1. Field of the Invention
The present invention relates generally to RF switches, and more particularly, to single-pole, multi-throw (micro-electro-mechanical) MEMS RF switches.
2. Prior Art
MEMS switches are called as such because they use electrostatic actuation to create movement of a beam or membrane that results in an ohmic contact (i.e. an RF signal is allowed to pass-through) or by a change in capacitance by which the flow of signal is interrupted and typically grounded.
In a wireless transceiver, pin diodes or GaAs MESFET's are used as switches. However, these have high power consumption rates, high losses (typically 1 dB insertion loss at 2 GHz), and are non-linear devices. MEMS switches on the other hand, have demonstrated insertion loss of less than 0.5 dB, are highly linear, and have very low power consumption since they use a DC voltage for electrostatic actuation. If the actuators are coupled to the RF signal in a series switch, then the DC bias would need to be decoupled from the RF signal. Usually, the DC current for the pin diodes in conventional switches is handled in the same way. Decoupling is never 100% and there are always some losses to the RF signal power either by adding resistive losses or by direct leakage. Another source of losses is capacitive coupling of actuators to the RF signal (especially when a series switch is closed). If high power is fed through the switch, then a voltage drop of about 10V is associated with the RF signal. That voltage is present at the RF electrode of the series switches in the open state. If these electrodes are also part of the closing mechanism (by comprising one of the actuator electrodes) that could cause the switches to close and thus limit the switch linearity (generate harmonics etc.). Usually transistor switches such as CMOS or FET suffer from non-linearity and high losses.
U.S. Pat. No. 5,619,061 to Goldsmith et al. has shown designs of MEMS switches comprised of metal and dielectric films for both capacitive coupling and ohmic contact but the metal films and the designs proposed by their invention rely on thin metal films either on top or below a beam made out of a dielectric material. A disadvantage of this type of switch is that unless the beam is made out of a single metal, there is no effective heat dissipation mechanism due to the Joule heating effect generated by the a high power RF signal that may go through.
Therefore, it is an object of the present invention to provide a single-pole, multi-throw MEMS RF switch that minimizes losses and improves on switch linearity as compared to the MEMS RF switches of the prior art.
It is another object of the present invention to provide a single-pole, multi-throw MEMS RF switch that improves heat dissipation as compared to the MEMS RF switches of the prior art.
Accordingly, a microelectromechanical switch is provided. The microelectromechanical switch comprises: at least one pair of actuator electrodes; at least one input electrode and at least one output electrode for input and output, respectively, of a radio frequency signal; and a beam movable by an attraction between the at least one pair of actuator electrodes, the movable beam having at least a portion electrically connected to the at least one input electrode and to the at least one output electrode when moved by the attraction between the at least one pair of actuator electrodes to make an electrical connection between the at least one input and output electrodes; wherein the at least one pair of actuator electrodes are electrically isolated from each of the at least one input and output electrodes.
Also provided is a microelectromechanical switch comprising: a first level portion having a first electrode for input or output of a radio frequency signal, at least one first actuator electrode electrically isolated from the first electrode, and a first contact electrically cooperating with the first electrode; and a second level portion having at least a portion separated from the first level portion by an air gap, the second level portion having a deflective beam capable of deflecting into the air gap, the beam having at least one second actuator electrode corresponding to the at least one first actuator electrode, the beam further having a second electrode corresponding to the first electrode for the other of the input or output of the radio frequency signal and a second contact electrically cooperating with the second electrode, the at least one second attractive electrode being electrically isolated from the second electrode; wherein creation of an electrical attraction between the at least one first and second actuator electrodes causes the beam to deflect into the air gap and to provide an electrical connection between the first and second contacts and their respective first and second electrodes for allowing the input radio frequency signal to one of the first and second electrodes to be output to the other of the first and second electrodes.
Preferably, the at least one first actuator electrode comprises two first actuator electrodes each of which are electrically isolated from the first electrode and wherein the at least one second actuator electrode comprises two second actuator electrodes, each of the two first actuator electrodes corresponding to a respective second actuator electrode when the beam is deflected into the air gap.
The microelectromechanical switch preferably further comprises at least one bumper arranged on the first level portion adjacent the first contact for urging contact between the first and second contacts when the beam is deflected into the air gap. More preferably, the at least one bumper comprises first and second bumpers, each of which is arranged on the first level portion adjacent the first contact for urging contact between the first and second contacts when the beam is deflected into the air gap.
Preferably, the creation of an electrical attraction between the first and second actuator electrodes comprises means for maintaining one of the first and second actuator electrodes at a ground state and the other of the first and second actuator electrodes energized with an applied voltage.
The beam preferably further having a plurality of access holes formed therein for facilitating creation of the air gap and for minimizing air damping during switch operation.
The first and second level portions preferably have a width and wherein at least one of the first and second electrodes is aligned in the direction of the width and has a first dimension in the direction of the width which is less than the width. More preferably, each of the first and second electrodes are aligned in the direction of the width and each has the first dimension in the direction of the width which is less then the width. In which case, the microelectromechanical switch preferably further comprises at least one dummy conductor disposed in the direction of the width and electrically isolated from a corresponding first and/or second electrode, the dummy conductor having a second dimension in the direction of the width which is less than the difference between the width and the first dimension.
Preferably, at least one of the first and second actuator electrodes are rectangular and wherein at least a portion of the first and second actuator electrodes correspond with each other across the air gap. More preferably, each of the first and second actuator electrodes comprises two first and second actuator electrodes, each of which are rectangular and disposed on both sides of their corresponding first and second electrodes.
The microelectromechanical switch of claim 1, wherein at least one of the second actuator electrodes are triangular having a base and an apex and wherein at least a portion of the first and second actuator electrodes correspond with each other across the air gap. Preferably, each of the first and second actuator electrodes comprises two first and second actuator electrodes, disposed on both sides of their corresponding first and second electrodes. More preferably, the base of each of the second actuator electrodes is proximate the second electrode.
Preferably, the microelectromechanical switch of claim 1, further comprising a ground plate electrically connected to one of the first or second actuator electrodes for grounding one of the first or second actuator electrodes.
Still provided is a multiple throw microelectromechanical switch comprising two or more single throw microelectromechanical switches. Each of the single throw microelectromechanical switches comprising: a first level portion having a first electrode for input or output of a radio frequency signal, at least one first actuator electrode electrically isolated from the first electrode, and a first contact electrically cooperating with the first electrode; and a second level portion having at least a portion separated from the first level portion by an air gap, the second level portion having a deflective beam capable of deflecting into the air gap, the beam having at least one second actuator electrode corresponding to the at least one first actuator electrode, the beam further having a second electrode corresponding to the first electrode for the other of the input or output of the radio frequency signal and a second contact electrically cooperating with the second electrode, the at least one second attractive electrode being electrically isolated from the second electrode; wherein creation of an electrical attraction between the at least one first and second actuator electrodes causes the beam to deflect into the air gap and to provide an electrical connection between the first and second contacts and their respective first and second electrodes for allowing the input radio frequency signal to one of the first and second electrodes to be output to the other of the first and second electrodes.
The multiple throw microelectromechanical switch preferably further comprises a ground plate electrically connected to one of the first or second actuator electrodes for each of the single throw microelectromechanical switches for grounding the one of the first or second actuator electrodes. The multiple throw microelectromechanical switch more preferably further comprises a substrate upon which is disposed one of the first or second level portions for each of the single throw microelectromechanical switches. The ground plate is preferably a continuous solid plate disposed on a lower surface of the substrate. Where the multiple throw microelectromechanical switch further comprises radio frequency input and output lines disposed on the substrate, one of which is connected to one of the first or second electrodes of each of the single throw microelectromechanical switches and the other of which is connected to the other of the first second electrodes of each of the single throw microelectromechanical switches, the ground plate is alternatively disposed on a lower surface of the substrate only in portions corresponding to the single throw microelectromechanical switches and the radio frequency input and output lines.
Still yet provided is a multiple throw microelectromechanical switch comprising two or more single throw microelectromechanical switches. Each of the single throw microelectromechanical switches comprises: at least one pair of actuator electrodes; at least one input electrode and at least one output electrode for input and output, respectively, of a radio frequency signal; and a beam movable by an attraction between the at least one pair of actuator electrodes, the movable beam having at least a portion electrically connected to the at least one input electrode and to the at least one output electrode when moved by the attraction between the at least one pair of actuator electrodes to make an electrical connection between the at least one input and output electrodes; wherein the at least one pair of actuator electrodes are electrically isolated from each of the at least one input and output electrodes.
These and other features, aspects, and advantages of the apparatus and methods of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:
a illustrates a top view of a preferred single-pole single-throw MEMS RF switch having a single contact.
b illustrates a sectional view of the switch of
c illustrates a sectional view of the switch of
a and 3b illustrate a sectional view of a MEMS switch and a graph, respectively, showing the Joule heating results thereof.
a illustrates a schematic view of paired single-pole, single-throw torsional switches having a single contact according to a preferred implementation.
b illustrates paired single-pole, single-throw torsional switches of
c illustrates the paired single-pole, single-throw torsional switches of
d illustrates the structure of the pivot point in greater detail.
a illustrates a schematic view of the paired single-pole, single-throw torsional switches having v-shaped beams with a single contact according to a preferred implementation.
b illustrates the paired single-pole, single-throw torsional switch of
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A first contact 114 is provided and is electrically connected to the lower electrode 112. The first contact 114 is raised above the top surface of the lower actuator electrodes 110 and first electrode 112. At least one bumper and preferably two bumpers 116 are disposed above the top surface of the lower actuator electrodes 110 and first electrode 112 and are not necessarily made out of metal and are electrically isolated from the other electrodes 110, 112. As will be discussed below, the bumpers 116 act to prevent stiction between the upper contact 126 and the lower contact 114. The above-described elements of the lower level portion 102 are formed on a substrate (not shown) by etching and deposition methods known in the art.
The upper level portion 104 includes a movable beam 121, which in the preferred implementation of
While the lower actuator electrodes 110 are preferably held at a ground potential, the upper actuator electrodes 120 are preferably and selectively held at contact voltage V1, to create an attractive electrostatic force between the beam 121 and the lower actuator electrodes 110 that are at ground. The beam 121 further has a upper electrode 124 for carrying the RF signal, which in the preferred implementation illustrated in
The MEMS 100 also includes voltage potential lines 105, 107 to create an electrostatic attraction between the first and second actuator electrodes. As discussed above, the lower actuation electrodes 110 are preferably maintained at a ground potential by connecting voltage potential line 105 to a ground while the upper actuator electrodes 120 are selectively held at a contact voltage V1 by connecting voltage potential line 107 to a power (voltage) source. In operation, when an electrostatic attraction is created between the upper and lower actuator electrodes 110, 120, the beam 121 bends or deflects towards the lower level portion 102 and the upper contact 126 touches the lower contact 114 and allows an RF signal go through from the input line 106 to the output line 108. The bumpers 116 act to prevent stiction between contacts 124 and 114 and also act to prevent shorting of the beam 100 to actuators 110. As discussed previously, the configuration of the MEMS 100 illustrated in
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As shown in
a and 12b, show a similar switch, referred to by reference numeral 400 in which similar reference numeral from
Therefore, to minimize losses and improve on a MEMS switch linearity, the switches 100, 200, 300, 400 disclosed herein separate entirely the RF signal electrodes from the DC actuators. Another reason for separating the DC actuators of the switch beam from the RF signal beam electrode is the need to design single-pole-multiple-throw switches for transmit/receive or frequency selection wireless applications. Integrating two or N number of switches in parallel provides a multiple throw switch with N number of throws.
Furthermore, the switches of the present invention solve the Joule heating dissipation problem of the prior art switches by using a composite metal-dielectric beam comprised of a metal actuator electrode, a thin layer of dieletric, a metal RF signal electrode and a second metal actuator electrode. A preferred metal is copper but other metals such as aluminum, nickel and their alloys can be used to fabricate the MEMS switch. Another advantage is the presence of a single contact for the RF signal. The RF signal is fed at an upper electrode of a fixed upper beam which, when actuated, is moved, such as by bending down to contact a lower electrode. A single RF contact with the use of appropriate contact materials give a lower contact resistance for the same contact force than a dual-contact metal-to-metal switch for the same contact force. Still another advantage of the switches of the present invention is the ability to fabricate very small gaps between the beam and the lower electrodes. Gaps between 0.1–0.5 microns typically yield actuation voltages of less than 10V. Finally, the switches of the present invention provide for a multi-throw MEMS switch for consumer wireless applications. The multi-throw design has typically one RF signal input and four to five RF signal output for selection of different frequencies and bands in GSM or UMTS system. The design of the multi-throw switch includes design of a ground plane to effectively terminate the electromagnetic field and to minimize RF signal losses within the silicon substrate.
While it has been shown and described what is considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention.
It is, therefore, intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.
This application is a divisional application of U.S. Ser. No. 10/150,285 filed on May 17, 2002 now U.S. Pat. No. 6,876,282 the disclosure of which is incorporated herein by its reference.
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Number | Date | Country | |
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20050156695 A1 | Jul 2005 | US |
Number | Date | Country | |
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Parent | 10150285 | May 2002 | US |
Child | 11053732 | US |