Abstract:
The invention describes a filter arrangement as well as an electronic component, each with a bulk acoustic wave resonator unit which is present on a carrier substrate ( 1 ). A reflection element ( 2 ) is provided between the carrier substrate ( 1 ) and the bulk acoustic wave resonator unit for the purpose of acoustic insulation of the generated oscillations. This reflection element ( 2 ) may consist either of several layers of alternately high and low impedance or, if the acoustically reflecting substance has a sufficiently low impedance, of a single layer. In addition, a mobile telephone device, a transmitter, a receiver, and a wireless data transmission system as well as a method of manufacturing an electronic component are described.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a filter arrangement with a carrier substrate, a resonator unit, and a reflection element between the carrier substrate and the resonator unit. The invention also relates to an electronic component with a carrier substrate, a resonator unit, and a reflection element between the carrier substrate and the resonator unit, as well to as a method of manufacturing such a component. 
     The extremely fast developments in the field of mobile telephony and the continuous miniaturization of cordless telephone equipment lead to increased requirements imposed on the individual components. Thus a high selectivity in the high-frequency range is necessary for protecting the receiver from the increasing number of potential interfering signals from other systems. 
     At the moment, filters with ceramic electromagnetic resonators are used for this purpose in the high-frequency range. A miniaturization of these filters, however, is restricted by the electromagnetic wavelength. Surface acoustic wave (SAW) filters can be constructed so as to be substantially smaller. The reason for this is that the acoustic wavelength is smaller by 4 to 5 orders of magnitude than the electromagnetic wavelength. A disadvantage is, however, that surface acoustic wave filters often have a complicated construction and have to be protected by means of complicated housings. 
     An alternative is formed by bulk acoustic wave (BAW) filters. Bulk acoustic wave filters have advantages as regards their size, power, and IC compatibility. Bulk acoustic wave filters can be realized with widely varying types of bulk acoustic wave resonators. Thus, for example, single-crystal resonators, resonators with membranes, or resonators with air gaps may be used. 
     In principle, bulk acoustic wave resonators are built up from three components. The first component generates the acoustic wave and comprises a piezoelectric layer. Two electrodes, which are arranged above and below the piezoelectric layer, represent the second component. The third component has the task of acoustically insulating the carrier substrate from the oscillations generated by the piezoelectric layer. 
     A possibility for acoustic insulation is formed by reflection layers which are provided between the carrier substrate and the resonator unit. Such reflection layers consist of layers having alternately a high and a low acoustic impedance. The thickness of an individual layer is one fourth of the resonance wavelength. These layers have the purpose of reflecting the acoustic waves at the respective boundary surfaces as well as possible, and thus keeping the acoustic energy inside the resonator unit. The number of layers required depends on the one hand on the differences in acoustic impedance between the individual layers and on the other hand on the resonator quality Q to be achieved. 
     The individual reflection layers may be made from a wide variety of materials. A material of low acoustic impedance which is often used is SiO 2  with an acoustic impedance of 13 Ggm −2 s −1 . AlN with an acoustic impedance of 34 Ggm −2 s −1 , W with an acoustic impedance of 101 Ggm −2 s −1 , and HfO 2  with an acoustic impedance of 40 Ggm −2 s −1  are used as materials in layers having a high acoustic impedance. 
     A bulk acoustic wave resonator is known from WO 98/16957 in which polymers such as, for example, polyimide are used as materials of low acoustic impedance in the reflection layers. The number of reflection layers necessary for acoustic insulation can be reduced owing to a low acoustic impedance of 2 Ggm −2 s −1 . 
     SUMMARY OF THE INVENTION 
     The invention has for its object to provide an improved bulk acoustic wave filter. 
     This object is achieved with a filter arrangement with a carrier substrate, a resonator unit, and a reflection element between the carrier substrate and the resonator unit which is characterized in that the reflection element comprises a layer of an acoustically reflecting substance. 
     Preferably, the acoustically reflecting substance belongs to the group of polymers and porous substances. 
     Porous or polymer acoustically reflecting substances have low acoustic impedance values and thus render it possible for only one layer to suffice for reflecting the total acoustic energy. The condition that the thickness of the layer should be one fourth of the resonance wavelength can even be dropped in this case. This simplifies the construction and renders the manufacture of the filter arrangement less expensive. 
     It is particularly preferred that the acoustically reflecting substance is an aerogel, a xerogel, a glass foam, a foam-type adhesive, a foamed synthetic resin, or a synthetic resin of low density. 
     The advantage of these materials is that they have extremely low impedance values of down to 10 −2  Ggm −2 s −1 , depending on the material used. The acoustic impedance thus lies only two orders of magnitude above the acoustic impedance of air (4·10 −4  Ggm −2 s −1 ) in the most favorable case. 
     It may be preferred that the reflection element comprises layers of alternately high and low acoustic impedance, with an acoustically reflecting substance being used for any layer of low acoustic impedance. 
     Only very few layers are necessary in the reflection element for reflecting the total acoustic energy owing to the low acoustic impedance values of polymers and porous acoustically reflecting substances. 
     It is preferred that the material of high impedance comprises HfO 2 , Mo, Au, Ni, Cu, W, Ti/W/Ti, W x Ti 1−x  (0≦x≦1), diamond, Ta 2 O 5 , Pt, Ti/Pt, or a synthetic resin of high density. 
     The material may be provided in thin-film processes such as reactive sputtering or vacuum deposition processes such as, for example, chemical vapor deposition (CVD), physical chemical vapor deposition (PCVD), or spin coating. 
     It is furthermore preferred in this filter arrangement that the thickness of the layers is one fourth of the resonance wavelength each time. 
     The reflections of each layer will combine in phase in the resonance wavelength in a sequence of layers of alternately high and low impedance which is combined with layer thicknesses of one fourth of the resonance wavelength. 
     It may be preferred that a further reflection element is arranged on the resonator unit. 
     The provision of a further reflection element on the resonator unit on the one hand has the advantage that no acoustic vibrations reach the upper side of the filter arrangement. On the other hand, the reflection elements protect the resonator unit from contamination with dust particles and the like. The provision of reflection elements above and below the resonator unit, which in the most favorable case consist of only one layer, is cheaper than other protection techniques such as, for example, a semi-hermetic envelope. 
     It is also preferred that a protective layer of an organic and/or inorganic material is provided over the filter arrangement. 
     The filter arrangement is protected from mechanical loads and corrosion through moisture by the protective layer. 
     It is preferred that the carrier substrate comprises a ceramic material, a ceramic material with a glass planarizing layer, a glass-ceramic material, a glass material, silicon, GaAs, or sapphire. 
     A carrier substrate of a ceramic material, a ceramic material with a glass planarizing layer, a glass-ceramic material, or a glass material can be inexpensively manufactured and the process cost for these components can be kept low. If the filter arrangement is to be integrated into an IC, the carrier substrate made of a semiconductor material may possibly be provided with a passivating layer, for example of SiO 2  or glass. 
     It is furthermore preferred that the resonator unit comprises a piezoelectric layer of PbZr 0.15 Ti 0.85 O 3  doped with 2% lanthanum. 
     PbZr 0.15 Ti 0.85 O 3  doped with 2% lanthanum has particularly good piezoelectric properties in the filter arrangement. 
     It may be preferred that an adhesive layer is arranged between the carrier substrate and the reflection element. 
     This layer serves to fasten the reflection element on the carrier substrate. 
     The invention further relates to mobile telephone appliances, transmitters, receivers, and wireless data transmission systems which are fitted with a filter arrangement comprising a carrier substrate, a resonator unit, and a reflection element between the carrier substrate and the resonator unit, wherein the reflection element comprises a layer of an acoustically reflecting substance. 
     The invention also relates to an electronic component with a carrier substrate, a resonator unit, and a reflection element between the carrier substrate and the resonator unit, wherein the reflection element comprises a layer of an acoustically reflecting substance. 
     Inexpensive components such as, for example, bulk acoustic wave resonators can be manufactured with the use of polymers and porous acoustically reflecting substances of extremely low impedance as the reflection elements. A reduction in the manufacturing cost is achieved first in that only one layer need be provided for the reflection element and in addition in that this layer need not necessarily have a layer thickness of one fourth of the resonance wavelength. 
     The invention further relates to a method of manufacturing an electronic component with a carrier substrate, a resonator unit, and a reflection element made from an acoustically reflecting substance, in which method 
     a resonator unit is provided on a substrate layer, 
     a reflection element of an acoustically reflecting substance is provided on the resonator unit, and 
     a carrier substrate is fastened on the reflection element, and the substrate layer is removed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will be explained in more detail below with reference to four Figures and eight embodiments, in which 
     FIG. 1 shows the construction of an embodiment of a bulk acoustic wave filter arrangement in cross-section, 
     FIG. 2 shows the circuit diagram of a bulk acoustic wave filter arrangement, 
     FIG. 3 shows a bulk acoustic wave resonator with two reflection elements in cross-section, and 
     FIG. 4 is a flow chart representing the manufacture of a bulk acoustic wave resonator. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, a bulk acoustic wave filter arrangement comprises a carrier substrate  1  which is made, for example, from a ceramic material, a ceramic material with a glass planarizing layer, a glass-ceramic material, a glass material, silicon, GaAs, or sapphire. If silicon or GaAs is used as the carrier substrate  1 , a passivating layer of, for example, SiO 2  or glass is additionally provided. A first reflection element  2 , which is a layer of an acoustically reflecting substance from the group comprising polymers and porous substances, is present on the carrier substrate  1 . Acoustically reflecting substances which may be used are, for example, an aerogel, a xerogel, a glass foam, a foam-type adhesive, a foamed synthetic resin, or a synthetic resin of low density. An aerogel which may be used is, for example, an inorganic aerogel made of silica gel, or porous SiO 2  structures, or an organic aerogel such as, for example, a resorcin-formaldehyde aerogel, a melamine-formaldehyde aerogel, or a phenol-formaldehyde aerogel. A xerogel which may be used is, for example, an inorganic xerogel such as highly condensed polysilicic acid or an organic xerogel such as glue or agar-agar. Foamed substances which may be used are chemically foamed or physically foamed polymers such as, for example, polystyrol, polycarbonate, polyvinylchloride, polyurethane, polyisocyanate, polyisocyanurate, polycarbodiimide, polymethacrylimide, polyacrylimide, acryl-butadiene-styrol copolymers, polypropylene, or polyester. Furthermore, foamed synthetic resins such as, for example, phenol-formaldehyde resins or furane resins may be used, which have a high porosity owing to carbonization. A synthetic resin of low density which may be used is, for example, a cross-linked polyvinylether, a cross-linked polyarylether, polytetrafluoroethylene, poly(p-xylylene), poly(2-chloro-p-xylylene), poly(dichloro-p-xylylene), polybenzocyclobutene, a styrol-butadiene copolymer, an ethylene-vinylacetate polymer, or an organic siloxane polymer. Two resonator units are provided on the first reflection element  2 , each having a first electrode  3 , a piezoelectric layer  4 , and a second electrode  5 . The electrodes  3  and  5  are preferably made from a well conducting material of low acoustic damping and may comprise, for example, Ag 1−x Pt x  (0≦x≦1), Pt (50 nm to 1 μm), Ti (1 to 20 nm)/Pt (20 to 600 nm), Ti (1 to 20 nm)/Pt (20 to 600 nm)/Ti (1 to 20 nm), Al, Al doped with a few percents of Cu, Al doped with a few percents of Si, Al doped with a few percents of Mg, W, Ni, Mo, Au, Cu, Ti/Pt/Al, Ti/Ag, Ti/Ag/Ti, Ti/Ag/Ir, Ti/Ir, Ti/Pd, Ti/Ag 1−x Pt x  (0≦x≦1), Ti/Ag 1−x Pd x  (0≦x≦1), Ti/Pt 1−x Al x  (0≦x≦1), Pt 1−x Al x  (0≦x≦1), Ti/Ag/Pt 1−x Al x  (0≦x≦1), Ti/Ag/Ru, Ti/Ag/Ir/IrO x  (0≦x≦2), Ti/Ag/Ru/RuO x  (0≦x≦2), Ti/Ag/Ru/Ru x Pt 1−x  (0≦x≦1), Ti/Ag/Ru/Ru x Pt 1−x /RuO y  (0≦x≦1, 0≦y≦2), Ti/Ag/Ru/RuO x /Ru y Pt 1−y  (0≦x≦2, 0≦y≦1), Ti/Ag/Ru x Pt 1−x  (0≦x≦1), Ti/Ag/Pt x Al 1−x  (0≦x≦1), Pt x Al 1−x /Ag/Pt y Al 1−y  (0≦x≦1, 0≦y≦1), Ti/Ag/Pt y (RhO x ) 1−y  (0≦x≦2, 0≦y≦1), Ti/Ag/Rh/RhO x  (0≦x≦2), Ti/Ag/Pt x Rh 1−x  (0≦x≦1), Rh, Rh/RhO 2 , Ti/Ag/Pt y (RhO x ) 1−y /Pt z Rh 1−z  (0≦x≦2, 0≦y≦1, 0≦z≦1), Ti/Ag x Pt 1−x /Ir (0≦x≦1), Ti/Ag x Pt 1−x /Ir/IrO y  (0≦x≦1, 0≦y≦2), Ti/Ag x Pt 1−x /Pt y Al 1−y  (0≦x≦1, 0≦y≦1), Ti/Ag x Pt 1−x /Ru (0≦x≦1), Ti/Ag x Pt 1−x /Ru/RuO y  (0≦x≦1, 0≦y≦2), Ti/Ag/Cr, Ti/Ag/Ti/ITO, Ti/Ag/Cr/ITO, Ti/Ag/ITO, Ti/Ni/ITO, Ti/Ni/Al/ITO, Ti/Ni, Ti/W/Ti, W x Ti 1−x  (0≦x≦1), W x Ti 1−x /Al(Cu)(0≦x≦1), W x Ti 1−x /Al(Si)(0≦x≦1), W x Ti 1−x /Al(0≦x≦1), or Ti/Cu. The material used for the piezoelectric layer  4  may be, for example, AlN, ZnO, PbTi 1−x Zr x O 3  (0≦x≦1) with and without dopants of La or Mn, LiNbO 3 , LiTaO 3 , PbNb 2 O 6 , or polyvinylidene fluoride (PVDF). A second reflection element  6 , for example a layer of an aerogel, a xerogel, a glass foam, a foam-type adhesive, a foamed synthetic resin, or a synthetic resin of low density, is provided on portions of the first electrode  3  and of the second electrode  5  as well as of the piezoelectric layer  4 . Alternatives for the construction are familiar to those skilled in the art. A protective layer  7  of an organic and/or inorganic material is provided over the entire filter arrangement. The organic material used may be, for example, polybenzocyclobutene or polyimide, and the inorganic material used may be, for example Si 3 N 4 , SiO 2 , or Si x O y N z  (0≦x≦1, 0≦y≦1, 0≦z≦1). 
     Alternatively, the reflection elements  2  and  6  may consist of several layers of alternately high and low impedance. The material of low impedance may then be, for example, an organic or inorganic aerogel, an organic or inorganic xerogel, a glass foam, a foam-type adhesive, a foamed synthetic resin, or a synthetic resin of low density. Materials of high acoustic impedance maybe, for example, HfO 2 , Mo, Au, Ni, Cu, W, Ti/W/Ti, W x Ti 1−x  (0≦x≦1), diamond, Ta 2 O 5 , Pt, Ti/Pt, or a synthetic resin of high density such as, for example, high-density polyethylene (HDPE). 
     In a further embodiment of the invention, furthermore, the second reflection element  6  and/or the protective layer  7  may be omitted. 
     A further alternative is that an additional adhesive layer, for example made of an acrylate glue or an epoxide glue, is provided between the reflection element  2  and the carrier substrate  1 . The acrylate glue may comprise, for example, acryl or methacryl monomers which polymerize during the adhesion process. 
     Furthermore, a layer of SiO 2  with a layer thickness of between 30 and 300 nm may be provided above and/or below a reflection element  2  made of porous SiO 2 . 
     Moreover, the filter arrangement may be provided with at least one first and one second current supply contact. For example, an electroplated SMD end contact of Cr/Cu, Ni/Sn, or Cr/Cu, Cu/Ni/Sn, or Cr/Ni, Pb/Sn, or a bump end contact, or a contact surface may be used as the current supply contact. 
     FIG. 2 shows a filter arrangement of a total of nine resonator units M 1  to M 5  and N 1  to N 4 . Five resonator units M 1  to M 5  are connected in series between an input  8  and an output  9 . Four further resonator units N 1  to N 4  are connected in parallel to said five resonator units M 1  to M 5 . One terminal of each of the four resonator units N 1  to N 4  is connected to ground potential. The other terminal of the resonator unit N 1  is connected between the resonator units M 1  and M 2 . The other terminal of the resonator unit N 2  is connected between the resonator unit M 2  and M 3 . The other terminal of the resonator unit N 3  is connected between the resonator units M 3  and M 4 , and finally, the other terminal of the resonator unit N 4  is connected between the resonator units M 4  and M 5 . 
     In FIG. 3, an electronic component comprises a carrier substrate  1  which is made, for example, from a ceramic material, a ceramic material with a glass planarizing layer, a glass-ceramic material, silicon, GaAs, or sapphire. If silicon or GaAs is used as the carrier substrate  1 , an additional passivating layer of, for example, SiO 2  or glass is provided. A reflection element  2  with several layers is provided on the carrier substrate  1 , i.e. with a bottom layer  10 , a central layer  11 , and an upper layer  12 . The individual layers have a layer thickness of one fourth of the resonance wavelength. The bottom layer  10  and the upper layer  12  are made from a material of low acoustic impedance and comprise an acoustically reflecting substance from the group of polymers and porous substances. The stically reflecting substance used may be, for example, an aerogel, a xerogel, a glass foam, a foam-type adhesive, a foamed synthetic resin, or a synthetic resin of low density. The aerogel used may be, for example, an inorganic aerogel made of silica gel or porous SiO 2  structures, or an organic aerogel such as, for example, a resorcin-formaldehyde aerogel, a melamine-formaldehyde aerogel, or a phenol-formaldehyde aerogel. The xerogel used may be, for example, an inorganic xerogel such as highly condensed polysilicic acid or an organic kerogel such as glue or agar-agar. Foamed substances may be chemically foamed or physically foamed polymers such as, for example, polystyrol, polycarbonate, polyvinylchloride, polyurethane, polyisocyanate, polyisocyanurate, polycarbodiimide, polymethacrylimide, polyacrylimide, acryl-butadiene-styrol copolymers, polypropylene, or polyester. In addition, foamed synthetic resins such as, for example, phenol-formaldehyde resins or furane resins may be used, which have a high porosity owing to carbonization. A synthetic resin of low density which is used may be, for example, a cross-linked polyvinyl ether, a cross-linked polyaryl ether, polytetrafluoroethylene, poly(p-xylylene), poly(2-chloro-p-xylylene), poly(dichloro-p-xylylene), polybenzocyclobutene, a styrol-butadiene copolymer, an ethylene-vinylacetate polymer, or an organic polysiloxane polymer. The acoustic impedance of the central layer  11  is higher than the acoustic impedances of the bottom layer  10  and the top layer  12 . The central layer  11  is made of a material having a high acoustic impedance such as, for example, HfO 2 , Mo, Au, Ni, Cu, W, Ti/W/Ti, W x Ti 1−x , diamond, Ta 2 O 5 , Pt, Ti/Pt, or a synthetic resin of high density such as, for example, high-density polyethylene (HDPE). A first electrode  3 , a piezoelectric layer  4 , and a second electrode  5  are provided on the upper layer  12 . The electrodes  3  and  5  are preferably made from a well conducting material of low acoustic damping and may comprise, for example, Ag 1−x Pt x  (0≦x≦1), Pt (50 nm to 1 μm), Ti (1 to 20 nm)/Pt (20 to 600 nm), Ti (1 to 20 nm)/Pt (20 to 600 nm)/Ti (1 to 20 nm), Al, Al doped with a few percents of Cu, Al doped with a few percents of Si, Al doped with a few percents of Mg, Ni, W, Mo, Au, Cu, Ti/Pt/Al, Ti/Ag, Ti/Ag/Ti, Ti/Ag/Ir, Ti/Ir, Ti/Pd, Ti/Ag 1−x Pt x  (0≦x≦1), Ti/Ag 1−x Pd x  (0≦x≦1), Ti/Pt 1−x Al x  (0≦x≦1), Pt 1−x Al x  (0≦x≦1), Ti/Ag/Pt 1−x Al x  (0≦x≦1), Ti/Ag/Ru, Ti/Ag/Ir/IrO x  (0≦x≦2), Ti/Ag/Ru/RuO, (0≦x≦2), Ti/Ag/Ru/Ru x Pt 1−x  (0≦x≦1), Ti/Ag/Ru/Ru x Pt 1−x /RuO y  (0≦x≦1, 0≦y≦2), Ti/Ag/Ru/RuO x /Ru y Pt 1−y  (0≦x≦2, 0≦y≦1), Ti/Ag/Ru x Pt 1−x  (0≦x≦1), Ti/Ag/Pt x Al 1−x  (0≦x≦1), Pt x Al 1−x /Ag/Pt y Al 1−y  (0≦x≦1, 0≦y≦1), Ti/Ag/Pt y (RhO x ) 1−y  (0≦x≦2, 0≦y≦1), Ti/Ag/Rh/RhO x  (0≦x≦2), Rh, Rh/RhO 2 , Ti/Ag/Pt x Rh 1−x  (0≦x≦1), Ti/Ag/Pt y (RhO x ) 1−y /Pt z Rh 1−z  (0≦x≦2, 0≦y≦1, 0≦z≦1), Ti/Ag x Pt 1−x /Ir (0≦x≦1), Ti/Ag x Pt 1−x /Ir/IrO y  (0≦x≦1, 0≦y≦2), Ti/Ag x Pt 1−x /Pt y Al 1−y  (0≦x≦1, 0≦y≦1), Ti/Ag x Pt 1−x /Ru (0≦x≦1), Ti/Ag x Pt 1−x /Ru/RuO y  (0≦x≦1, 0≦y≦2), Ti/Ag/Cr, Ti/Ag/Ti/ITO, Ti/Ag/Cr/ITO, Ti/Ag/ITO, Ti/Ni/ITO, Ti/Ni/Al/ITO, Ti/Ni, Ti/W/Ti, W x Ti 1−x  (0≦x≦1), W x Ti 1−x /Al(Cu) (0≦x≦1), W x Ti 1−x /Al(Si)(0≦x≦1), W x Ti 1−x /Al(0≦x≦1), or Ti/Cu. The material used for the piezoelectric layer  4  may be, for example, AlN, ZnO, PbTi 1−x Zr x O 3  (0≦x≦1) with or without dopants of La or Mn, LiNbO 3 , LiTaO 3 , PbNb 2 O 6 , Pb 1−x Ca x TiO 3 (0≦x≦1), [Pb(Mg 1/3 Nb 2/3 )O 3 ] x -[PbTiO 3 ] 1−x  (0≦x≦1), BaTiO 3 , K 1−x Na x NbO 3  (0≦x≦1), (Cd,Na)NbO 3 , (Bi,Na)TiO 3 , (Bi,Na,Pb,Ba)TiO 3 , Bi 7 Ti 4 NbO 21 , (Ba 1−x Sr x ) 2 NaNb 5 O 15  (0≦x≦1), (Ba 1−x Sr x ) 2 KNb 5 O 15  (0≦x≦1), 
     a) Pb(Mg 1/2 W 1/2 )O 3 , 
     b) Pb(Fe 1/2 Nb 1/2 )O 3 , 
     c) Pb(Fe 2/3 W 1/3 )O 3 , 
     d) Pb(Ni 1/3 Nb 2/3 )O 3 , 
     e) Pb(Zn 1/3 Nb 2/3 )O 3 , 
     f) Pb(Sc 1/2 Ta 1/2 )O 3 , combinations of the compounds a) to f) with PbTiO 3 , and Pb(Mg 1/3 Nb 2/3 )O 3  with and without excess lead, or polyvinylidene fluoride (PVDF). 
     Alternatively, a further reflection element  6  may be provided on the second electrode  5 , which element comprises either a layer of a material of extremely low acoustic impedance or several layers of alternately high and low impedance. 
     It is also possible for the reflection element  2  to comprise only a single layer, which need not necessarily have a layer thickness of one fourth of the resonance wavelength, or more than three layers. 
     Furthermore, a layer of SiO 2  with a layer thickness of between 30 and 300 nm may be provided above and below a reflection element  2  of porous SiO 2 . 
     Furthermore, a protective layer of an organic and/or inorganic material may be provided over the entire component. The organic material used may be, for example, polybenzocyclobutene or polyimide, and the inorganic material used may be, for example, Si 3 N4, SiO 2 , or Si x O y N z  (0≦x≦1, 0≦y≦1, 0≦z≦1). 
     In a further alternative embodiment, an additional adhesive layer, for example of an acrylate glue or an epoxide glue, is provided between the reflection element  2  and the carrier substrate  1 . The acrylate glue may comprise, for example, acryl or methacryl monomers which polymerize during the adhesion process. 
     At least one first and one second current supply contact may be provided on mutually opposed sides of the electronic component. Current supply contacts used may be, for example, an electroplated SMD end contact of Cr/Cu, Ni/Sn, or Cr/Cu, Cu/Ni/Sn, or Cr/Ni, Pb/Sn, or a bump end contact, or a contact surface. 
     The component manufactured may be, for example, a bulk acoustic wave resonator. Several of these bulk acoustic wave resonators may be joined together into a bulk acoustic wave filter arrangement. 
     FIG. 4 shows a possibility for manufacturing an electronic component according to the invention, where in a first step a resonator unit comprising a first electrode  3 , a piezoelectric layer  4 , and a second electrode  5  is deposited on a substrate layer  13  (step I in FIG.  4 ). The substrate layer  13  may be made, for example, from a ceramic material, a ceramic material with a glass planarizing layer, a glass-ceramic material, silicon, GaAs, or sapphire. A passivating layer of, for example, SiO 2  or glass is additionally provided if silicon or GaAs is used in the substrate layer  13 . The electrodes  3  and  5  are preferably made from a well conducting material of low acoustic damping and may comprise, for example, Ag 1−x Pt x  (0≦x≦1), Pt (50 nm to 1 μm), Ti (1 to 20 nm)/Pt (20 to 600 nm), Ti (1 to 20 nm)/Pt (20 to 600 nm)/Ti (1 to 20 nm), Al, Al doped with a few percents of Cu, Al doped with a few percents of Si, Al doped with a few percents of Mg, Ni, W, Mo, Au, Cu, Ti/Pt/Al, Ti/Ag, Ti/Ag/Ti, Ti/Ag/Ir, Ti/Ir, Ti/Pd, Ti/Ag 1−x Pt x  (0≦x≦1), Ti/Ag 1−x Pd x  (0≦x≦1), Ti/Pt 1−x Al x  (0≦x≦1), Pt 1−x Al x  (0≦x≦1), Ti/Ag/Pt 1−x Al x  (0≦x≦1), Ti/Ag/Ru, Ti/Ag/Ir/IrO x  (0≦x≦2), Ti/Ag/Ru/RuO x  (0≦x≦2), Ti/Ag/Ru/Ru x Pt 1−x  (0≦x≦1), Ti/Ag/Ru/Ru x Pt 1−x /RuO y  (0≦x≦1, 0≦y≦2), Ti/Ag/Ru/RuO x /Ru y Pt 1−y  (0≦x≦2, 0≦y≦1), Ti/Ag/Ru x Pt 1−x  (0≦x≦1), Ti/Ag/Pt x Al 1−x  (0≦x≦1), Pt x Al 1−x /Ag/Pt y Al 1−y  (0≦x≦1, 0≦y≦1), Ti/Ag/Pt y (RhO x ) 1−y  (0≦x≦2, 0≦y≦1), Ti/Ag/Rh/RhO x  (0≦x≦2), Ti/Ag/Pt x Rh 1−x  (0≦x≦1), Rh, Rh/RhO 2 , Ti/Ag/Pt y (RhO x ) 1−y /Pt z Rh 1−z  (0≦x≦2, 0≦y≦1, 0≦z≦1), Ti/Ag x Pt 1−x Ir (0≦x≦1), Ti/Ag x Pt 1−x /Ir/IrO y  (0≦x≦1, 0≦y≦2), Ti/Ag x Pt 1−x /Pt y A 1−y  (0≦x≦1, 0≦y≦1), Ti/Ag x Pt 1−x /Ru (0≦x≦1), Ti/Ag x Pt 1−x /Ru/RuO y  (0≦x≦1, 0≦y≦2), Ti/Ag/Cr, Ti/Ag/Ti/ITO, Ti/Ag/Cr/ITO, Ti/Ag/ITO, Ti/Ni/ITO, Ti/Ni/Al/ITO, Ti/Ni, Ti/W/Ti, W x Ti 1−x  (0≦x≦1), W x Ti 1−x /Al(Cu) (0≦x≦1), W x Ti 1−x /Al(Si) (0≦x≦1), W x Ti 1−x /Al (0≦x≦1), or Ti/Cu. The material used for the piezoelectric layer  4  may be, for example, AlN, ZnO, PbTi 1−x Zr x O 3  (0≦x≦1) with and without dopants of La or Mn, LiNbO 3 , LiTaO 3 , PbNb 2 O 6 , Pb 1−x Ca x TiO 3  (0≦x≦1), [Pb(Mg 1/3 Nb 2/3 )O 3 ] x -[PbTiO 3 ] 1−x  (0≦x≦1), BaTiO 3 , K 1−x Na x NbO 3  (0≦x≦1), (Cd,Na)NbO 3 , (Bi,Na)TiO 3 , (Bi,Na,Pb,Ba)TiO 3 , Bi 7 Ti 4 NbO 21 , (Ba 1−x Sr x ) 2 NaNb 5 O 15  (0≦x≦1), (Ba 1−x Sr x ) 2 KNb 5 O 15  (0≦x≦1), 
     a) Pb(Mg 1/2 W 1/2 )O 3 , 
     b) Pb(Fe 1/2 Nb 1/2 )O 3 , 
     c) Pb(Fe 2/3 W 1/3 )O 3 , 
     d) Pb(Ni 1/3 Nb 2/3 )O 3 , 
     e) Pb(Zn 1/3 Nb 2/3 )O 3 , 
     f) Pb(Sc 1/2 Ta 1/2 )O 3 , combinations of the compounds a) to f) with PbTiO 3  and Pb(Mg 1/3 Nb 2/3 )O 3  with and without excess lead, or polyvinylidene fluoride (PVDF). 
     A reflection element  2  made from an acoustically reflecting substance from the group of polymers and porous substances is provided on the second electrode  5  (step II in FIG.  4 ). The acoustically reflecting substance used may be, for example, an aerogel, a xerogel, a glass foam, a foam-type adhesive, a foamed synthetic resin, or a synthetic resin of low density. The aerogel may be, for example, an inorganic aerogel made of silica gel or porous SiO 2  structures, or an organic aerogel such as, for example, a resorcin-formaldehyde aerogel, a melamine-formaldehyde aerogel, or a phenol-formaldehyde aerogel. The xerogel used may be, for example, an inorganic xerogel such as highly condensed polysylicic acid, or an organic aerogel such as glue or agar-agar. The foamed synthetic resins may be chemically or physically foamed polymers such as, for example, polystyrol, polycarbonate, polyvinylchloride, polyurethane, polyisocyanate, polyisocyanurate, polycarbodiimide, polymethacrylimide, polyacrylimide, acryl-butadiene-styrol copolymers, polypropylene, or polyester. Furthermore, foamed synthetic resins such as, for example, phenol-formaldehyde resins or furane resins may be used, which have a high porosity through carbonization. The synthetic resin of low density used may be, for example, cross-linked polyvinyl ether, cross-linked polyaryl ether, polytetrafluoroethylene, poly(p-xylylene), poly( 2 -chloro-p-xylylene), poly(dichloro-p-xylylene), polybenzocyclobutene, styrol-butadiene copolymers, ethylene-vinylacetate polymers, or organic siloxane polymers. A carrier substrate  1  made from glass, a glass-ceramic material, a glass-ceramic material with a glass planarizing layer, a glass material, silicon, GaAs, or sapphire is fastened on this reflection element  2  by means of the adhesive properties of the material used or by means of an additional adhesive layer of, for example, an acrylate glue or an epoxide glue (step III in FIG.  4 ). If silicon or GaAs is used for the carrier substrate  1 , an additional passivating layer, for example made of SiO 2  or glass, is provided. Then the substrate  13  is mechanically or chemically removed (step IV in FIG.  4 ). 
     If PbTi 1−x Zr x O 3  (0≦x≦1) with and without dopants of La or Mn is used as the material for the piezoelectric layer  4 , an anti-reaction layer of TiO 2 , Al 2 O 3 , or ZrO 2  may be provided between the substrate layer  13  and the first electrode  3 . 
     In an alternative method of manufacturing an electronic component according to the invention, the reflection element  2  is directly deposited on the desired carrier substrate  1 . Subsequently, the resonator unit consisting of a first electrode  3 , second electrode  5  and the piezoelectric layer  4  is provided. The reflection element  2  may alternatively comprise several layers of alternately high and low impedance. 
     In all cases, a protective layer  7  of an organic and/or inorganic material may be provided over the entire component. The organic material used may be, for example, polybenzocyclobutene or polyimide, and the inorganic material may be, for example, Si 3 N 4 , SiO 2 , or Si x O y N z  (0≦x≦1, 0≦y≦1, 0≦z≦1). 
     Alternatively, a reflection element may be provided below and above the resonator unit of the component. The further reflection element  6  either comprises a layer of a material having an extremely low acoustic impedance or several layers of alternately high and low impedance. 
     Furthermore, a layer of SiO 2  with a layer thickness of between 30 and 300 nm may be provided above and/or below a reflection element  2  or  6  of porous SiO 2 . 
     At least one first and one second current supply contact may be provided at mutually opposed sides of the electronic component. Current supply contacts used may be, for example, an electroplated SMD end contact of Cr/Cu, Ni/Sn, or Cr/Cu, Cu/Ni/Sn, or Cr/Ni, Pb/Sn, or a bump end contact, or a contact surface. 
     Embodiments of the invention will be described in detail below, representing examples of how the invention may be realized. 
     Embodiment 1 
     First an adhesive layer of acrylate glue is deposited on a carrier substrate  1  of glass, and a layer of porous SiO 2  is deposited thereon as a reflection element  2 . A first electrode  3  of Pt is deposited on a given portion of the reflection element  2 . A piezoelectric layer  4  of AlN is provided on certain portions of the first electrode  3  and of the reflection element  2 . A second electrode  5  of Al is deposited on certain portions of the piezoelectric layer  4  and of the reflection element  2 . The piezoelectric layer  4  and the two electrodes  3 ,  5  are deposited and structured such that a filter arrangement in accordance with FIG. 2 comprising a total of nine resonator units M 1  to M 5  and N 1  to N 4  is created. Five resonator units M 1  to M 5  are connected in series, and the four further resonator units N 1  to N 4  are connected in parallel to these five resonator units M 1  to M 5 . One terminal of each of the four resonator units N 1  to N 4  is connected to ground potential, whereas the other terminals of the resonator units N 1  to N 4  each lie between a respective pair of the five resonator units M 1  to M 5 . A protective layer  7  Of SiO 2  is provided over the entire filter arrangement. Contact holes to the second electrode  5  are opened through the protective layer  7  by means of etching. Bump end contacts of Cr/Cu are grown in the contact holes. The filter arrangement thus obtained is used as a bandpass filter in mobile telephones. 
     Embodiment 2 
     To realize a filter arrangement with a reflection element  2  comprising several layers, first an adhesive layer of acryl ate glue is deposited on a carrier substrate I of glass, and a bottom layer  10  of porous SiO 2  is deposited thereon. A central layer  11  of Ta 2 O 5  is deposited on the latter layer. An upper layer  12  of porous SiO 2  is subsequently provided on the central layer  11 . A first electrode  3  of Mo is deposited on certain portions of the upper layer  12 . A piezoelectric layer  4  of AlN is provided on certain portions of the first electrode  3  and of the upper layer  12 . A second electrode S of Al is deposited on certain portions of the piezoelectric layer  4  and of the upper layer  12 . The piezoelectric layer  4  and the two electrodes  3 ,  5  are deposited and structured such that a filter arrangement in accordance with FIG. 2 comprising a total of nine resonator units M 1  to M 5  and N 1  to N 4  is created. The five resonator units M 1  to M 5  are connected in series, and the four further resonator units N 1  to N 4  are connected in parallel to these five resonator units M 1  to M 5 . One terminal of each of the four resonator units N 1  to N 4  is connected to ground potential, while the other terminals of the resonator unit N 1  to N 4  lie between respective pairs of the five resonator units M 1  to M 5 . A protective layer  7  of SiO 2  is provided over the entire filter arrangement. Contact holes to the second electrode  5  are opened through the protective layer  7  by means of etching. Bump end contacts of Cr/Cu are grown in the contact holes. The filter arrangement thus obtained is used as a bandpass filter in mobile telephones. 
     Embodiment 3 
     To realize an electronic component with a reflection element  2  comprising several layers, first an adhesive layer of acrylate glue is provided on a glass carrier substrate  1 , and a bottom layer  10  of porous SiO 2  is deposited thereon. A central layer  11  of Ta 2 O 5  is deposited on the latter layer. An upper layer  12  of porous SiO 2  is subsequently provided on the central layer  11 . A first electrode  3  of Pt is provided on the upper layer  12 , and a piezoelectric layer  4  of PbZr 0.35 Ti 0.65 O 3  is deposited on the electrode. A second electrode  5  of Pt/Ti is provided on the piezoelectric layer  4 . The entire component is provided with a protective layer of SiO 2 . In addition, Cr/Cu, Ni/Sn SMD end contacts are fastened to mutually opposed sides of the components so as to serve as current supply contacts. 
     Embodiment 4 
     A bulk acoustic wave resonator is manufactured in that a resonator unit comprising a first electrode  3 , a piezoelectric layer  4 , and a second electrode  5  is provided on an Si substrate layer  13  with a passivating layer of SiO 2 . The first electrode  3  comprises Ti/Pt, whereas the second electrode  5  is made of Pt. The piezoelectric layer  4  comprises AlN. In the next step, a layer of porous SiO 2  serving as the reflection element  2  is provided on the second electrode  5 . A carrier substrate  1  of glass is fastened on this reflection element  2  by means of acrylate glue. Then the Si layer of the substrate layer  13  is etched away. Contact holes for contacting the first electrode  3  are etched into the remaining SiO 2  layer. Then bump end contacts of Cr/Cu are grown in the contact holes. 
     Embodiment 5 
     To manufacture a bulk acoustic wave resonator, a resonator unit comprising a first electrode  3 , a piezoelectric layer  4 , and a second electrode  5  is provided on a substrate  13  of Si with an SiO 2  passivating layer. The first electrode  3  comprises Ti/Pt, while the second electrode  5  is made of Pt. The piezoelectric layer  4  comprises PbZr 0.35 Ti 0.65 O 3 . In the next step, a layer of porous SiO 2  is provided on the second electrode  5  so as to serve as the reflection element  2 . A carrier substrate  1  of glass is fastened on this reflection element  2  by means of acrylate glue. Then the Si layer of the substrate  13  is etched away. Contact holes for contacting the first electrode  3  are etched into the remaining layer of SiO 2 . Then bump end contacts of Cr/Cu are grown in the contact holes. 
     Embodiment 6 
     To manufacture a bulk acoustic wave resonator, a resonator unit comprising a first electrode  3 , a piezoelectric layer  4 , and a second electrode  5  is provided on a substrate  13  of Si with a passivating layer of SiO 2 . The first electrode  3  comprises Ti/Pt and the second electrode  5  comprises Pt. The piezoelectric layer  4  comprises PbZr 0.15 Ti 0.85 O 3  and is manufactured in a spinning process. In the next step, a 30 nm thick layer of SiO 2 , a reflection element  2  of porous SiO 2 , and a 300 nm thick layer of SiO 2  are provided on the second electrode  5 . A carrier substrate  1  of glass is fastened on this assembly by means of an acrylate glue. Subsequently, the Si layer of the substrate  13  is etched away. Contact holes for contacting the first electrode  3  are etched into the remaining layer Of SiO 2 . Then bump end contacts of Cr/Cu are grown in the contact holes. 
     Embodiment 7 
     To manufacture a bulk acoustic wave resonator, a resonator unit comprising a first electrode  3 , a piezoelectric layer  4 , and a second electrode  5  is provided on a substrate  13  of Si with a passivating layer of SiO 2 . The first electrode  3  comprises Ti/Pt, and the second electrode  5  comprises W 0.9 Ti 0.1 /Al(Cu). The piezoelectric layer  4  comprises PbZr 0.35 Ti 0.65 O 3  and is manufactured in a spinning process. In the next step, a 30 nm thick layer of SiO 2 , a reflection element  2  of porous SiO 2 , and a 300 nm thick layer of SiO 2  are provided on the second electrode  5 . A glass carrier substrate  1  is fastened on this assembly by means of an acrylate glue. Then the Si layer of the substrate  13  is etched away. Contact holes for contacting the first electrode  3  are etched into the remaining layer of SiO 2 . Then bump end contacts of Cr/Cu are grown in the contact holes. 
     Embodiment 8 
     To manufacture a bulk acoustic wave resonator, a resonator unit comprising a first electrode  3 , a piezoelectric layer  4 , and a second electrode  5  is provided on a substrate  11  of Si with an SiO 2  passivating layer. The first and second electrode each comprise Ti/Pt. The piezoelectric layer  4  comprises a PLZT layer with the composition PbZr 0.15 Ti 0.85 O 3  with 2% lanthanum doping. In the next step, a 30 nm thick layer of SiO 2 , a reflection element  2  of porous SiO 2 , and a 300 nm thick layer of SiO 2  are provided on the second electrode  5 . A glass carrier substrate  1  is fastened on this assembly by means of an acrylate glue. Subsequently, the Si layer of the substrate  13  is etched away. Contact holes for contacting the first electrode  3  are etched into the remaining layer of SiO 2 . Then bump end contacts of Cr/Cu are grown in the contact holes.