Electromechanical devices generally comprise a class of devices that combine electrical and mechanical parts. There are many types of electromechanical devices, and examples include microelectromechanical (MEM) devices, microelectromechanical systems (MEMS), microsystems (MST), nanoelectromechanical systems (NEMS), sensors, transducers, actuators and switches. Electromechanical devices having planar configurations offer several advantages over nonplanar configurations, including reduced size, lower power consumption, and lower fabrication costs.
The two most widely used techniques for fabricating planar electromechanical devices are surface micromachining (SM) and bulk micromachining (BM). While SM defines a structure by deposition and etching of different structural layers, BM defines a structure by selectively etching inside a substrate. The differences in these two manufacturing processes results in differences in structures and properties of devices fabricated thereby. For example, due to the conformal nature of SM, which involves successive depositions of metals and dielectrics, nonplanar structures also known as step beams are formed. Switches embodying these step beams are susceptible to latching or friction when a switch's cantilever conforms to its underlying electrical contact. In contrast, BM, which can include wafer bonding, yields planar structures.
Further, BM uses single crystal materials, which are superior to the deposited films used in SM. For example, single crystal substrates tend to have fewer crystal lattice defects than thin films. In addition, the mechanical properties of single crystal substrates (e.g., Young's modulus and Poisson's ratio) are highly repeatable, which again facilitates fewer crystal lattice defects. In contrast, the mechanical properties of thin films vary widely with the conditions under which such films are processed. Furthermore, while single crystal substrates are substantially free of built-in stresses, deposited thin films may include a variety of built-in compressive and tensile stresses that detrimentally affect manufacturing and performance. Due to these shortcomings, surface micromachined switches may develop stress concentration points during switch actuation which, over time, can lead to device failure. Similarly, contact dimples formed on switches using SM technology are prone to failure due to delaminations occurring between the thin film layers during extended periods of switch actuation.
In BM processing technology, the most popular substrate is silicon wafers due to the favorable anisotropic properties of silicon in which its crystal structure is arranged in lines and planes. Because of this structural arrangement, etching can be selectively performed on specific lines and planes that have relatively weak bonds. However, given the inferior insulation properties of silicon vis-a.-vis other materials, RF planar switches comprising silicon exhibit relatively low isolation and thus high insertion losses.
RF switches are widely used in a variety of applications including, for example, telecommunication applications. In this regard, RF switches are extremely important building blocks for reconfigurable RF communication systems. In one application, the use of planar RF switches can reduce the overall size, weight and cost of switch matrices on satellites. In other applications, planar RF switches can be incorporated into software programmable radio systems, reconfigurable antennas for radar, and antennas for mobile communications.
As can be seen, there exists a need in the art for improved methods and apparatus for planar RF switch technology offering a durable switch made from a single crystal in which the switch has high isolation, low insertion losses and highly repeatable mechanical properties. The embodiments of the present disclosure answer these and other needs.