Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H1/00—Contacts
  • H01H1/0036—Switches making use of microelectromechanical systems [MEMS]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H1/00—Contacts
  • H01H1/0036—Switches making use of microelectromechanical systems [MEMS]
  • H01H2001/0063—Switches making use of microelectromechanical systems [MEMS] having electrostatic latches, i.e. the activated position is kept by electrostatic forces other than the activation force
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H57/00—Electrostrictive relays; Piezoelectric relays
  • H01H2057/006—Micromechanical piezoelectric relay
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H61/00—Electrothermal relays
  • H01H2061/006—Micromechanical thermal relay
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H57/00—Electrostrictive relays; Piezoelectric relays
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H61/00—Electrothermal relays
  • H01H61/02—Electrothermal relays wherein the thermally-sensitive member is heated indirectly, e.g. resistively, inductively

Definitions

• a provisional utility patent application describing this device is 60/243,788, filed 10/27/2000, and bearing the same title the present application.
• a second application, describing a related device is 60/243,786, also filed on 10/27/2000, and titled "Microfabricated Relay with Multimo ⁇ h Actuator and Electrostatic Latch Mechanism.”
• Each of these provisional utility patents relate to aspects of the present invention and are incorporated herein by reference.
• This invention pertains to the general field of switching devices, and more specifically, to the field of microfabricated relays. Since the original concept of a microfabricated switching device was created by Petersen in 1979, many attempts have been made to develop switches and relays for applications of low power and high frequency. The goal of this work is to improve the cost-effectiveness and performance of switching technologies by using miniature, batch-fabricated, photolithographically-defined, moveable structures as part of a mechanical device.
• Microfabricated electromechanical systems promise high lifetimes, low cost, small sizes, and faster speeds than switching devices manufactured by conventional means, and offer higher performance than solid-state devices. In many applications, particularly those in high performance instrumentation, automated test equipment, radar, and communication systems, switching devices with certain qualities are required or preferred. Specific values vary by application and are quantified where appropriate in the detailed description of the invention:
• Electrostatically actuated devices employ two (or more) bias electrodes across which a voltage is applied. Opposite charges are generated on the surfaces of the facing electrodes, and an electrostatic force is generated. If the bias electrodes are allowed to deflect towards each other, actuation is enabled. The switch or relay contact electrodes in an electrostatically actuated device would be mechanically coupled to these moving bias electrodes, so that the contact electrodes would mate together or separate as the voltage was applied and removed. [008] Electrostatic actuation intrinsically supports a number of the operating qualities described, and, as a result, is the most widely examined MEMS actuation mechanism for switches and relays. Electrostatic actuators enable Ohmic-contact relays and switches, although low resistances are difficult to achieve.
• Bimorph actuators unlike electrostatic actuators, transduce the control signals into mechanical deformation within the actuator itself.
• Bimorph (or, more generally, multimorph) actuators are comprised of layers demonstrating different physical responses to a particular stimulus.
• a thermal bimorph might have a first layer with a high coefficient of thermal expansion (above 10 ppm/°C) and a second layer with a low coefficient of thermal expansion (below 5 ppm/°C).
• this bimorph is exposed to an increase in temperature, the relative expansion of the first layer is constrained by the intimate contact to the second layer, and the actuator curls in response. Devices employ this curl to perform work, and the forces generated by bimorphs can . be much higher than those attainable by electrostatic actuators.
• Bimorph actuation also intrinsically supports a number of the operating qualities described above, and, as a result, is the second most widely examined MEMS actuation mechanism for switches and relays. They can be used in Ohmic-contact devices, and the high forces generated by bimorph actuators result in low contact resistances. They can be designed to actuate with low power to toggle states, though only certain types of bimorphs allow for low power state latching. Bimorph actuators can be made to provide high speeds and high closure force, and can be designed to provide similarly high opening forces and . speeds. Some types of bimorph actuators can also be designed with low drive voltages and low drive currents.
• the advantage is an increase in closure force and reduction in drive voltage, at the penalty of heightened complexity and requiring simultaneous driving of both actuators for proper relay functionality.
• Multimorph actuators are used primarily because of their capacity to generate large forces for any given drive power, voltage, or electric current. Electrostatic actuators are used because of their capacity to use very low powers for actuation and holding switches or relays in an open or closed position. There has been a desire in the community to develop devices that incorporate large forces for reliable contacts while using low power, but no previous effort has been successful. This invention is the first attempt to achieve this goal, and does so by incorporating both high-force multimorph actuation with zero-power electrostatic latching mechanisms.
• the operation of the invention allows for different stable states for the device.
• the first state is a passive state, which is the natural condition of the relay when no control signals are applied to the device.
• a drive control signal is applied to the relay actuator(s), where the mechanical limitations of the device prevent further deflection of the relay armatures.
• a latch control signal is applied to capacitive elements to attract them and hold them together with electrostatic forces. It is then possible to remove the drive control signals from the actuator, and the relay will remain latched. Removal of the latch control signal can then send the relay back to the passive state.
• the double-throw configuration allows for a second active state wherein a second electrical contact is made with the relay in a second closed position.
• An associated second latch state is also incorporated to provide low-power latching capabilities for the second closed position.
• Milli-, m is the standard S.I. prefix for one one-thousanth (1/1,000).
• Micro-, ⁇ is the standard S.I. prefix for one one-millionth (1/1,000,000).
• Nano-, n is the standard S.I. prefix for one one-billionth (1/1,000,000,000).
• Newton, N is a standard S.I. unit of force equal to one kilogram-meter-per-second-squared.
• Micron, ⁇ m, or micrometer is a unit of length equal to one-one-thousandth of a millimeter.
• Microfabrication is defined as a fabrication method of defining components delineated through photolithographic techniques made popular by the integrated circuit developer community.
• Micromachining is defined as the action of delineating a microfabricated element that has been photolithographically defined, often performed by an etching process using acids or bases.
• An actuation is defined as the action of opening or closing a relay or other switching device.
• An actuator is defined as the energy conversion mechanism responsible for actuation.
• An armature is defined as any element that is deflected or moved by an actuator in order to open or close a relay or other switching device.
• a multimo ⁇ h is defined as an actuator comprised of a combination of layers that change size when exposed to a stimulus, the size changes varying for two or more different layers.
• a bimo ⁇ h is defined as a multimo ⁇ h with exactly two layers.
• a multimo ⁇ h layer is defined as any one layer of a multimo ⁇ h, where each specific layer may or may not be sensitive to the drive stimulus defined for the multimo ⁇ h.
• a piezoelectric multimo ⁇ h is defined as a multimo ⁇ h actuator sensitive to electric voltage stimuli, wherein one or more layers have non-zero coefficients of piezoelectricity.
• a thermal multimo ⁇ h is defined as a multimo ⁇ h actuator sensitive to heat or cold stimuli, wherein one or more layers have non-zero coefficients of thermal expansion.
• a buckling multimo ⁇ h is defined as a multimo ⁇ h actuator sensitive to deflection stimuli, wherein one or more layers have non-zero stress at levels pursuant to buckling phenomena.
• a fixed base is defined as a rigid, integral relay region that provides mechanical support.
• a base substrate is defined as a microfabrication substrate forming one part of a fixed base.
• a load signal is defined as the signal to be switched by a relay or other switching device.
• a load signal line is defined as a port (input or output) for the load signal to be switched.
• An armature contact element is defined as an element located on an armature that physically engages and or disengages with other contact elements in order to form and/or break a conductive path for a load signal to progress from an input to an output load signal line.
• a contact armature is defined as an armature that has attached armature contact elements.
• a base substrate contact element is defined as an element located on a base substrate that physically engages and/or disengages with other contact elements in order to form and/or break a conductive path for a signal to progress from an input to an output load signal line.
• a drive signal is defined as a signal that initiates the actuation of a relay or switch.
• a drive signal line is defined as a line upon which is directed a drive signal. At least two drive signal lines are necessary for electric drive signals, one for the signal and one for reference.
• a latch signal is defined as a signal that holds a relay or switch in an open or closed state.
• a latch signal line is defined as a line upon which is directed a latch signal. At least two latch signal lines are necessary for electric latch signals, one for the signal and one for reference.
• An armature electrode is defined as a conductive area attached to the armature, upon which latch signals or their references are directed.
• a base substrate electrode is defined as a conductive area attached to the base substrate, upon which latch signals or their references are directed.
• a latch electrode insulator is defined as an insulating region preventing electrical contact from occurring between the armature electrode and the base substrate electrode.
• This invention covers switching speeds and signal loads that are generally small compared to relay industry standards.
• a functional distinction between ⁇ A and mA, for example, is not made with regards to load signal strength for conventional relays, whereas the performance and design differences of microfabricated relays for these different load signals is significant.
• the following speeds and signal loads are defined, noting that these classifications differ from those defined in relay industry standards:
• Very fast switching times are defined as less than 100 nsec.
• Fast switching times are defined as 100 nsec to 1 ⁇ sec.
• Moderate switching times are defined as 1 ⁇ sec to 100 ⁇ sec.
• Slow switching times are defined as 100 ⁇ sec to 10 msec.
• Very slow switching times are defined as greater than 10 msec.
• Very low signal loads are defined as less than 10 ⁇ A DC current or 100 ⁇ W RF power.
• Low signal loads are defined as 10 ⁇ A to 10 mA or lOO ⁇ W to 100 mW.
• Moderate signal loads are defined as 10 mA to 500 mA or 100 mW to 5 W.
• High signal loads are defined as 500 mA to 5 A or 5 W to 50 W.
• Very high signal loads are defined as greater than 5 A of DC current or 50 W of RF power.
• Figure 1 is a functional plan- view illustration of one embodiment of the invention with cross-sectional lines and views provided for clarity, and with many elements that may be buried below the top surface shown in dashed outline.
• Figure 1 is a plan-view with the cover removed in order to expose the actuator elements of a representative embodiment.
• Two cross-sections shown along with Fig. 1 are Figs. 2A and 3A, which illustrate views of a load armature and actuator armature, respectively.
• Figure 4 pictures a cross-sectional schematic of the armatures in the region of a multimo ⁇ h actuator, to illustrate the relationship between electrical connections.
• Figures 5A, 5B, and 5C show cross-sections of the relay region with the latching and contact mechanisms in the one open (Fig.
• FIG. 5A closed down (Fig. 5B) and closed up (Fig. 5C) relay states.
• the bending function of a contact armature is illustrated in Figs. 5B and 5C, which depict the relay in fully latched states.
• Figures 2A, 2B, 2C, 2D, and 2E illustrate cross-sectional views of the load armature in five operational states of the device.
• Figure 2A is the load armature when the relay is in the passive state.
• Figure 2B illustrates the curvature induced in the load armature when a relay is driven into an active down state.
• Fig. 2C illustrates a curvature induced in the relay load armature when in the latched down state.
• Figure 2D illustrates the load armature curvature when a relay is driven into an active up state.
• Fig. 2E illustrates a curvature induced in the relay load armature when in the latched up state.
• Figures 3A, 3B, 3C, 3D, and 3E illustrate cross-sectional views of a piezoelectric multimo ⁇ h actuator armature in the same five operational states of the device.
• Figure 3 A is the actuator armature when the relay is in the passive state.
• Figure 3B illustrates the curvature induced in the actuator armature when a relay is driven into an active down state. Armature electrode contact is seen in Fig.
• FIG. 3C which illustrates a possible curvature induced in the actuator armature when in the relay latched down state.
• Figure 3D illustrates the curvature induced in the actuator armature when a relay is driven into an active up state.
• Armature electrode contact is again shown in Fig. 3E, which illustrates a possible curvature induced in the actuator armature when in the relay latched up state.
• Figures 6 through 10C illustrate an alternative embodiment.
• Figure 6 is a functional plan-view illustration of an embodiment employing a thermal multimo ⁇ h as a primary actuator. Two cross-sections shown along with Fig. 6 are Figs.
• FIG. 7A and 8A which illustrate cross-sectional views of a load armature and thermal multimo ⁇ h actuator armature, respectively.
• Figure 9 pictures a cross-sectional schematic of the armatures in the region of a multimo ⁇ h actuator.
• Figs. 10 A, 10B, and 10C show the cross-sections of the relay region with the latching and contact mechanisms in the open, closed down, and closed up relay states, respectively.
• Figures 7A, 7B, 7C, 7D, and 7E illustrate cross-sectional views of the load armature in five operational states of the device.
• Figure 7A is the load armature when the relay is in the passive state.
• Figure 7B illustrates the curvature induced in the load armature when a relay is driven into an active down state.
• Figure 7C illustrates a relay curvature induced in the load armature when in the latched down state.
• Figure 7D illustrates the curvature induced in the load armature when a relay is driven into an active up state.
• Figure 7E illustrates a curvature induced in the relay load armature when in the' latched up state.
• Figures 8A, 8B, 8C, 8D, and 8E are cross-sectional views of a thermal multimo ⁇ h actuator armature in the same five operational states of the device.
• Figure 8 A is the actuator armature when the relay is in the passive state.
• Figure 8B illustrates the actuator armature when the relay is driven into an active down state.
• Armature electrode contact is seen in Fig. 8C, which illustrates a curvature induced in the actuator armature when in the latched down relay state.
• Figure 8D illustrates the actuator armature when the relay is driven into an active up state.
• Armature electrode contact is seen in Fig. 8E, which illustrates a possible curvature induced in the actuator armature when in the latched up relay state.
• the relay can be comprised of multiple actuator armature structures, as illustrated in Fig. 11. This relay is shown with the actuator armatures pe ⁇ endicular to the load armature. Such configurations with different numbers of actuator armatures or load armatures are largely at the decision of a designer skilled in the art.
• Figure 12 illustrates a cross-sectional schematic of the load armature of this embodiment.
• Figures 13 A, 13B, and 13C are cross-sectional schematic illustrations of the actuator armatures of the relay in three of the five operational states of this third embodiment. Each figure depicts the thermal actuator armatures responsible for actuation to close the device and those responsible for actuation to open the device, as well as the contact armature region surrounding the contact electrodes.
• Figure 13 A depicts the actuator armatures when the relay is in the passive state.
• Figure 13B illustrates the curvature induced in the actuator armatures when a relay is driven into an active down state.
• Figure 13C illustrates the actuator armatures when in the latched down state. Illustrations of the actuator armatures in the active up and latched up states are not provided in the interest of brevity.
• This invention is a new type of relay that inco ⁇ orates the functional combination of multimo ⁇ h actuator elements with electrostatic state holding mechanisms in the development of a micromachined double-throw switching device.
• This combination of elements provides the benefits of high-force multimo ⁇ h actuators with those of zero-power electrostatic capacitive latching in microfabricated relays with high reliability and low power consumption. The following description first discusses this functional combination of actuator technologies, then continues with a detailed discussion of several specific device embodiments of this invention.
• a relay is a switching device with the added characteristic of having the control signal path isolated from the load signal path. Such a device enables the switching of varied or sensitive signals without interference from the control signals which might have fluctuations or irregularities capable of degrading the integrity of a sensitive load signal (such as a data stream or test equipment signal). This also protects control electronics in applications where the load signal might be dangerous in some form; a high voltage or high current load signal might overload the control electronics if allowed to interact with the control signal paths. Radio-frequency devices often require high isolation of the control electronics from the signal loads, as RF power cannot be perfectly contained due to capacitive or inductive coupling. Most single-throw relays have two stable operational states defining whether the load signal circuit is either 1) open or 2) closed. Such a device forms a valuable component in a wide variety of applications in direct current, low frequency, and radio frequency applications, and the many efforts to create microfabricated versions of relays attest to the industry interest.
• Multimo ⁇ h actuation mechanisms have been featured in switching devices for. decades due to their ability to generate comparably high forces (mN to N contact forces) at high speeds ( ⁇ sec to msec actuation times) over moderate distances (tens of ⁇ m to mm of armature deflection) with moderate power requirements (tens of ⁇ W to tens of mW for continuous operation).
• Multimo ⁇ h actuator technology is employed in this invention to generate moderate contact forces in order to reliably make and break electrical load signal contacts.
• multimo ⁇ h actuator technologies can have several of the significant disadvantages discussed in the background section. Some technologies require constant power to maintain, for example, whereas others demonstrate weakening, unreliability, or failure if an actuator drive signal or relay state is maintained for an extended period of time (seconds to years).
• this invention couples a secondary mechanism with the multimo ⁇ h actuator in order to provide a low-power, non- destructive alternative for holding the relay state.
• Electrostatic actuation has long been a core technology in the microfabricated actuator community seeking the benefit of its low power consumption (nW to ⁇ W) and fast closure times (100 nsec to 100 ⁇ sec).
• the forces (1 ⁇ N to 0.5 mN) and actuator travel distances (one to ten ⁇ m) typical for these devices are very limited, however, and most electrostatic relay efforts suffer accordingly in terms of relay insertion loss, reliability (both related to contact force), isolation, and standoff voltage (both related to gap separation).
• This invention is superior to prior microfabricated relays because two actuation technologies are combined to utilize the advantages of each.
• the electrostatic actuator is used to hold the device in each closed state, with the majority of the work required to attain the state performed by the comparably powerful multimo ⁇ h actuator. In such a combination, the advantages of each actuator are realized, with their disadvantages eliminated.
• This invention discusses microfabricated relays with overall planar dimensions of total width and length between 10 ⁇ m and 10 mm. The planar dimensions selected for a particular design would be primarily dependent on the required speed and the power level of the signal load to be switched, with ranges previously defined. Devices requiring fast or very fast switching would be designed at the low end of size ranges given, whereas devices handling high or very high signal loads would have sizes near the high end of the ranges recommended.
• a device according to the invention and intended for use with low to moderate signal loads and moderate to fast switching speeds may have planar dimensions of between 75 ⁇ m and 1.5 mm. Such dimensions might be appropriate for medium-range wireless communicators, transmit phased-array antenna electronics, or general telecommunications switching applications. It is contemplated that in applications where high or very high signal load switching is required and slower speeds are acceptable, such as general pu ⁇ ose industrial relays or high power RF systems, the overall planar dimensions for devices according to this invention could be between 0.5 and 10 mm.
• Figure 1 is a functional plan- view schematic of one general class of embodiments of this invention, wherein one cantilever load armature and one cantilever latch armature are fixed at a common end and free to deflect at the opposing end, these free ends being mechanically coupled together by means of a contact armature.
• Figure 1 is not a true plan- view schematic, as elements such as electrical connections and electrodes that may be buried within the device are depicted. If the top cover plate were removed, all fixed elements were constructed of transparent material, and conductors block line of sight through the device, the view provided by Fig. 1 would be accurate. Elements are shown with consistent cross-hatching even in plan- view, and sub-surface elements are shown with a dashed outline rather than a solid outline.
• FIG. 1 Two cross-sections shown along with Fig. 1 are Figs. 2 A and 3 A, which illustrate the load armature and latch armature, respectively.
• Figure 4 is a cross-sectional schematic of the armatures in the general region of a multimo ⁇ h actuator, to illustrate electrical connections and insulators.
• Figures 5 A, 5B, and 5C show cross-sections of the region with the latching and contact mechanisms in open, closed down, and closed up relay states, respectively. The bending of a contact armature is illustrated in Figs. 5B and 5C, which depict the relay in fully closed and latched states.
• One aspect of this relay invention is the functionality of the armatures, and whether each is responsible for the transmission of load signals and/or control signals.
• a fixed base (101) is a region that is rigid and integral, which may consist of a number of semiconductor, metallic, or dielectric elements that are fixed together to provide mechanical strength. The overall size of the fixed base can help define the maximum size of the attached relay and its load signal handling capabilities.
• a fixed base further comprises a base substrate (102) and a cover substrate (134), which may consist of one or more microfabrication-capable dielectric or semiconductor materials such as glass, polyimide or other polymer, alumina, quartz, gallium arsenide, or silicon.
• the preferred base substrate in this embodiment is polished quartz at least 250 ⁇ m thick and extending at least 1 mm in each planar dimension, providing for a rigid base of microfabrication-quality material that is sufficiently large to permit ease of automated manufacture, packaging, and system insertion.
• first load signal line (103), a second load signal line (104), a third load signal line (135), and a fourth load signal line (136) that represent the electrical paths of the inputs and outputs of the signal to be switched by the device.
• first drive signal line (105) and a second drive signal line (106) are attached to the fixed base.
• the drive signal lines will be electrical paths.
• the latching mechanism employed in this invention is electrostatic attraction of capacitive electrodes, the latch signal lines are electrical paths.
• the load signal lines are manufactured of 4 ⁇ m thick plated gold alloy for low relay electrical resistance, having a nickel adhesion and plating layer 0.4 ⁇ m thick.
• a metallization is sufficiently thick and of sufficiently low resistivity to permit low-loss lines for light to moderate load signals, and the nickel provides a plating layer while not considerably interfering with the electrical performance of the gold.
• the control signal lines and latch signal lines of this embodiment may be manufactured of the 0.4 ⁇ m nickel material without the plated gold. No load power is transmitted in the control and latch signal lines, so the low resistivity of the gold may not be needed, and lower manufacturing costs may be realized by its omission.
• Gold may be important for device packaging processes, such as wire bonding or flip-chip attachment, and in such instances gold plating may be used.
• one set of materials that can be used for any electrical path, line, or electrode element is a set of conductive materials, also called conductors.
• Conductors used to manufacture relay elements according to this invention may be selected from those materials having a low resistivity, defined as having a resistivity equal to or less than 0.2 ohm-centimeter, equivalent to that of a heavily doped semiconductor.
• the materials that could be used include metals such as gold, copper, silver, platinum, nickel, and aluminum.
• the materials that could be used include doped semiconductors such as silicon, gallium arsenide, silicon germanium, and indium phosphide. It is also contemplated that any alloy or combination of metals or semiconductors with an overall low resistivity could be employed.
• the material thicknesses for electrical paths in devices according to this invention might range from 0.1 to 100 ⁇ m, depending on the application and available manufacturing techniques. It is further contemplated that the thickness of one electrical path or line in one device according to this invention could differ substantially from the thickness of a second electrical path or line in the same device due to differing electrical and manufacturing requirements. It is generally recognized to those skilled in the art that the electrical resistance of any path is related to its resistivity, its thickness, its width, and its total length. As a result, power savings can be obtained by selecting materials and geometries in a way as to reduce path resistance, particularly for signal loads of high and very high powers. Use of materials that have a high resistivity and small width and thickness can result in Joule's Heating of relay elements, and can increase signal loss within the device.
• the material thickness of a path could range between 0.1 and 3 ⁇ m for a device according to the invention and intended for use with low signal loads and fast switching times. Such a path would be light, thin, and of higher resistance as compared to thicker paths of the same width and material, and considered useful in applications switching low or very low load signal powers. In applications with moderate signal loads and switching times, it is contemplated that the material thickness of an electrical path could range between 0.5 and 15 ⁇ m, depending on the resistivity and width of the path.
• a latch armature (109) is suspended from a region of the fixed base of Figs. 1 and 3 A.
• This actuator armature is in the form of a cantilever with one region fixed (110) and one region free to deflect (111).
• armatures are constructed of one or more layers of microfabrication-capable materials such as silicon, silicon dioxide, silicon nitride, gallium arsenide, quartz, polyimide or other polymer, or a metal.
• the actuator armature of the discussed embodiment contains a layer of silicon dioxide 8 ⁇ m thick, selected for ease of microfabrication by chemical vapor deposition or spin-on glass techniques, and to provide an insulating rigid armature structure.
• the vertical stiffness of a cantilever beam is approximately linear with the width of the beam, related to a third-order degree with respect to thickness, and to an inverse third-order degree with respect to length.
• the thickness and length are of greater design importance than width for a beam that is expected to deflect in a vertical direction normal to the substrate.
• the overall thickness of such an armature might range from 0.2 ⁇ m to 1 mm, depending on the application, the length, and the fabrication technology used in manufacture. It is reasonable to expect an armature in a device according to this invention could have a length between 5 ⁇ m and 5 mm.
• the actuator armature of the presently discussed embodiment is 40 ⁇ m wide and 180 ⁇ m long, providing sufficient width to reduce the line resistance and sufficient length for flexibility of the armature.
• an armature can range from 0.2 to 4 ⁇ m in thickness and between 5 and 50 ⁇ m in length. In a device designed for low to moderate signal loads with fast to moderate switching speed, it is considered that an armature can range from 1 to 40 ⁇ m in thickness, and between 25 and 500 ⁇ m in length. It is contemplated that in an application requiring moderate to high signal loads with moderate to slow switching speed, an armature thickness can range from 10 to 400 ⁇ m in thickness and between 100 ⁇ m and 2 mm in length. In a device designed for high to very high signal loads and slow to very slow switching speeds, it is contemplated that the armature could be between 200 ⁇ m and 1 mm in thickness and between 1 and 5 mm in length.
• armature size ranges apply not only to armatures and other elements of solid rectangular design, but also to armatures or other elements that vary in one or more dimensions by a linear or non-linear function.
• An example of such an armature would be a load armature that tapers from one width to a smaller width at the free end; it is recognized that such a structure may be of interest in RF applications as it can reduce input reflections and provide a higher performance than might a rectangular load signal armature.
• FIG. 3 A is a side view schematic of a multimo ⁇ h actuator and electrostatic latch armature in a passive state.
• a multimo ⁇ h is an element composed of two or more layers of material with different properties; the bimo ⁇ h illustrated is a multimo ⁇ h with exactly two such layers.
• the material layers of a multimo ⁇ h actuator each change by a different amount when exposed to a stimulus.
• the stimulus In the case of a piezoelectric or thermal multimo ⁇ h actuator, the stimulus would be applied voltage or heat, respectively.
• the stimulus would be a mechanical deformation in the direction of buckling sensitivity that would be magnified by the ensuing unstable physical action of the buckling element.
• layers are rigidly connected along one or more faces, so the different expansions of the materials tends to curve the multimo ⁇ h in a direction away from the layer or layers with the greatest expansion.
• the multimo ⁇ h actuator illustrated in Figs. 1 and 3 A comprises two materials (113) and (114). Each of the two materials of the multimo ⁇ h changes by a different amount due to a given stimulus.
• the multimo ⁇ h is a piezoelectric bimo ⁇ h, wherein the materials have differing coefficients of piezoelectricity. It is contemplated that in this embodiment, material (113) would have the highest coefficient of piezoelectricity out of the two materials, with element (114) representing a piezoelectrically neutral material.
• the piezoelectric actuator of this embodiment is formed from a 12 ⁇ m thick lead zirconate titanate (PZT) ceramic layer atop a 6 ⁇ m thick silicon dioxide layer, amounts sufficient to forcefully curl the actuator armature with readily achievable actuation voltages.
• PZT lead zirconate titanate
• piezoelectric multimo ⁇ h actuators employed by devices according to this invention could include piezoelectrically active materials manufactured of out of a ceramic such as barium titanite (BaTiO 3 ), barium titanate (BaTiO), lead niobate (PbNbO 3 ), lead titanate (PbTiO), lead zirconate (PbZrO 3 ), lead zirconate titanate ("PZT” or PbZr x Ti y O 3 ), or out of a piezoelectrically-active single crystal such as quartz (SiO 2 ), lithium sulfate (Li 2 SO ), lithium niobate (LiNbO 3 ), or zinc oxide (ZnO).
• a ceramic such as barium titanite (BaTiO 3 ), barium titanate (BaTiO), lead niobate (PbNbO 3 ), lead titanate (PbTiO), lead zirconate (Pb
• piezoelectric multimo ⁇ h actuators employed by devices according to this invention could include one or more multimo ⁇ h layers manufactured of an insulating material such as silicon dioxide (SiO 2 ), quartz, silicon nitride (Si x N y ), or undoped silicon.
• an insulating material such as silicon dioxide (SiO 2 ), quartz, silicon nitride (Si x N y ), or undoped silicon.
• the presently discussed embodiment employs a previously discussed silicon dioxide armature layer as element (114).
• piezoelectric multimo ⁇ h actuators employed by devices according to this invention could employ piezoelectrically-active materials with a different sensitivity to that of other multimo ⁇ h layers.
• one or both elements (113) and (114) may be comprised of multiple layers of materials having zero or non-zero coefficients of piezoelectricity.
• the material thicknesses of elements (113) and (114) might range from 0.5 ⁇ m to 1 mm, depending on the application, material, other actuator dimensions, and the fabrication technology used- in manufacture. In devices according to this invention for applications requiring low to very low signal loads and high to very high switching speeds, it is considered that elements (113) and (114) can range from 0.5 to 6 ⁇ m in thickness.
• elements (113) and (114) can range from 4 to 80 ⁇ m in thickness. It is further contemplated that some embodiments of this invention requiring high forces for high to very high signal loads, allowing for low to very- low switching speeds, may require actuators with elements (113) and (114) ranging between 50 ⁇ m and 1 mm in thickness.
• the drive signal required for actuation would be a voltage difference across the thickness or width of the piezoelectric material.
• Figures 1 and 3 A illustrate one possible configuration for the drive signal lines of a piezoelectric bimo ⁇ h.
• the drive signal lines are fabricated atop a region of the fixed base protruding above the planar surface of the base substrate. It is contemplated that in other devices according to this invention that the drive signal lines may be fabricated directly atop an electrically insulated region of the base substrate.
• Figure 3A depicts drive signal connections (170) and (171) to the top and bottom surfaces of the piezoelectric material
• an armature latch down electrode (115), which is electrically attached to the first latch signal line (107) by a conductive first latch signal path (116).
• a base latch down electrode (117), which is electrically attached to the second latch signal line (108) by a conductive second latch signal path (118).
• an armature latch up electrode (142), which is electrically attached to the first latch signal line by a conductive first latch signal path (143) by way of the armature latch down electrode.
• a cover latch up electrode Attached to the cover substrate above the armature latch up electrode is a cover latch up electrode (144), which is electrically attached to the third latch signal line (141) by a conductive second latch signal path (145).
• the latch down and latch up signals are voltage differences, so that the armature latch down electrode, base latch down electrode, armature latch up electrode, cover latch up electrode, and all conductive paths to the first, second, and third latch signal lines will be electrical paths. As with other electrical paths, it can be contemplated that conductors may be used to fabricate the armature electrode and base substrate electrode.
• material thicknesses for the armature electrodes and base substrate electrodes of devices according to this invention might range between 0.1 to 100 ⁇ m, depending on the application and material as previously discussed.
• the planar area of each latch electrode is expected to be between 25 ⁇ m 2 and 25 mm 2 . It is contemplated that for some devices according to this invention, the planar area of each armature electrode will be at least one half of the planar size of the multimo ⁇ h actuator upon which the actuator electrode is positioned.
• the area shape of the electrodes in some devices according to this invention are envisioned to be squares, rectangles, circles, or some combination of planar geometric figures.
• the armature latch electrodes, cover latch up electrode, and base latch down electrode may each be between 25 and 500 ⁇ m in planar area.
• the latch electrodes may each be between 300 and 50,000 ⁇ m 2 in planar area. It is additionally contemplated that in other devices according to this invention having moderate size, the latch electrodes would each range between 30,000 ⁇ m and 2 mm in planar area. If a particular device requires large areas to generation electrostatic latching signals on the order of 1 mN or greater, it is contemplated that each latch electrodes might range from 1 to 25 mm 2 in area.
• Low resistance transmission lines such as the gold load signal line of the presently discussed embodiment is not generally necessary for an electrostatic capacitive electrode. No appreciable DC current is needed to develop or dissipate a voltage across capacitive electrodes. By eliminating thick metal where it is not needed, the overall size and weight of the relay can be reduced to improve switching speed.
• Each of the latch electrodes for the presently discussed embodiment are 10,000 ⁇ m in rectangular area, and these electrodes as well as the latch and control signal lines are fabricated from nickel 0.4 ⁇ m thick. This nickel is the same as that is preferably used as the plating plane for the gold load signal lines, which simplifies manufacturing.
• a latch down electrode insulator (119) and a latch up electrode insulator (146) may be used to prevent electrical contact from occurring between the latch electrodes when the armature is deflected to the latch down or latch up states, respectively.
• the latch electrode insulators would be fabricated of insulating materials, where an insulating material is defined as a material with a resistivity at or above 10 ohm-centimeter.
• the electrode insulators of the present embodiment consist of a layer of silicon nitride 0.1 ⁇ m thick, due to the availability of high-quality thin silicon nitride films.
• insulating materials that may be used for a latch electrode insulator could include insulating microfabrication materials such as undoped silicon, silicon nitride, silicon dioxide, quartz, or polyimide or other insulating polymer. It is contemplated that the material used for a latch electrode insulator may be thin relative to other material layers used in a device according to this invention, with a range from 0.05 to 2 ⁇ m thick. It is contemplated that the material thickness of a latch electrode insulator in some devices having very low to moderate actuator sizes could range between 0.05 and 0.4 ⁇ m.
• a range might be desired in an application where thin layers of insulating materials are available and are of sufficient quality to prevent a breaking down of the dielectric due to electric field strength.
• the thickness of a latch electrode insulator could be between 0.3 and 2 ⁇ m.
• the latch down electrode insulator is envisioned as being affixed to the top surface of the base latch down electrode, and the latch up electrode insulator is envisioned as being affixed to the bottom surface of the cover latch up electrode.
• the latch down electrode insulator could be affixed to the lower surface of the armature latch down electrode, and the latch up electrode insulator could be affixed to the upper surface of the armature latch up electrode.
• latch electrode insulators could be suspended between the latch down or latch up electrode pairs and mechanically attached to the relay structure at its edges by some method. It is considered that the electrodes and insulator need not be a continuous film like a membrane, but may be in a hole, line, or grid pattern in different devices, provided they are mechanically coupled to the fixed base.
• armatures may be constructed of layers of microfabrication-capable materials such as silicon, silicon dioxide, silicon nitride, gallium arsenide, quartz, polyimide or other polymer, or metals.
• the actuator armature of the discussed embodiment inco ⁇ orates a layer of silicon dioxide 8 ⁇ m thick, selected to provide an insulating rigid armature structure that is compatible with microfabrication techniques.
• the thickness and length of a multimo ⁇ h actuator armature are of greater design importance than width for a beam that is expected to deflect in a vertical direction normal to the plane of the substrate.
• the load armature of the discussed embodiment is 180 ⁇ m long and 25 ⁇ m wide.
• a first armature contact element (120) which is electrically connected to the first load signal line by a first armature contact element path (121).
• a second armature contact element (137) which is electrically connected to the fourth load signal line by a second armature contact element path (138).
• the materials of the armature contact elements, conductive paths, and load signal lines are of similar materials and thicknesses for simplified manufacturing.
• the armature contact elements are of a different material and thickness than the conductive paths and load signal lines in order to improve mechanical and electrical properties of the contact itself.
• the armature contact elements, conductive paths, and load signal lines are of different and varying materials and thicknesses for reasons related to improved performance or ease of fabrication.
• the first armature contact element path and second armature contact element path in a preferred embodiment will be fabricated from a gold alloy, 4 ⁇ m thick [069]
• the size of armature contact elements in devices according to this invention may be between 0.5 ⁇ m and 1 mm in overall area.
• the specific area shape is envisioned to be a square, a circle, an oval, or some non-standard geometric figure.
• the armature contact elements may be between 0.25 and 30 ⁇ m 2 in area.
• the armature contact elements might be between 20 and 3,000 ⁇ m in area. It is further contemplated that in devices suitable for handling high or very high signal loads, the armature contact elements might be between 2,000 ⁇ m 2 and 1 mm 2 in total area.
• the performance demands of the contact element may require the use of different material layers to provide improved mechanical wear properties over those of the other electrical path materials used in a device according this invention.
• such different layers could include layers of hard metals such as nickel, tungsten, rhenium, rhodium, or ruthenium either below or on top of the nominal contact element surface. It is further contemplated that alloys or layered combinations of these and other low-resistivity metals can be used to fabricate the armature contact elements. In devices according to this invention, it is expected that each material used for armature contact elements will have a thickness suitable for the application, which is likely to range from 0.1 to 100 ⁇ m. It is contemplated that the thickness of armature contact elements can vary across its planar area, to provide for differences in element depth and shape for a given application and embodiment.
• the material thickness of armature contact elements in devices according to this invention suitable for very low to low signal load applications may range between 0.1 and 2 ⁇ m. Such contact elements would be light, thin, and of higher resistance than thicker paths of the same material and planar geometry. In a device suitable for low to moderate signal loads, it contemplated that the material thickness of contact elements could range between 0.5 and 10 ⁇ m, and would be of moderate mass and resistance as compared to other possible elements and paths of the same material. In other devices that may switch high or very high load signal powers, it contemplated that the material thickness of a contact element could range between 5 and 100 ⁇ m, and would be of high mass and low resistance as compared to thinner elements of the same material. In the embodiment illustrated in Figs. 1-5, the contact elements are of the same gold alloy used for the signal line, with the addition of a curved 0.5 ⁇ m rhenium ove ⁇ late to provide a wear-resistant contact area for reliable contacts.
• the geometry of the contact elements, the paths, and the signal lines need not be restricted to the specific configuration illustrated in Figs. 1 and 2.
• the conductive path could be affixed to the top or bottom of the armature rather than traverse its center. Such geometries are present in the second and third embodiments illustrated in Figs. 6-10 and Figs. 11-13, accordingly.
• the conductive paths could represent a majority of the material of the armature, unlike the depiction of Fig. 1 A, which suggests the conductor is less substantial than other armature materials.
• the mechanical properties of the armature conductor may not dominate the mechanical properties of the armature structure.
• armature contact elements are not restricted to flat geometric shapes, and could include curved, stepped, or surface-roughened shapes.
• Facing the first armature contact element shown in Fig. 2A is a base substrate contact element (122) that is electrically connected to the second load signal line by a conductive path (123). Facing the second armature contact element is a cover substrate contact element (139) that is electrically connected to the third load signal line by a conductive path (140).
• the geometry, materials, and thicknesses of the base substrate contact element, cover substrate contact element, first and third load signal lines, and conductive paths should be considered in a similar manner as with the armature contact elements, first and fourth load signal lines, and conductive paths, in terms of device expectations and for the embodiment shown in Figs. 1-5.
• the contact armature extends from a region rigidly connected (125) to a principal armature or armature electrode to a region free to deflect (126).
• the functional value of this rigid connection and free region appear in the discussion of the cross-sectional schematics of Figs. 5 A, 5B, and 5C.
• the contact armature may be constructed of an insulating material as defined. It is recognized that in some devices according to this invention, the contact armature can be of the same material as inactive elements of the load armature or the actuator armature. In such a device, it is contemplated that the contact armature is integral with these elements and rigidly connected.
• insulating materials used for the contact armature could include microfabrication materials such as silicon, silicon nitride, silicon dioxide, quartz, or polyimide or other insulating polymer. It is contemplated that the material used for a contact armature may range from 0.3 ⁇ m to 1 mm thick depending on material, armature geometry, and the application of the relay. In devices designed for very low or low signal loads, it is contemplated that the material thickness of a contact armature could range between 0.3 and 8 ⁇ m. In devices designed for applications of low to moderate signal loads, it is contemplated that the material thickness could range between 4 and 80 ⁇ m.
• the material thickness could range between 50 and 300 ⁇ m. In yet other devices with large planar dimensions and designed for applications of high to very high signal loads, the material thickness could range between 200 ⁇ m and 1 mm.
• planar dimensions of the contact armature are contemplated as being comparable or smaller in magnitude than those of the load signal armature and the multimo ⁇ h actuator armature. It is contemplated that such planar dimensions range between 2 ⁇ m and 5 mm in each of width and length depending on the application, the material thickness, and the required contact force for the relay in the latched state. In devices according to this invention where very low to low signal loads are to be switched with fast switching speeds, the planar dimensions might range between 2 and 20 ⁇ xn. In devices where low to moderate signal loads are to be switched, it is envisioned that the planar dimensions could range between 10 and 200 ⁇ m.
• planar dimensions could range between 100 ⁇ m and 1 mm. In the larger devices switching high or very high signal loads at slow to very slow speeds, the planar dimensions might range between 0.5 and 5 mm. As with the load signal armature, it is envisioned that such ranges not only apply to elements of solid rectangular design, but also to elements that vary in one or more dimensions by linear or non-linear functions.
• the contact armature of the embodiment illustrated in Figs. 1-5 is a 100 ⁇ m wide silicon dioxide beam that is 100 ⁇ m long and 6 ⁇ m thick. Such a device could provide the operating performance required for moderate power handling capabilities at moderate speed, and would mechanically couple the piezoelectric multimo ⁇ h actuation as well as the electrostatic latching mechanism to the force required at the contacts themselves.
• Figure 4 is a cross-sectional schematic of the device illustrated in Fig. 1, showing the portion of the relay inco ⁇ orating the multimo ⁇ h actuator.
• the base substrate (102) and cover substrate (134), parts of the fixed base, are present in this illustration, with the armatures of Figs. 2A and 3A suspended between these substrates.
• the multimo ⁇ h of Fig. 4 can be considered to be a piezoelectric multimo ⁇ h actuator.
• the actuator includes a top piezoelectric material (113) with electrical connections of the upper first drive signal connection (170) and lower second drive signal connection (171) to the top and bottom surfaces, respectively.
• the lower material (114) can be piezoelectrically neutral.
• This lower material (114) has the electrical connection (116) of the armature electrode affixed to the bottom surface. It is recognized that in other devices according to this invention, the armature electrode may be affixed in the middle or top of the lower material.
• the electrical connection (121) of the first armature contact element is shown in Fig. 4, as is the electrical connection (138) of the second armature contact element. It is recognized that each of the electrical connections could be on any insulated surface in any desired geometry in different devices. It is considered that the materials, thicknesses, and composition of the electrical paths and the multimo ⁇ h actuator are similarly flexible within the scope of the invention as discussed in the detailed description of Figs. 1, 2A, and 3 A.
• FIGs 5A, 5B, and 5C show cross-sectional schematics of the relay embodiment illustrated in Figs. 1-5, the cross-sectional views having been taken at the free region of the principal armature system. It is recognized by those skilled in the art that this region can be an important part of relay design, as it inco ⁇ orates the contact elements responsible for electrical conduction when the relay is in the closed state.
• the base substrate (102) and cover substrate (134), parts of the fixed base, are illustrated, with the contact armature (124) suspended nominally between these substrates.
• the contact armature is affixed (125) to the latch armature at the location of the armature latch down electrode (115) and armature latch up electrode (142).
• the contact armature has a free end (126) where the firs armature contact element (120) and second armature contact (137) are positioned. Opposite the armature latch down and latch up electrodes is the base substrate electrode (117) and cover substrate electrode (144), respectively. The base and cover substrate electrodes are illustrated with affixed latch down (119) and latch up (146) electrode insulators.
• the base substrate contact element (122) is located on the top surface of the base substrate, facing the first armature contact element, and the electrical connection (123) of the first armature contact element is seen extending into the center of the armature.
• the cover substrate contact element (139) is located on the bottom surface of the cover substrate, facing the second armature contact element, and the electrical connection (138) of the second armature contact element is also extended into the armature.
• FIG. 5B The bending function of the contact armature is illustrated in Figs. 5B and 5C, which depicts the same cross section as Fig. 5A except that the relay is in closed and latched states rather than in a passive state, with these states discussed in greater detail immediately following.
• the contact armature is responsible for generating a bending spring force that generally forms part of the contact force between armature contact elements and base or cover substrate contact elements.
• Figure 5B illustrates the bending in the contact armature when the relay is in a latched down state
• Fig. 5C illustrates the relay in a latched up state.
• the initial gap between the latch electrodes (and latch electrode insulator) is greater than the original gap spacing between the contact elements, and this difference is the amount by which the contact armature spring must deflect when the relay is closed. It is contemplated that in some devices according to this invention, the contact armature spring force is the total contact force between the contact elements. It is further contemplated that in other devices according to this invention, the contact armature is responsible for only part of the total contact force between the contact elements. In yet other devices, it is conceived that the contact armature may provide very little or no total contact force between the contact elements.
• the first stable operational state of the relay shown in Figs. 2A, 3A, and 5A is defined as the passive state, which is the condition of the relay when no control signals are applied to the device. This is considered to be a natural condition, with device stability defined by the mechanical geometry and fabrication details of a given relay.
• Figures 2A, 3 A, and 5A provide typical examples of load, latch, and contact armatures (respectively) in a passive state for some devices designed according to the invention, including the presently discussed embodiment. In these examples, the relay contact elements are not engaged, the multimo ⁇ h actuator is in a nominally neutral state of stress equilibrium, and all latch electrodes are separated.
• the multimo ⁇ h actuator armature or load signal armature can be upwardly curled rather than nominally flat when in the passive state.
• the multimo ⁇ h actuator armature or load signal armature can be downwardly curled rather than nominally flat when in the passive state.
• a drive down control signal can be applied to the relay actuator(s).
• An example of the results of such an action is a stable state defined as the first active state, where the mechanical limitations of the device prevent further deflection of the relay armatures.
• the first active state can be represented by the illustrations of Figs. 2B and 3B, wherein the multimo ⁇ h actuator of Fig. 3B is curled in a downward direction due to the drive control signal. It is considered that the armatures of Figs.
• the first latched state allows for the removal of the drive down control signal from the actuator, and the relay will remain in the first latched state. It is considered that in some devices, including the presently discussed embodiment, the later removal of the latch control signal can send the relay back to the passive state. In some devices, the return to the passive state occurs due to the restoring forces internal to the armatures themselves. In other devices, it is considered that forcible assistance from a multimo ⁇ h actuator will assist in the return of the relay to the passive state by employing a drive up control signal.
• the first active and first latched states for the embodiment describe one closed electrical contact path for the device.
• the present invention is for a double-throw device, and additional relay states allow for a second closed electrical path.
• a drive up control signal can be applied to the relay actuator(s).
• the results of such an action is a stable state defined as the second active state, where the mechanical limitations of the device prevent further deflection of the relay armatures.
• the second active state can be represented by the illustrations of Figs. 2D and 3D, wherein the multimo ⁇ h actuator of Fig. 3D is curled in an upward direction in response to the drive up control signal.
• the downward curvature induced in the latch armature is assumed to be mechanically coupled into the load signal armature, deflecting it to the point of engaging the second actuator contact element and the cover substrate contact element.
• the intimate contact of the armature latch up electrode to the latch up electrode insulator of the base substrate electrode is not required by the definition of the second active state, though such contact can be possible, and is illustrated in the embodiment of this invention of Fig. 3D.
• An additional relay state is initiated by applying a latch up control signal to capacitive elements of the armature latch up electrode and cover substrate electrode to attract them and hold them together with electrostatic forces. It is considered that in many devices according to this invention that such an action results in the flattening of the armature electrode and the holding of the closed contact.
• the embodiment illustrated in Fig. 3E reflects such a condition, where the flattening of the armature electrode is reflected in a flattening of the load signal armature.
• the second latched state allows for the removal of the drive up control signal from the actuator, and the relay will remain in the second latched state. It is considered that in some devices, including the presently discussed embodiment, the later removal of the latch control signal can send the relay back to the passive state. In some devices, the return to the passive state occurs due to the restoring forces internal to the armatures themselves. In other devices, it is considered that forcible assistance from a multimo ⁇ h actuator will assist in the return of the relay to the passive state by employing a drive down control signal. [089] In some devices according to this invention, the piezoelectrically actuated armature of the embodiment illustrated in Figs.
• each of the non-zero coefficient materials could be a layer constructed of one or more materials of the piezoelectric ceramics or crystals described previously.
• the upper piezoelectric material can be expanding while the lower is contracting.
• Such a multimo ⁇ h can generate as much as twice the force available for a particular device design given a fixed total actuator armature thickness.
• multimo ⁇ h actuators with one or more piezoelectric layers may be used to generate not only the closing forces as suggested in Fig. 3B, but also opening forces as well. It is considered that in some devices according to this invention, the opening forces of the multimo ⁇ h in a first latched (down) state can be achieved by reversing the drive down control signal and applying its inverse as a drive up control signal. It is generally recognized that the ability to drive an actuator in either direction based on the polarity of the control signal is one advantage of a piezoelectric multimo ⁇ h. It is noted that this advantage is present in piezoelectric multimo ⁇ h devices according to this invention.
• Figures 1-5 depict structural elements necessary for an embodiment featuring a single piezoelectric bimo ⁇ h actuator structure driving a single contact armature. It is contemplated that this invention is intended to consider the functional concept of any relay driven by a multimo ⁇ h actuator having electrostatic latching mechanisms. Additional embodiments wherein the multimo ⁇ h is comprised of a different actuator material combination, or a relay is comprised of multiple contact armatures, actuator armatures, or both, is within the scope of this invention.
• Figs. 6-10 illustrate a second embodiment with an operation functionally equivalent to that of the first embodiment illustrated in Figs. 1-5. A plan- view illustration is provided in Fig. 6, with Figs. 7-10 detailing cross-sectional views in an equivalent manner. Element numbers for this second embodiment begin with 200 instead of with 100, with the last two digits referring to functional equivalents from the first embodiment for the sake of clarity.
• Figure 6 is a functional plan view schematic of a relay composed of two primary armature structures in a similar manner as the relay of Fig. 1.
• the elements of Fig. 6 are considered to be similar to those of Fig. 1, with differences present in the actuator components and the geometric and material selections for equivalent elements in this embodiment.
• the cover substrate has been removed and elements normally not visible from the top view have been outlined in dashed lines for the sake of clarity.
• the specific geometry and location of the signal lines and paths are at the decision of designer, and are represented in the provided embodiments for pu ⁇ oses of illustrative example. It is considered that the materials, thicknesses, and composition of the electrical paths are flexible within the scope of the invention as previously discussed.
• the elements of the fixed base (201), base substrate (202), cover substrate (234), first (203), second (204), and third (235) load signal lines, first (205), second (206), third (255), and fourth (256) drive signal lines, and first (207) second (208), third (241) and fourth (285) latch signal lines are apparent as with Fig. 1.
• the latch armature (209) is illustrated, with one end fixed (210) and one end (211) free to deflect in the direction normal to the base substrate.
• the load armature (259) is similarly shown with one end fixed (260) and one end (261) free to deflect as well.
• actuator latch down electrode (215) and actuator latch up electrode (242) are seen, as well as the required actuator latch down (216) and latch up (242) electrode paths to the first and fourth latch signal control lines, respectively.
• the actuator latch electrode path is directed from the armature to the base substrate by means of a metallic anchor region, which in some devices may be a solder bump or other conductive mechanical and electrical connection.
• the substrate latch electrode (217), cover latch electrode (244) and their paths (218) and (245) to the second and third latch control signal lines, respectively, are similarly visible in Figs. 6 and 8A.
• Figure 8A illustrates that this embodiment has latch down (219) and latch up (246) electrode insulators covering the substrate and cover latch electrodes, respectively.
• the first actuator contact element (220) and first actuator contact element path (221) to the first load signal line is present, as is the electrical connection (223) from the substrate contact element (222) to the second load signal line.
• the first actuator contact element path in this embodiment is made from the armature to the base substrate by a metallic anchor region in a similar manner as discussed for the latch electrode path.
• the second actuator contact element (237) and second actuator contact element path (238) to the first load signal line is present, as is the electrical connection (240) from the substrate contact element (239) to the third load signal line (235).
• the second actuator contact element path in this embodiment is comprised of a via from the second actuator contact element to the first actuator contact element, electrically connecting both actuator contact elements.
• the load armature (224) is affixed at one end (226) at the latch electrodes and free to deflect (225) in the region of the armature contact element.
• the specific material and geometry for this embodiment have been selected to design a device capable of handling very low load signal powers with fast switching speeds.
• the load armature has planar width and length of 15 ⁇ m and 75 ⁇ m, respectively, and is fabricated from silicon nitride 2 ⁇ m thick.
• the load signal path and contact elements are constructed of 2 ⁇ m sputtered gold.
• the portion of the fixed base attached to the armature fixed ends is a section of a silicon handle wafer, which is bonded to a ceramic base substrate through a gold-platinum and solder connection. All conductors on the base substrate are 2 ⁇ m thick gold.
• the latch electrode insulator is 0.2 ⁇ m silicon nitride.
• the primary actuators for this embodiment are thermal multimo ⁇ hs.
• the thermal multimo ⁇ h of the latch armature is comprised of two primary bimo ⁇ h elements, an upper thermal multimo ⁇ h layer (227) and a lower thermal multimo ⁇ h layer (228).
• the upper thermal multimo ⁇ h layer is designed with a larger thermal coefficient of expansion.
• the thermal multimo ⁇ h of the load armature is comprised of two primary bimo ⁇ h elements, an upper thermal multimo ⁇ h layer (278) and a lower thermal multimo ⁇ h layer (280), where the lower layer in this actuator is designed with a larger thermal coefficient of expansion.
• the actuator of the latch armature is responsible for curling the relay down, whereas the actuator of the load armature is responsible for curling the relay up.
• the multimo ⁇ hs in the presently discussed embodiment features a 2 ⁇ m thick palladium for the upper multimo ⁇ h layer (227) of the latch armature, a 2 ⁇ m thick gold for the lower multimo ⁇ h layer (280) of the load armature, and a 2 ⁇ m thick silicon nitride for opposing layers (228) and (278).
• metals can be used for layers (227) and (280) and insulators used for layers (228) and (278).
• the materials that could be used for thermal multimo ⁇ h materials include metals such as gold, copper, silver, platinum, nickel, and aluminum.
• the materials that could be used for either layer include semiconductors such as silicon, gallium arsenide, silicon germanium, and indium phosphide. It is also contemplated that any alloy or layered combination of metals or semiconductors could be employed in devices according to this invention.
• thermal multimo ⁇ h materials include insulators such as silicon, silicon nitride, silicon dioxide, quartz, or polyimide or other insulating polymer. It is also recognized that each multimo ⁇ h layer can be comprised of a stack of layers in order to design specific properties into an actuator. [099] It is contemplated that the thicknesses of thermal multimo ⁇ h actuator layers may range from 0.1 to 500 ⁇ m, depending on the material, fabrication processes, application, and the geometries of other elements. In some devices according to this invention that may switch very low to low signal loads with high or very high switching speeds, it is considered that multimo ⁇ h layers may range from 0.1 to 3 ⁇ m in thickness.
• multimo ⁇ h layers might range from 2 to 30 ⁇ m in thickness. It is further contemplated that some devices require thicker multimo ⁇ h actuators, such as might be necessary in applications demanding moderate to heavy signal loads at moderate to slow switching speeds, and might employ multimo ⁇ h layers ranging between 20 and 200 ⁇ m in thickness. It is envisioned that applications of high or very high signal loads switching at slow or very slow speeds, multimo ⁇ h layers might range between 150 and 500 ⁇ m thick. It is recognized that the thicknesses or thickness ranges of multimo ⁇ h layers need not be similar for different layers.
• Figure 8 A includes a schematic representation of the cross-section of a first heating element (229), and Fig. 7A includes a second heating element (279). It is contemplated that in some devices such an element may be a resistive conductor trace in a path on the surface of an insulating layer. In the presently discussed embodiment, the heating element is fabricated from a 0.3 ⁇ m thick nickel-chrome alloy. It is contemplated that in some devices according to this invention, a heating element can be fabricated from a material with a resistivity between 0.001 and 10 ohm-cm. In some devices, a heating element may be constructed of a metal or semiconducting material.
• the thickness of a resistive heating element in a device can range between 0.05 and 10 ⁇ m. It is contemplated that in some devices, wherein the resistive material may have a resistivity less than 0.1 ohm- cm, the thickness may be between 0.05 and 2 ⁇ m. It is further contemplated that in some devices including a resistive material with a resistivity greater than 0.1 ohm-cm, the thickness may be between 0.5 and 10 ⁇ m.
• a heating element insulator (230), which in the present embodiment electrically isolates the heating element from a conductive multimo ⁇ h layer.
• the upper thermal multimo ⁇ h layer (227) were constructed of a metal in a device according to this invention, an insulating layer would insulate the heating element (229) from the layer (227) to allow the heating element to operate properly.
• the presently discussed embodiment considers that the upper thermal multimo ⁇ h layer (227) is conductive, and therefore benefit from insulation from the heating element.
• the embodiment depicted also considers that the lower multimo ⁇ h layer (228) is insulating, and could therefore be adjacent to the heating element without interfering with its proper operation.
• the multimo ⁇ h layer (278) of the load armature is insulating, and is therefore able to be adjacent to the second heating element (279).
• a heating element insulator would be fabricated of an insulating material as previously defined for the latch electrode insulator. It is contemplated that in some devices according to this invention, possible materials that may be used to fabricate the heating element insulator include silicon nitride, silicon dioxide, quartz, or polyimide or other insulating polymer. It is contemplated that the material used for a heating element insulator may be thin relative to some other material layers used in the fabrication of a particular device, with a range from 0.05 to 3 ⁇ m thick. It is contemplated that the material thickness of an insulating element in one device could range between 0.05 and 0.5 ⁇ m.
• FIG. 9 is a cross-sectional schematic of the device illustrated in Fig. 6, showing the portion of the relay inco ⁇ orating the multimo ⁇ h actuator.
• the base substrate (202) and cover substrate (234), part of the fixed base, is present in this illustration, with the armatures of Figs.
• the actuators are thermal multimo ⁇ hs.
• the actuator of the latch armature includes a top thermal multimo ⁇ h layer (227) with the heating element electrical connections of the first drive signal connection (270) and second drive signal connection (271) shown, each forming part of the first heating element itself and surrounded by the heating element insulator (230).
• the lower thermal multimo ⁇ h layer (241) is the same material as the actuator armature (209), and the actuator latch electrode path (216) is shown at the bottom surface of this armature.
• the load signal path (221) is shown at the bottom surface of the load armature in a similar manner and acts as the lower thermal multimo ⁇ h layer.
• the actuator of the load armature inco ⁇ orates the heating element electrical connections of the third drive signal connection (255) and fourth drive signal connection (256) shown, each forming part of the heating element itself.
• the drive signal paths are fabricated from the 0.3 ⁇ m nickel-chrome alloy of the heating element, the latch signal path is fabricated from a 0.2 ⁇ m nickel layer, and the load signal path is fabricated from a 2 ⁇ m sputtered gold layer.
• Figures 10 A, 10B, and 10C show cross-sectional views of the relay taken from the free region of the latch and load armatures. This region inco ⁇ orates the contact elements responsible for electrical conduction when the relay is in the closed state.
• the base substrate (202) and cover substrate (234), parts of the fixed base, are present, with the contact armature (224) suspended between these substrates.
• the contact armature is affixed (225) to the latch armature at the location of the armature latch down (215) and latch up (242) electrodes and has a free end (226) where the first (220) and second (237) armature contact elements are positioned.
• Opposite the armature latch down electrode is the base substrate electrode (217) and affixed latch down electrode insulator (219).
• Opposite the armature latch up electrode is the cover substrate electrode (244) and affixed latch up electrode insulator (246).
• the base substrate contact element (222) is located on the top surface of the base substrate, facing the first armature contact element.
• the cover substrate contact element (239) is located on the bottom surface of the cover substrate, facing the second armature contact element.
• the bending function of the contact armature is illustrated in Figs. 10B and 10C, which depict the same cross section as Fig. 10A except that the relay is in closed and latched states rather than in a passive state, with these states discussed in the detailed description of Figs. 5 A, 5B, and 5C.
• FIG 11 is a functional plan view schematic depicting a third embodiment, wherein the relay is composed of three primary armatures instead of two as with the first embodiments discussed.
• the relay of Fig. 8 has been designed such that the actuator armatures are pe ⁇ endicular to the load signal armature. It is recognized that the configuration for parallel or pe ⁇ endicular actuator armatures, and the specific number of each armature, in a specific device design is a feature at the decision of those skilled in the art for varying materials, geometries, and applications.
• Figure 12 is a cross-sectional schematic of the load armature of the relay embodiment illustrated in Fig. 11 in a passive, open state.
• Figures 13 A, 13B, and 13C depict cross-sections of the multimorph actuators and contact armatures of the embodiment.
• Element numbers for this third embodiment begin with 300, with the last two digits referring to functional equivalents from the first and second embodiments for the sake of clarity.
• Fig. 11 The elements of Fig. 11 are considered to be similar to those of Figs. 1 and 6, with differences present in the actuator components and the geometric and material selections for equivalent elements in this embodiment.
• the cover substrate has been removed, and elements normally not visible from the top view have been outlined in dashed lines for the sake of clarity.
• the specific geometry and location of the signal lines and paths are at the decision of designer, and are represented in the provided embodiments for p poses of illustrative example. It is considered that the materials, thicknesses, and composition of the electrical paths are flexible within the scope of the invention as previously discussed.
• the elements of the fixed base (301), base substrate (302), cover substrate (334), first (303), second (304), and third (335) load signal lines, first (305), second (306), third (355), and fourth (356) drive signal lines, and first (307), second (308), third (357), fourth (358), fifth (241), and sixth (291) latch signal lines are shown.
• the close down actuator armature (309) is seen, with one end fixed (310) and one end (311) free to deflect in the direction normal to the base substrate.
• the load armature (359) is shown pe ⁇ endicular to the closing actuator armature, with its one end fixed (360) and one end (361) free to deflect normal to the substrate.
• the close up actuator armature (389) is seen opposite the close down actuator armature, and has a fixed end (390) and free end (391) in a mirrored fashion.
• the armatures for the embodiment shown have been designed to carry a large load signal at slow switching speeds.
• the primary material for the armatures is a single-crystal silicon layer 12 ⁇ m thick.
• the load armature is 200 ⁇ m wide and 800 ⁇ m long.
• the actuator armatures are 250 ⁇ m wide and 650 ⁇ m long.
• the load signal lines and paths are fabricated from an 8 ⁇ m thick copper alloy.
• the control signal and latch signal lines and paths are fabricated from a sputtered 2 ⁇ m thick nickel-chrome alloy.
• Two actuator latch down electrodes (315) and (365) are seen, one at the underside of the close down actuator armature, and a second beneath the close up actuator armature, respectively.
• the required latch electrode paths (316) and (366) to the first and third latch signal control lines (307) and (357), respectively, can be seen clearly.
• Substrate latch down electrode paths (318) and (378) of the substrate latch down electrodes (317) and (367) to the second and fourth latch control signal lines, respectively, may be seen in Fig. 11.
• the first actuator contact element (320) and load signal path (321) to the first load signal line can be seen clearly in Fig. 12.
• the second actuator contact element (337) and load signal path (338) to the first load signal line by way of the first actuator contact element is also shown in Fig. 12.
• the substrate contact element path (323) from the substrate contact element (322) to the second load signal line is present, as is the cover contact element path (340) from the cover contact element (339) to the third load signal line (235).
• the close down actuator contact armature (324) is affixed at one end (326) at the latch electrodes and free to deflect (325) in the region of the armature contact elements.
• the close up actuator contact armature (374) is affixed at one end (326) at the latch electrodes and free to deflect (325) in the region of the armature contact elements.
• the close down actuator is comprised of an expansive upper thermal bimo ⁇ h layer (327) and a lower thermal bimo ⁇ h layer (328) with similar material and geometry considerations as the thermal multimo ⁇ h of the previous embodiment and illustrated clearly in Fig. 13 A.
• the drive up actuator is comprised of an expansive lower thermal bimo ⁇ h layer (377) beneath an upper thermal bimo ⁇ h layer (378).
• Layers (328) and (378) are comprised of the same nominal armature material layer for the depicted embodiment of Figs. 11 through 13.
• a resistive first heating element (329) provides a method of heating the closing bimo ⁇ h actuator with a control signal consisting of an electric current.
• a control signal consisting of an electric current.
• a second heating element (379) provides a method of heating the drive up bimo ⁇ h actuator in a similar manner as described for the second heating element of the previous embodiment. This element is electrically insulated by a second heating element insulator (380).
• FIG. 13A is a cross-sectional schematic illustration of the thermal bimo ⁇ h actuator relay embodiment depicted in Fig. 11, with elements in accordance with Figs. 11 and 12, and in a neutral state without actuation or latch signals applied. It is recognized in the presently discussed embodiment that the two multimo ⁇ h actuators actuate in opposing directions. In this embodiment, the close down actuator deflects the armature contact element in a downward direction when a close down control signal is applied, whereas the close up actuator deflects in an upward direction normal to the base substrate when a close up control signal is applied.
• FIG. 13B is a cross-sectional schematic of a device in the stable first active state, wherein the mechanical limitations of the device prevent further armature deflection.
• the closing actuator of Fig. 13B is curled in a downward direction from the close down control signal, though severely constrained by the fixed beam condition and bending forces of the contact armatures. It is considered that the armatures of Figs.
• the first latched state allows for the removal of the drive control signal from the actuator, and the relay will remain in the first latched state.
• the later removal of the latch control signal can send the relay back to the passive state due to the restoring forces internal to the armatures themselves.
• forcible assistance from the close up actuator may assist in the return of the relay to the passive state.
• the second active state and second latched state are not illustrated in the interest of brevity. Such states can be attained in a similar manner as described for the previous embodiment illustrated in Figs. 6 through 10.

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• Thermally Actuated Switches (AREA)

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• 2002
  • 2002-08-08 JP JP2004527503A patent/JP2005536013A/ja active Pending
  • 2002-08-08 EP EP02752736A patent/EP1527465A1/de not_active Withdrawn
  • 2002-08-08 WO PCT/US2002/025109 patent/WO2004015728A1/en active Application Filing
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