# Research and Analysis of MEMS Switches in Different Frequency Bands
## 3 The Research Status of MEMS Switches in Different Frequencies
### Research about Multiband MEMS Switches  
Nowadays, the system becomes more complicated with the development of science and technology, and complex systems need multiband operation. They require many small unit cells, such as RF MEMS switches, for multifrequency band functionality [119]. To overcome these problems, some studies have proposed multiband RF MEMS switches, which can be tuned to different frequency bands by tailoring the switch geometry and size. [PERSON] designed a novel capacitive MEMS switch with a high capacitance ratio for multiband and variable bandwidth [36]. The structure of the proposed switch is shown in Figure 2. \"A\", \"B\", \"C\", and \"D\" cantilevers mounted on the ground planes on both sides of the switch are designed to be used in various configurations to realize multiband operation. A thin metal layer was deposited over the dielectric layer to solve the reliability problems due to stiction with the dielectric layer. The insertion loss of this switch was 0.1-0.19 dB at 30-60 GHz. When all four of these cantilevers were pulled down, the isolation was better than 30 dB at 30-76 GHz (38 dB at 40 GHz), 30-36 dB at 50-75 GHz, and 26-30 dB at 75-110 GHz. When \"AB\" or \"CD\" cantilevers were pulled down, the isolation was better than 30 dB at 30-54 GHz and 50 dB at 40 GHz. When \"ABC\", \"ABD\", \"ACD\", or \"BCD\" cantilevers were pulled down, the isolation was better than 30 dB at 30-68 GHz and 57 dB at 36 GHz. [PERSON] et al. [40] proposed an asymmetric structure on either side of the transmission line utilizing the float metal concept to implement the switch. The structure is presented in Figure 3. The conventional membrane was replaced by two asymmetrical cantilevers. The novel structure was used to inductively tune the isolation, which enables the switch to be used in the C, X, and Ku bands. When right, left, or both cantilevers were in the down-state, the isolation peaks were 44.22 dB at  
Figure 2: The novel capacitive MEMS switch with high capacitance ratio for multiband. Reprinted by permission from [36]. 8.8 GHz, 42.63 dB at 7.2 GHz, and 47.75 dB at 16.5 GHz, respectively. The insertion loss was better than 0.10 dB, and the return loss was below 23.93 dB up to 25 GHz. [PERSON] et al. designed a new type of capacitive shunt MEMS switch for the X and K bands [42]. The switch structure was implemented with two dissimilar shapes of cantilevers attached to a bridge anchored in between the ground planes of the CPW on either side. Therefore, the inductance value was different on either side of the bridge, which enables the switch to be used in the X and K bands. The insertion loss was 0.01-0.11 dB at 1-25 GHz. When right, left, or both cantilevers were in the down-state, the isolation peaks were 34.33 dB at 11 GHz, 34.71 dB at 10.4 GHz, and 40.7 dB at 21.4 GHz, respectively. [PERSON] et al. [120] designed a frequency scalable MEMS capacitive shunt switch at the millimeter-wave frequency, The switch had different resonant frequencies by changing the size of the switch. When the size of the bridge was 450 \(\upmu\)m \(\times\) 450 \(\upmu\)m with the 52-65 GHz operating frequency range of the switch, the insertion loss was 0.6 dB at 60 GHz and the isolation was 3 2 dB at 60 GHz. When the size of the bridge was 400 \(\upmu\)m \(\times\) 350 \(\upmu\)m with the 68-88 GHz operating frequency range of the switch, the insertion loss was 0.3 dB at 78 GHz and the isolation was 25 dB at 78 GHz. When the size of the bridge was 350 \(\upmu\)m \(\times\) 340 \(\upmu\)m with the 86-102 GHz operating frequency range of the switch, the insertion loss was 0.3 dB at 94.5 GHz and the isolation was 27 dB at 94.5 GHz. [PERSON] et al. [121] properly modified the design and the fabrication process of MEMS switches, which resulted in devices differing only in the suspended/fixed bridge on the actuator, the presence/absence of the floating metal on the actuator, and the geometric parameters of the bridge, in order to tune the resonance frequency.