Patent Publication Number: US-2023160732-A1

Title: Thermoresistive Micro Sensor Device

Description:
This application is a divisional of U.S. patent application Ser. No. 16/868,912, filed May 7, 2020, which application claims the benefit of European Patent Application No. 19180341, filed on Jun. 14, 2019, which applications are hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     Embodiments relate to a thermoresistive micro sensor device for a mass flow meter for measuring a mass flow of a fluid or for a pressure meter for measuring a pressure in a fluid. Further embodiments relate to a mass flow meter for measuring a mass flow of a fluid and to a pressure meter for measuring a pressure in a fluid. 
     BACKGROUND 
     Thermoresistive micro sensor devices and thermal flow sensors in general are known in the art. Thermal flow sensors are transducers, which comprise heaters and temperature sensors. The heat interacts with the surrounding: a streaming liquid carries away some heat and the temperature distribution around the heater changes in conjunction with the moving fluid. In particular, the temperature of the heater depends on the flow. Silicon micromachining allows the fabrication of small components where many different functions (e.g. arrays of temperature sensors and heaters, pressure sensors, shear stress sensors, etc.) can be integrated so that the functionality of the sensors can be increased. Furthermore, due to the small size of the elements these sensors can be quite fast. Speed is important in turbulent flow and in acoustics. 
     SUMMARY 
     A thermoresistive micro sensor device for a mass flow meter for measuring a mass flow of a fluid or for a pressure meter for measuring a pressure in a fluid is provided. The thermoresistive micro sensor device comprises 
     a semiconductor chip having an upper side and a lower side; 
     at least one through hole, which runs through the semiconductor chip from the upper side to the lower side; 
     one or more electrically conductive structures, wherein each of the electrically conductive structures comprises a first end section, a second end section and a middle section being arranged between the first end section and the second end section, wherein the first end section and the second end section of each of the electrically conductive structures are mounted to the semiconductor chip so that the middle section of each of the electrically conductive structures spans over the through hole at the upper side of the semiconductor chip; 
     an electrically insulating arrangement configured for electrically insulating the one or more electrically conductive structures and the semiconductor chip from each other, wherein the through hole runs through the electrically insulating arrangement; and 
     a contact arrangement comprising a plurality of contacts, wherein each of the plurality of contacts is electrically connected to one of the first end sections or to one of the second end sections, so that electrical energy, which is supplied to the contact arrangement, is fed to at least one of the electrically conductive structures in order to heat the respective electrically conductive structure, and so that an electrical resistance of one of the electrically conductive structures may be measured at the contact arrangement. 
     In this document terms like “upper”, “lower” and other terms related to directions or locations refer to an orientation of the thermoresistive micro sensor device in which the semiconductor chip is orientated parallelly to the Earth&#39;s surface and in which the lower side of the semiconductor chip is facing towards the Earth&#39;s surface. 
     A thermoresistive sensor device is a sensor device which exploits the effect that an electrical resistance of an electrically conductive structure depends on its temperature. 
     The thermoresistive micro sensor device may have a vertical extension in the range of a few micrometers and a horizontal extension in the range of a few millimeters. The semiconductor chip can be made of silicon and the conductive structures may be made of polysilicon. 
     The electrically insulating arrangement can be made of any insulating material. In particular they can be made of Silicon nitride (SiN), which has a high tensile strength and is electrically and thermally insulating. It may comprise one or more layers which may be made of different insulating materials. The purpose of the electrically insulating arrangement is to separate the semiconductor chip on one hand and the contact arrangement on the on the other hand electrically. Furthermore, it may electrically separate different electrically conductive structures from each other. In the same way it may prevent one of the electrically conductive structures from being shortcut. Also it may electrically separate and insulate the contacts from each other. 
     The middle sections of the electrically conductive structures may be mechanically supported by a portion of the electrically insulating arrangement which spans over the through hole of the semiconductor chip. 
     The electrically conductive structures are preferably manufactured from materials having a high temperature coefficient, such as poly-silicon (poly-Si), platinum (Pt), tantalum (Ta) or tungsten (W). 
     The electrically conductive structures may have a wire-like shape having a (transverse) width between 0.5-20 μm (typical 3 μm), having a length between 100-2.000 μm (typical 800 μm) and a (vertical) thickness between 100-1.500 nm (typical 500 nm). 
     The contact arrangement is configured in such way that electrical energy fed to the contact arrangement whereas at least one of the electrically conductive structures in order to heat the respective electrically conductive structure. This will increase the temperature of at least one of the electrically conductive structures so that the resistance of the respective electrically conductive structure will change. The change of the resistance depends on a temperature coefficient of the material of the respective electrically conductive structure. 
     However, the temperature change does not only depend on the amount of electric energy fed to the electrically conductive structure but also on environmental conditions. For example, if the electrically conductive structure which is heated by the electric energy is surrounded by a fluid, which may be a gas or a liquid, the temperature distribution will change if the fluid is in motion adjacent to the electrically conductive structure. This is because the flowing fluid transports heat away from the electrically conductive structure, so that the temperature distribution around the electrically conductive structures depends on the mass flow of the fluid. As a result, the mass flow may be measured by measuring the resistance of the electrically conductive structure. 
     If, however, the mass flow of the fluid is zero, low or known the temperature distribution can be exploited for measuring the pressure of the fluid as a heat transport capacity of the fluid depends on the pressure of the fluid. Generally one can say that at higher pressures the heat transport capacity is higher so that more heat energy may be transported away from the heated electrically conductive structure. As a result, the pressure may be measured by measuring the resistance of the electrically conductive structure. The resistance can be measured by measuring a relative change of the resistance or by measuring a value of the resistance. 
     In order to measure the resistance of the electrically conductive structure, contact arrangement is configured in such way that the resistance can be measured at the contact arrangement. 
     The contact arrangement may comprise contact pads for connecting the thermoresistive micro sensor device to an external electrical energy supply unit for supplying the electrical energy and for connecting the thermoresistive micro sensor device to an external measuring unit for measuring the electrical resistance. However, the contact arrangement can also be configured for directly connecting the thermoresistive micro sensor device to an electrical energy supply unit and/or to a measuring unit which is/are arranged at the semiconductor chip of the thermoresistive micro sensor device. 
     The through hole, which runs through the semiconductor chip, minimizes an impact of the semiconductor chip to a temperature distribution around the electrically conductive structures. Whereby, a sensitivity of the disclosed thermoresistive micro sensor device may be increased. Moreover, a higher accuracy may be achieved. Furthermore, a response time of the thermoresistive micro sensor device may be decreased. 
     The thermoresistive micro sensor device is, in particular, suitable for applications in which low mass flows need to be detected. For example, it is suitable for precise dosage in microreactors, medical or chemical applications, in particular for in-situ analysis etc. It can be used as the sensing sub part (component) of a micro-dosing device or a particle monitoring device. Two (or more) thermoresistive micro sensor devices in a row can be used to detect a flow direction and/or for increased sensibility. The thermoresistive micro sensor device can enable mobile medical applications and is smaller and more cost economic compared to conventional state of the art sensors. Moreover, it can be integrated monolithically within other MEMS sensor and/or actuator systems. 
     The thermoresistive micro sensor device can alternatively be used for sensing pressure. In this case the fluid flow is either fixed (and known) or non-existent. The heat transport depends here directly on the pressure of the fluid. Changes in the heat transport result in a change of the temperature distribution of the electrically conductive structure or the electrically conductive structures. The changes in the temperature distribution can be detected by a shift in resistance, allowing for pressure sensing. 
     The thermoresistive micro sensor device can be produced on a single wafer using state of the art semiconductor manufacturing processes. The layout can be manufactured at all conventional chip sizes, which enables integration into mobile devices and a broad range of measurable flow velocities. It may provide a low fluidic resistance due to large inlet/outlet cross-section area and has no moving parts. 
     The thermoresistive micro sensor device can be driven either with a constant power, with a constant voltage, with a constant current or in a force feedback mode, each in AC or DC. 
     According to some embodiments the one or more electrically conductive structures comprise an electrically conductive heating and sensing structure, wherein the electrical energy from the contact arrangement is fed to the electrically conductive sensing and heating structure, and wherein the electrical resistance, which may be measured at the contact arrangement, is an electrical resistance of the electrically conductive heating and sensing structure. 
     The electrically conductive heating and sensing structure may be heated by an electrical heating current flowing through it. Also, it may be heated by applying external optical energy or electromagnetic energy to it. For example, the electrically conductive heating and sensing structure may be heated by shining light on it so that it absorbs the energy. In other examples, the electrically conductive heating and sensing structure may be heated by using high frequency electromagnetic fields which cause power losses in in the electrically conductive heating structure. 
     In this case at least one electrically conducting structure is, at the same time, used for heating and for sensing. The heat is transported away from the electrically conductive heating and sensing structure by the fluid so that the resistance of the electrically conductive heating and sensing structure changes due to a temperature change caused by a change of a mass flow or a pressure of the fluid. Such embodiments can be manufactured at very low costs. 
     According to some embodiments in a top view a cross section of the through hole in the electrically insulating arrangement is smaller than a cross section of the through hole in the semiconductor chip. By these features the effective cross-section of the through hole may be decreased so that—at a given mass flow—a speed of the fluid is increased, which results in a higher sensitivity, in particular at low mass flows. 
     According to some embodiments the first end section of one of the electrically conductive structures is connected to a first contact of the contact arrangement and to a second contact of the contact arrangement, and wherein the second end section of the one of the electrically conductive structures is connected to a third contact of the contact arrangement and to a fourth contact of the contact arrangement. Such embodiments enable the use of four-terminal sensing, which is also known as Kelvin sensing, and which allows to measure very low resistances at high precision so that the measuring accuracy of the device may be increased. 
     According to some embodiments in a top view a transverse width of the middle section of one of the electrically conductive structures increases from a central portion of the middle section to the first end section of the middle section and from the central portion of the middle section to the second end section of the middle section. In this case the resistance around the central portion of the middle section is higher than the resistance of the middle section close to the end sections which increases the sensitivity of the device. 
     According to some embodiments in a top view the middle section of one of the electrically conductive structures comprises a plurality of electrically conductive substructures parallelly arranged to a direction from the first end section of the one of the electrically conductive structures to the second end section of the one of the electrically conductive structures, wherein the electrically conductive substructures are separated by one or more elongated openings. These features further increase the sensitivity of the device. 
     According to some embodiments the middle section of the one of the electrically conductive structures comprises at least one electrically insulating support element, which mechanically connects at least some of the electrically conductive substructures, and which spans at least over one of the elongated openings at an angle to the direction from the first end section of the one of the electrically conductive structures to the second end section of the one of the electrically conductive structures. By these features a mechanical stability of the device may be increased. 
     According to some embodiments in a top view the middle section of one of the electrically conductive structures comprises a frame-like portion having in a top view a frame-like shape. The term frame-like shape refers to any shape of the electrically conductive structure which enframes in a top view a predominant portion of the cross-section of the through hole. For example, it may refer to the ring-like shape. These features may increase the sensitivity of the device by optimizing and heat transfer to or from the fluid. 
     According to some embodiments in a top view the middle section of one of the electrically conductive structures comprises a perforated portion having in a top view a two-dimensional perforation comprising a plurality of through holes. These features may increase the sensitivity of the device by optimizing and heat transfer to or from the fluid. 
     According to some embodiments the one or more electrically conductive structures comprise a plurality of electrically conductive structures which are spaced in a horizontal direction apart from each other. These features may increase the sensitivity of the device. 
     According to some embodiments the one or more electrically conductive structures comprise an electrically conductive heating structure and an electrically conductive sensing structure being different from the electrically conductive heating structure, wherein the electrical energy from the contact arrangement is fed to the electrically conductive heating structure, and wherein the electrical resistance, which may be measured at the contact arrangement, is the electrical resistance of the electrically conductive sensing structure. 
     The electrically conductive heating structure may be heated by an electrical heating current flowing through it. Also, it may be heated by applying external optical energy or electromagnetic energy to it. For example, the electrically conductive heating structure may be heated by shining light on it so that it absorbs the energy. In other examples, the electrically conductive heating structure may be heated by using high frequency electromagnetic fields which cause power losses in the electrically conductive heating structure. 
     By these features the functions of heating and sensing are executed by different structures so that a current for heating the device and a current for sensing the resistance are independent from each other. By these features the sensitivity, the accuracy and the time response may be further enhanced. 
     According to some embodiments an electrostatic actuator is configured for electro-statically deflecting the electrically conductive heating structure and/or the electrically conductive sensing structure so that a distance between the electrically conductive heating structure and the electrically conductive sensing structure may be changed by applying a first voltage to the electrostatic actuator. 
     According to some embodiments a piezoelectric actuator is configured for deflecting the electrically conductive heating structure and/or the electrically conductive sensing structure so that a distance between the electrically conductive heating structure and the electrically conductive sensing structure may be changed by applying a second voltage to the piezoelectric actuator. 
     According to some embodiments a thermomechanical actuator is configured for deflecting the electrically conductive heating structure and/or the electrically conductive sensing structure so that a distance between the electrically conductive heating structure and the electrically conductive sensing structure may be changed by applying a current to the thermomechanical actuator. 
     Different distances between heating/sensing-structures are beneficial for a high sensitivity in different pressure ranges and/or mass flow ranges and thus increase a total measurement range. 
     According to some embodiments the one or more electrically conductive structures comprise a plurality of electrically conductive structures which are spaced in a vertical direction apart from each other. Such features allow detecting the flow direction of the fluid and/or increasing the sensitivity of the device. 
     In a further aspect a mass flow meter for measuring a mass flow of a fluid is provided. The mass flow meter comprises 
     a thermoresistive micro sensor device as described herein; 
     an electrical energy supply unit for supplying the electrical energy to the contact arrangement; and 
     a measuring unit for measuring the electrical resistance at the contact arrangement; 
     wherein the measuring unit is configured for measuring the mass flow of the fluid flowing through the through hole depending on the electrical resistance. 
     In a further aspect a pressure meter for measuring a pressure in a fluid is provided. The pressure meter comprises 
     a thermoresistive micro sensor device as described herein; 
     an electrical energy supply unit for supplying the electrical energy to the contact arrangement; and 
     a measuring unit for measuring the electrical resistance at the contact arrangement; 
     wherein the measuring unit is configured for measuring the pressure of the fluid at the through hole depending on the electrical resistance. 
     In some embodiments the electrical energy supply unit of the mass flow meter or the pressure meter is configured for supplying the electrical energy as an alternating current or an alternating voltage. By these features a modulated signal can be generated so that the signal-to-noise ratio can be improved by an AC-band-pass filter. 
     In some embodiments the electrical energy supply unit of the mass flow meter or the pressure meter comprises a control unit configured for controlling the electrostatic actuator, the piezoelectric actuator and/or thermomechanical actuator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention are described herein making reference to the appended drawings. 
         FIG.  1    shows a schematic top view of a first embodiment of a thermoresistive micro sensor device; 
         FIG.  2    shows a schematic cross-sectional side view of the first embodiment of the thermoresistive micro sensor device; 
         FIG.  3    shows a schematic top view of a second embodiment of a thermoresistive micro sensor device; 
         FIG.  4    shows a schematic top view of a third embodiment of a thermoresistive micro sensor device; 
         FIG.  5    shows a schematic top view of a fourth embodiment of a thermoresistive micro sensor device; 
         FIG.  6    shows a schematic top view of a fifth embodiment of a thermoresistive micro sensor device; 
         FIG.  7    shows a schematic top view of a sixth embodiment of a thermoresistive micro sensor device; 
         FIG.  8    shows a schematic top view of a seventh embodiment of a thermoresistive micro sensor device; 
         FIG.  9    shows a schematic top view of an eighth embodiment of a thermoresistive micro sensor device, wherein an electrostatic actuator is switched off; 
         FIG.  10    shows a schematic top view of the eighth embodiment of a thermoresistive micro sensor device, wherein the electrostatic actuator is switched on; 
         FIG.  11    shows an exemplary diagram showing normalized sensor responses for different distances between the electrically conductive heating structure and the electrically conductive sensing structure of the eighth embodiment of a thermoresistive micro sensor device; 
         FIG.  12    shows a schematic top view of a ninth embodiment of a thermoresistive micro sensor device; 
         FIG.  13    shows a schematic cross-sectional side view of the ninth embodiment of the thermoresistive micro sensor device; 
         FIG.  14    shows a schematic top view of a tenth embodiment of a thermoresistive micro sensor device; 
         FIG.  15    shows a schematic top view of an eleventh embodiment of a thermoresistive micro sensor device; 
         FIG.  16    shows an exemplary temperature distribution at a thermoresistive micro sensor device according to the eleventh embodiment; 
         FIG.  17    shows a schematic top view of a twelfth embodiment of a thermoresistive micro sensor device; 
         FIG.  18    shows a schematic top view of a thirteenth embodiment of a thermoresistive micro sensor device; 
         FIG.  19    shows a schematic top view of a fourteenth embodiment of a thermoresistive micro sensor device; 
         FIG.  20    shows a schematic top view of a fifteenth embodiment of a thermoresistive micro sensor device; 
         FIG.  21    shows a schematic cross-sectional side view of a sixteenth embodiment of the thermoresistive micro sensor device; 
         FIG.  22    shows a schematic top view of an embodiment of a mass flow meter comprising a thermoresistive micro sensor device; and 
         FIG.  23    shows a schematic top view of an embodiment of a pressure meter comprising a thermoresistive micro sensor device. 
     
    
    
     Equal or equivalent elements or elements with equal or equivalent functionality are denoted in the following description by equal or equivalent reference numerals. 
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     In the following description, a plurality of details is set forth to provide a more thorough explanation of embodiments of the present invention. However, it will be apparent to those skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form rather than in detail in order to avoid obscuring embodiments of the present invention. In addition, features of the different embodiments described hereinafter may be combined with each other, unless specifically noted otherwise. 
       FIG.  1    shows a schematic top view of a first embodiment of a thermoresistive micro sensor device  1  and  FIG.  2    shows a schematic cross-sectional side view of the first embodiment of the thermoresistive micro sensor device  1 . 
     The thermoresistive micro sensor device for a mass flow meter for measuring a mass flow of a fluid or for a pressure meter for measuring a pressure in a fluid, the thermoresistive micro sensor device  1  comprises 
     a semiconductor chip  2  having an upper side  3  and a lower side  4 ; 
     at least one through hole  5 , which runs through the semiconductor chip  2  from the upper side  3  to the lower side  4 ; 
     one or more electrically conductive structures  6 , wherein each of the electrically conductive structures  6  comprises a first end section  7 , a second end section  8  and a middle section  9  being arranged between the first end section  7  and the second end section  8 , wherein the first end section  7  and the second end section  8  of each of the electrically conductive structures  6  are mounted to the semiconductor chip  2  so that the middle section  9  of each of the electrically conductive structures  6  spans over the through hole  5  at the upper side  3  of the semiconductor chip  2 ; 
     an electrically insulating arrangement  10  configured for electrically insulating the one or more electrically conductive structures  6  and the semiconductor chip  2  from each other, wherein the through hole  5  runs through the electrically insulating arrangement  10 ; and 
     a contact arrangement  11  comprising a plurality of contacts  12 , wherein each of the plurality of contacts  12  is electrically connected to one of the first end sections  7  or to one of the second end sections  8 , so that electrical energy, which is supplied to the contact arrangement  11 , is fed to at least one of the electrically conductive structures  6  in order to heat the respective electrically conductive structure  6 , and so that an electrical resistance of one of the electrically conductive structures  6  may be measured at the contact arrangement  11 . 
     According to some embodiments the one or more electrically conductive structures  6  comprise an electrically conductive heating and sensing structure  6 , wherein the electrical energy from the contact arrangement  11  is fed to the electrically conductive sensing and heating structure  6 , and wherein the electrical resistance, which may be measured at the contact arrangement  11 , is an electrical resistance of the electrically conductive heating and sensing structure  6 . 
     According to some embodiments the first end section  7  of one of the electrically conductive structures  6  is connected to a first contact  12 . 1  of the contact arrangement  11  and to a second contact  12 . 2  of the contact arrangement  11 , and the second end section  8  of the one of the electrically conductive structures  6  is connected to a third contact  12 . 3  of the contact arrangement  11  and to a fourth contact  12 . 4  of the contact arrangement  11 . 
       FIG.  1    and  FIG.  2    show a simple layout for four-terminal sensing with a single heating wire in a schematic representation. The electrically conductive structure  6  is used for sensing and for heating. It is suspended above the through hole  5 , supported (at the ends) by a membrane  10  manufactured from (thermally and electrically) isolating material. The contacts  12 . 1  and  12 . 2  are electrically connected to the first end section  7  and the contacts  12 . 3  and  12 . 4  are connected to the second and section  8  of the electrically conductive structure  6 . 
       FIG.  3    shows a schematic top view of a second embodiment of a thermoresistive micro sensor device  1 . The second embodiment is based on the first embodiment. 
     According to some embodiments in a top view a cross section  13  of the through hole  5  in the electrically insulating arrangement  10  is smaller than a cross section  14  of the through hole  5  in the semiconductor chip  2 . By the reduced opening in the electrically insulating arrangement  10  a higher sensitivity may be achieved as the speed of the fluid is increased for a certain mass flow. 
       FIG.  4    shows a schematic top view of a third embodiment of a thermoresistive micro sensor device  1 . The third embodiment is also based on the first embodiment. 
     According to some embodiments in a top view a transverse width TW of the middle section  9  of one of the electrically conductive structures  6  increases from a central portion of the middle section  9  to the first end section  7  of the middle section  9  and from the central portion to the second end section  8  of the middle section  9 . 
       FIG.  5    shows a schematic top view of a fourth embodiment of a thermoresistive micro sensor device  1 . The fourth embodiment is also based on the first embodiment. 
     According to some embodiments in a top view the middle section  9  of one of the electrically conductive structures  6  comprises a plurality of electrically conductive substructures  16  parallelly arranged to a direction from the first end section  7  of the one of the electrically conductive structures  6  to the second end section  8  of the one of the electrically conductive structures  6 , wherein the electrically conductive sub-structures  16  are separated by one or more elongated openings  17 . 
       FIG.  6    shows a schematic top view of a fifth embodiment of a thermoresistive micro sensor device  1 . The fifth embodiment is also based on the first embodiment. 
     According to some embodiments the middle section  9  of the one of the electrically conductive structures  6  comprises at least one electrically insulating support element  18 , which mechanically connects at least some of the electrically conductive substructures  16 , and which spans at least over one of the elongated openings  17  at an angle to the direction from the first end section  7  of the one of the electrically conductive structures  6  to the second end section  8  of the one of the electrically conductive structures  6 . 
       FIG.  7    shows a schematic top view of a sixth embodiment of a thermoresistive micro sensor device  1 . The sixth embodiment is also based on the first embodiment. 
     According to some embodiments in a top view the middle section  9  of one of the electrically conductive structures  6  comprises a frame-like portion  19  having in a top view a frame-like shape. Shown is an exemplary layout with a ring-shaped heating structure to optimize the heat transfer to and from the fluid. 
       FIG.  8    shows a schematic top view of a seventh embodiment of a thermoresistive micro sensor device  1 . The seventh embodiment is also based on the first embodiment. 
     According to some embodiments in a top view the middle section  9  of one of the electrically conductive structures  6  comprises a perforated portion  20  having in a top view a two-dimensional perforation comprising a plurality of through holes  21 . 
     Shown here is an exemplary layout with a perforated membrane acting as the heating/sensing structure  6 , to increase contact surface with the fluid and thus increase heat transfer. By shaping the holes and/or arranging the perforation density among the membrane, flow profiles can be integrated and weighted for measurements; featuring their thermal and flow gradients. 
       FIG.  9    shows a schematic top view of an eighth embodiment of a thermoresistive micro sensor device  1 , wherein an electrostatic actuator  24  is switched off and  FIG.  10    shows a schematic top view of the eighth embodiment of a thermoresistive micro sensor device  1 , wherein the electrostatic actuator  24  is switched on. 
     According to some embodiments the one or more electrically conductive structures  6  comprise a plurality of electrically conductive structures  22 ,  23  which are spaced in a horizontal direction HD apart from each other. 
     According to some embodiments the one or more electrically conductive structures  6  comprise an electrically conductive heating structure  22  and an electrically conductive sensing structure  23  being different from the electrically conductive heating structure  22 , wherein the electrical energy, which is supplied to the contact arrangement  11 , is fed to the electrically conductive heating structure  22 , and wherein the electrical resistance, which may be measured at the contact arrangement  11 , is the electrical resistance of the electrically conductive sensing structure  23 . 
     According to some embodiments an electrostatic actuator  24  is configured for electrostatically deflecting the electrically conductive heating structure  22  and/or the electrically conductive sensing structure  23  so that a distance DI between the electrically conductive heating structure  22  and the electrically conductive sensing structure  23  may be changed by applying a first voltage to the electrostatic actuator  24 . 
     According to some embodiments a piezoelectric actuator is configured for deflecting the electrically conductive heating structure  22  and/or the electrically conductive sensing structure  23  so that a distance DI between the electrically conductive heating structure  22  and the electrically conductive sensing structure  23  may be changed by applying a second voltage to the piezoelectric actuator. 
     According to some embodiments a thermomechanical actuator is configured for deflecting the electrically conductive heating structure  22  and/or the electrically conductive sensing structure  23  so that a distance DI between the electrically conductive heating structure  22  and the electrically conductive sensing structure  23  may be changed by applying a current to the thermomechanical actuator. 
     The electrically conductive heating structure  22  is electrically connected to the contacts  12 . 6  and  12 . 9 . The electrically conductive sensing structure  23  is electrically connected to the contacts  12 . 5  and  12 . 8 . Further, the electrostatic actuator  24  is electrically connected to the contacts  12 . 7  and  12 . 10 . By applying a first voltage to at least one of the contacts  12 . 7  and  12 . 10  the electrically conductive heating structure  22  may be deflected so that the distance DI between the electrically conductive heating structure  22  and the electrically conductive sensing structure  23  is changed. Different distances DI are in particular beneficial for sensitivity in different pressure ranges and thus increase total measurement range. 
     The electrostatic actuator  24  may be replaced by a piezoelectric actuator (not shown) or a thermomechanical actuator (not shown). 
       FIG.  11    shows an exemplary diagram showing normalized sensor responses for different distances between the electrically conductive heating structure  22  and the electrically conductive sensing structure  23  of the eighth embodiment of a thermoresistive micro sensor device  1 . 
     The normalized sensor responses Ke/KO depending on the pressure p are shown for distances DI having the values d=100 m, d=1 μm and d=10 μm. With decreasing the distance DI between the electrically conductive heating structure  22  and the electrically conductive sensing structure  23  the detectable pressure range is shifted up. Vice versa, with increasing distance DI it is shifted down, so that a plurality pressure ranges may be covered. 
       FIG.  12    shows a schematic top view of a ninth embodiment of a thermoresistive micro sensor device  1  and  FIG.  13    shows a schematic cross-sectional side view of the ninth embodiment of the thermoresistive micro sensor device  1 . 
     According to some embodiments the one or more electrically conductive structures  6  comprise a plurality of electrically conductive structures  6  which are spaced in a vertical direction VD apart from each other. 
     In this embodiment the electrically conductive sensing structures  23 . 1  to  23 . 5  are arranged parallelly in a mechanical and an electrical sense. The electrically conductive sensing structures  23 . 1  to  23 . 5  are connected to the contacts  12 . 1  to  12 . 4  so that four-terminal sensing is possible. The electrically conductive heating structures  22 . 1  to  22 . 5  are also arranged parallelly in a mechanical and an electrical sense. They are electrically connected to the contacts  12 . 6  and  12 . 9  so that they can be heated by applying electrical energy to the contacts  12 . 6  and  12 . 9 . The electrically conductive heating structures  22 . 1  to  22 . 5  and the electrically conductive heating structures  22 . 1  to  22 . 5  are arranged in such way that they are in the top view perpendicular to each other. However, we also could be arranged at an arbitrary angle with respect to each other. Exemplary a number of the electrically conductive heating structures  22 . 1  to  22 . 5  and the electrically conductive sensing structures  23 . 1  to  23 . 5  is five. However, the number can be adjusted. Exemplary two layers of electrically conductive structures  6 ,  22  and  23  are shown. However a person skilled in the art would understand that more or less layers could be used. 
       FIG.  14    shows a schematic top view of a tenth embodiment of a thermoresistive micro sensor device  1 . 
     Here, two electrically conductive structures  6 . 1  and  6 . 2  are shown. Further, two reference sensing structures  25 . 1  and  25 . 2  are shown. The two electrically conductive structures  6 . 1  and  6 . 2  and the two reference sensing structures  25 . 1  and  24 . 2  are connected in such way that they form a Wheatstone bridge. The four terminals of the Wheatstone bridge are electrically connected to the contacts  12 . 11 ,  12 . 12 ,  12 . 13  and  12 . 14 . The reference sensing structures  25 . 1  and  25 . 2  can be buried in the electrically insulating arrangement  10  or even in the semiconductor chip  2  in order to minimize thermal interaction with the environment. 
       FIG.  15    shows a schematic top view of an eleventh embodiment of a thermoresistive micro sensor device  1 . 
     The exemplary layout comprises three electrically conductive structures  6  which comprise the electrically conductive heating structure  22  and two electrically conductive sensing structures  23 . 1  and  23 . 2 . The latter two are arranged symmetrically with respect to the electrically conductive heating structure  22 . The electrically conductive heating structure  22  is electrically connected to the contacts  12 . 16  and  12 . 19 . The electrically conductive sensing structure  23 . 1  is electrically connected to the contacts  12 . 15  and  12 . 20  and the electrically conductive sensing structure  23 . 2  is connected to the contacts  12 . 17  and  12 . 18 . 
       FIG.  16    shows an exemplary temperature distribution TD at a thermoresistive micro sensor device  1  according to the eleventh embodiment. It&#39;s apparent that the temperature distribution TD depends on the mass flow MV of the fluid. 
       FIG.  17    shows a schematic top view of a twelfth embodiment of a thermoresistive micro sensor device  1 . 
     The embodiment shown here comprises two electrically conductive structures  6 . 1  and  6 . 2  which may be used for sensing and for heating. The electrically conductive structure  6 . 1  is connected to the contacts  12 . 22  and  12 . 23  and the electrically conductive structure  6 . 2  is connected to the contacts  12 . 21  and  12 . 24 . An AC voltage may be applied between the electrically conductive structures  6 . 1  and  6 . 2  to deflect them symmetrically so that the output a signal which is modulated by the AC voltage. In this case the signal-to-noise ratio may be improved by AC band-pass filters. The frequency of the AC voltage may be the resonance frequency of the electrically conductive structures  6 . 1  and  6 . 2 . 
       FIG.  18    shows a schematic top view of a thirteenth embodiment of a thermoresistive micro sensor device  1 . The exemplary layout comprises three electrically conductive structures  6  which comprise the electrically conductive heating structure  22  and two electrically conductive sensing structures  23 . 1  and  23 . 2 . The latter two are arranged symmetrically with respect to the electrically conductive heating structure  22 . The electrically conductive heating structure  22  is electrically connected to the contacts  12 . 26  and  12 . 29 . The electrically conductive sensing structure  23 . 1  is electrically connected to the contacts  12 . 25  and  12 . 30  and the electrically conductive sensing structure  23 . 2  is connected to the contacts  12 . 27  and  12 . 28 . Heating power and sensing power are two independent parameters which may be optimized separately. The electrically conductive heating structure  22  is mechanically stiffer than the two electrically conductive sensing structures  23 . 1  and  23 . 2 . If an AC voltage is applied to contacts  12 . 26  and  12 . 29 , the two electrically conductive sensing structures  23 . 1  and  23 . 2  will be deflected periodically so that the output signal is modulated. In this case the signal-to-noise ratio may be improved by AC band-pass filters. The frequency of the AC voltage may be the resonance frequency of the electrically conductive sensing structures  23 . 1  and  23 . 2 . 
       FIG.  19    shows a schematic top view of a fourteenth embodiment of a thermoresistive micro sensor device  1 . 
     The exemplary layout comprises three electrically conductive structures  6  which comprise two electrically conductive heating structures  22 . 1  and  22 . 2  and the electrically conductive sensing structure  23 . The first two are arranged symmetrically with respect to the electrically conductive sensing structure  23 . The electrically conductive heating structure  22 . 1  is electrically connected to the contacts  12 . 33  and  12 . 34 . The electrically conductive heating structure  22 . 2  is electrically connected to the contacts  12 . 31  and  12 . 36  and the electrically conductive sensing structure  23  is connected to the contacts  12 . 32  and  12 . 34 . Heating power and sensing power are two independent parameters which may be optimized separately. The two electrically conductive heating structures  22 . 1  and  22 . 2  are mechanically stiffer than the electrically conductive sensing structure  23 . If an AC voltage is applied between contacts  12 . 33  and  12 . 34  and between contacts  12 . 31  and  12 . 36 , the electrically conductive sensing structure  23  will be deflected periodically so that the output signal is modulated. In this case the signal-to-noise ratio may be improved by AC band-pass filters. The frequency of the AC voltage may be the resonance frequency of the electrically conductive sensing structure  23 . 
       FIG.  20    shows a schematic top view of a fifteenth embodiment of a thermoresistive micro sensor device  1 . 
     Here, two electrically conductive sensing structures  23 . 1  and  23 . 2  are shown. Further, two reference sensing structures  25 . 1  and  25 . 2  are shown. The two electrically conductive sensing structures  23 . 1  and  23 . 2  and the two reference sensing structures  25 . 1  and  24 . 2  are connected in such way that they form a Wheatstone bridge. The four terminals of the Wheatstone bridge are electrically connected to the contacts  12 . 37 ,  12 . 38 ,  12 . 39  and  12 . 4   o.  The reference sensing structures  25 . 1  and  25 . 2  can be buried in the electrically insulating arrangement  10  or even in the semiconductor chip  2  in order to minimize thermal interaction with the environment. In this embodiment the sensing function is separated from the heating function. For the heating function an additional electrically conductive heating structure  22 , which is stiffer than the two electrically conductive sensing structures  23 . 1  and  23 . 2 , is provided. The electrically conductive heating structure  22  is electrically connected to the contacts  12 . 41  and  12 . 42 . If an AC voltage is applied between contacts  12 . 41  and  12 . 42 , the electrically conductive sensing structures  23 . 1  and  23 . 2  will be deflected periodically so that the output signal is modulated. In this case the signal-to-noise ratio may be improved by AC band-pass filters. The frequency of the AC voltage may be the resonance frequency of the electrically conductive sensing structures  23 . 1  and  23 . 2 . 
       FIG.  21    shows a schematic cross-sectional side view of a sixteenth embodiment of the thermoresistive micro sensor device  1 . Here, the plurality of electrically conductive structures  6  are shown, wherein each of the electrically conductive structure  6  is supported by a portion of the electrically insulating arrangement  10 . It&#39;s well-known that the speed of the fluid which is guided through a through hole  5  has a maximum at the center of the through hole  5 , it is if there are no obstacles in the flow path. In order to compensate this, the electrically conductive structure  6  are arranged in such way that in a center portion of the through hole  5  higher partial mass flow is possible than in a peripheral portion of the through hole  5 . 
     All of the variants above can be stacked vertically for increased sensitivity as well as directionality of the flow measurement. 
       FIG.  22    shows a schematic top view of an embodiment of a mass flow meter  26  for measuring a mass flow of a fluid. 
     The mass flow meter  26  comprises 
     a thermoresistive micro sensor device  1  according to one of the claims  1  to  15 ; 
     an electrical energy supply unit  27  for supplying the electrical energy to the contact arrangement  11 ; and 
     a measuring unit  28  for measuring the electrical resistance at the contact arrangement  11 ; 
     wherein the measuring unit  28  is configured for measuring the mass flow MV of the fluid flowing through the through hole  5  depending on the electrical resistance. 
       FIG.  23    shows a schematic top view of an embodiment of a pressure meter for measuring a pressure in a fluid. 
     The pressure meter  29 , the pressure comprises 
     a thermoresistive micro sensor device  1  according to one of the claims  1  to  15 ; 
     an electrical energy supply unit  27  for supplying the electrical energy to the contact arrangement  11 ; and 
     a measuring unit  28  for measuring the electrical resistance at the contact arrangement; 
     wherein the measuring unit  28  is configured for measuring the pressure PR of the fluid at the through hole  5  depending on the electrical resistance. 
     Embodiments may comprise one or more of the following features: 
     One or more (poly-silicon) heating/sensing structures are suspended completely exposed above a hole that runs vertically through the whole chip. 
     The sensing/heating structures are arranged side-by-side and/or above each other (in multiple, separate layers). 
     At least one of those sensing/heating structures is used for resistive/joule heating. 
     The fluid flow is guided through the hole in the chip and has to pass the sensing/heating structure(s). 
     The fluid transports thermal energy away from the heating structure(s). 
     The sensing structure(s) receive(s) a temperature change, which can be measured as a shift in resistance. 
     This disclosure proposes in particular the placement of several polysilicon heating and sensing structures above a hole in the substrate of a silicon chip, in particular leaving those structures completely exposed to fluid passing through perpendicular to the chip surface. The exposed heating/sensing structures exhibit a high sensitivity to temperature changes due to their low volume-to-surface-ratio as well as the small heat capacity caused by the low mass and good thermal insulation at the heating/sensing structure support. Due to the low fluidic resistance, the sensor exhibits a flow optimized measurement principle for low flow rates. This device can both be used as an anemometer for measuring mass flow of fluids, as well as a pressure meter for measuring a pressure in different ranges. MEMS structure capabilities can be used to vary/adjust the sensor in field measurements by using moveable mechanical structures (example pressure meter with electrostatic actuation). 
     While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.