WO2013064409A1

WO2013064409A1 - Micromechanical switch

Info

Publication number: WO2013064409A1
Application number: PCT/EP2012/071094
Authority: WO
Inventors: Vadim Lebedev; Volker Cimalla
Original assignee: Fraunhofer Gesellschaft Zur Förderung Der Angew. Forschung E.V.
Priority date: 2011-11-02
Filing date: 2012-10-25
Publication date: 2013-05-10
Also published as: DE102011085566A1

Abstract

The invention relates to a micromechanical switch (1) having a substrate (100) on which at least one first contact element (101) and at least one second contact (102) are arranged, wherein at least one of the contact elements (101, 102) can be moved, with the result that the contact elements (101, 102) can be moved from a contact position to a disconnected position, wherein the contact elements (101, 102) are at a first distance (g) from one another in the contact position and are at a second distance (G) from one another in the disconnected position, wherein the second distance (G) is greater than the first distance (g) and the first distance (g) is approximately 10 nm to approximately 200 nm.

Description

Micromechanical switch

The invention relates to a micromechanical switch with a substrate, on which at least one first contact element and at least one second contact element is arranged, wherein at least one of the contact elements is movable, so that the contact elements can be brought from a contact position into a disconnected position, wherein the contact elements in the Contact position have a first distance from each other and in the disconnected position have a second distance from each other, wherein the second distance is greater than the first distance. Micromechanical switch of

The aforementioned type can instead of field effect or bipolar transistors as a switch with large

Transmission bandwidth can be used.

From G. Piazza, J. Vac. Be. Technol. A 27, 776 (2009) is known a micro-mechanical switch of the type mentioned. In this known switch, at least one contact element is moved piezoelectrically, so that switching times of about 1] can be realized. If high-frequency signals are routed via such a switch, the signal separation in the disconnected position can be more than 25 dB and in the contact position the coupling-in Losses at a signal frequency of 2 GHz be less than 0.5 dB.

Nevertheless, this known switch has the disadvantage that at high switching frequency with several thousand or even several million switching operations per second rapid wear of the contact elements occurs. This leads to a rapid deterioration of the electrical properties of the switch.

Based on this prior art, the object of the invention is therefore to provide a switch with which high-frequency signals with low losses and high switching frequencies can be reliably switched.

The object is achieved by a micromechanical switch according to claim 1.

According to the invention, a micromechanical switch

proposed, which on a substrate with conventional

Manufacturing process of semiconductor technology can be manufactured. These manufacturing methods include, for example, the deposition of thin layers of a metal, an alloy, a semiconductor material or a

Insulator, the deposition and patterning of masks, either in the form of a photoresist or as a hard mask, the etching of predetermined areas, the introduction of dopants or other, not explicitly mentioned here. In this way, a single or a plurality of micromechanical switches can be manufactured on a substrate. In addition, further electronic or micromechanical components may be arranged on the substrate, such as resistors,

Capacitors, transistors or micromechanical sensors. The substrate of the micromechanical according to the invention

Switch may include sapphire or silicon in some embodiments of the invention. The substrate can

be monocrystalline and have a predeterminable crystal direction. In addition to the main constituents, the substrate may contain dopants to a predeterminable lattice contant and / or a predetermined electrical conductivity

adjust. In addition, the substrate can be unavoidable

Contain impurities.

The substrate carries at least a first contact element and at least one second contact element. At least one of the contact elements is movable, either laterally, i. in the plane defined by the substrate surface, or transversely, i. starting from the substrate level upwards and / or downwards. By the movement of the at least one contact element, the relative position of the two contact elements to each other can be influenced so that the two contact elements of a contact position in one

Separation position can be brought. The contact position is defined so that the electrical resistance between the two contact elements or the insertion losses of a high-frequency electrical signal a first,

have lower value. In the disconnected position, the value of the electrical resistance between the two

Contact elements or the value for the insertion loss a second, larger value. Thus, an electrical signal can be transmitted in the contact position of a contact element to the other contact element, wherein the signal transmission is lower in the disconnected position. In some embodiments of the invention, the signal transmission in the disconnected position may be zero or at least nearly zero.

According to the invention, it has now been recognized that adequate signal transmission is possible if the contact elements in the contact position are at a first distance from one another and in the disconnected position have a second distance from each other, wherein the second distance is greater than the first distance. Thus, according to the invention

proposed that the contact elements do not touch directly in the contact position. By this distance or the avoidance of the direct contact, an abrasive wear of the contact elements is avoided, which has led to a decrease in the quality or an increase in the insertion losses in the known switches. Completely surprisingly, electrical signal transmission between the contact elements is possible despite the distance between the contact elements. This signal transmission is based on the field emission or the tunneling of electrons. These are due to the between the contact elements

prevailing electric field by Fowler Nordheim tunnels detached from a contact element and received by the second, connected as an anode contact element. Since the current density depends exponentially on the distance of the contact elements, even a small increase in the second distance from the first distance can lead to a significant signal decrease or to a complete disappearance of the electrical signal flow. Due to the lack of mechanical contact mechanical wear of the contact elements is avoided.

In order to allow an unimpeded flow of current between the contact elements, the switch according to the invention may be incorporated in operation in a vacuum in some embodiments of the invention. In some embodiments of the invention, the pressure between 1Ί0 ^"2 mbar and 1Ί0 ^{" may be 10} mbar. In some embodiments of the invention, the pressure may be between 1Ί0 ^"4 mbar and 1Ί0 ^"8 mbar.

In some embodiments of the invention, at least one of the contact elements contains at least two successive ones

arranged layers, wherein at least one layer contains a piezoelectric material. The piezoelectric Material can change its length when an electric field is applied. By the tight connection of both

Layers it comes to the training of a mechanical one

Stress in the respective contact element, so that the contact element orthogonal to the interface of the two

Layers is deformed. This deformation leads to a change in the distance between the two contact elements, so that the contact elements can be brought by applying an electrical voltage from a contact position to a release position.

In some embodiments of the invention, the piezoelectric material may be selected from AlN, zinc oxide or lead zirconate titanate. On the one hand, these materials can be deposited by known thin-film methods, for example a sputtering technique, and patterned by dry or wet-chemical etching. On the other hand, these ferroelectrics exhibit a sufficiently large piezoelectric effect to allow the required movement of the contact elements.

arranged layers, wherein at least a first layer contains diamond or A1N or at least one metal which is selected from Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, Re, Os, Ir and / or Pt. A layer of diamond or AlN may additionally comprise dopants, for example boron,

Phosphorus or silicon to allow a given conductivity. On the one hand, a layer of the abovementioned semiconductors, metals or alloys has a low electrical resistance so that an electrical signal can be conducted with low losses in the contact element. On the other hand, these materials show a low work function, so that even at low electric field strengths between the two contact elements, a sufficient electrical current density is achieved to the Transmit signal reliably and with low losses. The work function is defined as the difference between the electronic vacuum level and the Fermi energy of the solid of the first layer.

In some embodiments of the invention, the first conductive layer of a diamond, A1N, a metal or an alloy may also serve to apply an electric field to the layer of piezoelectric material disposed above it, as well as to produce a useful signal through the contact element mechanical stress in the contact element, when this conductive layer undergoes a smaller change in length when an electric field is applied than the ferroelectric or piezoelectric layer disposed above.

In some embodiments of the invention, the first distance of the two contact elements may be about 10 nm to about

200 nm. Such a distance is on the one hand

sufficiently low to allow the formation of an electric current by field emission between the two contact elements. On the other hand, this distance is large enough to avoid mechanical wear of the contact elements by continuous contact.

In some embodiments of the invention, the second distance of the two contact elements may be about 100 nm to about 10 μπι. Such a distance leads to a

sufficient attenuation or collapse of the electric current by field emission between two contact elements, so that only a capacitive coupling of the two contact elements remains.

In some embodiments of the invention, at least one of the contact elements may include a piezoelectric bimorph or a piezoelectric unimorph. Accordingly, the contact element contains at least one or at least two piezoelectric layers, which at

Length change induce a mechanical stress to allow the desired deformation, which allows movement from the contact position to the release position.

In order to apply an electric field to the at least one piezoelectric layer, at least one of the contact elements may further comprise at least one electrode of an electrically conductive material, which occupies at least one partial area of the contact element. In another embodiment of the invention, a contact element may also contain two or more electrodes, or the first conductive layer of a diamond, A1N, a

Metal or an alloy has a multilayer structure. As a result, the application of the electric field to the piezoelectric layer completely independent of

Transport of the electrical Nutzsignales along the contact element is made possible.

In some embodiments of the invention, further layers may be incorporated between two conductive layers, for example insulating layers. Such

Insulation layer can be an oxide, a nitrite or a

Contain oxinitrite. Such an insulating layer can improve the signal quality of the useful signal by achieving electrical isolation between the layer carrying the useful signal and the electrical voltage causing the piezoelectric effect.

In some embodiments of the invention, the first contact element may be movable in opposite directions to the second contact element. In this way, even with low mechanical stresses, which is a high operating strength of the contact elements and thus of the micromechanical

Switch allow to achieve a large change in the distance between the two contact elements. The operating Safety and / or the fatigue strength of the switch is thus increased.

In some embodiments of the invention, the

End face of at least one of the contact elements have a cross-section which is smaller than that

Cross section of the adjacent longitudinal section. In this way, a field increase in the space between the two contact elements can be achieved, which causes an increased current density between the two contact elements.

This allows the insertion loss between the two

Contact elements are reduced.

In some embodiments of the invention, at least one of the contact elements may be a magnetic material

contain or consist of. By coupling the

magnetic moment of the contact element to an external magnetic field, the contact element can be moved. Such a magnetic actuation of the contact element can take place alternatively or cumulatively to the movement by means of at least one piezoelectric layer.

In some embodiments of the invention, the substrate may carry at least one electrode with which the

Contact element can be exposed to an electric field. By capacitive coupling, the contact element can be moved. Such a capacitive control of the

Contact element can alternatively or cumulatively be made to move by means of at least one piezoelectric layer.

The invention will be explained in more detail below with reference to embodiments and figures without limiting the general concept of the invention. Showing:

Figure 1 shows the cross section through a micromechanical

Switch according to a first embodiment. FIG. 2 shows the cross section through a micromechanical switch according to a second embodiment.

FIG. 3 shows a three-dimensional representation of the

micromechanical switch according to FIG. 1.

Figure 4 illustrates the operation of the micromechanical

Switch according to the second embodiment.

Figure 5 explains the operation of the micromechanical

Switch according to the first embodiment.

Hereinafter, a first embodiment of the micromechanical switch according to the invention will be explained with reference to Figures 1, 3 and 5. The micromechanical switch 1 is arranged on a substrate 100. The substrate 100 may

For example, silicon, sapphire or gallium arsenide. A single micromechanical switch or a plurality of micromechanical switches can be arranged on the substrate 100. In addition, the substrate 100 can carry further electronic and / or micromechanical components, for example transistors, resistors,

Capacitors or printed conductors, so that on the substrate 100 further functions are realized. These may include, for example, amplifiers, couplers, logic modules or arithmetic units.

The substrate 100 may be provided at least in regions with a dopant to a specifiable value of the electrical conductivity in predeterminable areas

enable .

The surface 140 of the substrate 100 may comprise an electrically insulating layer, for example an oxide, a nitrite or an oxynitrite. This can be deposited on the substrate 100 in a manner known per se, for example by sputtering or annealing in a nitrogen or oxygen-containing atmosphere.

On the substrate 100, a first contact element 101 and a second contact element 102 are arranged. In the illustrated embodiment, each contact element has at least a first layer 111, a second layer 112 and a third layer 113. The first layer 111 serves as a conductive layer for the switching element to

transporting or to be interrupted electrical

Useful signal. The useful signal may in some embodiments of the invention be a high-frequency electrical signal, for example with a frequency between 500 MHz and

20 GHz, preferably between 1 GHz and 10 GHz. The first

Layer 111 may include or consist of a refractory metal or an alloy containing at least one refractory metal. In other embodiments of the invention, the first layer 111 may include diamond. The diamond may further contain a dopant, for example, boron or phosphorus. In yet another embodiment, the first layer 111 may include A1N whose conductivity is modified by a dopant, for example, silicon.

As can be seen from FIG. 3, the first layer 111 may be composed of a plurality of partial layers, for example a first partial layer 1110 and a second partial layer 1111. In this case, the first partial layer 1110 may consist of one metal or an alloy and the second Partial layer 1111 made of a metal, an alloy or a semiconductor material such as diamond or AlN. Between both sublayers one can

Insulation layer may be arranged, for example, an oxide or a nitrite or an oxynitrite, so that the first sub-layer 1110 of the second sub-layer 1111 is electrically isolated. If the first layer 111 has two partial layers, a partial layer for the Signal transmission of the Nutzsignales be used and the second sub-layer for applying an electric field, which is approximately perpendicular to the plane of extension of

Substrate 100 acts.

The second layer 112 may be a piezoelectric or

containing ferroelectric material. In some embodiments of the invention, the second sub-layer 112 may include A1N, zinc oxide or lead zirconate titanate. The second layer 112 may cover the first layer 111 over the entire area or only a partial area. The second layer 112 is adhesively attached to the first layer 111 so that, given a differential expansion of the first layer 111 and the second layer 112, a mechanical stress and, as a result, a deformation of the contact element 101 or 102 occurs.

To expose the second layer 112 to an electric field, a third layer 113 is an electrode

intended. The third layer 113 may cover the second layer 112 over the entire area or only a partial area of the second layer 112 of the contact element 101 or 102. The third layer 113 may also contain a metal, an alloy or a semiconductor material. In this way, the first layer 111 or a partial layer 1111 or 1110 of the first layer 111 and the third layer 113 can be connected to the poles of a voltage source. The first layer 111 and the third layer 113 thus form a plate capacitor in whose electric field the second layer 112 is located. Since the second layer 112 contains a piezoelectric material, this leads to a mechanical stress within the contact element 101 or 102, so that this deformed, as can be seen from Figure 5.

By appropriate polarity of the control voltage on the first contact element 101 and the second contact element 102 can these are moved in opposite directions, so that the first distance g in the second distance G between the end faces 1013 and 1023 of the first contact element 101 and the second

Contact element 102 is increased. In this way, the micromechanical switch can be transferred from the contact position shown in Figure 1 in the direction indicated in Figure 5 separating position. The deformation remains in the

Essentially limited to the cantilevered length L of the contact elements. In order to allow downward movement of the second contact element 102, a recess 120 is formed in the substrate 100 under the micromechanical switch. This can be introduced into the substrate 100 by dry or wet chemical etching. In some embodiments of the invention, the cantilevered length L of the contact elements may be between about μπι and about t μπι.

As FIG. 3 shows, the end face 1013 of the first is

Beveled contact element 101, so that the cross section of the end face 1013 is less than the cross section of the adjacent longitudinal portion 1011 of the first contact element 101. This leads in the contact position of the contact elements to a local increase in electrical

Field strength and thereby the field emission of electrons from the first layer 111, so that a tunneling current over the first distance g between the contact elements 101 and 102 is formed. Upon application of a control voltage to the first and third layers 111 and 113, this distance increases to the second distance G, so that the tunnel current between the end face 1013 of the first contact element 101 and the end face 1023 of the second contact element 102 is at least lower or comes to a standstill. For the purposes of the present invention, this is referred to as the disconnected position of the switch, since the signal voltage of the useful signal applied to the first contact element 101 is either no longer detectable on the second contact element 102 or at least attenuated. FIG. 3 also shows connection contacts 131 and 132 which can be used as input and output contacts of the micromechanical switch. Optional ground connections 133 may be provided on the substrate 100 so that the substrate can be brought to a predeterminable electrical potential.

With reference to Figures 2 and 4, a second embodiment of the invention will be described. The same parts are provided with the same reference numerals, so that only the

significant differences of the embodiments will be described. FIG. 2 again shows the contact position of the micromechanical switch, whereas in FIG

Separation position is shown.

The second embodiment is characterized in that the freely projecting length L of the first contact element 101 is greater than the freely projecting length of the second

Contact element 102. As can be seen from FIG. 4, only the first contact element 101 is designed to be movable. The second contact element 102 remains in contrast in its initial position. Thus, the enlargement of the first is based

Distance g to the second distance G alone on the movement of the first contact element 101. Since the second contact element 102 is immovable, this does not have in all

Embodiments of the invention, a piezoelectric

Contain material and are not supplied with a drive voltage. The structure of the switch according to the invention can therefore be simplified. If the first contact element 101 is lifted off the surface of the substrate 100 exclusively upwards, the recess 120 in the substrate 100 can also be dispensed with in some embodiments of the invention.

Both embodiments of the invention have in common that the micromechanical switch is usually operated in a vacuum in order to control the flow of electric current over the first distance g not to hinder by collisions with gas molecules or even ignite a plasma between the contact elements, which could damage the contact elements. In some embodiments of the invention, the vacuum may be between 1 x 10 ^-4 and 1 x 10 ^-8 mbar.

In the same way as described above for a piezoelectric unimorph, one of the contact elements or both contact elements in other embodiments of the invention may also contain a piezoelectric bimorph. In yet another embodiment of the invention, the contact elements may be electrostatically moved by capacitive coupling to an electrode or an electrode or a pair of electrodes. In this case, a piezoelectric material can be omitted.

Of course, the invention is not limited to the embodiments shown in the figures. The above description is therefore not to be considered as limiting, but as illustrative. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not exclude the presence of further features.

Claims

claims

Micromechanical switch (1) with a substrate

(100), on which at least a first contact element

(101) and at least one second contact element (102) is arranged, wherein at least one of the contact elements (101, 102) is movable, so that the contact elements (101, 102) can be brought from a contact position into a disconnected position, wherein the contact elements (101 , 102) in the contact position have a first distance (g) from one another and in the disconnected position have a second distance (G) from one another, wherein the second distance (G) is greater than the first distance (g)

characterized in that

the first distance (g) is about 10 nm to about 200 nm.

Switch according to claim 1, characterized in that in the contact position a tunnel current and / or a

Field emission current between the first contact element (101) and the second contact element (102) can be formed.

Switch according to one of claims 1 or 2, characterized in that at least one of the contact elements (101, 102) at least two successive arranged

Layers (111, 112), wherein at least one second layer (112) contains a piezoelectric material, which is in particular selected from AIN and / or ZnO and / or PbZr _x Tii_ _x 0 _3rd

Switch according to one of claims 1 to 3, characterized in that at least one of the contact elements (101, 102) at least two successive arranged

Layers (111, 112), wherein at least a first layer (111) contains diamond or AIN or at least one metal selected from Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, Re, Os , Ir and / or Pt.

5. Switch according to claim 4, characterized in that the diamond is doped with boron or phosphorus and / or the AlN is doped with silicon.

6. Switch according to one of claims 1 to 5, characterized

characterized in that at least one of the contact elements (101, 102) contains at least one insulating layer.

7. Switch according to one of claims 1 to 6, characterized

in that at least one of the contact elements (101, 102) contains a piezoelectric bimorph or a piezoelectric unimorph.

8. Switch according to one of claims 1 to 7, characterized

characterized in that at least one of the contact elements (101, 102) further comprises at least one electrode (113) made of an electrically conductive material, which occupies at least a partial surface of the contact element.

9. Switch according to one of claims 1 to 8, characterized

characterized in that the first layer (111) has a

multi-layer structure, in particular a two-layer structure, wherein at least one layer

(1110) contains diamond and / or A1N and at least one layer contains a metal or an alloy.

10. Switch according to one of claims 1 to 9, characterized

characterized in that the first contact element (101) is movable in opposite directions to the second contact element (102).

11. Switch according to one of claims 1 to 10, characterized

characterized in that the end face (1013, 1023) of at least one of the contact elements (101, 102) has a

Have cross-section which is less than that

Cross-section of an adjacent longitudinal section (1011, 1021) of the contact element (101, 102).