Paper MN-MoM3
Nano-Scale, Directional Contact Metal Transfer in Hot-Switched MEMS Actuators

Monday, October 15, 2007, 8:40 am, Room 615

We have investigated failure mechanisms of metal-contact Micro-electro-mechanical Systems (MEMS) switches using a new accelerated lifetime test facility. The facility utilizes a double-contact upper cantilever from commercial MEMS contact switches, and tests these against bottom gold contact pads within a modified AFM. After a number of switching cycles, both the upper contacts and bottom electrode were characterized by atomic force microscopy (AFM). In this paper, a new phenomenon we term "nano-scale, directional contact metal transfer" during hot switching is reported. The material (gold) in the contact area transfers between the bottom contacts and upper contacts during hot-switching, following the electric field direction. The field-directional transfer was confirmed by DC signal (open circuit voltage, Voc = 6 V) test and reversed DC signal (Voc = -6 V) test. It has been found that the material transfer process is accelerated with the increase of cycling number. Volume analysis of the damaged contact area shows that using an AC signal (with the amplitude of Voc = 6 V) yields an order of magnitude less material transfer damage than DC current, and the material transfer under AC does not have any directional characteristics. This indicates that under the condition of "hot-switching", signal type (AC/ DC; biased or not) may have a significant effect on MEMS switches' failure mechanism. Different material transfer related theories and models are reviewed and examined. A new micro-contact degradation mechanism is proposed.