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RF MEMS tuners with wide impedance coverage have been developed for 6-24 GHz noise parameter and load-pull measurement systems. The tuners are based on triple-, double-, and single-stub topologies loaded with switched MEMS capacitors. Several designs are presented, and they use 10-13 switched MEMS capacitors to produce 1024-8192 (2 10 -2 13 ) different impedances. The measured impedance coverage agrees well with simulations and it is the widest ever measured impedance coverage from any planar tuner to-date.

This paper presents a paradigm shift in RF MEMS, and shows the development of miniature switched capacitors for RF applications*. The MEMS bridges are 21 µm long by 8 µm wide, and are 150-300× smaller than the standard Raytheon switch or other switched capacitors [1]. The bridges are integrated in an NxM array implemented in coplanar waveguide t-lines (CPW). The bridges are 3400 Å thick, and are suspended 2400 Å above the CPW center conductor (with a 1600 Å SiN layer), resulting in an actuation voltage of 25 V. The measured capacitance ratio of a single bridge is 2.8, and that of a 3x20 array is 1.9. These MEMS switched capacitors have a very high spring constant, and correspondingly a very high pull-up force per unit contact area with the dielectric layer. They are not sensitive to charging in the dielectric layer and also, are not sensitive to temperature variation. Also, the simulated switching time is 250 ns for gold switches and 110 ns for Al switches. We believe that this novel design will be very useful for high reliability RF MEMS switches in the coming years.

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