Quality factor for RF-MEMS capacitive switch on semi-suspended CPW

Abstract

This paper presents a new electrical model for RF-MEMS capacitive switch which is implemented on semi-suspended coplanar-waveguide. The model has been extracted from two previous works and it was able to describe the switch and take the effect of substrate into consideration with acceptable approximation. Regarding to the two similar structures of capacitive switches, a new formula for quality factor has been derived and the parameters which involve the quality factor have been studied with assumption of previous works. Moreover, the parameters which contribute to determining peak value of operating switch have been observed. According to the results, the fluctuation of the quality factor over frequency was very distinctive between 1–20 GHz and beyond that range, the variation of the quality factor was not very obvious. The results also indicate that increasing the series resistance which consists of resistance of T-line and bridge affected the quality factor. The increasing the series resistance reduced the quality factor and this effect was very noticeable at lower frequencies than 10 GHz. Increasing the capacitance of down-state also decreased the quality factor so that at lower than 3 GHz, it had considerable effect but higher than 5 GHz the effect was not very noticeable. On the other hand, increasing the resistance of substrate improved the quality factor but the effect is not very obvious for frequencies higher than 10 GHz. In addition, Peak value of operating as an important parameter, has been studied and the result suggested that the series resistance had almost no effect on determining the peak value of operating for the switch. The substrate resistance has the same influence. On the other hand, the capacitance of down-state has great effect on determining the peak value. It can change the bandwidth in which the switch can operate with higher quality factor. The capacitance of down-state did not have any effect on the value of quality factor.