# Research and Analysis of MEMS Switches in Different Frequency Bands
## 3 The Research Status of MEMS Switches in Different Frequencies
### Research on Reliable Contacts of MEMS Switches
The switches with binary alloy contacts resulted in contact resistance values ranging from 1 \(\Omega\) to 2 \(\Omega\). The reliability testing presented a 3\(\times\) increase in switching lifetime compared to switches with Au contacts. The ternary alloy showed about a 6\(\times\) increase in switching lifetime and contact resistance values between 0.2 \(\Omega\) and 1.8 \(\Omega\). Gold alloying with other metals can also improve their power-handling capability because they can handle large contact temperatures. [PERSON] et al. (2018) showed that a welding problem of the Au-Ir contact occurred at 1.4 W and at 0.5 W for the Au-Au contact. The power-handling capability of the Au-Ir contact was approximately 2.8 times that of the Au-Au contact. [PERSON] et al. (2018) reported that the softening of the contact surface occurred at 3 mW for Au-Au contact and at 4.25 mW for Ru-Ru contact, whereas it occurred at 14 mW for Au-Ru contact. Contamination by materials such as oxygen, carbon, and organic polymers ([PERSON] et al., 2018; [PERSON] et al., 2018) can also lead to failure in contacts. [PERSON] et al. (2018) found that contact resistance increased with the number of cycles for alloy films due to the accumulation of contaminants on the contact. The noble metals Ru, Rh, and Pt were more sensitive to the growth of a contamination film compared with Au. Thus, the contamination rate could be changed when these metals are alloyed with Au, and high Au content in the alloy could make the metal less vulnerable to contamination failure. [PERSON] et al. (2018) observed that switches with Au-Au contacts failed because of adhesion. Switches with Au-Pt and Au-Ir contact did not fail due to adhesion, but instead show lifetime limitations from carbon accumulation on the contacts. Ag-Ag contacts were vulnerable to corrosion and were difficult to operate in a device fabrication process flow. Therefore, it is necessary to realize a hermetic and reliable packaging to minimize contamination from the environment when the switch is working. Switches in ([PERSON] et al., 2018) were cleaned and sealed using typical metal-sealed hermetic packaging approaches to prevent contamination. [PERSON] et al. (2017) proposed that the catalytic behavior of RuO\({}_{2}\) film delays or prevents the failure of the switches because of accumulation of carbon at the contacts. [PERSON] et al. (2010) reported an Au-Au/carbon nanotubes (CNTs) contacts RF MEMS switch, which presented better lifetime cycle than the Au-Au contacts switch. In the above studies, gold alloying with other metals (such as Au-Pt and Au-Ir contacts) shows reliable characteristics for better lifetime at hot switching conditions and for better power-handling capability. But it is observed that the contact resistance increased compared with the Au-Au contact. [PERSON] et al. [88] showed that the measured contact resistance of Au/(6.3%)Pt-Au/(6.3%)Pt was 0.72 \(\Omega\) and Au/(15%)Pt-Au/(15%)Pt was 1.1 \(\Omega\). [PERSON] et al. [101] presented that the measured contact resistance of Au/(7.8%)Ni-Au/(7.8%)Ni was 0.62 \(\Omega\) and Au/(16.7%)Ni-Au/(16.7%)Ni was 0.88 \(\Omega\). In order to reduce the contact resistance, some multi-contact MEMS switches were proposed. [PERSON] et al. [95] reported a novel design capable of achieving mN-level Au-Ru contact; two 0.3-m-thick dimples were designed to form the metal-to-metal contact. The design was capable of achieving low resistance. The contact resistance of 2.4-1.8 \(\Omega\) at 90-100 V was achieved in open laboratory environments (nonpackaged). [PERSON] et al. [102] designed a metal-to-metal contact MEMS switch based on a Pt-Au micro-spring contact. The thickness of the top contact part was decreased alone. The micro-spring contact alleviated mechanical wear on the contacts. The current handling ability was 150 mA per contact, and the lifetime was 1.2 \(\times\) 10\({}^{6}\) cycles for hot switching. [PERSON] et al. [103] designed a MEMS metal-contact switch based on mN-level Au-Ru contact.