Sputtered Ruthenium as a Contact Material for Sealed Reeds

Cobalt-hardened gold is used as a contact material on remreed sealed contacts. A possible change of material for contacts of this type has been studied. The contact material investigated consists of a thin film of ruthenium over a thicker film of hardened gold. Both films are deposited by dc sputtering. The advantages of this contact finish compared to electroplated hard gold are reviewed: lower erosion per arcing operation, reduced arcing, and better resistance stability due to lower foreign element comtamination. The reliability of ruthenium contacts is related to that of hard gold contacts. A small change of contact geometry (gap and overlap) is needed to maintain the contact resistance at the level found with hard gold. The reliability is better in low-voltage (~5 V) level operation, due to the elimination of carbonaceous contaminants. The ruthenium contacts exhibit longer life in erosion tests involving cable discharges. Ruthenium contacts can be sealed off in a water free atmosphere so they could be used at below-freezing temperatures. Ruthenium contacts are able to withstand magnetostrictive scrubbing without sticking failures. However, the life of the ruthenium contact when switching current of 100mA (make and break) at 50V in a resistive load does not show significant improvement over hard gold. This is explained in terms of bridge transfer due to chattering during the make operation of the contacts.