# A New Concept of Reconfigurable Antenna Structure Based on an Array of RF-MEMS Switches
## 3 Development of a 7 \(\times\) 7 Reconfigurable Matrix Structure Prototype
### 7 \(\times\) 7 Matrix Prototype Description  
In this subsection, the description of the \(7\times 7\) reconfigurable prototype is detailed. The complete CAD layout obtained with the Cadence software is reported in Figure 7. As stated above, one of the main advantages of this technology is that every component (gold patches, switches, feeding, and control lines) can be designed on the same substrate, and the final prototype, once completed and printed, is immediately operative. The fabrication consists of eight different masks (the same procedure used for the production of the MEMS switches).  
The first mask is used to realize the central buried electrode (in pink in Figure 7), the serpentine-shaped resistors connecting the movable membrane to the ground planes, and the lines laying under the anchoring points of the metallic bridge. It consists of a poly-silicon layer. In particular, the former is meant to keep the MEMS switches membrane to null voltage while preventing the RF signal from flowing toward the ground. The second mask extends the device's reliability by acting as a micro-heater and restoring the membrane to  
Figure 6: RF-MEMS switch simulated vs. measured \(S_{21}\), (**a**) open, (**b**) closed position.  
the rest position in case of stiction. Stiction is the missed release of the membrane when the voltage of the buried electrode is set to zero, and it occurs because of microwelding or trapped charge within the oxide since the voltage applied to the two pads implies a flow of current along the resistor, which results in a thermal expansion of the locked membrane and in an induced restoring force [43]. The third mask consists of a multi-metal layer based on aluminum composing the buried sections of the RF underpass signal line (in blue in Figure 7). It ends in the correspondence of two contact pads laying on the surface of silicon oxide, obtained by evaporating gold (fifth mask). The suspended membrane provides the interrupted electrical connection of the signal lines, which is deployed onto a photoresistant sacrificial layer (sixth mask). Then, two layers of electroplated gold (seventh and eighth masks) compose the connection frames, the movable membrane (in brown), and the two anchoring points. The MEMS membranes' nominal actuation (pull-in) is obtained with a voltage signal at 21 V, which is the amount of voltage at which the membrane would reach its maximum displacement of about 2.5 \(\upmu\)m. Further details concerning the fabrication procedure and the stress residual estimation of the thin films are reported in [48; 49].  
Figure 8 shows a photo of the Si wafer with different prototypes, and Figure 9 reports a high-resolution photo of a single prototype obtained with an optical microscope. The entire dimensions of the prototype are \(5230\times 5230\)\(\upmu\)m\({}^{2}\). Each gold patch is \(430\times 430\)\(\upmu\)m\({}^{2}\), and it is connected with the other surrounding patches by four MEMS switches. On the left side of Figure 9, it can be observed that the gold pad is used as a feeding point for the RF signal. The prototype structure presents a thickness of \(t\) = 656.4 \(\upmu\)m; specifically, the gold layer has a thickness of \(t_{g}\) =5 \(\upmu\)m, the silicon dioxide is characterized by a thickness of \(t_{diox}\) = 1.4 \(\upmu\)m and a dielectric permittivity of \(\varepsilon_{diox}=3.94\), and the last layer made of silicon has a thickness of \(t_{Si}\) = 650 \(\upmu\)m and a dielectric permittivity of \(\varepsilon_{Si}=11.9\). A matrix prototype has been cut from the Si wafer and predisposed for the experimental assessment.  
Figure 8: Photo of the Si wafer with the obtained prototypes.  
Figure 7: Complete CAD layout of the \(7\times 7\) elements reconfigurable matrix, obtained with the Cadence software.