# Research and Analysis of MEMS Switches in Different Frequency Bands
## 4 Conclusions  
The following conclusions are drawn through the analysis of the above research:  
Conclusion 1: Insertion loss and isolation are two critical performance parameters, which are determined by the structures and materials of MEMS switches. MEMS switches have excellent performance and are widely used in low frequency. However, the parasitic effect of the switch is significantly enhanced as the frequency increases, resulting in a drastic deterioration of the isolation performance. At the same time, the skin effect of the conductor is also significantly increased in the high frequency, so the insertion loss performance will be dramatically worsened. MEMS switches with serpentine flexure structures can achieve high isolation and low actuation in the centimeter, Q, and V bands, as well as switches using combinations of several switches in series. However, the latter present higher isolation for high frequency applications. Serpentine flexure structures could reduce the  
Figure 3: The capacitive MEMS switch with asymmetrical cantilevers. Reprinted by permission from [40]. spring constant and increase series inductance of the bridge, therefore high isolation and low actuation voltage were achieved. The RF signal can be isolated several times in condition of combinations of several switches in series, therefore, the isolation of the MEMS switch is greatly improved. MEMS switches with a float metal layer on the dielectric layer demonstrate very low insertion loss and excellent isolation in the centimeter, Q, and V bands. This structure is the equivalent of two capacitors in series in the up-state, leading to the reduction of the capacitance and low insertion loss. Using dielectric layer materials with high dielectric constants, such as Si\({}_{3}\)N\({}_{4}\) or SiO\({}_{2}\), and conductor materials with low resistance, such as Au, are also key for the high performance of MEMS switches. T-match and \(\pi\)-match both provide an excellent match at the design frequency. Although, there are fewer studies in submillimeter band, MEMS waveguide switches based on reconfigurable MEMS surface design and BiCMOS technology present good performance in submillimeter applications. Conclusion 2: The accumulation of charge in the dielectric layer due to a strong electric field will cause the drift of the pull-down voltage, and this even causes \"self-locking\" of the switch, which seriously affects reliability. The peak voltage, temperature, humidity, thickness of the dielectric film, dielectric material, and the contact surface roughness are significant acceleration factors on charging effects. Dielectric charging increases with increasing temperature, humidity, peak voltage, and thickness of low-frequency dielectric film. However, the charging decreases with the increasing thickness of the dielectric film. Dielectric charging could be reduced by selecting Ultra-NanoCrystalline diamond and aluminum nitride dielectric materials instead of conventional materials. Applying a bipolar driving voltage, separation posts, polysilicon stoppers, and a double-dielectric-layer structure could also weaken charging effects. Conclusion 3: Contact stiction and contact degradation are the main failures of metal-contact switches related to the contact metal structure and the geometry of the contact area. Temperature rise is the direct cause of stiction. If the RF power level is increased, the contact failure is exacerbated by the raised temperature in the contact area. Au is the most widely used contact material in MEMS switches due to its very low resistivity, high conductivity, and high oxidation resistance, but contact wear, deformation, and adhesive failure are prone to occurring due to the low hardness and low melting point of Au. Strategies to improve hardness usually make use of bimetallic contacts and gold alloying with other metals, such as Ru or Pt, or with other noble metals. Bimetallic contacts and gold alloying show better switch lifetimes at hot switching conditions and excellent power-handling capability.