Micro electro mechanical system power relay

Abstract

A power relay having an actuator with a microelectromechanical system stator assembly and a plunger assembly moving along a central longitudinal axis between a first position and a second position, the plunger assembly including a plunger including a pair of ferromagnetic plates with a magnet disposed therebetween, and a first ferromagnetic plate of the pair of ferromagnetic plates is disposed between the first ferromagnetic layer and the second ferromagnetic layer in the stator assembly, and a second ferromagnetic plate of the pair of ferromagnetic plates is disposed between the second ferromagnetic layer and the third ferromagnetic layer in the stator assembly. The contact formed by the ferromagnetic plate and the ferromagnetic layer may include an array of micromachined flexure or a stable liquid-solid electrical contact.

Description

Technical Field

[0001] This disclosure relates to devices for power management, and more specifically, to power relays constructed with microelectromechanical systems (MEMS). Background Technology

[0002] In today's electrified world, power control is crucial in many areas. A smarter power grid allows power companies to manage electricity at a very localized level, enabling suppliers or users to shut down specific equipment during peak hours. This allows suppliers to stop high-current loads such as washing machines and air conditioners before peak loads ease, rather than implementing rolling blackouts to prevent grid collapse.

[0003] To achieve this level of control, power companies require remotely addressable relay-type switches. Existing relays are bulky and inefficient, generating significant heat at the required current levels, necessitating large heat sinks. These relays are also too large to be installed in existing circuit breakers, requiring upgrades to the load center to support their installation. Therefore, a small relay with low contact resistance is needed to address this issue.

[0004] Another application scenario for these small relays is in data processing centers. These centers may have hundreds of thousands of servers, and operators need (or provide this as a cloud service) the ability to remotely power off and on each server individually. Power distribution units (PDUs) used for this purpose typically have an independent circuit breaker and a separate relay for each outlet. Integrating the relays into the circuit breakers (only feasible if the relays are small enough and do not require heat sinks at the required current levels) and reducing the size of the circuit breakers can significantly reduce PDU size, an important metric for high-density modern data centers. Summary of the Invention

[0005] This disclosure relates to a power relay constructed using a microelectromechanical (MEMS) architecture. The relay utilizes three novel MEMS architectures, individually or in combination.

[0006] According to one aspect of this disclosure, a power relay is provided, the actuator of which includes a stator assembly having a cavity defined along a central longitudinal axis. The stator assembly includes: a non-conductive substrate having a top surface; one or more layers including components that mechanically or electrically interact with a load; a first ferromagnetic layer adjacent to a spacer; a plurality of first coils adjacent to the first ferromagnetic layer; a second ferromagnetic layer adjacent to the plurality of first coils; a plurality of second coils adjacent to the second ferromagnetic layer; and a third ferromagnetic layer adjacent to the plurality of second coils, wherein the bottom surface of the third ferromagnetic layer defines the top of the cavity.

[0007] The power relay also includes a plunger assembly disposed within the stator assembly cavity. During operation, the plunger assembly moves along a central longitudinal axis between a first position and a second position. The plunger assembly includes a plunger having a pair of ferromagnetic plates, with a magnet disposed between the plates. The first ferromagnetic plate of the pair is disposed between a first ferromagnetic layer and a second ferromagnetic layer of the stator assembly, and the second ferromagnetic plate of the pair is disposed between a second ferromagnetic layer and a third ferromagnetic layer of the stator assembly.

[0008] According to another aspect of this disclosure, the contacts used in the aforementioned power relay, in a first alternative, include: a first contact member having an exposed surface having an uneven structure, on which one or more high points and low points are formed; a second contact member having a contact surface and a plurality of conductive flexible elements extending from the contact surface, wherein the first contact member and the second contact member are movable relative to each other to provide different open and closed positions, and wherein, when the first contact member is adjacent to the second contact member and positioned in the closed position, the contact surface of the second contact member is not in electrical contact with one or more high points on the exposed surface of the first contact member, while each of the plurality of conductive flexible elements is in electrical contact with the exposed surface of the first contact member.

[0009] According to another aspect of the contact according to this disclosure, all plurality of conductive flexible elements extending from the contact surface of the second contact member have the same height above the contact surface of the first contact member, which is greater than the sum of a first distance between the high point and the low point on the exposed surface of the first contact member and the separation distance between the exposed surface of the first contact member and the high point of the contact surface of the second contact member when the first contact member is in the closed position.

[0010] Optionally, according to another aspect of this disclosure, the power relay with actuator described above includes contacts comprising: a first contact member having a base with an exposed surface, the base having a first groove opening toward the exposed surface, the first groove having circumferential sidewalls and a bottom wall defining its interior; a first metal layer disposed on the bottom wall of the first groove, the top surface of which is lower than the exposed surface of the first contact member; a liquid metal layer disposed only on the top surface of the first metal layer and extending above the exposed surface of the first contact member; and a second contact member having a contact surface, the second contact member being adjacent to the first contact member and positioned in an open position, and movable to a closed position, in which the contact surface of the second contact member contacts and presses against the liquid metal layer and the first metal layer until the contact surface of the second contact member abuts against the exposed surface of the first contact member.

[0011] According to another aspect of the power relay contact described above, the contact includes a second groove formed on the exposed surface of the first contact member, the second groove surrounding the first groove, the bottom wall of which is lower than the exposed surface of the first contact member and higher than the bottom wall of the first groove, the second groove also having circumferential sidewalls and a bottom wall defining its interior, and a portion of the interior of the second groove overlapping the interior of the first groove.

[0012] According to another aspect of the contact described above in this disclosure, the liquid metal layer is formed of a compliant material that is displaced in the closed position by pressure applied by the second contact member and returns to its original shape when the second contact member moves to the open position.

[0013] According to another aspect of this disclosure, a power relay is provided, comprising the aforementioned actuator and a contact having: a first contact member having an exposed surface having an uneven structure forming one or more high points and low points on the exposed surface; and a second contact member having a contact surface and a plurality of conductive flexible elements extending from the contact surface, wherein the first contact member and the second contact member are movable relative to each other to provide different open and closed positions, and wherein when the first contact member is adjacent to the second contact member and positioned in the closed position, the contact surface of the second contact member is not in electrical contact with one or more high points on the exposed surface of the first contact member, while each of the plurality of conductive flexible elements is in electrical contact with the exposed surface of the first contact member.

[0014] According to another aspect of this disclosure, a power relay is provided, comprising the aforementioned actuator and a contact having: a first contact member having a base with an exposed surface, the base having a first groove opening toward the exposed surface, the first groove having circumferential sidewalls and a bottom wall defining its interior; a first metal layer disposed on the bottom wall of the first groove, the top surface of which is lower than the exposed surface of the first contact member; a liquid metal layer disposed only on the top surface of the first metal layer and extending above the exposed surface of the first contact member; and a second contact member having a contact surface, the second contact member being adjacent to the first contact member and positioned in an open position, and movable to a closed position, in which the contact surface of the second contact member contacts and presses against the liquid metal layer and the first metal layer until the contact surface of the second contact member abuts against the exposed surface of the first contact member.

[0015] According to another aspect of the power relay contact described above, the contact includes a second groove formed on the exposed surface of the first contact member, the second groove surrounding the first groove, the bottom wall of which is lower than the exposed surface of the first contact member and higher than the bottom wall of the first groove, the second groove also having circumferential sidewalls and a bottom wall defining its interior, and a portion of the interior of the second groove overlapping the interior of the first groove.

[0016] According to another aspect of the contact described above in this disclosure, the liquid metal layer is formed of a compliant material that is displaced in the closed position by pressure applied by the second contact member and returns to its original shape when the second contact member moves to the open position.

[0017] According to another aspect of the contact described above in this disclosure, the first metal layer and the liquid metal layer can be directly disposed on the top flat surface of the first contact member without the need for a first groove or a second groove. Attached Figure Description

[0018] The above and other features and advantages of this disclosure will be more readily understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Figure 1 A schematic diagram of a solenoid or actuator having a conventional electromagnetic form; Figure 2A Cross-sectional views of each layer of the actuator according to various embodiments of this disclosure; Figure 2B and Figure 2C Show Figure 2A The layers of the microelectromechanical actuator shown generally correspond to one of two “stacks”: a static stack (also known as a “stator assembly”) or an actuable stack (also known as a “rotor assembly” or “plunger assembly”). Figure 3 A simplified schematic diagram illustrating the latching behavior of a microelectromechanical actuator caused by the magnetic circuit in the "open position" and "closed position"; Figure 4 A schematic diagram illustrating how an approximately constant magnetic force is applied to the plunger when current is passed through the coil; Figures 5A to 5E The magnetic flux in the plunger assembly is shown as it moves from a first position to a second position and then back to the first position. Figure 6 A three-dimensional cross-sectional view illustrating how the flexible element connected to the plunger assembly restricts the movement of the plunger assembly relative to the stator assembly; Figure 7 A schematic cross-sectional view of the plunger assembly, contact assembly, and stator assembly; Figure 8 A cross-sectional view of a microelectromechanical actuator and a schematic diagram of possible assembly sequences; Figure 9 A high-level flow chart of the manufacturing process for microelectromechanical actuators; Figure 10A and Figure 10B A diagram illustrating a contact array formed according to this disclosure; Figure 11A and Figure 11BThis is a schematic diagram illustrating the operation of traditional contacts; Figure 12A and Figure 12B Adopted in accordance with this disclosure Figure 10B A schematic diagram illustrating the structure and operation of the contacts in the contact array; Figure 13 This illustrates an array of flexible elements formed according to the present disclosure; Figure 14 This illustrates a feature including a circumferential hard stop according to the present disclosure. Figure 13 Flexible element array; Figure 15A and Figure 15B This illustrates a contact member formed according to an embodiment of the present disclosure, wherein, Figure 15B For along Figure 15A Cross-sectional view of line 15B-15B in the middle; Figure 16 Show Figure 15A and Figure 15B Wetting of the tantalum layer in the contact components; Figure 17 The contact is shown in the open state according to this disclosure; Figure 18 The contact is shown in the closed state according to this disclosure; Figure 19 This illustrates a contact pair according to the present disclosure in which neither contact has a groove machined. Figure 20A An isometric diagram illustrating a method of assembling contacts by laminating multiple layers; Figure 20B For along Figure 20A A cross-sectional view of line BB in the middle; Figure 21A An isometric view of a liquid metal droplet in a disconnected contact with a dendritic channel; Figure 21B for Figure 21A Enlarged detail images of the parts; Figure 22A An isometric view of a liquid metal droplet being pressed into a closed contact within a channel; Figure 22B for Figure 22A Enlarged detail images of the parts; Figure 22C for Figure 22A An enlarged top view of the part; Figure 23A and Figure 23B The relays according to this disclosure are shown in the open and closed states, respectively. Figure 24 This illustrates the use of a liquid layer on a contact according to the present disclosure; Figure 25A and Figure 25B This illustrates a bipolar relay formed according to the present disclosure; Figure 26 This is a top plan view of a bipolar relay formed according to this disclosure. Detailed Implementation

[0019] In the following description, specific details are set forth to provide a thorough understanding of the various disclosed embodiments. However, those skilled in the art will understand that these embodiments may be implemented without one or more of these specific details, or by other methods, components, materials, etc. In other instances, well-known structures associated with circuit breakers, relays, coils, and typical electrical components have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments.

[0020] Unless the context otherwise requires, throughout the specification and subsequent claims, “comprise” and its variations (e.g., “comprises” and “comprising”) shall be interpreted in an open-ended, inclusive sense, meaning “including but not limited to”.

[0021] "Connection," "coupling," and any variations thereof are intended to include any direct or indirect connection or coupling between two or more elements, which can be physical, logical, or a combination thereof. For example, objects may be electrically or communicatively connected even if there is no physical connection between them.

[0022] Throughout this specification, references to "one embodiment" or "implementation" mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment. Therefore, the phrases "in one embodiment" or "in an embodiment" appearing throughout this specification do not necessarily refer to the same embodiment. Furthermore, particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. It should be understood that, for the sake of simplicity and clarity, reference numerals may be repeated in the drawings where appropriate to indicate corresponding or similar elements or steps.

[0023] The titles and summaries of the disclosures provided herein are for convenience only and do not explain the scope or meaning of the embodiments.

[0024] Operating principle

[0025] Overview

[0026] How to use

[0027] The device is driven by a set current pulse passed through the coil. A positive current pulse causes the relay to open, while a negative pulse (i.e., a pulse in the opposite direction) causes the relay to close.

[0028] Magnetic latch

[0029] To avoid the need for a continuous drive current to maintain the open or closed state, this implementation is designed to "latch" at the corresponding position each time a switch is made, which is achieved by designing the actuator to be magnetically bistable.

[0030] low resistance contacts

[0031] For relays to be practical in small spaces and with high current, they must have extremely low contact resistance. As described in more detail below, this disclosure employs two different methods to achieve contact resistance of less than 100 microohms: using liquid metal wetting and microfabricated flexible element arrays. Other methods can also meet the low resistance requirements of such MEMS relay designs.

[0032] Liquid metal contacts

[0033] A thin layer of liquid metal can fill the gaps between the contacts and the crossbar surface caused by roughness and misalignment, and should be as thin as possible to achieve this function. Both the liquid metal and the contact material should be selected for their high conductivity, sufficient surface adhesion, and adequate service life (diffusion-limited) at operating temperatures.

[0034] As described in more detail below, the currently preferred embodiment employs a gallium-indium-tin eutectic or near-eutectic alloy disposed on a tungsten-based contact with a tantalum adhesive layer. Other substrate materials include copper and molybdenum. Suitable liquid contact layers include cesium-potassium-sodium alloys, elemental gallium and other gallium-based alloys (e.g., alloys with indium, tin, zinc, and / or bismuth), mercury, sodium-potassium alloys (NaK), cesium, rubidium, and francium. Adding other components to the liquid metal mixture can enhance its properties; for example, adding cesium to NaK to lower its freezing point to -78°C, or adding lithium to NaK to improve its bonding ability with copper or other metals. The base contact material can be treated to form a thin intermetallic compound layer to prevent diffusion into or from the liquid metal, or to promote adhesion between the liquid metal and the base contact.

[0035] Micromachined flexible contact

[0036] Contact resistance is typically inversely proportional to the square root of the force applied to press a pair of contacts together. Using multiple small arrays of flexible contacts allows for the creation of numerous small contact points with relatively small forces, which is crucial for achieving the small physical size of MEMS relays. Since resistance is inversely proportional to the square root of the number of flexible contacts, a contact with 100 micro-flexible elements on its surface will have a resistance that is 1 / 10th that of a single solid contact.

[0037] Packaging and internal environment

[0038] For wetted contacts, the package must be sufficiently sealed, and the internal environment must be completely anhydrous and oxygen-free to prevent the wetted contacts from being damaged by oxidation.

[0039] The package is filled with a chemically inert, electrically insulating gas at a pressure above 1 atmosphere to provide sufficient dielectric voltage resistance over a given stroke length. The pressure above 1 atmosphere also applies pressure bias to any leakage path of the package, preventing atmospheric ingress or egress.

[0040] Preferred embodiments use a gas primarily or entirely composed of nitrogen, but it can also be mixed with other insulating gases to improve arc resistance. Helium is a gas that can be mixed with nitrogen; it is commonly used for leak detection and thus helps verify the sealing of the relay package. Other possible embodiments may use insulating liquids (such as hexamethyldisiloxane, a low molecular weight silicone oil).

[0041] The above-described microfabricated structures will be described in more detail below. These microfabricated structures can be used alone or in specific combinations as described herein to form the power relays of this disclosure.

[0042] Microelectromechanical system (MEMS) actuators with magnetic latches and their manufacturing and application methods

[0043] Figure 1 This is a schematic illustration of a solenoid or actuator 100 in a conventional electromagnetic configuration. The conventional electromagnetic configuration includes a control coil 102 wound around a ferromagnetic core 104. Passing current through the control coil 102 generates a magnetic field, the general direction of which is parallel to the axis of the control coil 102. This magnetic field attracts the upper contact of two contacts 108, causing it to move downwards until it contacts the lower contact 108, thereby closing the switch and allowing current to flow from the power source to the load. When the current in the control coil 102 is cut off by the open control switch 106, the upper contact 108 returns to its neutral open position under the action of a spring force.

[0044] Traditional microelectromechanical actuators (MEMS) are typically several centimeters long and wide, requiring coil windings that must be formed using a spool winding machine. These coil windings increase the manufacturing complexity and cost of such actuators. In contrast, the MEMS actuator described in this paper allows for the use of planar circuits, reducing the complexity of coil formation and significantly reducing the size of the resulting device to 1 mm × 6 mm × 6 mm or smaller, thus enabling its use in applications requiring small dimensions.

[0045] Traditional solenoid actuators typically do not latch at the end of their stroke, and even in implementations where latching is possible, it is usually achieved mechanically. Mechanical latching adds moving parts to the design, increasing cost and reducing reliability. The microelectromechanical actuator described in this article provides magnetic latching at each end of the stroke through its design, requiring no additional components. This magnetic latching is completely passive and holds the plunger at either end of the stroke without external energy.

[0046] Overview of Microelectromechanical Actuators

[0047] In general, the microelectromechanical actuators described in this paper are laminated devices, typically manufactured by cutting thin sheets of material and then bonding these sheets into a stack, as discussed further below. Through successive cut / bond iterations, the structures that together constitute the microelectromechanical actuator can be placed in the same plane in almost any configuration.

[0048] Figure 2A This is a cross-sectional view of each layer of the microelectromechanical actuator 200 according to various embodiments of this disclosure. Meanwhile, Figure 2B and Figure 2C This illustrates how the layers of the microelectromechanical actuator 200 generally correspond to one of two “stacks”: a static stack 232 (also referred to as a “static assembly,” “stator assembly,” or simply a “stator”) or an actuable stack 234 (also referred to as an “actuable assembly,” “rotor assembly,” “plunger assembly,” or “plunger”). As discussed further below, the plunger assembly 234 can be vertically displaced within the stator assembly 232 to controllably move a load 218 disposed below the spacer 220.

[0049] Refer again Figure 2A The stator assembly 232 represents an assembly of multiple layers defining a chamber 236 that partially extends along a central longitudinal axis 238. The central longitudinal axis 238 approximately bisects the width of the microelectromechanical actuator 200. The substrate 202 may be the bottom layer of the stator assembly 232. The substrate 202 may be a small piece of insulating material on which functional components (such as relays or valves) are fabricated to form a microelectromechanical device. The insulating material may be, for example, ceramic or glass. Insulation is not always necessary (for example, insulation may be beneficial if the microelectromechanical actuator 200 constitutes part of an electrical switch). Therefore, the substrate 202 may also be formed of a non-insulating material on which functional components are fabricated to form a microelectromechanical device. Some embodiments may exclude the substrate 202 entirely, in which case the load stops 204A-204B may be the bottom layer of the microelectromechanical actuator 200.

[0050] In terms of "footprint," it is generally desirable to keep the microelectromechanical actuator 200 as small as possible within the constraints of the current density setting. Cost and magnetic properties typically vary advantageously with size reduction. For example, the actuation force may be proportional to the square root of the mass of the moving magnet of the microelectromechanical actuator 200 and the square root of the power consumed. Typically, the thickness of the substrate 202 may be less than 4 mm (preferably less than 3 mm). The thickness of the substrate 202 may be critical to the operation of the microelectromechanical device and therefore may be less dependent on the intended application of the microelectromechanical actuator 200. The shape, length, and width of the substrate 202 may vary depending on the intended application of the microelectromechanical actuator 200. However, in some embodiments, the length may not exceed 10 mm, 20 mm, 25 mm, or 50 mm, and the width may not exceed 10 mm, 20 mm, 25 mm, or 50 mm. Therefore, the surface area of ​​the substrate 202 may be less than 100 mm². 2 (i.e., 10 mm × 10 mm), 400 mm 2 (i.e. 20 mm × 20 mm), 625 mm 2 (i.e., 25 mm × 25 mm) or 2500 mm 2 (i.e., 50 mm × 50 mm). In other embodiments, the length and / or width may exceed 50 mm, thus the surface area of ​​the substrate 202 may exceed 625 mm². 2 Because the microelectromechanical actuator 200 has no basic size limitations.

[0051] like Figure 2B As shown, stator assembly 232 and plunger assembly 234 can be connected to each other via one or more flexible elements designed to limit lateral movement of plunger assembly 234 during vertical movement within the cavity of stator assembly 232, and to control, suppress, or limit tilting. Specifically, the flexible elements may be designed to provide a desired axial force when plunger assembly 234 is latched, such that the axial force provided by the flexible elements is opposite to the latching force, to enable and support faster movement of plunger assembly 234 when current is applied to the coils of stator assembly 232. In some embodiments, multiple flexible elements are used to limit the torsional (“tilt”) and lateral movement of plunger assembly 234, while in other embodiments, a single flexible element is used to limit the lateral movement of plunger assembly 234, while the degree of torsional restriction is generally less.

[0052] Flexible elements 208 and 222 are compliant mechanisms, requiring relatively little force to deflect in the actuation direction (i.e., along the central longitudinal axis 238), but significantly more force to deflect in any other direction. As discussed further below, flexible elements 208 and 222 may represent different portions of the same flexible element that flexibly connects the stator assembly 232 and the plunger assembly 234. This characteristic largely restricts the plunger assembly 234 from moving along the same path along the center of the stator assembly 232 during each actuation. Furthermore, this characteristic largely or completely eliminates friction between the stator assembly 232 and the plunger assembly 234 and limits the rotation of the plunger assembly 234 within the chamber 236 of the stator assembly 232. Figure 2A In the illustrated embodiment, the flexible elements 208 and 222 (again, they may represent different components of a single flexible element) can apply a "biasing force" in either direction to the plunger assembly 234, thereby providing a higher initial actuation force during actuation (and thus enabling faster displacement). Typically, the flexible elements 208 and 222 are formed of metal, metal alloy, or polymer.

[0053] like Figure 2A As shown, the stator assembly may include a series of ferromagnetic layers, with coils disposed between the ferromagnetic layers. During actuation, a current is passed through the coils to magnetically polarize the series of ferromagnetic layers, as discussed further below. Figure 2A In the illustrated embodiment, the stator assembly 232 includes three ferromagnetic layers: a first ferromagnetic layer 210 (also referred to as the "bottom ferromagnetic layer"), a second ferromagnetic layer 214 (also referred to as the "intermediate ferromagnetic layer"), and a third ferromagnetic layer 216 (also referred to as the "top ferromagnetic layer"). Typically, the bottom ferromagnetic layer 210 and the intermediate ferromagnetic layer 214 extend circumferentially around the cavity 236, thus having an annular shape. Meanwhile, the top ferromagnetic layer 216 may extend across the entire width of the stator assembly 232, with its bottom surface defining the upper end of the cavity 236. Although Figure 2A The top ferromagnetic layer 216 shown has a disk shape, but it can also have an annular shape similar to the intermediate ferromagnetic layer 214 and the bottom ferromagnetic layer 210. In this type of embodiment, a hole in the top ferromagnetic layer 216 allows for observation and / or measurement of the movement of the plunger assembly 234, and / or connection of an additional load to the top of the plunger. Note that the size of this hole should ensure that its diameter is smaller than the diameter of the top ferromagnetic plate 230 to ensure that the plunger assembly 234 is completely confined within the cavity of the stator assembly 232.

[0054] The thicknesses of the bottom ferromagnetic layer 210, the middle ferromagnetic layer 214, and the top ferromagnetic layer 216 are typically only required to prevent magnetic saturation when the plunger assembly 234 is actuated within the chamber 236 of the stator assembly 232. Typically, the thicknesses of the bottom ferromagnetic layer 210, the middle ferromagnetic layer 214, and the top ferromagnetic layer 216 do not exceed 0.4 mm (preferably 0.3 mm). Most of the other layers included in the stator assembly 232 have fewer restrictions and can therefore be determined based on the intended application of the microelectromechanical actuator 200. For example, the thickness of the "coil stack" can vary depending on the number of coils, and the thickness of the spacer 206 can depend on the plunger assembly 234, since the bottom of the plunger assembly 234 must be able to move within the chamber 236 between the top surface of the load stops 204A-204B and the bottom surface of the bottom ferromagnetic layer 210. The load stops 204A-204B are the surfaces that the load contacts at the "closed" end of its stroke. Depending on the device incorporating the actuator, load stops 204A-204B can have different applications. For example, in a relay, when the load 218 is in the closed position, load stops 204A-204B can be conductive elements that short-circuit through the load 218. In a MEMS valve, load stops 204A-204B (or a single load stop) can be a valve seat. In this case, the load 218 itself becomes the valve and seals against the valve seat in the closed position. Therefore, Figure 2A The load stoppers 204A-204B are shown to illustrate the surfaces of the plunger contacts. Note that this is for simplification. Figure 2A Various intermediate layers (such as flexible elements and spacers) are not shown. These various intermediate layers typically have a thickness between 25 and 375 micrometers and a width between 1.5 mm and 6 mm. Generally, Figure 2A All layers shown have a thickness of 25 micrometers (μm) to 375 μm and a width of 1.5 mm to 6 mm, but their dimensions may vary depending on the intended application of the microelectromechanical actuator 200.

[0055] One or more coils can be placed between each group of ferromagnetic layers. For example, in Figure 2AIn the illustrated embodiment, a plurality of first coils are disposed between a bottom ferromagnetic layer 210 and an intermediate ferromagnetic layer 214, while a plurality of second coils are disposed between an intermediate ferromagnetic layer 214 and a top ferromagnetic layer 216. This design arranges the bottom ferromagnetic layer 210 adjacent to load stops 204A-204B, the plurality of first coils adjacent to the bottom ferromagnetic layer 210, the intermediate ferromagnetic layer 214 adjacent to the plurality of first coils, the plurality of second coils adjacent to the intermediate ferromagnetic layer 214, and the top ferromagnetic layer 216 adjacent to the plurality of second coils. Note that the term "adjacent" as used herein can broadly refer to the spatial relationship between two components. A first component may be "adjacent" to a second component without their respective side surfaces being abutted against each other. Therefore, one or more intermediate components may exist between "adjacent" components. Conversely, "directly adjacent" typically refers to components being abutted against each other without any intermediate components, but adhesives or other materials may be required to bond them together.

[0056] exist Figure 2A In the illustrated embodiment, the plurality of first coils include a pair of coils 212A-212B, and the plurality of second coils also include a pair of coils 212C-212D. Although Figure 2A The multiple first coils and multiple second coils may include the same number of coils, but may include different numbers of coils. For example, a single coil may be disposed between a pair of ferromagnetic layers. The required number of coils may depend on the force required for actuation under a given latching force, the desired drive voltage and current, and the acceleration required to meet the desired open time requirements and / or close time requirements.

[0057] During operation, current is supplied to coils 212A-212D, as discussed further below. At this time, coils 212A-212D generate magnetic fields in opposite directions, causing the inner poles of the bottom ferromagnetic layer 210, the middle ferromagnetic layer 214, and the top ferromagnetic layer 216 in stator assembly 232 to be configured in a north-south-north (“NSN”) or south-north-south (“SNS”) configuration from top to bottom, depending on the direction of the current. Note that “inner pole” is used to describe the radial end of each ferromagnetic layer closest to plunger assembly 234. Since plunger assembly 234 has two fixed poles (i.e., a north-south or south-north configuration, determined during the manufacture of plunger assembly 234 by the orientation of permanent magnet 228), all adjacent poles between stator assembly 232 and plunger assembly 234 will push and pull in the same direction, and reversing the current direction will reverse the push and pull directions of stator assembly 232 and plunger assembly 234.

[0058] The plunger assembly 234 is another set of layers disposed within the chamber 236 of the stator assembly 232, and moves between a first position and a second position along the central longitudinal axis 238 during operation.

[0059] As described above, stator assembly 232 and plunger assembly 234 can be connected to each other via one or more flexible elements. Figure 2A In the illustrated embodiment, features 208 and 222 represent different regions of a single flexible layer. Therefore, the inner flexible region 222 can be directly connected to the outer flexible region 208, and while the inner flexible region 222 moves vertically with the plunger assembly 234 due to the elastic deformation of the flexible layer, the outer flexible region 208, although connected to the inner flexible region 222, can remain stationary (embedded in the layer of the stator assembly 232). The flexible element can be designed to allow vertical displacement of 0-25 micrometers, 25-100 micrometers, 100-150 micrometers, 150-200 micrometers, 200-250 micrometers, or greater than 250 micrometers. The flexible element can have various forms. For example, the flexible element can be in the form of a disk with an annular ring, or the flexible element can have a central circular portion and a hexagonal annular ring connected by three interconnecting segments (also called "branches") that are flexible. Figure 2A In this configuration, the outer flexible region 208 is a hexagonal annular ring, while the inner flexible region 222 is a central circular portion. Therefore, the outer flexible region 208 and the inner flexible region 222 are portions of the same layer. In embodiments where the microelectromechanical actuator 200 includes multiple flexible elements, the flexible elements can be arranged at different heights along the "stack". Having multiple flexible elements will better (i.e., more rigidly) control the angle of movement of the plunger assembly 234, preventing the plunger assembly 234 from "tilting" during vertical movement. Additional flexible elements also allow stress to be distributed among them, thereby enabling longer fatigue life and / or more material choices.

[0060] The spacer 224 can be disposed along the top surface of the flexible member 222 such that when the plunger assembly 234 is in the first position, the bottom of the spacer 224 is horizontally aligned with the bottom ferromagnetic layer 210 of the stator assembly 232, as shown below. Figure 2A As shown. When the plunger assembly 234 is in the second position, the top of the spacer 224 can be horizontally aligned with the bottom ferromagnetic layer 210 of the stator assembly 232. Generally, the thickness of the spacer 224 can be selected to accommodate the controlled movement of the plunger assembly 234.

[0061] A plunger element (or simply "plunger") may be disposed along the top surface of spacer 224. The plunger element may include a permanent magnet 228, to which ferromagnetic plates are bonded, laminated, or otherwise fixed. Specifically, a bottom ferromagnetic plate 226 may be connected to the bottom pole of permanent magnet 228, and a top ferromagnetic plate 230 may be connected to the top pole of permanent magnet 228. Figure 2AAs shown, the top ferromagnetic plate 230 and the bottom ferromagnetic plate 226 may be located between the ferromagnetic layers of the stator assembly 232. Specifically, the bottom ferromagnetic plate 226 may be located between the bottom ferromagnetic layer 210 and the intermediate ferromagnetic layer 214, while the top ferromagnetic plate 230 may be located between the intermediate ferromagnetic layer 214 and the top ferromagnetic layer 216. In operation, the top ferromagnetic plate 230 and the bottom ferromagnetic plate 226 can couple the permanent magnet 228 to the bottom ferromagnetic layer 210, the intermediate ferromagnetic layer 214, and the top ferromagnetic layer 216 by providing a low magnetic reluctance path for the magnetic field generated by the coils 212A-212D.

[0062] Therefore, the plunger assembly 234 may include: (i) a load 218, which is an actuator-driven assembly that performs certain functions during movement; (ii) a flexible element 222 for controlling vertical movement along the central longitudinal axis 238; (iii) a spacer 224; and (iv) a permanent magnet 228, on which a top ferromagnetic plate 230 and a bottom ferromagnetic plate 226 are fixed. The top ferromagnetic plate 230 may be located between the top ferromagnetic layer 216 and the intermediate ferromagnetic layer 214 of the stator assembly 232, while the bottom ferromagnetic plate 226 may be located between the intermediate ferromagnetic layer 214 and the bottom ferromagnetic layer 210.

[0063] The thickness of the permanent magnet 228 is typically maximized within the mechanical and magnetic constraints set by the surrounding layers of the microelectromechanical actuator 200 and the application. For example, the magnet thickness may be selected to not exceed the saturation magnetic flux density of the ferromagnetic plates 226 and 230. Similarly, the magnet thickness may be selected such that the total magnetic flux is sufficient to produce a sufficient latching force required for the intended application of a particular embodiment. Mechanical constraints on the magnet thickness may include a vertical distance between the top surface of the bottom ferromagnetic plate 226 and the bottom surface of the top ferromagnetic plate 230 not exceeding the difference between the thickness of the intermediate ferromagnetic layer 214 and the intended stroke length. The thickness of the permanent magnet 228 is typically set such that at the top of the stroke, the top ferromagnetic plate 230 contacts the top ferromagnetic layer 216 while the bottom ferromagnetic plate 226 contacts the intermediate ferromagnetic layer 214; and at the bottom of the stroke, the top ferromagnetic plate 230 contacts the intermediate ferromagnetic layer 214 while the bottom ferromagnetic plate 226 contacts the bottom ferromagnetic layer 210 (i.e., equal gaps on both sides). This can maximize the magnetic force during latching and actuation by minimizing the gap in the magnetic circuit at either end of the stroke.

[0064] Similar to stator assembly 232, the dimensions of the middle layer of plunger assembly 234 are generally unrestricted and can therefore be determined based on the intended application of microelectromechanical actuator 200. However, the design of permanent magnet 228, bottom ferromagnetic plate 226, and top ferromagnetic plate 230 can be considered in stator assembly 232. For example, the design of permanent magnet 228, bottom ferromagnetic plate 226, and top ferromagnetic plate 230 should satisfy: (i) the top ferromagnetic plate 230 is movable within the gap between the top surface of the middle ferromagnetic layer 214 and the bottom surface of the top ferromagnetic layer 216; and (ii) the bottom ferromagnetic plate 226 is movable within the gap between the top surface of the bottom ferromagnetic layer 210 and the bottom surface of the middle ferromagnetic layer 214.

[0065] like Figures 2A to 2C As shown, chamber 236 may not be purely cylindrical. Instead, the layers of stator assembly 232 and / or plunger assembly 234 may have specific dimensions and arrangements such that chamber 236 has structural features along its longitudinal side surfaces to better control plunger assembly 234. For example, consider Figure 2A The embodiment shown. In this embodiment, the top ferromagnetic layer 216 extends across the entire periphery of the stator assembly 232. Meanwhile, the intermediate ferromagnetic layer 214 and the bottom ferromagnetic layer 210 have the form of annular pillars (also referred to as "coaxial pillars"), with a central hole corresponding to the chamber 236. These annular pillars are defined by an inner radius extending from the central longitudinal axis 238 to the inner periphery and an outer radius extending from the central longitudinal axis 238 to the outer periphery. Similarly, each "coil stack" may have the form of annular pillars. However, the inner radius of the "coil stack" may differ from the inner radius of the intermediate ferromagnetic layer 214 and the bottom ferromagnetic layer 210. When the inner radius of the "coil stack" is larger than the inner radius of the intermediate ferromagnetic layer 214 and the bottom ferromagnetic layer 210, structural features commonly referred to as "grooves" or "boobs" are formed, which may accommodate the top ferromagnetic plate 230 and the bottom ferromagnetic plate 226 as described above.

[0066] Operating principle overview

[0067] As described above, the microelectromechanical actuator 200 can be driven by applying fixed current pulses to coils 212A-212D.

[0068] To move the plunger assembly 234 from the first position to the second position, current is supplied to coils 212A-212D such that the current flows in the first direction. When the plunger assembly 234 moves from the first position to the second position, the downward movement may be hindered by any of the following factors: (i) mechanical resistance of the flexible members 208, 222; (ii) contact between the top ferromagnetic plate 230 and the top surface of the intermediate ferromagnetic layer 214; (iii) contact between the bottom ferromagnetic plate 226 and the top surface of the bottom ferromagnetic layer 210; or (iv) contact between the load 218 and the assembly at the end of the stroke.

[0069] To move the plunger assembly 234 from the second position to the first position, current is supplied to coils 212A-212D such that the current flows in a second direction opposite to the first direction. When the plunger assembly 234 moves from the second position to the first position, upward movement may be hindered by any of the following: (i) mechanical resistance of the outer flexible region 208 and the inner flexible region 222; (ii) contact between the top ferromagnetic plate 230 and the bottom surface of the top ferromagnetic layer 216; or (iii) contact between the bottom ferromagnetic plate 226 and the bottom surface of the intermediate ferromagnetic layer 214. Therefore, upward movement may be hindered because the flexible element reaches its extension limit, causing its restoring force to prevent further axial movement; or upward movement may be hindered by the top ferromagnetic plate 230 or the intermediate ferromagnetic layer acting as a physical barrier.

[0070] Therefore, to actuate the plunger assembly 234, a fixed current pulse can be supplied from a power source (not shown) to the coils 212A-212D of the stator assembly 232. This action magnetically polarizes the top ferromagnetic layer 216, the middle ferromagnetic layer 214, and the bottom ferromagnetic layer 210. A positive current moves the plunger assembly 234 to a first position, thereby moving the load 218 to the "disconnected" position. Conversely, a negative current moves the actuator assembly 234 to a second position, thereby moving the load 218 to the "closed" position. Figure 3 This is a simplified schematic diagram illustrating the latching behavior of a microelectromechanical actuator caused by the magnetic circuit in the "open position" and "closed position". Figure 3 In the diagram, dashed lines represent magnetic flux in one magnetic circuit, while dotted lines represent magnetic flux in another. Magnetic flux in one direction (represented by dashed lines) causes the microelectromechanical actuator (MEMS) to "disconnect," while magnetic flux in the opposite direction (represented by dotted lines) causes the MEMS to "close." Note that... Figure 3 Part of the plunger assembly is shown in the image.

[0071] Note that although load 218 may be described as being in an “open” or “closed” position, those skilled in the art will understand that these positions may simply be relative end positions. Thus, the “open” position may also be referred to as the “first end position” or simply the “first position,” and the “closed” position may also be referred to as the “second end position” or simply the “second position.”

[0072] A. Magnetic latch

[0073] An important aspect of microelectromechanical actuators (MEMS) is their actuation method. Traditional MEMS actuators may require a continuous current supply to maintain a specific state (such as a closed state). To avoid the need for a continuous current supply to keep an MEMS actuator in an open or closed state, it can be designed to "latch" at the corresponding position each time a state is switched. This is achieved by designing the actuator to be magnetically bistable.

[0074] refer to Figure 2A The spacing between the top ferromagnetic layer 216, the middle ferromagnetic layer 214, and the bottom ferromagnetic layer 210 in the stator assembly 232 can be matched with the spacing between the top ferromagnetic plate 230, the bottom ferromagnetic plate 226, the permanent magnet 228, and the spacer 224 in the plunger assembly 234. When the plunger is in its highest and lowest positions, the magnetic field lines generated by the coils 212A-212D travel the shortest distance through the non-ferromagnetic material; this effect is maximized when the spacing is matched. This creates two local minima of magnetic reluctance (and thus potential energy) at these positions, causing the plunger to "latch" in its highest and lowest positions, with the magnetic "locking force" maximized when the spacing is matched.

[0075] The dimensions of the permanent magnet 228, the thicknesses of the top ferromagnetic plate 230 and the bottom ferromagnetic plate 226, the vertical spring constants of the outer flexible region 208 and the inner flexible region 222, and the distance between the highest and lowest positions all affect the latching force. To maximize actuation speed, the net latching force (including contributions from the magnetic and flexible elements) can be minimized within the constraints of vibration and shock resistance settings. Since the actuation force (which should be maximized to optimize switching speed) is primarily determined by the sum of the magnetic latching force and the vertical flexible force, the geometry of the flexible element is generally the easiest parameter to manipulate. Therefore, selecting the flexible element spring constant to set the net latching force at an appropriate value is generally preferred over redesigning or reselecting the permanent magnet 228 or the top ferromagnetic plate 230, the bottom ferromagnetic plate 226, or using a larger distance (also known as the "gap dimension").

[0076] B. Magneto-actuation

[0077] Figure 4 This is a schematic diagram illustrating how current flowing through coils 406A-N and 410A-N applies a constant magnetic force to plunger 402. To better illustrate the magnetic force, the microelectromechanical actuator 400 has been "disassembled" so that the layers are separated and "magnified" so that the layers are not drawn to scale.

[0078] As described above, the stator assembly 420 may include three ferromagnetic layers with coils disposed between them, such that (i) at least one coil is disposed between the bottom ferromagnetic layer 404 and the intermediate ferromagnetic layer 408; and (ii) at least one coil is disposed between the intermediate ferromagnetic layer 408 and the top ferromagnetic layer 412. For example, one set of coils 406A-N may be disposed between the bottom ferromagnetic layer 404 and the intermediate ferromagnetic layer 408, and another set of coils 410A-N may be disposed between the intermediate ferromagnetic layer 408 and the top ferromagnetic layer 412. The plurality of first coils 406A-N and the plurality of second coils 410A-N may include the same number of coils, or the plurality of first coils 406A-N and the plurality of second coils 410A-N may include different numbers of coils. Typically, each set of coils 406A-N, 410A-N includes at least two coils, but any number of coils may be disposed between the bottom ferromagnetic layer 404 and the intermediate ferromagnetic layer 408 or between the intermediate ferromagnetic layer 408 and the top ferromagnetic layer 412. For example, the thickness of each "coil stack" may depend on the size of the plunger 402. The thickness of each "coil stack" is generally proportional to the number of coils included.

[0079] The plunger 402 may include a permanent magnet 414, on which ferromagnetic plates 416 and 418 are fixed. For example, here the bottom ferromagnetic plate 416 is connected to the bottom pole (i.e., the south pole) of the permanent magnet 414, and the top ferromagnetic plate 418 is connected to the top pole (i.e., the north pole) of the permanent magnet 414.

[0080] The top ferromagnetic layer 412, the middle ferromagnetic layer 408, and the bottom ferromagnetic layer 404 can be alternately arranged with the top ferromagnetic plate 418 and the bottom ferromagnetic plate 416, such as... Figure 4 As shown. The top ferromagnetic plate 418 may be located between the top ferromagnetic layer 412 and the middle ferromagnetic layer 408, and the bottom ferromagnetic plate 416 may be located between the middle ferromagnetic layer 408 and the bottom ferromagnetic layer 404.

[0081] As described above, the current flowing through coils 406A-N and 410A-N applies a constant magnetic force to plunger 402 (more specifically, to top ferromagnetic plate 418 and bottom ferromagnetic plate 416). This constant magnetic force is typically proportional to the current and the number of turns of coils 406A-N and 410A-N. When this constant magnetic force overcomes the "locking force" of plunger 402 (more specifically, permanent magnet 414), plunger 402 will begin to move downward (e.g., toward bottom ferromagnetic layer 404) or upward (e.g., toward top ferromagnetic layer 412).

[0082] By applying a positive current to coils 406A-N and 410A-N, movement in one direction (e.g., upward) can be achieved. Applying a negative current to coils 406A-N and 410A-N achieves movement in the other direction (e.g., downward). For example, a positive current can cause plunger 402 to move upward until the top ferromagnetic plate 418 contacts the bottom surface of the top ferromagnetic layer 412 and / or the bottom ferromagnetic plate 416 contacts the bottom surface of the intermediate ferromagnetic layer 408. When plunger 402 is in this position, the microelectromechanical actuator 400 can be described as "off". Conversely, a negative current can cause plunger 402 to move downward until the top ferromagnetic plate 418 contacts the top surface of the intermediate ferromagnetic layer 408 and / or the bottom ferromagnetic plate 416 contacts the top surface of the bottom ferromagnetic layer 404. When plunger 402 is in this position, the microelectromechanical actuator 400 can be described as "on".

[0083] Several parameters can affect the constant magnetic force and the speed at which the plunger 402 moves between positions. These parameters include: The thickness and composition of the top ferromagnetic layer 412, the middle ferromagnetic layer 408, and the bottom ferromagnetic layer 404, for example, the thickness of the top ferromagnetic layer, the middle ferromagnetic layer, and the bottom ferromagnetic layer can be 25 μm-325 μm; The thickness and grade of the permanent magnet 414, for example, the thickness of the permanent magnet 414 can be 0.2 mm-0.5 mm; Number of turns for coils 406A-N and 410A-N; The magnitude of the current flowing through coils 406A-N and 410A-N; The diameters of coils 406A-N and 410A-N and permanent magnet 414; The spacing and overlap between the top ferromagnetic layer 412, the middle ferromagnetic layer 408, and the bottom ferromagnetic layer 404 affect the direction of the magnetic field gradient due to spatial relationships.

[0084] During operation, current is supplied to coils 406A-N and 410A-N. At this time, coils 406A-N and 410A-N generate magnetic fields in opposite directions to induce magnetic poles in the top ferromagnetic layer 412, the middle ferromagnetic layer 408, and the bottom ferromagnetic layer 404. Depending on the direction of the current, the inner poles of the top ferromagnetic layer 412, the middle ferromagnetic layer 408, and the bottom ferromagnetic layer 404 can be arranged in an NSN configuration or an SNS configuration. The permanent magnet 414 has two fixed poles. For example, here the permanent magnet has an NS configuration. Therefore, when the top ferromagnetic layer 412, the middle ferromagnetic layer 408, and the bottom ferromagnetic layer 404 are magnetically polarized, all the inner poles of the stator assembly 420 will push and pull the plunger 402 in the same direction. Reversing the current direction will reverse the direction in which the inner poles of the stator assembly 420 push and pull the plunger 402. Figure 4 This illustrates how passing current through coils 406A-N and 410A-N induces magnetic polarization, thereby applying a magnetic force to plunger 402.

[0085] Figures 5A to 5E A visualization illustrating the magnetic field strength and direction as the plunger assembly moves between a first and a second position. Specifically, Figure 5A The plunger assembly is shown in the first position. To move the plunger assembly to the second position, a fixed positive current pulse can be applied to the coil to magnetically attract the plunger assembly downwards. Figure 5B This shows the state of the plunger assembly as it moves to the second position. Figure 5C This shows the plunger assembly in the second position. To move the plunger assembly back to the first position, a fixed negative current pulse can be applied to the coil to magnetically attract the plunger assembly upwards. Figure 5D This shows the state of the plunger assembly as it moves to the first position. Figure 5E This shows the plunger assembly returning to its first position.

[0086] C. Restricted motion and flexible components

[0087] Flexible components (e.g.) Figure 2A The flexible elements (208, 222) can be used to hold the plunger assembly at the center of the stator assembly chamber to ensure that movement is largely (if not entirely) perpendicular to the central longitudinal axis. Furthermore, these flexible elements can suppress or prevent friction between the layers of the plunger assembly and the stator assembly. To achieve this, the stiffness of the flexible elements relative to lateral movement should be at least the maximum lateral magnetic force (within the worst-case assumptions about the geometry within manufacturing tolerances) divided by the worst-case clearance (within the manufacturing tolerances).

[0088] To ensure load (e.g.) Figure 2A The load 218 in the middle can be positioned flatly on the load stop (e.g. Figure 2AThe maximum lateral asymmetry of the force of the flexible element on the top surface of the load stop (204A-204B) should be less than the remaining closing-side latching force after taking into account any force applied by the flexible element.

[0089] Figure 6 This is a perspective cross-sectional view illustrating how the flexible element 602 connected to the plunger assembly 604 restricts the movement of the plunger assembly 604 relative to the stator assembly 606. To ensure proper positioning, the flexible element 602 may be "clamped" between layers of the plunger assembly 604 and / or the stator assembly 606. For example, the flexible element 602 may be positioned between ceramic layers.

[0090] For the sake of simplicity, Figure 6 Only some components of the plunger assembly 604 and the stator assembly 606 are shown. Specifically, Figure 6 This illustrates how the flexible element 602 ensures that the movement of the load 608 is substantially vertical or longitudinal, i.e., along the longitudinal axis 610. Although some degree of tilting may occur, the plunger assembly 604 does not experience any significant horizontal or lateral movement, nor does it experience any significant rotation about the longitudinal axis.

[0091] like Figure 6 As shown, this method of guiding the movement of the plunger assembly 604 not only allows for highly consistent and repetitive motion but also avoids friction caused by contact between the plunger assembly 604 and the inner wall of the stator assembly 606. Such friction can lead to poor performance and / or unreliability, so avoiding it is crucial.

[0092] Packaging and internal environment

[0093] Implementations of microelectromechanical actuators can benefit from hermetically sealed encapsulation to prevent fluids (such as gases and liquids) from entering the stator assembly chamber from the surrounding environment or from leaking from the stator assembly chamber into the surrounding environment.

[0094] In addition to hermetically sealed encapsulation, implementations of microelectromechanical actuators can be evacuated or incorporating an insulating fluid. For example, a defined chamber within a stator assembly can be filled with a chemically inert, electrically insulating gas at a pressure above or below one atmosphere, or a chemically inert, electrically insulating liquid at a pressure above or below one atmosphere. If used in a microelectromechanical relay, the chamber can be filled with an insulating fluid to provide sufficient dielectric voltage resistance for a given stroke length of the plunger assembly. Pressures exceeding one atmosphere will also result in a pressure bias applied to any leakage path of the hermetically sealed housing, thereby suppressing or preventing atmospheric ingress into the chamber or leakage from the stator assembly chamber into the surrounding environment. The liquid in the chamber can be electrically insulating or conductive, depending on the application. The liquid can serve as a means of transmitting hydraulic pressure or to provide resistance to dielectric breakdown.

[0095] Typically, insulating fluids are chemically inert, electrically insulating gases composed entirely or primarily of nitrogen. However, nitrogen can be mixed with one or more other electrically insulating gases, for example, to improve arc resistance (which may be useful for microelectromechanical relays). Other fluids can also be used. For example, insulating fluids can be other chemically inert electrically insulating gases (such as argon), or they can be chemically inert electrically insulating liquids (such as hexamethyldisiloxane or octamethyltrisiloxane), which are low molecular weight, low viscosity silicones.

[0096] Design Choices

[0097] Since the actuating force is proportional to the acceleration, the total initial force at the start of the "stroke" significantly affects the time required for the relay to switch from one state to another. It should be noted that the total initial force can generally be represented as the sum of the latching force, the actuating force, and the flexible force. To maximize the force at the start of the "stroke," the flexible element can be used as a spring to counteract the latching force. In this way, even if the latching force cannot be completely counteracted, at least partial counteracting can be achieved, and the total initial force can be correspondingly represented as the sum of the actuating force and the flexible force.

[0098] Methods for designing and manufacturing microelectromechanical actuators

[0099] To design a microelectromechanical actuator according to the embodiments disclosed herein, it is most convenient to consider the microelectromechanical actuator as a combination of two components: (i) a stator assembly that defines a cavity along a central longitudinal axis; and (ii) a plunger assembly disposed within the cavity of the stator assembly and movable between a first position and a second position along the central longitudinal axis during operation. Generally, the stator assembly includes two sub-components: (i) a contact assembly; and (ii) a drive electromagnetic assembly. Figure 7 This is a schematic illustration of the plunger assembly 702 and stator assembly 708 of relay 704. As described above, stator assembly 708 actuates plunger assembly 702 by generating a magnetic field when current is applied. Actuation of plunger assembly 702 causes its bottom surface to engage or disengage with load stop 706 (a contact in the relay).

[0100] Manufacturing microelectromechanical actuators requires manufacturing their sub-components separately. Figure 8 A set of steps for assembling the relay 200 into multiple layers is shown. Note that, for convenience, reference may be made to... Figure 2A and 2B The components discussed herein. The assembly sequence is important because the flexible layers represented by flexible regions 208 and 222 are part of the same flexible element, included in two sub-assemblies. Furthermore, the interlocking characteristics of the ferromagnetic layers require the plunger assembly to be assembled in the correct position, because the plunger assembly 234 cannot be inserted through the opening in the intermediate ferromagnetic layer 214 after assembly. For ease of explanation, Figure 8One possible assembly sequence shown is as follows: Step 1: From spacer 1 ( Figure 2A Starting at 220, spacer 1 is rigidly connected between plunger assembly 234 and stator assembly 232 via a removable tab marked "×".

[0101] Step 2: Laminate load 2 onto spacer 1.

[0102] Step 3: Laminate the bottom ferromagnetic layer 210 onto the component produced in Step 2.

[0103] Step 4: Laminate the spacer 224, bottom ferromagnetic plate 226 and permanent magnet 228 of plunger assembly 234 into the opening left inside the bottom ferromagnetic layer 210.

[0104] Step 5: Laminate multiple first coils 212A-212B and intermediate ferromagnetic layer 214 onto the assembly produced in step 4.

[0105] Step 6: Lay the top ferromagnetic plate 230 onto the top of the permanent magnet 228.

[0106] Step 7: Laminate multiple second coils 212C-212D and top ferromagnetic layer 216 onto the top of the assembly produced in Step 6.

[0107] Step 8: Lay the spacer layer 206 onto the bottom of the assembly produced in Step 7. Then, remove the tabs (×) that connect the inner and outer portions of the spacer 220 applied in Step 1 to release the movement of the plunger assembly 234, which is restricted by the flexible elements (together represented by 208 and 222).

[0108] Step 9: Place the components produced in Step 8 on top of the load stops 204A-204B. The load stops 204A-204B may be laminated or clamped in the appropriate position below the components.

[0109] Those skilled in the art will understand that other assembly sequences are possible, and in some embodiments, other assembly sequences may be preferred depending on the assembly speed or precision of the microelectromechanical actuator 200.

[0110] Figure 9 This is a high-level flowchart of a method 900 for manufacturing a microelectromechanical actuator according to another aspect of this disclosure. Again, for convenience, please refer to... Figure 2A The components discussed in [the document]. However, Figure 9This is specific to the design of a microelectromechanical actuator that does not include a flexible element connecting the stator assembly and the plunger assembly. First, the manufacturer may fabricate the top ferromagnetic layer (step 901), for example, by cutting a single layer from a piece of ferromagnetic material (such as steel). Then, the manufacturer may fabricate the plunger (step 902). For example, the manufacturer may fabricate or obtain a permanent magnet and then laminate ferromagnetic plates onto its top and bottom poles. These ferromagnetic plates may be referred to as the "top ferromagnetic plate" and the "bottom ferromagnetic plate," respectively. Subsequently, the manufacturer may fabricate the plunger assembly by laminating, bonding, or otherwise attaching spacers and loads to the bottom ferromagnetic plate (step 903). Note that additional layers may be included in the plunger assembly.

[0111] To manufacture the stator assembly, the manufacturer can obtain a substrate (step 904), bond the components that interact with the load to the upper surface of the substrate (step 905), and then alternately laminate ferromagnetic layers and coils to the upper surface of a pair of contacts (step 906). Typically, the lamination method of the ferromagnetic layers and coils results in a microelectromechanical actuator comprising three ferromagnetic layers, with one or more coils disposed between the first and second ferromagnetic layers, and another one or more coils disposed between the second and third ferromagnetic layers. In some embodiments, the lowermost ferromagnetic layer is directly laminated to the adjacent area of ​​a pair of contacts, while in other embodiments, such as... Figure 2A As shown, there are one or more intermediate layers.

[0112] To manufacture a microelectromechanical actuator, the manufacturer can place a plunger assembly within a defined cavity in a stator assembly and then bond a top ferromagnetic layer to the stator assembly (step 907). Bonding the top ferromagnetic layer to the stator assembly defines a completely enclosed cavity within the stator assembly. As described above, during operation, the plunger assembly can move between different positions within the completely enclosed cavity.

[0113] It should be understood that the actuator described above can be used alone or in combination with any of the following alternative micromachined contacts according to this disclosure. The first contact embodiment employs a design of an array of micromachined flexible elements on one of the contact members, while the second contact embodiment employs a design of a liquid-solid interface between the contact members. The two embodiments will be described below in this order.

[0114] Electrical contacts using micro-machined flexible element arrays

[0115] According to another aspect of this disclosure, a structure is provided for minimizing the force required to achieve a desired (low) contact resistance at switch contacts. This results in inelastic deformation of the two surfaces, which, by definition, requires a greater force than elastic deformation because the yield point of inelastic deformation always exceeds the limit of elastic deformation.

[0116] Multiple flexible spring elements (“finger elements”) are used to form a composite contact, allowing each contact to conform to the mating side without lifting the surrounding fingers off the surface, thereby allowing all or at least most of the fingers to make contact.

[0117] The available contact force is distributed to all fingers according to the amount of stroke each finger needs to adapt to. A desired improvement to this scheme is to make the individual spring elements constant force or at least non-linear, in order to better balance the force on each spring element.

[0118] Multi-finger contacts can be manufactured using micromachining techniques, including wire electrical discharge machining (EDM) and femtosecond laser micromachining. The contacts can be formed from metallic materials, including copper, beryllium copper, and other conductors.

[0119] Multiple conductive flexible elements can be formed by laser micromachining. Alternatively, multiple conductive flexible elements can be formed by additive manufacturing, or multiple conductive flexible elements can be formed by carbon nanotubes grown on a base surface.

[0120] The flexible cantilever finger structure is cut at an angle relative to the base surface of the contact point. The fingers can be cut into rectangular arrays, linear arrays, or other patterns, such as flexible elements arranged in hexagons or circles. Figure 10A and Figure 10B The diagram shows an array of 13 × 20 = 260 fingers, but only 21 fingers are shown. Figure 10A A set of vertical cuts (gap 22) made by a machining tool is shown. Figure 10B This illustrates the angled finger 20 formed by orthogonal cutting groups (gap 22) at a 45-degree angle. The result will be as follows: Figure 13 The array 50 shown may consist of 260 fingers 24. If microfabricated, the preferred size of each finger 20, 24 is in the range of 3 μm × 3 μm to 100 μm × 100 μm, and the spacing 22, 26 between rows of fingers 20, 24 is in the range of 10 μm to 200 μm. If the fingers 20, 24 are formed by growing carbon nanotubes, the preferred diameter is in the range of 0.4 nm to 100 nm, and the spacing between the fingers is in the range of 1 nm to 10 nm.

[0121] As the size of microelectromechanical relays decreases, the available force for pressing the contacts to achieve contact becomes smaller due to the reduced volume of magnetic material and current-carrying conductors in the electromagnetic actuator. The available force is distributed across all contacts in the array. It can be shown that, given a total array force and a total array area, the resistance of an array with N flexible elements is related to 1 / Proportional. Therefore, a contact with a 10×10 array of fingers on its surface will have 100 contacts, and its resistance will be 1 / 10 of that of a single contact compressed under the same total force. See the mathematical derivation of this result in "Mathematical Analysis of the Array Scale Effect of Contact Flexible Elements" below for details.

[0122] Figure 11A and Figure 11B This shows the traditional contact structure. Figure 12A and Figure 12B The operating principle of the contact structure of this disclosure is shown. Figure 11A and Figure 11B as well as Figure 12A and Figure 12B All four views show the same rigid lower contact member 28 with an undulating upper surface 30 that forms a groove 32 between two concave-convex structures 34 or high points. For clarity, the undulations of the surface are exaggerated in the figures. Note that the undulations in the figures do not represent intentional features of the contact, but rather unintentional marks left by manufacturing or wear of the contact material. Figure 11A and Figure 11B The conventional solid contact 38 is shown in both the open and closed states.

[0123] During operation, Figure 11A The movable solid upper contact member 38 is located above the lower contact member 28. Figure 11B The upper contact member 38 is shown to contact the lower contact member 28, but only the two protrusions 34 or high points on the lower contact member 28. This limits the available surface area for electrical contact and conduction. In conventional relays or switches, the solution to this problem is to apply a greater force to the upper contact member 38. With sufficient force applied, either the upper contact member 38 or the lower contact member 28 will undergo plastic deformation, which will provide a larger surface contact with the lower contact member 28, thereby reducing resistance.

[0124] Next reference Figure 12A and Figure 12B The novel flexible contact array device 40 formed according to the present disclosure is shown. The previously described lower contact member 28 is shown located below the upper contact member 42 formed according to the present disclosure. Figure 12A The upper middle contact member 42 is in the disconnected position. Figure 12B The upper contact member 42 is in the closed position. The upper contact member 42 has a plurality of flexible elements (also referred to herein as fingers) 44 extending from the lower surface 46. Figure 3 As shown in Figure A, the finger 44 is in a relaxed, extended position and is not in contact with the lower contact member 28.

[0125] When the contact 40 is closed by moving the upper contact member 42 toward the lower contact member 28 to the closed position, the finger 44 bends as it moves to contact the upper surface 30 of the lower contact member 28. The finger 44 contacts the highest protrusion 34 on the lower contact member 28 and bends the most compared to the finger 44 at the lowest point in the contact groove 32. The total force required to bend the finger 44 is much less than the total force required to plastically deform the upper contact member 38 in a typical contact design. When the contact 40 is in... Figure 12B In the closed position shown, the number of contact points is now equal to the number of fingers 44 contacting the lower contact member 28. In this closed position, the lower surface 46 of the upper contact member 42 is located at a first distance above the lowest point 32 of the upper surface 30 of the lower contact member 28. This first distance includes the separation distance between the lower surface 46 of the upper contact member 42 and one or more high points 34 of the upper surface 30 of the lower contact member 28, which is shorter than a first distance.

[0126] Ideally, all the plurality of conductive fingers 44 extending from the upper contact member 42 have the same height or distance above the contact surface of the lower contact member 28. This distance is greater than a first distance between the high point 34 and the low point 32 on the exposed upper surface 30 of the lower contact member 28, and the sum of the separation distances between the lower surface 46 of the upper contact member 42 and one or more high points 34 on the upper surface 30 of the lower contact member 28 when the upper contact member 42 is in the closed position.

[0127] The reduced contact force requirements of this flexible element array design are a key factor in achieving low-resistance contacts using small, relatively weak electromagnetic actuators.

[0128] An array of tilted suspension spring flexible elements can be fabricated from a solid conductor using micromachining (laser) or EDM (electrical discharge machining). This allows for the use of base material of arbitrary thickness with optimal possible conduction paths because no additional adhesives are required. The geometry and material of the springs can be optimized to provide the lowest contact resistance for a given normal force and range of flexibility (surface roughness). The springs or fingers 44 can be coated post-processed to improve oxidation resistance or provide other beneficial properties, such as reduced friction on the contact surfaces, or to provide soft material at the tips to increase the degree of plastic deformation at the contact point between the flexible element and the opposing contact. The spring flexible elements can be formed in a variety of shapes, not limited to simple tilted suspensions, including S-shaped springs, helical springs, buckling springs, or any shape of structure that elastically deforms under a force perpendicular to the main contact surface. Such flexible elements can be formed using a variety of processes, including 3D printing using metals or electroplated polymers, photochemical etching, reactive ion etching, or deposition or growth of carbon nanotube structures.

[0129] As can be readily understood from the foregoing, this disclosure provides a contact structure that can form a low-resistance contact member when only a low normal force is available. This is particularly significant for miniature relays or general-purpose relays requiring optimized low-power coil drive.

[0130] If the fingers bend excessively under excessive pressure, they may be damaged. The geometry of the contacts can be modified to provide a hard stop that controls the maximum degree of bending of the fingers. This hard stop can be formed on either of the two contact members, or partially on both contact members. The hard stop can take the form of a wall 52 surrounding the array 50 of the fingers 24, but with a total height lower than the fingers 24, such as... Figure 14 As shown. Rigid stops can also be formed as a discontinuous set of rigid structures. The height of the rigid stop can be optimized to allow for the desired degree of deformation of the flexible element.

[0131] Mathematical Analysis of the Scaling Effect of Contact Flexible Array (CFA)

[0132] Upper limit analysis of CFA resistance and the number scale effect

[0133] Assumption: 1. The total contact array force (“F”) is evenly distributed across all (“n”) contact flexures, with the force at each individual contact being F / n.

[0134] 2. An array of “n” contact flexible elements is distributed over a fixed area (occupied area) “A”.

[0135] 3. The effective conductor area is a fixed proportion of the occupied area (A / n). f a ).

[0136] 4. The actual electrical contact area of ​​each flexible component is controlled by Hertzian elastic contact mechanics or the approximate relationship between the plastic deformation area and the force [2].

[0137] 5. Each contact point is arranged in parallel with each other.

[0138] CFA resistance calculation

[0139] Individual contact extended resistor [1]:

[0140] in: R s Resistance of the contact area of ​​the flexible component ρ Resistivity of flexible components a Effective flexible section radius b Effective contact radius c i Equation fitting constants f a : Flexible cross-sectional shape factor that correlates area with effective radius A Total area (occupied area) of the flexible element array. n Quantity of flexible components p Contact force-area index for concave-convex structures (elastic concave-convex structure = 1 / 3, plastic concave-convex structure = 1 / 2) F Total force on the flexible element array H p Parameters of elastic or plastic concave-convex structures For the most critical case of plastically deformable concave-convex structures, the total contact resistance of the array (excluding the volume resistance of individual flexible elements) is 1 / It is directly proportional to the square root of the number of flexible elements; for any given total array force and total array area, the more contact elements, the lower the resistance.

[0141] Stable liquid-solid electrical contact

[0142] It has been found that wetting one or two switch contacts with a conductive fluid can provide improved surface contact with minimal force. Depending on the surface energy (or surface tension) of the liquid-solid, liquid-vapor, and solid-vapor interfaces, liquid-solid contact interfaces can support liquid films of finite static thickness (repulsive or non-wetting cases) or tend to zero thickness at a finite number of interface points (attractive or wetting cases). Both phenomena can be used to obtain favorable electrical contact characteristics. However, existing liquid contact solutions have their own set of problems. Ideally, liquids should simultaneously possess high thermal and electrical conductivity, preferential metallic bonding, and the ability to operate over a wide temperature range, including room temperature. This can be achieved by using liquid metals. Other classes of conductive fluids (such as ionic liquids) do not meet many of these requirements, including their conductivity, which is several orders of magnitude lower than that of liquid metals. Mercury, a liquid metal at room temperature, was used in switches in thermostats until its toxicity became apparent.

[0143] Other liquid metals, such as sodium-potassium alloys (NaK), gallium, and gallium alloys, are less toxic, but they can react with most metals, making them unreliable as wetting contacts. "Galinstan®" is a specific near-eutectic alloy of gallium, indium, and tin with a freezing point of -19°C and a boiling point of 1300°C. Gallium is known to react with many metals to form intermetallic phases, which can threaten the stability of solid metal electrode surfaces. For example, copper is a common electrode material due to its excellent conductivity, but at temperatures slightly above room temperature, copper forms intermetallic compound crystals with gallium. This ongoing reactivity damages the contact interface because: (a) gallium is depleted from the gallium-indium-tin alloy (Galinstan), altering its chemical composition and raising its liquidus temperature (e.g., becoming "slushy," semi-solid rather than liquid); and (b) surface roughness and unevenness increase due to the growth of intermetallic compound crystals.

[0144] This disclosure pairs one of several liquid metals with a solid contact material, utilizing a stable interface between the liquid and solid to promote adhesion between the liquid metal and the solid contact while limiting reactions between the liquid and solid metals. This disclosure includes various embodiments in which the interface is formed within a recessed groove to eliminate the detrimental effects of the unevenness of the intermetallic compound crystal structure during repeated opening and closing (i.e., switching) of the contact surface. Switching contacts formed according to this disclosure have been tested and exhibit a resistance of less than 100 microohms, which is 10 to 100 times lower than the several milliohms of solid-state relays or the tens of milliohms of conventional MEMS contacts.

[0145] Liquid metals, including gallium indium tin alloys, have been used as flow bridges between two stationary electrodes. Some of these studies have been used to demonstrate the possibility of stabilizing electrode surfaces before exposing them to gallium indium tin alloys. U.S. Patent No. 6,570,110 describes bridging the space between two stationary electrodes using liquid gallium or gallium alloys.

[0146] In this disclosure, a multilayer material interface is provided within a topological geometry fabricated on one or two solid contact surfaces. In summary, the engineered system includes one or more of the following key functional features: (1) a liquid metal that maximizes mechanical compliance and conductive surface area; (2) a rationally designed and intentionally reactive intermetallic layer (which may be crystalline, quasi-crystalline, or amorphous) that establishes chemical stability between the liquid metal and the adjacent underlying material, thereby promoting adhesion between the liquid metal and the solid contact surface; (3) a continuous diffusion barrier layer that prevents atomic migration and chemical reactions between the liquid metal and the underlying material; (4) a master base contact material layer that forms most of the current path; and (5) a fabricated topological geometry (e.g., ...) within the base contact layer. (a) recesses and / or bumps), which are used to (a) align and level solid-solid contact interactions in the closed state (e.g., to provide “hard stops”), (b) remove intermetallic layers that may have natural / accidental or intentionally created nano- to micron-scale topological features from the solid-solid contact interface, thereby limiting the possibility of arc discharge, and (c) protect intermetallic layers and / or barrier layers from repeated mechanical shocks and potential deformation during switch closure; and (6) a second contact formed of a conductor that is resistant to reaction with liquid metal but may not be easily wetted by liquid metal and may be wetted or not wetted by liquid metal itself.

[0147] The following describes each key technology and feature in more detail.

[0148] Liquid metal: Gallium-based alloys (nominal weight percentages of 68.5% gallium, 21.5% indium, and 10.0% tin) are used in thin film or droplet form to continuously cover the contact surface or are disposed in selected areas defined by a photolithographic pattern and / or physical topological geometry (e.g., physical constraints) of an underlying intermetallic adhesive layer. The underlying intermetallic adhesive layer and the liquid metal are applied to one (preferably) or both sides of the opposing contact surface using a liquid dispenser. It should be understood that these metals may also be deposited in a colloidal suspension or by physical vapor deposition (e.g., sputtering, thermal evaporation, or electron beam evaporation), followed by annealing to homogenize the alloy. Other suitable conductive liquids at or near room temperature may include elemental gallium and other gallium-based alloys (e.g., alloys with indium, tin, zinc, and / or bismuth), mercury, sodium-potassium alloys (NaK), cesium, rubidium, and francium. Adding other components to liquid metal mixtures can enhance their properties; for example, adding cesium to NaK lowers its freezing point to -78°C, or adding lithium to NaK improves its bonding ability with copper or other metals.

[0149] Intermetallic layer: A tantalum-gallium binary intermetallic crystal serves as the interface between the liquid metal and the underlying material. Tantalum is chosen in one embodiment because of its excellent properties, low solubility in gallium compared to most other metals (e.g., ≤0.1 wt% at 600°C), and its dominant phase on the gallium-rich side of the phase diagram (TaG). TaG Tantalum is stable at least below 520°C in the presence of gallium. Tests and experiments confirmed that no detectable intermetallic compound formation reaction occurred between tantalum and indium or tantalum and tin. Tantalum is deposited by magnetron sputtering to form a film with a thickness of approximately 500 nm to 1000 nm (but can be in the range of 1 nm to 1 mm), a thickness crucial for overcoming the surface roughness of the underlying layer (e.g., the root mean square roughness of tungsten used in one embodiment is 400 nm to 1200 nm). Other methods for depositing tantalum include electron beam evaporation, thermal evaporation, chemical vapor deposition, electrochemical deposition, and colloidal film casting.

[0150] During contact formation, gallium or a gallium-based alloy is subsequently deposited (see above) onto a tantalum film, and the material is annealed in an inert atmosphere for 10 minutes to 70 hours at temperatures ranging from 200°C to 650°C. Typically, this process is carried out under atmospheric argon atmosphere (≤0.2 ppm). ≤0.5 ppm The mixture is subjected to 550°C for 2 hours in O, and then cooled to room temperature without quenching or removing excess liquid metal. It can be further heated to up to 1060°C (TaG) using a radiant heater. The process is accelerated by rapid thermal annealing at a temperature close to the melting point of tantalum (TaG). During this annealing process, tantalum reacts with gallium to form tantalum-gallium crystals with dimensions ranging from 0.1 μm to 15 μm. Energy-dispersive X-ray spectroscopy (EDS) analysis indicates that these crystals are primarily TaG. and TaG Excess liquid metal can be removed (e.g., physically by pressurized gas flow or chemically by anhydrous hydrochloric acid in ethanol) and replaced with fresh gallium-indium-tin alloy to maintain the eutectic stoichiometry in the bulk liquid for subsequent contact operations. Other useful metals that can react to form an intermetallic interface layer in this application include titanium, vanadium, chromium, iron, zirconium, niobium, ruthenium, molybdenum, tungsten, and rhenium.

[0151] Diffusion Barrier Layer: The diffusion layer should be continuous and non-porous with minimal vacancy defects, preventing liquid metal from diffusing through these defects and reaching the pure solid metal in the base contact. The diffusion layer should be thick enough to prevent unwanted interactions, yet thin enough to maintain low resistance. Depending on the application, the thickness of this barrier layer can range from 10 nm to 10,000 nm. In one embodiment, the thickness of this diffusion barrier layer can be between 10 nm and 200 nm. In other embodiments, the thickness can be between 200 nm and 500 nm, 500 nm and 1000 nm, 1000 nm and 5000 nm, or 5000 nm and 10,000 nm. Two embodiments of the diffusion barrier layer are described herein. One embodiment utilizes a highly stable intermetallic phase formed in situ between the liquid metal and the base contact metal to limit further reactions between the two materials. There may be one intermetallic phase that acts as both an adhesion promoter and a diffusion barrier layer, or multiple intermetallic phases may be present. In one embodiment, a highly stable γ-phase C is used on the copper base contact. G The top is the less stable θ phase CuG (Verified by cross-sectional SEM / EDS) in contact with liquid metal gallium indium tin alloy.

[0152] Another embodiment of the diffusion barrier layer involves depositing a third material within a stack between the intermetallic layer and the base contact material. In one embodiment, tungsten is used because it is known to be an excellent barrier layer against copper diffusion, and tests and experiments have shown that tungsten is stable and does not degrade in the presence of gallium at temperatures up to 650°C. Tungsten can be deposited on the copper base contact material via magnetron sputtering, chemical vapor deposition, electrochemical deposition, co-sputtering of copper and tungsten (to create a gradient transition from copper to tungsten and mitigate thermal mismatch effects), or diffusion bonding of two foils of copper and tungsten. Other diffusion barrier layer materials may include ruthenium, titanium, tantalum, titanium nitride, tantalum nitride, tungsten nitride, niobium nitride, molybdenum nitride, titanium-tungsten alloys, tantalum carbide, cerium oxide, and graphene.

[0153] Base contacts: Copper contacts provide low on-resistance in switching devices. The aforementioned diffusion barrier implementation allows for the use of copper with liquid metals that would otherwise react with and corrode the copper base contacts. Other base contact materials with lower conductivity (including tungsten, molybdenum, tantalum, and niobium) can be selected to replace copper in exchange for better chemical compatibility and stability with liquid metals and other materials in multilayer systems.

[0154] Topological geometry: In this embodiment, a hard stop is created for the contact by machining one or more grooves in at least one electrode. The unwetted opposing electrode will make mechanical contact with the top of the groove wall, providing a defined gap and volume in which liquid metal can be retained. As described in the representative embodiments below and shown in the accompanying drawings, the groove may be formed with two portions of different depths.

[0155] refer to Figure 15A and Figure 15B The diagram shows a representative first contact 60, which has a centrally located circular groove 62 with a wall 63 (as shown in the diagram). Figure 16 As shown), both grooves are surrounded by shallow annular grooves 64. Both grooves are surrounded by a larger annular surface area 69, which serves as a stop. It should be understood that grooves 62 and 64 can be formed into other geometric planar shapes, including ellipses. Grooves 62 and 64 can be formed using any acceptable technique known to those skilled in the art, including but not limited to machining on a milling machine, laser processing using pulsed or continuous wave lasers, photochemical etching, electrical discharge machining (EDM), reactive ion etching, or any other technique suitable for manufacturing grooves of the desired geometry.

[0156] These grooves 62, 64, with different areas or geometries, can be formed by stacking and laminating layers of planar material. The material can then be completely cut through using a saw, laser, waterjet, or other cutting techniques. These layers can be bonded using adhesives, welding, soldering, or any other technique. This method of forming grooves... Figure 20A and 20B As shown in the figure. For example, groove 62 can be formed by bonding a layer 602 with a circular cut to the surface of a non-porous layer 601. Groove 64 can then be formed by bonding a layer 603 with a larger diameter hole to the top of layer 602.

[0157] Alternative geometries can achieve the same purpose: firstly, to contain the liquid metal, and secondly, to allow the liquid metal to diffuse when pressure is applied to the movable contacts. Figure 21A , Figure 21B as well as Figures 22A to 22C This method is illustrated. The complex cut shape includes a central groove 2101, 2201 and one or more branches or "tree branches" 2102, 2202 radiating from the shape. Figure 21A and 21BThe disconnected contact where the liquid metal 2103 is not compressed is shown. The liquid metal 2103, when at rest, naturally accumulates in the central groove 2101 for two reasons. First, the bottom surface of the central groove 2101 can have different surfaces to wet or attract the liquid metal, while the bottom surface of the branch can be treated to repel the liquid metal. Second, as described below, surface tension will cause the liquid to tend to not extend into the shape of the branch.

[0158] Figures 22A to 22C Closed contacts are shown (upper contacts not shown). In these... Figure 22A and 22B In the process, liquid metal 2203 is pushed into dendrite 202, increasing its surface area. Surface tension then exerts a restoring force, pulling the metal back into the central chamber. The geometry of dendrite 2202 can affect this restoring force. If dendrite 2202 is too wide, the restoring force is weakened because the surface area is not maximized. If dendrite 2202 is too narrow, the liquid metal may not be able to significantly enter the dendrite. If dendrite 2202 is both long and narrow, some liquid metal may form spherical or near-spherical droplets within the dendrite cavity, and this metal may separate from the majority of the liquid metal.

[0159] The ideal width of a branch or twig can be calculated by considering the pressure exerted on the liquid metal and the surface tension generated when it is pushed into the branch. For example, given the actuation force available for extruding the material, the increase in pressure within the liquid metal is limited. In one design, this pressure could be 9.4 pounds per square inch (PSI). This pressure must be balanced by the resistance pressure generated when the liquid metal surface bends into the branch. As described by Laplace's law, pressure is inversely proportional to the radius of curvature. The pressure of 9.4 PSI will be balanced at a specific curvature based on the surface tension of the liquid metal. The literature values ​​for the surface tension of eutectic gallium indium tin alloy range from 534 mN / m to 718 mN / m. This results in a minimum radius of curvature between 0.017 mm and 0.022 mm. This radius of curvature is 2204 in... Figure 22C As shown in the diagram, using a lower surface tension value, when the branch width is 0.034 mm, the liquid metal can be completely pushed into the branch at a pressure of 9.4 PSI. If the branch is narrower than twice the minimum radius of curvature mentioned above, the liquid will only partially enter the branch, forming a dome-shaped protrusion with a minimum radius. This will result in a significant reduction in the available movement of the liquid metal. If the branch is significantly wider than twice the minimum radius, the restoring force will be reduced due to the larger radius of the liquid metal pushed into the branch.

[0160] The available volume in one or more branches is the sum of the accessible volumes in each branch at a given pressure. The number of branches can be calculated by determining the volume of liquid metal extending above the hard stop at the second contact. This volume must be drained into the miniature reservoir created by the branches. Calculating the accessible volume in each branch and dividing it by the volume above the hard stop minus the available volume in the main reservoir yields the minimum number of branches required to prevent liquid metal from escaping from the reservoir or pushing up the hard stop.

[0161] This alternative geometry using branches may be superior to the previously discussed method of using stepped diameter grooves. In the case where the grooves are formed by stacking layers, the dendritic grooves are formed by only two layers: one is a solid layer, and the other is a layer with dendritic branches and a main reservoir, while the stepped method requires three layers: the first layer provides the bottom of the hole, and the second and third layers provide two stepped grooves of different diameters.

[0162] Another embodiment of this disclosure uses a simple first groove, the bottom of which is only partially treated to wet the liquid metal. When the liquid metal is squeezed, it flows outward onto the unwetted surface. When the pressure is released, the liquid metal returns to its resting position under the force of surface tension and the repulsive force from the untreated portion at the bottom of the groove.

[0163] The dimensions described below are for illustrative purposes only. Depending on the application, other dimensions may also be valid. Figure 15A and Figure 15B The shallower groove 64 in one representative embodiment has a diameter of 400 micrometers and a depth of 10 micrometers. At the center of this groove 64 is a deeper portion, or groove 62, which in one representative embodiment has a diameter of 200 micrometers and a total depth of 35 micrometers. The bottom 66 of the deeper groove 62 is larger in one representative embodiment than the bottom 68 of the shallower groove 64, which is 65 micrometers lower. The exposed bottom surfaces 66, 68 of each groove 62, 64 may have an intentionally designed surface finish. For example, each bottom surface 66, 68 may be polished, finished with a matte texture, or finished with a patterned and / or custom structure. In a sputtering coating machine, a mask is used to prevent the bottom surface 68 of the larger groove 64 or the top surface 69 of the first contact 60 from being coated.

[0164] Figure 16An enlarged view of the tantalum layer 72 on the bottom surface 66 of the deeper groove 62 is shown. This layer 72 is typically very thin. It can be deposited as a single atomic layer, with a minimum thickness of four angstroms (the diameter of a single atom). The layer 72 can be continuous or can have some voids or pinholes. Its thickness can range from 4 angstroms to 100 angstroms, 1 nanometer to 10 nanometers, 10 nanometers to 1 micrometer, 1 micrometer to 100 micrometers, or 100 micrometers to 1000 micrometers. The liquid metal coating 74 is formed from gallium indium tin alloy droplets dispensed onto the tantalum layer 72. The first contact 60 is treated as described above to drive the reaction between the tantalum layer 72 and the gallium indium tin alloy liquid metal coating 74 to a stable point. The volume of the applied liquid metal coating 74 should be sufficient to form as... Figure 16 The convex meniscus shown is higher than the top surface 69 of the first contact 60. Therefore, when the metal contact 60 contacts the movable flat electrode (as described below and in...) Figure 18 When the second contact 76 shown in the figure is in contact, no intermetallic layer on the surface of the tantalum layer 72 is in contact with the movable flat electrode or the second contact 76.

[0165] More specifically, Figure 17 This shows the open state where the second contact 76 is located above the first contact 60. Figure 18 The diagram illustrates the contact between opposing second contacts 76 and the liquid metal coating 74 in the closed state. Ideally, the second contact 76 is fitted within the boundary of the larger, shallower outer recess 64. Hard stops for the two contacts 60, 76 are provided by metal-to-metal abutment at the bottom surface 68 around the shallower outer recess 64. The liquid metal coating 74 is flattened by contact pressure from the second contacts 76. The liquid metal coating 74 is mechanically held by the sidewalls 63 of the deeper recess 62 and further held in the desired position by the chemical attraction of the tantalum layer 72 on the bottom 66 of the recess 62 and the capillary repulsion from bare metal (e.g., tungsten) elsewhere. Any excess liquid metal displaced by the pressure of the opposing second contacts 76 flows into the shallower recess 64. When the contacts 76 open, the liquid metal coating 74 is driven back to its meniscus shape due to the repulsive force between the metal (e.g., tungsten) of the first contact 60 and the liquid metal coating 74, as well as the surface tension within the liquid metal coating 74.

[0166] Figure 19 A pair of contacts 71 are shown, neither of which has a groove machined. In this case, the first contact, or base contact 73, is composed of multiple materials. The base contact 73 has a flat, planar upper surface 75, which is first coated with an adhesive layer 77. Then, a liquid metal layer 78 is deposited on top of the adhesive layer 77. The second contact 79 has a flat lower surface 70. Figure 19In the diagram, contact 71 is shown in the open position. In the closed position, the second contact 79 is pressed against the liquid metal layer 78, forming an electrical contact. In this case, the liquid metal layer 78 is contained by its attraction to the adhesive layer 77.

[0167] As can be further understood from the above, one advantage of this disclosure is the addition of grooves to accommodate the gallium indium tin alloy, which prevents mechanical damage to the wetting intermetallic layer and improves the durability of the contacts. Furthermore, coating the metal contacts (e.g., tungsten) with a thin tantalum layer allows for wetting of liquid metals (such as gallium indium tin alloy) and allows tungsten to be used as the body material. Tungsten has a resistivity (5.6 × 10⁻⁶). Ohm-meter (Ω·m) is lower than tantalum (1.3 × 1 Ω·m) (ohm-meter), thus providing a lower resistance for the device.

[0168] Power relay circuit design selection

[0169] The above-described actuator and contact implementations can be combined to provide a power relay circuit, as discussed in more detail below.

[0170] Relay construction

[0171] A microelectromechanical system (MEMS) relay is a component of a MEMS actuator and one or more contact groups. The MEMS actuators discussed earlier are constructed using a set of microfabricated layers, and the two methods previously discussed for forming extremely low-resistance contacts are building blocks of the relay. This low contact resistance is crucial for constructing miniature high-current relays because it enables the relay to operate without a large heatsink used to dissipate energy that would be converted into heat in a conventional contact group.

[0172] Dielectric withstand voltage (insulation withstand voltage)

[0173] When a relay is in the open position, it must be able to prevent an electric arc from forming between the input and output contacts. The relationship between the voltage applied between the two contacts and the distance the arc will travel between them is described by the Paschen curve for a specific gas at a given pressure. Other factors also apply, including the type and pressure of any gas or liquid filling the gap between the contacts. The maximum voltage that can be applied without producing an arc for a given contact configuration is called the dielectric voltage. Relays are rated based on the dielectric voltage between the contacts. For example, a typical commercial relay designed for 120 volt AC is listed with a dielectric voltage of 750 volts or 1000 volts.

[0174] Contact geometry

[0175] Contact geometry plays a crucial role in the function of a power relay. The resistance of a metal structure is inversely proportional to the cross-sectional area through which current flows and directly proportional to the path length of the current through the metal. In microelectromechanical systems (MEMS) devices, the cross-sectional area is inherently limited by the small size of the device. To minimize resistance, we must also minimize the current path length through the entire relay. This design achieves this by using a crossbar approach. A variation of this design is... Figure 23A and Figure 23B As shown in the image. Figure 23A The relay 80 is shown in the off state. Figure 23B The illustration shows a relay 80 in a closed or open state. Input contacts 81 and output contacts 82 are arranged horizontally relative to each other, with a gap 83 between them. The gap 83 is sized to provide sufficient separation to prevent arcing at the relay's rated voltage. This gap size is calculated based on the required voltage the relay must withstand, as well as the dielectric value and pressure of the gas or liquid filling the gap.

[0176] In addition to the fixed contacts 81 and 82, the relay also includes a movable contact 84. This contact is connected to a magnetic rotor 85. The rotor 85 is located in an opening of one or more coils (not shown in this view), which, when carrying current, can apply an axial force to the rotor 85 and thus to the movable contact 84.

[0177] When the movable contact 84 is in Figure 23A When in the open position shown, relay 80 is disconnected, and current cannot flow from input contact 81 to output contact 82.

[0178] Figure 23B The same relay 80 is shown, with contact groups 81, 82 and rotor 85 in the closed position. In this state, the movable contact 84, in the form of a crossbar, forms physical and electrical contact with the input contact 81 and the output contact 82. Current can now flow through the relay 80 from the input contact 81 through the movable contact 84 or the crossbar to the output contact 82, or vice versa, from contact 82 through the movable contact 84 to the other contact 81.

[0179] Actuator considerations

[0180] Since the actuation force is proportional to acceleration, the total initial force at the start of the stroke (the sum of latching force, actuation force, adhesive force of the liquid metal, dynamic resistance caused by fluid dynamics, and flexible element force) largely determines the time required for switching. To maximize the force at the start of the stroke, the flexible element can be used as a spring or preload. In this application, the flexible element can be designed to provide a smaller opening force in the opposite direction to the latching force. This opening force of the flexible element, added to the force generated by the magnet in the coil's magnetic field, increases the acceleration of the plunger as it moves away from the latching position.

[0181] The actuator must provide sufficient travel distance to open a adequate gap between the crossbar and the contact pair. This gap must be at least half the required dielectric voltage withstand distance. The gap 86 between the input contact 81 and the movable contact 84 or the crossbar, and the associated gap between the movable contact 84 and the output contact 82, are electrically connected in series. Therefore, the dielectric voltages of the two gaps are additive. Because the crossbar and contacts are designed to have equal gap sizes, each gap must withstand an equal portion of the total dielectric voltage. The microelectromechanical system (MEMS) actuator travel supports a gap of 200 micrometers. Other gap distances that provide useful withstand voltage are 100 to 150 micrometers, 150 to 200 micrometers, or 200 to 250 micrometers or greater.

[0182] Contact considerations

[0183] One of the most important characteristics of a relay is its contact resistance. When current flows through a relay, some of the energy is converted into heat. The energy released, measured in watts, is equal to the product of the resistance and the square of the current. When two rigid surfaces come into contact, they only contact at the highest points on the surfaces (i.e., the uneven surface). When a greater force is applied to press the contacts together, the uneven surface deforms and flattens, resulting in an increased surface contact area and a corresponding decrease in resistance. In miniature relays, it is difficult to generate large contact forces due to the small physical size of the magnets and coils. In standard small relays, the contact resistance is typically in the range of 30 to 50 milliohms. The novel solution to this contact resistance problem in this invention is to incorporate one of two low-resistance, low-contact-force contact options. These methods (described separately elsewhere) are stable liquid-solid contacts and micro-machined flexible contact arrays.

[0184] For the aforementioned stable liquid-solid contact or micro-machined flexible contact array solutions, specialized contact materials can be located on fixed contacts, movable contacts, or both. Figure 24 In this process, the wetted surface 74 of the liquid-solid contact can be applied to the surface of the two fixed contacts 81 and 82 that is closest to the movable contact 84, or it can be applied to the surface of the movable contact 84 that is closest to the fixed contacts 81 and 82.

[0185] For the micro-machined flexible contact array described previously, the flexible contacts are machined into one contact surface of each contact pair. Therefore, the surface of the input contact 81 and the output contact 82 closest to the movable contact 84 may have a micro-machined contact array, or the surface of the movable contact 84 closest to the two contacts 81, 82 may be covered with such an array.

[0186] Other contact arrangements

[0187] Traditional relays are available in various circuit configurations or "forms." Each form specifies the number of poles and the number of throws. The number of poles refers to the number of parallel switches controlled by the relay. The number of poles can be any number, but is typically between 1 and 3. The number of throws refers to the number of positions the relay can be in. The number of throws is usually 1 or 2, often referred to as single-throw or double-throw. For example, a relay that includes multiple open-close switches can be described as single-pole, double-pole, or triple-pole, where each pole refers to a single switch. A double-pole double-throw relay will have two independent switches, each with a common terminal that can be connected to one of the two switching terminals. In non-latching relays, one of the two switching terminals is typically designated normally open (NO), and the other normally closed (NC). Since latching relays are stable in both open and closed states without an applied power supply, the terms NC and NO do not apply.

[0188] Multi-throw arrangement

[0189] The microelectromechanical system relays described in this article can also be configured to support multi-pole and multi-throw operation. Figure 25A and 25B The configuration supporting normally open (NO) and normally closed (NC) contacts is shown. Figure 25A In the relay 87, two crossbars 88 and 89 are arranged at opposite ends of the rotor 90 and attached to the rotor 90. The relay 87 also includes two pairs of fixed contacts: an upper pair of 91 and 92 and a lower pair of 93 and 94. Figure 25A In the middle section, contacts 93 and 94 are open, while upper contacts 91 and 92 are closed. Current cannot flow from contact 93 to contact 94 because the crossbar 89 is not in contact with these contacts 93 and 94. Current can flow from contact 91 to 92 through the upper crossbar 88.

[0190] Figure 25B The alternative state of relay 87 is shown. Rotor 90 has been electromagnetically driven to the lower position in the view. Current can now flow from contact 93 to contact 94 through crossbar 89. Upper contacts 91 and 92 are now disconnected from upper crossbar 88, causing upper contact group 91 and 92 to be in the open state.

[0191] Multi-pole arrangement

[0192] Microelectromechanical system (MEMS) relays can be assembled with more complex bar and contact arrangements. Figure 26The diagram shows a top view of a bipolar relay design 95. The device 95 includes two parallel crossbars 96 and 97 attached to a common rotor. Each of the two crossbars is positioned above a pair of fixed contacts. The left crossbar 96 is positioned above fixed contact 98, while the crossbar 97 is positioned above fixed contact 99. All four fixed contacts 98 and 99 are arranged such that their upper surfaces are coplanar. When the rotor pushes the crossbars 96 and 97 toward the fixed contacts 98 and 99, two independent circuits are closed. When the rotor pulls the crossbars 96 and 97 away from the fixed contacts 98 and 99, both circuits are opened.

[0193] As can be seen, more than two poles can be created by adding additional crossbars and contact groups. Liquid-solid contacts or micro-machined contact arrays provide the necessary flexibility, allowing connection of all contact surfaces even when the fixed contact surfaces are not perfectly coplanar.

[0194] Multi-throw, multi-level arrangement

[0195] Those skilled in relay design can see that Figure 25A and 25B as well as Figure 26 The two concepts shown can be combined to form multi-throw, multi-pole relays.

[0196] Dielectric filler material

[0197] The withstand voltage between contact groups is affected by the medium filling the gap between the contacts. Various gases and liquids can provide much higher withstand voltages than air (for a given distance between contacts). The relationship between pressure, distance, and withstand voltage is described by Paschen's Law, which allows for the prediction of withstand voltage. Relay design includes encapsulating it in a hermetically sealed housing. The housing can be filled with a gas or liquid with a high dielectric constant to increase the withstand voltage. The withstand voltage can be further increased by increasing the pressure of the gas inside the housing. Gases suitable for this application include nitrogen, argon, and sulfur hexafluoride (SF6). The liquid includes hexamethyldisiloxane or octamethyltrisiloxane.

[0198] Extended Implementation

[0199] Multiple crossbars and contact groups for N-pole M-throw switching

[0200] Replace dielectric gas with liquid (hexamethyldisiloxane)

[0201] Replace flexible components with support surfaces.

[0202] Replace wetting contacts with suspended branch microarrays

[0203] Replace adhesives used in lamination with welding.

[0204] It should be understood that various changes can be made to this disclosure to enhance its utility. The above-described embodiments can be combined to provide further embodiments. If necessary, aspects of the embodiments can be modified to employ the concepts of various patents, applications, and publications to provide even more advanced embodiments.

[0205] This application claims priority to U.S. Patent Application No. 63 / 508,748, filed June 16, 2023, which is incorporated herein by reference in its entirety.

Claims

1. An electrical relay circuit for a load, comprising: A stator assembly having a cavity partially defined along a central longitudinal axis, wherein the stator assembly includes: a non-conductive substrate having a top surface; one or more layers including components that mechanically or electrically interact with the load; a first ferromagnetic layer adjacent to a spacer; a plurality of first coils adjacent to the first ferromagnetic layer; a second ferromagnetic layer adjacent to the plurality of first coils; a plurality of second coils adjacent to the second ferromagnetic layer; and a third ferromagnetic layer adjacent to the plurality of second coils, wherein the bottom surface of the third ferromagnetic layer defines the top of the cavity; and A plunger assembly disposed within the cavity of the stator assembly and movable between a first position and a second position along the central longitudinal axis during operation, the plunger assembly comprising a plunger comprising a pair of ferromagnetic plates with a magnet disposed between the pair of ferromagnetic plates, wherein (i) a first ferromagnetic plate of the pair of ferromagnetic plates is disposed between a first ferromagnetic layer and a second ferromagnetic layer, and (ii) a second ferromagnetic plate of the pair of ferromagnetic plates is disposed between the second ferromagnetic layer and the third ferromagnetic layer.

2. The electrical relay circuit according to claim 1, wherein, The pair of ferromagnetic plates, together with the first, second, and third ferromagnetic layers, also cooperate to drive at least one contact, each contact comprising: A first contact member has an exposed surface, the exposed surface having a concave-convex structure forming one or more high points and low points on the exposed surface; and The second contact member has a base surface and a plurality of conductive flexible elements extending from the base surface. The first contact member and the second contact member are movable relative to each other to provide different open and closed positions. Wherein, when the first contact member is adjacent to the second contact member and positioned in a closed position, in the closed position, the base surface of the second contact member is not in electrical contact with the one or more high points on the exposed surface of the first contact member, while each of the plurality of conductive flexible members is in electrical contact with the exposed surface of the first contact member.

3. The electrical relay circuit according to claim 1, wherein, The pair of ferromagnetic plates, together with the first, second, and third ferromagnetic layers, also cooperate to drive at least one contact, each contact comprising: A first contact member has a base with an exposed surface, the base having a first groove opening toward the exposed surface, the first groove having circumferential sidewalls and a bottom wall defining the interior of the first groove; A first metal layer is disposed on the bottom wall of the first groove and has a top surface that is lower than the exposed surface of the first contact member; A liquid metal layer is disposed only on the top surface of the first metal layer and extends above the exposed surface of the first contact member; and The second contact member has a contact surface, is adjacent to the first contact member and positioned in an open position, and is movable to a closed position, in which the contact surface of the second contact member contacts and presses the liquid metal layer and the first metal layer until the contact surface of the second contact member abuts against the exposed surface of the first contact member.

4. The electrical relay circuit according to claim 1, comprising a cavity having the stator assembly and the plunger, the cavity being filled with a dielectric gas.

5. The electrical relay circuit of claim 1, comprising a cavity having the stator assembly and the plunger, the cavity being filled with a dielectric fluid.

6. The electrical relay circuit according to claim 1, wherein, The electrical relay circuit is configured to provide double-throw functionality.

7. The electrical relay circuit according to claim 2, wherein, The electrical relay circuit is configured to provide double-throw functionality.

8. The electrical relay circuit according to claim 3, wherein, The first groove includes one or more branches extending from the main groove, the branches being narrower relative to the dimensions of the first groove, and the branches having a bottom surface and a side surface.

9. The electrical relay circuit according to claim 8, wherein, The surface of the bottom wall of the first groove is treated to attract liquid metal, and the bottom and side surfaces of the branch are treated to repel the liquid metal.

10. The electrical relay circuit according to claim 9, wherein, The bottom surface of the first groove is treated by applying a coating of a material that wets the liquid metal.

11. The electrical relay circuit according to claim 3, wherein, Only a portion of the bottom of the first groove is treated to attract liquid metal.

12. The electrical relay circuit according to claim 11, wherein, The portion of the bottom wall of the first groove is treated by applying a coating of a material that wets the liquid metal.

13. An electrical relay circuit for a load, comprising: A stator assembly having a cavity partially defined along a central longitudinal axis, wherein the stator assembly includes: a non-conductive substrate having a top surface; one or more layers including components that mechanically or electrically interact with the load; a first ferromagnetic layer adjacent to a spacer; a plurality of first coils adjacent to the first ferromagnetic layer; a second ferromagnetic layer adjacent to the plurality of first coils; a plurality of second coils adjacent to the second ferromagnetic layer; and a third ferromagnetic layer adjacent to the plurality of second coils, wherein the bottom surface of the third ferromagnetic layer defines the top of the cavity; A plunger assembly disposed within the cavity of the stator assembly and movable during operation between a first position and a second position along the central longitudinal axis, the plunger assembly comprising a plunger comprising a pair of ferromagnetic plates with a magnet disposed between the pair of ferromagnetic plates, wherein (i) a first ferromagnetic plate of the pair of ferromagnetic plates is disposed between a first ferromagnetic layer and a second ferromagnetic layer, and (ii) a second ferromagnetic plate of the pair of ferromagnetic plates is disposed between the second ferromagnetic layer and the third ferromagnetic layer; and The pair of ferromagnetic plates, together with the first, second, and third ferromagnetic layers, also cooperate to drive more than one contact, each contact comprising: A first contact member has an exposed surface, the exposed surface having a concave-convex structure forming one or more high points and low points on the exposed surface; and The second contact member has a contact surface and a plurality of conductive flexible elements extending from the contact surface; The first contact member and the second contact member are movable relative to each other to provide different open and closed positions. Wherein, when the first contact member is adjacent to the second contact member and positioned in a closed position, in the closed position, the contact surface of the second contact member is not in electrical contact with the one or more high points on the exposed surface of the first contact member, while each of the plurality of conductive flexible members is in electrical contact with the exposed surface of the first contact member.

14. The electrical relay circuit according to claim 13, wherein, All of the plurality of conductive flexible elements extending from the contact surface of the second contact member have the same height above the contact surface of the first contact member, the height being greater than the sum of a first distance between the high point and the low point on the exposed surface of the first contact member and the separation distance between the exposed surface of the first contact member and the one or more high points of the contact surface of the second contact member when the first contact member is in the closed position.

15. The electrical relay circuit according to claim 13, wherein, The plurality of conductive flexible elements form an angle less than a right angle with the contact surface of the second contact member.

16. The electrical relay circuit according to claim 13, wherein, Each of the plurality of conductive flexible elements has a planar profile with a dimension of 10 to 50 micrometers in one direction and a dimension of 10 to 50 micrometers perpendicular to the one direction, and a gap of 20 to 200 micrometers between adjacent flexible elements.

17. An electrical relay circuit for a load, comprising: A stator assembly having a cavity partially defined along a central longitudinal axis, wherein the stator assembly includes: a non-conductive substrate having a top surface; one or more layers including components that mechanically or electrically interact with the load; a first ferromagnetic layer adjacent to a spacer; a plurality of first coils adjacent to the first ferromagnetic layer; a second ferromagnetic layer adjacent to the plurality of first coils; a plurality of second coils adjacent to the second ferromagnetic layer; and a third ferromagnetic layer adjacent to the plurality of second coils, wherein the bottom surface of the third ferromagnetic layer defines the top of the cavity; A plunger assembly disposed within the cavity of the stator assembly and movable during operation between a first position and a second position along the central longitudinal axis, the plunger assembly comprising a plunger comprising a pair of ferromagnetic plates with a magnet disposed between the pair of ferromagnetic plates, wherein (i) a first ferromagnetic plate of the pair of ferromagnetic plates is disposed between a first ferromagnetic layer and a second ferromagnetic layer, and (ii) a second ferromagnetic plate of the pair of ferromagnetic plates is disposed between the second ferromagnetic layer and the third ferromagnetic layer; and The pair of ferromagnetic plates, together with the first ferromagnetic layer, the second ferromagnetic layer, and the third ferromagnetic layer, further cooperate to drive at least one contact, the at least one contact comprising: A first contact member has a base with an exposed surface, the base having a first groove opening toward the exposed surface, the first groove having circumferential sidewalls and a bottom wall defining the interior of the first groove; A first metal layer is disposed on the bottom wall of the first groove and has a top surface that is lower than the exposed surface of the first contact member; A liquid metal layer is disposed only on the top surface of the first metal layer and extends above the exposed surface of the first contact member; and The second contact member has a contact surface, is adjacent to the first contact member and positioned in an open position, and is movable to a closed position, in which the contact surface of the second contact member contacts and presses the liquid metal layer and the first metal layer until the contact surface of the second contact member abuts against the exposed surface of the first contact member.

18. The electrical relay circuit of claim 17, further comprising a second groove formed in the exposed surface of the first contact member, the second groove surrounding the first groove and having a bottom wall below the exposed surface of the first contact member and above the bottom wall of the first groove, the second groove further comprising circumferential sidewalls and a bottom wall defining the interior of the second groove, a portion of the interior of the second groove overlapping the interior of the first groove.

19. The electrical relay circuit according to claim 17, wherein, The liquid metal layer is formed of a compliant material that is displaced in the closed position by pressure applied by the second contact member and returns to its original shape in response to the second contact member moving to the open position.

20. The electrical relay circuit according to claim 18, wherein, Excess material from the liquid metal layer is displaced into the second groove in response to pressure as the second contact member moves to the closed position, and once the second contact member moves to the open position, the excess material from the liquid metal layer is driven back to its original meniscus shape in response to the repulsive force generated between the material forming the first contact member and the material forming the liquid metal layer.

21. The electrical relay circuit according to claim 20, wherein, The repulsive force is also generated by the surface tension in the liquid metal layer.

22. An electrical relay circuit for a load, comprising: A stator assembly having a cavity partially defined along a central longitudinal axis, wherein the stator assembly includes: a non-conductive substrate having a top surface; one or more layers including components that mechanically or electrically interact with the load; a first ferromagnetic layer adjacent to a spacer; a plurality of first coils adjacent to the first ferromagnetic layer; a second ferromagnetic layer adjacent to the plurality of first coils; a plurality of second coils adjacent to the second ferromagnetic layer; and a third ferromagnetic layer adjacent to the plurality of second coils, wherein the bottom surface of the third ferromagnetic layer defines the top of the cavity; A plunger assembly disposed within the cavity of the stator assembly and movable during operation between a first position and a second position along the central longitudinal axis, the plunger assembly comprising a plunger comprising a pair of ferromagnetic plates with a magnet disposed between the pair of ferromagnetic plates, wherein (i) a first ferromagnetic plate of the pair of ferromagnetic plates is disposed between a first ferromagnetic layer and a second ferromagnetic layer, and (ii) a second ferromagnetic plate of the pair of ferromagnetic plates is disposed between the second ferromagnetic layer and the third ferromagnetic layer; and The pair of ferromagnetic plates, together with the first ferromagnetic layer, the second ferromagnetic layer, and the third ferromagnetic layer, further cooperate to drive at least one contact, the at least one contact comprising: The first contact member has a base with an exposed surface, and a first metal layer is located on the top surface; A liquid metal layer is disposed only on the top surface of the first metal layer and extends above the exposed surface of the first contact member; and The second contact member has a contact surface, is adjacent to the first contact member and is positioned in an open position, and is movable to a closed position, in which the contact surface of the second contact member contacts and presses the liquid metal layer and the first metal layer until the contact surface of the second contact member abuts against the surface of the first contact member.

23. The electrical relay circuit according to claim 22, wherein, The liquid metal layer is formed of a compliant material that is displaced in the closed position by pressure applied by the second contact member and returns to its original shape in response to the second contact member moving to the open position.

24. The circuit according to claim 23, wherein, The first contact member contains tungsten, and the liquid metal layer contains a gallium indium tin alloy. The liquid metal layer has a meniscus shape when not under pressure, and the meniscus shape is compressed into a compressed shape in response to pressure applied to the liquid metal layer by the second contact member. Excess material displaced from the liquid metal layer is also displaced into a groove in the first contact member in response to pressure from the second contact member. Once the second contact member moves to the disconnected position, the excess material from the liquid metal layer returns to the meniscus shape in response to the repulsive force between the tungsten in the first contact member and the gallium indium tin alloy in the liquid metal layer.

25. The electrical relay circuit according to claim 24, wherein, The repulsive force includes the surface tension in the liquid metal layer.

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