, a customized Atomic Force Microscope was used to study the electrical contacts. The contacts were cycled at approach rates of 115 µm/s, 440 µm/s and 4400 µm/s and at different polarities. While material transfer is confirmed to be the primary source of contact damage, the results suggest that two different mechanisms could be at play at the leading and trailing edge of a hot switched cycle. A polarity driven mechanism and a contact separation rate dependent mechanism were observed. Low-level transient currents up to a few µA that may or may not be related to the material transfer, were observed at the leading edge of the switching cycle.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.