Patent Description:
One of applications of the present invention is atomic-force-microscopy (AFM), which is a subclass of scanning-probe-microscopy (SPM). The purpose of SPM is to obtain a three-dimensional nanoresolution image of the object under study. The specifics of AFM application is the registration and measurement of interatomic forces acting as a function of the distance between the object under study and the AFM sensor.

The mechanical part of a typical AFM sensor comprises of a cantilever-shaped sensitive element, the free-end of which has a tip tapered to nanometer dimensions, while the anchored-end of said cantilever is excited by a coupled electromechanical system. The displacement of the free-end of the cantilever is sensed and recorded by an optical sensor, as disclosed in the patent <CIT>. However, this classic AFM sensor has significant performance limitations due to the relatively low excitation frequency, optical scan delay, and sequential method of scanned image acquisition. To increase the AFM performance, the authors of the document [<NUM>, <NUM>] have proposed to employ several or several tens of parallel AFM channels for image formation. Further research on parallel AFMs has demonstrated several opportunities for AFM sensors based on arrays of chips [<NUM>, <NUM>, <NUM>]. However, these solutions reduced the resolution of AFM and created new performance limitations related to the technical problems of processing large amounts of parallel data.

In recent years, the concept of an AFM sensor with no cantilevers has been dislosed, based on a three-dimensional nanoprinted array of AFM probes [<NUM>], registering displacements using the principle of distributed optical leverage [<NUM>]. This device demonstrated the parallel operation of <NUM> individual sensors operating in a <NUM> aperture. However, the resulting resolution appeared far behind of modern AFM capabilities. Another way to improve AFM performance is to increase the excitation frequency. In order to increase the excitation frequency, it is proposed to integrate capacitive micro-mounted ultrasonic transducers (CMUT) into the AFM sensor cantilever. A cantilever-type element operating at a frequency of <NUM> in air was demonstrated, but only its radiation pressure was measured, without AFM operation [<NUM>]. A few years later, a combined AFM sensor containing a CMUT element with a nanometer-sized tip in the classic AFM probe-type sensor has been developed and disclosed [<NUM>], (<CIT>, <CIT>, Georgia Tech Research Corp). This device (FIRAT) used an electrostatically excited and optically readable CMUT-type or microbridge-type cell with a nanometer-sized tip in the center. This microstructure was integrated into the free-end of the AFM probe of conventional dimensions, and it has exceeded significantly the performance and dynamic sensitivity technical capabilities of known devices. Also, this device made possible to quantify interatomic forces. However, the FIRAT structure was too complex, expensive to manufacture, and the vertical range (along z-axis) of AFM operation remained limited by the vacuum gap size of the CMUT structure. Also, in this sensor, it was impossible to resolve the contradictions between the mass of the stylus (tip) integrated on the CMUT membrane and the need to increase the overall sensitivity and dynamic range of the device along the vertical axis.

One more improvement of the electrostatically excited AFM sensor was disclosed in the US Patent <CIT>. The main objective technical problem of the invention was the limitation of performance due to the previously used principle of external excitation of the AFM cantilever. This invention describes several embodiments of electrostatic excitation that at least partially solve the problem of the vertical axis limitation inherent by electrostatic devices. The actual length of the vertical axis here depends not only on the gap size of the electrostatic device, but also on the length of the cantilever element. However, when attached to the cantilever structure, it practically works only in the resonant mode, since static modes in large z-axis sections are associated with high operating voltages, and the risk of entering the well-known snap-in (collapse) mode. Also, the solutions proposed in this patent rely to the optical reading of the displacement of the sensor, therefore, the probes had to be made of a transparent material, which increased the complexity and cost of the sensor.

Recently, a new type of electrostatic actuators was disclosed, in which electrostatic force causing tensile or compressive stresses in the transverse direction has been used to deform various structures, as disclosed in the <CIT>, by Fraunhofer Gesellschaft zur Förderung der Angewandten Forschung eV [<NUM>]. This invention reveals how transverse stresses are employed to induce bending forces in various microstructures (micro-cantilevers, microbridges, and micromembranes). This invention is a significant step in the field of microelectrostatic devices, enabling to decouple electrostatic gap-related structural limitations from the maximal operating range of the microstructure along the vertical axis.

It should be noted that the discussed technical solutions improving AFM sensors and using electrostatic excitation are related to the design and manufacturing technology of capacitive micromachined ultrasonic transducers (CMUT) disclosed in Stanford university's <CIT>. This transducer comprises membranes of a chosen size and shape, supported at their edges by supports, where many membranes are placed next to each other, the first electrode is the base for fixing the membranes, and the second electrode is a thin layer of a conductor covering the surface of the membranes. The membrane supports form cavities under the membranes and channels between these cavities, so the membrane cells are not hermetic in relation to each other.

However, in the mentioned invention by Fraunhofer Gesellschaft <CIT>, and in many other known designs, AFM sensors or electrostatically excited micro-electromechanical structures of other purposes, having a relatively large displacement travel (greater than <NUM>) did not use deformable elements being fixed around the entire perimeter. Those would be an advantage for achieving larger working frequencies and higher working energies of the AFM sensor, related to higher equivalent stiffness of deformable elements.

Also, the perimetric mounting of the deformable elements inherently provides hermetic properties, therefore, the structures based on such elements are less sensitive to contamination and less damped during operation, for example, when the AFM sensor works in liquids. Also, hermeticity is an essential property of such electrostatic actuator, when employing it in microfluidic control systems.

A further document <CIT> shows an electrostatic transducer comprising a membrane, a plate-shaped element and supporting elements.

This invention discloses a micro-electromechanical actuator, as claimed in claim <NUM>, distinguished by the following special constructional features:.

Such structure being fixed by perimeter, when electrostatically excited, is deformed in the vertical direction in the range of several to tens of micrometers, in a variety of static and dynamic ways. These properties allow to use it for scanning-probe microscopy operating in static and/or dynamic modes. For example, one of the application fields of this actuator is atomic force microscopy (AFM), where an individual such actuator can act as a single AFM sensor, or several such actuators - as a one-dimensional or two-dimensional array of parallel AFM sensors, forming a three-dimensional nanoscale image. Another possible application of this hermetic actuator is a flow controller for microfluidic systems.

The invention also discloses a production technology of this fixed-by-perimeter plate structure with integrated asymmetric capacitive cells, as claimed in claim <NUM>, by employing the principle of wafer bonding.

The micro-electromechanical actuator has advantages by the following technical effects:.

The essential aspects of the invention are explained by the drawings and diagrams. The drawings and diagrams are an integral part of the invention description and provided as a reference to possible implementations or visual explanations of the invention, but should not limit the scope of the invention. The drawings are schematic and principal, while the sizes, proportions and specific implementation options of the objects depicted may differ within the scope of the invention.

Construction and operation of the actuator. The invention comprises an electrostatically excited perimetrically-anchored and hermetically sealed plate structure comprising a plurality of asymmetric electrostatic capacitive cells formed on one of the plate surfaces. During excitation of the actuator, a vertical deflection of the perimeter-fixed plate is created, resulting from the sum of the local torques generated by many non-symmetrical cells. The operation of the basic element of the actuator - the electrostatic-capacitive cell - is illustrated in <FIG>. -<FIG> show the basic structure of a capacitive cell: a) cross-section of the capacitive cell, b) top view of the cell structure after removing the membrane <NUM>. The most important parts of the electrostatic-capacitive cell are the membrane <NUM>, which is mechanically and hermetically anchored along its entire perimeter to the vertical support <NUM> and the anchor support <NUM>, the lower electrode <NUM> and the vacuum gap <NUM>. The upper electrode of the capacitive cell can be combined with the membrane <NUM> (if the membrane is made of an electrically-conductive material) or formed on the surface of the membrane if the membrane is made of a dielectric material. If the membrane <NUM> is made of an electrically-conductive material, it must be electrically isolated from the vertical support <NUM> and the anchor support <NUM> which support the membrane. In <FIG> and <FIG>, the mechanical base <NUM> of a single capacitive cell forms an integral part of the actuator moving base <NUM>, in other words, the actuator's moving base <NUM> comprises integrally connected moving bases <NUM> of multiple capacitive cells. A special feature of this cell design is that the vacuum gap <NUM> has horizontal and vertical segments allowing deformation of the support <NUM> with torque <NUM> (as shown in <FIG>). A cross-section of a capacitive cell with membrane <NUM> attracted by an electrostatic force is shown here. <FIG> shows the A-A position of the cross-section and the top view of the capacitive cell without the membrane, during electrostatic attraction. When the deformation of the vertical support <NUM> occurs, a torque <NUM> is transmitted to the base <NUM> of the cell, which deforms the base <NUM> or another structural element associated with the asymmetric electrostatic cell, as shown in <FIG>. The size and direction of the torque <NUM>, and at the same time, the size of the deformation caused by the base <NUM> or another structural element created by one cell, depends on: the dimensions and proportions of the cell elements, the way how several cells are interconnected, and properties of materials from which the elements of the entire structure are made. These parameters are selected and optimized during the design of the actuator, according to the intended purpose characteristics of the actuator.

The arrangement of non-symmetrical cells in the actuator plane can be: symmetric with respect to the selected symmetry axis or center of symmetry, non-symmetrical, circular, and various other options. The arrangement of cells is chosen during the design of the actuator, is subject to optimization, and depends on the purposive characteristics of the actuator. <FIG> show the case of the AFM sensor, where a symmetrical orientation of the capacitive cells with respect to the central axis of the actuator has been chosen. Cells to the left from the axis of symmetry are oriented so that anchor support <NUM> is oriented to the right, and cells to the right of the axis of symmetry have their anchor support <NUM> oriented to the left. Such an orientation of the cells means that the torques <NUM> created by the cells on the opposite sides of the axis of symmetry will be opposite and will combine in the central part of the actuator's moving base <NUM>, where the AFM tip <NUM> is located. In this way, the maximum deformation of the central part of the moving base <NUM> in the vertical direction occurs.

<FIG> a shows a view of the actuator-based AFM sensor from the side of the AFM tip <NUM>. The stationary base of the device <NUM> is separated from the moving base <NUM> by recesses <NUM> which have breaks in the corners <NUM>". The corner-breaks improve the mechanical stability of the actuator device and are used for electrical connections to the contact pads <NUM> (for connecting the upper electrode) and <NUM> (for connecting the lower electrode) on the stationary base <NUM>. The recess <NUM> (<FIG>) terminates in the membrane of the capacitive cells, ensuring the hermeticity of the perimetrical attachment. The purpose of the recess <NUM> is to create the necessary elasticity around the perimeter of the moving base <NUM>. The design and shape of recess <NUM> can be varied. The design and optimization of the shape of recess <NUM> and its cross-sectional profile is selected/defined during the construction of a specific actuator's device. <FIG> also show a method of assembling the actuator onto the printed circuit board <NUM>. The printed circuit board has a set of conductors <NUM> that are used to electrically and mechanically connect the actuator to the AFM electronics using solder balls <NUM>. Also, the printed circuit board can be equipped with an actuator's deformation optical scanning system <NUM> that measures light reflection from the actuator's top electrode <NUM>. Other methods of reading the AFM signal, such as measuring electrical capacitance can also be used.

<FIG> shows a diagram of the static vertical center point displacement of actuators having various dimensions when the capacitive cells are in the pull-in (collapse) mode. Different curves correspond to different transverse dimensions of the perimeter-anchored actuator's structure. The horizontal axis of the diagram plots the nonlinear parameter ϑ of the capacitive cells, which is linearly related to the collapse voltage. This parameter estimates the the relationship between the critical dimensions of a capacitive cell: membrane thickness h, membrane side length a, and gap g: <MAT>.

The solid line represents the collapse voltage, along the right vertical axis. Displacements are shown for <NUM> thick (here, "thickness" is the thickness of the moving base <NUM>, not taking into account thickness of the spring structures <NUM>) for square-shaped actuators, having side lenght from <NUM> to <NUM> (here, "side" is the side of the moving base <NUM> according to <FIG>). The side length is indicated by numbers crossing the corresponding lines showing the deflections of the central point of the structure. Accordingly, the number of capacitive cells fitting into one row is varied from <NUM> to <NUM> according to the actuator's structure's side length, to cover the range of critical cell dimensions. From the diagram in <FIG>, it is evident that perimeter-anchored structures can be used to achieve relatively large (of several micrometers) static displacements by using relatively low voltages (up to 200V). After proper optimization of the dimensions of the capacitive cells and the moving base <NUM>, it is possible (under adequate conditions) to achieve vertical displacements of the moving base <NUM> of up to <NUM>, which correspond to AFM sensors' usual deflection range in the vertical direction when the AFM sensor operates in static mode. The actuator can also be excited with dynamic modes used in practical AFM applications. Actuator structures with higher equivalent stiffness can be useful in AFM applications where high excitation frequencies and AFM speed are important, while thinner ones applicable where higher static sensitivity and resolution are important.

Applications of the actuator. Single-channel AFM sensor. One possible application of the actuator is shown in <FIG>. The design of a single-channel AFM sensor with an integrated optical scanning system is shown here. AFM tip <NUM> is formed on the outer side of actuator's movable base <NUM>. The movable base <NUM> may be made of an electrically conductive material with a relatively high modulus of elasticity, such as highly-doped monocrystalline silicon or other suitable material. The movable base <NUM> of the actuator is connected through the spring structure <NUM> to the mechanical strength-providing part in the periphery <NUM>, which is named the stationary (immovable) base. Appropriate number of asymmetric electrostatic cells is formed on the inner side (the upper side, in <FIG>) of the movable base <NUM>. Membranes <NUM> of asymmetric electrostatic cells are electrically isolated from the movable base <NUM> and, together with the supporting elements <NUM> and <NUM>, form hermetic vacuum cavities. The lower electrode <NUM> is integrated with movable base <NUM>, which is electrically and mechanically common to all electrostatic cells. The upper electrode <NUM> may be common to all electrostatic cells, or there may be several upper electrodes grouping the electrostatic cells into functional groups. The structure of the capacitive cells used to illustrate the single-channel AFM actuator is completely analogous to the structure shown in detail in <FIG>, and their operation corresponds to the explanation in the "Construction and operation of the actuator" section of the description of the present invention. The lower electrode is electrically connected to the contact pad <NUM>, and the upper electrode (or electrodes) are connected to one or more connection pads <NUM>, which are electrically isolated from the base <NUM>. The actuator is electrically and mechanically connected directly to the printed circuit board <NUM>, which carries and contains the necessary electronic components by using solder balls <NUM>. The carrier printed circuit board <NUM> also has electrical conductors <NUM> used to connect the sensor to the signal processing electronics. The carrier printed circuit board <NUM> is mechanically connected to the electromechanical positioner of the microscope, and electrically to the signal processing electronics. Both of the latter assemblies may be standard AFM assemblies, therefore, not the subject of the present invention. The optical scanning system <NUM> is also mounted onto the conductors of the carrier printed circuit board <NUM> by soldering. It emits light and reads the reflection from the upper surface of the electrostatic cells <NUM>. The intensity of the reflection is modulated by the movement of the movable base <NUM>. The practical transverse dimensions of this integrated AFM sensor (not counting the dimensions of the printed assembly board <NUM>) can reach from one to several millimeters. <FIG> presents more detailed view of the cross-section shown in <FIG>, providing more visible elements of the microstructure: the spring structure <NUM>, the membranes <NUM> of the electrostatic cells, and the vacuum gaps <NUM> of these cells.

<FIG> illustrates the case where all capacitive cells of the AFM sensor are operating simultaneously, and the cross-section shows the symmetrical base deflection. In this case, all the electrostatic cells are subjected to the electrostatic force caused by the electric charge between the upper electrodes and the lower electrodes, and act together to deform the movable base <NUM>, as explained in detail in the previous section of the description of the present invention. Thus the AFM tip <NUM> mounted on the actuator's movable base will move straight down. The practical range of the vertical movement of the tip will depend on the selected dimensions of the structure and the properties of the materials from which the structure is made.

<FIG> shows the vertical cross-section of the AFM sensor in the case of asymmetric deflection. In this case, the right (according to the figure) group of capacitive cells is actuated by electrostatic force. On one side of the base, the torques produced by the group of cells will cause an asymmetric deformation of the moving base, and the tip <NUM> will be rotated to the left, as shown in the figure. The dotted line of the AFM tip <NUM>' indicates a strictly vertical (with no rotation) movement of the AFM sensor tip. <FIG> depicts the case where only a half of the electrostatic cells are active, causing the structure to deform asymmetrically, giving the tip <NUM> additional rotational motion. The ability to provide additional rotary motion to the tip is a unique feature of an embodiment of the present invention that can be employed to create modified scanning modes and achieve higher three-dimensional AFM resolution.

Multi-channel AFM sensor. Another application example is a one-dimensional or two-dimensional AFM sensor comprising an array of integrated actuator structures equivalent to the previously explained one-channel AFM sensor. A cross-section of an AFM sensor array with four tips <NUM> is shown in <FIG>. The number of tips may vary depending on a specific application. The concept shown in <FIG> also applies to the matrix type (two-dimensional) AFM sensor configuration shown in <FIG>. In both the one-dimensional and two-dimensional arrays of AFM sensors, the tip <NUM> of each AFM sensor can be individually electrostatically excited by a number of electrostatic cells <NUM>. The electrostatic cells <NUM> are connected to the moving base <NUM> of the AFM sensors, in the same way, as in the case of the single actuator shown in <FIG>. In <FIG>, the electrostatic cell <NUM> comprises the structural elements shown in <FIG>: the top-electrode <NUM>, the membrane <NUM>, the vacuum gap <NUM>, and the movable base <NUM>. The stationary base <NUM> of the device is equivalent to the corresponding structure shown in <FIG>. The electrostatic cells <NUM> are excited by the upper electrodes <NUM>, which are electrically isolated from the movable base <NUM>, have a reflective surface, and are connected to the external electronics through the contact pads <NUM>. The lower electrode is integrated with the movable base <NUM>, and is connected to the external control electronics through the contact pad <NUM>. The entire actuator is soldered with the solder balls <NUM> to an optically transparent holding plate <NUM>, on which a one-dimensional or two-dimensional array of optical scanning elements <NUM> is installed. A suitable implementation option for the optical scanning system is a number of optical pairs consisting of a light (laser) diode and a photodiode, which corresponds to the number of AFM sensors in the array. Another possible implementation option: a high-speed CMOS image sensor with side-illuminating elements. The supporting plate <NUM> includes a network of conductors <NUM> connecting the elements of the multi-channel AFM sensor to the external control electronics. The practical dimensions of individual AFM sensor elements of the array can match the field-of-view dimensions of a conventional single-channel AFM. For example, the distance between adjacent AFM tips <NUM> may be in the range of <NUM>-<NUM>. In this way, the data obtained by several AFM sensors during the normal scanning process are combined into a high-quality large field of view (in the described example with a 4x4 AFM sensor matrix, the field of view is from 400x400 µm to 800x800 µm, respectively). A larger field-of-view allows expanding the application possibilities of AFM and is improving the data acquisition rate from larger areas under investigation by AFM. In the range of the abovementioned dimensions, the resonant operation mode of the AFM sensor is more efficient. The practical resonant frequency range is from <NUM> to <NUM>.

<FIG> shows another example of application of the invention, in which the multi-channel AFM sensor is implemented on the basis of a two-dimensional array (matrix) of actuators and has a two-dimensional array of AFM tips <NUM>. The device's stationary base <NUM>, as in the case of the one-dimensional array shown in <FIG>, is the common base for all actuators <NUM> of the array. The microstructure of a single actuator <NUM> in the array is equivalent to microstructurs of the actuator elements shown in the other figures.

Microfluidic controller. Another example of the use of the actuator is the control of liquid flows in microfluidic devices. This example is illustrated in <FIG>.

<FIG> illustrates how a perimeter-anchored hermetically sealed array of actuators can be used in a microfluidic device. The figure depicts a longitudinal cross-section of a microfluidic channel. The movable base <NUM> of the actuator, due to the deformations of the membranes of the electrostatic cells integrated on its upper surface (see <FIG>), creates a deflection in the upper wall of the microchannel <NUM>. The microchannel <NUM> is mounted on the base <NUM>. Selecting proper moments of time at which the actuator elements are excited, peristaltic pumping of the non-pressurized liquid is created in the selected direction <NUM>. The actuator's element <NUM> has an appropriate number of electrostatic cells, which is optimized according to the scope of application and the dimensions of the microchannel. The width of the microchannel can be equipped with one or more such actuators, depending on the required microfluidic control characteristics.

<FIG> shows (the top perspective view) a part of the microchannel <NUM> and a peristaltic pump installed in its upper wall, comprising four integrated actuators <NUM>. These pump-actuators are excited in a certain order, so, that by locally and dynamically creating pressure to the non-compressible fluid in the microchannel <NUM>, the chosen direction of the liquid flow <NUM> is created. The dimensions of the actuators <NUM> and number thereof within the width of the microchannel <NUM> are selected according to the intended characteristics of the microflow control.

<FIG> shows the use of a single actuator <NUM> to perform the function of a microfluidic valve. The microfluidic device <NUM> has a branch to the valve and a baffle <NUM> narrowing the microchannel of this branch. Upon electrostatic excitation of the actuator <NUM>, its curvature profile will coincide with the upper profile of the microchannel baffle <NUM>, thus closing the flow of fluid in the branch. The dimensions of the actuators and the number of valves above the narrowing partition <NUM> can be selected various depending on the desired technical characteristics of the device.

Method of fabrication of the actuator. The described embodiments of the actuator can be produced by using CMOS-compatible micromachining processes.

The invention alse-covers the actuator fabrication technology based on wafer bonding and bulk micromachining processes, the essential steps of which are presented in <FIG>.

Fabrication of the actuator device begins with preparation of two silicon wafers as shown in <FIG> shows two prepared wafers: <NUM> - monocrystalline silicon wafer with under-membrane microstructures of capacitive cells <NUM> formed by thermal oxidation and lithography methods; <NUM> - monocrystalline silicon wafer with an insulated silicon layer <NUM> (SOI). The term "under-membrane structures" herein encompases the series of structural elements shown in <FIG> (see <FIG>): the anchoring support <NUM>, the lower electrode <NUM>, and the vertical support <NUM>. These elements are formed by deep-etching down to the heavily doped monocrystalline silicon wafer <NUM>. Supporting elements for bonding with the SOI wafer <NUM>, i.e. the anchoring support <NUM> and the vertical support <NUM> according to <FIG> are selectively oxidized using a local thermal oxidation process (LOCOS). Thereby, a layer providing electrical insulation is formed, the locations of which are marked by <NUM> (the layer itself is not shown, to keep the drawing simpler). The under-membrane elements can also be etched in the thermally grown silicon oxide layer, thus avoiding the step of selective oxidation of the supporting elements. In this case, the surface of the lower electrode <NUM> must be covered with an electrically conductive material, for example, a layer of doped polycrystalline silicon, before the wafer bonding step. The latter layer must be electrically connected with the wafer <NUM> array.

<FIG> shows bonded wafers thinned to the required thickness. The wafers are thinned using chemical-mechanical polishing method (CMP), providing the high quality surface suitable for thin layer deposition and lithography. The object <NUM> is a protective silicon-nitride mask formed by chemical vapor deposition and lithography methods, prepared after bonding and thinning the wafers.

Then, removing the unmasked portions of the wafer by deep reactive ion etching exposes the electrostatic cell membranes <NUM> as shown in <FIG>. The burried oxide located in the wafer <NUM> between the carrier wafer and the device layer <NUM> acts as an etch stop in the vertical direction during release. The parts of the wafer protected by the mask establish the stationary base <NUM> of the actuator. If necessary (e.g., dictated by the logic of the electrical connections), after the release of the membranes, their outer surface and the remaining silicon array forming the stationary base <NUM> can be coated with a thin film of silicon oxide, thus ensuring electrical isolation. Electrostatic cells are metallized by deposition and lithography, to form a thin metal film that acts as the top electrode and as the contact pads <NUM>. The connection of the top electrode to the contact pads <NUM> is done by angled metal vapor deposition and/or using a deposition mask to produce a thin metal layer that would cover the side walls of the base <NUM>. If the produced actuator will be used in an aggressive and/or electrically conductive environment, this technological step is followed by passivation of the outer side of the device (at the bottom, according to the figure) by plasma enhanced deposition of a thin film of silicon nitride. The inner side of the actuator, which contains the upper electrodes and contact pads, is not required to be passivated, because the construction of the actuator is hermetic, i.e. protected from the environment. After assembly of the actuator with the electronics board and/or microfluidic device, the electrical connections may be additionally protected from the environment.

Claim 1:
An electrostatically excited microelectromechanical actuator comprising at least
- an actuator membrane (<NUM>) with a first electrode (<NUM>),
- a plate-shaped deformable element (<NUM>) with a second electrode (<NUM>), and
- supporting elements (<NUM>, <NUM>) separating the deformable element (<NUM>) and the actuator membrane (<NUM>) with a vacuum gap (<NUM>) and combining them into an electrostatically excited two-layer structure,
wherein the supporting elements (<NUM>, <NUM>) divide this structure into more than one hermetic cells, hermetically separated by closed lines of the supporting elements (<NUM>, <NUM>), where a closed line of the supporting elements (<NUM>, <NUM>) of each cell comprises at least two segments, wherein
o a first segment is an anchor supporting element (<NUM>) not changing due to deformations of the deformable element (<NUM>, <NUM>) and/or the actuator membrane (<NUM>), during electrostatic attraction, and
∘ a second segment is the rest part of the supporting element (<NUM>), which deforms due to the deformations of the actuator membrane (<NUM>) occurring during electrostatic attraction, thereby creating in the cell a local torque (<NUM>), which deforms the deformable element (<NUM>) of the actuator.