Abstract:
A micro-electro mechanical system (MEMS) switch having a single anchor is provided. The MEMS switch includes a substrate; grounding lines installed on the substrate to be distant away from each other; signal transmission lines positioned at predetermined intervals between the grounding lines; an anchor placed between the signal transmission lines; a driving electrode that encircles the anchor while not being in contact with the anchor, the signal transmission lines and the grounding lines; and a moving plate that is positioned on the driving electrode to be overlapped with portions of the signal transmission lines, and connected to the anchor elastically.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a high-frequency micro-electro mechanical system (hereinafter, “MEMS”), and more particularly, to an MEMS switch having a single anchor. 
     2. Description of the Related Art 
     An MEMS switch is a switch that is commonly adopted for signal routing or impedance matching networks in a wire communication system that uses microwave or millimeter wave. 
     In the existing monolithic microwave integrated circuits, a radio frequency (RF) switch is realized mainly with GaAs FET or a pin diode. However, the use of these elements causes a considerable insertion loss when the RF switch is switched on, and deteriorates signal separation characteristics when the RF switch is switched off. 
     To improve these problems, much research is made on developing various MEMS switches, and further, a tremendous increase in Mobile communication phone markets increases the importance of the MEMS switches. As a result, a variety of MEMS are suggested. 
     FIG. 1 is a plan view of a conventional MEMS switch. Referring to FIG. 1, a moving plate  10  is bilateral symmetry, being placed across input-output transmission lines  12  and  14  and a grounding line  16 , as shown in FIG.  2 . Referring to FIG. 2, the input-output transmission lines  12  and  14  are installed on a substrate S to be distant away from each other, and the moving plate  10  is placed over these input-output transmission lines  12  and  14 . 
     Here, reference numerals  18  and  20  denote first and second anchors for holding the moving plate  10 . The first and second anchors  18  and  20  are symmetrical with regard to the input-output transmission lines  12  and  14 , and connected to the both ends of the moving plate  10  via first and second springs  22  and  24 , respectively. Due to this structure, with the first and second anchors  18  and  20  as holding points, the moving plate  10  is in contact with the input-output transmission lines  12  and  14  by a driving electrode (not shown) when a driving force is given to the moving plate  10 , and returns back to the original position when the driving force is canceled from the moving plate  10 . 
     FIG. 3 is a cross-sectional view of the conventional MEMS switch of FIG. 1, taken along the line  3 - 3 ′. Referring to FIG. 3, first and second driving electrodes  26  and  28  are installed between the first and second anchors  18  and  20 , and actuate the moving plate  10  to be in contact the first and second anchors  18  and  20 . The first and second driving electrodes  26  and  28  are separated from each other at a predetermined interval. 
     Although not shown in the drawings, the input-output transmission lines  12  and  14  and the grounding line  16  are positioned between the first and second driving electrodes  26  and  28 . 
     Referring to FIGS. 1 and 2, the conventional MEMS switch has the moving plate  10  across the input-output transmission lines  12  and  14  and the grounding line  16 . Thus, when the moving plate  10  is actuated, it comes in contact with the grounding line  16 , which causes the leakage of a transmitted signal. Also, the both ends of the moving plate  10  are fixed by the first and second anchors  18  and  20 . For this reason, the moving plate  10  may transform upward and downward in the event that it thermally expands. A change in the shape of the moving plate  10  may increase driving voltage or power consumption when the MEMS switch is turned on. 
     SUMMARY OF THE INVENTION 
     To solve the above-described problems, it is an object of the present invention to provide an MEMS switch capable of preventing an increase in driving voltage due to the leakage of a transmitted signal or the transformation of a moving plate, or power consumption when the MEMS switch is on. 
     Accordingly, to achieve the above object, there is provided an MEMS switch including: a substrate; grounding lines installed on the substrate to be distant away from each other; signal transmission lines positioned at predetermined intervals between the grounding lines; an anchor placed between the signal transmission lines; a driving electrode not being in contact with the anchor, the signal transmission lines and the grounding lines, the driving electrode for encircling the anchor; and a moving plate positioned on the driving electrode to be overlapped with portions of the signal transmission lines, the moving plate connected to the anchor elastically. 
     Here, the moving plate is connected to the anchor via springs, and the moving plate and the anchor are connected to each other via four planar springs. 
     Preferably, the width of the moving plate perpendicular to the grounding lines is the same as the widths of the signal transmission lines. 
     Preferably, the driving electrode is geometrically shaped the same as the moving plate. 
     One end of each of the four planar spring is connected to the four corners of the anchor, but the one end of each plate spring is connected to one of two surface consisting of each corner, and the other end of each planar spring is extended from the one end along the surface of the anchor, to which the one end is connected, to connect to the inner surface of the moving plate which is opposite to the other surface of the anchor adjacent to the surface to which the one end is connected. 
     In an MEMS switch according to the present invention, a moving plate is positioned between grounding lines such that it can be actuated not in contact with these grounding lines. Thus, the MEMS switch according to the present invention is capable of completely transmitting a signal even if the moving plate comes in contact with the grounding lines, or these grounding lines are broken or become narrow. Also, the moving plate is hold by a single anchor, and thus, it is possible to prevent deformation of the moving plate upward and downward even if a substrate expands due to heat from the outside. Therefore, power consumption can be prevented when driving voltage for actuating the moving plate increases or the MEMS switch is switched on. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above object and advantages of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which: 
     FIG. 1 is a plan view of a conventional MEMS switch; 
     FIG. 2 is a cross sectional view of the MEMS switch of FIG. 1, taken along the line  2 - 2 ′; 
     FIG. 3 is a cross-sectional view of the MEMS switch of FIG. 1, taken along the line  3 - 3 ′; 
     FIG. 4 is a plan view of a preferred embodiment of an MEMS switch having a single anchor according to the present invention; 
     FIG. 5 is a cross-sectional view of the MEMS switch of FIG. 4, taken along the line  5 - 5 ′; and 
     FIG. 6 is a cross-sectional view of the MEMS switch of FIG. 4, taken along the line  6 - 6 ′. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 4, reference numerals  40  and  42  denote first and second grounding lines, respectively. The first and second grounding lines  40  and  42  are separated from each other at a predetermined interval in parallel. Between the first and second grounding lines  40  and  42 , first and second signal transmission lines  44  and  46  are positioned at a predetermined interval while not being in contact with the first and second grounding lines  40  and  42 . Here, the first and second signal transmission lines  44  and  46  are an input signal transmission line and an output signal transmission line, respectively. Also, an anchor  48  is placed between the first and second signal transmission lines  44  and  46 . Here, the anchor  48  is a rectangular single anchor while being distant away from the first and second grounding lines  40  and  42 , as well as the first and second signal transmission lines  44  and  46 . In this embodiment, the anchor  48  is rectangular shaped, but it may be variously shaped, e.g., round, triangular, pentagonal or hexagonal shaped. A moving plate  50  is located around the anchor  48 . The moving plate  50  is a rectangular band having a predetermined width, and encircles the anchor  48 . The shape of the moving plate  50  depends on the shape of the anchor  48 . If the anchor  48  is round or polygonal, rather than rectangular, the moving plate  50  must be also round or polygonal shaped. 
     Meanwhile, the moving plate  50  is overlapped with portions of the first and second signal transmission lines  44  and  46 , and thus comes in contact with the first and second signal transmission lines  44  and  46  when the moving plate  50  is actuated. Preferably, the width of the moving plate  50  perpendicular to the first and second grounding lines  40  and  42  is the same as the width W of the first and second signal transmission lines  44  and  46 , but it may be shorter or longer than the width W of the first and second signal transmission lines  44  and  46  within a range that the moving plate  50  is not in contact with the first and second grounding lines  40  and  42 . The anchor  48  and the moving plate  50  are elastically connected to each other. 
     Four planar springs  52  are installed between the moving plate  50  and the anchor  48  to elastically connecting the anchor  48  with the moving plate  50 . The moving plate  50  is elastically connected to the anchor  48  via the four planar springs. One end of each planar spring  52  is connected to the four corners of the anchor  48 . However, the one end of each plate spring  52  is connected to one of two surfaces consisting of each corner. The other end of each planar spring  52  is extended from the one end along the surface of the anchor  48 , to which the one end is connected, to connect to the inner surface of the moving plate  50  which is opposite to the other surface of the anchor  48  adjacent to the surface to which the one end is connected. In other words, connection form of the planar spring  52  is equal to connecting one of two surfaces consisting of each corner of the anchor  48  with the inner surface of the moving plate  50  one to one and then rotating the anchor  48  counterclockwise or the moving plate  50  clockwise by 90°. 
     Therefore, due to the elasticity of the planar springs  52 , the moving plate  50  can return back to the original position when it is actuated upward or downward. 
     Here, reference numeral  54  denotes a driving electrode for actuating the moving plate  50 . The driving electrode  54  is installed to cover the anchor  48 , being distant away from the first and second signal transmission lines  44  and  46 , and the first and second grounding lines  40  and  42 . The driving electrode  54  has a function of actuating the moving plate  50  to be in contact with the first and second signal transmission lines  44  and  46 . For this reason, preferably, the driving electrode  54  is shaped such that its driving force affects the moving plate  50  entirely, and thus, the driving electrode  54  may be taken a geometrical shape the same as the moving plate  50 . However, the driving electrode  54  may be geometrically shaped unlike the moving plate  50 , if necessary. 
     The positions of the driving electrode  54 , the moving plate  50 , and the first and second signal transmission lines  44  and  46  are clarified referring to FIG. 5, and the positions of the driving electrode  54 , the moving plate  50 , and the first and second grounding lines  40  and  42  are clarified referring to FIG.  6 . 
     First, referring to FIG. 5, the driving electrode  54  is placed between the anchor  48 , and the first and second signal transmission lines  44  and  46 , on a substrate  60 . At this time, the driving electrode  54  is not in contact with the anchor  48 , and the first and second signal transmission lines  44  and  46 . Also, the anchor  48  consists of a base  48   a  formed on the substrate  60 , and a holder  48   b  on the base  48   a . The holder  48   b  conforms to a wing shape, and thus it is inferred that the holder  48   b  is connected to the planar springs  52  with reference to FIGS. 4 and 5. Further, the moving plate  50  is placed on the driving electrode  54 , and extended to the first and second signal transmission lines  44  and  46 . The moving plate  50  comes in contact with the first and second signal transmission lines  44  and  46  when the moving plate  50  is actuated, because a portion of the moving plate  50  is overlapped with portions of the first and second signal transmission lines  44  and  46 . 
     From FIG. 6, it is noted that the driving electrode  54  is not in contact with the first and second grounding lines  40  and  42 , and the moving plate  50  is not overlapped with the first and second grounding lines  40  and  42 . 
     While this invention has been particularly described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Accordingly, those skilled in the art could have derived another embodiment of an MEMS switch from an MEMS switch having a single anchor according to the present invention. For instance, he or she can invent another MEMS switch by reducing the number of the planar springs  52 , changing the way the planar springs  52  are connected to the anchor  48  and the moving plate  50 , or forming the moving plate  50  or the planar springs  52  of a different material. Otherwise, portions of the moving plate  50  overlapped with first and second signal transmission lines  44  and  46  may be minimized. 
     As described above, in an MEMS switch according to the present invention, a moving plate is positioned between grounding lines such that it can be actuated not in contact with these grounding lines. Thus, the MEMS switch according to the present invention is capable of completely transmitting a signal even if the moving plate comes in contact with the grounding lines, or these grounding lines are broken or become narrow. Also, the moving plate is hold by a single anchor that is positioned between input and output signal transmission lines and grounding lines. For this reason, it is possible to prevent the deformation of the moving plate upward and downward even if a substrate expands due to heat from the outside. Therefore, power consumption can be prevented when driving voltage for actuating the moving plate increases or the MEMS switch is switched on.