Design and Demonstration of Radio Frequency Micro Electro-Mechanical System Switches with Meandered Beams for Reduced Actuation Voltage +
Footnote †: This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ([[https://creativecommons.org/licenses/by/creativecommons](https://creativecommons.org/licenses/by/creativecommons)]([https://creativecommons.org/licenses/by/creativecommons](https://creativecommons.org/licenses/by/creativecommons)). ones, which are often avoided because of drawbacks like parasitic and unwanted actuations and incompatibility with standard Complementary Metal-Oxide-Semiconductor (CMOS) fabrication [6], higher power consumption and switching time, or thermal fatigue to the movable parts [7]. The classification of RF-MEMS switches can be carried out on the basis of the movement of the membrane (vertical or lateral), on the basis of the established mechanical contact (metal-to-metal or metal-to-oxide), or on the basis of their electrical role (series or shunt connection), as examined in depth in many other reference texts [5; 8]. A research challenge of constant interest in recent years has been that of devices characterized by a low actuation voltage (or \"pull-in\" voltage). There are many reasons behind this trend; in fact, devices with a low pull-in, in the order of 6.5 V, can use the same voltages of common circuitry and devices based on CMOS technology. In fact, most RF-MEMS devices in the literature are operated by voltages in the order of tens of volts, and step-up converters are required in order to integrate them into common circuits, increasing the footprint and complexity of the whole circuit [9]. Low pull-in voltages also determine a reduced mechanical shock on the movable membrane during the actuation, which increases the lifetime of the devices [10]. Therefore, using RF-MEMS devices with low pull-in voltages represents a solution that might be beneficial to the reliability of the device, surely improving the integrability, compactness, and cost of the final device. From a designer's point of view, different strategies can be followed to obtain low pull-in RF-MEMS switches, each of which is represented by numerous examples in recent works in the literature. Despite their practical drawbacks, piezoelectric, electro-thermal, and electro-magnetic mechanisms are particularly suitable for obtaining low actuation voltages. Within the piezoelectric context, the adoption of materials with high piezoelectric coefficients is permitted to achieve actuation voltages in the range of 2 V [11] to 2.5 V [12]. The electro-thermal device reported in [13] features chevron lateral actuators driven by an 11 V source, while in [14], the combination of driving and latching electro- thermal actuators allowed the authors to obtain a lateral actuation at 6 V. In the case of electro-magnetic devices, the proper dimensioning of the coil generating the magnetic field which triggers the collapse of the membrane allows the designer to achieve arbitrarily low pull-in voltages, such as 3 V [15] or 4.3 V [16]. Within the framework of electrostatic actuation, the most common strategy to reach reduced pull-in voltages is to combine the maximization of the \"effective area\" (the overlapping area between the fixed electrodes and the movable structure) with the design of a movable membrane characterized by a small spring constant [6]. Structures with a low spring constant can be attained by elongated shapes (long straight membranes or beams) or by meandered, folded, or serpentine-shaped beams. While the choice of elongated structures may be problematic from the point of view of miniaturization, meandered beams represent a more viable solution. In fact, elongated membranes may determine an excessive footprint or aspect ratio for such basic switching components. As an example, the sole membrane employed in [17] has a footprint of 1600 \(\times\) 240 \(\upmu\)m\({}^{2}\).