Patent Application
20220293382
The present invention relates to a microelectromechanical system (MEMS) switch, systems, and devices. In particular, the present invention relates to a MEMS switch with a beam contact portion continuously extending between input and output terminal electrodes to limit on-state resistance.
Microelectromechanical system (MEMS) switches provide high-performance relays that operate across a wide variety of frequency ranges. Unwanted or parasitic resistance may occur in MEMS switches, such as between the input terminal electrode and the output terminal electrode. Such parasitic resistance is undesirable as it results in electrical loss.
Embodiments of the disclosure are directed to microelectromechanical system (MEMS) switches with a beam contact portion continuously extending between input and output terminal electrodes. In exemplary aspects disclosed herein, the movable beam includes a body and a contact with more conductivity and stiffness than the body. The contact continuously extends between and electrically couples the contact of the movable beam with the input and output terminal electrodes. Differing materials between the body and the contact allow for inclusion of the mechanical properties of the body (e.g., to reduce mechanical fatigue, creep, etc.) while utilizing the electrical properties of the contact (e.g., to reduce on-state electrical resistance). Accordingly, the MEMS switch provides low resistance loss during an on-state while maintaining high levels of isolation during an off-state.
One embodiment of the disclosure relates to a microelectromechanical system (MEMS) switch including an input terminal electrode, an output terminal electrode, a pull-down electrode positioned between the input terminal electrode and the output terminal electrode, and a movable beam positioned proximate the input terminal electrode and the output terminal electrode. The movable beam includes a body comprising a first conductivity and first stiffness and a contact comprising a second conductivity and a second stiffness more than the first conductivity and the first stiffness. The contact is proximate to and continuously extending between the input terminal electrode and the output terminal electrode to limit on-state resistance therebetween. The movable beam is configured to move between an on-state and an off-state. The on-state electrically couples the contact of the movable beam with the input terminal electrode and the output terminal electrode. The off-state electrically isolates the contact of the movable beam from the input terminal electrode and the output terminal electrode.
An additional embodiment of the disclosure relates to a microelectromechanical system (MEMS), including a plurality of MEMS switches. Each switch includes an input terminal electrode, an output terminal electrode, a pull-down electrode positioned between the input terminal electrode and the output terminal electrode, and a movable beam positioned proximate the input terminal electrode and the output terminal electrode. The movable beam includes a body comprising a first conductivity and first stiffness and a contact comprising a second conductivity and a second stiffness more than the first conductivity and the first stiffness. The contact is proximate to and continuously extending between the input terminal electrode and the output terminal electrode to limit on-state resistance therebetween. The movable beam is configured to move between an on-state and an off-state. The on-state electrically couples the contact of the movable beam with the input terminal electrode and the output terminal electrode. The off-state electrically isolates the contact of the movable beam from the input terminal electrode and the output terminal electrode.
Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.
The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description, serve to explain the principles of the disclosure.
The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.
It should be understood that, although the terms first, second, etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It should also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.
It should be understood that, although the terms “upper,” “lower,” “bottom,” “intermediate,” “middle,” “top,” and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed an “upper” element, and, similarly, a second element could be termed an “upper” element depending on the relative orientations of these elements, without departing from the scope of the present disclosure.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including” when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having meanings that are consistent with their meanings in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
MEMS technology is currently one of the best available options for the implementation of very high-performance relays that operate from DC up to radio frequency and mm-Wave spectrum range. The most important figure of merit for such devices is generated from on-state resistance (Ron) and off-state capacitance (Coff). The product of these two quantities (Ron*Coff), measured in seconds, is an indicator of the intrinsic capability. A smaller Ron*Coff is desired to allow the design of relays that provide low loss when the electrical path is closed (on-state) while maintaining high levels of isolation when the electrical path is open (off state).
The MEMS switch 100 (may also be referred to herein as a MEMS relay, MEMS ohmic switch, etc.) further includes a moveable beam 116 (may also be referred to as a floating beam) mechanically anchored at both ends by flexible anchors 117 (e.g., springs). In this way, the moveable beam 116 is configured to move between a first position (off-state) and a second position (on-state) for up and down electrostatic actuation. The moveable beam 116 is connected to a ground connection 118. The moveable beam 116 further includes a body 119, an input contact 120A proximate the input electrode 106, and an output contact 120B proximate the output electrode 108. In certain embodiments, the moveable beam 116 is coupled to an RF node.
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In certain embodiments, the MEMS switch 100 further includes an up isolation circuit 121 between the pull-up electrode 102 and the Vup coupling 112 (may also be referred to as Vup connection, Vup source, etc.), a second isolation circuit 122 disposed between the moveable beam 116 and electrical ground connection 118, and a down isolation circuit 124 between the pull-down electrode 104 and the Vdn coupling 114 (may also be referred to as Vdn connection, Vdn source, etc.). The isolation circuits 121, 122, 124 isolate the MEMS switch 100 to prevent RF leakage (e.g., through the Vup coupling 112, the Vdn coupling 114, and/or the ground connection 118) by adding electrical impedance at RF leakage points. In certain embodiments, each of the isolation circuits 121, 122, 124 (may be referred to as Ziso) includes at least one resistor. The source impedance connected to the MEMS switch 100 is represented by Zsrc 126, and the load impedance connected to the MEMS switch 100 is represented by Zload 128. Additionally, the isolation circuits 121, 124 are utilized to isolate the control voltage sources, such as the Vup coupling 112 and Vdn coupling 114.
The isolation circuits 121, 122, 124 provide several benefits. The isolation circuits 121, 122, 124 bias the direct current potential to allow for electrostatic actuation and further provide a path for transient currents during switching. The components of each of the isolation circuits 121, 122, 124 are chosen such that the resistance levels limit RF leakage while enabling the MEMS switch 100 to function as intended (e.g., movement speed of moveable beam 116, maintain electric potential at the pull-up electrode 102 and pull-down electrode 104 during the switching transients), among other advantages (e.g., accurate engineering of actuation waveforms). In particular, the isolation circuits 121, 122, 124 help maintain RF performance such as voltage handling, insertion loss, isolation, and linearity.
In certain embodiments, each MEMS switch 100 has an on-resistance of 10's of Ohm and a very low off-state capacitance Coff, resulting in a Ron*Coff of 25-30 fs. A low on-resistance is achieved by operating many of these small MEMS RF-switch elements in parallel in an array. In this way, an on-resistance of 0.5 Ohm with an off-state capacitance of 50-60 fF can be achieved. However, further reductions can enable even lower loss and/or higher operating frequency as telecommunication bands move increasingly toward higher frequencies.
In certain embodiments, the pull-down electrode 104 is respectively coupled to a down isolation circuit 124 to isolate a lower voltage source from the plurality of pull-down electrodes 104. In certain embodiments, a second isolation circuit 122 is positioned between the movable beam 116 and an electrical common ground connection 118. In certain embodiments, the pull-up electrode 102 is coupled to an up isolation circuit 121 to isolate an upper voltage source from the pull-up electrode 102.
The movable beam 116 is configured to move between an on-state adjacent to the plurality of pull-down electrodes 104A, 104B to electrically couple the input terminal electrode 106 and the output terminal electrode 108 to the movable beam 116, and an off-state away from the plurality of pull-down electrodes 104A, 104B to electrically isolate the input terminal electrode 106 and the output terminal electrode 108 from the movable beam 116.
Instead of using multiple contacts, the MEMS switch 200 utilizes one continuous contact 120′ that continuously extends between the input terminal electrode 106 and the output terminal electrode 108. The moveable beam 116 includes a body 119 and a contact 120′ positioned toward a bottom of the body 119 extending between the input terminal electrode 106 and the output terminal electrode 108. In certain embodiments, the contact 120′ is embedded within the body 119. In certain embodiments, portions of the contact 120′ are exposed, and portions of the contact 120′ are covered (e.g., by a dielectric film).
Electrical current flows from the input terminal electrode 106 through the contact 120′ to the output terminal electrode 108. The contact 120′ has a higher conductivity (i.e., lower resistance) than the body 119 of the moveable beam 116. In other words, the electrical flow path includes a resistance R′ formed from the electrical current flowing through the contact 120′. However, resistance R′ of the contact 120′ is less than resistance R of the body 119. In certain embodiments, the contact-resistance between the contact 120′ and each of the input terminal electrode 106 and the output terminal electrode 108 is about 15-45 Ohms. In certain embodiments, the on-state resistance reduces from 0.5 Ohms to 0.35 Ohm, resulting in a 30% improvement. Accordingly, the contact 120′ has reduced the parasitic resistance R′ without increasing any contact resistance.
It is also noted that electrical current may also flow through the body 119, but that the electrical current through the body 119 is in parallel with the electrical current through the contact 120′. The contact 120′ of the moveable beam 116 provides higher conductivity (i.e., lower resistance) than the body 119 but may also be stiffer than the body 119. A thickness t of the contact 120′ can be adjusted based on the mechanical and/or electrical requirements of the MEMS switch 200. In certain embodiments, the thickness t is between about 30 to 80 nm. Further, the body 119 may be altered to compensate for the additional stiffness and/or weight of the larger surface area of the contact 120′. For example, the body 119 may require adjusted stress levels applied during deposition to straighten out the body 119 to compensate for the contact 120′ and prevent any mechanical deflection or bowing.
The contact 120′ further decreases the on-resistance of the MEMS switch by 25-30% without sacrificing the off-state capacitance, thus providing further reduction of the Ron*Coff.
Although described above as a single switch, other arrangements may be utilized. Multiple relays may be included together into one arrangement. In some non-limiting embodiments, four relays may be provided.
Accordingly, disclosed herein is a MEMS switch with a movable beam 116 positioned proximate to the input terminal electrode 106 and the output terminal electrode 108. The movable beam 116 includes a body 119 having a first conductivity and first stiffness, and a contact 120′ having a second conductivity and a second stiffness more than the first conductivity and the first stiffness. The contact 120′ proximate to and continuously extending between the input terminal electrode 106 and the output terminal electrode 108 limits on-state resistance therebetween. The movable beam 116 is configured to move between an on-state and an off-state. In the on-state, the movable beam 116 electrically couples the contact 120′ of the movable beam 116 with the input terminal electrode 106 and the output terminal electrode 108. In the off-state, the movable beam 116 electrically isolates the contact 120′ of the movable beam 116 from the input terminal electrode 106 and the output terminal electrode 108.
The pull-down electrode 104 is covered with a dielectric layer 306 to avoid a short-circuit between the movable beam 116 and the pull-down electrode 104 in the on-state. Suitable materials for the dielectric layer 306 include silicon-based materials including silicon-oxide, silicon-dioxide, silicon-nitride, and silicon-oxynitride. The thickness of the dielectric layer 306 is typically in the range of 50 nm to 150 nm to limit the electric field in the dielectric layer 306.
On top of the input terminal electrode 106 is the input terminal contact 308 (may also be referred to as an input RF contact), and on top of the output terminal electrode 108 is the output terminal contact 310 (may also be referred to as an output RF contact). The movable beam 116 forms an ohmic contact with the input terminal electrode 106 and the output terminal electrode 108 in the pulled-down state. In particular, the moveable beam 116 includes a body 119 with a contact 120′ continuously extending between the input terminal electrode 106 and the output terminal electrode 108.
On top of the anchor electrodes 302A, 302B are anchor contacts 312A, 312B, to which the movable beam 116 is anchored. Suitable materials used for the contacts 120′, 308, 310, 312A, 312B include Ti, TiN, TiAl, TiAIN, AIN, Al, W, Pt, Ir, Rh, Ru, RuO2, ITO, and Mo and combinations thereof.
In certain embodiments, the MEMS switch 300 includes a center stopper 314 (e.g., positioned on the dielectric layer 306). In certain embodiments, suitable materials that may be used for the stopper 314 include Ti, TiN, TiAl, TiAIN, AIN, Al, W, Pt, Ir, Rh, Ru, RuO2, ITO, Mo, and/or silicon-based dielectric materials such as silicon oxide, silicon-dioxide, silicon-nitride, and silicon-oxynitride and combinations thereof.
The movable beam 116 (may also be referred to as a switching element, MEMS bridge, etc.) includes lower conductive layer 316 and upper conductive layer 318, which are joined together using an array of vias 320. Opposing ends of the upper layer 318 are anchored to opposing ends of the lower layer 316 by vias 322A, 322B. Opposing ends of the lower conductive layer 316 of the moveable beam 116 are anchored to the anchor contacts 312A, 312B by vias 324A, 324B, which provide low compliance to permit operating voltages (e.g., 25V to 40V) to pull the moveable beam 116 in contact with the terminal contacts 308, 310 and center stopper 314. This allows for a cheap integration of the CMOS (complementary metal-oxide-semiconductor) controller with a charge-pump to generate the voltages to drive the MEMS switch 300. In other words, ends of the movable beam 116 are mounted to the substrate 304 such that the movable beam 116 is suspended above the input terminal electrode 106, output terminal electrode 108, and pull-down electrode 104 in the off state.
The lower conductive layer 316 includes the contact 120′ embedded within the body 119 at a bottom thereof. The contact 120′ includes exposed input portions 326 aligned with the input terminal electrode 106, exposed output portions 328 aligned with the output terminal electrode 108, and covered portion 330 therebetween.
The body 119 of the moveable beam 116 is configured for mechanical properties that allow for stable mechanical operation over many cycle-events (and avoid suffering from mechanical fatigue or creep). For example, in certain embodiments, the body 119 of the moveable beam 116 includes TiAl and/or TiAIN, etc.
The contact 120′ of the moveable beam 116 includes a corrosion-resistant metal that provides good electrical contact resistance. For example, in certain embodiments, the contact 120′ of the moveable beam 116 includes Ruthenium, Ruthenium-oxide, platinum, and/or gold, etc.
In certain embodiments, the MEMS switch 300 includes a cover 332 mounted to the substrate 304 and defines a cavity 334 between the cover 332 and the substrate 304. The movable beam 116 is positioned within the cavity 332.
MEMS switch 500 is similar to the MEMS switch 300 of
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Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.
