EP2283935A1 - Ultrasound converter system and method for its operation - Google Patents

Abstract

The system has a set of electrodes (2) arranged discrete to each other on a surface of an electrically non-conductive or semi-conductive substrate (1). Each electrode is formed as a metallic thin layer. The electrode with a feedthrough (4) is led into a substrate rear side and connected to an electrical voltage source at the rear side via an electrical contact surface. An active layer (3) made of piezoelectric material is applied on a surface of the electrodes. The active layer is connected to an electrode (8) and to a pole or mass potential of the source in an electrically conductive manner. An independent claim is also included for a method for emitting ultrasonic waves with an ultrasonic transducer system.

Description

The invention relates to an ultrasonic transducer system and method for its operation. In particular, ultrasonic waves with very high frequencies can be emitted and used, for example, for the non-destructive testing of workpieces or components. This allows a resolution in the range of 10 microns can be achieved, so that even very small reflectors, such. Defects, cracks, voids or delaminations are detectable.

Since very small structures are to be detected with the invention, a high resolution is required, which is only possible by using ultrasound at very high frequencies. Frequently, an application of ultrasonic transducers is required in which structures are to be detected spatially resolved in the volume of bodies and the ultrasonic transducer should not be placed on the surface of the body and moved over its surface. This requires a targeted influencing of the direction in which sound waves are to be emitted by the ultrasound transducer. It has been common in recent years to use multi-element ultrasound transducers for such applications.

Since ultrasound is to be used at a very high frequency, miniaturization is required. It is also noteworthy that a targeted emission direction of emitted sound waves is often required. The frequencies in the middle to upper megahertz range also require a high resolution, ie a very small area, from which ultrasonic waves have to be emitted. But this is to be considered for the guidance of the electrical leads.

It is therefore an object of the invention to propose ways in which ultrasonic waves with increased frequency and high resolution can be emitted in different directions and detected again.

According to the invention, this object is achieved with an ultrasonic transducer system having the features of claim 1. It can be operated by a method according to claim 9. Advantageous embodiments and further developments of the invention can be realized with features described in the subordinate claims.

An inventive ultrasonic transducer system is designed so that on a surface of an electrically insulating or semiconductive substrate Discrete formed to each other electrodes are formed as a metallic thin film. In this case, each electrode is individually connected to a voltage source via an electrically conductive through-hole guided through the substrate.

On the surface of the substrate on which these electrodes are formed, at least one active layer formed of a piezoelectric material is formed. This one or more active layer (s) is / are then electrically connected to at least one further electrode and thus to the other pole of the high-frequency voltage source or the ground contact.

As a result, an active layer assigned to the respective electrode or a surface area of an active layer can be excited with the electrodes present directly on the surface of the substrate, which are each individually electrically controllable, in order to emit ultrasonic waves from this position.

In this case, the control can take place such that a time offset by a specific phase shift, in which electrical voltage is applied to the active layer via these electrodes and an electric current flows, influences the direction with which ultrasonic waves are emitted from the respective position. be achieved.

By applying an electrical voltage, the piezoelectric active material is excited to high-frequency mechanical vibrations, which have then been placed as ultrasonic waves, possibly after coupling into a body on the system is, spread. In this case, the activation of the individual discretely arranged electrodes can be carried out in such a way that the sound waves emitted in each case by these surface regions on which the electrodes are arranged can be influenced in a targeted manner. If electrodes arranged on the outer edge are actuated offset in time from the electrodes arranged successively further inwardly, a focused acoustic emission is possible. However, it is also possible to achieve a sound emission directed at a certain angle, deviating from 90 ° to the surface of the active layer (s), by a subsequent subsequent activation of electrodes.

By a time-delayed activation of the electrodes, it is possible to influence the respective direction of the sound waves emitted there, since the individual sound waves emitted in the area of electrodes are superimposed in a specific direction to form a resulting wavefront. For the emission of sound waves with the largest possible angles, the center distance of discrete juxtaposed electrodes should be less than half the wavelength of the sound waves in a material or body into which the sound waves are emitted. The wavelength depends on the speed of sound in the material and the frequency of the sound waves. The wavelength decreases with increasing frequency. This also requires miniaturization of the ultrasonic transducers, which can be achieved with a system according to the invention and the advantageous electrical contacting, even with conventional connection techniques.

The arranged on the surface of the substrate Electrodes can form a series, line, ring or matrix arrangement. The respective arrangement spatially limits the possible acoustic emission. In the case of a series or line arrangement, for example, the influencing of the sound emission direction can take place only in one spatial plane. In matrix or ring arrangements, a three-dimensional full influence can be achieved.

Ultrasonic transducers are also commonly used for testing and diagnostic purposes. The emitted ultrasonic waves are reflected in an adjacent material or material at defects, interfaces or the back of a body to be tested. A part of the reflected sound waves again hits the respective ultrasonic transducer. The sound pressure of these reflected sound waves causes mechanical deformation of the piezoelectric layer, which are converted by the layer into correspondingly proportional electrical voltage signals. By evaluating the amplitudes and the time profiles of the individual measurement signals thus acquired, a spatially resolved image of the internal structure of an examined body can be reconstructed by calculation.

In particular, because of the required miniaturization, it is advantageous to form the large number of electrically conductive connections to the electrodes by means of vias (via's). These can, as already mentioned, be passed through the substrate. In addition, however, further plated-through holes can be used, which are guided as electrically conductive connections through one or more electrically nonconductive layer (s). This layer (s) can be on the back of the substrate, that is, on the side opposite to the side on which the electrodes are formed. Between or on these layers, electrical conductor tracks, which can be used to widen contact surfaces arranged on the rear side, may be present. On the outwardly facing electrically non-conductive layer, the contact surfaces may form a widened connection structure in which these contact surfaces are distributed on a surface that is larger than the area of the active layer (s) on the front side of the substrate. As a result, an electrical contact with conventional connection techniques, such as soldering, wire bonding or gluing is possible.

Various materials for the substrates can be used for the production of systems according to the invention. These may be, for example, semiconductor materials (preferably monocrystalline silicon), ceramics, glass or polymers.

The electrodes on the surface of the substrate can be applied as metallic thin films. The structuring can be carried out by known methods additively (via change masks or adhesive masks) or subtractive (etching). Suitable metals are copper, gold, aluminum, platinum or multilayer systems, such as e.g. a Cr-Au, Ni-Au or Ti-Cu-Au. There should be good adhesion to the substrate and the active layer (s).

For the active layer (s), any desired piezoelectric materials such as AlN, ZnO or PZT can be used. Again, an order can be made by physical vapor deposition. For the production of the plated-through holes through a substrate, the openings can be formed by reactive ion etching (DRIE), plasma etching, wet-chemical etching or by laser ablation. After the formation of the openings whose inner walls can be metallized and / or filled with an electrically conductive material. The metallization can be applied by physical vapor deposition, which can be galvanically enhanced if necessary.

Filling with an electrically conductive material can also be done with such a vapor deposition, but also by screen printing. In this case, a metal or an electrically conductive polymeric material can be introduced in openings.

The already mentioned electrically non-conductive layers can also be applied as thin layers to the substrate. These may be, for example, suitable oxide or nitride layers. Through-connections may also be present in the electrically non-conductive layers with which the conductor tracks in the different planes can be electrically conductively connected. However, conventional multilayer substrates (for example printed circuit boards, ceramic multilayer circuits) with corresponding interconnect structures can also be used for this purpose.

In a system according to the invention, there is the possibility that an active layer covers all electrodes formed on the surface of the substrate. In a further alternative, however, each electrode can also be assigned its own active layer be. At least the electrodes should be designed so that no electrical current flow from one electrode to another electrode is possible.

The total thickness of the substrate, including the plated-through wiring planes, would be significantly greater than the wavelength of the ultrasound in the substrate. Since the piezoelectric material vibrates mechanically in both directions, the backward emitted sound waves should be absorbed in the substrate. Possible reflections in the substrate material should not hit the piezoelectric active layer again in order to avoid undesired interference signals.

The individual electrodes formed on the substrate surface should, depending on the selected geometric configuration, have a width which is smaller than the wavelength of the sound waves in a material into which the sound waves are emitted.

The further electrode (s) may be formed on an active layer. This then forms, at least in some areas, the surface of the element from which ultrasonic waves are emitted.

When using a system according to the invention, it is possible to proceed in such a way that a pulsed electrical voltage is applied to the electrodes. Preferably, there is a single pulse, which can be carried out repeatedly with time interruptions. In periods when no sound waves are emitted, a detection of reflected sound waves can take place.

With the invention, ultrasound can be emitted and detected at frequencies of at least 30 MHz.

The electrically conductive connections of the system for connection to a voltage source can be realized at the contact surfaces in an expanded arrangement at the rear side of the substrate with known technologies. This can e.g. by soldering, wire bonding or gluing (e.g., with electrically conductive adhesive).

The ultrasonic transducer systems according to the invention achieve both a higher lateral and a low resolution in the micrometer range. New areas of application, such as an effective nondestructive testing in electronics manufacturing, can be developed.

The invention will be explained in more detail with reference to examples.

• Figur 1 eine schematische Schnittdarstellung eines Beispiels eines erfindungsgemäßen Systems;
• Figur 2 eine schematische Schnittdarstellung eines weiteren Beispiels;
• Figur 3 eine Linienanordnung von Elektroden und
• Figur 4 eine Matrixanordnung von Elektroden.

Showing:

• FIG. 1 a schematic sectional view of an example of a system according to the invention;
• FIG. 2 a schematic sectional view of another example;
• FIG. 3 a line arrangement of electrodes and
• FIG. 4 a matrix arrangement of electrodes.

With the representation of FIG. 1 It is clear that on a surface of a substrate 1 electrodes 2 (here only one electrode 2 shown) is formed are. These can be electrically contacted via the through-hole 4 guided through the substrate 1 to the rear side, with an electrical voltage source (not illustrated). For this purpose, an electrical contact surface 9 is formed on the back with a metallization, which can be used for soldering or wire bonding or for any other means of connection.

On the electrodes 2, an active layer 3, here made of aluminum nitride applied, which in turn is covered by a further electrode 8. The further electrode 8 serves to connect to the ground potential. When an electrical voltage is applied between the electrodes 2 and 8, the active layer 3 is vibrated in the surface area of the electrodes 2, which propagate on contact with a body to be tested or a coupling medium as an ultrasonic wave. In pauses in which no electrical voltage is applied between electrodes 2 and 8, a time-resolved detection of measurement signals between electrodes 2 and 8 as a result of reflected back sound waves can take place.

At the in FIG. 2 As shown, a possible widening of electrical connection structures should be clarified.

In this case, electrodes 2 are again discretely and electrically insulated from one another on a surface of the substrate 1. On the electrodes 2, an active layer 3 of piezoelectric material, which is covered with a further electrode 8, is present.

Through the substrate 1 are to each individual electrode 2 each have their own through-hole 4 guided to the back of the substrate 1. On this back, six electrically non-conductive layers 6.1 to 6.6 are formed as a multi-layer structure in this example. On the electrically insulating layers 6.1 to 6.5 conductor tracks 7 are formed, which are electrically conductively connected by means of the plated-through holes 5 in the electrically non-conductive layers (6.1 to 6.6) with contact surfaces 10. Thus, it can be seen that with a small area that can be used for the emission of sound waves, due to the widening, a much larger area for electrical connections at the rear can be obtained.

With the Figures 3 and 4 Examples of arrangements and configurations of electrodes 2 on a system according to the invention are shown.

When in FIG. 3 1, strip-shaped electrodes 2 are formed on the surface of a substrate 1 in a series arrangement or line arrangement. The maximum possible center distance of the elements determines the maximum possible width of the individual strip-shaped electrodes (2).

At the in FIG. 4 shown matrix arrangement, the electrodes 2 are formed with a square surface, each having the same area size and equal distances from each other. The maximum possible center distance of the electrodes 2 determines the maximum possible side lengths of the individual electrodes (2).

However, it is also possible to use other geometric electrode surface forms than those shown here. It is also possible the size and / or the distances of electrodes 2 in a series or matrix arrangement to vary.

Claims (12)

Ultrasonic transducer system in which on a surface of an electrically nonconductive or semiconducting substrate (1) discretely arranged electrodes (2) formed as a metallic thin film and each individually with vias (4) led to the back of the substrate and at the substrate back over a contact surface ( 9) are connected to an electrical voltage source; at least one active layer (3) formed of a piezoelectric material is formed on the surface of the electrodes (2), which is electrically conductively connected to at least one further electrode (8) and thus to the other pole of the voltage source or the ground potential of the voltage source , System according to claim 1, characterized in that at least one electrically non-conductive layer (6.1 to 6.6) is formed on the rear side of the substrate (1), which is opposite to the surface on which the electrodes (2) are formed,
between or on which / which electrical conductor tracks (7) are present, which are guided by means of further plated-through holes (5) through which the electrically nonconductive layer (s) (6.1 to 6.n) are electrically conductive with contact surfaces (10 ) are connected on the back side of the substrate (1) and the contact surfaces (10) are distributed on a surface which is larger than the area of the active layer (s) (3) on the front side of the substrate (1) is. System according to claim 1 or 2, characterized in that the electrodes (2) form a series arrangement, a line arrangement, a ring arrangement or a matrix arrangement. System according to one of the preceding claims, characterized in that an active layer (3) covers all electrodes (2) formed on the surface of the substrate (1). System according to one of the preceding claims, characterized in that the substrate (1) has a thickness which is greater than the wavelength of the emitted sound waves in the substrate material. System according to one of the preceding claims, characterized in that the electrodes (2) have a width which is smaller than the wavelength of the sound waves in a material into which the sound waves are emitted. System according to one of the preceding claims, characterized in that each individual electrode (2) is assigned a separate active layer (3) and formed thereon. Element according to one of the preceding claims, characterized in that the further electrode (s) (8) is or are formed on an active layer (3). A method for emitting ultrasonic waves with a system according to any one of the preceding claims, characterized in that for influencing the ultrasonic emission direction electrical voltage with a time offset to individual electrodes (2) and electrodes (8) is applied. A method according to claim 9, characterized in that ultrasonic waves are emitted at a frequency of at least 30 MHz. Method according to one of claims 9 or 10, characterized in that reflected ultrasonic waves are detected time-resolved and with the detected measuring signals a spatially resolved image of the internal structure of a body, have been detected in the ultrasonic waves and reflected from there, calculated. Method according to one of claims 9 to 11, characterized in that electrical voltage is applied as a single pulse.

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