Cryogenic Performance of RF MEMS Switch Contacts

Abstract

Abstract-A series of experiments was performed to characterize RF microelectromechanical system switch performance under variable environmental conditions and cryogenic temperatures. Data were recorded in helium and nitrogen environments to lower stiction failure rates as well as to circumvent switch bouncing arising from low pressure at cryogenic temperatures. Contact resistance values were observed to be lower at cryogenic temperatures but still two orders of magnitude higher than the values predicted for the constriction resistance of gold asperity contacts, consistent with the presence of adsorbed films on the contacts. An asperity-heating model was applied, from which it was deduced that contact voltages can selectively disassociate adsorbed films from the contact surface while not softening the gold asperity contacts. The results are consistent with the reduced mobility of the adsorbed surface films at cryogenic temperatures.[

Electrical Contact Resistance and Device Lifetime Measurements of Au-RuO2-Based RF MEMS Exposed to Hydrocarbons in Vacuum and Nitrogen Environments

“…One possible explanation, which will be discussed at length in a separate publication [52], could be that vacuum tunneling currents present in the nearby regions are suppressed upon uptake of adsorbed films [31][32][33][34][35][36]. This scenario, which theoretically would increase the resistance by levels that are consistent with the experiment [52], is also consistent with the fact that the change in resistance is constant after the switch remains closed for 30 min with a contact force of *300 lN [42,43]. Alternatively, the molecules may in fact be confined to within the contacts or subsurface defects and exhibit far more conductive behavior than might first be expected [31][32][33][34][35][36].…”

“…The actuation voltage to close the switches ranged from 87 to 99 V, corresponding to 280-365 lN [42,43]. Once a device was closed, the actuation voltage was held constant for over 30 min to allow the time dependence of the contact resistance to be documented.…”

“…The results of the various lifetime studies are summarized in Table 2. One issue that must be considered carefully when comparing data recorded in vacuum to data recorded at atmospheric pressure is the lack of gas damping, which can result in switch bounce [42] and accelerated contact damage. For cycling at a low frequency with a slow rise-time signal, as is the case here, this mechanism is not likely to be a major factor.…”

“…At room temperature, the adsorbates are largely comprised of hydrocarbon species and water vapor [11,[15][16][17], and the coverage levels, especially for very thin films, are very sensitive to both temperature [10,18,19] and thermal fluctuations [12]. It is believed that residual hydrocarbon films at the surface lead to decomposition and then deposition of highly resistive carbon deposits [3,4,[20][21][22].…”

Impact of in situ oxygen plasma cleaning on the resistance of Ru and Au-Ru based rf microelectromechanical system contacts in vacuum

“…1,2 Gold is often used for rf MEMS contacts because of its chemical inertness and low resistivity but its softness resulted in insufficient reliability for commercial applications. [4][5][6][7][8] Since these studies were performed in conditions where condensation of contaminants can easily occur, their reproducibility is uncertain. [4][5][6][7][8] Since these studies were performed in conditions where condensation of contaminants can easily occur, their reproducibility is uncertain.…”