Process flow indicating the main technological steps for obtaining the final geometry of the switch by means of an eight-mask process.
Diagram (top) and photograph detail (bottom) of the implemented Ohmic series switch configuration. Lateral wings have been included for improving the electrical contact. A number of switches with different geometrical and physical characteristics have been produced on the base of changes with respect to this one. Actually, the number of dimples as well as the thickness of the bridge and other details of the geometry contributes to the electrical performances. When the switch is actuated, the bridge, isolated with respect to the ground, closes the central conductor of the CPW with a metal-to-metal contact and the device is in the on state (device S1).
Coplanar shunt capacitive switch. When the switch is actuated, the bottom side of the bridge touches the dielectric layer placed along the central conductor of the CPW, providing a shunt to ground in a limited frequency range (resonant response), and the device is in the off state (device CL).
Schematic of the measurement system used for testing the rf MEMS switches.
Shape of the pulse trains used for the experiments on the charging effects. (a) is the unipolar scheme, while (b) is the bipolar one.
Response of S1 actuated by using positive voltages only. , , and for both trailing and leading edge of the pulse.
CL actuated by using positive voltage only. , , , for both trailing and leading edge of the pulse.
S1 actuated by using positive and negative voltages. Only the absolute value of the voltage is plotted, but changed from to after each pulse, with , , , and .
S1 actuated by using positive and negative voltages. Only the absolute value of the voltage is plotted, but changed from to after each pulse, with , , , and . The measurement has been performed after 5 min from that in Fig. 8. The difference between actuation and deactuation voltages is a bit decreased, which should indicate a charging not completely readsorbed.
S1 actuated by using positive and negative voltages. The same parameters used in Fig. 9 have been imposed, i.e., , , , and . Measurement performed the day after. The result is quite similar to that shown in Fig. 3, with T1 decreased from 1 min to 30 s and ramp passed from 1 to 2 V/s. Then, no influence of these parameters seems to be important in the utilized range. Moreover, the first actuation is still between 39 and 41 V, but by using positive and negative values is maintained at a constant value as well as the deactuation voltage, and lower than in the positive case only.
CL actuated by using positive and negative voltages. , , , and .
CL response by using the same parameters as in the case of Fig. 11, but with and measurement performed after 30 min. In this case no change in the two levels is obtained.
Bipolar scheme imposed for the actuation of the switch S1.
Fitted actuation and deactuation voltages for the S1 device following an exponential trend.
Fitted actuation and deactuation voltages for the CL device following an exponential trend.
Charging of a MIM capacitor used to emulate the situation of the collapsed bridge. The measured current decreases as a function of the voltage because of the induced electrical field contradirected with respect to the applied one.
curve as a function of the by using data from Fig. 16.
Measured trend of the current as a function of the applied voltage for a MIM made by before (curve a) and after (curve b) cycling the sample with pulses as high as 50 V. Generally, a linear response is always obtained as a function of the applied voltage, while a constant value is expected for an almost ideal dielectric material. By cycling the sample such a response is flattened, maybe due to the recombination of residual charges belonging to defects of the material surface coming out from the technological process.
Fitted values for the exponential trend of the actuation (Act) and deactuation (Deact) of both S1 and CL devices by using Eqs. (4) and (5).
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