DE102011119660B4 - Microacoustic device with waveguide layer - Google Patents

Abstract

Microacoustic component with a waveguide (WG) - which has a waveguide layer (WL) which has a first acoustic wave velocity VL and a first cladding layer (M1) directly adjoining the waveguide layer, in which a second acoustic wave velocity VM1 applies - with an electrode (E1) for the excitation of an acoustic wave in the waveguide - in which VL <VM1 applies to the wave speeds - in which the waveguide layer (WL) is a glass that comprises a component with abnormal thermomechanical behavior - in which the waveguide layer (WL) is germanium dioxide, chalcogenide glass or zinc metaphosphate as a component.

Description

The invention relates to a microacoustic component having a waveguide layer and adjacent thereto a cladding layer.

Frequency determining properties of working with acoustic waves components such. B. SAW components (SAW = surface acoustic wave) usually show a dependence on the temperature. For example, the temperature coefficient of the center frequency (TCF) of SAW devices is typically z. B. 40 ppm / K. This is due to the fact that, when the temperature increases, thermal expansion of the substrate generally takes place, which leads to an increase in the electrode spacing in interdigital transducer structures. Since this distance determines the center frequency of the transducer and thus of the SAW device, so does the wavelength, whereby the center frequency is lowered. However, associated with the thermal expansion is also a change in the speed of sound, as change with the temperature and the properties of the piezoelectric material. In addition, most commonly used piezoelectric wafer materials exhibit strong anisotropy and have a crystal axis-dependent temperature response of their properties.

From the US 2007/0018536 A1 Microacoustic components are known which have a multilayer structure for improving the temperature coefficient of the center frequency.

From the DE 11 2007 001 259 T5 Further microacoustic components are known which, in addition to a layer for improving the temperature characteristic, have a frequency adjustment layer.

By doing U.S. Patent 7,589,452 B2 a working with acoustic waves component is proposed, which combines various measures to lower the temperature response (TK compensation) in particular the resonant frequency. The component has electrically conductive component structures on the upper side and a compensation layer on the underside, which is mechanically firmly connected to the substrate in such a way that a mechanical stress arises or builds up when the temperature changes. Above the component structures, a relatively thick SiO ₂ layer is arranged. A disadvantage of this solution is that the required reflectivity of the electrodes is obtained only with heavy electrodes. Even with this combination of temperature-compensating measures, complete TC compensation is not achievable.

Improved waveguiding can be achieved with microacoustic devices having thicker or heavier electrodes, for example metals heavier than aluminum. However, suitable metals have the disadvantage that they increase the temperature coefficient (TCF) of the center frequency and thus increase the total TCF. When producing thick electrodes, a broad distribution of the properties is obtained. In addition, such electrodes show high reflection, are difficult to coat with topcoats, which then tend to include voids (voids formation), and can be difficult to planarize. In the structures known hitherto, the heavy electrode binds the acoustic wave energy to the interface with the piezo material. As a result, there is also a significant proportion of the acoustic energy in these electrodes, which leads to problems in the performance compatibility.

The object of the present invention is to specify a microacoustic component which has a waveguide layer and adjacent thereto a cladding layer which is improved in its temperature coefficient of frequency and / or its waveguide properties.

This object is achieved by a microacoustic component having the features of claim 1. Advantageous embodiments of the invention will become apparent from further claims.

The microacoustic device has a waveguide comprising a waveguide layer having a first acoustic wave velocity VL. Directly adjacent to the waveguide layer, a first cladding layer is arranged, which has a second acoustic wave velocity VM1. For exciting an acoustic wave in the waveguide layer, an electrode is provided. To guide the acoustic wave within the waveguide layer, the following applies for the wave velocity: VL <VM1. The waveguide layer comprises a glass having as a constituent a material exhibiting abnormal thermomechanical behavior.

There are a number of materials with abnormal thermo-mechanical behavior known, but of which so far only crystalline, amorphous or glassy SiO _{2 has found} application in microacoustic devices. Other materials are now proposed which have abnormal thermomechanical properties and which can be used in glassy modification or embedded in a glass which serves as a waveguide layer in a waveguide. These materials can be a micro-acoustic device with partial or even complete Compensation of the temperature-induced frequency shifts obtained.

A waveguide layer with germanium dioxide, chalcogenide glass or zinc metaphosphate as constituent is proposed. These new materials make it possible to model and in particular optimize the waveguide properties of the waveguide layer. A waveguide layer with temperature compensation and improved waveguide properties, regardless of the thermo-mechanical behavior of the waveguide layer, results in a microacoustic device whose temperature coefficient of center frequency is improved because a higher wave fraction propagates within the waveguide in the better waveguide so that its thermomechanical properties affect the acoustic wave more take as a worse waveguide.

Advantageously, the first cladding layer is a piezoelectric layer or a piezoelectric substrate. The piezoelectric layer may be applied to a non-piezoelectric substrate, in particular on a crystalline and in particular on a semiconductor substrate. The piezoelectric substrate is preferably a piezoelectric crystal, or a wafer cut from a piezoelectric monocrystal.

A waveguide layer having an improved compensation effect of the temperature constant of the center frequency includes, for example, germanium dioxide as a main component. A glass based on germanium dioxide has a higher density than the silicon dioxide layers hitherto known for compensation layers and therefore leads to a higher mass load on the cladding layer or on the piezoelectric substrate. A higher mass loading is advantageous for the waveguide properties of the waveguide over a piezoelectric substrate or a piezoelectric layer in that the higher mass loading causes better guiding of the acoustic wave, particularly an acoustic shear wave on the surface of the piezoelectric substrate or the piezoelectric layer and descent prevents the shear wave in the volume of the substrate inside. A waveguide whose waveguide layer generates a higher mass load than known waveguides results in lower losses in wave propagation. In addition, the acoustic wave velocity is reduced in a material with higher mass load. With an unchanged cladding layer, a higher difference in acoustic wave velocity within waveguide and cladding layer leads to improved waveguide properties.

Compared to a waveguide layer made of SiO ₂ , the same waveguide properties can already be realized with a thinner layer of germanium oxide-containing glass. Thinner layers require shorter process times in manufacture and therefore exhibit lower manufacturing variability, particularly with respect to layer thickness uniformity and film thickness control.

With the improved waveguide properties, the use of thinner and lighter electrodes is also possible. This avoids all the problems that were previously encountered with thick and / or heavy electrodes. With the improved waveguide and the ability to make the germanium-containing glass layer thicker, a stronger TC compensation is possible, which is significantly better than the TK compensation achieved so far with SiO ₂ waveguide layers. In one embodiment, the waveguide layer comprises germanium oxide-containing glasses. Germanium dioxide is a good glass former and does not require any additives to form the glassy state. However, it is possible for the waveguide layer to comprise a glass which contains glass formers and / or other customary glass aggregates which in particular determine or modify the flow and melting properties of the glass. Such glass-formers and / or glass aggregates for a germanium-containing glass or other glass whose main constituent comprises a material having a normal thermomechanical behavior are, for example, selected from... (See selection of claim 5).

In one embodiment, the waveguide layer contains as its main constituent a chalcogenide or a zinc metaphosphate. Both materials can be used to obtain a glass which, used as a waveguide layer, generates an increased mass load compared with SiO ₂ . At the same time, chalcogenide glass and zinc metaphosphate glass are materials with abnormal thermomechanical behavior. This means that, used in microacoustic components, they have a positive coefficient of the center frequency and thus cause a compensation of the temperature-induced frequency drift of the microacoustic component.

In a further embodiment of the component, the waveguide is improved in that the waveguide layer is embedded between the first cladding layer and a second cladding layer. For wave velocity VM2 of the second cladding layer, as well as for the wave velocity within the first cladding layer, it is valid that it is higher than the wave velocity VL in the waveguide layer. In such a waveguide delimited on both sides by a cladding layer, an improved waveguide takes place. Opposite a waveguide whose waveguide layer only has an interface to a (first) cladding layer and another air or vacuum interface, this sandwiched and three-layered waveguide has less sensitivity to external influences on the waveguide. Mechanical action on the waveguide layer itself may result in altered waveguiding or leakage of the waveguide. This is prevented by two cladding layers which bound the waveguide layer on both sides.

With an improved waveguide, it is possible to use thinner and thus lighter electrodes in the microacoustic device. These electrodes are usually arranged in direct contact with the piezoelectric substrate or with the piezoelectric layer and are thus located between the first cladding layer and the waveguide layer.

A device with a three-layer waveguide view according to the invention makes it possible to arrange an unlimited number of further layers on the waveguide without impairing the properties of the waveguide. In particular, it is possible to arrange another waveguide over the first waveguide and use this to construct another filter. This results in a stacked filter whose two individual filters are each temperature-compensated.

For the second cladding layer, the selection of suitable materials is greater than for the first cladding layer, so that any other dielectrics can be used which further improve the properties of the microacoustic device. Such structures with further dielectrics may have improved trimmability because of the waveguiding of the waveguide layer, there is more acoustic wave energy present at the interface between the waveguide layer and the second cladding layer. This is in particular a significant difference to the shaft connection to the boundary layer of the waveguide layer to the first cladding layer by means of heavy electrodes. This allows more accurate trimming processes, which help to better control the frequency at a specific value. The material of the second cladding layer can be chosen such that a speed jump of the acoustic wave between the waveguide layer and the second cladding layer is greater than between the first cladding layer and the waveguide layer. However, the conditions can also be reversed.

The second cladding layer may comprise, as its main constituent, a material selected from DLC (Diamond Like Carbon), SiO _x N _y , BN, α-CH, Ge, Si, TiO ₂ , WC, AlN, ZnO, SiN, Al ₂ O ₃ and SiO ₂ .

This freedom of selection makes it possible to give the second cladding layer a broad spectrum of properties, or to select the cladding layer in accordance with a desired property.

In a preferred embodiment, the first cladding layer is a piezoelectric material which is selected from LiNbO ₃ , KNbO ₃ , NaNbO ₃ , LiTaO ₃ , quartz, ZnO, AlN, ScAlN, LiB ₄ O ₇ , GaPO ₄ , Langasite, Langanite, Langatat PZT ( Lead zirconate titanate) and RECOB (calcium oxoborate of RE), where RE is an element or mixture of several rare earth elements.

In addition to the families of the Langasite (LGS = La ₃ Ga ₅ SiO _14), Langanite (LGN = La ₃ Ga _5.5 Nb _0.5 O ₁₄₎ and Langatate (LGT = La ₃ Ga _5.5 Ta _0.5 O ₁₄ ) also mixed crystals from these three families are suitable. Examples are CNGS (= Ca ₃ NbGa ₃ Si ₂ O ₁₄ ), CTGS (= Ca ₃ TaGa ₃ Si ₂ O ₁₄ ), SNGS (= Sr ₃ NbGa ₃ Si ₂ O ₁₄ ), STGS (= Sr ₃ TaGa ₃ Si ₂ O ₁₄ ), NGS (= Nd ₃ Ga ₅ SiO ₁₄ ) LGAS (= La ₃ Al _x Ga _5-x SiO ₁₄ ) with 1 ≤ x ≤ 0, SGG (= Sr ₃ Ga ₂ GeO ₁₄ ), NCG (= Na ₂ CaGe ₆ O ₁₄ ), REGS (where RE is a rare earth element, for example Pr corresponding to PGS = Pr ₃ Ga ₅ SiO ₁₄ ) and BTGS (= Ba ₃ TaGa ₃ Si ₂ O ₁₄ ). Also suitable for PZT are substituted family members in which lead, zirconium or titanium are replaced by corresponding substituting elements.

The second cladding layer comprising a piezo layer can be applied to a carrier substrate. It is also possible to arrange one or more intermediate layers between this carrier substrate and the piezo layer. Such intermediate layers are in particular dielectric layers which are used for a better adhesion between the piezoelectric layer and the carrier substrate, for a better growth of the piezoelectric layer or for a barrier effect as a diffusion barrier layer.

The electrode of the microacoustic component may be a planar electrode, as used in particular for BAW components. However, the electrode can also be an interdigital electrode, as it can be used in SAW and GBAW devices.

The electrode comprises at least one conductive material, in particular a metal or an alloy whose constituents may be selected, for example, from Al, Cu, Au, Ag, Pt, Pd, W, Ni, Mo, Nb, V, Ti, Cr, Mg , Fe, Ir, Ru, Ra, Os and highly doped semiconductors such as in particular poly-Si and poly-Ge.

The electrodes may consist of a uniform layer. It is also possible to carry out the electrodes in multiple layers, wherein different layers have different conductive properties May have materials and different layer thicknesses.

Regardless of the technology (SAW, BAW, GBAW), the proposed device can be designed as a filter, duplexer, resonator, sensor, resonator filter, module, bandstop filter or notch filter.

The device may also be a microacoustic device that is not based on or does not include a piezoelectric material. A microacoustic component may, for example, also be a silicon microresonator, that is to say a dielectric resonator. Such dielectric resonators consist for example of a dielectric material coated with electrodes, in particular a crystal. Semiconductors are also suitable for dielectric resonators.

A microacoustic component equipped with a waveguide layer can also be a SAW component in which the interdigital electrode is at least partially embedded in the waveguide layer. In this case, it is possible for the surface of the interdigital electrode and together with the waveguide layer to form a planar surface.

The electrode may also be disposed on a mesa structure formed in the cladding layer disposed thereunder. In this case, the piezoelectric material or the material of the first cladding layer is removed up to a given depth between the electrode fingers of the interdigital electrode. The electrode fingers of the interdigital electrode and the mesa structure form a common edge. The waveguide layer then has such a height over the cladding layer that the electrode at least partially embeds. With such a configuration, it is possible, the reflectivity of the interdigital electrode z. B. over said depth to a certain value to optimize the overall properties of the waveguide layer.

It is also possible to sink the interdigital electrode in the first cladding layer and z. B. at the bottom of a trench in the first cladding layer. First cladding layer and interdigital electrode can together form a planar surface on which the waveguide layer is then arranged. But it is also possible that the remaining trench over the electrode is filled with the waveguide layer, which then additionally covers the entire surface of the cladding layer. Further, mixed forms of these embodiments are possible in which the interdigital electrode is sunk, for example, only partially in the first cladding layer.

A further possibility is to arrange the electrode at a distance above the surface of the first cladding layer and to surround it with the waveguide layer from all sides, so that it is completely embedded therein.

The component may be formed as a BAW resonator. In one embodiment, the waveguide layer is then arranged between the substrate of the BAW resonator and a bottom electrode of the resonator. The bottom electrode may then form the second cladding layer of the waveguide.

The waveguide may be formed as a sandwich of first cladding layer, waveguide layer and second cladding layer and forming part of an acoustic mirror, which is arranged between the substrate and the bottom electrode of a BAW resonator. An acoustic mirror typically includes layers of alternating relatively high and relatively low acoustic impedance. In this way, the interfaces with impedance jump act as reflectors, so that with a suitable choice of the layer thicknesses by interference of different reflected wave components, an extinction of certain frequencies can take place. Preferably, the sublayers of an acoustic mirror have a thickness of approximately one quarter of the wavelength of the wave to be extinguished.

In a waveguide that can be integrated in an acoustic mirror, the cladding layers and the waveguide layer are selected with regard to large impedance differences.

In a preferred arrangement, the waveguide layer is part of a GBAW device. Such, working with guided bulk acoustic waves device is constructed on a first substrate having at least as the uppermost layer a piezoelectric layer. The first substrate may also be a piezoelectric crystal. Piezo layer or piezocrystal can serve as the first cladding layer. On the first cladding layer, an electrode is arranged, which may be formed flat or which is an interdigital electrode similar to a SAW device.

Arranged over the electrode is the waveguide layer, which according to the invention comprises a glass with a main constituent which has an abnormal thermomechanical behavior. The layer thickness of the waveguide layer may correspond to 1-100%, preferably 5-50% of the wavelength of the wave propagatable in the waveguide at center frequency.

On the waveguide layer comprising the glass, the second cladding layer is arranged. This can be another thin layer. However, it is also possible to use a second substrate as the second cladding layer. This can with a suitable connection method applied over the waveguide layer and be connected to this. However, it is also possible to carry out a layer deposition on the second substrate for the production, which comprises at least the waveguide layer.

In the case of a GBAW component, it is possible to apply a second waveguide layer above the second substrate, above this a further electrode and above a second substrate, thereby realizing a second component operating with acoustic waves. The waveguide of the second acoustic component and the waveguide of the first microacoustic component use the second cladding layer as a common cladding layer. Such a design saves time, material and costs. It can be obtained so highly integrated components with reduced space and volume requirements.

For two such stacked devices it is possible to use different waveguide layers in the two waveguides. This makes it possible, for example, to equip a first component with overcompensated temperature characteristic TK and a second component with uncompensated TC, which then has a negative temperature coefficient of center frequency TCF. By optimizing the waveguide and the electrode, it is possible to symmetrically adjust the temperature-related deviations in both components by the zero value, so that a fully compensated combined component is obtained with suitable interconnection of the two components.

In the following, the invention will be explained in more detail with reference to embodiments and associated figures. The figures are schematic and not drawn to scale, therefore, no real size proportions again.

1A and 1B show simple versions of microacoustic components with interdigital electrode or with flat electrode in cross section.

2 shows in cross-section a component with an applied on a piezoelectric layer interdigital electrode and a waveguide comprising a second cladding layer.

3 shows in cross-section a similar component as 2 in which, however, the interdigital electrode is buried in the substrate.

4 shows a variation in which the electrode is partially buried in the substrate.

5 shows a device in cross section, wherein the waveguide layer follows the contours of the electrode.

6 shows in cross section a stacked device of two GBAW devices sharing the second cladding layer.

7 shows a BAW resonator in cross section, in which the waveguide is part of the acoustic mirror between the resonator and the substrate.

8th shows the simulated TCF for a reference structure and five different embodiments.

9 shows the TCF for five further simulated embodiments.

10 shows the simulated penetration depth of the wave in the waveguide according to the reference example.

11 shows the simulated penetration depth of the shaft in the waveguide according to embodiment V6.

12 shows the simulated penetration depth of the shaft in the waveguide according to embodiment VE.

1A shows a detail of a schematic cross section through a micro-acoustic device with a simple waveguide. The waveguide comprises a first cladding layer M1 and arranged thereon a waveguide layer WL. The first cladding layer is a piezoelectric layer or a piezoelectric substrate. In order to excite an acoustic wave, an interdigitated electrode E1 is arranged between the first cladding layer M1 and the waveguide layer WL. The microacoustic device is, for example, a SAW device on a lithium niobate or lithium tantalate substrate. The waveguide layer WL comprises a vitreous material whose main component is a material having a negative temperature coefficient of the center frequency.

1B shows a detail of a schematic cross-section of another microacoustic component with a waveguide. The component comprises a first cladding layer M1, a waveguide layer WL and a first electrode E1 applied flat on the waveguide layer WL. The generation of acoustic waves succeeds with a in the 1B not shown resonator whose first electrode is the electrode E1. Such a resonator may be formed on the basis of a piezoelectric material or other dielectric crystal.

2 shows a detail of a schematic cross-section of a micro-acoustic device according to 1A in which the waveguide WL is now additionally covered with a second cladding layer M2. The first electrode E1 is formed interdigitally and arranged on the first cladding layer M1, which is a piezoelectric layer or as a piezoelectric substrate. The material of the second cladding layer M2 regularly differs from that of the first cladding layer M1, but obeys only the condition that the acoustic velocity within the second cladding layer is greater than that in the waveguide layer WL. Also within the first cladding layer M1 of the embodiments according to the 1 to 3 the acoustic wave velocity is greater within the first cladding layer than in the waveguide layer WL.

3 shows a detail of a schematic cross section through another microacoustic component, which similar to that in 2 is formed, but in which the first electrode E1 is recessed into the first cladding layer M1, so that the interdigital first electrode E1 and the first cladding layer M1 form a common planar surface, on which the waveguide layer WL is arranged.

4 shows a further modification for the execution of such a microacoustic device, in which the first interdigitated electrode layer E1 is only partially embedded in the first cladding layer M1.

5 shows a detail of a schematic cross section through a SAW device. Here, an interdigital first electrode E1 is disposed on a cladding layer M1, which is a piezoelectric substrate. The waveguide layer WL is deposited in conformity with the surface by means of an isotropic process and thus follows the contours of the interdigital first electrode E1. Such an embodiment of the waveguide layer WL has the advantage that above the electrode fingers of the interdigital first electrode E1, mesa structures form from the waveguide layer WL, at the side edges of which reflections can take place. This increases the reflectivity of the first electrode E1, which was reduced by the application of the waveguide layer WL. Thus, reflection at the electrode fingers of the first electrode E1 and reflection at the edges of the mesa-like structures of the waveguide layers WL combine to form an overall reflection for acoustic waves. The reflection of the first electrode E1 within the waveguide layer WL is reduced with respect to an electrode not provided with a waveguide layer because the speed difference of the wave between the electrode on the one hand and the waveguide layer WL or air or vacuum on the other hand is substantially greater for the first mentioned case.

Over the patterned waveguide layer WL according to FIG 5 a second cladding layer can be deposited.

However, it is also possible to remove the waveguide layer WL by mechanical abrasion or by a planarizing etching process to the extent that on the one hand a planar surface of the waveguide layer is formed and on the other hand in this surface, the tops of the first electrode layer E1 are exposed, which together with the remaining Waveguide layer WL form a common planar surface.

In a further embodiment of the invention, the topography on the surface of the waveguide layer WL can be designed by subsequent structuring and other measures. The period, the relative finger width, the edge angle or the edge shape of the elevations on the surface of the waveguide layer WL are varied.

In addition, it has been found that a variation of the edge angle of the metallization structures, that is to say the electrode fingers themselves, makes possible an improved layer deposition of the waveguide layer WL and in particular a better edge coverage. While known waveguide layers tend to cracks greatly from a certain layer thickness, is counteracted with a deviating from 90 ° edge angle of the metallization and thus a corner angle following this topography of the waveguide layer WL, thus avoiding cracks. A waveguide layer WL over electrode structures with oblique and, for example, 75 ° inclined edge angles has significantly fewer cracks than a layer of the same thickness with conventional edge angles of 90 °. Alternatively, with an edge angle of the electrode fingers smaller than 90 °, the layer thickness of the waveguide layer WL can be increased and the compensation of the TCF can be improved without causing increased cracks.

6 shows a detail of a schematic cross section through a stacked GBAW device. This is a first GBAW device, which, for example, accordingly 2 is formed and a first cladding layer M1, a first electrode layer E1 on the cladding layer, a waveguide layer WL1 and a second cladding layer M2, which together form a waveguide WG1. The first cladding layer M1 is formed by the piezoelectric substrate or the piezoelectric layer of the GBAW device. Over the second cladding layer M2, a second waveguide layer WL2 is formed, over which the third cladding layer M3 is arranged. Between the second waveguide layer WL2 and the third cladding layer M3, the second electrode E2 is arranged, preferably on the planar surfaces of the third cladding layer M3.

The second GBAW device now comprises a second waveguide WG2, which uses the second cladding layer M2 together with the first waveguide WG1. The component may be formed symmetrically to the second cladding layer M2. However, it is also possible to form the two waveguides with different materials or other different properties. In particular, the first and second GBAW components may differ in the center frequency, in the material of the waveguide layer WL and in the layer thicknesses or the electrode material. In particular, it is possible to design the second waveguide layer WL2 with a different temperature coefficient of the center frequency than the first waveguide layer WL1. It is also possible to interconnect the first and second components.

7 shows a detail of a schematic cross-section of a trained as a BAW resonator microacoustic device. The component is arranged on a support SU serving as substrate. This comprises a mechanically solid, preferably crystalline formed material, in particular a semiconductor such as crystalline silicon. However, other substrate materials are also possible.

Above the substrate SU, an acoustic mirror AS is initially formed, which alternately comprises layers with relatively high and relatively low acoustic impedance. At least one pair of such high and low impedance layers is required for the mirror effect, the thickness of which is generally about one quarter of the wavelength to be reflected. In the present case, the acoustic mirror AS comprises a waveguide which is formed from a second cladding layer M2, a waveguide layer WL1 and a first cladding layer M1. The first waveguide layer WL1 is formed as a glass and includes as a main component a material that improves the temperature coefficient of frequency (TCF) of the device. The two cladding layers M1 and M2 have a higher wave velocity of the acoustic wave relative to the waveguide layer WL1. Directly above the waveguide, the resonator itself is arranged, which comprises a flat first electrode E1, a piezoelectric layer PL and a flat second electrode E2.

The layer thickness of the piezoelectric layer PL is about a half wavelength or an odd multiple thereof.

Between the substrate and the second cladding layer M2 further layers can be arranged, which represent further mirror layer pairs with relatively high and relatively low acoustic impedance and complete the acoustic mirror AS. The reflection effect of the acoustic mirror AS is improved by each additional layer. At the same time, however, the bandwidth of the waves reflected by the acoustic mirror is lowered.

In the following, the compensation effect of a waveguide comprising a germanium oxide-containing waveguide layer will be examined on the basis of simulation calculations for different embodiments of GBAW devices. It is governed by a GBAW structure 2 assumed, in addition as a second cladding layer M2, a dielectric layer is arranged. The first cladding layer M1 for the reference example V1 and the embodiments V2 to V6 is a piezoelectric LN15rotYX substrate which consists of a lithium niobate substrate with propagation direction X and 15 ° cutting angle, referred to below as LN15, rotated about the Y-axis. All exemplary embodiments V2 to V6, like the reference example V1, comprise as the first electrode E1 an interdigital electrode which is applied with a pitch of 1.64 μm and a metallization ratio η of 0.6. The embodiment V1 serves as a reference and comprises as the electrode metal gold in a thickness of 230 nm, which corresponds to a relative Metallisierungshöhe of about about 7%. A layer surrounding the heavy electrodes, which does not correspond to the waveguide layer WL in the reference example V1, but in all subsequent embodiments, is formed as PVD silicon dioxide and has a thickness of 800 nm. In addition, a second cladding layer M2 is provided, which is formed from 4.5 μm PECVD SiO ₂ .

The embodiment V2 differs from the reference experiment V1 in that now actually a waveguide layer WL is formed by replacement of the PVD silicon dioxide by germanium dioxide glass. This results in completely new properties that offer many advantages. In the case of the known use of PVD SiO ₂ , the wave is located at the interface to the piezoelectric, which is enforced by using the heavy electrodes, which has disadvantages, for. As the above, entails. By contrast, when glass containing germanium dioxide is used, the wave is already guided by means of this layer alone. This results in advantages, in particular improved trimmability, temperature compensation and better performance compatibility.

Since the electrodes no longer have to take on the task of waveguiding or shaft binding to the interface, they can regardless of other properties are optimized, for. B. in terms of conductivity or power compatibility. Compared to V2, the metal of the first electrode E1 is replaced by copper in experiment V3. In the exemplary embodiment V4, the thickness of the first electrode layer E1 is reduced to 115 nm. In the embodiment V5, the thickness of the copper electrode is increased to 330 nm. The thickness of the germanium dioxide glass waveguide layer WL is increased to 1000 nm. In the embodiment according to V6, the thickness of the first electrode layer (Cu) is reduced to 300 nm. All other parameters of an experiment V (x) are selected like the parameters of the previous experiment V (x - 1).

8th shows the temperature coefficients TCF of the center frequency simulated or calculated for such GBAW components, plotted for the tests V1 to V6. It turns out that, with the exception of experiment V4, all exemplary embodiments (V2, V3, V5 and V6) have an advantageously small TCF, which is decisively improved compared to a GBAW component with known SiO ₂ waveguides. V4 even shows the possibility of overcompensation, which can be beneficial in certain circuits. The embodiments according to V3, V5 and V6 have a TCF which is close to zero. This is the first time a structure has been found that combines a near-zero TCF with a high bandwidth.

9 shows a graphical representation of the simulated TCF for five further embodiments VA, VB, VC, VD and VE. In VA, a first electrode layer of gold in a thickness of 230 nm, corresponding to approximately 7% relative metallization height, is applied to an LN15 substrate. The waveguide layer is a 1300 nm thick germanium dioxide glass layer. The second cladding layer is 4.5 μm PECVD silicon dioxide. In experiment VB, the thickness of the gold electrode is reduced to 115 nm. Also, the thickness of the germanium dioxide glass waveguide layer is reduced to 800 nm.

In the exemplary embodiment VC, a lithium niobate substrate with a cutting angle of 0 ° is used, hereinafter referred to as LN0. The remaining parameters are selected as in embodiment VB.

In the exemplary embodiment VD, aluminum is selected as the electrode material compared with the exemplary embodiment VC, and the first electrode is applied in a thickness of 230 nm. The waveguide layer is germanium dioxide glass in a thickness of 800 nm.

In the exemplary embodiment VE, the electrode material selected is aluminum with a thickness of 100 nm, which is provided with a thin passivation layer of Al ₂ O ₃ . At the same time, the thickness of the waveguide layer WL is increased to 875 nm, and the metallization thickness η is reduced to 0.3.

Experiments VA to VE also show that with a waveguide containing germanium dioxide a very good compensation of the TCF in GBAW devices can be obtained. With the exception of the VD test, the simulations indicate TCF values close to zero, which corresponds to a nearly fully compensated TCF. Trial VE shows that good TK compensation and even TK overcompensation can be achieved even with light electrodes.

The good waveguide properties of waveguide structures according to the invention result from simulations in which the strength of the deflection of individual atoms of the waveguide is plotted against the depth of the waveguide. The depth of zero is chosen to be the surface of the piezo substrate or the interface between the second cladding layer and the electrode layer. The maximum of the deflection corresponds to the center of the shaft and indicates the relative location of the wave in the respective waveguide.

10 shows the penetration depth of the wave in a waveguide according to reference experiment V1. The interfaces between the individual layers of the waveguide are indicated. Above the upper first cladding layer, vacuum is assumed. It turns out that the wave is localized in the upper part of the heavy Au electrode and there are almost no waveguide properties in the layers above the electrode.

11 In contrast, the penetration depth of the shaft in a waveguide according to embodiment V6. It turns out that the wave is located here in the middle of the waveguide layer. In V6, the electrodes are made of the relatively heavy Cu. This shows the improved waveguiding of a waveguide comprising germanium oxide, since the wave is clearly drawn into the waveguide layer.

12 shows the penetration depth of the wave in a waveguide according to experiment VE. Although here a relatively light and relatively thin A1 electrode is used, also here the maximum deflection takes place practically in the middle of the germanium oxide waveguide layer. The first cladding layer selected is alumina.

The improved TCF compensation associated with improved waveguiding becomes, as in the embodiments and FIGS 8th to 12 shown proved for GBAW devices. Corresponding results are also to be expected for SAW components, BAW resonators and other microacoustic components with a germanium dioxide glass and matching waveguide layer. The invention is therefore not limited to the embodiments and includes all components with a waveguide with a glassy waveguide layer and in particular from germaniumdioxidglashaltigen glasses or glasses with zinc metaphosphate or a chalcogenide.

LIST OF REFERENCE NUMBERS

• WL, WL1, WL2

  Waveguide layer

  VL

  Wave velocity in waveguide layer

  M1

  first cladding layer

  VM1

  Wave velocity in the first cladding layer

  PS

  piezoelectric layer or a piezoelectric substrate

  M2

  second cladding layer

  VM2

  wave velocity

  AS

  acoustic mirror

  PL

  Piezoelectric layer

  WG1, WG2

  waveguides

  M3

  third cladding layer

  SU

  substratum

Claims (16)

Microacoustic component with a waveguide (WG), - Having a waveguide layer (WL) having a first acoustic wave velocity VL and to the waveguide layer directly adjacent first cladding layer (M1) in which a second acoustic wave velocity VM1 applies - With an electrode (E1) for exciting an acoustic wave in the waveguide In which for the shaft speeds VL <VM1 - Wherein the waveguide layer (WL) is a glass comprising a component with abnormal thermo-mechanical behavior - Wherein the waveguide layer (WL) germanium dioxide, chalcogenide glass or zinc metaphosphate as an ingredient. Component according to Claim 1, in which the first cladding layer (M1) is a piezoelectric layer (PL) or a piezoelectric substrate. A device according to claim 1 or 2, wherein the waveguide layer (WL) is a glass having germanium dioxide as its main constituent. A device according to claim 3, wherein the waveguide layer (WL) comprises germanium dioxide in an amount of 55 to 100% by weight. Component according to Claim 3 or 4, in which glass-forming agents, glass modifiers and / or glass stabilizers are contained as a further constituent in the waveguide layer (WL). Component according to Claim 5, in which the glass formers, glass modifiers and / or glass stabilizers are selected from B ₂ O ₃ , SiO ₂ , P ₂ O ₅ , As ₂ O ₃ , Sb ₂ O ₃ , In ₂ O ₃ , Sn ₂ O ₃ , PbO ₂ , Li ₂ O, CaO, Na ₂ O, K ₂ O, MgO, Rb ₂ O, Cs ₂ O, SrO, TeO ₂ , SeO ₂ , MoO ₂ , WO ₃ , BiO ₃ , Al ₂ O ₃ , BaO, V ₂ O and SO ₃ . Component according to one of Claims 1 or 2, in which the waveguide layer (WL) contains as main constituent a chalcogenide glass or zinc metaphosphate. A device according to any one of claims 1-7, wherein the waveguide layer is embedded between the first cladding layer and a second cladding layer, the second cladding layer having a third acoustic wave velocity VM2, for which: VM2> VL. Component according to one of Claims 1-8, in which the second cladding layer comprises as main component a material which is selected from DLC, SiO _x N _y , BN, α-CH, Ge, Si, TiO ₂ , WC, AlN, ZnO, SiN, Al ₂ O ₃ and SiO ₂ . Component according to one of claims 2-9, wherein the first cladding layer is a piezoelectric material selected from LiNbO ₃ , KNbO ₃ , NaNbO ₃ , LiTaO ₃ , quartz, ZnO, AlN, ScAlN, LiB ₄ O ₇ , GaPO ₄ , langasite, Langanite, Langatat PZT and RECOB, where RE is an element or mixture of several rare earth elements and COB is a calcium oxoborate. A device according to any one of claims 1-10, wherein the first cladding layer is a piezoelectric layer or a piezoelectric substrate for a SAW device, wherein the electrode is disposed on the piezoelectric layer or the piezoelectric substrate and formed as an interdigital electrode and wherein the waveguide layer on the substrate between electrode fingers of the electrode or on the substrate, the electrode is arranged overlapping. Component according to one of claims 1-10, wherein the device is arranged on a substrate BAW resonator, wherein the waveguide layer between the substrate and a bottom electrode of the resonator is arranged. The device of claim 12, wherein the combination of the first cladding layer, the waveguide layer and the second cladding layer is a sandwich forming a part of an acoustic mirror and disposed between the substrate and the bottom electrode of the BAW resonator. A device according to any one of claims 1-13, wherein the waveguide layer is part of a GBAW device and disposed over the substrate provided with the electrode. The device of claim 14, wherein the second cladding layer is formed by a second substrate disposed over the waveguide layer. Component according to one of claims 1-15, comprising A first filter in which the temperature response of the center frequency is positively and thus overcompensated by an appropriately set waveguide layer, and A second filter electrically connected to the first filter, in which: The second filter has a negative temperature response of the center frequency, - The interconnection of the first and second filter is carried out so that the component has a total total compensation of the temperature coefficient of the center frequency.

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