DE102008049541A1 - Ultrasonic transducer for recording ultrasonic images, has monolithic, stacked piezo element which has two electrode layers and piezo ceramic layer arranged between electrode layers - Google Patents

Abstract

The ultrasonic transducer (1) has a monolithic, stacked piezo element (10) which has two electrode layers (12,13) and a piezo ceramic layer (14) arranged between the electrode layers. A photo-structured electrical insulating layer (19) is arranged for selective electrical contacting of the outer electrode and the former electrode layer together and for selective electric insulation of the outer electrode and the latter electrode layer from each other at the surface section. An independent claim is included for a method for manufacturing an ultrasonic transducer.

Description

The The invention relates to an ultrasonic transducer with at least one monolithic, stacked piezoelectric element in the stacking direction an electrode layer, at least one further electrode layer and at least one disposed between the electrode layers Having piezoceramic layer, wherein the electrode layer until to a side surface portion of the piezoelectric element extends and an outer electrode so on the surface portion of the piezoelectric element is arranged such that the outer electrode at the surface portion selectively with the electrode layer electrically connected and on the surface portion selectively electrically isolated from the further electrode layer is. In addition to the ultrasonic transducer with the monolithic piezoelectric element be a method of manufacturing the ultrasonic transducer as well a use of the ultrasonic transducer specified.

An ultrasonic transducer of the type mentioned is, for example RL Goldberg et al., IEEE Ultrasonic Symposium, 1993, pp. 1103-1106 known. The ultrasonic transducer is a so-called 2D ultrasonic transducer. In the known 2D ultrasonic transducer 3 × 43 individual piezo elements are arranged to a piezo element matrix. The piezoelectric elements are used to convert sound waves into an electrical signal. Each of the piezoelectric elements has a multilayer capacitor structure with a stack of capacitor elements arranged one above another and electrically connected in parallel. Each of the capacitor elements has a piezoelectric layer. On opposite major surfaces of the piezoelectric layer electrode layers are arranged. In the stack adjacent capacitor elements each have a common electrode layer. Piezoelectric material of the piezoelectric layers is lead zirconate titanate (PZT). A stack height of the stack is, for example, 660 μm. A footprint of the stack is 370 μm × 3,500 μm.

From the US 5,329,496 is an ultrasonic transducer with piezo elements in a monolithic multilayer construction known. To produce the piezoelectric elements, for example, green ceramic films with PZT, which are printed in a screen printing process with a silver-palladium paste, are stacked on top of one another, debinded and sintered together. The result is a stack in which electrode layers (inner electrodes) made of silver-palladium and piezoelectric layers of PZT are arranged alternately one above the other to form a monolithic stack. A stack height is 500 .mu.m to 1000 .mu.m.

to electrical contacting of the electrode layers are in the stacking direction adjacent electrode layers alternately on two electrically from each other isolated, lateral surface sections of the stack led, in each case an outer metallization is appropriate. Each of the electrode layers of a capacitor element does not extend over the entire main surface the respective piezoelectric layer. The areas with the two External metallizations are used as contact zones of the piezoelectric element designated. In the region of these contact zones are the piezoelectric layer and thus the piezoelectric element piezoelectrically inactive. By the electric Control of the electrode layers is in the piezoelectric Layer coupled an electric field, which is used to deflect the piezoelectric layer leads. In a piezoelectric Inactive region of the piezoelectric layer is thereby an electric Field coupled, which differs significantly from the electric field, that in a piezoelectrically active region of the piezoelectric Layer is coupled. The piezoelectrically active region of piezoelectric layer is located directly between the adjacent ones Electrode layers. In the electrical control of the electrode layers, So when polarizing and / or during operation of the piezoelectric element comes it due to the different electrical fields to different Deflections of the piezoelectric layer in the piezoelectrically active Area and in the piezoelectrically inactive area.

The known ultrasonic transducers are used in medical diagnostics used. In this case, the ultrasonic transducer acts as an antenna, the sends or receives short sound pulses. A thickness (stack height) of the piezo elements determines a Working frequency of the antenna. In the case of piezo elements in monolithic Multilayer construction is the working frequency between 1 MHz and 10 MHz. A lateral dimension of the piezo elements (length and a width) represent a measure of a lateral Resolution of the antenna. The smaller a stack length and the smaller a stack width of the piezo elements, the more Piezo elements can per unit area in one corresponding sensor head are placed and the higher is therefore the resolution. A high resolution is necessary for creating three-dimensional images.

A small dimensioning of the piezo elements with simultaneously high efficiency is possible with an ultrasonic transducer with fully active piezo elements. From the WO 2005/075113 A1 Such an ultrasonic transducer is known. A lateral stack dimension of the piezo elements is for example 250 μm. The stack height amounts, for example, to 500 μm. In the piezoelectric element stack, the electrode layers cover the adjacent piezoceramic layer over the entire surface. This results in a high piezoelectrically active volume of the piezoelectric element.

Problematic however, with this ultrasonic transducer, there is a need to contact the electrode layers individually. This succeeds here by Electrophoretic deposition of insulating material on a surface portion of the piezoelectric element, on which the electrode layer, during the deposition is controlled, to be electrically isolated. This method is time consuming.

task The present invention is to show how a simple Single contact of the electrode layers of a piezoelectric element an ultrasonic transducer can be realized.

to Solution of the task is an ultrasonic transducer with at least given a monolithic, stacked piezoelectric element, in the stacking direction, an electrode layer, at least one further Electrode layer and at least one between the electrode layers arranged piezoceramic layer, wherein the electrode layer to a side surface portion of the piezoelectric element extends, an outer electrode so on the surface portion of the piezoelectric element is arranged such that the outer electrode at the surface portion selectively with the electrode layer electrically conductively connected and selective on the surface portion is electrically isolated from the further electrode layer. Of the Ultrasonic transducer is characterized in that the selective electrical contacting of the outer electrode and the electrode layer together and for selective electrical insulation of the outer electrode and the further electrode layer from each other at the surface portion arranged a photostructured electrical insulation layer is.

Preferably the further electrode layer is also electrically contacted accordingly or isolated. According to a particular embodiment the further electrode layer extends to another one lateral surface portion of the piezoelectric element. A from the outer electrode electrically isolated further outer electrode is arranged on the further surface portion of the piezoelectric element, that the further outer electrode on the further surface portion selectively electrically conductively connected to the further electrode layer and at the further surface portion selectively from the electrode layer is electrically isolated. For selective electrical contacting the further outer electrode and the further electrode layer with each other and for selective electrical isolation of the others Outer electrode and the electrode layer from each other at the further surface portion another photostructured electrical insulation layer is arranged. The insulation layers For example, have a layer thickness of 5 microns up to 10 μm. Higher layer thicknesses up to 20 μm are also conceivable.

to Solution to the problem is also a method of manufacturing of the ultrasonic transducer indicated with the following process steps: a) providing a ceramic green bar with alternately one above the other arranged piezoceramic green sheets and in between arranged metal layers, b) temperature treatment of the green bar, wherein a ceramic bar with a down to a bar surface portion extending bar electrode layer, at least one other up to another bar surface section extending further bar electrode layer and an intermediate the bar-electrode layers arranged bar-piezoceramic layer c) contacting the bar electrode layer by applying a bar metallization on the bar surface section the ceramic bar, and d) cutting the ceramic bar into one Plurality of piezo elements. The ceramic bar and the ceramic bar are cuboid. They are available as a cuboid.

In the same way with respect to the contacting of the other Bar electrode layer proceeded. Before cutting the ceramic bar the following further process step is carried out: e) further contacting the further bar electrode layer further application of a further bar metallization on the other Bolt surface section of the ceramic latch.

The Applying the metallization is done for example by sputtering. The resulting metallization webs have, for example, a web strength from 2 μm to 5 μm.

One Spray method in which, for example, one at low Temperature sintering metal is applied, is also conceivable. Such a metal is for example silver with nano-particles. In this case, for example, web thickness of the metallization from 5 .mu.m to 10 .mu.m.

The resulting ceramic bars can be divided into individual piezo elements. These individual piezo elements are then placed on a support and fixed, for example by gluing. Due to the small dimensions of the piezoelectric elements (less than 1 mm), it is advantageous to first place the ceramic bars on a support, for example on a support of an ultrasonic sensor head, and only then to divide. The ceramic bar can be aligned much easier compared to the isolated piezo elements. According to a particular embodiment, therefore, after contacting and further contacting and before Zertei len performed an application of the ceramic bar on a support. Here, too, attaching by gluing offers particular.

To the Parting of the ceramic bar is preferably sawn. The saw cut creates trenches. The Trench width of the trenches can be determined by variation adjust the sawing gap. This makes it possible a desired local resolution of the ultrasonic transducer to achieve.

in the With regard to contacting, according to a special embodiment before applying the bar metallization producing a photostructured bar insulation layer performed on the bar surface section and / or before further application of the further bar metallization further producing a further photostructured bar insulation layer performed on the other bar surface section. For producing the bar insulating layer on the bar surface portion and / or for producing the further bar insulation layer further Bar surface section is in particular an application of a Photosensitive layer performed. In the angry Photosensitive layer is exposed by means of at least one Contact opening generated. Through the contact opening becomes the electrode layer to be contacted at the corresponding bar surface portion exposed.

The described single contact is particularly suitable for fully active piezo elements. Limit in a particular embodiment the electrode layer and the further electrode layer, the piezoceramic layer essentially full surface. This leads to a maximum possible piezoelectrically active volume of the piezoceramic layer. In addition, this is associated with improved frequency response.

Especially the piezoelectric element has a range of 100 μm up to 500 μm selected lateral stack dimension on. The lateral dimension is a length or width of the piezoelectric element.

The Piezoelement preferably has a plurality of electrode layers, a plurality of further electrode layers and a plurality of piezoceramic layers. The piezoelectric element is in multilayer construction in front. The individual piezo elements have in particular one from the range of 200 microns to 1000 microns, and preferably selected from the range of 500 microns to 1000 microns stack height on. It is advantageous, for example, if the piezoelectric element in Multilayer construction an odd number of internal electrodes (electrode layers and further electrode layers). The number of internal electrodes is for example five or seven. In this Case, the top and bottom electrode layers (outermost Electrode layers) with the same electrical potential. Thus, elaborate insulation between a top Position as adjustment layer for ultrasonic emission and the carrier (Base plate) avoided, on which the piezo elements are glued.

in the In view of a good resolution with the ultrasonic transducer is to be achieved, the following features are particularly advantageous: A plurality of piezoelectric elements is on a support next to each other and spaced apart by trenches. Between The piezo elements are trenches. The trenches in particular have a range from 20 microns to 60 μm selected trench width. For example the trench width is 40 μm. Advantageously the trenches contain electrical insulation material. Thereby an electrical insulation of adjacent piezoelectric elements is improved.

According to one special embodiment is a plurality of piezoelectric elements as a two-dimensional matrix arranged on the carrier. With the described manufacturing process Such a matrix is particularly easy to produce.

Of the Ultrasonic transducer is used in particular for receiving an ultrasound image used. Preferably, ultrasonic transducer is used in the medical Diagnostics or in non-destructive materials testing (Ultrasonic testing) used.

• – Durch die Erfindung sind vollaktive Piezoelemente für einen Ultraschallwandler zugänglich. Vollaktive Piezoelemente zeigen ein im Vergleich zu einem Piezoelement mit piezoelektrisch aktiven und piezoelektrisch inaktiven Bereichen verbessertes Frequenzverhalten.
• – Aufgrund der vollflächig auf eine Piezokeramikschicht aufgebrachten Elektrodenschichten resultiert eine hohe Schichthomogenität.
• – Durch die elektrische Kontaktierung auf der Stufe eines Keramik-Riegels ist eine Nutzen-Verarbeitung möglich. Die Kontaktierung ist nicht nur kostengünstig. Die Kontaktierung erfolg insbesondere mit hoher Genauigkeit.

In summary, the following advantages of the invention should be emphasized:

• - Fully active piezoelectric elements for an ultrasonic transducer are accessible by the invention. Fully active piezoelectric elements show an improved frequency response compared to a piezoelectric element with piezoelectrically active and piezoelectrically inactive regions.
• - Due to the entire surface applied to a piezoceramic layer electrode layers results in a high layer homogeneity.
• - By the electrical contacting at the level of a ceramic bar a benefit processing is possible. The contact is not only inexpensive. The contacting succeeds in particular with high accuracy.

Based an embodiment and the associated Figures, the invention is explained in detail. The Figures are schematic and are not to scale Illustrations

1A shows a piezoelectric element of the ultrasonic transducer in a lateral cross-section.

1B shows a section of the piezoelectric element in a lateral cross section.

2 shows a section of a piezoelectric element array of an ultrasonic transducer in a plan view.

3 shows a method of manufacturing the piezoelectric element.

The ultrasonic transducer 1 is a 2D ultrasound antenna. This 2D ultrasonic antenna consists of 64 × 64 individual piezo elements 2 , The piezo elements are a 64 × 64 elements containing piezo element matrix 110 summarized ( 2 ). The plurality of piezo elements is on a common carrier 2 arranged. Among other things, the carrier serves the electrical control of the piezoelectric elements.

Each of the piezoelectric elements is a monolithic piezoelectric element in multilayer construction, in the stacking direction 11 at least one electrode layer 12 , at least one further electrode layer 13 and at least one piezoelectric layer in the form of a piezoceramic layer arranged between the electrode layers 14 having. In a first embodiment, five piezoceramic layers and six electrode layers or further electrode layers are stacked on top of each other (cf. 3 ). In a further embodiment, four piezoceramic layers and five inner electrode layers are stacked on top of each other (cf. 1A ). The stack ends with two piezoelectrically inactive layers 21 from a ceramic.

The Piezoceramic layers are made of a lead zirconate titanate (PZT). The electrode layers are made of a silver-palladium alloy. A base of piezoceramic layers and a base the electrode layers are square and substantially the same. This means that the electrode layer and the further electrode layer the interposed piezoceramic layer over the entire surface limit. The piezo elements are fully active.

An edge length of the base area of each of the piezo elements and thus their lateral dimension 101 is about 100 microns. The base of the piezoelectric element is 100 .mu.m.times.100 .mu.m. The stack height 102 along the stacking direction 11 the piezoelectric elements is about 500 microns.

The electrode layer 12 a piezoelectric element extends to the lateral surface portion 15 of the piezoelectric element. The further electrode layer 13 is also led to this surface section. At this surface portion is the electrode layer with the external electrode applied 17 electrically contacted. The outer electrode is formed by a metallization path applied to the surface section.

The outer electrode is at the surface portion of the further electrode layer 13 electrically isolated. For this purpose, photostructured insulation layer is on the surface portion 19 arranged.

The further electrode layer 13 a piezoelectric element extends to the further lateral surface portion 16 of the piezoelectric element. The electrode layer 12 is also guided to this other surface section. At this further surface portion is the further electrode layer with the applied further outer electrode 18 electrically contacted. The further outer electrode is formed by a further metallization web applied to the further surface section.

The production process is in 3 indicated. The right part of the 3 represents a respective section along the connecting line AA. The procedure for producing the ultrasonic transducer is as follows: A ceramic green block with green sheets stacked on top of one another and laminated metal layers is sawn into green bars. These green bars are debinded and sintered. There are corresponding ceramic rule 22 , These ceramic bars each have at least one up to a side bar surface portion 26 extending bar electrode layer 23 at least one further bar electrode layer extending to the side bar surface portion 24 and a bar-piezoceramic layer disposed between the bar electrode layers 25 on.

The bar electrode layers are electrically contacted. For this purpose, a photostructurable insulation layer is formed on the bar surface section 27 applied and opened to the bar electrode layer. In the applied insulating layer is a contact hole 28 produced by photostructuring, for example by exposing and developing the insulating layer. For this purpose, the ceramic bar is measured optically before the application of the insulating layer. At the point at which the electrode layer is to be contacted, the contacting opening is produced.

Subsequently, electrically conductive material is deposited, so that the contacting window is filled with the electrically conductive material. The result is a metallization 29 with the contact with the electrode layer. The deposition of the electrically conductive material takes place from the gas phase by means of sputtering. Alternatively, the spraying process is carried out, in which nanoparticles be applied from silver.

In the same way, with regard to the contacting of the further bar electrode layer on the further bar surface section 30 proceed. There will be another metallization track 31 applied for contacting the other bar electrode layers.

The resulting ceramic bars are at a distance of about 40 microns parallel to each other on the support 2 glued. Subsequently, the ceramic bars are sawed transversely to their parallel orientation. In 3 is this division by the reference numerals 32 indicated. The sawing takes place in such a way that sawing gaps with a gap width of approx. 40 μm are formed. This results in individual piezoelectric elements, which are arranged side by side on the common carrier and separated by trenches with a trench width of about 40 microns. In a first embodiment, the trenches are filled with a plastic. In another embodiment, the trenches are filled with a ceramic.

With The described ultrasonic transducer can be an active component surface (Area of the piezo element array on the carrier) estimated at over 72% (with 2 × insulation layers each with about 15 microns, 2 × Metallisierungsbahnen each with about 5 microns web thickness and a trench width of 40 μm).

The The result is an ultrasonic transducer with the piezo element array. The piezo element array is used in medical technology. It comes in a sensor head of an ultrasonic transducer device Commitment.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - US 5329496 [0003]
• WO 2005/075113 A1 [0006]

Cited non-patent literature

• Goldberg, RL et al., IEEE Ultrasonic Symposium, 1993, pp. 1103 to 1106 [0002]

Claims (16)

Ultrasonic transducer ( 1 ) with - at least one monolithic, stacked piezoelectric element ( 10 ), in the stacking direction ( 11 ) an electrode layer ( 12 ), at least one further electrode layer ( 13 ) and at least one arranged between the electrode layers piezoceramic layer ( 14 ), wherein - the electrode layer extends as far as a lateral surface section ( 15 ) of the piezoelectric element extends, - an outer electrode ( 17 ) is arranged on the surface portion of the piezoelectric element, that the outer electrode at the surface portion selectively electrically connected to the electrode layer and the surface portion selectively electrically insulated from the further electrode layer, characterized in that - for selective electrical contacting of the outer electrode and the electrode layer with each other and selective electrical insulation of the outer electrode and the further electrode layer from each other at the surface portion of a photostructured electrical insulation layer ( 19 ) is arranged. Ultrasonic transducer according to Claim 1, in which - the further electrode layer extends as far as a further lateral surface section ( 16 ) of the piezoelectric element extends, - a further external electrode electrically isolated from the outer electrode ( 18 ) is arranged on the further surface portion of the piezoelectric element in such a way that the further outer electrode is selectively electrically conductively connected to the further electrode layer at the further surface section and selectively electrically insulated from the electrode layer at the further surface section, and - for selective electrical contacting of the further outer electrode and the further electrode layer with each other and for the selective electrical insulation of the further Au ßenelektrode and the electrode layer from each other on the further surface portion a further photostructured electrical insulation layer is arranged. Ultrasonic transducer according to claim 1 or 2, wherein the electrode layer and / or the further electrode layer the Limit piezoceramic layer substantially over the entire surface. Ultrasonic transducer according to one of claims 1 to 3, wherein the piezoelectric element one from the range of 100 microns up to 500 μm selected lateral stack dimension having. Ultrasonic transducer according to one of claims 1 to 4, wherein the piezoelectric element has a plurality of electrode layers, a plurality of further electrode layers and a plurality having piezoceramic layers. Ultrasonic transducer according to one of claims 1 to 5, wherein the piezoelectric element one from the range of 200 microns to 1000 microns and in particular one from the range of 500 microns up to 1000 microns selected stack height has. Ultrasonic transducer according to one of claims 1 to 6, wherein a plurality of piezo elements on a support ( 2 ) are arranged side by side and spaced apart by trenches. An ultrasonic transducer according to claim 7, wherein said plurality is arranged as a two-dimensional matrix on the carrier. Ultrasonic transducer according to claim 7 or 8, wherein the trenches a from the range of 20 microns to 60 microns selected trench width. Ultrasonic transducer according to one of the claims 7 to 9, wherein the trenches comprise an insulating material. Method of manufacturing an ultrasonic transducer according to one of claims 1 to 10, with the following process steps: a) Providing a ceramic green bar with alternately one above the other arranged piezoceramic green sheets and in between arranged metal layers, b) tempering the green bar, wherein a ceramic bar with a down to a bar surface portion extending bar electrode layer, at least one further extending to another latch surface portion another bar electrode layer and one between the bar electrode layers arranged bar-piezoceramic layer arises, c) contact the bar electrode layer by applying a bar metallization at the bar surface portion of the ceramic bar, d) Parting the ceramic bar into a plurality of piezo elements. The method of claim 11, wherein prior to dicing the ceramic bar, the following further process step carried out becomes: e) further contacting the further bar electrode layer by further application of another bar metallization on another latch surface portion of the ceramic latch. The method of claim 12, wherein after contacting and further contacting and before splitting an application carried out of the ceramic bar on a support becomes. Method according to one of claims 11 to 13, wherein before applying the bar metallization generating a photostructured bar insulation layer on the bar surface portion is carried out and / or before further application the further bar metallization Wei teres generating another photostructured bar insulation layer at the further bar surface section is carried out. The method of claim 14, wherein for generating the Bolt Insulation Layer at Bar Surface Section and / or for producing the further bar insulation layer further Bar surface section applying a photosensitive Layer is carried out and in the photosensitive Layer by exposure at least one contact hole is produced. Use of the ultrasonic transducer according to one of Claims 1 to 10 for receiving an ultrasound image.