Dual layer thermal wide range gas microflowmeter

Abstract

The application provides a double-layer thermal wide-range gas micro-flowmeter, which is composed of a first wafer, a second wafer and a third wafer which are bonded together in sequence; the first wafer is provided with a first inlet and a first outlet, and a first cavity is arranged on the side of the first wafer which is bonded with the second wafer; the second wafer is provided with a second inlet, a second outlet and a first connecting contact, a second cavity is arranged on the side of the second wafer which is bonded with the first wafer, and a third cavity is arranged on the side of the second wafer which is bonded with the third wafer; the third wafer is provided with a second connecting contact, and a fourth cavity is arranged on the side of the third wafer which is bonded with the second wafer; the first cavity and the second cavity form a main flow channel, and the third cavity and the fourth cavity form a secondary flow channel; the double-layer structure is adopted to realize the flow division of the input fluid, the signal of the first thermal flow sensor in the main flow channel is read under small flow, the signal of the second thermal flow sensor in the secondary flow channel is read under large flow, and the purpose of widening the range is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of micro-electro-mechanical system, and particularly relates to a double-layer thermal sensing wide-range gas micro-flowmeter. BACKGROUND

[0002] With the development of MEMS technology, the application field of micro-sensor is continuously widened, such as aerospace, biochemical detection, medical instrument, fine industry, medical biological analysis, etc. The micro-sensor is a device for detecting and measuring chemical and physical phenomena, which can be divided into thermal type and non-thermal type. Compared with the non-thermal micro-sensor, the thermal sensor has no movable parts, so the performance is more reliable, the wear rate of the device is greatly reduced, and the service life is longer. Among the thermal sensors, the thermal micro-flowmeter has great development potential due to its high sensitivity, fast response time and low manufacturing cost.

[0003] According to different measurement principles, the thermal micro-flow sensor can be divided into: heat loss type, heat temperature difference type and heat pulse type. The heat loss type micro-flowmeter is represented by the hot-wire type and hot-film type micro-flowmeter, which is mainly used as an anemometer; the measurement principle of the heat pulse type micro-flowmeter is that a pulse is emitted from a heater with a fixed distance from the temperature detector, and the time required for the pulse to reach the temperature detector from the heater is measured to obtain the response flow; the heat temperature difference type micro-flow sensor is usually composed of two temperature detectors symmetrically distributed on the heater, which adopts the heat balance principle and establishes the functional relationship between the heat loss of the thermal element and the fluid flow.

[0004] Compared with the heat loss type and heat pulse type micro-flow sensors, the heat temperature difference type micro-flow sensor has the advantages of simple structure, easy miniaturization, high detection precision and low power consumption. When a constant temperature working mode is adopted, the heating element of the micro-flow sensor generates a symmetrical heat distribution, and the flow of the fluid carries the heat upstream to downstream, so that the flow direction can be judged from the changed temperature field distribution, and the flow can be converted into an electrical signal by the thermistor. Generally, the heat temperature difference type micro-flow sensor has two packaging methods, namely, open space type and micro-channel type, and the micro-channel type packaging method can make the sensor obtain higher sensitivity.

[0005] The existing heat temperature difference type micro-flow sensor has a very limited range of measurable fluid flow, and its accuracy is limited to the micro-range segment. When the range exceeds, the sensor is likely to fail. In order to solve this problem, a sub-flow channel generated by a laminated structure is used to divide the flow of the main flow channel, and then the flows in the main and sub-flow channels are measured by the heat temperature difference type micro-flow sensor. Through the switching of the main and sub-flow channel signals, the range is widened.

[0006] At present, the flow range measurable by most thermal type micro flow sensors is very limited. Patent ZL201810993995.4 "A wide-range dual-mode bridge type micro flowmeter" proposes a method combining power mode and calorimetric mode to improve the range. In order to further improve the range, a micro flow sensor with a laminated structure is proposed. The double-layer structure is provided with a main flow channel and a secondary flow channel. The flow of the secondary flow channel is a small branch of the flow of the main flow channel. Through the optimization design of the geometric structure parameters of the inlet and outlet and the flow channel, it is ensured that the flow of the secondary flow channel is proportional to the flow of the main flow channel (i.e. scaled down). The sensor represents the flow in the main flow channel at low flow, and represents the flow in the secondary flow channel at high flow. Then, through the switching of the main and secondary flow channel signals, the range of the flowmeter can be widened. The conversion of the hot-wire mode and the power mode similar to patent ZL201810993995.4 can be used to further widen the range of the flowmeter. SUMMARY

[0007] The purpose of the present application is to provide a double-layer thermal type wide-range gas micro flowmeter, which can effectively reduce heat loss and improve sensitivity while widening the range of the flowmeter, so as to achieve wider application.

[0008] In order to achieve the above purpose, the present application realizes the technical scheme as follows:

[0009] A double-layer thermal type wide-range gas micro flowmeter, which is bonded together by a first wafer, a second wafer and a third wafer in sequence; the first wafer is provided with a first inlet and a first outlet, and a first cavity is arranged on the bonding side of the first wafer and the second wafer; the second wafer is provided with a second inlet and a second outlet, a first connecting contact, and a second cavity arranged on the bonding side of the first wafer and the second wafer and a third cavity arranged on the bonding side of the second wafer and the third wafer; the third wafer is provided with a second connecting contact, and a fourth cavity is arranged on the bonding side of the second wafer and the third wafer; the first cavity and the second cavity constitute a main flow channel, and the third cavity and the fourth cavity constitute a secondary flow channel; a first thermal flow sensor is arranged in the main flow channel and crosses the first cavity and the second cavity, and a second thermal flow sensor is arranged in the secondary flow channel and crosses the third cavity and the fourth cavity; a heater and upstream and downstream temperature sensors symmetrically distributed on both sides of the heater along the gas flow direction are arranged in the first thermal flow sensor and the second thermal flow sensor respectively, for measuring the temperature difference between the upstream and downstream of the heater at different flow rates, and converting the temperature difference signal into an electric signal and then transmitting it out through the first connecting contact and the second connecting contact respectively; the double-layer thermal type wide-range gas micro flowmeter reads the signal of the first thermal flow sensor in the main flow channel at low flow, and reads the signal of the second thermal flow sensor in the secondary flow channel at high flow.

[0010] The application adopts double-layer structure to realize the flow separation of input fluid, reads the signal of the first thermal flow sensor in the main flow channel at low flow, and reads the signal of the second thermal flow sensor in the sub-flow channel at high flow, so as to widen the range.

[0011] Further, the first wafer, the second wafer and the third wafer are bonded together by Al and Ge eutectic bonding in sequence.

[0012] Further, the first inlet and the second inlet are distributed in staggered positions, and the first outlet and the second outlet are arranged in corresponding positions.

[0013] Further, the flow in the sub-flow channel is in proportional relationship with the flow in the main flow channel, and the proportional coefficient is determined according to the positions and sizes of the first inlet, the first outlet, the second inlet and the second outlet.

[0014] Further, the heaters, the upstream temperature sensors and the downstream temperature sensors of the first and second thermal flow sensors are all multi-layer structures, and the materials of the layers from top to bottom are SiO2 layer, Si3N4 layer, Pt layer, Si3N4 layer, SiO2 layer and Al layer in sequence, wherein the Pt layer is the working material and has good TCR coefficient, and is used for signal sensing and output.

[0015] The advantages of the application are as follows: compared with the traditional mechanical flow meter, the thermal flow meter has no moving parts, is more reliable in performance and has longer service life; compared with the single-flow-channel thermal micro-flow meter, the double-flow-channel micro-flow meter has larger measurement range. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed for the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0017] Figure 1 A three-dimensional view of the double-layer thermal wide-range gas micro-flow meter.

[0018] Figure 2 A sectional view of the double-layer thermal wide-range gas micro-flow meter.

[0019] Figure 3 A front view and a back view of the first wafer.

[0020] Figure 4The second wafer front surface three-dimensional view of the present application.

[0021] Figure 5 The third wafer front surface three-dimensional view of the present application.

[0022] Figure 6 The temperature difference voltage signal changes with flow rate graph of the double-layer thermal type wide-range gas micro-flow meter of the present application at low flow rate.

[0023] Figure 7 The temperature difference voltage signal changes with flow rate graph of the double-layer thermal type wide-range gas micro-flow meter of the present application at high flow rate.

[0024] DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0026] REFERENCE Figures 1-7 The double-layer thermal type wide-range gas micro-flow meter comprises three wafers and two thermal flow sensors. The three wafers are a first wafer 1, a second wafer 2 and a third wafer 3 which are bonded together in a stack. The first wafer 1 is provided with a first inlet 8, a first outlet 9 and a first cavity 4 on the back surface. The second wafer 2 is provided with a second inlet 11, a second outlet 12, a second cavity 5 on the front surface and a third cavity 13 and a first connecting contact 14 on the back surface. The third wafer 3 is provided with a fourth cavity 16 and a second connecting contact 17 on the front surface. The first cavity 4 of the first wafer and the front surface second cavity 5 of the second wafer constitute a main flow channel 6. The back surface third cavity 13 of the second wafer and the front surface fourth cavity 16 of the third wafer constitute a secondary flow channel 7. The first thermal flow sensor 10 and the second thermal flow sensor 15 are respectively located in the main flow channel 6 and the secondary flow channel 7 and each comprises a heater A2, an upstream temperature sensor A1 and a downstream temperature sensor A3 which are symmetrically distributed. The upstream temperature sensor A1 and the downstream temperature sensor A3 are used to measure the temperature difference between the upstream and downstream of the heater at different flow rates and convert the temperature difference signal into an electric signal which is transmitted out through the first connecting contact 14 and the second connecting contact 17. The double-layer structure is used to realize the flow splitting of the input fluid. The signal of the first thermal flow sensor 10 located in the main flow channel 6 is read at low flow rate, and the signal of the second thermal flow sensor 15 located in the secondary flow channel 7 is read at high flow rate, so as to achieve the purpose of widening the range.

[0027] The first thermal flow sensor 10 and the second thermal flow sensor 15 are arranged across the back cavity 4 of the first wafer 1, the front cavity 5 of the second wafer 2, the third cavity 13 of the second wafer 3 and the front cavity 16 of the third wafer respectively, which reduces power consumption and increases sensitivity.

[0028] The gas with different flow rates (or flow rates for calculating flow rate) enters the first inlet 8 of the micro flowmeter, when the gas flow rate is 0, the upstream temperature sensor A1 and the downstream temperature sensor A3 of the first thermal flow sensor 10 are symmetrically arranged on both sides of the heater A2, at this time, the temperature difference between the upstream and downstream is 0, and the output electric signal is 0. When the flow rate is small, the signal value output by the first thermal flow sensor 10 in the main flow channel 6 can be read, at this time, the temperature difference increases with the increase of the flow rate; the temperature difference and the flow rate first change linearly, and with the increase of the flow rate, the linear relationship is destroyed due to the viscous dissipation, when the flow rate exceeds a certain value, the temperature difference decreases with the increase of the flow rate due to the sharp increase of the viscous dissipation, that is, it enters the "reverse rising region", the first thermal flow sensor 15 is invalid, but at this time, due to the shunt effect, the flow rate in the auxiliary flow channel 7 is still small, the signal of the second thermal flow sensor 15 in the auxiliary flow channel 7 can be used, and since the flow rates in the main flow channel 6 and the auxiliary flow channel 7 are proportional, the measured flow rate signal can be obtained by conversion. Thus, the purpose of widening the range is achieved.

[0029] In addition, the first thermal flow sensor 10 and the second thermal flow sensor 15 both adopt a bridge structure, which can reduce vibration and improve signal stability compared with a cantilever structure. The heater A2, the upstream temperature sensor A1 and the downstream temperature sensor A3 are made of a multi-layer structure, and the materials of the layers from top to bottom are SiO2 layer A4, Si3N4 layer A5, Pt layer A6, Si3N4 layer A7, SiO2 layer A8 and Al layer A9, wherein the Pt layer A6 has a good TCR coefficient, which is used for signal sensing and output.

[0030] It is obvious for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application. Any reference signs in the claims should not be regarded as limiting the claims involved.

[0031] Furthermore, it should be understood that although the specification is described in terms of embodiments, not every embodiment includes every feature described. The specification can include implicit combinations of explicitly mentioned features and / or explicit combinations of implicitely mentioned features. Each embodiment depends on the explicit combinations of features and / or the implicit combinations of features made specifically within that embodiment, and each such embodiment can be combined with every other such embodiment to create further embodiments.

Claims

1. A double-layer thermal wide-range gas micro-flowmeter, which is composed of a first wafer, a second wafer and a third wafer which are bonded together in sequence; characterized in that, The first wafer is provided with a first inlet on one side and a first outlet on the other side, and is bonded with the second wafer on one side to form a first cavity; the second wafer is provided with a second inlet on the side corresponding to the first inlet, a second outlet on the side corresponding to the first outlet, a first connecting contact between the second inlet and the second outlet, a second cavity on the side bonded with the first wafer, and a third cavity on the side bonded with the third wafer; the third wafer is provided with a second connecting contact on the side bonded with the second wafer, and a fourth cavity on the side bonded with the second wafer; the first cavity and the second cavity form a main flow channel, and the third cavity and the fourth cavity form a secondary flow channel; the main flow channel is provided with a first thermal flow sensor across the first cavity and the second cavity, and the secondary flow channel is provided with a second thermal flow sensor across the third cavity and the fourth cavity; the first thermal flow sensor and the second thermal flow sensor are respectively provided with a heater, and an upstream temperature detector and a downstream temperature detector symmetrically distributed on both sides of the heater along the gas flow direction, for measuring the temperature difference between the upstream and downstream of the heater at different flow rates, and converting the temperature difference signal into an electric signal and transmitting it out through the first connecting contact and the second connecting contact respectively; the double-layer thermal type wide-range gas micro-flow meter reads the signal of the first thermal flow sensor in the main flow channel at low flow, and reads the signal of the second thermal flow sensor in the secondary flow channel at high flow.

2. A dual layer thermal wide range gas micro-flow meter according to claim 1, wherein, The first wafer, the second wafer and the third wafer are bonded together in sequence through Al and Ge eutectic bonding.

3. A dual layer thermal wide range gas micro-flow meter according to claim 1, wherein, The first inlet and the second inlet are staggered and distributed, and the first outlet and the second outlet are correspondingly arranged.

4. A dual layer thermal wide range gas micro-flow meter according to claim 1, wherein, The flow in the secondary flow channel is in a proportional relationship with the flow in the main flow channel, and the proportional coefficient is determined according to the position and size of the first inlet, the first outlet, the second inlet and the second outlet.

5. A dual layer thermal wide range gas micro-flow meter according to claim 1, wherein, The heater, the upstream temperature detector and the downstream temperature detector of the first thermal flow sensor and the second thermal flow sensor are all multi-layer structures, and the materials of each layer from top to bottom are SiO2 layer, Si3N4 layer, Pt layer, Si3N4 layer, SiO2 layer and Al layer, wherein the Pt layer is the working material.

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