Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – Polarity-responsive
Reexamination Certificate
2000-02-22
2001-02-20
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
Polarity-responsive
C200S181000, C257S421000
Reexamination Certificate
active
06191671
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a micromechanical electrostatic relay having
a base substrate with a base electrode and with at least one stationary contact,
an armature spring tongue which is linked on one side to a carrier layer connected to the base substrate, has an armature electrode opposite the base electrode, is elastically curved away from the base substrate in the rest state forming a wedge-shaped air gap, and is fitted at its free end with at least one moving contact opposite the stationary contact. In addition, the invention relates to a method for producing such a relay.
2. Description of the Prior Art
Such a micromechanical relay and an appropriate production method have already been disclosed, in principle, in German Patent Document No. 42 05 029 C1. The essential feature in this case is that the armature spring tongue, which is exposed from a substrate, is curved in such a manner that the armature electrode forms a wedge-shaped air gap with the opposite base electrode, which air gap, when a voltage is applied between the two electrodes, produces a rapid attraction movement on the basis of the so-called moving-wedge principle. Refinements of this principle have been disclosed, for example, in German Patent Document No. 44 37 259 C1 and German Patent Document No. 44 37 261 C1.
In the case of all these known relays with a micromechanical construction, a relatively high manufacturing effort is involved since two substrates, namely on the one hand a base substrate with the base electrode and the stationary contact, and on the other hand an armature substrate with the armature spring tongue, the armature electrode and the moving contact, have to be produced separately and connected to one another. In addition to the said main functional elements of the two substrates, further coating and etching processes are involved, for example for insulating layers, leads and the like. Each of the two substrates therefore has to be subjected on its own to all of the complex processes involved before their main functional layers can be connected, facing one another. Since the switching elements are also intended to be protected against environmental influences, an additional covering part is, as a rule, required as a closing element, although there is no need to describe this in any more detail.
In order to simplify production, it would be desirable if it were possible to form all the functional elements of the relay on a substrate from one side. In this case, it is in principle feasible to form a stationary contact element and a spring tongue with a moving contact on one and the same substrate, in which case, for example, the stationary contact and the moving contact can be produced one above the other, and the contact gap can be formed by etching away a so-called sacrificial layer. Such an arrangement has been disclosed in principle in U.S. Pat. No. 4,570,139. However, in the case of the micromechanical switch there, a cavity that is not accurately defined is created underneath the armature spring tongue, and this cavity is not suitable for the formation of an electrostatic drive. In the case of the switch there, provision is therefore made for both the armature spring tongue as well as the stationary contact to be provided with a magnetic layer in each case, and for the switch to be operated via an externally applied magnetic field. Even in the case of the relatively short contact gap which can be achieved between the moving contact and the rigid stationary contact using the sacrificial layer technique, such a magnetic field can be used to produce the required contact force. However, to do this, an additional device is required to produce the magnetic field, for example a coil, and this occupies considerably more space than is available for a micromechanical relay in certain aplications.
SUMMARY OF THE INVENTION
The aim of the present invention is to develop the design of a micromechanical relay of the type mentioned initially such that greater contact forces can be produced even with the electrostatic drive, but in which the functional elements of the relay can be produced on the base substrate by action from one side.
According to the invention, this aim is achieved in that the at least one stationary contact is arranged on a stationary-contact spring tongue which, opposite the armature spring tongue, is linked like this on one side to a carrier layer and is elastically curved away from the base substrate in the rest state, and in that the at least one moving contact is formed at the free end of the armature spring tongue such that it projects beyond said armature spring tongue and overlaps the stationary contact.
Thus, in the case of the invention, in contrast to previous proposals for micromechanical relays and switches, the stationary contact is also no longer rigidly arranged on the base substrate but is seated, like the moving contact, on a curved spring tongue, which allows an additional switching movement to be achieved. The moving contact is seated on the armature spring tongue and overlaps the stationary contact. The prior curvature of the two mutually opposite spring tongues thus allows an adequate over-travel to produce the desired contact force to be achieved from the start of contact-making to the final position of the armature during switching. This effect is achieved even if only a relatively small free space can be created underneath the armature when the armature spring tongue is formed on a base substrate using the sacrificial layer technique, by virtue of which relatively small free space the armature is given only a small, specific over-travel beyond its extended position when attraction to the opposing electrode occurs.
Production is particularly advantageous if both the armature spring tongue and the stationary-contact spring tongue are formed from the same carrier layer, and can thus be produced in one and the same etching process. The spring tongues, whose free ends are opposite one another, can engage in one another in an advantageous manner like teeth, so that the projecting moving contact can be connected, not only at its rear end but at least on one side as well, to the surface of the armature spring tongue. The specific design is dependent on whether the intention is to create a make contact or a bridge contact.
Silicon is the preferred material for the base substrate, in which case the carrier layer for the spring tongues is deposited or bonded on as a silicon layer with the interposition of the respectively required functional and insulating layers, and is etched free in the appropriate processes. Alternatively, the base substrate may be composed of glass or ceramic; these materials are considerably more cost-effective than silicon. However, ceramic requires an additional surface treatment in order to obtain the smooth surface required for the relay structures. The carrier layer which forms the spring tongues may, for example, be composed of deposited polysilicon or polysilicon with recrystallisation, or may be an exposed, doped silicon layer of a bonded-on silicon wafer. This layer can be produced by epitaxy or diffusion in a silicon wafer. Alternatively, a deposited layer of a spring metal, such as nickel, a nickel-iron alloy or nickel with other additives can be used in addition to this silicon structure. Other metals may also be used; the important factor is that the material has good spring characteristics and suffers little fatigue.
An advantageous method for producing a relay according to the invention has the following steps:
a metal carrier layer is applied, with the interposition of an insulating layer and an intermediate space, to a base substrate which is provided with a metal layer as the base electrode,
two spring tongues which are linked on one side and whose free ends are opposite one another are formed in the carrier layer,
at least in places, the spring tongues are provided with a tensile stress layer on their top surface,
a—preferably shorter—spring tongue is provided at its free
Kiesewetter Lothar
Schlaak Helmut
Donovan Lincoln
Nguyen Tuyen T.
Schiff & Hardin & Waite
Siemens Electromechanical Components GmbH & Co. KG
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