Composite Polysilicon-Platinum Lateral Nanoelectromechanical Relays

Abstract

This paper reports the fabrication and performance of laterally actuated, polysilicon-platinum composite nanoelectromechanical (NEM) relays. Laterally actuated relays are defined in a single lithography step, enabling symmetric electrode and beam structures. The platinum coating serves as the conducting contact material and can also provide a local routing layer. Decoupling mechanical and electrical properties of the NEM relay allows independent optimization of each property. The NEM relays exhibited less than 3kΩ contact resistance and can operate for 10 8 cycles in room ambient.

From Transistors to NEMS

“…This forms an ohmic contact that permits current to flow from the source to the drain. A wide range of contact resistances have been reported, ranging from 83 with gold contacts [Fruehling et al 2009], to several thousand with contact materials such as platinum [Parsa et al 2010] or aluminum oxide [Jeon et al 2010]. The primary reason for this wide range is that most prototypes are designed for NEMS-based digital logic, where the high mechanical delay completely dominates the electrical delay (and a high resistance is beneficial by limiting the current draw).…”

“…Finally, the sacrificial layer is removed leaving an air-gap above which the beam is suspended. Detailed fabrication steps of NEMS switches using standalone MEMS/NEMS processes can be found in Czaplewski et al [2009], Dadgour et al [2010], Parsa et al [2010], and Nathanael et al [2009]. Additionally, a CMOS-NEMS hybrid manufacturing flow is proposed in Dadgour and Banerjee [2007] that requires the addition of only three process steps to the standard CMOS process flow.…”

“…Figure 1 gives a compact layout of a laterally actuated electrostatic NEMS switch and is based on previously fabricated devices [Czaplewski et al 2009;Dadgour et al 2010;Parsa et al 2010]. The device operates by electrostatic force between the gate and a cantilever beam suspended across a trench in the substrate.…”

“…The overriding motivation of NEMS researchers has been to develop entire circuits comprised solely of NEMS switches, and in fact complementary and complex logic built solely with these switches has been demonstrated [Dadgour et al 2010]. Two major drawbacks have stifled progress on this front: first, the switching speed ranges from 10-100 ns, which is too slow for logic [Czaplewski et al 2009]; second, the reported lifetime has ranged from 10 8 to 10 12 on-off cycles [Maciel 2009;Parsa et al 2010], which does not guarantee a long enough lifetime for logic implementation. Since the switching is much less frequent with power gating, the implications of these drawbacks are not as severe.…”

“…Researchers of these devices envision entire circuits comprised of NEMS-based complementary logic, which would be entirely free of static power, but issues with switching speed and device lifetime have hampered these efforts [Parsa et al 2010]. A more feasible intermediate step would be a hybrid system with ondie NEMS switches acting as power gates for CMOS circuitry.…”