EP1335398A1 - Micro-electrical-mechanical switch - Google Patents

Abstract

The device has a base element and a switch element with auxiliary electrodes in the lateral direction. A voltage is applied to electrodes and the auxiliary electrodes to open switch contacts so the electrodes and auxiliary electrodes have first and second potentials, resulting in electrode and auxiliary electrode surface areas with positive and negative charge carriers in the lateral direction and equal charge carriers in the orthogonal direction. The device has a base element and a switch element with auxiliary electrodes (EG,ES) in the lateral direction to which a voltage can be applied. The voltage is applied to electrodes (HG,HS) and the auxiliary electrodes to open switch contacts so the electrodes have a first potential (U1) and the auxiliary electrodes a second potential (U2), resulting in surface areas on the electrodes and auxiliary electrodes with positive and negative charge carriers in the lateral direction and with equal charge carriers in the orthogonal direction. AN Independent claim is also included for the following: a portable terminal with an inventive device.

Description

The invention relates to a microswitch according to the Preamble of claim 1. In particular, relates to Invention a micro switch in micro electromechanical Systems.

As microelectromechanical or micromechanical systems (MEMS) are components that use special Procedures and processes such as that Lithography processes are produced. You allow that Realization of electrical or mechanical Functions in the smallest space in the µm range. So are for example from: Brown, Elliott R .; RF-MEMS switches for Reconfigurable Integrated Circuits; IEEE transaction on Microwave Theory and Techniques; vol.46; No11; Nov98, Microswitch for use in the radio part of Cellular phones known.

Microelectromechanical components consist of several in the vertical direction, superimposed thin Layers of different lateral structures and Material properties. Depending on the desired function the individual layers, for example of conductive or insulating materials or from materials the particular mechanical properties such as Have spring constant. Let through appropriate processes even more complex three-dimensional structures are created. Simplified, a microswitch can be considered essentially three lateral layers are shown, whereby the middle layer at the end of the manufacturing process is removed again. This creates a microswitch that from a basic element as the bottom layer and one flexible switching element as the top layer. The two layers or the elements of the Microswitches are located at a defined distance opposite, the one in between by the distant one Layer is reached. This distance largely corresponds the stroke that the flexible switching element has to overcome in order to a switching contact between the basic element and switching element close. For example, the basic element is a Silicon substrate, there will be an additional one on it conductive layer as a contact surface to which one Voltage can be applied. The switching element can consist of a metallic material, and thus forms itself the contact area to which a voltage is then applied can. This material of the switching element has one Spring constant on and the switching element is with the Basic element at least partially connected. Will now between the contact surfaces that together form the switch contact, a voltage difference is created due to this caused the flexible electrostatic attraction Switching element deflected in the direction of the basic element and the switch contact closed. To be as high as possible To achieve attraction, they show opposite contact surfaces as large as possible on. A insulation can be placed on the contact surfaces additional oxide layer can be applied. Then can at the same time a DC voltage which is an electrostatic Attraction and an AC voltage as too switching signal are present at the same contact surfaces. How already mentioned, the flexible switching element is at least on fixed in one place on its edge. Depending on the type of fixation and the shape of the flexible switching element Microswitch in microelectromechanical systems then usually as a cantilever switch, bridge switch or also called membrane switch.

2a and 2b show the basic structure of a the prior art known microswitch in the Version as a bridge switch in the open and closed positions. The flexible switching element S is in two places Fixed on the base element G so that it is in Open position a defined distance from the basic element having. The flexible switching element has the Spring constant of the selected material and the fixation one counteracting the deflection of the switching element S. Restoring force. On the base element G there is one Contact surface KG together with the switching element S as form the switch contact. Will be sent to the a voltage is applied to both contact surfaces, that will Switching element S due to this electrostatic attraction against the restoring force in Direction of the basic element G moves. Exceeds that applied voltage a certain value, the Switch contact S closed. Will the tension of the Contact surfaces are removed due to the restoring force the switching element S back to its original shape return and the switch contact is opened. adversely with such switches is that it is due to atomic and molecular surface forces when closing the contacts for gluing the surfaces of the switching element and the Contact surface of the basic element can come. If the Surface forces are stronger than the restoring force the switch contact no longer opens. To do that One will avoid sticking together, additionally on the Contact applied dielectric layer proposed. It is also conceivable, by appropriate shape and Choice of material of the switching contact to its restoring force increase. As a result, a higher one to close Tightening force and therefore a higher tension is necessary to to overcome this greater restoring force. Just then, if such microswitches in MEMS devices with less Power supply should not be integrated desirable and not applicable. There is also a higher one Tensions and the resulting greater attraction the risk that the contact when closing by the so-called bouncing of the contact surfaces rather glued.

From US 6,143,997 a microswitch is known, which at low voltages works. The basic element has one Contact surface and several separate electrodes. On the Basic element is still applied several layers, that work as brackets for the switching element. The Switching element is guided through these brackets and is in a stroke range, which is determined by the brackets, free movable. Another layer is on top of the basic element opposite side of the brackets additional Counter electrodes applied. The fact that the switching element is movable, i.e. is not firmly connected, stands for No mechanical restoring force opens the switch contact to disposal. Rather, here is a first to open Voltage potential to the counter electrodes and a second Voltage potential applied to the switching element and thus an attractive force between the counter electrodes and the Switching element causes. To close the switching contact a first voltage potential to the electrodes of the Basic element and a second voltage potential to the Switching element created, in addition, the Gravitational force with a suitable position of the microswitch be exploited. Because no mechanical Restoring force is present, acts to open the Switch contact only the attraction that is caused by the Voltage at the counter electrodes is determined and at appropriate position acts against the force of gravity. Due to the lower forces, the danger of The contact surfaces stick together less large. adversely is that with such microswitches with the structures described in microelectromechanical systems additional and more complex layer structures are necessary, which make their manufacturing process more complex and therefore more expensive do.

The present invention is therefore the object to provide a microswitch that corresponds to that from the stand counteracts the known disadvantage of bonding and the simplest possible manufacturing process for the microelectromechanical system guaranteed.

The object is achieved by a Microswitch with the features of claim 1.

The invention is therefore based on the idea of providing a microswitch which consists of a base which is referred to below as the basic element and a movable element which is referred to as the switching element. The switching element has a spring constant and is firmly connected to the base element at least in part of its edge region. As a result, when the movable switching element is deflected, a restoring force is generated which is opposite to the deflection.
Both the basic element and the switching element each have at least two electrodes, hereinafter referred to as the electrode and auxiliary electrode. The electrode of the basic element and that of the switching element lie opposite each other at a defined distance. The auxiliary electrode is provided both in the basic element and in the switching element in the lateral direction at the same distance from the respective electrode. Furthermore, both the base element and the switching element each have a contact surface which together form the switching contact of the microswitch. The distance between the electrodes of the base element and the switching element essentially determines the stroke that the movable switching element needs to close the switching contact. If there is a voltage with a first voltage potential at the electrodes and a second voltage potential at the auxiliary electrodes to open the switching contact, the voltage difference that arises in this way causes an electrical field between the base element and the switching element in the lateral direction between the electrode and the auxiliary electrode. Corresponding to the direction of the electric field, there is an accumulation of negative or positive charge carriers on the surface regions of the electrodes and auxiliary electrodes which are directly opposite each other in the lateral direction. In the orthogonal direction, that is, in the direction of the stroke of the switching element, the electrodes with the same charge carriers lie opposite each other. This means that, for example, an accumulation of positive charge carriers on the surface region of the electrode of the switching element is opposed by an accumulation of positive charge carriers on the surface region of the electrode of the base element. The same applies to the accumulation of negative charge carriers. This results in repulsive forces between the accumulations of the same surface charges on the electrodes with the same voltage potential. Since these repulsive forces act essentially in the same direction as the restoring force of the switching element, they support the restoring force of the switching element just at the time of opening. This means that just at the beginning of the release or separation of the contact surfaces of the switching contact, the repulsive forces initially act in the direction of the restoring force. Because the electrodes or the auxiliary electrodes with the same voltage potential and thus surface charges with the same sign are very close to one another before the switching contact is opened, the repulsive forces are particularly great at this time due to the small distance. Because the repulsive forces act in the direction of the restoring force, they support the opening of the switching contact and thus counteract permanent sticking of the switching contact. It is advantageous that in the microswitch according to the invention, additional mechanical measures, such as the increase in the spring constant known from the prior art, can be dispensed with. In addition, it is possible to dispense with the application of additional complex structures, such as the clips and counter electrodes known from the prior art, and additional, complex process steps can thus be avoided.

Further advantageous designs and preferred Developments of the switch according to the invention are the See subclaims.

Fig.1a: Schematische Darstellung einer ersten Ausführungsform eines Mikroschalter gemäß der Erfindung;

Fig.1b: Querschnitt durch den Mikroschalter nach Fig.1a;

Fig.1c: Querschnitt durch eine weitere Ausführungsform eines Mikroschalter gemäß der Erfindung;

Fig.1d: Schematische Darstellung der Ladungsverteilung an den Elektroden des Mikroschalters;

Fig.2a: bekannter Membranschalter in Offenstellung;

Fig.2b: bekannter Membranschalter in Schließstellung.

The invention will now be explained in more detail with reference to the following figures.
It shows:

1a: Schematic representation of a first embodiment of a microswitch according to the invention;

Fig.1b: cross section through the microswitch according to Fig.1a;

1c: cross section through a further embodiment of a microswitch according to the invention;

Fig.1d: Schematic representation of the charge distribution on the electrodes of the microswitch;

Fig.2a: known membrane switch in the open position;

Fig.2b: known membrane switch in the closed position.

1a and 1b schematically show the structure of a first one Embodiment of a microswitch according to the invention. The Basic element G, usually produced as a base layer, has a recess in which the contact surface KG as well as the electrode EG and auxiliary electrode HG. The Contact area KG and the two electrodes EG and HG can, as shown in Fig.1b, as additional Layers on the surface of the depression of the basic element G applied or in the, the basic element G forming layer can be integrated. The latter arrangement requires more complex lateral structures, but none additional layers in the vertical direction. In a another layer, the switching element S is then formed that there is a bridge over the recess of the base element G tense and firmly attached to the two edge areas of the bridge the basic element is connected. On the bottom, that is on the side facing the base element G, the Switching element S is the contact surface KS and the Electrode ES and the auxiliary electrode HS. Here, too Electrodes ES and HS, as shown in Fig. 1b, as additional layer may be applied to the switching element S. or also in the layer forming the switching element S. be integrated. The electrodes EG and ES as well as the Auxiliary electrodes HG and HS can be made using suitable feeders be connected to a voltage source, not shown. The Contact areas KG and KS can be made using suitable inlets be connected to the signal path to be switched, so that in Closed position of the switch contact, that is when the touch both contact surfaces KG and KG, the signal path closed is. Will now between the electrodes EG and ES a voltage is created due to the Voltage difference between the electrodes EG and ES electrostatic field that creates an attractive force. The Switching element S is thus in the direction of the basic element G, or more precisely in the direction of the electrode EG located in the Depression of the base element G is deflected. This, a deflection generated by the applied voltage acts Resetting force opposed by the material used and determines the type of attachment of the switching element S. is. If the force of attraction is greater than the restoring force the switch contact is closed. Will the tension of the Removed contacts EG and ES, the switching element S due to the restoring force back to its original Return position and thus the switch, or the Switch contact, opened. Now it can, as already mentioned described when closing the switching contact due to Adhesion or other surface properties for gluing the contact areas KG and KS or others Surface parts of the switching element with the basic element come. The surface force generated by this acts Restoring force and causes the Switch contact can no longer be opened. That is why suggested that in the lateral direction in both Basic element G and the switching element S in each case Distance a next to the electrode EG, ES an auxiliary electrode HG, HS is provided, and these electrodes EG and ES or Auxiliary electrodes HG and HS so with the voltage source are connected that to open the switching contact on the two electrodes EG and ES a first, positive Voltage potential U1 and on the auxiliary electrodes HG and HS a second, negative voltage potential U2 of the voltage is applied. Because of the different voltage potentials between electrode EG, ES and auxiliary electrode HG, HS it comes in lateral direction on the surface areas of the electrodes EG, ES, HG, HS to a collection of surface charges and indeed on the surfaces that are directly in the lateral direction opposite. That means that in the present Example on a surface area of the electrodes EG, ES too an accumulation of positive charge carriers and on one Surface area of the auxiliary electrodes HG, HS to one Accumulation of negative charge carriers comes. As a result of which lie in the orthogonal direction, that is in vertical direction of the microelectromechanical layers, Surface areas opposite, which is a accumulation of Have surface charges with the same sign. This in turn causes repulsive forces between the rectified charge carriers and thus between Electrode ES of the switching element S and the electrode EG of the Basic element G and correspondingly for the auxiliary electrodes HG and HS. The repulsive forces are just at the time of Opening the switch contact S, especially when the Electrodes EG and ES or auxiliary electrodes HG and HS on next are greatest. They work in the same direction like the mechanical restoring force and support it when opening the switch contact. Ideally they are Electrodes EG, ES, HG, HS are designed so that they are as in Fig. 1a are shown schematically as a strip line. These have a width b and a length of 1, whereby the certain surface area of the electrodes EG, ES, HG, HS for caused by the electric field Attractive forces to close the switch sufficiently large should be dimensioned. The stripline also point a thickness d that is much smaller than that Longitudinal dimension 1 is. The strip electrodes EG, ES, HG, HS are on the base element G and the switching element S to each other arranged that they are parallel in their length dimension 1 lie to each other. This leads to an accumulation of Charge carriers on the surface area of the electrodes EG, ES, HG, HS, which by the length dimension 1 and the thickness d is determined. That is, by applying a voltage to the Electrodes EG, ES and auxiliary electrodes HG, HS will look like shown schematically in Fig.1d, on the electrodes EG and ES Accumulate positive charges on the surface, which the the respective auxiliary electrode is closest. Corresponding there will be negative charges on the surface of the Auxiliary electrodes HG and HS accumulate that of the respective Electrode is closest. Because these surfaces in the same distance a from each other, the Charge accumulation also in the vertical direction opposite and an orthogonal system of Surface areas with a collection of same load carriers. The caused by it Repulsive forces in the vertical direction support the Restoring force. Appropriately located between the Electrode EG, ES and the auxiliary electrode HG, HS dielectric material with the dielectric constant εr. This creates a between the electrode and auxiliary electrode generates even greater electrostatic field, resulting in a increased accumulation of surface charges on the Surface areas of the electrodes EG, ES, HG, HS leads. This makes it possible to work in the vertical direction Further increase rejection forces. Ideally, one such arrangement as a lateral structure in a single Realize shift. That means the electrodes EG, ES, HG, HS and the dielectric material essentially form the switching element S.

To close the switch contact at least one of the electrodes the voltage potential between U1 and U2 switchable so that it is as described input due to the different voltage potentials Attraction of electrodes EG, ES, HG, HS between basic element G and switching element S comes. These attractions can still be increased if the voltage potential is also present another electrode EG, ES, HG, HS is switched, see above that then, for example, on the electrode ES and the Auxiliary electrode HS of the switching element S the first Voltage potential U1 and at the electrode EG and the Auxiliary electrode HG of the base element G the second Voltage potential U1 is present or vice versa.

As shown in Fig.1a, the contact surfaces KS, KG of the switching element S and the base element G between the electrodes EG, ES and auxiliary electrodes HG, HS arranged his. The contact areas KS and KG are only located directly in a section that forms the switch contact across from. The embodiment of the shown here Contact surfaces KS, KG of a microswitch are suitable especially for applications where switching RF signals are, such as in the radio part of portable Terminals. With RF signals, it is advantageous that the Signal paths, here the contact areas, as little as possible overlap to avoid capacitive coupling. moreover can be microswitches according to the present invention use advantageously here, because in such portable devices Power supply is low, so the ones used Components have the lowest possible supply voltages should.

1c schematically shows a further embodiment a microswitch according to the invention. As from Fig.1c can be seen, the contact surfaces KS, KG des Switching element S and the basic element G also between two Pairs of one electrode and auxiliary electrode each be arranged. That is, the basic element G and the Switching element S each have a further electrode EG1 and ES1 and another auxiliary electrode HG1 and HS1. This are again arranged parallel to each other at a distance a. The contact areas KG and KS are located between the first pair of electrode EG, ES and auxiliary electrode HG, HS and the second pair from the further electrode EG1, ES1 and Auxiliary electrode HG1, HS1. Here too are the Contact areas KG and KS only in one area, which forms the switch contact. Such an arrangement is especially preferable if the contact surfaces are a Have a width that does not allow this between one Arrange electrode and auxiliary electrode, that is if for example, the width of the contact area is larger than that Distance a between the electrode and auxiliary electrode is. To the same effect as in the first embodiment achieve, that is the generation of repulsive forces to Opening the contact is at least always a pair of Electrode and auxiliary electrode necessary.

The present invention is not limited to that described embodiments. Rather, it is independent on the type and shape of the suspension of the switching element. The means that for example with cantilever or membrane switches the concept of the invention applicable accordingly is. The same applies to the design of the contact areas. For example, it is conceivable that two contact surfaces the basic element are provided by a Contact surface of the switching element are bridged. The same applies to the shape of the electrodes, auxiliary electrodes or Contact surfaces. So it is conceivable that, for example are meandering or spiral. Essential in all embodiments, that is according to the inventive concept of arrangement and design and Wiring of the electrodes and auxiliary electrodes when opening of the switching contact by generating Repulsive forces support the restoring force is caused to reduce the risk of sticking.

The microswitches shown in Figures 1a-d are kept very abstract around only the essence of the invention to show. Depending on the application or the technology used the person skilled in the art will find a wide variety of embodiments received a wide variety of structures without Deviate the basic principle of the invention.

Claims (10)

Microswitch consisting of a base element (G) with a contact surface (KG) and an electrode (EG), and a switching element (S) with a contact surface (KS) and an electrode (ES) which lies opposite the electrode (EG) of the basic element (G) at a distance (g), wherein the switching element (S) has a spring constant and is firmly connected to the base element (G) at least in part of its edge region, and wherein the contact surfaces (KG, KS) form a switching contact and the switching contact can be closed by means of a voltage applied to the electrodes (EG, ES) against a restoring force caused by the spring constant characterized in that the base element (G) and the switching element (S) in the lateral direction, at a distance (a) from the electrode (EG, ES), have an auxiliary electrode (HG, HS) to which a voltage can be applied, and to open the switching contact on the electrodes (EG, ES) and auxiliary electrodes (HG, HS) the voltage can be applied so that the electrodes (EG, ES) a first voltage potential (U1) and the auxiliary electrodes (HG, HS) a second voltage potential (U2), which cause an accumulation of positive or negative charge carriers on surface areas of the electrodes (EG, ES) and auxiliary electrodes (HG, HS) in such a way that surface areas with positive and negative charge carriers are located in the lateral direction and surface areas in the orthogonal direction with the same load carriers. Microswitch according to claim 1,
characterized in that
to close the switching contact one of the electrodes (EG, ES) or auxiliary electrodes (HG, HS) can be switched between the first (U1) and the second (U2) voltage potential. Microswitch according to claim 2,
characterized in that
to close the switching contact, another of the electrodes (EG, ES) or auxiliary electrodes (HG, HS) can be switched between the first (U1) and second (U2) voltage potential, so that on the electrode (ES) and auxiliary electrode (HS) of the switching element (S) the first voltage potential (U1) and the second voltage potential (U2) is applied to the electrode (EG) and auxiliary electrode (HG) of the basic element (G). Microswitch according to claims 1-3,
characterized in that
the electrodes (EG, ES) and auxiliary electrodes (HG, HS) each have a surface area which is determined by their thickness (d) and length (1), the length (1) being greater than the thickness (d), and wherein the base element (G) and the switching element (S) each have the electrode (EG, ES) and the corresponding auxiliary electrode (HG, HS) with this surface area arranged parallel to one another. Microswitch according to claims 1-4,
characterized in that
in the base element (G) and / or the switching element (S) a dielectric material is arranged between the electrode (EG, ES) and that of the auxiliary electrode (HG, HS). Microswitch according to claims 1-5,
characterized in that
the contact area (KG, KS) is arranged between the electrode (EG, ES) and the auxiliary electrode (HG, HS), the contact areas (KG, KS) only lying opposite one another in a partial area which forms the switching contact. Microswitch according to claims 1-5,
characterized in that
the contact surface (KG, KS) is part of the electrode (EG, ES) or auxiliary electrode (HG, HS). Microswitch according to claims 1-5,
characterized in that the base element (G) and the switching element (S) each have a further electrode (EG1, ES1) and a further auxiliary electrode (HG1, HS1), which in turn are arranged parallel to one another at a distance (a), and the contact surface (KG , KS) is arranged between the first pair of electrode (EG, ES) and auxiliary electrode (HG, HS) and the second pair of the further electrode (EG1, ES1) and auxiliary electrode (HG1, HS1), the contact surfaces (KG , KS) are only opposite in a partial area that forms the switch contact. Portable terminal with a microswitch according to one of the Claims 1-8. Portable terminal according to claim 9,
wherein the portable terminal is a cell phone.

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