Sensor device for determining a pressure difference in a liquid or gaseous medium

Abstract

The present disclosure describes a sensor device for determining a pressure difference in a liquid medium or a gas medium, comprising: a housing frame for the sensor device, including a first and a second opening; a sensing element including a first side and a second side, and configured and located within the housing frame to form a first cavity at its first portion and a second cavity at its second portion, wherein the sensing element is configured to determine the pressure difference between the first side and the second side; a first and a second corrugated diaphragm, wherein the first corrugated diaphragm is configured to close the first opening to seal the first cavity of the housing frame; and the second corrugated diaphragm is configured to close the second opening to seal the second cavity of the housing frame; an inert hydraulic fluid within the first cavity and the second cavity, configured to couple an external pressure acting on the respective corrugated diaphragm to the respective side of the sensing element, wherein the first and second corrugated diaphragms are constructed by a conformal coating process using a substrate having a structured surface.

Description

Technical Field

[0001] Embodiments of the present disclosure relate to sensor devices for determining a pressure difference in a liquid medium or a gas medium. Background Art

[0002] The vast majority of commercial pressure sensors employ silicon microelectromechanical system (MEMS) devices as sensing elements. In a typical MEMS pressure sensor chip, a portion of the silicon substrate is removed by etching from the underside, leaving a thin silicon membrane on the top surface. The pressure difference between the top and the bottom will cause the membrane to deflect, and the stress generated in the membrane can be measured by piezoresistors placed at the periphery of the membrane. By appropriately selecting the membrane area and thickness, a full-scale differential pressure range varying from a few mbar to several tens of bar can be achieved.

[0003] Silicon pressure sensors can be designed for absolute pressure measurement or gauge pressure / differential pressure measurement. In the former case, a zero-pressure reference cavity is formed on the bottom surface of the membrane by attaching a backplane to the bottom surface of the substrate under vacuum. Usually, the backplane is made of glass with a thermal expansion coefficient very well matched to that of silicon. In the case of an instrument or differential sensor, it is common practice to attach a backplane with holes to provide access to the bottom surface of the membrane. The backplane increases the mechanical stiffness of the sensor chip.

[0004] Many applications of silicon pressure sensors involve relatively inert dry gases, in which both sides of the sensor can be directly exposed to the process medium. The bottom surface of the silicon sensor can usually also be exposed to other media, including both dielectric and conductive liquids, as long as they do not corrode the silicon or the glass. However, the range of media that can come into contact with the top side of the silicon sensor is more restricted. Specifically, water and aqueous media are excluded because the electrical connections to the piezoresistors are exposed and would cause electrolysis and corrosion when in contact with a conductive fluid. Summary of the Invention

[0005] A common method for manufacturing a wet-wet differential pressure sensor that can operate in a conductive liquid or a corrosive liquid is to encapsulate the silicon sensor chip such that the top side of the silicon chip is isolated from the process medium while still allowing the external pressure to be coupled to the membrane. In a typical configuration, sealed cavities are formed on both sides of the sensor chip, where each cavity is closed by a corrugated diaphragm that will deflect in response to a change in the external pressure. The cavities are filled with an inert hydraulic fluid (e.g., silicone oil), so the volume of each cavity is fixed; in this way, the displacement of the diaphragm and the silicon membrane are coupled.

[0006] Typically, this type of sensor has a stainless steel housing produced by conventional machining and a corrugated diaphragm made by stamping a stainless steel plate. The volume of the smallest commercially available device is about 10 cm 3, the diaphragm has a diameter of approximately 2 cm. In order for the diaphragm to transmit external pressure changes to the silicon membrane with negligible attenuation, the stiffness of the diaphragm must be small compared to the stiffness of the membrane. This requirement sets a lower limit on the diaphragm diameter for a given diaphragm thickness. The diaphragms in commercial sensors typically have a thickness of approximately 20 μm. Using a thinner diaphragm may reduce the diaphragm diameter, but this is not practical for current methods used in diaphragm manufacturing.

[0007] Aspects of the present invention relate to a sensor device for determining a pressure difference in a liquid medium or a gas medium, a method for manufacturing a corrugated diaphragm, and a method for sealing a cavity of the sensor device, where the subject matter is as described in the independent claims.

[0008] Advantageous modifications of the present invention are stated in the dependent claims. All combinations of at least two of the features disclosed in the specification, claims, and drawings fall within the scope of the present invention. To avoid repetition, the features disclosed according to the method are also applicable according to the mentioned system and are claimable.

[0009] Throughout the description of the present invention, reference numerals are provided to some features to improve readability or make the assignment clearer, but this does not imply the presence of certain features.

[0010] To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a sensor device for determining a pressure difference in a liquid medium or a gas medium, having a housing frame for the sensor device, including a first opening and a second opening and a sensing element, the sensing element including a first side and a second side, and being configured and located within the housing frame to construct a first cavity at a first portion of the housing frame and a second cavity at a second portion of the housing frame, wherein the sensing element is configured to determine the pressure difference between the first side and the second side.

[0011] The sensor device further includes a first corrugated diaphragm and a second corrugated diaphragm, wherein the first corrugated diaphragm is configured to close the first opening to seal the first cavity of the housing frame; and the second corrugated diaphragm is configured to close the second opening to seal the second cavity of the housing frame. The sensor device further includes an inert hydraulic fluid within the first cavity and the second cavity, the inert hydraulic fluid being configured to couple the external pressure acting on the respective corrugated diaphragms to the respective sides of the sensing element, wherein the first corrugated diaphragm and the second corrugated diaphragm are constructed using a substrate having a structured surface by a conformal coating process.

[0012] The housing of the sensor device may be constituted by the housing frame, wherein the housing frame includes a first opening and a second opening, and the first opening and the second opening are sealed using the first corrugated diaphragm and the second corrugated diaphragm to enclose the housing of the sensor device.

[0013] In other words, the sensor device is configured for pressure sensing, specifically, for measuring pressure differences in a liquid medium or a gas medium, which may be incompatible with standard silicon pressure sensor technology.

[0014] This means that the sensor device involves a micro wet-wet differential pressure sensor of the corrugated diaphragm type (“micro sensor”).

[0015] The material of the substrate with a structured surface may include copper.

[0016] The sensor device can be designed as a wet-wet pressure differential sensor and can be used, for example, for measuring the flow rate in a clean water supply network. However, the sensor device can be applied to other industrial fields, including chemical, food and beverage, automotive, and aerospace.

[0017] Advantageously, the sensor device can provide a total package volume of less than 0.2 cm 3 , which is much smaller than that of commercially available wet-wet pressure sensors.

[0018] Reducing the package volume can be achieved by fabricating the sensor device using microfabrication methods commonly used in electronics manufacturing.

[0019] The sensing element of the sensor device can be a standard MEMS piezoresistive / differential pressure sensor chip that is mounted in a housing frame made, for example, of a stack of four ceramic plates. The housing frame can be made of different techniques and suitable materials including stainless steel. The bottom plate and the top plate can include and / or be corrugated diaphragms, where each corrugated diaphragm can provide filling holes to facilitate filling the cavity of the sensor device with a hydraulic fluid. The bottom plate and the top plate and / or the corrugated diaphragms can include thinning regions to facilitate the initial balancing of the cavity pressure during factory calibration.

[0020] Reducing the package volume can be achieved by fabricating the sensor package using microfabrication methods commonly used in electronics manufacturing.

[0021] According to one aspect, the substrate with a structured surface is formed by a lithography process to define the corrugations of the corrugated diaphragm.

[0022] Such miniaturization of the sensor device including a wet-wet pressure differential sensor element can include reducing the diaphragm diameter so that it is commensurate with the sensor chip size. To maintain a sufficiently low diaphragm stiffness, the diaphragm thickness must be reduced as the diameter decreases. For example, when reducing a diaphragm with a diameter of 20 mm and a thickness of 20 µm to a diameter of 4 mm, the thickness must be reduced to 2.34 µm to maintain the same pressure difference to deflection ratio.

[0023] The batch microfabrication methods commonly used in electronic manufacturing can be used to fabricate micro corrugated diaphragms, thereby allowing a large number of diaphragms to be fabricated in parallel.

[0024] According to one aspect, a laser process is performed on an annular channel within a substrate having a structured surface that defines the corrugations of the corrugated diaphragm to smooth the corners of the annular channel.

[0025] Advantageously, smoothing the corners of the annular channel can improve the reliability and stability of the corrugated diaphragm.

[0026] According to one aspect, the corresponding corrugated diaphragm includes a filling hole to facilitate filling the corresponding cavity with a hydraulic fluid.

[0027] Since the filling hole can be an integral part of the corrugated diaphragm, it is simple to install the sensor device because the housing frame can be easily constructed without additional filling holes to supply the hydraulic fluid to the cavity of the sensor device.

[0028] According to one aspect, the corresponding corrugated diaphragm includes an adjustment window to facilitate an initial balancing of the cavity pressure during factory calibration.

[0029] Advantageously, since only the corrugated diaphragm needs to be constructed using miniaturization methods, including the adjustment window into the corrugated diaphragm simplifies the construction of the sensor device.

[0030] According to one aspect, the diameter of the corrugated diaphragm is less than 1 cm, preferably less than 20 mm, and most preferably less than 4 mm.

[0031] Constructing a sensor device with a corrugated diaphragm having such a diameter can achieve a very small sensor device, which improves the usability of these small sensor devices.

[0032] According to one aspect, the material of the corrugated diaphragm includes a metal sheet, where the metal sheet is preferably made of gold and / or nickel and / or titanium and / or stainless steel.

[0033] Advantageously, the adaptation of the corrugated diaphragm material enables the user to select the material according to the specific needs of the application from the sensor device.

[0034] According to one aspect, the metal plate is fabricated using a sputtering process and / or a vacuum deposition process and / or an electroplating process.

[0035] Using different metal layer deposition methods enables sensor devices with different materials to be used for the corrugated diaphragm.

[0036] According to one aspect, a first volume of a first cavity and a second volume of a second cavity are configured to have similar dimensions to minimize the thermal drift of the sensor device due to the thermal expansion of the hydraulic fluid.

[0037] According to one aspect, the housing frame is constructed by stacking ceramic plates, each ceramic plate including holes for constructing corresponding cavities.

[0038] Because laser cutting is limited in terms of the thickness of the ceramic plate to be cut, by using a stack of ceramic plates, individual ceramic plates can be produced by laser cutting.

[0039] According to one aspect, the sensing element is mounted at a hole in one of the ceramic plates of the stack of ceramic plates.

[0040] Mounting the sensing device on one of the ceramic plates improves manufacturability because it enhances the stability of the sensing device during manufacturing.

[0041] The sensor device may include a sensor chip silicon microelectromechanical systems (MEMS) device as the sensing element. The sensing element may be a standard MEMS piezoresistive / differential pressure sensor chip including a silicon die.

[0042] According to one aspect, a method for manufacturing a corrugated diaphragm is provided, including the following steps:

[0043] In one step, lithography is performed on both sides of a metal substrate to construct a substrate with a structured surface to define the corrugations of the corrugated diaphragm through a conformal coating process. In another step, at least one side and preferably both sides of the substrate with the structured surface are conformally coated with a first metal sheet. In another step, at least one first metal sheet is removed from the back side of the substrate. In another step, the metal substrate exposed after removing at least the first metal sheet from the back side of the metal substrate is removed from at least the first metal sheet on the front side of the metal substrate to construct the corrugated diaphragm.

[0044] According to one aspect, after the step of conformally coating the substrate with the structured surface using the first metal sheet, the first metal sheet at the substrate with the structured surface is used to conformally coat both sides of the substrate with the structured surface using a second metal sheet.

[0045] According to one aspect, the method for manufacturing a corrugated diaphragm includes the following steps: before numbering both sides of the substrate with the structured surface conformally with the first metal layer, laser machining is performed on an annular channel that is lithographed within the metal substrate to define the corrugations of the corrugated diaphragm for smoothing the corners of the annular channel.

[0046] According to one aspect, the method for manufacturing a corrugated diaphragm includes the following steps: constructing a filling recess within the corrugated diaphragm.

[0047] According to one aspect, the first metal sheet and / or any additional metal sheets are conformally coated by an electroplating process.

[0048] Preferably, the first metal sheet and / or the second metal sheet are conformally coated by an electroplating process.

[0049] According to one aspect, a method for sealing a cavity of a sensor device for determining a pressure difference in a liquid medium or a gas medium is provided, wherein the sensor device includes a corrugated diaphragm having a filling hole for supplying a hydraulic fluid to the cavity, and the method includes the following steps.

[0050] In one step, the sensor device is placed into a filling chamber for filling the chamber with a hydraulic fluid, wherein the filling chamber is filled with the hydraulic fluid to completely cover the sensor device. In another step, a metal plug is provided, which is configured to seal the filling hole of the corrugated diaphragm. In another step, the metal plug is bonded to the filling hole of the corrugated diaphragm using a thermoacoustic bonding process to seal the cavity of the sensor device.

[0051] The hydraulic fluid included in the sensing device may include silicone oil.

[0052] According to one aspect, the metal plug of the method for sealing a cavity of a sensor device includes a copper wire that is tinned with solder. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this application. The drawings illustrate embodiments of the present invention and, together with the description, are used to explain the principles of the present invention. The drawings show:

[0054] Figure 1 A cross-sectional view of the sensor device is schematically depicted;

[0055] Figure 2 An exploded view of the sensor device is schematically depicted;

[0056] Figure 3 Steps of a method for manufacturing the corrugated diaphragm are schematically depicted;

[0057] Figure 4 Filling the sensor device with a hydraulic fluid is schematically depicted;

[0058] Figure 5 A method for sealing the cavity of the sensor device is schematically depicted;

[0059] Figure 6a 、 Figure 6b A pressure adjustment process of the cavity of the sensor device is schematically depicted. DETAILED DESCRIPTION

[0060] Figure 1A cross-sectional view of the sensor device 2000 before filling the cavity of the sensor device 2000 with hydraulic fluid is schematically depicted. The sensing element 100 can be a standard MEMS piezoresistive / differential pressure sensor chip, which includes a silicon die 110 that has been locally thinned to provide a membrane 115, and wherein the silicon die 110 is mounted on its backplane 120 having holes with channels for accessing the second side of the sensing element.

[0061] Electrical connection to the sensing element is made via a plurality of metal contact pads 140 on the top surface of the sensor chip.

[0062] The sensor device 2000 is composed of a stack of four ceramic plates 200, 250, 300, 350, which construct the housing frame, the metal bottom plate 400, and the metal top plate 500. The ceramic plates 200, 250, 300, 350 are designed to create cavities closed by corrugated diaphragms 410, 510 on both sides of the sensor chip 100. The corrugated diaphragms 410, 510 include filling holes 460, 560, meaning openings 470, 570 for supplying hydraulic fluid to the cavities; and thinning regions 470, 570 for facilitating the initial equilibration of the cavity pressure during factory calibration.

[0063] The sensor chip 100 mounts its backplane 120 on the first ceramic plate 200 using die attachment methods known in the art. For example, if a solderable metal layer 130 is provided on the underside of the sensor chip 100 and a solderable metal layer 220 is deposited on the ceramic plate, the sensor chip 100 can be attached by reflow soldering. Alternatively, if the metal layers 130 and 220 are suitable for solid-state bonding, thermosonic die attachment can be employed. As a third option for die attachment, bonding can be used, preferably in cases where the metal layers 130 and 220 can be omitted. Using solder or bonding attachment, the resulting joint between the sensor chip and the ceramic plate will include a bonding material layer 160, which is absent in the case of thermosonic attachment.

[0064] The die attachment method may have a certain impact on the thermal drift of the encapsulated sensor. Regardless of which method is used, the joint must form a seal around the holes 210 in the ceramic plate to provide separation between the first cavity and the second cavity. The ceramic plate 200 can also include a plurality of metal tracks 230 that extend from near the sensor chip to contact pads 240 at the periphery of the plate. Each metal track 230 is connected to one or more of the contact pads 140 on the sensor chip 100 via one or more bonding wires 150.

[0065] Two other ceramic plates 300, 350 having holes for accommodating the sensor chip 100 are stacked on top of the first ceramic plate 200 to form a first cavity. A fourth perforated ceramic plate 250 is attached to the bottom surface of the first ceramic plate 200. The holes in the fourth ceramic plate, the holes in the first ceramic plate, and the internal cavity of the sensor chip together form a second cavity. The size of the holes in the fourth ceramic plate is selected such that the volumes of the first cavity and the second cavity are equal. This is crucial for minimizing the thermal drift in the sensor caused by the thermal expansion of the hydraulic fluid.

[0066] The ceramic plates 200, 250, 300, 350 can be joined together using any of several techniques known in the art. For example, if all the materials present can withstand the required process temperature of approximately 450 °C, frit bonding can be used. Alternatively, a lower temperature adhesive bonding can be used. A third option for joining the ceramic plates 200, 250, 300, 350 is reflow soldering if a suitable metal coating is applied to the respective surfaces of the ceramic plates 200, 250, 300, 350. Preferably, the ceramic plates 200, 250, 300, 350 should first be bonded together in pairs, where, for example, the ceramic plate 200 is bonded to the ceramic plate 250 and the ceramic plate 300 is bonded to the ceramic plate 350. Then, sensor chip attachment and wire bonding can be carried out, and then, the ceramic plates 200 and 300 can be bonded together. As Figure 1 shown, the bonding layers 260, 310, 360 at the interfaces between the ceramic plates 200, 250, 300, 350 can cover the entire bonding surface. This is likely the case for adhesive bonding. Alternatively, in the case of frit bonding or soldering, the bonding material is preferably defined in a strip around the periphery of the bonding interface. An advantage of using some combination of frit bonding, soldering, and thermosonic bonding is that these techniques can produce hermetically sealed joints. If multiple soldering steps are involved, solders with successively lower reflow temperatures should be used to avoid re-melting the joints after formation.

[0067] Figure 2 An exploded view of the sensor device 2000 before filling with hydraulic fluid is shown, which shows the shapes of the holes 255, 305, 355 in the respective ceramic plates 250, 300, 350. The ceramic plate 250 also includes channels connecting the main holes to additional holes that are directly above the filling holes 460 and the thinning regions 470 on the bottom plate. Similar features are included in the ceramic plate 350.

[0068] Figure 2 The arrangement of the metal tracks 230 and contact pads 240 on the ceramic plate 200 is also shown. It should be noted that the number of components can be reduced by replacing each of the upper and lower ceramic plate pairs with a single thicker ceramic plate.

[0069] However, in this case, the upper plate would need to be thicker than the height of sensor chip 100, which is typically about 1.0 mm. It is convenient to create holes in the ceramic plate by laser cutting, while commercial laser cutting processes are typically limited to a material thickness of about 0.5 mm. Therefore, it is convenient to make up the 1.0 mm thickness by stacking two plates with a thickness of 0.5 mm each. This method also avoids setting blind holes in the ceramic plate.

[0070] The bottom plate 400 and the top plate 500 are preferably attached to the ceramic plates 250 and 350 by reflow soldering. Other bonding methods such as thermosonic bonding or adhesive bonding can also be employed. In the case of reflow soldering, the bottom and top plates are finished with weldable metal layers 440, 540, and opposing weldable metal tracks 270, 370 should be provided on the ceramic plates 250 and 350. The reflow temperature of the solder used should be lower than the maximum service temperature of any adhesives present in the assembly, and also lower than the reflow temperature of any solder used for mounting the sensor chip or bonding the ceramic plates.

[0071] The described sensor device 2000 can be used as a small wet-wet differential pressure sensor by reducing the diaphragm diameter to match the sensor chip size.

[0072] To maintain a sufficiently low diaphragm stiffness, it is also necessary to reduce the diaphragm thickness. For example, when reducing a diaphragm with a diameter of 20 mm and a thickness of 20 μm to a diameter of 4 mm, the thickness must be reduced to 2.34 μm to maintain the same pressure difference to deflection ratio.

[0073] The state-of-the-art methods for manufacturing corrugated diaphragms for wet-wet pressure sensors are not applicable to this scale. However, batch microfabrication methods commonly used in electronics manufacturing can be applied, allowing for the parallel fabrication of a large number of diaphragms.

[0074] Figure 3 A method for manufacturing the corrugated diaphragms 410, 510 is schematically depicted, which can include the peripheral regions defining the bottom plate 400 and the top plate 500 of the sensor device 2000. The starting material is a copper substrate 1000 with a thickness greater than the proposed corrugation depth.

[0075] In a first process step 1110, standard lithography techniques (e.g., from microelectronics manufacturing) are used to etch several concentric circular channels 1020 into the top surface of the substrate, which are configured to define the corrugations in the diaphragm.

[0076] The bottom surface of the circular recess 1025 covering the entire diaphragm area of the bottom plate 400 or the top plate 500 is also etched. The top-side etch depth and the bottom-side etch depth are controlled such that the minimum thickness of the remaining copper in the diaphragm area is small but greater than zero at all parts of the substrate. Methods for such controlled-depth etching are known in the art. The top-side etching process and the bottom-side etching process are also used to create recesses on both sides of the substrate at the locations for positioning the fill holes 1060, 1065, at the thinning areas for pressure balancing 1070, 1075, and at the rectangular channel lines 1090, 1095 defining the periphery of the plate.

[0077] In the second process step 1120, the etched substrate is conformally coated (e.g., by electroplating) with a first metal layer "Metal 1". This metal layer will form the corrugated diaphragms 410, 510, so it must exhibit elastic behavior up to the maximum strain level expected in the corrugated diaphragms 410, 510. It must also be able to act as an etch stop for copper. Nickel meets both requirements and is a preferred option because electroplating nickel onto copper is a standard process.

[0078] In the third process step 1130, a second metal layer "Metal 2" can be applied (e.g., by electroplating) on top of Metal 1. Metal 2 can be compatible with the selected bonding method for attaching the bottom plate 400 and the top plate 500 to the sensor device 2000. It can also be chemically compatible with the process medium characterized by the sensor device 2000. For a sensor device 2000 intended for use in water, gold is the first choice because it is chemically inert and compatible with reflow soldering and thermosonic bonding. It can also be easily electroplated onto nickel. Metal 2 will inevitably affect the mechanical properties of the diaphragm, so it should also exhibit acceptable elastic behavior.

[0079] To form the corrugated diaphragms 410, 510, the copper remaining in the bottom-side recess 1025 needs to be removed. This can be accomplished by removing the first metal layer and / or the second metal layer from the bottom of the back-side recess 1025 in process step 1140 and then removing the exposed copper through a chemical etching process step 1150. The first metal layer and / or the second metal layer can be conveniently removed by laser machining using, for example, a pulsed ultraviolet laser. Alternatively, a photolithography process can be employed.

[0080] In the next process step 1160, the material remaining between the front-side hole fill recess 1060 and the back-side hole fill recess 1065 is removed to create the fill holes 460, 560. The material between the front-side rectangular channel 1090 and the back-side rectangular channel 1095 can also be removed to separate the plate from the fabricated substrate.

[0081] It should be noted that Figure 3The process flow shown is one of the many possible processes for fabricating the bottom plate and the top plate. Alternative methods may include, but are not limited to, using silicon or other materials as the substrate to be patterned and depositing a metal layer by sputtering or any other vacuum deposition process. The latter may allow the use of alternative diaphragm materials that are not suitable for electroplating, such as titanium or stainless steel.

[0082] The sensor device 2000 can be filled with hydraulic fluid using a method similar to that used for traditional corrugated diaphragm-type sensors. Figure 5 A filling device is schematically depicted, which may include a vacuum chamber 610 having a removable top plate 620 and a bottom plate 630. The chamber has a first port 640 and a second port 650. The first port 640 is equipped with a shut-off valve 645 connected to a vacuum pump, while the second port 650 is equipped with a shut-off valve 655 connected to a hydraulic fluid reservoir.

[0083] Starting with both valves open, the pipe from the reservoir is free of hydraulic fluid, and the fluid level in the reservoir is below the reservoir outlet level. The filling chamber and the reservoir are evacuated to degas the hydraulic fluid and remove air from the filling chamber and the sensor cavity.

[0084] Once the degassing is complete, the valve 645 can be closed, and the fluid level in the reservoir can be raised until the fluid flows by gravity from the reservoir into the filling chamber. Once the filling chamber is full of hydraulic fluid, the valve 655 can be closed to isolate the filling chamber from the reservoir. Figure 4 The device at this stage in the process is shown.

[0085] Figure 5 A method for sealing the cavity of the sensor device 2000 is shown, which may include: thermosonically bonding a metal plug to the filling holes 460, 560 of the sensor device 2000. This thermosonic bonding can be carried out with the help of a suitable thermosonic bonding machine and with the open sensor device 2000 still in the filling chamber to avoid any risk of air entry. To seal the upper cavity of the sensor device 2000, the top plate of the filling chamber can be removed, and a metal plug 750 held in a bonder pick-up tool 660 can be inserted into the filling hole of the top plate. Then, heat and ultrasonic energy are applied via the pick-up tool to form a thermosonic bond between the portion 760 of the plug 750 and the top plate 500 of the sensor device 2000. To seal the lower cavity using the plug 700 and the bonding site 710 but with the filling chamber flipped, the same process can be followed to have the lower cavity of the sensor device 2000 at the top. The cover components suitable for thermosonic bonding can be fabricated by the same process as the bottom plate and the top plate.

[0086] It should be noted that alternative methods (e.g., friction welding or brazing) can be employed to seal the cavity. Some form of expansion plug device can also be used.

[0087] After the sealing process, it is desirable for the initial pressures in the upper and lower cavities to be positive relative to atmospheric pressure. The cavity pressures should also be balanced so that there is no initial offset in the output of the sensor device. The thinning regions 470 and 570 in the bottom and top plates allow for an initial adjustment of the cavity pressures to ensure these requirements are met.

[0088] Figure 6a The pressure adjustment process for the upper cavity of the sensor device 2000 is schematically depicted. To adjust the cavity pressure, a hard tool with an appropriate conical tip is pushed against the thinning region 570 to cause it to plastically deform. The displacement of the hydraulic fluid from behind the thinning region will cause the corrugated diaphragm 510 to deflect outwards and increase the cavity pressure, which can be monitored via the output signal of the sensor chip 100. Assuming the initial cavity pressure is close to atmospheric pressure, the process is to deform the lower thinning region until the sensor chip 100 records the desired initial pressure subtracted, and then deform the upper thinning region until the sensor chip 100 reads zero.

[0089] Figure 6b The sensor device 2000 filled with hydraulic fluid, sealed and adjusted as described above, is schematically depicted.

Claims

1. A sensor device (2000) for determining a pressure difference in a liquid medium or a gas medium, comprising: A housing frame for the sensor device (2000), including a first opening and a second opening; A sensing element (100), including a first side and a second side, and the sensing element (100) is configured and located within the housing frame to construct a first cavity at a first portion of the housing frame and a second cavity at a second portion of the housing frame, wherein the sensing element (100) is configured to determine the pressure difference between the first side and the second side; A first corrugated diaphragm (400, 410) and a second corrugated diaphragm (500, 510), wherein the first corrugated diaphragm (400, 410) is configured to close the first opening to seal the first cavity of the housing frame; And the second corrugated diaphragm (500, 510) is configured to close the second opening to seal the second cavity of the housing frame; An inert hydraulic fluid within the first cavity and the second cavity, configured to couple an external pressure acting on the respective corrugated diaphragms (400, 410, 500, 510) to the respective sides of the sensing element (100); Wherein the first corrugated diaphragm (400, 410) and the second corrugated diaphragm (500, 510) are constructed by a conformal coating process using a substrate having a structured surface; Wherein the housing frame is constructed from a stack of ceramic plates (200, 250, 300, 350), each ceramic plate including holes (255, 305, 355) for constructing the respective cavities.

2. The sensor device (2000) according to claim 1, wherein the substrate having a structured surface is formed by a lithography process to define the corrugations of the corrugated diaphragms (400, 410, 500, 510).

3. The sensor device (2000) according to claim 2, wherein a laser process is performed on an annular channel defining the corrugations within the substrate having a structured surface to smooth the corners of the annular channel.

4. The sensor device (2000) according to any one of the preceding claims, wherein the respective corrugated diaphragms (400, 410, 500, 510) include adjustment windows (470, 570) to facilitate an initial equalization of the cavity pressures during factory calibration.

5. The sensor device (2000) according to any one of claims 1 - 3, wherein the diameter of the corrugated diaphragms (400, 410, 500, 510) is less than 1 cm.

6. The sensor device (2000) according to claim 5, wherein the diameter is less than 20 mm.

7. The sensor device (2000) according to claim 5, wherein the diameter is less than 4 mm 8. The sensor device (2000) according to any one of claims 1 - 3, wherein the material of the corrugated diaphragms (400, 410, 500, 510) includes a metal sheet.

9. The sensor device (2000) according to claim 8, wherein the metal sheet is made of gold and / or nickel and / or titanium and / or stainless steel.

10. The sensor device (2000) according to claim 8, wherein the metal sheet is made by a sputtering process and / or a vacuum deposition process and / or an electroplating process.

11. The sensor device (2000) according to any one of claims 1-3, wherein the first volume of the first cavity and the second volume of the second cavity are configured to have similar dimensions so as to minimize the thermal drift of the sensor device due to the thermal expansion of the hydraulic fluid.

12. The sensor device (2000) according to any one of claims 1-3, wherein the sensing element (100) is mounted at a hole of one of the ceramic plates (200) in the stack of ceramic plates (200, 250, 300, 350).

13. A method for manufacturing a corrugated diaphragm (400, 410, 500, 510), comprising: Performing photolithography on both sides of a metal substrate to construct a substrate with a structured surface, so as to define the corrugations of the corrugated diaphragm (400, 410, 500, 510) through a conformal coating process; Coating both sides of the substrate with the structured surface conformally using a first metal sheet; Removing the at least one first metal sheet from the back side of the metal substrate; Removing the metal substrate exposed after removing the at least first metal sheet from the back side of the metal substrate from the at least first metal sheet on the front side of the metal substrate to construct the corrugated diaphragm (400, 410, 500, 510).

14. The method according to claim 13, comprising: Performing laser machining on an annular channel (520) which is lithographed in the metal substrate to define the corrugations of the corrugated diaphragm for smoothing the corners of the annular channel (520).

15. The method according to claim 13 or 14, wherein the first metal sheet and / or any additional metal sheets are conformally coated by an electroplating process.

16. A method for sealing a cavity of a sensor device (2000) for determining a pressure difference in a liquid medium or a gas medium, wherein the sensor device (2000) includes a corrugated diaphragm (400, 410, 500, 510) having filling holes (460, 560) for supplying a hydraulic fluid to the cavity, the method comprising: Placing the sensor device (2000) in a filling chamber for filling the cavity with the hydraulic fluid, wherein the filling chamber is filled with the hydraulic fluid to completely cover the sensor device (2000); Providing metal plugs (700, 750) configured to seal the filling holes (460, 560) of the corrugated diaphragm (400, 410, 500, 510); The metal plugs (700, 750) are bonded to the filling holes (460, 560) of the corrugated diaphragms (400, 410, 500, 510) using a thermosonic bonding process to seal the cavity of the sensor device (2000).

17. The method according to claim 16, wherein the metal plugs (700, 750) comprise copper wires, and the copper wires are tinned with solder.

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