METHOD FOR MANUFACTURING A MICROMECHANICAL ULTRASOUND TRANSDUCER AND ULTRASOUND TRANSDUCER

Description

[0001] The invention relates to a method for manufacturing a micromechanical ultrasound transducer and an ultrasound transducer according to the first and ninth claims.

[0002] Micromachined ultrasonic transducers (MUTs) consist of mechanical and electrical elements, as well as electromechanical transducers. The geometry of the mechanical components (e.g., a diaphragm) determines the transducer's natural frequencies. Electromechanical transducers transform electrical energy into mechanical energy and vice versa, for example, through electrostatics, piezoelectricity, or other transducer methods. The electrical components are electrical conductors. In state-of-the-art MUTs, these basic components are defined in a layout.

[0003] The chip size and electrical interconnection of MUTs are defined in the lithography layers. After fabrication using microtechnologies at the wafer level, the chips are separated, for example, by sawing. The chip size for a MUT layout is fixed, and the electrical interconnection of the individual converter elements on the chip is not adaptable.

[0004] Document US 7,531,371 B2 describes a process involving multi-area arrays that differ in their spatial arrangement, where microdevices are placed on one or more wafers. The individual chips are then separated and positioned on a substrate. Subsequently, the connections between the individual chips are fabricated. A disadvantage is that the electronic configuration is fixed in the layout and cannot be modified afterward.

[0005] The publication EP 3 684 081 B1 describes a manufacturing process for multiple MEMS transducers. A large number of MEMS transducers are arranged on a wafer. These are interconnected by piezoelectric elements, which are fixed in a potting compound. Depending on the requirements of the specific application, the necessary piezoelectric elements are exposed to activate. This exposure is achieved by etching or laser treatment. A disadvantage is that the transducers must be encapsulated with a molding compound. This compound makes the sawn chips manageable and allows them to be subsequently assembled into a larger chip (transducer).

[0006] German patent application DE 10 2020 204 773 A1 describes, according to claim 1, a sensor arrangement of individual sensor elements that are independently functional and, in particular, have a sawing line for singulation. A disadvantage of this method is that the sensor area must have a defined singulation structure and a defined sawing line, thus limiting the shape and size of the chip.

[0007] A further disadvantage of the method described in German patent application DE 10 2020 204 773 A1 is the assembly and electrical wiring of the individual sensors as defined in paragraph

[0021] . These are connected to each other on a separate electrical carrier, and additional mounting technologies are required. Furthermore, this method is only adaptable to a limited extent, since the wiring design is fixed within the electrical carrier. The solution according to this document provides for electrical wiring on a separate carrier.

[0008] The publication US 2017 / 0165715 A1 describes a method for singulating sensor elements with a defined singulation structure, but without a defined sawing line. The shape of the chip is predefined by an additional lithographic mask and deep reactive ion beam etching of the substrate in the mask layout. The chip size and shape are therefore predefined in the manufacturing design and cannot be freely chosen. Paragraph

[0012] defines that the chip size must necessarily be a multiple of the base cell. The inventive step of claim 1 and the dependent claims arises from the fact that the chip geometry is not defined in the wafer-level layout. Furthermore, the electrical wiring at the chip level is predefined in the publication and cannot be freely chosen, which is explained, among other things, by the fact that... Figure 6as illustrated. If it had been possible for a person skilled in the art to formulate the claims for a free-form chip geometry and a free design for wiring the acoustic channels without inventive activity, these would have been described, among other things, in sections

[0012] ff.

[0009] The related prior art solutions define the interconnection of individual transducer elements on the substrate via an electrical connection using a thin-film metal that is photolithographically defined and non-adaptable. Due to the defined electrical contacts and the positions of the transducer elements, the chip size is fixed in the design. The wafer is sawn according to the chip dimensions. The sawing dimensions are also fixed in the design and non-adaptable.

[0010] A disadvantage of the current state of the art is that customer-specific requirements for custom chip geometries and interconnection types of the converter elements, such as the number of independently operating electrical channels or the shape of a channel (line, rectangular area, circular area, ring, etc.), can only be met through a new design and fabrication process. The initial setup costs are very high, and the manufacturing time is long. Economical systems cannot be offered for small and medium production runs. The technology design according to the current state of the art dictates the interconnection type and chip size in the lithography layers during manufacturing using microtechnology. The repeating basic elements of the MUTs correspond to the representation of a chip. According to the current state of the art, the electrical pathways of the individual channels are fixed at the wafer level in the design and cannot be subsequently modified.The mechanically movable membranes with the electrodes are also non-modular, non-adaptable, and cannot be subsequently modified due to the lithographic structuring of the elements within each channel. The chip cannot be isolated at an arbitrary position, as this would destroy its functionality. New setup costs arise for each customer-specific design.

[0011] The object of the invention is to develop a method for manufacturing a micromechanical ultrasound transducer and an ultrasound transducer that allows micromechanical ultrasound transducers to be built at the substrate level as modularly adaptable in chip size and channel shape and number, and to be provided as "off the shelf" components with one-time setup costs.

[0012] This problem is solved by the features of the first and ninth patent claims.

[0013] Advantageous embodiments result from the dependent claims.

[0014] In the inventive method for manufacturing a micromechanical ultrasonic transducer, the micromechanical ultrasonic transducer is formed from several modular base cells, wherein a plurality of base cells are arranged in a grid pattern on a substrate and each base cell has at least one electrode and at least one electromechanical transducer. A plurality of base cells form a chip, wherein the chip is individually separated from the substrate by separation along at least one separation line, depending on the requirements.

[0015] In a first embodiment of the invention, the base cells are contacted with each other only after microtechnological fabrication. In a second embodiment, the base cells are electrically connected to each other at the level of the thin-film electrodes, and their electrical connection is individually severed after microtechnological processing.

[0016] The micromechanical ultrasound transducers are manufactured as semi-finished products with identical layouts and subsequently separated according to individual requirements, so that a large number of base cells are available depending on the requirements and contact between the base cells is made or removed as required.

[0017] The ultrasonic transducers can be interconnected without the use of an additional electrical carrier.

[0018] The base cells are advantageously produced on the substrate in the form of a wafer using thin-film deposition and lithographic processes.

[0019] The separation and singulation is carried out in a freeform shape, and particularly preferably by sawing along a saw line or by fracture edges. The distance between the singulation structures is not necessarily a multiple of the dimensions of the base cells.

[0020] The singulation process creates an actively usable chip area, where the actively used chip area corresponds to a multiple of a base cell and can be connected or separated. Depending on the singulation method, an additional passive chip area may be created. The passive chip area lies within the region of at least one singulation line and is not usable for the acoustic function of the chip.

[0021] The micromechanical ultrasonic transducer according to the invention comprises several base cells, at least partially arranged in a grid pattern and interconnected, each containing at least one electrode and an electromechanical transducer. A plurality of base cells are arranged on a substrate and form a chip, and the micromechanical ultrasonic transducer is bounded at its edge by at least one singulation line. This is possible because the base cells are not interconnected at the substrate level. After singulation, each base cell that is not located in the area of ​​the singulation line (break line, saw line, etc.) is functionally present on the chip. Depending on the embodiment, the base cells are either electrically interconnected or disconnected at the substrate level.The assignment of electrical functionalities, such as electrical connections, to each other takes place after wafer processing by separating the connections or respectively contacting the base cells with each other.

[0022] The singulation line is preferably designed in the form of a straight line, freeform shape or a radius / circular shape.

[0023] In a preferred embodiment, the electrical plane is fully present for each base cell.

[0024] In one embodiment of the ultrasonic transducer, the chip has a passive chip area and an actively usable chip area, wherein the actively used chip area corresponds to a multiple of a base cell and the passive chip area lies in the region of at least one singulation line. A chip design without a passive chip area is also possible.

[0025] The basic cells are arranged in a grid and, in one possible configuration, extend side by side along a first direction and an orthogonal second direction. However, other arrangements are also possible, for example a freeform or a radially symmetrical arrangement.

[0026] Depending on how the base cells are connected to each other, the ultrasound transducer can have multiple channels. The connections are determined by the requirements of the ultrasound transducer.

[0027] Preferably, the ultrasonic transducer has at least one electrical channel, wherein one channel is contacted with another ultrasonic transducer or other electrical functionality.

[0028] The inventive method allows for the effective production of an ultrasound transducer according to the invention.

[0029] Compared to the prior art, the invention provides base cells that can be electrically assigned at the chip or wafer level only after the fact, and the chip areas can be defined after manufacturing at the substrate level. The presence of the micromechanical ultrasonic transducers in the form of modular base cells allows the basic costs for MUT manufacturing at the substrate level to be incurred only once, enabling the production of a larger number of MUT base cells with modularly adaptable chip areas and electrical connections, such as the number of channels, on substrates. Customer-specific MUTs can be manufactured by downstream processing of the substrate following microtechnological production, including singulation and electrical interconnection. The substrates are available as "off-the-shelf" components. The production of MUTs for small and medium quantities becomes economical, and the delivery times for customer-specific components are significantly reduced.SMEs thus gain access to MUT components that were previously only worthwhile for large companies, and new fields of application can be opened up.

[0030] The invention is explained in more detail below using an exemplary embodiment and accompanying drawings.

[0031] They show: Figure 1: A base cell of an electromechanical ultrasonic transducer; Figure 2: A three-channel ultrasonic transducer; Figure 3: A two-channel ultrasonic transducer; Figure 4: A single-channel ultrasonic transducer; Figure 5: A group of base cells that are electrically connected to each other during microtechnological production at the level of the thin-film electrodes and can be separated into individual electrical channels; Figure 6: Individual singulation of the chip from the wafer assembly by separation; Figure 7: Individual singulation of the chip from the wafer assembly by separation with functionally represented base cells; Figure 8: An alternative separation from the wafer assembly; Figure 9: Another alternative separation of the base cells; Figure 10: Section AA according to... Figure 1 , Figure 11 Section AA acc. Figure 1 with an alternative setup, Figure 12, Chip 15 on circuit board

[0032] In the Figure 1Figure 1 shows a base cell 1 of an electromechanical ultrasonic transducer, wherein the base cell comprises a substrate 2 and, arranged thereon, one or more electrodes 3, at least one or a group of electromechanical transducer elements 4, and optionally further electrical contacts 5 as thin films, which were fabricated at the substrate level by thin-film deposition and photolithographic processes. The arrangement of the individual electromechanical transducer elements 4, the electrodes 3, and connections (not shown here) to another base cell or another substrate can vary depending on the design. The specific design of the base cell in Figure 1 This is merely an illustration. The arrangement of the electrodes 3 and the electrical contacts 5 may also differ from the exemplary representation in Figure 1 differ.

[0033] The Figures 2 , 3 and 4Figure 1 shows an arrangement of nine base cells 1 in a 3 x 3 configuration. After microtechnological processing, these base cells 1 can be individually electrically connected via contacts 6 on the upper surfaces of the electrodes 3. Base cells arranged side by side are contacted with each other. Figure 2 A three-channel ultrasound transducer with three basal cells per channel is shown. In the Figure 3 is a two-channel ultrasound transducer with three or six basic cells 1 per channel. Figure 4 shows a single-channel ultrasound transducer with nine basic cells 1 per channel.

[0034] An alternative design of the basic cells is in the Figure 5 depicted.

[0035] The base cells 1 are designed such that they are electrically connected to each other via a contact area 7 at the thin-film electrode level during microtechnological production. Only after their microtechnological processing is the electrical connection individually severed. This separation can take place along a singulation line or in freeform. Laser ablation is one possible technology for this separation.

[0036] In the Figure 6 and 7 The individual separation of the chip 15 from the substrate / wafer assembly 2 by separation, for example by sawing along a separation line 8, is shown, resulting in a sawn chip area 10 with an actively usable chip area 9 and a passive chip area 11. The actively used chip area 9 corresponds to a multiple of a base cell 1.

[0037] Figure 7Figure 1 shows the actively usable chip area 9, which lies within the singulation line 8. The sawn chip area 10 and the unused chip area 11 are also visible.

[0038] It is possible to create the actively usable chip area 9 before or after the production of the singulation line 8 by connecting the base cells 1 using the contacts 6 (not shown here).

[0039] Figure 8Figure 1 shows an alternative individual singulation of the chip 15 and its base cells 1 from the substrate / wafer composite 2 by separation along the singulation line 8. The singulation line 8 is circular. The singulation process creates a passive chip area 11 and an actively usable chip area 9. The actively used chip area 9 is again a multiple of a base cell 1. The base cells 1 are connected to each other by electrical contacts 6. The ultrasonic transducer has two channels, each of which has an electrical connection from the chip 15 to another electrical component such as an electronic component or printed circuit board (not shown).

[0040] Figure 9Figure 1 shows the individual separation of the base cells 1 from the substrate / wafer composite 2 by separation, for example by sawing along a straight separation line 8 in the form of a saw line, whereby no passive chip area is created due to optimal division. The actively used chip area 9 corresponds to a multiple of a base cell 1. The base cells 1 can be connected to each other by electrical contacts (not shown).

[0041] In Figure 10 and Figure 11 is the AA cut according to Figure 1 Two possible manufacturing technologies are shown. It is evident that in the substrate 2 of the base cell 1, recesses 12 are present in the area of ​​the electromechanical transducer element 4, which allow mechanical movement of the overlying membrane 13 or, if applicable, a free support. The dashed-edged areas in the Figures 10 and 11Each recess 12 defines or surrounds an electromechanical transducer element 4. Alternatively, another electrically insulating material could be arranged in the recesses 12. The mechanically movable substrate 13, which extends over the recesses 12, is located on the top side of the substrate 2. The arrangement of the electromechanical transducer elements 4 and the electrodes 3 on the substrate 2 depends on the transducer principle and design-specific parameters. The arrangement in Figure 10 and 11 This is merely an illustration. Figure 10 and 11The structure of a piezoelectric, electromechanical transducer element 4 is shown as an example. The mechanically movable substrate 13 can function as an electrode. Alternatively, an electrode layer can be placed between the mechanically movable substrate 13 and the piezoelectric layer 14 (not shown here). The piezoelectric layer 14 of the electromechanical transducer element 4 was deposited on the mechanically movable substrate 13. One or more electrodes 3 are located on the top surface of the base cell 1 as an electrically conductive deposited layer(s). One or more gaps b are present in the upper electrode layer, such that areas are electrically insulated from one another and the electrode(s) 3 and the contacts 5 are formed. The geometry and connection of the electrodes 3 can vary depending on the design.

[0042] When a capacitive ultrasound transducer is built, the cross-section and the horizontal design differ.

[0043] For example, in a capacitive transducer (not shown), its two electrodes are usually positioned vertically between a recess. A piezoelectric layer is not present in a capacitive transducer.

[0044] Substrate 2 preferably consists of silicon, but can also consist of silicon oxide and other suitable materials.

[0045] The electrode 3 of the electromechanical transducer 4 preferably consists of an electrically conductive material, e.g. in the form of an electrically conductive metallic coating made of aluminum, gold, copper, silver or an electrically conductive semiconductor material.

[0046] The mechanically movable substrate 13 preferably consists of silicon, or alternatively of silicon oxide, silicon nitride, or glass or carbonate glass. The use of a polymer or metals is also possible. If the substrate material 13 is not electrically conductive, then an additional electrode layer must be incorporated between the substrate material 13 and the piezoelectric layer 14.

[0047] Layer 14 of the electromechanical transducer preferably consists of piezoelectric material.

[0048] The electromechanical transducer element is essentially formed from the electrically conductive layer 3 and layer 14 made of piezoelectric material. The piezoelectric layer 14 requires two electrodes, usually vertical, which enable the generation or measurement of an electric field within the electromechanical transducer element. These electrical contacts are formed by layers 3 and 13.

[0049] The typical operating principle of the electromechanical ultrasonic transducer 4, in this case a piezoelectric ultrasonic transducer, is essentially as follows: A material with an asymmetrical lattice forms centers of electric charge. Consequently, the material deforms mechanically under an electric field or a dielectric flux. By applying the piezoelectric layer to a mechanically movable substrate, this deformation is converted into movement and generates a sound pressure. If the piezoelectric ultrasonic transducer is used as a sensor, the conversion chain is reciprocal. This means that a sound pressure leads to a mechanical deformation of the components on the mechanically movable substrate, and the charge carrier differences generated by the piezoelectric layer are conducted through the electrodes to a measuring device.

[0050] The electromechanical conversion can also be achieved using capacitive transducers. In this case, an electric field is generated in the recess 12 by electrodes. A change in field strength leads to a mechanical deformation, and vice versa.

[0051] Furthermore, with Figure 12 A further insight into PMUTs (piezoelectric micromechanical ultrasonic transducers) will be given to improve the understanding of the invention. Figure 12Figure 1 shows a PMUT manufactured according to the patentable process. In this design, each base cell 1 contains 36 individual ultrasonic transducer elements (not shown here) with a resonance frequency of approximately 2.5 MHz. The base cells 1 (1 x 1 mm²) were arranged in a grid pattern on a chip 15 (12 x 12 mm²). The electrical wiring, in the form of electrical contacts 6 between the top surfaces of the electrodes (not shown here), was assembled into 10 acoustic channels, each with dimensions of 1 x 10 mm², for an optoacoustic application (several of these chips 15 on a non-planar substrate are used, for example, for optoacoustic imaging). This connection was made by automated wire bonding without the use of an electrical carrier and without wiring layers at the wafer level (lithography layers, etc.).For another application (not shown), the same wafer material is used, for example, to build a square PMUT (1 x 1 mm²) or a round PMUT with a 5 mm diameter, each with one acoustic channel. For each application, the use of an electrical substrate with wiring layers or additional mask lithography can be omitted. In this example, only one actively used chip area 9 is present.

[0052] In Figure 12 The commonly used printed circuit board 16 and the associated electrical components, such as a contact 17 from chip to an electrical pad on the printed circuit board 18 and further contacts 19 from printed circuit board to a measuring device, are still visible.

[0053] With the solution according to the invention, the shape of the chip and the acoustic channels can be freely chosen after the microtechnological process.

[0054] The chips are pre-manufactured and then later configured according to customer requirements using the inventive method, resulting in significant time and cost savings.

[0055] Customers can have their custom-made ultrasonic transducers manufactured in a very short time. Reference symbol list

[0056] 1 Base cell 2 Substrate / wafer composite 3 Electrode 4 Electromechanical transducer element 5 Optional contact 6 Electrical contact / contacting 7 Contact area 8 Singulation line 9 Actively used chip area 10 Sawed chip area 11 Passive chip area 12 Recesses / Holes / Insulation 13 Mechanically movable substrate / Membrane 14 Layer of the electromechanical transducer 15 Chip 16 Printed circuit board 17 Chip-to-PCB contacting 18 Contact pad on the PCB 19 Contact connector for pre-assembled cables to the measuring device / electronics b Distance between electrodes

Claims

1. Method for manufacturing a micromechanical ultrasonic transducer, wherein the micromechanical ultrasonic transducer is formed from a plurality of modular base cells (1) on a substrate (2) in a microtechnological production process using thin-film deposition and lithographic methods, wherein a plurality of base cells (1) are arranged in a grid pattern on a substrate (2) and each base cell (1) has at least one electrode (3) and at least one electromechanical transducer element (4), and a group of base cells (1) forms a chip (15), wherein the chip (15) is separated from the substrate (2) by cutting along at least one freely definable separation line (8), and - adjacently arranged base cells (1) are only connected to each other after microtechnological production by means of an electrical contact (6) or - the adjacently arranged base cells are electrically connected to each other during microtechnological production via a contact area (7) and their electrical connection is separated after microtechnological production by separating the contact area (7).

2. Method according to claim 1, characterized in that the chip (15) is separated individually from the substrate (2) depending on the requirements by cutting along the freely definable separation line (8).

3. Method according to claim 1 or 2, characterized in that the separation along the separation line (8) creates a passive chip area (11) and an actively usable chip area (9) of the chip (15).

4. Method according to one of claims 1 to 3, characterized in that the actively used chip area corresponds to a multiple of a base cell (1) that has been connected to each other or separated from each other.

5. Method according to one of claims 1 to 4, characterized in that the passive chip area (11) was created in the area of or outside the at least one separation line (8).

6. Method according to one of claims 1 to 5, characterized in that the base cells (1) through which the separation lines (8) are created form an unused sawn chip area.

7. Method according to one of claims 1 to 6, characterized in that the contacting of adjacently arranged base cells (1) is established by means of a contact (6) in the form of a contact wire - from an upper side of an electrode (3) on the upper side of a base cell (1) - to the upper side of an electrode (3) of an adjacent base cell (1).

8. Method according to one of claims 1 to 3, characterized in that the separation along the at least one freely definable separation line (8) is carried out along a saw line or break edge.

9. Micromechanical ultrasonic transducer, wherein the micromechanical ultrasonic transducer has a plurality of base cells (1) arranged at least partially in a grid-like manner and in contact with each other, having at least one electrode (3) and at least one electromechanical transducer element (4), wherein a plurality of base cells (1) are arranged on a substrate (2) and form a chip (15), wherein the base cells (1) are not electrically connected to each other at the substrate level, and the micromechanical ultrasonic transducer is bounded at the edge by at least one freely definable separation line (8).

10. Micromechanical ultrasonic transducer according to claim 9, characterized in that at least one separation line (8) is formed in the shape of a straight line, free form, or radius / circle.

11. Micromechanical ultrasonic transducer according to one of claims 9 or 10, characterized in that an electrical plane is completely present for each base cell (1).

12. Micromechanical ultrasonic transducer according to one of claims 9 to 11, characterized in that the chip (15) has a passive chip area (11) and an actively usable chip area (9), wherein the actively usable chip area (9) corresponds to a multiple of a base cell (1) and preferably the passive chip area (11) lies in the area of or adjacent to the at least one separation line (8) and / or the base cells (1) have a sawed chip area (10) along the separation lines (8).

13. Micromechanical ultrasonic transducer according to one of claims 9 to 12, characterized in that the base cells (1) are arranged in a grid and extend adjacent to each other along a first direction and / or along an orthogonal second direction.

14. Micromechanical ultrasonic transducer according to one of claims 9 to 13, characterized in that the ultrasonic transducer has several channels depending on the contacting of the base cells with each other.

15. Micromechanical ultrasonic transducer according to one of claims 9 to 14, characterized in that the ultrasonic transducer has at least one electrical channel and the one channel is contacted with another ultrasonic transducer or another electrical functionality.