EP0968530A4 - Relais micro-electromecaniques - Google Patents

Relais micro-electromecaniques

Info

Publication number
EP0968530A4
EP0968530A4 EP97906500A EP97906500A EP0968530A4 EP 0968530 A4 EP0968530 A4 EP 0968530A4 EP 97906500 A EP97906500 A EP 97906500A EP 97906500 A EP97906500 A EP 97906500A EP 0968530 A4 EP0968530 A4 EP 0968530A4
Authority
EP
European Patent Office
Prior art keywords
relay
micro
layer
coil
deflectable structure
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP97906500A
Other languages
German (de)
English (en)
Other versions
EP0968530A1 (fr
Inventor
Yu-Chong Tai
John A Wright
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
California Institute of Technology
Original Assignee
California Institute of Technology
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by California Institute of Technology filed Critical California Institute of Technology
Publication of EP0968530A1 publication Critical patent/EP0968530A1/fr
Publication of EP0968530A4 publication Critical patent/EP0968530A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H50/00—Details of electromagnetic relays
    • H01H50/005—Details of electromagnetic relays using micromechanics
    • 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

Definitions

  • Electromechanical relays are switching devices typically used to control high power devices. Such relays generally comprise two primary components - a movable conductive cantilever beam and an electromagnetic coil. When activated, the electromagnetic coil exerts a magnetic force on the beam in the same way that a magnet will pick up a nail.
  • the beam itself acts as the second contact and a wire, passing current through the device.
  • the beam spans two contacts, passing current only through a small portion of itself.
  • the strength of the magnetic force produced by the coil is a function of the material used in the device, the number of turns in the coil itself, and the amount of current passing through the coil. In a typical device, a large number of turns is used so that the current drawn by the coil is much less than the current switched by the relay.
  • relays are treated as short-circuits when closed and as open-circuits when open.
  • Typical "ON" resistances are 0.5 ⁇ or less.
  • the switches are a physical break in the circuit, providing very high "OFF" resistance on the order of 10 M ⁇ or more.
  • a relay is a closeable break in the wiring of a circuit, there are very few constraints as to how or where they can be used in a circuit.
  • circuits using solid state switches such as power transistors and MOSFETs must be designed to allow one of the terminals of the switch to be connected to one of the power rails.
  • the "ON” and “OFF” resistances of such devices also tend to be worse by an order of magnitude or more than those of electromagnetic relays.
  • solid state relays often require large, expensive heat sinks when passing high current loads, a limitation eliminated by electromechanical relays.
  • Micro electromechanical relays have been proposed as an alternative to power electronics with most of the benefits of conventional electromechanical relays but sized to fit the needs of modern electronic systems. See, for example, Hosaka et al.. Electromagnetic Microrelays: Concepts and Fundamental
  • micro-electromechanical relay of the present invention is designed to both miniaturize and improve upon present day electromechanical relays.
  • the micromachining fabrication process used to make the inventive micro-relay is based upon technology originally used by integrated circuit (IC) manufacturers and, other than packaging, eliminates the need for expensive device assembly.
  • the preferred inventive process consist of three steps, all performed using micromachining techniques. First, a layer of magnetic material is laid down on a substrate and patterned into a desired shape. Next, an electromagnetic coil is created adjacent this material. Finally, a second layer of very efficient magnetic material (such as permalloy) is laid down adjacent the first two layers, forming a magnetic circuit, and having a portion fashioned into a deflectable structure, such as a cantilever beam. The deflectable structure has at least a portion that is suspended over or adjacent to at least one electrical contact. In operation, current passes through the coil, causing the deflectable structure to deflect, and either make or break contact with the electrical contacts.
  • very efficient magnetic material such as permalloy
  • the integrated fabrication process for the inventive micro-relay makes possible a unique unpowered hold feature.
  • the inventive micro-relay uses an electrostatic hold feature which holds the relay in the "ON" position by applying a small, zero-current voltage.
  • an electrostatic force can be generated between the deflectable structure and the substrate of the micro-relay that is strong enough to hold the relay in the "ON” position.
  • Turning the relay "OFF” requires only that the voltage be removed. Since the voltage is applied to a small capacitor, negligible current is drawn for this holding function.
  • This method removes the need for additional parts and labor during fabrication since the addition of the electrostatic actuating capacitor can be integrated into the design of the micro-relay with almost no change to the process.
  • the prior art technique of adding a magnet to the circuit can also be easily inco ⁇ orated into the design. By changing the first layer material from a high permeability magnetic material to a permanent magnetic material, a hold relay similar to comparable commercial designs can be produced with negligible change to the process.
  • micromachining fabrication process permits a magnetic circuit to be incorporated into the design in an economical and practical manner. This feature can be used to either reduce fabrication complexity or operating power of the device. Because the process is based on
  • Fabrication of integrated circuits can also be integrated into the micro-relay process. permitting control circuitry to be added on a micro-relay chip. Since the "ON" resistance of the micro-relay device is potentially very low, heat dissipation and power loss due to relatively high currents is not a large constraint on miniaturization.
  • an additional benefit of the invention is a higher frequency response.
  • the higher frequency response is a direct result of miniaturization since, as the mass of the deflectable structure becomes smaller, the speed with which it can deflect becomes faster. This can allow the device to be used in faster circuits or it can be viewed as reducing the device's "bounce" time (i.e., the length of time during switching when electrical contact between the input and output is unstable).
  • FIGURE 1 A is a top view of a first embodiment of a micro-relay made in accordance with the present invention.
  • FIGURE IB is a first cross-sectional view of the micro-relay of FIGURE 1 A. taken along line A- A' of FIGURE 1 A.
  • FIGURE I C is a second cross-sectional view of the micro-relay of FIGURE 1A, taken along line B-B' of FIGURE 1A.
  • FIGURE ID is a cross-sectional view of an alternative embodiment for the micro-relay of FIGURE 1A, taken along line B-B' of FIGURE 1A.
  • FIGURE IE is a cross-sectional side view of an alternative cantilever beam for the micro-relay of FIGURE 1A.
  • FIGURE 2 A is a top view of a second embodiment of a micro-relay made in accordance with the present invention.
  • FIGURE 2B is a first cross-sectional view of the micro-relay of FIGURE 2 A, taken along line A-A' of FIGURE 2A.
  • FIGURE 2C is a second cross-sectional view of the micro-relay of FIGURE 2A, taken along line B-B' of FIGURE 2A.
  • FIGURE 3 A is a top view of a third embodiment of a micro-relay made in accordance with the present invention.
  • FIGURE 3B is a cross-sectional view of a first embodiment for the micro-relay of FIGURE 3 A, taken along line A-A * of FIGURE 3A.
  • FIGURE 3C is a cross-sectional view of an alternative embodiment for the micro-relay of FIGURE 3 A, taken along line A-A 1 of FIGURE 3 A.
  • FIGURE 3D is a cross-sectional view of another alternative embodiment for the micro-relay of FIGURE 3 A, taken along line A-A' of FIGURE 3 A.
  • FIGURE 4A is a top view of a fourth embodiment of a micro-relay made in accordance with the present invention.
  • FIGURE 4B is a first cross-sectional view of the micro-relay of FIGURE 4A, taken along line A- A' of FIGURE 4 A.
  • FIGURE 4C is a second cross-sectional view of the micro-relay of FIGURE 4A, taken along line B-B' of FIGURE 4A.
  • FIGURE 5A is a top view of a single-contact embodiment of a micro-relay made in accordance with the present invention.
  • FIGURE 5B is a first cross-sectional view of the micro-relay of FIGURE 5 A, taken along line A- A' of FIGURE 5 A.
  • FIGURE 5C is a second cross-sectional view of the micro-relay of FIGURE 5 A. taken along line B-B' of FIGURE 5 A.
  • FIGURE 6 A shows a cross-section of a relay contact head of a micro-relay incorporating mini-lightening rods.
  • FIGURE 6B is a top x-ray view of the head shown in FIGURE 6A.
  • FIGURE 7 is a schematic diagram of an embodiment of the present invention showing lightening rods patterned into stationary contacts.
  • FIGURE 9 is a cross-sectional view of the preferred fabrication stages for the embodiment of the present invention shown in FIGURE 4A, taken along line B-B' of FIGURE 4A.
  • FIGURES 10A and 10B are cross-sectional side views of the preferred fabrication stages for the coil structure of a three-coil embodiment of the present invention.
  • FIGURES 11 A and 1 IB are cross-sectional side views of the preferred fabrication stages for the cantilever beam of a three-coil embodiment of the present invention.
  • FIGURE 12A is top view of an alternative embodiment of the present invention, showing three coils.
  • FIGURE 12B is a cross-sectional view of the structure in FIGURE 12 A, taken along line A-A' of FIGURE 12 A.
  • FIGURE 12C is a cross-sectional view of the structure in FIGURE 12 A, taken along line B-B' of FIGURE 12 A.
  • FIGURE 13 is a cross-sectional view of the preferred fabrication stages for the embodiment of the present invention shown in FIGURE 12 A, taken along line A-A' of FIGURE 12 A.
  • FIGURE 14 is a cross-sectional view of the preferred fabrication stages for the embodiment of the present invention shown in FIGURE 12A, taken along line B-B' of FIGURE 12 A.
  • FIGURE 15 A is top view of an alternative embodiment of the present invention, showing a recessed fabrication switch design.
  • FIGURE 15B is a cross-sectional view of the structure in FIGURE 15 A, taken along the cantilever beam in FIGURE 15 A.
  • FIGURES 16A and 16B are cross-sectional views of the preferred fabrication stages for the embodiment of the present invention shown in FIGURE 15 A, taken along the cantilever beam in FIGURE 15 A.
  • FIGURE 17A is top view of an alternative embodiment of the present invention, showing a double-sided fabrication switch design.
  • FIGURE 17B is a cross-sectional view of the structure in FIGURE 17 A, taken along the cantilever beam in FIGURE 17A.
  • FIGURE 18 is a cross-sectional view of the preferred fabrication stages for the embodiment of the present invention shown in FIGURE 17 A, taken along the cantilever beam in FIGURE 17A.
  • FIGURES 19A and 19B are top views of alternative cantilever beam designs in which the flux path and bending force properties can be designed separately.
  • micro-electromechanical relay of the present invention is designed to both miniaturize and improve upon present day electromechanical relays.
  • the micromachining fabrication process used to make the inventive micro-relay is based upon technology used by integrated circuit (IC) manufacturers and, other than packaging, eliminates the need for expensive device assembly.
  • micromachined micro-relay The motivation for a micromachined micro-relay is two-fold. On the financial level, a simple, inexpensive fabrication process is needed to ensure the device can compete with products already on the market. On the technical level it is desired as a small and reliable relay capable of passing several amps of current. An additional benefit of using micromachining is that the circuitry used to control the latching of the relay and to provide the power for that latching can be incorporated into the device, reducing component count and assembly time and cost.
  • the micro-relay of the present invention is fabricated by a process that is based upon micromachining technology originally used by IC manufacturers and, other than packaging, eliminates the need for expensive device assembly.
  • FIGURES 1A through 4C depict several different types of structures that can be made by the present invention.
  • Each structure features a magnetic circuit, an electromagnetic coil, and a deflectable structure, such as a cantilever beam, with at least one contact point. They differ mainly in the design of the electromag- netic coil and in the manner in which the magnetic circuit is implemented.
  • a first layer 1 of magnetic material such as a permanent magnet or a material having high magnetic permeability (i.e.
  • "soft" magnetic materials such as permalloy, SendustTM, supermalloy, etc.
  • an electromagnetic coil 3 is created in magnetic circuit with this first layer 1 .
  • the coil 3 is spirally wound over the first layer 1.
  • Other structures, including multiple windings and stacked windings, may be used.
  • the ends 3 a, 3 b of the coil 3 are coupled to a power source (not shown).
  • a second layer 4 of very efficient magnetic material having high magnetic permeability is laid down in magnetic circuit with the first two layers 1 , 3 to complete the process.
  • a portion of the second layer 4 of magnetic material is fashioned into a cantilever beam 6 such that the free end 7 of the beam is suspended over at least one electrical contact 8.
  • any deflectable structure can be used, such as a "see-saw" pivotable beam or plate, a double-end supported beam or plate that deflects near the middle, a torsion beam, etc.
  • a cantilever beam is used in the following embodiments.
  • FIGURES 1A, IB, IC, and ID depict a coreless planar type structure having an input contact 8a and an output contact 8b.
  • One end 3a of the planar coil 3 is coupled to a power source through the first layer 1.
  • more than one coil 3 may be used if desired.
  • application of current to the coil 3 pulls the free end 7 of the cantilever beam 6 into contact with both the stationary contacts 8a and 8b.
  • current can either pass in either direction between contacts 8a and 8b through the free end 7 of the cantilever beam 6.
  • the contacts 8a and 8b can be patterned with contact bumps 10 made of a conductive material, such as contact metal, as shown in
  • FIGURE IC to provide more reliable contact points.
  • FIGURES 2A, 2B, and 2C depict an electromagnet type structure having stationary contacts 8a and 8b.
  • one end of the second layer 4 is in electrical contact with the first layer 1 to form a solenoid core 12, with the planar coil 3 formed around the core 12.
  • the efficiency of the concentration of the magnetic field generated upon energizing the coil 3 is greater than in the design of FIGURE 1 A.
  • application of current to the coil 3 pulls the free end 7 of the cantilever beam 6 into contact with both the contacts 8a and 8b. Again, current can pass between the contacts 8a and 8b through the free end 7 of the cantilever beam 6.
  • the core makes fabrication slightly more difficult and sets constraints on the circuit in which the micro-relay can be used if the magnetic material is to be used as one of the terminals of the coil 3.
  • the greater magnetic field generated by this structure means that less current is required for operation.
  • the free end 7 of the cantilever beam 6 is coated with an insulating layer 13 and conductive contact 14, as shown in FIGURE IE.
  • This contact 14 for the cantilever beam 6 is isolated from the magnetic circuit. Isolating the contact 14 removes most electrical restrictions on the use of the micro-relay that might be imposed if the magnetic material of the end of the cantilever beam 6 is used as part of the electrical circuit.
  • the inventive micro-relay uses an electrostatic hold feature which holds the relay in the
  • FIGURES 3A and 3B depict a structure (coreless solenoid or electromagnet) that makes use of this electrostatic hold concept.
  • the cantilever beam 6 is lengthened to form an interaction point.
  • the interaction point includes a capacitor 19 comprising an upper holding electrode 20 separated by an insulating layer 21 from the end of the cantilever beam 6, a lower holding electrode 22, and a contact 23 coupled to the upper holding electrode 20 (e.g. , by wire bond connection).
  • the magnetic material layers 1 and 4 are electrically isolated.
  • application of current to the coil 3 pulls the free end 7 of the cantilever beam 6 into contact with both stationary contacts 8a and 8b. Again, current can pass between the contacts 8a and 8b through the free end 7 of the cantilever beam 6.
  • FIGURE 3B the capacitor 19 is shown at the very end of the cantilever beam 6, but the position of the capacitor 19 and free end 7 can be switched at the expense of some leverage, as shown in FIGURE 3C.
  • the upper hold electrode 20 is formed along the length of the cantilever beam 6. Couplings are otherwise essentially the same as in FIGURES 3A and 3B.
  • FIGURE 3D depicts an alternative structure (coreless solenoid or electromagnet) that makes use of the electrostatic hold concept.
  • This structure is similar to that shown in FIGURE 3C, but the beam 6 itself comprises the upper electrode 20 of the capacitor 19.
  • the typical size of the cantilever beam 6 allows it to be used as a large plate electrode.
  • the prior art technique of adding a magnet to the circuit can also be easily incorporated into the design.
  • the permanent magnetic material biases the relay such that activating the coil 3 switches the relay with little force, and the permanent magnet holds the relay in the switched position. Reversing the current in the coil counteracts the permanent magnet and reverses the switching action.
  • FIGURES 4A, 4B, and 4C depict an electromagnet type structure having stationary contacts 8a and 8b.
  • the first layer 1 is changed in shape and laid over conductive traces 30 forming a bottom part of the coil 3, with conductive traces 31 forming a top part of the coil 3 laid over the first layer 1.
  • the bottom conductive traces 30 and top conductive traces 31 are electrically cross-connected (for example, by etched and filled vias) to form at least one helical coil wrapped around a length of the magnetic material forming the first layer 1.
  • application of current to the coil 3 pulls the free end 7 of the cantilever beam 6 into contact with both contacts 8a and 8b. Again, current can pass between the contacts 8a and 8b through the free end 7 of the cantilever beam 6.
  • This structure is a more traditional type of solenoid relay.
  • the number of turns in the coil 3 can be substantially larger than the number in a planar coil as described above.
  • the cantilever beam 6 closes the micro-relay by its free end 7 shorting two metal contacts 8a, 8b.
  • This general design permits the micro-relay to have the least possible "ON" resistance.
  • this design also requires that two reliable contact points be created with each switching event.
  • An alternative design uses the cantilever beam 6 to pass current in from one side of the device, to a single contact point with a contact strip 8, and out the other side of the device, as shown in FIGURE 5C; the base of the beam 6 serves as the second point for electrical connection.
  • a single contact point may make the micro-relay more reliable but may make the design of the cantilever beam 6 more critical in order to have proper performance and minimum "ON" resistance.
  • FIGURE ID This limitation is overcome by the design shown in FIGURE ID, in which an extra conductive arm 9 is formed under the cantilever beam 6 separated by an insulating layer 11. In this configuration, current can be conducted through the conductive arm 9 to a single contact 8; the base of the conductive arm 9 serves as the second point for electrical connection.
  • FIGURES 5 A, 5B, and 5C one preferred embodiment of a single contact micro-relay is shown in FIGURES 5 A, 5B, and 5C.
  • the planar coil structure of FIGURE 1A is used in general, but the second layer 4 is partitioned into three legs, 4a, 4b, 4c, which are electrically isolated but magnetically coupled. This design isolates the input I m from the output I out when the device is open.
  • Electromechanical relays usually fail due to welding of the cantilever beam to an electrical contact. This occurs due to sparking in the gap between the beam and a contact when the relay opens and closes. The sparking is caused by the tendency of a circuit not to permit abrupt steps in current flow. When a relay switches, it generates such a step in current, typically resulting in a large voltage across the relay terminals. The large voltage causes sparking and initiates current flow which ""smooths" the current step.
  • micro-relay Several techniques can be incorporated into the inventive micro-relay which can help suppress these sparks. Because the technology used to fabricate the micro-relay is borrowed from the IC industry, conventional power diodes and transistors can be added in parallel with a relay. Such devices can be designed such that they are only active during the switching periods of the relay. Thus, they would dissipate very little power and produce very little heat. Designed correctly, they could effectively eliminating sparking.
  • a second method believed to be completely unique as applied to relays, is the integration of spark gaps or micro-lightning rods into the design of the micro-relay. It is possible to produce very sharp discharge points at one terminal of a micro-relay in very close proximity to the second terminal. Acting as micro-lightning rods, the discharge points would concentrate the electric fields produced by large voltages generated during switching, creating preferential sparking points. While sparking would still occur, it would be directed away from the moving contact points, reducing the likelihood of contact welding, thereby extending the life of the device.
  • the benefits of this technique over integrated ICs is the simplicity of fabrication and the elimination of the requirement that silicon be the substrate.
  • FIGURE 6A shows a cross-section of a relay contact head of a micro-relay incorporating micro-lightening rods 60 underneath the free end 7 of a cantilever beam 6.
  • the rods 60 may be made of the coil material, and should be rugged enough to take the discharge of approximately 10-100 times the nominal switched current.
  • the head is poised above a contact 8.
  • FIGURE 6B is a top x-ray view of the same head. This design can be used with either single-contact or double-contact micro-relay designs.
  • the rods 60 need not touch the contact 8, and indeed the tips of the rods 60 are preferably spaced a short distance
  • the rods 60 intensify the E-field at their tips and therefore are preferential regions for sparks to generate. In this embodiment, the rods 60 may even touch the contact 8 during switching.
  • the lightening rods are designed such that they have negligible stiffness so that they flex to allow the free end 7 of the cantilever beam 6 to touch the contact 8.
  • the rods 60 can be configured to just touch the sides of the contact 8 and be out of the way when contact is made; thus, stiffness is irrelevant.
  • FIGURE 7 shows an embodiment of the present invention showing lightening rods 61 patterned as an extension of the stationary contacts 8a and 8b.
  • the tips of the rods 61 are separated by less than about 1 ⁇ m.
  • the rods 61 may be of any conductive material, and may be fabricated using standard IC fabrication techniques. This design can be used with either single-contact or double-contact micro-relay designs. When the relay contact opens, sparks tend to be generated. If the sparks were generated at contact points, the life of the micro-relay would decrease.
  • the lightening rods 61 intensify the E-field at their tips and therefore are preferential regions for sparks to generate.
  • a complete micro-relay comprises three main components. These are the mechanical relay itself, the actuator which opens and closes the relay, and the electronic circuitry. While this invention focuses on the first two components, the fact that the relay is fabricated using micromachining techniques allows the structure to be built on top of a previously processed silicon die which contains both control and power circuitry. Ultimately, a completely integrated system can be created to produce an intelligent, high-current load micro-relay.
  • the micro-relay As a starting design for the micro-relay, its basic geometry is chosen to be a cantilever beam structure. Preferred dimensions of the beam can be determined as follows. A conservative estimate for the current carrying capability of micromachined wires is about 10 ⁇ A/ ⁇ m 2 . Assuming the relay must be able to pass a full amp of current, then the cross sectional area of the cantilever beam would be:
  • the length of the beam we arbitrarily choose it to be:
  • the most efficient magnetic design is a magnetic circuit consisting of a loop of magnetic material with a gap at the point of actuation and a solenoid to generate the magnetic flux.
  • the magnetic loop directs and magnifies the flux generated by the solenoid through the gap where the force is generated. This force can be shown to be:
  • N number of turns in the coil
  • I 0 current in the coil
  • ⁇ 0 vacuum permeability 4 x 10 '7 H/m
  • the z used in this equation will be the minimum magnetic circuit gap, z mm , when the beam is at its maximum displacement. Assuming some insulation is present in the circuit, this value will be:
  • the length of the beam we arbitrarily choose it to be:
  • 71 turns can be fabricated in a straightforward manner, which permits a relatively small current to be used. Increasing the current reduces the number of turns needed and makes fabrication easier. If power is an issue, increasing the number of turns, while increasing fabrication difficulty slightly, will proportionately reduce the coil current.
  • plating is the preferred method of depositing metal elements and magnetic circuit elements.
  • any method that provides for equivalent structure can be used, such as screen printing, vapor deposition, etc.
  • the design requires that two distinct components be integrated into a single device.
  • the solenoid is built from several layers of conductive material, such as metal, which are separated by insulating layers of photoresist. At the end of the process, this resist remains between the metal layers to prevent short circuits from rendering the solenoid inoperable. This is contrary to the process needed to produce the cantilever beam.
  • a two-layer metal design is used with the top layer being extremely thick. While photoresist is used during processing to separate the layers, it is all removed in the last step to create a freestanding structure.
  • each plating is preferably followed by planarization. This is done by first choosing a plating thickness that is thinner than that of the resist mold defining it. After plating, the resist can be globally etched back with oxygen plasma until its level is comparable to that of the electroplated metal.
  • the beam that needs to be undercut may be many hundreds of microns wide. Accordingly, the following examples provide a workable but not necessarily perfect method of fabricating the micro-relays in accordance with the present invention.
  • FIGURES 8 and 9 are cross-sectional views of the preferred fabrication stages for the embodiment of the present invention shown in FIGURE 4 A, taken along lines A-A' and B-B', respectively, of FIGURE 4A. The following steps describe stages a) through h) of
  • FIGURES 8 and 9 Step a): - Create permanent planarizing form with Ultra-baked AZ4620.
  • Soft baked photoresist can be removed with acetone or dedicated photoresist stripper.
  • the Cr/Cu/Cr seed layer can be etched in a single step with commercial chrome mask etchant which attacks both metals, or in several steps which remove one layer of metal at a time. Cr can be selectively etched with
  • Cu can be selectively etched with a solution of acetic acid, water and hydrogen peroxide.
  • this step intends to produce an electromagnetic coil with very low resistance and high current carrying capabilities.
  • Many other techniques can be used to accomplish the same goal. These include, but are not limited to. evaporating or sputtering thick metal (e.g. Al. Au, Cu, Ag, etc. ) and patterning with wet or dry etching techniques.
  • Plating of permalloy is chosen for ease of deposition and resulting excellent magnetic properties. Additional deposition techniques and materials may be used. These include, but are not limited to, sputtering of most any magnetic material or silk screening of magnetic particles suspending in a polyimide matrix.
  • Step f) - Evaporate Cr/Cu/Cr ( 100 A/ 1000 A/ 100 A) electroplating seed layer.
  • FIGURES 10A and 10B are cross-sectional views of the preferred fabrication stages for a three coil embodiment of the present invention, similar to FIGURE 12A described below, taken along the cantilever beam 6.
  • FIGURES 11A and 11B are cross-sectional views of the preferred fabrication stages for the embodiment of FIGURE 1 OA, taken along the magnetic circuit. The following steps describe stages a) through q) of these sets of figures:
  • Step a): Grow oxide layer on substrate 2 of about 5000 A for insulation. Deposit plating seed layer - preferably Cr/Ni but for now Cr/Cu > lOOA to lOOOA.
  • Can overetch because have metal seedlayer beneath area being etched.
  • Step f): Strip Cr RIE mask. Coat with layer of PI 3 ⁇ m.
  • Step o Evaporate Cr/Cu seed layer. Pattern to remove seed layer from core areas so second layer 4 of permalloy will plate from the core metal and not the Cu.
  • Step q Plasma ash to remove second layer permalloy PI mold, and free structures with Cu etchant, thereby freeing the cantilever beam 6 (which is supported by electroplated Cu) and removing the seed layer for the second layer 4.
  • FIGURE 12A is top view of an alternative embodiment of the present invention, showing three coils 3 rather than one.
  • FIGURES 12B and 12C are cross-sectional views of the structure in FIGURE 12A. All structures are formed on one side of the substrate 2.
  • FIGURES 13 and 14 are cross-sectional views of the preferred fabrication stages for the embodiment of FIGURE 12A, taken along lines A-A' and B-B', respectively. The following steps describe stages a) through o) of these sets of figures:
  • Insulation is required so the subsequently deposited electromagnetic coils 3 will not be short circuited. While almost any insulating material can be used, nitride or oxide is most suitable for the silicon substrate. 1 -
  • a plating seed layer which adheres well to the substrate and is compatible with permalloy plating.
  • Cr/Ni is used.
  • other possible seed layers are Cr, Al/Cu and Ti/Cu.
  • Patterning of the seedlayer is done so that it will not need to be stripped after the first permalloy plating. Dicing will be used to electrically isolate those structures that cannot be shorted together. This step is intended to enhance the process but the traditional stripping of the mold material and seed layer can also be done if preferred. An additional step to planarize the surface would probably be needed if this was done.
  • the permalloy structure would be shorted by subsequent metal layer depositions if they were not covered by an insulating layer.
  • Polyimide is chosen for its ease of deposition, ease of patterning and its mechanical properties.
  • Other insulators, such photoresist or oxide, could be used.
  • the insulating layer needs to be patterned to allow access to bond pads and contact points.
  • Photoresist is used due to its easy patterning characteristic.
  • Soft baked photoresist can be removed with acetone or dedicated photoresist stripper.
  • the stripper used should not damage the underlying polyimide layers.
  • the Cr/Cu/Cr seed layer can be etched in a single step with commercial chrome mask etchant which attacks both metals or in several steps which remove one layer of metal at a time.
  • Cr can be selectively etched with HC1.
  • Cu can be selectively etched with a solution of acetic acid, water and hydrogen peroxide.
  • steps d) through f) need to be repeated.
  • RIE plasma can be used to etch the polyimide.
  • a thin Cr masking layer can be use to protect the areas of the device that are not to be etched. Overetching in this step should not be a problem as there should be permalloy beneath the polyimide in the areas being etched.
  • RIE plasma can be used to etch the polyimide.
  • a thin Cr masking layer can be use to protect the areas of the device that are not to be etched.
  • This copper will be used as a sacrificial layer. Many other sacrificial materials, such as aluminum, photoresist, or oxide could be used. A seed layer for this may need to be deposited prior to plating or, with special attention in previous steps, the seed layer used to plate the first permalloy could be used.
  • Step 1) - Spin and pattern AZ4620 to produce optional dimple in cantilever beam.
  • Photoresist is used because it can be easily patterned and easily removed.
  • This layer can be patterned for two effects. First, it can be patterned over the permalloy cores plated in step i) to allow direct contact between the permalloy cores and the top permalloy layer. Second, it can be patterned in such a way as to eliminate the need to remove the seed layer after the top permalloy is plated. As with the seed layer used to plate the first permalloy layer, dicing can be used to isolate the plated structures.
  • tep n - Create a mold with soft-bake AZ4620. Mold plate a thick (> 5 ⁇ m) layer of permalloy. After plating, remove the photoresist mold. Strip the electroplating seed layer if necessary.
  • Photoresist is used due to its easy patterning characteristic.
  • Plating of permalloy is chosen for ease of deposition and resulting excellent magnetic properties. Additional deposition techniques and materials may be used. These include, but are not limited to, sputtering of most any magnetic material or silk screening of magnetic particles suspending in a polyimide matrix.
  • a copper etchant such as a mixture of acetic acid, water and hydrogen can be used as well as other etchants which will not attack the magnetic material.
  • FIGURE 15A is top view of an alternative embodiment of the present invention, showing three coils 3 rather than one.
  • FIGURE 15B is a cross-sectional view of the structure in FIGURE 15 A. taken along the cantilever beam 6. All structures are formed on one side of the substrate 2. In contrast to the embodiment shown in FIGURE 12A. where all structures are formed on top of the substrate 2, the embodiment shown in FIGURE 15A creates structures in part by etching recesses into the substrate. Hence, as used herein, the term "'on the substrate” includes formation on the original surface of a substrate and formation within the substrate.
  • FIGURES 16A and 16B are cross-sectional views of the preferred fabrication stages for the embodiment of FIGURE 15 A, taken along the cantilever beam 6. The following steps describe stages a) through n) of these sets of figures:
  • step d second layer 4 of magnetic circuit with integrated free standing structure 6.
  • Step 1) - PR pattern with sacrificial etch mask.
  • FIGURE 17A is top view of another alternative embodiment of the present invention, showing a single coil design but with structures formed on both the top and bottom of the substrate 2.
  • FIGURE 17B is a cross-sectional view of the structure in FIGURE 17A. taken along the cantilever beam 6.
  • FIGURE 18 is a cross-sectional view of the preferred fabrication stages for the embodiment of FIGURE 17A, taken along the cantilever beam 6. The following steps describe stages a) through k) of this set of figures:
  • Insulation is required so the subsequently deposited electromagnetic coil will not be short circuited. While almost any insulating material can be used, nitride or oxide is most suitable for the silicon substrate.
  • KOH potassium hydroxide
  • EDP ethylene diamine pyrochatecol
  • TMaH TMaH
  • the thickness of the substrate insulates the two magnetic layers from interaction from one another, reducing losses due to stray fields.
  • the holes through the wafer provides the magnetic flux path of the design which produces the actuating force in the switch.
  • Anisotropic etch is chosen to form the through-holes due to convenience of access and use and its applicability to silicon processing.
  • the holes could also be formed by RIE, drilling or other technique. If a substrate other than silicon is employed, many other options are possible. The requirement is selective placement of the holes and control of the ultimate size of the opening seen at the front side of the wafer.
  • insulating material that is not attacked by acetone can be used. These include, but are not limited to, oxide, nitride, Teflon, polyimide and ultra-baked photoresist.
  • Photoresist has the added benefit that it can be laid down in several layers. Arbitrary thicknesses can be achieved. Each layer can be patterned separately to achieve desired effects such as dimpling the contact portion of the cantilever beam 6.
  • Plating of permalloy is chosen for ease of deposition and resulting excellent magnetic properties. Additional deposition techniques and materials may be used. These include, but are not limited to, sputtering of most any magnetic material or silk screening of magnetic particles suspending in a polyimide matrix.
  • Global plate very thick (> 1 O ⁇ m) layer of permalloy.
  • step i) Forms bottom layer 1 of the device's magnetic circuit. See step i) for explanation of choice of permalloy and alternative techniques.
  • the inventive micro-relay requires proper design of its cantilever beam.
  • the cantilever performs two primary functions. First, it defines the electromagnetic force that must be generated to close the relay. Secondly, it is part of the magnetic flux path in the magnetic circuit. The two properties need to be balanced. A beam with larger cross-sectional area provides a flux path with lower magnetic resistance and reduces losses due to stray fields. A larger beam also means that a greater magnetic force is required to close the relay. Thus, too large a beam and the relay cannot be closed; too small a beam and the magnetic resistance of the beam overwhelms the magnetic circuit and no electromagnetic force is generated, and again the relay will not close.
  • a second design produces a cantilever beam in which the flux path and bending force properties can be designed separately.
  • Two examples of this second design are shown in FIGURES 19A and 19B. Key to this design is the addition of at least two magnetic strips
  • the switched current path can be isolated from or integrated with the magnetic circuit
  • micro-relay Possible applications for the inventive micro-relay are very extensive.
  • the micro-relay will be able to act as a one-to-one replacement in areas where traditional electromechanical relays are presently being used.
  • Micro-relays capable of carrying low current loads will be extremely useful in communications type circuitry. While transistors can carry similar loads at similar and ever lower cost, the "ideal" electrical nature of micro-relays make it possible to implement circuit configurations excluded by the operational properties of transistors. For example, passing of AC signals can be implemented with a single micro-relay whereas two transistors or a special silicon device would need to be used.
  • Micro-relays in accordance with the present invention with current carrying capabilities in the range of 1 to 3 amps will be able to switch normal home appliances and computer equipment.
  • micro-relays built either into appliances themselves or incorporated in wall sockets could allow all electrical devices (e.g., lights, stereo equipment, etc.) to be controlled by a central computer. If the life-time of micro-relays can be extended to be significantly longer than present day relays, they potentially could be used in switching power supplies that could be 99%+ efficient. Such supplies presently use transistors or MOSFETs and the resistances and costs of such solid state devices are one of the limiting factors on the performance of such power supplies. If micro-relays which are capable of switching 20 to 30 amps are designed, applications in products that require the control of high power can be targeted.
  • the invention can be used in a line of micro-relays whose current carrying capability ranges from microamps to tens of amps and which have a potential application in almost every single electrical device being produced today.
  • the micro-relay By forming contacts on top of the cantilever beam 6 and defining the electrical contacts 8 to overhang a portion of the cantilever beam 6, the micro-relay can be used in a "normally closed" mode, where application of current to the coil 3 is necessary to open the circuit by pulling the cantilever beam 6 away from the overlying electrical contacts 8. Also, while the preferred embodiment uses explicitly defined magnetic circuit return paths, partial magnetic circuit return paths may be used as well. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiment, but only by the scope of the appended claims.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Micromachines (AREA)

Abstract

L'invention concerne un relais micro-électromécanique ('micro-relais') conçu pour permettre une miniaturisation et un perfectionnement des relais électromécaniques actuels. Le procédé de fabrication par micro-usinage du micro-relais de l'invention, se fonde sur une technologie utilisée à l'origine par des fabriquants de circuits intégrés (CI). Plus simplement, le procédé préféré selon l'invention comprend trois étapes, toutes exécutées grâce à des techniques de micro-usinage. D'abord, on applique sur un substrat une couche de matière magnétique à laquelle on donne une forme voulue. Ensuite, on crée une bobine électromagnétique (3) à côté de ladite matière. Enfin, on applique une deuxième couche de matière électromagnétique très efficace à côté des deux premières couches, de manière à créer un circuit magnétique, et à former une partie en une structure pouvant être déviée telle qu'une poutre en porte-à-faux (4A). La structure pouvant être déviée (4A, 4B) comprend au moins une partie qui est suspendue au-dessus ou à côté d'au moins un contact électrique. Pendant le fonctionnement, le courant passe dans la bobine (3), ce qui provoque la déviation de la structure pouvant être déviée (4A, 4B), et l'établissement ou la rupture du contact avec les contacts électriques. L'invention comprend un dispositif unique de retenue non alimenté. En intégrant un condensateur excité par énergie électrostatique dans le micro-relais, on peut générer une force électrostatique entre la poutre en porte-à-faux et le substrat (1) du micro-relais qui est assez grande pour retenir le relais en position 'marche'. Pour mettre le relais en position 'arrêt', il suffit de supprimer la tension.
EP97906500A 1997-02-04 1997-02-04 Relais micro-electromecaniques Withdrawn EP0968530A4 (fr)

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PCT/US1997/001885 WO1998034269A1 (fr) 1997-02-04 1997-02-04 Relais micro-electromecaniques

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JP2004533710A (ja) 2001-01-18 2004-11-04 アリゾナ ステイト ユニバーシティ 永久磁石のアライメント要件が緩和されたマイクロ磁気ラッチスイッチ
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WO1998034269A1 (fr) 1998-08-06

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