Sensor device with surface acoustic wave resonator

Abstract

The invention relates to a sensor device (100) having a metal carrier substrate (200) and a surface acoustic wave resonator (300) with a chip body (310). The resonator structure (320) is embedded in or mounted on the top side (313) of the chip body (310). The surface acoustic wave resonator (300) is fastened to the carrier substrate (200) by means of a glass layer (400).

Description

Technical Field

[0001] The present invention relates to a sensor device having a passive surface acoustic wave resonator (hereinafter referred to as a SAW resonator for short, as the English is "surface acoustic wave resonator"), and the sensor device is particularly designed for measuring mechanical stress or for measuring strain on a deformable body. Background Art

[0002] Passive acoustic surface acoustic wave sensors (SAW resonators) are commonly used for wireless monitoring of physical conditions, especially in harsh environments. However, the limitations of strain measurement applications usually come from the design of the functional intermediate layer connecting the SAW resonator to the surface of the deformable body.

[0003] In applications of mechanical strain measurement (such as torque or force measurement), the SAW resonator is usually adhered to the surface of the deformable body by means of an intermediate layer or directly placed on the deformable body. Hereinafter, the surface of the deformable body is also referred to as the carrier substrate, and the possible intermediate layer is referred to as the SAW resonator substrate, SAW wafer substrate or chip body.

[0004] Direct integration of SAW resonators on the surface of metal deformable carriers has high requirements for the deposition of piezoelectric layers. Compared with the manufacturing on traditional SAW wafer substrates, the quality factor of these structural elements is significantly lower and the signal performance is worse. In addition, the production cost of each sensor is significantly higher. Moreover, the piezoelectric layer is prone to cracking under high loads.

[0005] Similar to the assembly of polymer film-based strain sensors, when assembling the SAW resonator on the carrier substrate, proven adhesives are also used. The use of high-performance adhesives proves the ability of this connection technology to achieve a high strain transfer ratio. Compared with polymer film-based elastic strain sensors, the piezoelectric SAW resonator has a significantly higher stiffness. Despite the optimized design of the bonding, this still leads to time- and temperature-dependent effects. In particular, within the glass transition temperature range of the adhesive, the strain transfer characteristics will change significantly until the SAW resonator is irreversibly detuned.

[0006] The method of fusing the back metallization of the SAW sensor with the metal carrier substrate using a highly active nano-film results in strong local thermal stresses due to the temperature gradient within the SAW resonator. In addition, the high temperature required to melt the metal interface will damage the crystal structure of the SAW resonator substrate.

[0007] Therefore, an alternative bonding process (hereinafter also referred to as a bonding process) is needed to fasten the SAW resonator to the metal deformable body, so as to broaden the operating temperature range and achieve a high strain transfer rate under harsh environmental conditions. Summary of the Invention

[0008] It is an object of the present invention to provide a novel sensor device having a surface acoustic wave resonator.

[0009] This object is solved by a sensor device having the features given in claim 1.

[0010] Advantageous embodiments of the present invention are the subject matter of the dependent claims.

[0011] According to the present invention, the sensor device includes a metallic carrier substrate and a surface acoustic wave resonator.

[0012] The metallic carrier substrate is here, for example, part of a deformable body, subjected to mechanical loads or forces and deformed due to these mechanical loads and forces. By means of the surface acoustic wave resonator (which can also be referred to as a sensor element), the deformation of the deformable body can be made detectable. In particular, the carrier substrate (i.e., at least a part of the deformable body) is made of stainless steel. Thereby, the deformable body can be used for various purposes. For example, the deformable body can be configured as a pressure measuring cell or a force receiver.

[0013] The surface acoustic wave resonator includes a chip body. In addition, the resonator structure is embedded in or mounted on the top side of the chip body.

[0014] For example, the resonator structure can include a so-called single-port resonator that has a transmit-receive interdigital transducer between two almost completely reflective electrode gratings, and the two electrode gratings form a resonant cavity. The outgoing wave and the reflected wave between the interdigital transducer and the reflective electrode grating interfere with each other to form a standing wave. The wave field thus generated has an extremely narrow frequency band due to multiple reflections.

[0015] The surface acoustic wave resonator is fastened to the carrier substrate by means of a glass layer. Here, in particular, it can be a lead-free glass layer because, due to the increasing environmental awareness in the market and standards, lead-containing glass is increasingly avoided. In the context of using glass as an adhesive, the glass can also become a glass solder or solder glass. The glass layer can be produced, for example, by applying a glass frit or glass paste on the carrier substrate and then melting the glass frit or glass paste.

[0016] By using glass to connect the surface acoustic wave resonator to the carrier substrate instead of an adhesive as known in the prior art, the sensor device can be used significantly more widely and under significantly more demanding environmental conditions. Thus, glass solder is generally insensitive to moisture and, as long as the ambient temperature is below the glass transition temperature, has material properties that are almost independent of temperature over a wide temperature range. This applies in particular to its storage modulus as well as the coefficient of thermal expansion (CTE). In addition, compared to adhesives, glass exhibits significantly weaker viscoelastic properties. Thus, a continuously high and load-duration-independent transfer of mechanical stress from the carrier substrate to the surface acoustic wave resonator can be achieved over a wider temperature range, and thus the measurement accuracy can be improved.

[0017] In an exemplary configuration of the sensor device, the glass layer is arranged at least locally between the bottom side of the chip body, which is opposite to the top side, and the carrier substrate. Here, the glass layer has an outer edge that frames the edge side constructed between the top side and the bottom side of the chip body. Here, the outer edge of the glass layer delimits a defined surface section of the carrier substrate that is covered by the glass layer; in particular, the glass layer adheres to the entire surface of this surface section on the carrier substrate and there are no gas or air inclusions. The edge region of the chip body is surrounded by the outer edge of the glass layer, which means that the chip body is fastened to the carrier substrate along its entire bottom surface defined by the basic shape by means of glass solder and does not protrude beyond the outer edge of the glass layer at any position (i.e., any corner). On the contrary, the outer edge of the glass layer protrudes completely beyond the basic shape of the chip body, which means that in a top view, the distance between the outer edge and the chip body does not disappear at any position. In particular, there are no gas or air inclusions between the glass layer and the chip body. By means of this exemplary configuration, a particularly uniform transfer of mechanical stress from the carrier substrate to the surface acoustic wave resonator can be achieved. In addition, in this configuration, the connection of the surface acoustic wave resonator is particularly stable with respect to its adhesion strength on the carrier substrate. In this configuration, the glass layer is arranged "at least locally" between the bottom side of the chip body and the carrier substrate, which means that a part of the glass layer is exactly located there. However, other parts of the glass layer, especially the parts that laterally protrude beyond the chip body in a top view, can also extend completely into the region above the bottom side. Here, the glass layer can in particular partially or even completely cover the edge side constructed between the top side and the bottom side of the chip body, so that only the top side of the chip body completely protrudes beyond the glass layer, or at least is not covered by the glass layer, as will be explained in more detail below with the help of another exemplary configuration.

[0018] In an exemplary extension of this construction scheme, the chip body can have a basic shape, and the glass layer has a base shape that is symmetrical to the basic shape of the chip body. However, the dimensions of the base shape are larger than those of the basic shape, so that the chip body can be reliably framed by the glass layer, as described in the foregoing exemplary construction scheme. The chip body is positioned centrally and symmetrically within the glass layer. Thus, in particular, the centers of gravity and the axes of symmetry of the base shape and the basic shape also coincide, and the base shape protrudes at least substantially equally far from the basic shape on all sides. This means that the distance between the outer edge of the base shape and the outer edge of the basic shape is at least substantially constant.

[0019] In an exemplary construction scheme of the sensor device, both the chip body (i.e., its basic shape) and the base shape of the glass layer are configured as polygons. In particular, the chip body has a height and a defined basic shape perpendicular to its height here. The basic shape is determined, for example, by at least four even-numbered corners and the corresponding number of straight side edges constructed between each two adjacent corners. In addition, the basic shape has at least two axes of symmetry, for example. Thus, the basic shape of the chip body can be, for example, a rectangle or a square. Different from this here, the basic shape and the base shape can also have other numbers of corners. It is also possible that the basic shape and the base shape are configured without corners, for example, as a circle or an ellipse, or as a free form. In a cornered construction, side edges are constructed between each two adjacent corners, where the number of corners of the base shape is the same as the number of corners of the basic shape. Due to the surface tension and viscosity of typical glass solders, especially in the case of low-melting solder glasses (such solder glasses can be particularly advantageous in this application, as will be described below in the context of the exemplary construction scheme), it is possible to achieve the absence of any sharp corners or completely straight edge regions. In other words, the outer edge of the glass layer extends continuously without exception, without any sudden changes or inflection points. In this construction scheme, the "corners" of the base shape thus correspond, in particular, to rounded corners of a greater or lesser radius, and the side edges of the base shape can deviate from a straight course, having rounded corners, convex portions, or concave portions, without departing from the teachings of this exemplary construction scheme. In the case of the same axis of symmetry, the side length ratio of the base shape is the same as that of the basic shape, at least within the range of technical achievable accuracy during the application of glass frits or glass slurries and during the melting of the glass frits or glass slurries.

[0020] In an exemplary construction scheme of the sensor device, the outer edge of the glass layer has outwardly directed convex portions at each corner of the base shape. Thereby, it is possible to advantageously achieve that a raised platform region is constructed in the center of the glass layer, and this raised platform region does not tilt too much in the region of the corners of the base shape. In this raised platform region, the chip body can be reliably connected on its entire bottom surface and side surfaces, especially when the chip body is to be partially sunk into the glass layer for placement.

[0021] In an exemplary configuration of the sensor device, the outer edge of the glass layer can be at least partially spaced from the nearest side of the chip body by a maximum first length at at least one position between two consecutive corners of the basic shape. At the same time, the outer edge is at least partially spaced from the nearest corner of the chip body by a minimum second length at at least one convex portion, where the second length is at least 10% longer than the first length. In particular, the second length is even at least 50% longer than the first length, especially at least 100%. The above-mentioned spacing should exist at "at least one position between consecutive corners of the basic shape" or "at least one convex portion", meaning that, while maintaining the above-mentioned symmetry, the same spacing does not have to be maintained at all positions between all possible pairs of two consecutive corners of the basic shape, or at all convex portions.

[0022] However, in an exemplary configuration of the sensor device, the outer edge has a position between each pair of two adjacent convex portions, at which position the outer edge is at least partially spaced from the nearest side of the chip body by a maximum first length. At the same time, in this configuration, the outer edge is at least partially spaced from the respective nearest corner of the chip body by at least a second length at each convex portion. In the context of this example and in all subsequent paragraphs with a similar context, "at least partially" means that the corresponding feature (i.e., the corresponding minimum or maximum spacing) is achieved at at least one point along the outer edge. However, in particular, the corresponding feature is maintained not only at one point but also along a continuous segment of the outer edge. By the maximum or minimum spacing given in this configuration, the features and advantages of the above-mentioned exemplary configuration can be particularly effectively realized. Thus, by locally maintaining a maximum spacing of at most the first length in the region between two convex portions, the total size of the surface section covered by the glass layer is limited and thus also the total amount of glass frit or glass solder required to manufacture this surface covering. At the same time, by at least partially maintaining a minimum spacing of at least the second length at the convex portions, it is ensured that a raised platform area is constructed in the center of the glass layer, within which the chip body can be placed reliably, stably, and precisely.

[0023] In addition, by way of example, the basic shape of the glass layer can extend laterally overall beyond or protrude by 3 to 7 times, especially 4 to 6 times, and especially exactly 5 times the height of the basic shape chip body. This means that the outer edge is always at least this distance away from the nearest corner or side of the chip body; thus, this distance given as a multiple of the height of the chip body defines the minimum spacing between the outer edge and the chip body. Within this parameter range, the force flow or mechanical stress transfer from the carrier substrate to the surface acoustic wave resonator can be achieved particularly effectively and at optimized material costs. Here, in combination with the above-described configuration, it can be provided that the first length is exactly equal to the multiple of the height of the chip body mentioned in this example, or is chosen to be slightly larger, for example, 5% to 10% larger. Thereby, the advantages of the two exemplary configurations can be combined.

[0024] In another exemplary extension of the previously mentioned configuration, regardless of the specific basic shape of the glass layer, it can be provided that the outer edge is at least locally spaced from the side at most by the first length in the region along at least one side of the chip body, and is at least locally spaced from the corner by at least the second length in the region at at least one corner of the chip body, where the second length is at least 10% longer, especially at least 50% longer, and especially at least 100% longer than the first length. Here, the first length or the second length in this example can be understood to correspond to the first length or the second length mentioned in the previous example. The explanations of concepts such as "at least one" and "at least locally" in the previous paragraph can be similarly applied to this example. Similarly, the same advantages as those described for the first and second lengths in the previous paragraph can be achieved using the features in this example. Different from the previous example, this example is not limited to the glass layer having a recognizable basic shape with protrusions.

[0025] Here, the chip body can also have a basic shape formed by sides and at least four even-numbered corners, where the basic shape, for example, has at least two axes of symmetry. However, different angular configurations of the basic shape are also possible here.

[0026] In addition, in this extension, it can be provided that the outer edge is spaced from the corresponding nearest side or corner of the chip body by at least 3 to 7 times, especially 4 to 6 times, and especially 5 times the height of the chip body at every point. Thus, through this exemplary design, the minimum spacing between the outer edge and the chip body is defined. Within this parameter range, the force flow or mechanical stress transfer from the carrier substrate to the surface acoustic wave resonator can be achieved particularly effectively and at optimized material costs. Here, in combination with the above features of this extension, it can be provided that the first length is exactly equal to the multiple of the height of the chip body mentioned in this example, or is chosen to be slightly larger, for example, 5% to 10% larger. Thereby, the advantages of the two exemplary extensions can be combined.

[0027] In another exemplary configuration of the sensor device, the surface of the glass layer at least substantially flushly adjoins the top side of the chip body at least along the edge section of the chip body. Here, the edge section may at least include a part of the edge surface of the chip body, in particular one or more side edges of the chip body and / or one or more corners of the chip body. In this context, "substantially flush" means that the glass layer does not cover any part of the top side of the chip body, that is, it does not extend beyond the side edges of the top side of the chip body. It also means that there are no stepped jumps remaining between the surface of the glass layer and the top side of the chip body. Thus, the surface of the glass layer ends exactly at the edge section defining the top side of the chip body. In particular, the surface of the glass layer continuously transitions into the top side of the chip body at the edge section here. However, in the context of this configuration, a jump in slope, that is, a bend in the transition direction from the glass layer to the top side, should also be understood as substantially flush. Through this configuration, a particularly effective force flow or a particularly effective mechanical stress transfer can be achieved between the carrier substrate and the surface acoustic wave resonator. In particular, the force or mechanical stress can be directly transferred to the uppermost layer of the chip body, in which the surface acoustic wave moves within the resonator structure. At the same time, the function of the surface acoustic wave resonator is effectively prevented from being impaired by the substantially flush joint. That is, it has been proven that surface acoustic waves excited in the chip body at its top side are strongly disturbed even if only a small amount of glass extends through the edge section onto the top side of the chip body. In addition, a glass layer component that locally extends onto the top side of the chip body may cause tensions in the top side during temperature changes, and these tensions also strongly disturb the wave field or the measurement characteristics of the surface acoustic wave resonator. In addition, by flushly connecting the glass layer to the edge section, it can be achieved that due to the geometric characteristics of this configuration, microcracks and small edge damages or chippings on the chip body are healed by using solder glass, and these microcracks and small edge damages or chippings may in principle be generated due to the process during the manufacturing process of the chip body. This means that the glass can flow in and fill these cracks and chippings during the bonding of the chip body to the carrier substrate. Thereby, the measurement characteristics of the surface acoustic wave resonator can be improved and its sensitivity to environmental influences can be reduced, and the mechanical stability of the sensor device and its reliability under long-term and alternating loads can be improved. Accordingly, in one example, it can be advantageously provided that the surface of the glass layer adjoins all the side edges and corners of the chip body substantially flushly, so that the surface of the glass layer does not adjoin the top side non-flushly at any edge section of the chip body.

[0028] In another exemplary configuration of the sensor device, the corners of the basic shape of the chip body are configured as rounded. Such a corner shape can be achieved, for example, by an etching method. With this configuration, the bonding of the chip body to the glass layer can be improved. In particular, in this configuration, the overall, at least substantially flush adjacency of the surface of the glass layer to the top side of the chip body is simplified, as proposed in the aforementioned exemplary configuration.

[0029] In another exemplary configuration, the surface of the glass layer first rises to a highest point at least along the edge section of the chip body in its run from this edge section away towards the outer edge of the glass layer, and this highest point is higher than the top side of the chip body. Here, depending on the surface tension, viscosity and the angle at which the surface of the glass layer meets the edge section of the chip body, the surface can change its curvature from an initially concave shape to a convex shape; however, the surface can also extend convexly throughout its run from the edge section to the outer edge. After reaching the highest point, it continuously descends to the outer edge at least without macroscopically configured concave sections. Thus, the curvature remains convex by further extension, although the curvature can decrease towards the edge. Thus, seen from a cross-section extending, for example, perpendicular to the carrier substrate and the edge section, the surface of the glass layer follows a curve that has at most one inflection point, then a vertex and then no other inflection points, step points or vertices in the direction away from the edge section of the chip body towards the outer edge of the glass layer. The above does not prevent the glass layer from possibly having a convex end section on the micro-surface directly at the outer edge according to its surface tension, viscosity and the possible micro-structure of the surface of the carrier substrate. The surface of the glass layer adjacent to the edge section has a defined run according to this configuration, and this edge section can here at least partially include one or more side edges of the chip body and / or one or more corners of the chip body. With this configuration, it can be achieved in an advantageous manner that the effective cross-sectional area of the part of the glass layer enclosing the chip body is increased and thus mechanical stress peaks are reduced or shifted. Thereby, the stability of the sensor device can be improved and stronger deformations can be transferred from the carrier substrate to the surface acoustic wave resonator without damaging the glass layer. This means that the maximum allowable rated strain is increased. In addition, due to the run with a highest point above the top side of the chip body, the surface acoustic wave resonator can be partially protected against contact with other bodies, which will be elaborated in more detail especially in the context of subsequent expansion scenarios.

[0030] Based on the above advantages, in an exemplary expansion of this construction solution, it can be correspondingly stipulated that the surface of the glass layer extends in the described manner along the edge section away from the edge section towards its outer edge, and this edge section includes all the sides and corners of the chip body. This means that the glass layer is configured with an annular wall-like flange that comprehensively frames the surface acoustic wave resonator. Thus, the aforementioned advantages can be effectively utilized for the entire perimeter of the chip body.

[0031] For example, the highest point of the surface orientation of the glass layer described in this construction solution can be 10% to 75%, especially 25% to 50%, higher than the top side of the chip body by the height of the chip body. Thus, the advantageous effects of this construction solution can be achieved particularly effectively and at optimized material costs. By restricting the height of the highest point within the limits given here, an excessive increase in the tensile stiffness of the sensor device is prevented and thus the sensitivity is reduced.

[0032] In another exemplary expansion of this construction solution, the sensor device further includes a cover plate and a fixing frame. The fixing frame frames the entire surface section covered by the glass layer and connects the cover plate to the carrier substrate. Here, this connection is especially hermetically sealed. It is known in the prior art that the surface acoustic wave resonator is protected by the cover plate against damage, especially against the influence of dust, liquid, and other mechanical environments. However, so far, during the assembly of the cover plate and the fixing frame, if one of the mentioned components falls onto or hits the top side of the chip body, the surface acoustic wave resonator may be damaged. The highest point of the upward-pointing curved part of the glass layer is higher than the top side of the chip body. Through this curved part, such an error can be avoided because the glass layer will intercept the glass plate or the frame before they hit the sensitive top side of the surface acoustic wave resonator or the chip body. When the glass layer is configured with a wall-like flange that completely surrounds the chip body (as shown in one of the aforementioned expansion solutions), this protective effect can be exerted particularly effectively accordingly.

[0033] In an exemplary embodiment of the aforementioned expansion solution of this construction solution, the fixing frame is formed by an additional glass solder ring or an additional frame made of glass solder. Thus, the fixing frame can be manufactured by the same or similar process steps and parameters as the bonding between the chip body and the carrier substrate, and thus the sensor device can be effectively manufactured. In particular, a glass solder with a melting temperature lower than that of the glass solder used for constructing the glass layer is used for the fixing frame. Thus, the fixing frame can be manufactured after the glass layer without having to raise the process temperature to the extent that the glass layer itself melts again.

[0034] In the description of the foregoing exemplary configuration, the concept of "edge section" is used on the one hand to refer to sections where the surface of the glass layer at least substantially adjoins the top side of the chip body flushly; on the other hand, the same concept is also used for sections where the surface of the glass layer first rises above the highest point of the top side of the chip body in its direction towards its outer edge starting from these sections, and then continuously descends to the outer edge without the construction of macroscopic concave sections. To avoid ambiguity, it should be clearly stated here that in the exemplary configuration of the sensor device, it can not only involve the same edge section, that is, the flush connection and the corresponding direction towards the highest point are combined at the same edge section, but also involve different edge sections, that is, the flush connection only occurs at sections where the surface of the glass layer does not rise to the highest point in its direction towards its outer edge starting from these sections. Similarly, the edge section with one of the characteristics can also partially overlap with the edge section with the other characteristic. Similarly, both forms can also be used comprehensively at the same time, which means that they are arranged continuously along all the sides and corners of the chip body.

[0035] In another exemplary configuration of the sensor device, the chip body is formed of an anisotropic material that has a first coefficient of thermal expansion and a first strain sensitivity in a first direction and a second coefficient of thermal expansion and a second strain sensitivity in a second direction orthogonal to the first direction, with both being different from the first coefficient of thermal expansion or the first strain sensitivity, respectively. Here, the chip body is shaped and cut such that the first and second directions lie in a plane parallel to the top side of the chip body. Here, the second coefficient of thermal expansion is lower than the first coefficient of thermal expansion. In addition, the coefficient of thermal expansion of the carrier substrate is selected to be less than the first coefficient of thermal expansion and greater than the second coefficient of thermal expansion. This enables a mismatch in the coefficient of thermal expansion to exist between the chip body and the carrier substrate, and yet this mismatch has different signs along the first and second directions, respectively. This results, for example, in the chip body being relatively compressed in the first direction (which means negative strain or reduced tension) when the temperature rises, while at the same time being relatively stretched in the second direction (which means positive strain or reduced compression). Since the surface acoustic wave resonator is fastened to the carrier substrate using glass solder, during the course of the bonding process in which the glass solder cools and solidifies, the surface acoustic wave resonator is stretched (positive strain) in the first direction and compressed (negative strain) in the second direction. Thus, the chip body is pre-stressed due to the defined mismatch in the coefficient of thermal expansion at the end of the bonding process technology. Now, in this configuration, the material of the chip body is selected and oriented such that the first strain sensitivity is negative and the second strain sensitivity is positive. In this context, a negative strain sensitivity means that the resonant frequency of the surface acoustic wave resonator decreases as positive strain (i.e., tension) increases. Correspondingly, a positive strain sensitivity means that the resonant frequency increases as positive strain (i.e., tension) increases. In a surface acoustic wave resonator, the strain sensitivity can in particular be expressed as the rate of change of the resonant frequency, i.e., where Δf is the difference between the current resonant frequency and the original frequency and ε is the strain. Thus, the pre-stress of the chip body causes a decrease in the resonant frequency in both directions, respectively. However, the material of the chip body should simultaneously have a temperature response, i.e., a temperature dependence of the resonant frequency, which causes an increase in the resonant frequency during the cooling process. Correspondingly, the influence of the mismatched coefficients of thermal expansion cancels out the temperature response of the chip body in both directions and thus effectively reduces the thermal cross-sensitivity of the surface acoustic wave resonator. Correspondingly, when the resonator structure and the wave field direction (also called the wave field propagation direction) extend parallel to the first or second direction, a sensor device according to this configuration can achieve high measurement accuracy over a wide temperature range.

[0036] The effectiveness of this pre-stress and the reduction of the thermal cross-sensitivity can be used over a wide temperature range precisely because bonding is carried out using glass solder instead of an adhesive according to the present invention. Adhesives typically have a temperature-dependent coefficient of thermal expansion, while the coefficient of thermal expansion of glass solder is substantially independent of temperature.

[0037] In another exemplary configuration of the sensor device, the surface acoustic wave resonator has an average resonance frequency of 434 MHz or 2.4 GHz, and the chip body has a side length of at least 1.5 mm to a maximum of 5 mm, in particular a side length of at least 2 mm to a maximum of 3 mm. By using the frequencies mentioned, non-contact reading of the surface acoustic wave resonator can be performed in many regions without a license and usually even license-free, since these frequencies are within the standardized ISM frequency bands. Alternatively or additionally, the resonator structure has a length of at least 1 mm, in particular at least 1.5 mm. Through the combination of these parameters, small structural dimensions are achieved while the resonator quality is high enough, so that the sensor device can be reliably used to perform measurement tasks.

[0038] In another exemplary configuration of the sensor device, the chip body has a thickness of at least 20 μm to a maximum of 100 μm, in particular a thickness of at least 25 μm to a maximum of 60 μm. At the same time, the glass layer has a thickness of at least 10 μm to a maximum of 200 μm in the planar region directly below the chip body, in particular a thickness of at least 12.5 μm to a maximum of 120 μm. With these dimensions, a stable bond between the chip body and the carrier substrate and reliable force transfer from the carrier substrate to the chip body can be achieved while optimizing the material requirements.

[0039] In another exemplary configuration of the sensor device, the chip body is made of α-quartz, where Y-35°X cutting, Y-34°X cutting or Y-33°X cutting is involved. Here, the resonator structure is oriented such that it extends along the X direction. This material selection is particularly used to implement the above-mentioned configuration for specifically generating a certain thermal prestress in the chip body, since all requirements for the chip body are thus met and glass solder that meets the necessary conditions in combination with this chip body material is available. Here, Y-35° cutting is currently understood as a Y-type cutting that is rotated 35° around the X axis. The non-rotated Y-type cutting is a cutting that extends perpendicular to the Y axis. Thus, according to the standard of ANSI / IEEE Std176-1987, this cutting can be designated as YXwlt 0° / 35° / 0°.

[0040] In a further exemplary embodiment of the sensor device, the glass layer is made of a low-melting glass solder, in particular a glass solder with a melting temperature below 500 °C. Thereby, the high temperature required for melting the glass solder is lower, so that the sensor device can be manufactured at low cost and in a shorter time. In addition, since the temperature difference during the manufacturing process is lower, the thermal stress can be reduced overall, although this should not be construed as being contradictory to the foregoing exemplary embodiment, in which a specific thermal prestress is specifically adjusted to reduce the thermal cross-sensitivity of the surface acoustic wave resonator. What can be achieved with this embodiment is that, although the difference between the melting temperature required during manufacturing and the usually significantly lower operating temperature may be large, no such high mechanical stress that would cause damage to the surface acoustic wave resonator is caused in the surface acoustic wave resonator due to thermal mismatch and internal stress, regardless of whether the thermal mismatch between the material of the chip body, the glass layer and / or the carrier substrate is intentional or unintentional.

[0041] In a further exemplary embodiment of the sensor device, the resonator structure is oriented in or on the top side of the chip body such that the wave field direction of the resonator structure extends parallel to one of at least two symmetry axes of the basic shape of the chip body. In particular, at least two symmetry axes of the chip body are perpendicular to each other, and the resonator structure is centered on the intersection of these symmetry axes, wherein the wave field direction extends parallel to one of these two symmetry axes. What can be achieved with this orientation is that the forces and deformations of the chip body act on the resonator structure substantially symmetrically, whereby the measurement accuracy can be improved and the cross-sensitivity can be reduced. When the symmetry axes of the chip body and the crystal orientation match the corresponding material properties, this embodiment can be particularly advantageously combined with the exemplary embodiment described in the foregoing paragraph, in which a specific thermal prestress is specifically used to reduce the thermal cross-sensitivity. Thereby, the advantages of the two embodiments can be combined with each other.

[0042] Embodiments of the present invention, as well as some of their exemplary embodiments, implementations and extensions, are subsequently elaborated in detail with the aid of the drawings. Description of the Drawings

[0043] Herein:

[0044] Figure 1 An exemplary embodiment of the sensor device is schematically shown in a top view;

[0045] Figure 2 An exemplary embodiment of the surface acoustic wave resonator is schematically shown in a perspective view;

[0046] Figure 3A 、 3B 3C, 3D respectively schematically show exemplary embodiments of the chip body in a top view;

[0047] Figure 4A 、 4B 4C, 4D schematically show exemplary embodiments of the sensor device in a top view;

[0048] Figure 5A schematically show an exemplary embodiment of the sensor device in a perspective view;

[0049] Figure 5B schematically show in a cross-section Figure 5A of the edge region;

[0050] Figure 6A schematically show an exemplary embodiment of the sensor device in a perspective view;

[0051] Figure 6B schematically show in a cross-section Figure 6A of the edge region; and

[0052] Figure 7 schematically show an exemplary embodiment of the sensor device in a cross-section.

[0053] Corresponding components are provided with the same reference numerals in all the figures. Detailed Description of the Invention

[0054] In Figure 1 a top view shows an exemplary embodiment of the sensor device 100. The surface acoustic wave resonator 300 is fastened to the carrier substrate 200 by means of a glass layer 400. The carrier substrate 200 is only shown locally here and can, for example, be locally formed by the surface of a deformable body, such as a pressure measurement cartridge, a pressure measurement film or a force receiver. The surface acoustic wave resonator 300 includes a chip body 310, which in this example has a square basic shape defined by four corners 311 and four side edges 314. A resonator structure 320 is arranged on or in the top side 313 of the chip body 310, which is only schematically and very simply shown in this figure and the subsequent figures. The glass layer 400 has a surrounding outer edge 410 that surrounds the surface portion of the carrier substrate 200 that is completely covered by the glass layer 400. Here, the glass layer 400 has a basic shape 413 shown in detail in Figures 4A to 4D which corresponds to that also shown in Figures 4A to 4DThe basic shape 316 of the chip body 310 shown in detail, but with a larger size, so that this basic shape fully overlaps or frames the basic shape 316 of the chip body 310. In addition, the outer edge 410 has a convex portion 416 in the region of each corner 311 of the chip body 310. The chip body 310 is placed concentrically and symmetrically on or in the glass layer 400. From this, it follows that the outer edge 410 is at least partially spaced from the respective nearest side 314 by a maximum first length L1 in the region along the side 314. At the same time, the outer edge 410 is at least partially spaced from the respective nearest corner 311 of the chip body 310 by at least a second length L2 in the region of the convex portion 416. Here, the second length L2 is at least 10% longer than the first length L1.

[0055] Figure 2 Shows an exemplary embodiment of the surface acoustic wave resonator 300, corresponding to Figure 1 of the surface acoustic wave resonator. The chip body 310 has a square basic shape 316 and the chip body 310 has a height H, which can also be referred to as the thickness of the chip body 310.

[0056] Figure 3A , Figure 3B , Figure 3C and Figure 3D Show different exemplary embodiments of the chip body 310, the respective basic shapes 316 of which are different. In addition, the axes of symmetry 312 of the different basic shapes 316 are drawn. Views of the resonator structure 320 are omitted in these figures, but the resonator structures are all oriented such that the wave field direction of the resonator structure 320 is parallel to the axis of symmetry 312 and the resonator structures 320 are all centered on the intersection of the axes of symmetry 312.

[0057] Figure 3A The chip body 310 in has a square basic shape 316 and thus is similar to the embodiments in Figure 1 and Figure 2 . While Figure 3B The chip body 310 in has a rectangular basic shape 316 and thus has a smaller number of axes of symmetry 312. Figure 3C shows a chip body 310 having a hexagonal basic shape 316, where, in this example, all sides 314 are of the same length. In Figure 3D The basic shape 316 of the chip body 310 shown in is similar to Figure 3A 's basic shape, but the corners 311 are rounded. Each different basic shape 316 is defined by at least four even corners 311 and the same number of sides 314 between every two adjacent corners 311. In Figure 3CIn the figure, for the sake of clarity, the reference numerals of the side 314 are omitted.

[0058] In Figure 4A , Figure 4B , Figure 4C and Figure 4D the corresponding Figure 3A , Figure 3B , Figure 3C and Figure 3D are shown in a top view as exemplary chip bodies 310 as part of an exemplary embodiment of the sensor device 100. For this purpose, these chip bodies are respectively positioned in the glass layer 400. The glass layer 400 respectively has a base shape 413 with a symmetry axis 415, which corresponds in shape and orientation to the basic shape 316 of the respective assigned chip body 310, but is larger, so that the outer edge 410 of the glass layer 400 frames the edge surface extending between the top side 313 and the bottom side of the chip body 310 of the chip body 310 on all sides. The chip bodies 310 are all placed concentrically and symmetrically inside the glass layer 400, so that the outer edge 410 of the glass layer 410 and the chip bodies 310 are spaced apart symmetrically about a point (within the technically possible manufacturing accuracy). Here, the base shape 413 protrudes at least with a minimum spacing M on all sides beyond the basic shape 316. Additionally, the glass layer 400 has convex portions 416 in the regions of all corners 311 of the respective basic shape 316 (and thus in the regions of all corners 414 of the base shape). Along the side 314 of the chip body 310 (in Figure 4A , Figure 4B , Figure 4C and Figure 4D the reference numerals are not provided for the sake of clarity), the outer edge 410 is locally spaced apart from the chip body 310 by a maximum spacing L1. In the region of the convex portion 416, the outer edge 410 is in turn locally spaced apart from the respective nearest corner 311 (in Figure 4A , Figure 4B , Figure 4C and Figure 4D the reference numerals are not provided for the sake of clarity) by at least a second length L2.

[0059] Figure 5A shows another exemplary embodiment of the sensor device 100 in a perspective view. The chip body 310 is placed partially sunken in the glass layer 400. Here, the surface 411 of the glass layer 400 abuts flush with the top side 313 of the chip body 310 along the edge section 315.

[0060] In Figure 5B it is shown in a cross-sectional view through the plane A drawn in Figure 5A Figure 5A ​The surface 411 of the glass layer 400 adjoins the top side 313, i.e. the surface of the chip body 310, flushly, and adjoins the side edge 314 of the surface. Here, “flush” means that the glass layer 400 does not extend beyond the side edge 314 and thus does not cover any part of the top side 313, but at the same time, no image remains between the surface 411 and the top side 313. Figure 5A In particular, the surface 411 of the glass layer 400 adjoins the top side 313 along all corners 311 and all side edges 314 in a fully continuous and flush manner. Figure 5B In the embodiment, the transition between the surface 411 and the top side 313 extends continuously, however, in this embodiment, Figure 5B The slight bend in the slope indicated by the dashed line in FIG. 1 is also to be understood as a flush connection.

[0061] exist Figure 6A 1 shows a further exemplary embodiment of a sensor device 100 in a perspective view. Here, the surface 411 of the glass layer 400 first rises to a peak 412 in its course away from the chip body 310 toward its outer edge 410, which is higher than the top side 313 of the chip body 310. Then, it drops continuously to the outer edge 410 without forming a macroscopic concave section. This does not prevent the glass layer 400 from being formed with a convex end section directly at the outer edge 410 on a microscopic plane, depending on its surface tension, viscosity and possible microstructure of the surface of the carrier substrate 200. The glass layer 400 is thus formed with a circumferential annular wall-like flange, which fully frames the surface acoustic wave resonator 300 or the chip body 310.

[0062] exist Figure 6B Through Figure 6A The cross section of plane B shown in FIG. Figure 6A Here, the surface 411 can be seen running from the side 314 of the chip body 310 toward the outer edge 410. Here, the highest point 412 is higher than the top side 313 of the chip body 310 by 10%-75% of the height H of the chip body 310, for example.

[0063] Figure 7Another exemplary embodiment of the sensor device 100 is shown in cross-section. In this example, the glass layer 400 forms a surrounding flange around the chip body 310, where the highest points 412 are all higher than the top side 313 of the chip body 310. In addition, the surface acoustic wave resonator 300 and the glass layer 400 are framed by a fixing frame 510, which carries a cover plate 500. The fixing frame 500 is formed of glass solder and, together with the cover plate 500, hermetically encloses the surface acoustic wave resonator 300 and the glass layer 400. Since the glass layer 400 is configured with a flange having the highest points 412, the sensitive top side 313 of the chip body 310 will not be damaged by the cover plate 500, even if the cover plate sinks too deeply into the fixing frame 510 or is placed obliquely during the manufacturing process. In this case, the cover plate 500 will hit the stable flange formed by the glass layer 400 instead of the top side 313 of the chip body 310.

[0064] The disclosure herein is not limited to the features of the exemplary embodiments, configurations, and / or extensions mentioned above, but also includes any combination of these features, as long as they are not logically mutually exclusive. In addition, it can be modified within the scope of the following claims. Similarly, the aspects of the dependent claims can be combined with each other.

[0065] List of reference numerals

[0066] 100 Sensor device

[0067] 200 Carrier substrate

[0068] 300 Surface acoustic wave resonator

[0069] 310 Chip body

[0070] 311 Corner of the basic shape or of the chip body

[0071] 312 Axis of symmetry of the basic shape of the chip body

[0072] 313 Top side of the chip body

[0073] 314 Side of the basic shape or of the chip body

[0074] 315 Edge section

[0075] 316 Basic shape of the chip body

[0076] 320 Resonator structure

[0077] 400 Glass layer

[0078] 410 Outer edge of the glass layer

[0079] Surface of the 411 glass layer

[0080] 412 Highest point

[0081] 413 Basic shape of the glass layer

[0082] 414 Corners of the basic shape

[0083] 415 Axis of symmetry of the basic shape

[0084] 416 Protrusion

[0085] 500 Cover plate

[0086] 510 Fixed frame

[0087] Planes A, B

[0088] L1 First length

[0089] L2 Second length

[0090] H Height of the chip body

[0091] M Minimum spacing

Claims

1. A sensor device (100), comprising: a metallic carrier substrate (200), and A surface acoustic wave resonator (300) having a chip body (310), and a resonator structure (320) embedded in or mounted on the top side (313) of the chip body (310), in, The surface acoustic wave resonator (300) is fastened to a carrier substrate (200) by means of a glass layer (400).

2. The sensor device (100) according to claim 1, wherein: The glass layer (400) is at least partially arranged between the bottom side of the chip body (310) opposite to the top side (313) and the carrier substrate (200), and the outer edge (410) of the glass layer (400) frames an edge surface constructed between the top side (313) and the bottom side of the chip body (310).

3. The sensor device (100) according to claim 2, wherein: The chip body (310) has a basic shape (316), and The glass layer (400) has a basic shape (413) symmetrical to the basic shape (316) of the chip body (310), and The chip body (310) is positioned centrally and symmetrically to the base shape of the glass layer (400).

4. The sensor device (100) according to claim 3, wherein: The outer edge (410) has an outwardly directed projection (416) at each corner (414) of the basic shape (413).

5. The sensor device (100) according to claim 4, wherein: The outer edge (410) is at least partially spaced apart from the nearest side edge (314) of the chip body (310) by at most a first length (L1) at at least one location between two consecutive corners (414) of the basic shape (413), and At least one of the protrusions (416) is at least partially spaced apart from the nearest corner (311) of the chip body (310) by at least a second length (L2), in, The second length (L2) is at least 10% longer, in particular at least 50% longer, in particular at least 100% longer than the first length (L1).

6. The sensor device (100) according to claim 5, wherein: The outer edge (410) At least one position between each pair of two adjacent protrusions (416) is at least partially spaced from the nearest side edge (314) of the chip body (310), and the spacing is at most equal to the first length (L1); and At each protrusion (416), at least partially, there is a distance from the corresponding nearest corner (311) of the chip body (310), and the distance is at least equal to the second length (L2).

7. The sensor device (100) according to any one of claims 3 to 6, wherein: The basic shape (413) protrudes laterally on all sides beyond the basic shape (316) of the chip body (310) by a minimum distance (M), wherein the minimum distance (M) is 3 to 7 times, in particular 4 to 6 times, in particular 5 times, the height (H) of the chip body (310).

8. The sensor device (100) according to any one of claims 3 to 7, wherein: The basic shape (316) has at least four even angles (311) and at least two axes of symmetry (312), and The base shape (413) has a corresponding number of corners (414) and an axis of symmetry (415).

9. The sensor device (100) according to claim 2, wherein: The outer edge (410) In a region along at least one side (314) of the chip body (310), the chip body (310) is at least partially spaced apart from the side by a maximum of a first length L1, and In a region at least partially at at least one corner (311) of the chip body (310), the chip body (310) is spaced at least partially from the corner by at least a second length (L2), in, The second length (L2) is at least 10% longer, in particular at least 50% longer, in particular at least 100% longer than the first length (L1).

10. The sensor device (100) according to claim 9, wherein: The outer edge (410) In a corresponding region along each side (314) of the chip body (310), each of the chip body (310) is at least partially spaced apart from the side by a maximum of a first length L1, and In a corresponding region at each corner (311) of the chip body (310), the chip body (310) is at least partially spaced apart from the corner by at least a second length (L2).

11. The sensor device (100) according to claim 9 or 10, wherein: The outer edge (410) is laterally spaced apart from the corresponding nearest side (314) or corner (311) of the chip body (310) at each point by a minimum spacing (M), wherein the minimum spacing (M) is 3 to 7 times, in particular 4 to 6 times, in particular 5 times, the height (H) of the chip body (310).

12. The sensor device (100) according to any one of claims 9 to 11, wherein: The chip body (310) has a basic shape (316), wherein the basic shape is formed by side edges (314) and at least four even-numbered corners (311). Therein, the basic shape (316) has at least two axes of symmetry (312).

13. The sensor device (100) according to one of the preceding claims, wherein: A surface (411) of the glass layer (400) adjoins the top side (313) at least substantially flush, at least along an edge section (315) of the chip body (310).

14. The sensor device (100) according to one of the preceding claims, wherein: The surface (411) of the glass layer (400) is at least along an edge section (315) of the chip body (310) in a direction from the edge section away from the glass layer to the outer edge (410) of the glass layer. First, it rises to a highest point (412) that is higher than the top side (313) of the chip body (310), and Then, there is a continuous descent to the outer edge ( 410 ) without forming a macroscopic concave section.

15. The sensor device (100) according to claim 14, wherein: The highest point (412) is higher than the top side (313) of the chip body (310) by 10% to 75%, in particular 25% to 50%, of the height (H) of the chip body (310).

16. The sensor device (100) according to any one of claims 13 to 15, wherein: The edge section (315) includes all edge surfaces of the chip body (310), in particular all side edges (314) and all corners (311) of the chip body (310).

17. The sensor device (100) according to any one of claims 2 to 16, comprising a cover plate (500), and A fixed frame (510), in, The fixing frame (510) frames the outer edge (410) and the cover plate (500) is connected to the carrier substrate (20).

18. The sensor device (100) according to claim 17, wherein: The fixing frame (510) is formed of glass solder, wherein the fixing frame (510) is particularly is formed of a glass solder different from the glass layer (400), and The different glass solder has a melting temperature lower than the melting temperature of the glass solder forming the glass layer (400).

19. The sensor device (100) according to one of the preceding claims, wherein: The chip body (310) is formed of anisotropic material. has a first coefficient of thermal expansion and a first strain sensitivity in a first direction, and having a second coefficient of thermal expansion and a second strain sensitivity in a second direction orthogonal to the first direction, in, the second coefficient of thermal expansion is lower than the first coefficient of thermal expansion, And among them, The thermal expansion coefficient of the carrier substrate (200) and / or the thermal expansion coefficient of the glass layer (400) is smaller than the first thermal expansion coefficient and larger than the second thermal expansion coefficient. the first strain sensitivity is negative and the second strain sensitivity is positive, And wherein the chip body (310) is formed in the following manner: The first direction and the second direction are in a plane parallel to the top side (313) of the chip body (310), and The resonator structure (320) extends parallel to the first direction or parallel to the second direction.

20. The sensor device (100) according to one of the preceding claims, wherein: The surface acoustic wave resonator (300) has an average resonant frequency of 434 MHz or 2.4 GHz, and The chip body (310) has a side length of at least 1.5 mm and at most 5 mm, in particular at least 2 mm and at most 3 mm, and / or In this case, the resonator structure (320) has a length of at least 1 mm, in particular at least 1.5 mm.

21. The sensor device (100) according to one of the preceding claims, wherein: The chip body (310) has a thickness of at least 20 μm and at most 100 μm, in particular at least 25 μm and at most 60 μm, wherein in particular The glass layer (400) has a thickness of at least 10 μm and at most 200 μm, in particular at least 12.5 μm and at most 120 μm, in a plane region directly below the chip body (310).

22. The sensor device (100) according to one of the preceding claims, wherein: The chip body (310) is made of α-quartz, wherein a Y-35° X-cut, a Y-34° X-cut or a Y-33° X-cut is involved and the resonator structure (320) extends along the X direction.

23. The sensor device (100) according to one of the preceding claims, wherein: The glass layer (400) is made of glass solder with a low melting point, in particular, made of glass solder with a melting temperature below 500°C.

24. The sensor device (100) according to one of the preceding claims, wherein: The corners (311) of the chip body (310) are configured to be rounded.

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