FI118401B - High frequency semiconductor resonator - Google Patents

Description

. \ 1 118401

FIELD OF THE INVENTION

The invention relates to micromechanical components and in particular to the implementation of a high frequency resonator.

Background of the Invention

Micro-mechanical systems comprising micromechanical components have rapidly evolved and become more common in recent years. The various microstructures and combinations thereof may be referred to as the generic microsystem technology (MST), which may be defined as, for example, the technique of manufacturing and assembling various miniature mechanical, electronic, optical and other components into a functional assembly. The microsystem typically comprises at least one part having a micrometer class dimension and a component manufactured using micromechanics. Micro-systems can be further subdivided into, for example, microelectromechanical systems (MEMS), mik-15 ro-optoelectromechanical systems (MOEMS) and microfluidics.

Microelectromechanical systems are typically based on thin-film based surface micromechanics. Generally, amorphous or polycrystalline thin films are deposited on a silicon wafer by physical or chemical coating techniques, and then micromechanical structures are formed using etching techniques typically developed to make integrated circuits. Mik- • ·: ·. *. moving films of romechanical components are typically made either single or '. polycrystalline silicon. The film is made movable so that there is typically a thin · layer of insulation (oxide) beneath the film that can be etched off the silicon film • ·· | J through the holes.

! .. * 25 Currently the most widely used surface micromechanics technology is • # * · ♦ · * so-called. SOI micromechanics (Silicon-on-Insulator) in which a thin monocrystalline silicon layer is formed on the substrate's silicon substrate with a very thin insulating oxide layer between them. In this case, the thickness of the silicon substrate may be about 300 to 500 µm, the thickness of the oxide layer is about 1 µm, and the thickness of the upper silicon layer, for example, 5 to 25 µm. Such a silicon wafer structure is typically very well suited as a raw material for a variety of micromechanical components because it has a pre-etched oxide layer as described above with a monocrystalline silicon layer having higher mechanical properties than polycrystalline silicon.

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One of the most important applications of micromechanics in the near future will be wireless communication devices and systems. Particularly in wireless communications, there would be a need for various high quality resonators and accurate bandpass filters capable of operating well at high frequencies as well as various relay type switches. In addition, micromechanical components can significantly reduce the power consumption of portable communication devices.

The prior art micromechanical resonator circuitry has several problems. One problem is the oscillation frequency of the resonators, which is too low-sex. Known micromechanical resonators are typically elongated, narrow semiconductor springs which are subjected to oscillatory motion. Current resonators are at their best capable of oscillating at frequencies of about 300 to 400 MHz, whereas for example wireless communications nowadays typically use frequencies of about 1 to 2 GHz.

A further problem is the large size of such resonators, with a surface area of about 20-100 pm2. For example, in the manufacture of microcircuits used in mobile stations, this is too large an area to optimize the miniaturization of the components.

Another problem is optimizing the efficiency of manufacturing processes. Components are manufactured from silicon wafers as described above, wherein:. component yields are maximized. The yield is usually / good if the resonators are made as separate components, but then different • · ·; · * However, non-standard components must be connected with either so-called. flip-chip micro- *: in a circuit or on a separate substrate together with an integrated circuit. This coupled solution 25 is further connected to other electronics of the device, which makes implementation complicated and uncertain due to multiple connections. In addition, the terminals use pin connectors, which typically raises the required operating voltage too high (up to 20-30 V) to utilize such a MEMS component in wireless communication devices.

30 Brief Description of the Invention

It is therefore an object of the invention to provide a resonator solution and a method for manufacturing a resonator such that the above-mentioned problems. disadvantages can be avoided. The objects of the invention are achieved by a resonator and a method characterized by what is stated in the independent claims.

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Preferred embodiments of the invention are claimed in the dependent claims.

The invention is based on the advantage of forming a micromechanical resonator in the SOI structure, comprising in the same SOI layer a first and a second self-supporting semiconductor film, which are mechanically substantially bonded to the semiconductor element and substantially electrically weak. When ac voltage is applied to the resonator, the semiconductor wells begin to oscillate in opposite phase to each other. According to a preferred embodiment of the invention, the semiconductor wells are of substantially circular shape and at least partially overlapping in area, wherein said at least partially overlapping area forms said connecting semiconductor element.

The electrical properties of the resonator are desirable such that the semiconductor wells are doped semiconductor, the semiconductor layer 15 surrounding the semiconductor films is a semiconductor, and the area overlapping the semiconductor films (the interconnecting semiconductor element) is at least partially semiconducting The resonator of the invention can be fabricated on the same semiconductor layer as the SOI integrated circuits.

An advantage of the resonator according to the invention is that it is characterized by a · ·. . Several gigahertz can be defined as hair, which greatly expands the application areas of the resonator. A further advantage is that the resonator can be • · ·; f integrate into the same semiconductor layer as the SOI microcircuits, thereby improving the efficiency of the manufacturing process and making the connections more reliable with other components. A further advantage is that the resonator can be operated at a very low, preferably integrated circuit operating voltage. A further advantage is that the resonator has a very small surface area, only a few micrometers.

BRIEF DESCRIPTION OF THE DRAWINGS * * "* 30 The invention will now be described in more detail with reference to the preferred embodiments, with reference to the accompanying drawings, in which: Figures 1a and 1b illustrate the structure of a resonator according to the invention; Figures 2a, 2b and 2c show masks used in the resonator actuator of the invention; 118401 Figure 3 shows a simplified resonator according to an embodiment; Figures 4a and 4b show three resonators forming a filter and signal passage through the filter; and Figures 5a, 5b and 5c show different filter structures comprising a resonator according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to Figures 1a and 1b, the structure of a resonator according to the invention will be described below. Fig. 1a is a schematic top view of the resonator and Fig. 1b is a schematic cross-sectional view of the resonator taken along section A-A. Figures 1a and 1b use a common reference numbering. The dimensions of the structures shown in Figures 1a and 1b are shown so that the invention can advantageously be illustrated, so that the dimensions do not correspond to those of the actual resonator.

Preferably, a silicon wafer comprising a substrate 102, an oxide layer 104 and an upper thin layer of silicon, or so-called "silicon", is used as the material for making the resonator 100. The thickness of the substrate 102 is preferably in the order of 50 to 500 µm, the thickness of the oxide layer 104 is about 50 to 200 nm and the thickness of the SOI layer 106 is also approximately 50 to 200 nm, which corresponds substantially to λ. 20 thickness of the top layer used in thin-film transistors of integrated circuits. The material used for the SOI layer is a solid state semiconductor, preferably ♦ · · f l most non-doped, single crystal silicon. The material of the SOI layer may also be * ·: · used, for example, in silicon germanium (SixGey) or other thin-film * * *. * ·: Transistors, making it easier to integrate resonator fabrication into microcircuit fabrication, which will be described in more detail below. Since semiconductors other than silicon may be used as the material of the SOI layer, the term SOI may be extended to mean "Semi-conductor-On-Insulator". The thickness of the oxide layer 104 correlates with the exponential ···. The oxide layer should preferably be kept as thin as possible to minimize the operating voltage. Thus, a low-voltage resonator is preferably provided, the operating voltage of which can be used with the typical operating voltage of the integrated circuit, *. for example, about 3V today, but maybe 1.8V in the future, up to 0.6V.

The substrate 102 is preferably doped with a substantially high conductivity, typically of the order of 0.01 to 0.1 (Qcm) -1, whereby the RC time constant damping the response of the ac voltage applied to the resonator is preferably kept low.

118401 From the top, the top layer of the resonator 100, i.e. the SOI layer 106, can be divided into two regions by electrical properties: an alloyed membrane region 108 consisting of two substantially circular, partially overlapped membrane vibrators 108, 110, and an alloyed membrane region 10 thereof. a highly doped SOI film, while the surrounding region 112 is an unalloyed solid state semiconductor. In addition, a thin base 114 is provided in the overlapping region of the membrane vibrators 108, 110, which is similar to the unalloyed semiconductor region surrounding the region 112. The width of the base may advantageously be about a quarter of the diameter of the membrane vibrators 108, 110. Thus, it can be defined that structurally and electrically, the base 114 forms a semiconductor element which interconnects the membrane oscillators 108, 110 such that the mechanical coupling therebetween is substantially strong and the electrical coupling substantially weak.

The oxide layer 104 below the membrane vibrators 108, 110 is etched away through the holes 116 in the membrane, whereby the etching process results in a substantially circular shape of the membrane vibrators as the etching proceeds uniformly radially from the holes 116. The size of the overlapping area of the membrane vibrators 108,110 can advantageously be adjusted by the distance between the holes 116 and the size of the etched films. The diameter of the holes 116 may be considerably less than 1 µm. The shape of the diaphragm vibrators may also be different from the circular one, but due to the small mechanical losses, the circular shape is * * · \ \ the most advantageous form of the diaphragm vibrator. In the previously formed · * ·:: space 118 under the membrane oscillators, a vacuum may be created or filled with a gas such as dry air, nitrogen or argon. Thus, the membrane vibrators 108, 110 form a mechanically strongly coupled, self-supporting region.

However, due to the unalloyed base 114 comprising the overlapping region of the membrane vibrators, the membrane vibrators 108, 110 are preferably electrically weakly interconnected. Resonator pin, ···. Further, contact metalization 120 may be provided.

The vibration characteristics of the resonator according to the invention are substantially affected by the thickness of the SOI film, on the one hand, and by the combined length of the film vibrators 108, 110, on the other. Because an advantage of the invention is that reso -. ***. the observator can be fabricated on the same semiconductor layer with the other integrated circuit 35, and since the thickness of the SOI membrane affects the operation of the other RF circuit, it is not generally sought to adjust the thickness of the SOI membrane, but is typically a given value for which membrane vibrators 108, 110. the overall length is determined to achieve the desired vibration characteristics.

The operation of the resonator is based on applying an alternating voltage to the resonator 100, i.e., its diaphragm oscillators 108, 110, whereby the diaphragm oscillator-5 whose base 114 filters out the DC component from the alternating voltage but allows the bias voltage to pass through. The magnitudes of the voltages used can typically be in the range of 0.5-100 V for the DC component, for example, the AC component may be 0-1 V. The frequency of the AC voltage used will depend on the desired oscillation frequency of the resonator, typically about 2 GHz. but it can advantageously vary, for example, between 1 and 15 GHz.

The DC voltage biases both diaphragm oscillators 108, 110 so that the electrostatic force it exerts bends both diaphragm oscillators down. The amount of bending can be controlled by the value of the DC voltage so that a higher DC voltage causes greater deflection. Thus, both diaphragm oscillators 108,110 are biased with a DC voltage, in addition to which an AC component is introduced to the second diaphragm oscillator, wherein said diaphragm oscillator is affected by the sum of the voltages according to formula 1: U s DC + AC · sin cat (1.) 20. The electric force acting on the diaphragm oscillator, i.e. the oscillation power, is li / proportional to the sum of the square of the voltage obtained by formula 2: * · · • · • ♦ «♦ | U2 = DC2 + 2DC · AC · sin urt + AC2 · sin2 urt (2.) 4 · · _ ·. *: 25 In this case, the membrane oscillator is affected by a static bias force (DC2), in addition to a variable force having a fundamental frequency component (2DC · AC · sin urt) and a second harmonic component (AC2 · sin2 urt). In this case, the membrane vibrators 108, 110 are mechanically strong. **. 30, coupled to each other like a rocking board, begin to oscillate as a result of the coupling in alternation such that as the first diaphragm 108 moves upward ** / ·: toward the base 114, the second diaphragm 110 is subjected to an oscillation opposing phase and moves downwardly to the base 114. · **. the membrane oscillators together form, in a way, a rocking board which oscillates at a resonance of · * /: 35 at the fundamental frequency and having a support point at the base 114.

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As stated above, the vibration characteristics of the resonator are primarily controlled by the combined length of the diaphragm vibrators 108, 110. The thickness of the SOI layer is typically assumed to be a given value, which is determined by the silicon wafer used, but as such, various silicon wafer types may be used in the manufacture of the resonator, for example the thickness of the SOI layer may vary from 50 to 200 nm. The following describes both computationally and simulatively determined results for the oscillation frequency using different values for the length of the membrane oscillators and the thickness of the SOI layer.

It is known that the spring constant k of a vertical beam oscillator, such as the present membrane oscillator, by its physical properties, is determined by the formula 3: k = 16 · E · w 1 (h / L) 3 (3.) 15 where E is Young's modulus ( in this context 200 GPa), w is the width of the beam, h is the height of the beam and L is the length of the beam. The force F on the beam or, in this case, the diaphragm, which causes the DC voltage-dependent diaphragm vibration deflection, as described above, to be calculated is given by formula: 20 F = 1/2 · V2 · ε0ε · (A / d2) (4.) φ 1 • # where V is the DC voltage, εοε is the permittivity of the (vacuum), A is the surface area of the films: V, and d is the distance between the planes (thickness of the etched oxide layer). Further, the oscillation frequency f of such a spring-mass system can be calculated by the formula 5: • · ·: 1 · 1: f = (1 / 2ht) · (w / w)% (5) where m is the effective mass. Using different values for membrane vibration • length and SOI layer thickness, both these formulas ”2 and simulated by Ansys 5.6 FEM analysis have determined · / ·: the corresponding vibration frequency values shown in Table 1 below.

9 · * «· • ·« · ··· · «» · 2 • M * · 8 118401 h (nm) L (nm) k__m (kg) f (GHz) 100 800 51000 1.624E-23 6.9 200 800 122000 6.790E-24 10.6 100 10000 I 45 1.841E-20 0.008

Table 1.

Table 1 appended shows that when using a silicon wafer having a 100 nm SOI layer to form a pair of 800 nm membrane vibrators according to the invention, very high oscillation frequencies of nearly 7 GHz are achieved. Doubling the film thickness to 200 microns will stiffen the well structure and raise the oscillation frequencies above 10 GHz, but also the voltages required to operate the resonator will increase significantly, whereby the operating voltage may be considerably higher than the operating voltage used in mobile stations. Further, increasing the film thickness may adversely affect the operation of the other RF circuit, so typically no adjustment is made by adjusting the film thickness. On the other hand, if the length L of the membrane oscillator is significantly increased (L = 10 µm, h = 100 nm), the resonator according to the invention can be used at frequencies as low as a few MHz. The size, especially the surface area, of the resonator is then considerably increased. As described above, the surface area of the GHz resonator according to the invention is preferably T | 20 very small, only a few (about 1-5) pm2. Thus, it can be stated that the resonator according to the invention works best when the SOI layer has a thickness of substantially 50-150 nm, especially at 70-100 nm.

Referring now to Figures 2a, 2b and 2c, the construction of the resonator of the invention is illustrated, showing the structure of the masks used in the manufacturing process. The manufacturing process itself comprises the steps known to the person skilled in the art in the manufacture of integrated circuits. The starting point for the manufacturing process is the silicon wafer described above, which; J comprises a substrate 102, an oxide layer 104, and a top SOI layer 106. Initially, the silicon wafer is resisted with a positive resist, i.e., a thin film of resist is formed on its surface by frying the photosensitive solution briefly in an oven. Next, a first mask M1 is placed on the resistor, comprising a pattern of • diaphragm vibrators 108, 110 and contact metals of 118401 g to be attached thereto. The silicon wafer is exposed to UV wavelength, whereby the exposed areas of the resin are polymerized. Next, the mask M1 is removed from the surface of the resin and the resin is developed, i.e. treated with a suitable chemical such as trichlorethylene, whereupon the non-polymerized areas of the resin are dissolved and the pattern of the mask M1 remains. Ion implantation is then performed on the entire SOI surface, but this does not affect the protected silicon layer sites. Next, the resistor is removed as a chemical solvent.

The SOI layer is then subjected to an alloy activation heat treatment whereby the desired impurities are added to the crystal structure by ion-10 implantation. The silicon wafer is then metallised over its entire surface with a contact metal, such as aluminum, for example, having a thickness of 100 nm. Next, the silicon wafer is subjected to a new resistance with positive resistance and normal resist frying is performed. A second mask M2 is placed over the baked resistor, comprising a pattern of contact metals. The silicon wafer is again exposed to ultra-15 violet light, after which the mask M2 is removed from the surface of the resistor and the resistor is developed. In this case, the pattern M2 in the form of a mask, in which the metallization is revealed except in the area of contact metallization, remains in the resistance. The disc is then etched with a suitable metal etcher to remove the contact metal from unwanted areas. The resistor is dissolved and finally the disk is heat treated to minimize contact-20 resistance.

,. The silicon wafer is further subjected to a third resistor, after which a third mask M3 is applied over the resistor, comprising the locations of etching holes 116 to etch the ox-V bond layer under the membrane oscillators 108,110. The silicon wafer is exposed again with mask M3 and mask M3 removed. After that, etching holes V ·! After opening the SOI layer with, for example, a plasma detector, the oxide layer underneath the SOI-: * ·: layer is etched, for example, with HF. Hydrofluoric acid, which is so dilute, is preferably etched that the dimensions of the opening formed in the oxide layer can be controlled by adjusting the etching time. Preferably, the oxide layer is removed only under the membrane vibrators 108, 110 * 9 ... 30, whereby a self-supporting film in the form of the membrane vibrators is formed.

*: * 'The opening formed in the oxide layer can be left vacant or: / ·· filled with a gas such as dry air, nitrogen or argon. The etching holes are closed to *: **, after which the silicon wafer is washed and the resistor is removed.

The manufacturing process described above thus comprises a person skilled in the art -! **. 35 steps known per se, but essential in the manufacturing process is kek- ** *! providing a resonator structure according to the invention.

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The resonator according to the invention can in principle also be implemented as one round membrane oscillator, such a solution as shown in Fig. 3. Such a simplified resonator solution according to one embodiment comprises only one circular membrane oscillator 300 made in the same manner as described above 302 through oxide layer etching. Similarly, in the center of the diaphragm vibrator 300 is an unalloyed diaphragm region 304 which electrically separates the halves 306 and 308 of the diaphragm vibrator 300. However, the halves 306 and 308 of the diaphragm oscillator 300 are mechanically strongly coupled to each other and this coupling cannot be adjusted during manufacture. Such a resonator has only one specific frequency and is simpler to manufacture than the resonator shown in Figures 1a and 1b. However, the operation of both resonator solutions is the same so that the halves 306 and 308 of the diaphragm vibrator 300 function in the same manner as the diaphragm sources 15 and 108 of the resonator 100.

The resonator of the invention can be utilized, for example, in high frequency wireless terminals, such as mobile stations. In particular, the resonator can be utilized in signal reception for post-antenna band pass filtering. Further, the resonator can be used for intermediate frequency filtering and phase lock feedback (PLL, Phase Lock .a. Loop). The following describes, by way of example, various embodiments of the bandpass / filter.

The resonator according to the invention acts as a bandpass filter, the frequency of which is determined by the mechanical vibration frequency of the diaphragm. For example, in the simplified resonator of Fig. 3, the si- "2: input signal S1 and the output signal S0 are isolated by an unalloyed half-i1" conductor. If the specific frequency of the resonator is denoted by ωο and the electrical and acoustic losses t0 of the resonator, the energy state of the resonator can be described by a complex variable eo, where the real part corresponds to potential energy and, 30 imaginary part kinetic energy. The instantaneous energy state can be defined by * · 1 in the differential equation 6: • · • 1 «I« · * 1 "1" · deo / dt - i ωοβο - βο / το + Sj (6.) «·· • · * ·« «· 2 • M * · 11 118401 where i is the Imaging Unit and t is the time. If the input signal Si is a sinusoidal signal at frequency thi, equation 7 gives the energy of the resonator 7: 5 eo2 - (SjTo) 2 / [(ca> i - ωο) 2Το2 + 1] (7.)

As can be seen from Equation 7, the energy of the resonator relative to the frequency difference is only quadratic. In other words, the filtering band becomes a parabell graph having a single peak and not having large angle-10 coefficients. Such a filtering band, whose edges are not steep and whose bandwidth is quite wide, is not very useful in most bandpass applications where the exact form of the filtering window (frequency band) is an important criterion. However, the shape of the filter window can be easily influenced by connecting several resonators in series.

1a and 1b have already described how two diaphragm vibrators can be mechanically connected and simultaneously electrically isolated. Fig. 4a shows how similarly three membrane vibrators can be combined into a single filter. The diaphragm oscillators 400, 402 and 404 are mechanically coupled to each other and electrically separated from each other by non-doped semiconductor bases 406 and 408.

. Figure 4b shows a principle view of signal propagation through membrane vibrators 400, 402 and 404. The frequency of the first diaphragm vibrator 400 is denoted by • # t [· * and the electrical and acoustic losses of the television The second diaphragm vibrator 402 has a characteristic frequency u> 2 and the losses T2 and the third λ · 25 vibrator 404 have a characteristic frequency ω3 and loss. The intensity of the mechanical coupling between the first and second diaphragm vibrators 400 and 402 is described by the coupling constant Ki and the coupling constant k2 between the second and third diaphragm vibrators 402 and 404.

If the characteristic frequencies of the membrane vibrators are in such a filter, ···. If the structure is substantially the same, the edge of the filter window will steepen considerably. On the other hand, if the specific frequencies differ slightly, the bandwidth of the filtering window becomes wider. It will be obvious to one skilled in the art that the desired ***** filtering window format can be achieved, for example, by utilizing a whiteboard, ···. *** if 35 coupling constants and membrane switching constants are known. In the manufacture of such a filter structure, the values of the coupling constants, i.e. mechanical coupling strength, can be adjusted by adjusting the area of the common area of the film vibrator, which in turn can be adjusted by the distance of etching holes and the size of the etched films. The larger the area of the common area, the stronger the mechanical coupling between the membrane oscillators. Conversely, if there is no common area 5, the connection is poor or non-existent. In turn, the membrane oscillator quality indexes are most reliably determined by measuring values from prototypes.

Figure 4a shows one way of connecting a plurality of membrane vibrators to form a filter structure. Figures 5a, 5b and 5c show exemplary examples of other alternative filter structures. In Fig. 5a, three diaphragm oscillators are arranged in a triangle such that the signal path between the incoming signal S1 and the outgoing signal S0 is illustrated by an arrow. Similarly, in Fig. 5b, four diaphragm vibrators are arranged in a square shape. Fig. 5c is a filter structure similar to Fig. 4a with a fourth diaphragm vibrator attached to the middle diaphragm vibrator acting as a suction circuit. The fourth diaphragm oscillator allows two different filters for the same incoming signal Sj and thus two different output signals S0i and SO2. It will be apparent to one skilled in the art that the filter structures described above are only some examples of how membrane vibrators can be combined to provide the desired filter structure.

. The resonator according to the invention can also be used as a switch *. * / So as to supply only 1 · * alternating voltage (AC · sin wt) to the first diaphragm oscillator, but omitting the DC component. In this case, the alternating: voltage tries to cause the second diaphragm vibrator to oscillate at the frequency of the second harmonic V'i 25 component, but this fails because the resonance *: ** is at the fundamental frequency. The output voltage of the resonator is then substantially zero at optimum. Thus, the switch used as the resonator can be controlled by bias voltage supply.

The resonator structures according to the invention are particularly filter. 30 I can utilize a variety of wireless communication devices, such as * 1 * such as GSM / GPRS and UMTS mobile stations, as well as upcoming V ·! networks such as Bluetooth, WLAN IEEE 802.11, and HIPERLAN (High Perfor- mance Radio Local Area Network). The terminals running on these systems are ···. use frequencies that range from about 900 MHz to 5.8 GHz.

It is obvious to a person skilled in the art that as technology advances, the basic idea of the invention can be implemented in many different ways. The invention and its embodiments are thus not limited to the examples described above, but may vary within the scope of the claims.

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Claims (11)

14 118401 Micromechanical resonator (100), characterized in that it comprises, in the same semiconductor layer (106), a first and a second self-supporting semiconductor film (108, 110) connected mechanically substantially strongly and electrically substantially weakly by the semiconductor element 5 (114), and which semiconductor membranes (108, 110) are arranged to oscillate in opposite phase to each other in response to the ac voltage applied to the resonator. A resonator according to claim 1, characterized in that said semiconductor films (108, 110) are substantially circular in shape and at least partially overlapping in area, wherein said area of at least partially overlapping area forms said semiconductor element (114). A resonator according to claim 2, characterized in that said semiconductor films (108, 110) are doped semiconductor, the semiconductor layer (112) surrounding said semiconductor films is an it-semiconductor, and the area (114) between said semiconductor films is at least overlapping. partially semiconductor such that the electrical connection between the semiconductor: * · *: membranes is substantially weak. • ·:. ·. A resonator according to any one of the preceding claims,! ·! characterized in that the resonator is made of an SOI structure comprising a substrate (102), an insulating oxide layer (104) and an upper semiconductor layer (106), said first and the second semiconductor film is formed. A resonator according to claim 4, characterized in that said top semiconductor layer (106) is non-doped,. single crystal silicon, silicon germanium, or any other semiconductor used in thin film transistors *! ' The resonator according to claim 4 or 5, characterized in that said top semiconductor layer (106) has a thickness of 50 to 200 nm, most preferably 70 to 100 nm. A high frequency filter, characterized in that it comprises a plurality of electrically interconnected micromechanical resonators (400, 402, 5404), the resonators comprising, in the same semiconductor layer, a first and second self-supporting semiconductor membranes connected by a semiconductor element , and which semiconductor membranes are arranged in an oscillating phase opposite to each other in response to the ac voltage applied to the resonator. A method for manufacturing a micromechanical resonator, characterized in that a resonator (100) is provided, comprising first and second self-supporting semiconductor films (108, 110) connected by a semiconductor element (114) with mechanically substantially strong and electrically substantially opaque, to the same semiconductor layer (106) as the SOI integrated circuits. Method according to Claim 8, characterized in that manufacture is started from an SOI structure whose top semiconductor film (SOI layer) is a substantially unalloyed semiconductor. The method according to claim 9, characterized in that the parts comprised in the first and second semiconductor films are alloyed · 1 · 1. from the top semiconductor film (SOI layer). • ·:. ·. 11. A method according to claim 10, characterized in that: · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · Etching the insulating oxide layer of the SOI structure under said semiconductor membranes with hydrogen fluoride acid diluted *** The aperture size can be adjusted with the length of the etching time. · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · m mmm m ·· • m 118401 16