# Comprehensive Review of RF MEMS Switches in Satellite Communications
## 3 Strategies for Optimizing RF MEMS Switch Performance
### High Reliability
#### 3.1.3 Improvement of Contact Materials and Structures
Novel structural designs can also prolong the lifespan of switches by reducing contact stiction, contact degradation, and charge injection, beyond improving the materials of  
Figure 6: Atomic-scale contact-separation simulation using DFT calculations. [122]**(a)** DFT-optimized atomic structures of the gold (Au) tip and nickel (Ni) surface; (**b**) calculated atomic force of the Au tip, \(F_{tip}\) Ftip, during approach (left) and retraction (right). \(F_{tip}\) fluctuates considerably and gradually recovers during approach and retraction, respectively, because of the rearrangement of Au atoms, resulting in significant hysteresis; (**c**) DFT-optimized atomic structures of the Au tip and graphene (Gr)-coated surface; (**d**) calculated \(F_{tip}\) Ftip during approach (left) and retraction (right). Reprinted/adapted with permission from [122]. the contacts [73; 92]. The innovative design shown in Figure 7a [123] utilizes a method of paralleling sacrificial contacts with low-resistance contacts, significantly reducing the electric field strength and thereby minimizing contact degradation associated with field-induced material transfer. This design allows the use of a single actuator and bias electrode to implement the correct protective driving sequence, resulting in more than a 100-fold increase in thermal switch lifespan compared to unprotected switches. [PERSON] et al. [124] introduced a parallel protection technique. Protective contacts are placed before the main contact points of the RF MEMS metal contact switch to block the RF signal when the main contact operates, as depicted in Figure 7b. This method creates a local cold switch condition for the main contact, thereby extending the switch's lifespan under thermal conditions. Figure 7: **(a)** Top view of switch with series protection contact [123]. Reprinted/adapted with permission from [123], 2016, IEEE. **(b)** Top view of the shunt-protected switch [124]. Reprinted/adapted with permission from [124], 2017, IEEE. **(c)** The structure of the compact single-cantilever multicontact switch [125]. Reprinted/adapted with permission from [125], 2018, IEEE. **(d)** The structure of levitation-based micro-switch [126]. Reproduced with permission from Springer Nature. **(e)** The structure of a non-contact-type switch [127]. Reprinted/adapted with permission from [127], 2009, IEEE. **(f)** The structure of a three-state contactless switch [128]. The inset shows the initial gap between the signal lines and grounded movable electrodes. Reprinted/adapted with permission from [128], 2015, IEEE. Figure 7c [125] presents an innovative cantilever and electrode bias design that integrates multiple contact points within a single cantilever, aimed at enhancing the reliability of the switch. These contact points are used to sequentially conduct RF current until one of them fails. By alternating contact points, the device can refresh and reduce the contact resistance of the switch, thus improving its overall lifespan. Traditional actuation relies solely on reducing voltage to detach the movable electrode (i.e., opening the switch), but any degradation of the contact surface may cause changes in switch characteristics, such as permanent collapse due to strong surface adhesion. The design studied by [PERSON] et al. [126], as shown in Figure 7d, employs twoside electrodes to operate a normally closed switch. This design incorporates repulsion auxiliary excitation into the traditional gap-closing capacitor design, overcoming the stiction caused by adhesion forces and providing better switch control. Even with surface degradation, switch operation can be achieved by increasing the side voltage, although this may necessitate higher side voltages. Further, to avoid common stiction and charge injection issues in contact RF MEMS switches, a design with no physical contact between the signal line and the movable electrode can be implemented by separating the DC bias from the RF signal path. A non-contact RF MEMS switch for radar applications has been reported, as shown in Figure 7e [127].