EP1706883A1

EP1706883A1 - Electronic apparatus with a microelectromechanical switch made od a piezoelectric material

Info

Publication number: EP1706883A1
Application number: EP04806609A
Authority: EP
Inventors: Heiko Pelzer; Peter G. Steeneken; Astrid Lewalter
Original assignee: Philips Intellectual Property and Standards GmbH; Koninklijke Philips Electronics NV
Current assignee: NXP BV
Priority date: 2003-12-22
Filing date: 2004-12-21
Publication date: 2006-10-04
Also published as: WO2005064634A1; US20090211884A1; US7952259B2; CN1898762A; JP2007522609A

Abstract

An electronic apparatus contains a micro-electromechanical switch (MEMS) which comprises a piezoelectric element with a piezoelectric layer (12) between a first and a second electrode layers (11, 13), at least one of the electrode layers being structured into separate electrodes (41,42,43;51,52,53) that can be independently controlled.

Description

ELECTRONIC DEVICE WITH A MICRO-ELECTROMECHANICAL SWITCH MADE OF PIEZOELECTRIC MATERIAL

The invention relates to an electronic device with a microelectromechanical switch, comprising: a piezoelectric element with a piezoelectric layer located between a first and second electrode layer; a first and a second MEMS electrode, which first MEMS electrode is on a surface of the piezoelectric element, and which second MEMS electrode is on the surface of a substrate, so that the first MEMS electrode is applied to the piezoelectric element by an actuation voltage and / or moved to or away from the second MEMS electrode.

Such a device is known from the literature. Micro-electromechanical switches (MEMS) represent an interesting alternative to semiconductor switches. In particular, the prospect of avoiding the intrinsic capacities of semiconductor switches and at the same time achieving lower volume resistances has put MEMS at the center of a vigorous research and development activity in recent years. The first products are already being used, but due to the relatively high switching voltages they have so far been limited to applications that can make them available. There is particular interest in solutions that operate at voltages below 5 V in that the MEMs would be able to access the entire field of mobile telecommunications. For this reason, research is increasingly being carried out on piezo MEMS, since significantly lower switching voltages are required than is the case with purely electrostatically switched MEMS. Figure 1 shows a schematic diagram of a one-sided clamped and a two-sided clamped plate made of piezoceramic, the heart of a piezo MEMS. The basic principle is the same in both cases. Electrode layers 11, 13 are attached to the top and bottom of the piezoceramic 12, which, when voltage is applied, ensure that the piezoceramic contracts or contracts. The piezoceramic 12 forms the piezoelectric element with the electrode layers 11, 13. This is with one Substrate connected over one or more supports, to which the element 10 is clamped on one side 30, or on two sides 30, 31. The d31 piezocoefficient is used in the configuration shown, ie the piezoceramic 12 is polarized along the surface normal of the electrodes in the + z direction. The bending of the piezoceramic is now generated by a gradient in the stiffness. Accordingly, the electrodes 11, 13 on the top and bottom can consist of the same metals, but then they must have different layer thicknesses. Another possibility is to use different electrode materials with different stiffnesses. A combination of both principles is also possible. Figure 2 shows both switches when one between the top and bottom

Voltage is applied. The switch clamped on one side has the advantage that even a low voltage is sufficient to switch (large deflection at low voltage). The double-sided switch, on the other hand, promises greater mechanical stability, but requires a significantly higher voltage in order to achieve the same deflection as the single-sided switch. However, a closer look at the switch clamped on both sides shows that the bending shape is very unfavorable when the voltage is applied. As FIG. 3 shows, this switch would only be closed at the edges, which would result in a large impedance. In this configuration, the switch clamped on both sides, despite its mechanical advantages, is not an alternative to the switch clamped on one side.

It is therefore an object of the present invention to provide a device of the type mentioned in the opening paragraph which results in a MEMS switch with low switching voltages and nevertheless good mechanical stability. This goal has been achieved in that at least one of the electrode layers is structured into electrodes, defining a dislocation area in the piezoelectric element, in which dislocation area the first MEMS electrode is located and which dislocation area using at least one actuation voltage on the electrodes in relation to the rest of the piezo element is highly displaceable from and / or to the substrate. In the invention, at least one electrode layer is structured in such a way that only a part of the piezoelectric element is deformable. Therefore, the entire element does not become the substrate using an actuation voltage, and brought especially to the second MEMS electrode, but only a specific part, ie the area of displacement. In particular, the plurality of electrodes enables the entire piezoelectric element not to be deflected. The ceramics are also contracted locally. This is especially done so that the first MEMS electrode has a flat surface. Preferably, the piezoelectric layer has been polarized in a polarization mode during manufacture. For this purpose, the electrodes have been defined in such a way that an actuation voltage can be applied locally, which causes the piezoelectric layer to contract locally. The use of a polarization mode is known per se to the person skilled in the field of piezoceramic. Usually higher actuation voltages and a higher temperature are used. Here the polarization mode differs from the working mode in that the distribution of the actuation voltages across the electrodes is different. This design is of particular interest for double or multiple clamped piezoelectric elements. What is meant by the opposite sides is not the sides usually designated as the top and bottom, but the "edges" or the "spaced ends" of the piezoelectric element, between which the deformable piezoelectric element is located, in a fully open position substantially parallel to the substrate. The piezoelectric element is thus “beam-shaped”. The literature also speaks of being clamped on both sides. It has been shown that such a double-sided clamped piezoelectric element shows good deformation properties in combination with the electrode design, so that at low Voltages (<5V), deformations that are sufficient to bridge switching paths of more than 1 μ. The switching path of 1 μm is characteristic of MEM switches. It is advantageous if the electrodes are arranged symmetrically around the displacement area can be both a capacitive and a galvanic switch. In addition, the switch can be used as a resonator and as a sensor. The piezoelectric layer preferably contains a material with a perovskite structure, such as the materials from the group of the lead zirconate titanates and the like, known to the person skilled in the art as PbZrTi0 ₃ , Pb (X _a Nbb) 0 ₃ -PbTi0 ₃ , with a = 0.33 or 0.5 and b = 1 -a and X = In, Mn, Mg, Y, Er, Zn, Ni, Sc, or other, and with or without doping La, Mn, Fe, Sb, Sr, Ni, W or Combination of them. Such materials can be applied to the substrate in a number of ways, as is known to those skilled in the art. The piezoelectric Element can further comprise a structural layer, but asymmetry in stiffness can also be achieved with different electrode layers. Various possibilities for the production of such MEMS elements are still known per se. In a first embodiment, the second electrode layer has also been divided into several electrodes. There are preferably at least two electrodes per layer, the potential of which can be controlled independently of one another. This embodiment can be used in several configurations. In a first configuration there is a dielectric layer on the second MEMS electrode, that is to say the counter electrode. Both the lower

Center electrode as well as the top center electrode of the piezoelectric element carry the signal. In the closed state, the signal is capacitively coupled into the second MEMS electrode. However, the dielectric is thicker if the upper center electrode carries the signal, but it can also have a low internal resistance due to the layer thickness and the choice of material. In a second configuration, there is no dielectric layer on the second MEMS electrode. If the lower center electrode carries the signal, there is galvanic contact with the second MEMS electrode when closed. This enables a DC switch. If the upper center electrode carries the signal, this is coupled into the lower center electrode via the dielectric even in the open state. If the switch is closed, the signal is short-circuited by contact with the second MEMS electrode (counter electrode). In a third configuration, the switch is designed in such a way that the signal is routed via a “transmission line”. This transmission line can be interrupted, so that the first MEMS electrode attached to the piezoceramic connects the connection galvanically or capacitively via a dielectric However, the transmission line can also run without interruption, in which case the signal is electrically or capacitively short-circuited to the first MEMS electrode on the piezoceramic surface, which can also be covered with a dielectric A distinction is made between two modes of control: a polarization mode and a working mode The polarization mode causes the part of the piezoelectric layer opposite the second MEMS electrode to be polarized in the opposite direction to the parts which are arranged next to it. The MEMS switches can be further differentiated with regard to the structuring of the electrodes attached to the piezoceramic. In one embodiment, the second electrode layer is an uninterrupted metal layer, and the first electrode layer is at least three electrodes, the middle of which is arranged opposite the second MEMS electrode. Different configurations can also be distinguished here: In a first configuration, the signal runs along the continuous lower electrode when the switch is open and is galvanically short-circuited when the switch is closed (FIG. 9A). In a second configuration, the signal runs along the continuous upper electrode when the switch is open and is capacitively short-circuited via the piezoceramic when the switch is closed (FIG. 9B). In a third configuration, the signal runs along the continuous lower electrode when the switch is open and is capacitively short-circuited via the counter electrode covered with a dielectric when the switch is closed (FIG. 9C). In this embodiment there are also different operating modes, ie the polarization mode and the working mode. In a special variant of this embodiment, the electrodes on the structured electrode layer are designed as so-called “interdigital electrodes”. The voltage is now present between the narrow electrodes. The polarization of the piezoceramic is accordingly largely oriented in the + x or -x direction The field created is now parallel to the desired expansion or contraction along the x-axis. In this case, the d33 piezocoefficient is decisive for the deflection that can be achieved. This is more than twice the d31 piezocoefficient, which is due to the fine structuring of the electrodes and the adjustment The potential sequence of the electrodes to the curvature behavior of the switch enables even greater deflection with small switching voltages. The invention also relates to a method for preparing the MEMS switch. This preparation is essentially the application of actuation voltages in polarization mode. This step is a cheap way to bring about local contraction and deflection in the piezoelectric element. The invention further relates to the use of the MEMS switch. In use, also in the working mode, the actuation voltages are applied in such a way that the displacement area moves as desired. The actuation voltages will be Usually attached by a control device (English: Driver and especially Driving Integrated Circuit).

These and other aspects of the invention are explained in detail with the following drawings, in which: FIG. 1 shows schematic diagrams of a piezo-MEM clamped on one or two sides with an electrode on the top and bottom, FIG. 2: a representation of the deflection Both switches show when a voltage is applied to the electrodes, Fig. 3: shows a representation of the deflection of the switch clamped on both sides from different angles. The bending profile shows an unfavorable course, since the contact area is very small due to the strong additional curvature in the middle, Fig. 4: Schematic diagram of switches or switchable capacitors according to a first embodiment of the invention, Fig. 5: Switch clamped on both sides with two electrodes on the top and two electrodes on the bottom, Fig. 6: shows the switch according to the invention in polarization mode (left) or working mode (right). The specified voltages are exemplary. B. the side electrodes have a different voltage than the center electrodes, Fig. 7: shows the bending profile of the switch in the working mode, Fig. 8: shows different connection configurations of the electrodes, Fig. 9: schematic diagram of switches or switchable capacitors of the invention according to one 10 shows a switch according to a second embodiment; 11 shows the control of the switch of the second embodiment; FIG. 12: shows different connection configurations of the structured electrode, FIG. 13 shows a further sketch of the switch in the second embodiment, specifically in the special variant. 14 shows a schematic diagram of the switch according to the particular embodiment, with behavior in the polarization mode (left) and working mode (right). In both cases, a voltage of 5 V is present at the continuous lower electrode, FIG. 15: shows a simulated bending profile of the second embodiment, and Fig. 16: shows a simulated bending profile of the special variant of the second embodiment.

The same reference number in different figures refer to the same features. The figures are just sketchy. The basic structure of the piezoelectric switch or the switchable capacitance is shown in FIG. 4. The MEMS element comprises a piezoelectric element 10 with a first electrode layer 11, a piezoelectric layer 12 and a second electrode layer 13. A first MEMS electrode 42 is located on a surface of the piezoelectric element 10. A second MEMS electrode 21, furthermore also a counter electrode is located on the substrate 20. The first and the second MEMS electrodes 42, 21 are arranged such that they are in contact with one another, either galvanically or capacitively, when the MEMS element is closed. The piezoelectric element 10 is clamped on supports on two sides 30, 31. The supports (not shown) are located on the substrate 20. FIG. 4A shows a switch with a dielectric layer 22 on the second MEMS electrode 21. This leads to a capacitive contact in the closed state. FIG. 4B shows a switch without a dielectric layer on the second MEMS electrode. This leads to a galvanic or capacitive

Contact. If the first MEMS electrode 42 - also called the lower center electrode - is directly connected to the input, the switch is galvanic. However, if the upper center electrode 52 carries the signal, a capacitive switch results, even if the first and the second MEMS electrodes 42, 21 are electrically connected to one another. Figures 4A (I) and 4B (I) show the switches in the open state, the

Figures 4A (II) and 4B (II) show the switches in the closed state. In addition to the lower center electrode 42, further electrodes 41, 43 are arranged in the first electrode layer 11. Further electrodes 51, 53 are also located in the second electrode layer 13. During operation, these 41, 43, 51, 53 are set to a voltage that is different from the voltage of the middle electrode 42, 52. In this way, the piezoceramic 12 can advantageously be bent. It is not excluded that the further electrodes 41, 43; 51, 53 are connected to one another in an electrode layer 11, 13. Further figures show further configurations. In a favorable embodiment of the switch of the invention, a layer is selected as the piezoelectric layer 12 which can be applied wet-chemically using sol-gel technology. A cheap material is, for example, lead-lanthanum zirconate-titanate (PbLao _.02 Zro. ₅₃ Tio _.4 7O3), but many alternatives are known to the person skilled in the art. However, such ferroelectric layers require heat treatment at a higher temperature, generally between 500 and 900 ° C. For this purpose, an electrode layer preferably contains platinum (Pt) which can withstand these temperatures. But there are also other options, such as conductive oxides. For the other electrode layer, one can choose Pt, but also aluminum or another favorable material. Conveniently, adhesive layers and barrier layers are used as far as necessary, as is known to those skilled in the art. A MEMS switch is usually produced with a “sacrificial layer”, which sacrificial layer is subsequently removed by etching. In this case, the Pt layer is closest to the substrate. Alternatively, the piezoelectric element 10 can be produced separately and then in a soldering process or similar process to the substrate 20. In this case, the Pt layer is located on the side of the piezoelectric element 10 facing away from the substrate 20. Figure 5 shows the piezoelectric element 10. This is a movable part of the switch on which the invention is based The second MEMS electrode 21 and the substrate 20 are not shown The construction of the switch according to the invention is characterized in that at least two electrodes are applied to at least one side of the piezoceramic 12, the potentials of which can be controlled independently of one another both electrode layers 1 1.13 in three electr oden 41 -43, 51- 53. In this construction, it is favorable, but not absolutely necessary, that the electrode design in the first electrode layer 11 is completely identical to that of the second electrode layer 13. Insulation, for example of benzocyclobutane (BCB) or similar material with a low dielectric constant, can be arranged between the middle top electrode 52 and the side electrodes 51, 53. If the piezoceramic 12 has the length 4L between the clamps 30, 31 on both sides, the length of the side electrodes 41, 43 is preferably approximately L and the length of the center electrode is approximately 2L in order to deflect the deflection as large as possible

Piezoceramic 12 to achieve with low switching voltage. The insulation gap between the electrodes 41, 42, 43 should be reduced to the technological minimum. The electrode materials are chosen so that the elasticity modules are as different as possible, since this is in combination with the layer thicknesses of the electrodes the curvature of the piezoceramic increases. The lower electrode 11 is preferably made of platinum with an elastic modulus of 165 GPa and, according to the above statements, the upper electrode preferably consists of aluminum, which has an elastic modulus of only about 71 GPa. Specifically, this means that a piezoceramic of 200x50 μm clamped on both sides with a thickness of 0.5 μm achieves a maximum deflection of 0.73 μm at 1 V voltage if the thickness of the platinum sub-electrode is 0.1 μm and the layer thickness the aluminum top electrode is 0.31 μm. This results in an improvement of approx. 70 percent compared to a platinum upper electrode with an optimized layer thickness. This means that longer switching distances can be covered with the same voltage or the same switching paths can be covered with a lower voltage. The former increases the potential power that the

Can apply switches to the counter electrode, so that a better contact is guaranteed, the latter reduces the requirements for the voltage supply and thus increases the area of application of these microswitches. FIG. 6 shows the piezoelectric element 10 again, the control voltages being shown. There are two different modes. The first mode, the polarization mode, is used to set the piezoceramic 12. This preferably takes place immediately after the layers of the piezoelectric element 10 have been produced. Higher voltages and higher temperatures are used. This is still possible, particularly during production, because no package or other layers are then attached that have more limited temperature stability than the piezoelectric element 10. The second mode is the working mode, that is, the mode that is present during use. FIG. 6A shows the application of the control voltages in the polarization mode. The piezoceramic is poled in the z direction, i. H. the electrodes in the first electrode layer 11 are at a potential which is different from the potential of the

Differentiates electrodes in the second electrode layer 13. In this case, the potential on the first electrode layer is 1 10 volts, and on the second electrode layer 5 V. It is noted that here and otherwise the voltage of 5 V only shows one example. FIG. 6B shows the application of the control voltages in the working mode. The voltage sequence alternates here: the lower center electrode 42 and the side electrodes

51, 53 in the second electrode layer 13, is at 5 V. The side electrodes 41, 43 in the first electrode layer 11, and the upper center electrode 52, are at 0 V. The voltage sequences of polarization mode and working mode can also be interchanged, so that the piezoceramic z. B. is polarized on the sides in the + z direction and below the center electrodes in the -z direction. This electrode configuration in connection with the selection of the electrode materials and their layer thicknesses, together with the shading described above, mean that the piezoceramic is curved on the right at both edges and curved on the left in the middle. The curvature behavior of the piezoceramic thus corresponds to that imposed by the boundary conditions (both sides of the switch fixed) and is supported by the choice of the electrode materials. This increases the deflection of the switch at the same voltage. Simulations with the Ansys 6.0 software tool resulted in a deflection of around five times greater for a double-sided clamped piezoceramic with the above-described dimensions 200 μm x 50 μm and a voltage of switching voltage of 1 V, but otherwise optimized electrode materials and layer thicknesses ( Figure 3). Furthermore, the bending profile changes in such a way that a large contact area and thus reliable contacting is ensured (FIG. 7). The configuration described can also be used as an electrode of a controllable capacity. Almost independent of the electrode materials, the deflection of the piezoceramic clamped on both sides with a preferred layer thickness between 0.3 μm and 1 μm (thinner, if technologically possible) reaches its maximum if the ratio of the layer thicknesses of the electrodes is between 1 to 2 and 1 to 6. Figure 8 shows different configurations to drive the split electrodes. The left half of the illustration shows the underside of the ceramic covered with electrodes (hatched), while the top shows on the right side. In the top configuration, the electrodes run across the entire width of the piezoceramic. The electrodes on the underside are mirror images of those on the top so that the forces in the material remain symmetrical. In the middle configuration, the center electrode is only connected from one side. Here, too, the electrodes are arranged mirror-symmetrically on the underside for reasons of symmetry. In the lower arrangement, the top center electrode is connected to a third base. This configuration offers the possibility of transmitting the signal to the center electrode over a wide line with little loss (another base point can also be added for symmetry). Figure 9 and other figures show a second embodiment of the switch of the invention. In this embodiment, only one of the two electrode layers 11, 13 has been sub-distributed in several electrodes. This embodiment also contains the important feature that the activation of the electrodes in the polarization mode (for setting the piezoceramic) and in the working mode (for bending the piezoceramic) can be different; in such a way that not only the applied voltages, but also the distribution of the voltages across the electrodes are different. In the working mode, the continuous electrode, ie the non-structured electrode layer, will carry the signal. Figure 9 shows a basic structure of a piezoelectric switch or the switchable capacitance in the second embodiment of the invention. There are various configurations for this, which are characterized in that the continuous electrode carries the signal: FIG. 9A shows a switch with a continuous, uninterrupted sub-electrode 11. When the switch is open, the signal runs along this sub-electrode 11. When the switch is closed, the signal is galvanically short-circuited or coupled. This lower electrode 11 is therefore also the first MEMS electrode figure. 9B shows a switch with a continuous, uninterrupted upper electrode 13. When the switch is open, the signal runs along the continuous upper electrode and is capacitively short-circuited or coupled in via the piezoceramic when the switch is closed. Figure. 9C shows another switch with a continuous, uninterrupted sub-electrode 11. In this case, there is a dielectric 22 on the second MEMS electrode 21 on the substrate 20. The signal runs along the continuous sub-electrode when the switch is open and becomes capacitive when the switch is closed the second MEMS electrode 21 is short-circuited or coupled. Short-circuited means that the signal is forwarded to ground. If the signal is coupled in, the second MEMS electrode is connected to a signal line. Figure 10 shows the piezoelectric element 10 of this embodiment. The structure of the switch according to the invention is characterized in that at least two electrodes are applied to one side of the piezo ceramic 12, the potentials of which can be controlled independently of one another. The electrode on the other side of the piezoceramic, however, is continuous. If the piezoceramic has a length of 4L, the length of the side electrodes is approx. L and the length of the center electrode is approx. 2L in order to achieve the greatest possible deflection of the piezoceramic with a low switching voltage. The insulation gap between the electrodes should be reduced to the technological minimum. The electrode materials are chosen so that on the one hand the greatest possible deflection is achieved and on the other hand the conductivity of the material used for the continuous metallization is as large as possible. Platinum would preferably be used as a thin structured electrode and a thicker aluminum layer as an unstructured electrode. However, materials with a higher electrical conductivity, such as copper, silver or gold, are also particularly suitable for the unstructured electrode. Almost independent of the electrode materials, the deflection of the piezoceramic clamped on both sides with a preferred layer thickness between 0.3 μm and 1 μm (thinner, if technologically possible) using this electrode configuration reaches its maximum if the ratio of the layer thicknesses of the electrodes is between 1 to 2 and 1 to 10. Figure 1 1 shows in their sketches A and B the applied voltages in the two operating modes. In the polarization mode (FIG. 1A), the piezoceramic is poled in the region of the side electrodes in the + z direction (or vice versa) while it is poled in the region of the center electrode in the z direction (or vice versa), ie the potential of the structured electrodes on z. B. the bottom of the piezoceramic alternates. At least three different electrical potentials are therefore required during production. In contrast, only two different potentials are required in the working mode (FIG. 12 right). In principle, the voltage sequences of polarization mode and work mode can also be interchanged, but this places greater demands on the control electronics in the application. The specified voltages of 5 V and 0 V are only meant as examples. Other voltages can also be selected. In particular, it is said that the voltages in the polarization mode can be higher than those in the working mode. It may well be that the voltages on the electrodes, where the

Ceramic contracting under the voltages is smaller than that on the electrodes where the ceramic expands. In the example, the center electrode 42 is polarized in the opposite direction by applying a negative potential in the polarization mode. It is possible, for example, that the control voltage is at the middle In the working mode, the lower electrode 42 is only 3 V or even 1 V instead of 5 V. It should namely be prevented that the control voltage reverses the polarity of the piezoceramic in the opposite direction of the polarization. FIG. 12 shows different configurations for driving the structured electrode. The contacting of the center electrode 42 can be very narrow

Connections 42A are made because no signal is passed through them. The influence on the deflection of the piezoceramic 12 is thus minimized. In the arrangement of FIG. 12A, the center electrode 42 is connected to a third base 45. A further variant of this embodiment of a double-sided switch, which enables complete metallization of one side of the piezoceramic, is shown in FIG. FIG. 13B shows a detail from FIG. 13A that serves to explain the polarization in the piezoceramic. In comparison to the configuration described above, which uses the d31 piezo coefficient to deflect the switch, the d33 piezo coefficient is used in this case. The advantage is that with the same electrical voltage, the deformation of the piezoceramic 12 along the

The polarization axis is approximately three times larger than that perpendicular to the polarization axis. This advantage is particularly evident when the structured electrode 13 is very finely structured. In this example, this is the upper electrode 13, but can also be the lower electrode layer 11. In particular, a platinum layer is selected as the upper electrode and an aluminum layer as the lower electrode. This fits in a method in which the piezoelectric element is joined to the substrate only after manufacture. The voltage sequence is chosen so that the piezoceramic extends along the sides along the polarization axis. Since the electrical field strength at the top of the piezoceramic between the electrodes with different potentials is at a maximum, it expands the most so that the piezoceramic is curved downward in the side region. This effect is reinforced by the fact that the piezoceramic extends below the top electrodes in the vertical direction and thus contracts in the lateral direction. Because of the greater stiffness of the upper thin Pt electrode than the lower thicker aluminum electrode, this area is also curved downwards. Due to the change in the voltage sequence, the curvature behavior changes in the middle of the piezoceramic. The deflection of the switch can also be optimized in this configuration by the curvature behavior of the piezoceramic on the clamping on both sides is adjusted. This is done by changing the voltage sequence between 1/10 and 4/10 ^preferably] A of the total length of the piezoelectric ceramic and between 6/10 and 9/10 preferably ³ λ the overall length of the piezoelectric ceramic. Accordingly, as shown in FIG. 9, it is necessary for the voltage sequence to be different in the polarization mode and the working mode. It is also possible to swap the two modes. Furthermore, the voltages can also be selected differently depending on the polarization of the piezoceramic in the working mode, so that the voltage on the sides of the piezoceramic between z. B. 5 V and 0 V and in the middle z. B. between 1 V and 0 V (or vice versa) to avoid depolarization effects. The potential of the continuous contact electrode is at a maximum

To obtain deflection at low voltages, choose so that the deformation of the piezoceramic beneath the structured electrodes in conjunction with the stiffness and layer thicknesses of the electrodes supports the deflection of the piezoceramic. If the switch is open without applied voltage, ie the piezoceramic is not deflected, polarization and voltage sequence must be coordinated so that the completely metallized surface of the piezoceramic is curved outwards when the working voltage is applied. Alternatively, the piezoceramic can also be mechanically pretensioned so that the switch closes without working voltage. In this case, the polarization and voltage sequence must be coordinated so that the completely metallized surface of the piezoceramic is curved inwards when the working voltage is applied. FIG. 14 shows a top view of an example of the electrode configuration of the second electrode layer 13, the piezoelectric layer 12 being visible between the structured electrode. The control that is placed on the electrodes is indicated. FIG. 14A shows the control in polarization mode and in FIG. 14B the control in work mode. As with the figures already discussed, these controls are different; not only or according to the magnitude of the voltages, but also according to the distribution over the electrodes. In Figure 14A, the distribution (on a similar average to that shown in Figure 13) is: 0V-5V-0V-5V-0V-5V-0V-5V-0V-5V-0V. In polarization mode, the piezoceramic in particular is poled in the direction in the surface of the piezoelectric element (in the direction of the d33 coefficient). In Figure 14B, the distribution is as in Figure 13: 0V-5V-0V-0V-5V-0V-5V-0V-0V-5V-0V. This is not just an alternating pattern, but a pattern divided into three parts. Forces occur through the transition that go in against the direction of polarization. In this case, this takes place on the sidelines. This pulls the piezoceramic locally, whereby it extends to other places. This alternation of contraction and expansion provides for the movement of the piezoelectric element 10 in the direction towards or away from the second MEMS electrode on the substrate. All configurations of the second embodiment in connection with the

Selection of the electrode materials and their layer thicknesses together with the shading described above cause the curvature behavior of the piezoceramic to change between the edges and the center. Accordingly, the boundary conditions (both sides of the switch fixed) are met. This behavior is supported by the choice of electrode materials. This increases the deflection of the switch at the same voltage. The resulting bending profiles of both configurations can be seen in FIGS. 15 and 16. The configuration described can also be used as an electrode of a controllable capacity. In summary: The invention describes a novel, double-sided, clamped piezo-electromechanical switch (P-MEMS) which, despite its extremely small size, is able due to its special electrode design in connection with the coordinated electronic control, the electrode material and its layer thickness, To overcome switching distances of several μm. At the same time, there is a very flat contact surface, which leads to an improvement in the contact. Compared to switches clamped on one side, a significantly increased mechanical stability is guaranteed. The advantage of piezo-electromechanical switches (P-MEMS) is a reduction in the switching voltage to less than 5 V. This enables the use of such components in mobile applications. In addition to this aspect, it is the greatest

The importance of minimizing losses. The described invention meets all of these requirements. This is detected by the fact that the piezoceramic is controlled locally and in such a way that forces are generated in opposite directions in the piezoceramic using actuation voltages. This leads to a transition in the ceramic between expansion and contraction. This creates different curvatures. In the case of an element clamped on both sides, these are a left curvature and a right curvature. In the case of a multiple clamped element, these are preferably twice a left curve and a right curve, once that Along the X axis, once along the Y axis (both in the surface of the piezoceramic). The forces in opposite directions occur because the piezoceramic has been polarized beforehand in a polarization mode. An actuation voltage that is applied against the (local) polarization direction ensures contraction, an actuation voltage that is applied in the polarization direction ensures expansion. In the first embodiment, there are structured electrodes on both sides of the piezoceramic layer, as a result of which parts of the piezoceramic can be controlled in different ways. In the second embodiment, the resistance of this signal-carrying metal layer of the double-sided clamped switch is drastically reduced by completely metallizing one side of the piezoceramic. At the same time, the special electrode design, despite an extremely small size (e.g. 200 μm x 50 μm), enables switching paths of several micrometers to be overcome with a switching voltage of less than 5 volts and ensures, due to the coordination of the curvature behavior of the piezoceramic to the (double-sided ) Clamping, a large-area and therefore low-loss contact to the counter electrode. In a particularly favorable variant of the second embodiment, the top electrode 13 is structured very finely, that is to say that there are many parallel lines defined therein which can be set to different potentials. The piezoceramic can thus be controlled locally, and not only the piezocoefficient d31 in the direction normal to the piezoelectric element can be used, but also the piezocoefficient d33 in the surface of the piezoelectric element. This results in a much larger expansion. In a further variant, the second MEMS electrode 21 is formed on the substrate 20 as a transmission line. The base area required for this is located in the substrate 20. The first MEMS electrode can have been designed as a relay (ie as bridging two parts of the transmission line). However, the transmission line can also be uninterrupted, the MEMS element with a dielectric on the second MEMS electrode being a capacitor. In both embodiments, the electrode layers 11, 13 are also designed such that the voltage distribution in the polarization mode can be different from that in the working mode. In the polarization mode, the piezoceramic 12 can be adjusted for optimal deflection. In the working mode, the deflection is then achieved using rather low control voltages. In the second In the embodiment, it is advantageous to apply three different potentials in the polarization mode. In working mode of the like, however, two potentials are sufficient. It is also advantageous that the piezoelectric layer 12 can also be used as a coupling surface. Particularly high-frequency signals can be listed in an electrode layer 1, 13 in which they have only a low internal resistance. The signal can then be transmitted further by coupling over the piezoelectric layer. Thanks to the high dielectric coefficient of the piezoceramic - a size ε _r of more than 1000 is quite achievable - the high-frequency signal is not significantly disturbed. It is particularly favorable that the second electrode layer has been made entirely or for the most part in aluminum, and preferably also has a thickness of more than 0.5 μm, particularly approximately 1 μm or more.

Claims

EXPECTATIONS:

Electronic device with a microelectromechanical switch, comprising: a piezoelectric element (10) with a piezoelectric layer (12) located between a first and second electrode layer (1, 13) in each of these electrode layers (11, 13) at least one electrode is arranged (52, 42); a first and a second MEMS electrode (42, 21), which first MEMS electrode (42) is located on a surface of the piezoelectric element (10) and which second MEMS electrode (21) is located on the surface of a substrate (20) so that the first MEMS electrode (42) moves away from and / or towards the second MEMS electrode (21) using an actuation voltage on the piezoelectric element (10), characterized in that at least one of the electrode layers ( 1 1, 13) to electrodes (41 -43; 51-53) is structured defining a displacement area in the piezoelectric element (10), in which displacement area the first MEMS electrode (42) is located and which displacement area using at least one actuation voltage the electrodes (41-43, 51-53) can be displaced from and / or to the substrate (20) in relation to the rest of the piezo element (10).

2. Apparatus according to claim 1, characterized in that the piezoelectric layer (12) has been polarized in a polarization mode during manufacture, and that the electrodes have been defined in such a way that an actuation voltage can be locally applied, which causes a local contraction of the piezoelectric layer (12) causes.

3. Apparatus according to claim 1 or 2, characterized in that the piezoelectric layer (12) is curved on the left on one side of the displacement area, and curved on the right on an opposite side.

4. Apparatus according to claim 1, characterized in that the piezoelectric Element (10) on a first and a second opposite side (30, 31) is connected to mechanical supports.

5. Apparatus according to claim 4, characterized in that the electrodes have been defined symmetrically around the displacement area.

6. Apparatus according to claim 1, characterized in that the first and the second electrode layer each contain at least two electrodes.

7. Electronic device according to claim 1, characterized in that the second

Electrode layer (13) is an uninterrupted metal layer and the first electrode layer

(11) contains at least three electrodes (41, 42, 43), of which the middle one (42) is arranged essentially opposite the second MEMS electrode (21).

8. Electronic device according to claim 7, characterized in that the first

Electrode layer (11) is arranged on the surface that looks like the second MEMS electrode (21).

A method of preparing an electronic device according to claim 1, wherein the piezoelectric element (10) is brought into a polarization mode using actuation voltages on the electrodes, wherein the piezoelectric layer

(12) is polarized such that when suitable actuation voltages are applied in the working mode, the piezoelectric layer (12) is locally expanded and contracted locally.

10. Use of an electronic device according to claim 1, wherein the actuation voltages are applied to the electrodes in such a way that the piezoelectric layer (12) is locally expanded and locally contracted.

11. Use according to claim 10, wherein the actuation voltage which causes a local contraction of the piezoelectric layer is lower than the actuation voltage in the direction of the polarization already introduced.