CN111964742B - MEMS flow sensing chip, manufacturing method thereof and flow sensor - Google Patents
MEMS flow sensing chip, manufacturing method thereof and flow sensor Download PDFInfo
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- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/76—Devices for measuring mass flow of a fluid or a fluent solid material
- G01F1/86—Indirect mass flowmeters, e.g. measuring volume flow and density, temperature or pressure
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Abstract
The invention provides an MEMS flow sensing chip, a manufacturing method thereof and a flow sensor, relates to the field of flow testing, and is designed for solving the problem that the application of the flow sensor is limited because the traditional thermal mass flow sensing chip is easily influenced by the change of gas components. The MEMS flow sensing chip comprises a matrix and a plurality of sensing elements arranged on the matrix, wherein the plurality of sensing elements comprise a calorimetric element, a time-of-flight sensing element and a wind speed sensing element, the matrix is provided with a heating element, the heating element is used for providing heat for the time-of-flight sensing element, the calorimetric element and the wind speed sensing element, the time-of-flight sensing element is configured to measure the volume flow rate of fluid and the thermophysical property value of fluid, and the calorimetric element and the wind speed sensing element are configured to measure the mass flow rate and the flow rate of fluid. The MEMS flow sensing chip and the flow sensor provided by the invention can be used for simultaneously measuring the thermophysical property, the flow velocity and the volume flow of gas in the process of measuring the mass flow.
Description
Technical Field
The invention relates to the field of flow test, in particular to a MEMS (Micro Electro Mechanical System, micro-electro-mechanical system) sensing chip, a manufacturing method thereof and a flow sensor.
Background
Thermal mass flow sensors sense medium flow primarily through the principle of heat conduction in the medium, where a heating element provides a constant temperature or constant power, while sensing elements located upstream and downstream of the heating element measure the flow of a mass-dependent temperature-varying flowing medium. The measurement mode is not influenced by temperature and pressure, so the measurement mode has great attraction to gas measurement, and has been applied to medical treatment, industrial process control, internet of things and urban natural trade measurement in recent years. However, since conventional thermal mass flow measurements are sensitive to gas composition, there is additional uncertainty or even large deviations in the metering of the composition-complex gas, thereby limiting the scope of application of this technique.
Disclosure of Invention
A first object of the present invention is to provide a MEMS flow sensor chip, so as to solve the technical problem that the existing thermal mass flow sensor chip is easily affected by the change of gas components, and thus the application of such a flow sensor is limited.
The MEMS flow sensing chip comprises a matrix and a plurality of sensing elements arranged on the matrix, wherein the plurality of sensing elements comprise a calorimetric element, a time-of-flight sensing element and a wind speed sensing element, the time-of-flight sensing element is arranged on a fluid flow path between the wind speed sensing element and the calorimetric element, the matrix is provided with a heating element for providing heat for the time-of-flight sensing element, the calorimetric element and the wind speed sensing element, the time-of-flight sensing element is configured to measure the volume flow rate of fluid and the thermophysical value of fluid, and the calorimetric element and the wind speed sensing element are configured to measure the mass flow rate and the flow rate of fluid.
Further, among the plurality of sensing elements, a temperature sensing element is further included, the temperature sensing element is disposed upstream of the wind speed sensing element, and the temperature sensing element is used for sensing the ambient temperature of the fluid.
Further, the number of the time-of-flight sensing elements is two, and the two time-of-flight sensing elements are respectively located upstream and downstream of the heating element, or both the two time-of-flight sensing elements are located downstream of the heating element.
Further, the substrate comprises a chip layer, an insulating layer and a silicon device layer which are sequentially stacked, and the plurality of sensing elements are arranged on the silicon device layer.
Further, the substrate is provided with a first surface and a second surface which are arranged opposite to each other, wherein the first surface is provided with a first silicon nitride layer, the second surface is provided with a second silicon nitride layer, and a plurality of sensing elements are arranged on the first silicon nitride layer.
Further, the substrate is provided with an insulating cavity configured to prevent heat generated by the heating element from being conducted to the substrate.
Further, the heating element comprises a micro-heater that provides heat to both the time-of-flight sensing element and the wind speed sensing element.
Further, the substrate is provided with a through hole, the through hole is filled with conductive material to form a conductive path, and the plurality of sensing elements are electrically connected to the conductive path.
The MEMS flow sensing chip has the beneficial effects that:
when the MEMS flow sensing chip works, the heating element works and is used for providing heat for the flight time sensing element, the calorimetric element and the wind speed sensing element, wherein in the heating element, heat modulation waves or heat pulses are used for flight time sensing, and pulse amplitude is used for calorimetric sensing. When fluid passes through the MEMS flow sensing chip, the calorimetric element and the wind speed sensing element measure the mass flow f (v, P, T) and the speed of the fluid, the time-of-flight sensing element measures the volume flow f (v) and the thermophysical property value of the fluid, specifically, the flow of the fluid changes the temperature distribution of a micro heat source in the process of the flow of the fluid, and the calorimetric element and the wind speed sensing element obtain the mass flow and the speed of the fluid by measuring the quantity of heat conducting molecules in the fluid; the time-of-flight sensing element then obtains the volumetric flow rate and thermophysical properties of the fluid based on the flow rate of the fluid.
The MEMS flow sensing chip integrates a sensing element for measuring the mass flow of the fluid and a sensing element for measuring the volume flow and thermophysical property of the fluid into the same matrix, so that the mass flow, the volume flow and the thermophysical property of the fluid can be obtained at the same time, and the influence of the change of the gas component is measured in the measuring process, thereby eliminating the influence of the change of the component and realizing the measurement of the mass flow irrelevant to the component.
A second object of the present invention is to provide a manufacturing method for manufacturing the MEMS flow sensor chip.
The manufacturing method provided by the invention is used for manufacturing the MEMS flow sensing chip and comprises the following steps of:
depositing silicon nitride on the first and second sides of the substrate;
forming a through hole in the substrate, and filling conductive materials into the through hole to form a conductive path;
depositing a heating element and a plurality of sensing elements onto a first side of a substrate and connecting with a conductive path;
the side of the substrate opposite the heating element is grooved to form a thermally insulated cavity.
Further, the method further comprises the steps of: the base body is provided with a first sinking table and a second sinking table, so that the base body is provided with a base seat positioned between the first sinking table and the second sinking table, wherein the first sinking table is used for installing a temperature sensing element, the second sinking table is used for forming an access point of a conductive path, and the base seat is used for installing a calorimetric element, a flight time sensing element and a wind speed sensing element.
Further, the method further comprises the steps of: the vertical face of the base close to the conductive path is processed by using a step dry etching process, so that the sharp edge of the base becomes an inclined plane.
Further, the method further comprises the steps of: the two ends of the conductive path are metallized prior to the step of depositing the heating element and the plurality of sensing elements onto the first side of the substrate and connecting the conductive path.
Further, the method further comprises the steps of: after the step of depositing the heating element and the plurality of sensing elements on the first side of the substrate and connecting the first side of the substrate to the conductive path, surface passivation is performed on all areas of the first side of the substrate to cover the first side of the substrate and the heating element and the plurality of sensing elements disposed on the first side.
Further, the method further comprises the steps of: a pad is disposed on the second side of the substrate and electrically connected to the conductive path.
The manufacturing method of the invention has the beneficial effects that:
when the MEMS flow sensing chip is manufactured, silicon nitride is respectively deposited on the first surface and the second surface of the matrix, and passivation treatment is carried out on the surface of the matrix so as to enhance the corrosion resistance of the MEMS flow sensing chip; the substrate is provided with a through hole, conductive materials are filled in the through hole, and conductive paths of the MEMS flow sensing chip are formed by the conductive materials filled in the through hole, so that the MEMS flow sensing chip is electrically connected with the corresponding module; depositing the heating element and the plurality of sensing elements onto the first side of the substrate and connecting the heating element and the plurality of sensing elements to the conductive paths, thereby effecting signal transfer between the heating element and the plurality of sensing elements and the respective modules; the substrate is grooved on the side opposite the heating element to form a thermally insulating cavity providing thermal isolation of the heating element from the fluid medium, thereby ensuring the sensitivity of the heating element.
The MEMS flow sensing chip obtained by the manufacturing method has the advantages that the basic function of the MEMS flow sensing chip is realized, and meanwhile, the binding of metal wires is avoided during packaging, so that the MEMS flow sensing chip has better corrosion resistance and higher measurement sensitivity.
A third object of the present invention is to provide a flow sensor, so as to solve the technical problem that the existing sensor chip is easily affected by the change of gas components, resulting in the limitation of the application of the flow sensor.
The flow sensor provided by the invention comprises the MEMS flow sensing chip.
The flow sensor has the beneficial effects that:
by arranging the MEMS flow sensor chip in the flow sensor, the flow sensor has all advantages of the MEMS flow sensor chip, and will not be described in detail herein.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic structural diagram of a MEMS flow sensor chip according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a process for manufacturing a MEMS flow sensor chip according to an embodiment of the present invention;
FIG. 3 is a second schematic diagram of a process for manufacturing a MEMS flow sensor chip according to an embodiment of the present invention;
FIG. 4 is a schematic diagram III of a process for manufacturing a MEMS flow sensor chip provided by an embodiment of the present invention;
FIG. 5 is a schematic diagram of a process for manufacturing a MEMS flow sensor chip provided by an embodiment of the present invention;
FIG. 6 is a schematic diagram of a process for manufacturing a MEMS flow sensor chip provided by an embodiment of the present invention;
FIG. 7 is a schematic diagram of a process for manufacturing a MEMS flow sensor chip provided by an embodiment of the present invention;
FIG. 8 is a schematic diagram of a process seventh for manufacturing a MEMS flow sensor chip provided by an embodiment of the present invention;
FIG. 9 is a schematic diagram eight of a process for manufacturing a MEMS flow sensor chip provided by an embodiment of the present invention;
FIG. 10 is a schematic diagram of a process for manufacturing a MEMS flow sensor chip provided by an embodiment of the present invention;
FIG. 11 is a schematic diagram of a process for manufacturing a MEMS flow sensor chip provided by an embodiment of the present invention;
FIG. 12 is a schematic diagram of an eleventh process for manufacturing a MEMS flow sensor chip provided by an embodiment of the present invention;
in which only the silicon device layer is shown in fig. 2 to 12, the insulating layer and the chip layer are omitted.
Reference numerals illustrate:
100-substrate; 300-connecting end; 400-interconnection; 500-a surface passivation layer; 600-bonding pads;
110-a silicon device layer; 120-an insulating layer; 130-a chip layer; 140-through holes; 150-a first sedimentation table; 160-a second sedimentation stage; 170-a base;
111-a first side; 112-a first silicon nitride layer; 113-a first silicon substrate layer; 114-a silicon oxide layer; 115-a second silicon substrate layer; 131-a second side; 132-a second silicon nitride layer; 141-conductive paths; 171-incline;
210-calorimetric element; 220-a first time-of-flight sensing element; 230-a heating element; 240-wind speed sensing element; 250-a temperature sensing element; 260-a second time-of-flight sensing element.
Detailed Description
In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
As shown in fig. 1, the present embodiment provides a MEMS flow sensing chip, including a substrate 100 and a plurality of sensing elements disposed on the substrate 100, in particular, the plurality of sensing elements including a calorimetric element 210, a time-of-flight sensing element, and a wind speed sensing element 240, wherein the time-of-flight sensing element is disposed on a fluid flow path between the wind speed sensing element 240 and the calorimetric element 210, the substrate 100 is provided with a heating element 230, the heating element 230 is used to provide heat for the time-of-flight sensing element, the calorimetric element 210, and the wind speed sensing element 240, the time-of-flight sensing element is configured to measure a volumetric flow rate of a fluid and a thermophysical value of the fluid, and the calorimetric element 210 and the wind speed sensing element 240 are configured to measure a mass flow rate and a flow rate of the fluid.
In operation, the MEMS flow sensor chip operates with the heating element 230 providing heat to the time-of-flight sensing element and the wind speed sensing element 240, and with the heating element 230, thermally modulated waves or pulses are used for time-of-flight sensing and pulse amplitudes are used for calorimetric sensing. The calorimetric element 210 and the wind speed sensing element 240 measure the mass flow rate f (v, P, T) and the velocity of the fluid as the fluid passes through the MEMS flow sensing chip, and the time-of-flight sensing element measures the volumetric flow rate f (v) and the thermophysical values of the fluid, specifically, the flow of the fluid changes the temperature distribution of the micro heat source during the flow of the fluid, and the calorimetric element 210 and the wind speed sensing element 240 obtain the mass flow rate and the velocity of the fluid by measuring the number of heat conducting molecules in the fluid; the time-of-flight sensing element then obtains the volumetric flow rate and thermophysical properties of the fluid based on the flow rate of the fluid.
The MEMS flow sensing chip integrates a sensing element for measuring the mass flow of fluid and a sensing element for measuring the volume flow and thermophysical property of fluid into the same substrate 100, so that the mass flow, the volume flow and the thermophysical property of fluid can be obtained at the same time, the influence of the change of gas components is measured in the measuring process, the influence of the change of components can be eliminated, and the mass flow measurement irrelevant to the components is realized.
It should be noted that if the fluid is the same as the medium used for calibration of the mass flow rate f (v, P, T), the pressure value of the fluid may also be calculated from the above measured values by the following formula: p= (T/(f (v))) x f (v, P, T), where P is the pressure value of the flowing medium and T is the temperature of the flowing medium. And determining the thermal conductance k of the fluid by measuring the power of the heating element 230 and measuring the diffusion coefficient D with the time-of-flight sensing element at rest, the thermal capacity Cp of the fluid being obtained from d=k/(ρxcp), where ρ is the fluid density.
Alternatively, the MEMS flow sensor chip alerts the possible difference of the composition or thermal characteristics of the fluid from the calibrated or expected value by comparing the measured mass flow value with a calculated mass flow value from the volume and a comprehensive evaluation of the measured temperature and calculated pressure.
With continued reference to fig. 1, in the present embodiment, the heating element 230 is a micro-heater, which provides heat for both the time-of-flight sensing element and the wind speed sensing element 240. By the arrangement, the number of parts is reduced, so that the structural size of the MEMS flow sensing chip is reduced, and the miniaturization design of the MEMS flow sensing chip is facilitated.
Preferably, in this embodiment, the MEMS flow sensor chip uses platinum or doped polysilicon as the material of the sensor element and the micro heater. Platinum is a stable metal material with excellent temperature coefficient to achieve the desired sensitivity, while doped polysilicon can be fabricated using standard compatible metal oxide semiconductor processes. Both materials can ensure the stability of the output of the MEMS flow sensor chip and provide the required reliability.
With continued reference to fig. 1, in this embodiment, the plurality of sensing elements further includes a temperature sensing element 250, specifically, the temperature sensing element 250 is disposed upstream of the wind speed sensing element 240, and the temperature sensing element 250 is configured to sense an ambient temperature of the fluid.
When the MEMS flow sensor chip works, the temperature sensing element 250 can be used to measure the environmental temperature of the fluid, and when the temperature sensing element 250 senses the temperature signal of the fluid, the temperature signal can be fed back to the heating element 230, so that the heating element 230 can maintain constant power or constant temperature above the environmental temperature, a stable temperature field is ensured, and the fluid is heated at a corresponding temperature (for example, 5 ℃ higher than the environmental temperature of the fluid) so as to ensure accurate measurement of the corresponding parameter of the fluid.
Preferably, the temperature sensing element 250 comprises a thermocouple. The arrangement is such that in the non-power supply state, the temperature sensing element 250 can sense the signal of the temperature change of the fluid, so as to feed back the corresponding temperature control signal to the heating element 230, so as to control the heating element 230 to start, and heat the fluid by setting the temperature. The temperature sensing element 250 is arranged in the form of a thermocouple, so that the automatic wake-up of the MEMS flow sensing chip is realized, the electricity and the energy are saved, and a battery power supply can be adopted for various applications without an external power supply.
It should be noted that, in the present embodiment, the heating element 230 and the sensing element of the heat sensing function may be collectively referred to as a heat sensitive element, and are preferably made of a stable high temperature coefficient material by electron beam evaporation or physical vapor deposition, for example: platinum, gold, nickel, permalloy, and doped conductive polysilicon. In particular, the calorimetric element 210 or the wind speed sensing element 240 may be made in a thermopile configuration, so that power consumption of the MEMS flow sensing chip may be minimized. In order to optimize the material stability and sensitivity of the MEMS flow sensor chip performance, the thickness of each thermistor is preferably 80-200nm, but most preferably 100nm.
With continued reference to fig. 1, in the present embodiment, the number of the time-of-flight sensing elements is two, namely the first time-of-flight sensing element 220 and the second time-of-flight sensing element 260, which are located upstream and downstream of the heating element 230 or both downstream. By the arrangement, the MEMS flow sensing chip can meet the measurement requirement of the bidirectional flow velocity.
Referring to fig. 1, in this embodiment, the substrate 100 may include a chip layer 130, an insulating layer 120, and a silicon device layer 110 that are sequentially stacked, and a plurality of sensing elements are disposed on the silicon device layer 110.
By providing the substrate 100 in a structure where the chip layer 130, the insulating layer 120 and the silicon device layer 110 are laminated, the silicon device layer 110 may act as a thermal barrier and provide the necessary mechanical strength to weaken or even eliminate the pressure applied to the surface of the MEMS flow sensing chip during measurement.
Referring to fig. 1, in the present embodiment, the substrate 100 has a first surface 111 and a second surface 131 disposed opposite to each other, wherein the first surface 111 is provided with a first silicon nitride layer 112, the second surface 131 is provided with a second silicon nitride layer 132, and a plurality of sensing elements are disposed on the first silicon nitride layer 112.
By the arrangement, the films of the silicon nitride layers are formed on the two opposite sides of the substrate 100, so that the pressure exerted by a flowing medium can be resisted, the flatness of the surface of the substrate 100 is ensured, and the substrate has certain corrosion resistance and can prevent corrosion damage caused by possible elements in fluid.
Specifically, the strength of the silicon device layer 110 may be adjusted by changing its thickness during fabrication, and the center deformation d= (α×p×b) of the silicon device layer 110 4 )/(E*t 3 ) Where α is a constant value under the condition that a uniform pressure p is applied to the support layer, b is the side length of the first silicon nitride layer 112, t is the thickness of the silicon device layer 110, and E is the young's modulus of the first silicon nitride layer 112. Thus, for the accuracy requirements that can be calculated from the d/b bias in an application, the thickness of the silicon device layer 110 can be determined for the preferred MEMS flow sensor chip.
In this embodiment, the substrate 100 is provided with an insulating cavity, wherein the insulating cavity is configured to prevent heat generated by the heating element 230 from being conducted to the substrate 100. The provision of the insulating cavity provides thermal isolation of the heating element 230 from the fluid medium, thereby ensuring sensitivity of the heating element 230.
With continued reference to fig. 1, in the present embodiment, the substrate 100 is provided with a through hole 140, and the through hole 140 is filled with a conductive material to form a conductive path 141, and the plurality of sensing elements are electrically connected to the conductive path 141.
By the arrangement, the purpose of creating an interface on the back of the sensing chip is achieved, so that the metal connecting wire binding process in the packaging process of the MEMS flow sensing chip can be eliminated, the reliability of connection can be improved, and the size of the MEMS flow sensing chip can be reduced, so that the packaging size is reduced. In some cases, small-sized sensor chips are also advantageous for cost-sensitive applications.
The MEMS flow sensing chip can be easily manufactured in batches for civil gas metering or liquid flow metering of medical microfluidics with large-scale requirements. The MEMS flow sensing chip may also be used in consumer applications where cost sensitivity requires simplicity and low cost.
The embodiment also provides a manufacturing method for manufacturing the MEMS flow sensing chip, which comprises the following steps: depositing silicon nitride on the first side 111 and the second side 131 of the substrate 100; forming a through hole 140 in the substrate 100, and filling a conductive material into the through hole 140 to form a conductive path 141; depositing a heating element 230 and a plurality of sensing elements onto the first face 111 of the substrate 100 and in connection with the conductive path 141; the side of the substrate 100 opposite the heating element 230 is grooved to form an insulating cavity.
As shown in fig. 2, in manufacturing the MEMS flow sensor chip, silicon nitride is deposited on the first surface 111 and the second surface 131 of the substrate 100, specifically, the first silicon nitride layer 112 is deposited on the first surface 111 of the substrate 100, the second silicon nitride layer 132 is deposited on the second surface 131 of the substrate 100, and the surface of the substrate 100 is subjected to passivation treatment to enhance the corrosion resistance of the MEMS flow sensor chip.
Preferably, the first silicon nitride layer 112 and the second silicon nitride layer 132 have high conductivity, or are lightly boron doped. In other embodiments, it may also be heavily doped, for example: phosphorus or boron. The insulating layer 120 of the substrate 100 is not conductive and does not have any doping. The first silicon nitride layer 112 is deposited on the first surface 111 by low pressure chemical vapor deposition, and the second silicon nitride layer 132 is deposited on the second surface 131 by low pressure chemical vapor deposition. Wherein the thickness of the first silicon nitride layer 112 and the second silicon nitride layer 132 is between 100-300nm, preferably 200nm.
As shown in fig. 3, after the above steps, the method further includes providing a first sinking stage 150 and a second sinking stage 160 on the substrate 100, such that the substrate 100 has a base 170 between the first sinking stage 150 and the second sinking stage 160, wherein the first sinking stage 150 is used for mounting the temperature sensing element 250, the second sinking stage 160 is used for forming an access point of the conductive path 141, and the base 170 is used for mounting the calorimetric element 210, the time-of-flight sensing element and the wind speed sensing element 240.
Through the above steps, the first deposition table 150 provides a separate installation space for the temperature sensing element 250, which is far away from the heating element 230 disposed on the first silicon nitride layer 112, so that the measured temperature value thereof can represent the fluid temperature more accurately. In addition, the connection terminal 300 may be disposed on the second sinking stage 160, and the sensing element may be connected to the conductive path 141 by using the connection terminal 300 to achieve signal transmission.
As shown in fig. 4 and 5, after the above steps, the substrate 100 is further provided with a through hole 140, the through hole 140 is filled with a conductive material, and the conductive path 141 of the MEMS flow sensor chip is formed by using the conductive material filled in the through hole 140, so as to electrically connect the MEMS flow sensor chip and the corresponding module.
With continued reference to fig. 4, specifically, when the through hole 140 is formed in the substrate 100, the through hole 140 may be directly formed in the substrate 100, or a portion of the through hole may be first drilled through the substrate 100, and the remaining portion may be removed by using a chemical mechanical planarization method. Wherein the diameter of the through holes 140 is between 50-2000nm, preferably the diameter of the through holes 140 is 1000nm.
With continued reference to fig. 5, the conductive material filled in the via 140 may be a metal, for example: nickel, permalloy or metallic copper, but also highly doped conductive polysilicon, or conductive polymers such as: polypyrene (ploypyrene) or polycarbazole (ploycarbazoles).
As shown in fig. 6, after the above steps, the vertical surface of the susceptor 170 near the conductive path 141 is further processed by using a step dry etching process, so that the sharp edge of the susceptor 170 becomes the inclined surface 171, and the first silicon nitride layer 112 is deposited on the processed inclined surface 171, and the resulting substrate 100 has the structure shown in fig. 7.
Through the steps, the step-by-step or smooth transition or interconnection of the metallization lines can be established, and the connection interruption or unreliability caused by singular points generated by steep edges is avoided.
As shown in fig. 8, following the above steps, the heating element 230 and the plurality of sensing elements are deposited onto the first side 111 of the substrate 100 and connected to the conductive path 141, thereby effecting signal transfer between the heating element 230 and the plurality of sensing elements and the respective modules.
As shown in fig. 9, following the steps described above, the sensing and heating elements 230 are connected to the conductive paths 141 using the interconnect 400. It should be noted that before the step of depositing the heating element 230 and the plurality of sensing elements on the first surface 111 of the substrate 100 and connecting the conductive paths 141, the two ends of the conductive paths 141 may be metallized. Wherein the interconnect 400 is preferably made of gold or aluminum or doped conductive polysilicon by electron beam evaporation or physical vapor deposition.
In this embodiment, the thickness of the interconnect 400 is preferably in the range of 100-300nm, but most preferably 200nm, so that material stability and performance of the MEMS flow sensor chip can be optimized.
As shown in fig. 10, the above steps further include surface passivation of all areas of the first side 111 of the substrate 100 to cover the first side 111 of the substrate 100 and the heating element 230 and the plurality of sensing elements disposed on the first side 111. By doing so, it is possible to prevent damage to the MEMS flow sensor chip due to abrasion between the heating element 230 and the sensing element and the interconnect 400 caused by fine particles inside the fluid, thereby realizing protection of the MEMS flow sensor chip.
Specifically, the coverage of the first side 111 of the substrate 100 and the heating elements 230 and the plurality of sensing elements disposed on the first side 111 is achieved with the surface passivation layer 500. The material used for the surface passivation layer 500 has excellent thermal conductivity and good mechanical strength, preferably, the material of the surface passivation layer 500 is silicon nitride or silicon carbide deposited by a plasma enhanced chemical vapor deposition method, and the thickness of the material ranges from 100nm to 500nm, preferably, the material has a value of 300nm, so as to obtain the best surface coverage path, mechanical strength and material stability.
As shown in fig. 11, the above steps further include disposing a pad 600 on the second surface 131 of the substrate 100, and electrically connecting the pad 600 to the conductive path 141.
Preferably, the pad 600 is made of gold or aluminum or doped conductive polysilicon by electron beam evaporation or physical vapor deposition. Most preferably gold. The thickness of the bonding pad 600 is preferably in the range of 100-300nm, but is most preferably 200nm, so that the material stability and the performance of the MEMS flow sensor chip of the present embodiment can be optimized.
As shown in fig. 12, the above steps further include recessing the side of the substrate 100 opposite the heating element 230 to form an insulating cavity for the substrate 100 to provide thermal isolation of the heating element 230 from the fluid medium, thereby ensuring the sensitivity of the heating element 230.
Specifically, in the present embodiment, the insulating chamber is manufactured by ion etching back the substrate 100 or wet etching chemical etching using a chemical agent such as potassium hydroxide or tetramethylammonium hydroxide. The silicon oxide layer 114 below the silicon device layer 110 or above the cavity may be removed by wet chemical etching or may remain as part of the silicon device layer 110 and silicon nitride layer composite structure. After the heat insulation cavity is manufactured, the micro-machining process of the MEMS flow sensing chip is completed, cutting and separating are prepared, and then further sealing and testing are performed.
The MEMS flow sensing chip obtained by the manufacturing method has the advantages of realizing the basic function of the MEMS flow sensing chip, and simultaneously having better corrosion resistance and higher measurement sensitivity.
With continued reference to fig. 2, the silicon device layer 110 includes a first silicon substrate layer 113, a silicon oxide layer 114, and a second silicon substrate layer 115 that are sequentially stacked. It should be noted that, in the present embodiment, the structure of the silicon device layer 110 is the same as that of the silicon device layer 110 provided in the prior art, and this embodiment is not improved, so that a detailed description is omitted.
The manufacturing method and the manufacturing process of the MEMS flow sensing chip have the following characteristics: for MEMS flow sensing chip products, the higher the yield, the lower the production cost. The manufacturing method of the MEMS flow sensing chip also enables the MEMS flow sensing chip to have the characteristics basically completely consistent, and is convenient for realizing the final mass production of the MEMS flow sensing chip.
The embodiment also provides a flow sensor, which comprises the MEMS flow sensing chip.
By arranging the MEMS flow sensor chip in the flow sensor, the flow sensor has all advantages of the MEMS flow sensor chip, and will not be described in detail herein.
Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention, and the scope of the invention should be assessed accordingly to that of the appended claims.
Finally, it is further noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
In the above embodiments, descriptions of orientations such as "up", "down", and the like are shown based on the drawings.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (8)
1. A MEMS flow sensing chip comprising a substrate (100) and a plurality of sensing elements disposed on the substrate (100), the plurality of sensing elements comprising a calorimetric element (210), a time-of-flight sensing element and a wind speed sensing element (240), the time-of-flight sensing element being disposed on a fluid flow path between the wind speed sensing element (240) and the calorimetric element (210), the substrate (100) being provided with a heating element (230), the heating element (230) being for providing heat to the time-of-flight sensing element, the calorimetric element (210) and the wind speed sensing element (240), wherein the time-of-flight sensing element is configured to measure a volumetric flow rate of a fluid and a thermophysical value of the fluid, the calorimetric element (210) and the wind speed sensing element (240) are configured to measure a mass flow rate and a flow rate of the fluid; the MEMS flow sensing chip is used for simultaneously obtaining the mass flow, the volume flow and the thermophysical property of the fluid, and measuring the influence of the gas component change in the measuring process so as to eliminate the influence of the component change; the number of time of flight sensing elements is two, both being located upstream and downstream of the heating element (230), respectively, or both being located downstream of the heating element (230).
2. The MEMS flow sensor chip of claim 1, further comprising a temperature sensing element (250) among the plurality of sensor elements, the temperature sensing element (250) being disposed upstream of the wind speed sensing element (240), the temperature sensing element (250) being configured to sense an ambient temperature of the fluid.
3. The MEMS flow sensor chip according to any one of claims 1-2, wherein the substrate (100) comprises a chip layer (130), an insulating layer (120) and a silicon device layer (110) stacked in that order, the plurality of sensor elements being disposed on the silicon device layer (110).
4. The MEMS flow sensor chip according to any one of claims 1-2, wherein the substrate (100) has a first face (111) and a second face (131) arranged opposite each other, wherein the first face (111) is provided with a first silicon nitride layer (112), the second face (131) is provided with a second silicon nitride layer (132), and a plurality of the sensor elements are arranged on the first silicon nitride layer (112).
5. The MEMS flow sensor chip according to any one of claims 1-2, wherein the substrate (100) is provided with an insulating cavity configured to prevent heat generated by the heating element (230) from being conducted to the substrate (100).
6. The MEMS flow sensor chip according to any one of claims 1-2, wherein the heating element (230) comprises a micro-heater that provides heat to both the time-of-flight sensing element and the wind speed sensing element (240).
7. The MEMS flow sensor chip according to any one of claims 1-2, wherein the substrate (100) is provided with a through hole (140), the through hole (140) being filled with a conductive material to form a conductive path (141), a plurality of the sensor elements each being electrically connected to the conductive path (141).
8. A flow sensor comprising the MEMS flow sensor chip of any one of claims 1-7.
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