Monolithic integrated design method, manufacturing method and sensor of micro flow sensor

Abstract

The present invention discloses a monolithic integrated design method, a manufacturing method and a sensor for a micro flow sensor. The monolithic integrated design method includes: constructing a thermoelectric coupling equivalent model of a microheater; performing heat transfer analytical analysis on a microstrip line component to obtain thermal information, wherein the microstrip line component is composed of a microheater and two pairs of thermistors; constructing a first equivalent circuit model based on the thermoelectric coupling equivalent model of the microheater and a constant temperature difference control circuit structure; and constructing a second equivalent circuit model corresponding to the two pairs of thermistors; and performing force-heat-electric coupling on the first equivalent circuit model and the second equivalent circuit model to obtain a system-level equivalent circuit model. Through the above method, a heat transfer analytical model with thermophysical properties can be coupled to establish a nonlinear system-level equivalent model associated with temperature and humidity, so as to achieve efficient simulation of the impact of temperature and humidity changes on sensor output, and the MEMS microstructure and CMOS interface circuit can be quickly collaboratively designed and optimized based on the system-level model.

Description

Technical Field

[0001] The present invention relates to the technical field of airflow sensors, and in particular to a monolithic integrated design method, a manufacturing method and a sensor for a micro flow sensor. Background Art

[0002] CMOS-MEMS thermal flow sensor is composed of MEMS (Micro-Electro-Mechanical System) microstructure and CMOS (Complementary Metal Oxide Semiconductor) interface circuit. Its working process involves computational fluid dynamics (CFD), thermal and electrical multi-field coupling. For thermal flow sensors belonging to the MEMS sensor type, circuits manufactured by complementary metal oxide semiconductor (CMOS) technology are usually required to process the detected signals, such as analog-to-digital conversion, amplification, temperature compensation, storage or filtering, and logic and communication functions of system testing. With the development of semiconductor technology, people have made great efforts to integrate MEMS structure with integrated circuit (IC) on a single CMOS substrate. CMOS-MEMS technology has also been steadily applied to the manufacture of miniature thermal flow sensors, the so-called monolithic CMOS-MEMS integration.

[0003] However, the design process of micro flow sensors involves multiple parameters, such as the size of the micro suspension bridge, the thermal properties of the film and fluid, and the interface circuit parameters. Most of the existing designs are based on computational fluid dynamics simulation or "empirical" error setting methods. The process is cumbersome and inefficient, and is limited to the optimization of microstructure parameters. The electrical response characteristics cannot be predicted, which hinders the monolithic integrated design of the sensor. In addition, the existing sensor design methods are mostly based on fixed environmental conditions, ignoring the impact of temperature and humidity changes on the performance of the flow sensor. Therefore, the design method of the micro flow sensor in the existing technical method is imperfect and has low design efficiency. Summary of the invention

[0004] The embodiments of the present invention provide a monolithic integrated design method, a manufacturing method and a sensor for a micro flow sensor, aiming to solve the problem of imperfect integrated sensor design and performance optimization methods in the prior art methods.

[0005] In a first aspect, an embodiment of the present invention provides a monolithic integrated design method for a micro flow sensor, which includes:

[0006] According to King's law of thermal effect and the law of conservation of energy, a thermoelectric coupling equivalent model of the microheater is constructed;

[0007] Performing heat transfer analysis on the microstrip line component according to the heat transfer analysis model of the micro flow sensor to obtain thermal analysis information corresponding to the microstrip line component;

[0008] Constructing a first equivalent circuit model according to the thermoelectric coupling equivalent model and the circuit structure of the constant temperature difference control circuit;

[0009] Constructing a second equivalent circuit model corresponding to the two pairs of thermistors according to a preset resistance function and the thermal analysis information;

[0010] The first equivalent circuit model and the second equivalent circuit model are subjected to force-heat-electric coupling according to the heat transfer analytical model to obtain a system-level equivalent circuit model corresponding to the sensor.

[0011] In a second aspect, an embodiment of the present invention provides a monolithic integrated manufacturing method of a micro flow sensor, which includes:

[0012] A flow sensor and an on-chip integrated interface circuit are manufactured on a substrate by complementary metal oxide semiconductor technology; the substrate is composed of a silicon substrate and a silicon dioxide layer covering the surface of the silicon substrate, and the flow sensor is embedded in the bottom of the silicon dioxide layer;

[0013] spraying photoresist to deposit a photoresist cover film on the top layer of the flow sensor;

[0014] Removing the silicon dioxide covering the upper layer of the flow sensor by silicon dioxide reactive ion etching;

[0015] Remove the metal aluminum on the upper layer of the microstrip line component of the flow sensor for blocking oxide reactive ion etching by metal Al dry etching;

[0016] The silicon substrate is etched at the component gap of the microstrip line component by deep reactive ion etching to form a silicon groove; the component gap is a gap formed between microstrip lines arranged in parallel in the microstrip line component;

[0017] Etching the silicon substrate at the bottom of the microstrip line by xenon difluoride isotropic silicon-based etching to form a micro-suspended bridge based on the microstrip line;

[0018] The residual photoresist is removed by O2 plasma etching and the circuit connection port of the micro suspension bridge is electrically connected to the constant temperature difference control circuit and the current feedback instrument amplifier in the interface circuit respectively, so as to obtain a monolithic integrated CMOS-MEMS micro flow sensor.

[0019] In a third aspect, an embodiment of the present invention provides a micro flow sensor, which is manufactured by the monolithic integration design method described in the first aspect and the monolithic integration manufacturing method described in the second aspect, and the sensor includes a microstrip line component, a constant temperature difference control circuit and a current feedback instrument amplifier arranged on the substrate; a substrate bottom cavity is arranged on the substrate, and the substrate bottom cavity is obtained by a Post-CMOS post-processing process;

[0020] The microstrip line assembly is composed of a microheater and two pairs of thermistors, one pair of thermistors is arranged upstream of the microheater, and the other pair of thermistors is arranged downstream of the microheater, and the two pairs of thermistors are equidistant from the microheater; the microheater and the two pairs of thermistors are parallelly mounted on the bottom cavity of the substrate in the form of micro-suspension bridges;

[0021] The micro heater is electrically connected to the constant temperature difference control circuit so as to control the micro heater to maintain a constant temperature through the constant temperature difference control circuit;

[0022] The first pair of thermistors includes a first thermistor and a second thermistor, the second pair of thermistors includes a third thermistor and a fourth thermistor, the first thermistor, the fourth thermistor, the second thermistor and the third thermistor are sequentially connected end to end to form a Wheatstone bridge, the connection point between the first thermistor and the third thermistor and the connection point between the second thermistor and the fourth thermistor are both electrically connected to the current feedback instrument amplifier, the two pairs of thermistors sense voltage changes caused by temperature changes, and output electrical signals to the current feedback instrument amplifier;

[0023] The current feedback instrument amplifier is used to amplify the electrical signal to obtain an amplified signal and output it.

[0024] The embodiment of the present invention provides a monolithic integrated design method, manufacturing method and sensor for a micro flow sensor. A thermoelectric coupling equivalent model of a micro heater is constructed according to King's law of thermal effect and the law of conservation of energy; a heat transfer analysis of the microstrip line component is performed according to the heat transfer analysis model of the micro flow sensor to obtain thermal analysis information; a first equivalent circuit model is constructed according to the thermoelectric coupling equivalent model of the micro heater and the circuit structure of the constant temperature difference control circuit; a second equivalent circuit model corresponding to two pairs of thermistors is constructed according to the resistance function and thermal analysis information; and the first equivalent circuit model and the second equivalent circuit model are subjected to force-heat-electric coupling according to the heat transfer analysis model to obtain a system-level equivalent circuit model corresponding to the sensor. Through the above method, a heat transfer analysis model with thermophysical properties can be coupled to establish a nonlinear system-level equivalent model associated with temperature and humidity, so as to achieve efficient simulation of the influence of temperature and humidity changes on the sensor output, and the MEMS microstructure and CMOS interface circuit can be quickly collaboratively designed and optimized based on the system equivalent circuit model. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0026] Figure 1 A schematic flow chart of a monolithic integrated design method for a micro flow sensor provided by an embodiment of the present invention;

[0027] Figure 2 A schematic diagram of the circuit structure of a monolithic integrated design method for a micro flow sensor provided by an embodiment of the present invention;

[0028] Figure 3 A schematic flow chart of a method for manufacturing a micro flow sensor provided by an embodiment of the present invention;

[0029] Figure 4 A schematic diagram showing the effect of a method for manufacturing a micro flow sensor provided by an embodiment of the present invention;

[0030] Figure 5 A three-dimensional structural diagram of a micro flow sensor provided by an embodiment of the present invention;

[0031] Figure 6 A schematic cross-sectional structure diagram of a micro flow sensor provided in an embodiment of the present invention;

[0032] Figure 7 A partial structural diagram of a micro flow sensor provided in an embodiment of the present invention;

[0033] Figure 8 A partial circuit structure diagram of a micro flow sensor provided in an embodiment of the present invention;

[0034] Fig. 9 Another partial circuit structure diagram of the micro flow sensor provided by an embodiment of the present invention;

[0035] Fig.10 Another partial circuit structure diagram of the micro flow sensor provided by an embodiment of the present invention;

[0036] Fig.11 A schematic diagram of the effect of a micro flow sensor provided by an embodiment of the present invention;

[0037] Fig.12 Another schematic diagram of the effect of the micro flow sensor provided by an embodiment of the present invention;

[0038] Fig.13 Another effect schematic diagram of the micro flow sensor provided by an embodiment of the present invention;

[0039] Fig.14 Another effect schematic diagram of the micro flow sensor provided by an embodiment of the present invention;

[0040] Fig.15 A schematic diagram of the latter effect of the micro flow sensor provided by an embodiment of the present invention;

[0041] Fig.16 This is a schematic diagram of the subsequent effect of the micro flow sensor provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0044] It should also be understood that the terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0045] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0046] See also Figure 1 and Figure 2 , Figure 1 It is a schematic flow chart of a monolithic integrated design method of a micro flow sensor provided by an embodiment of the present invention; Figure 2 A schematic diagram of the circuit structure of a monolithic integrated design method for a micro flow sensor provided in an embodiment of the present invention. The monolithic integrated design method is applied to a temperature-compensated micro thermal flow sensor. The specific structure of the micro thermal flow sensor is described in detail in the following embodiments, wherein the sensor includes a microstrip line component, a constant temperature difference control circuit, and a current feedback instrument amplifier arranged on a substrate; the microstrip line component is composed of a micro heater and two pairs of thermistors, one pair of thermistors is arranged upstream of the micro heater, and the other pair of thermistors is arranged downstream of the micro heater, such as Figure 1 As shown, the method includes steps S110 to S150.

[0047] S110, constructing a thermoelectric coupling equivalent model of the microheater according to King's law of thermal effect and the law of conservation of energy.

[0048] In order to realize the temperature compensation of CMOS-MEMS micro thermal flow sensor (C 2 To perform system-level simulation of MTF sensor, two important equivalent circuit models (ECM) need to be established for the interface circuit. One is the circuit structure for constant temperature difference control of micro heater (CTD feedback circuit), which is composed of micro heater and corresponding constant temperature difference control circuit. The other is the Wheatstone bridge circuit composed of thermistor, such as Figure 2 As shown in the figure, the thermal conduction process of the micro heater and the two pairs of thermistors upstream and downstream can be modeled. Then, combined with the heat transfer analytical model, the entire flow sensor system model is built in the Cadence Virtuoso platform. Finally, the C 2 System-level simulation and optimization of MTF sensors.

[0049] Specifically, for the feedback control circuit composed of the micro heater and the corresponding constant temperature difference control circuit, it is necessary to perform force-heat-electric coupling simulation, and the semi-empirical equations describing the dynamic behavior of fluid and heater transfer can be used. The most common one is King's law of thermal effect describing the convective heat transfer of cylinders, but the micro heater is a thermal film, not a cylinder. We use the modified King's law of thermal effect to describe it. The specific description can be expressed as formula (1):

[0050] P=(A+BU n )(T h -T a ) (1);

[0051] Where A is the heat loss due to conduction, radiation and free heat, and is not a function of the flow velocity U. n is the strong convective heat transfer in the thermal boundary layer, T h is the temperature value of the micro heater, n depends on the structure of the sensor, usually 0.5, in this design n = 0.5742. And for the micro heater, there is the law of energy conservation, so we can further get formula (2):

[0052]

[0053] T h and T a are the operating temperature and ambient temperature of the micro heater, respectively, h is the density, C h is the heat capacity, V h is the volume, τ is the time, so the thermoelectric coupling equivalent model of the microheater can be established according to formula (2).

[0054] S120. Perform heat transfer analysis on the microstrip line component according to the heat transfer analysis model of the micro flow sensor to obtain thermal analysis information corresponding to the microstrip line component.

[0055] The heat transfer analytical model can be a theoretical analysis model of a micro thermal flow velocity sensor with thermophysical properties related to temperature and humidity. After substituting the parameter information of the microstrip line component into the analytical model, the corresponding thermal information can be expressed by formula (3):

[0056]

[0057] where k m , m , and C pm are the thermal conductivity, density and heat capacity of moist air respectively. t is the thermal boundary layer, h is the height of the substrate bottom cavity, k sis the thermal conductivity of the film, t is the thickness of the film (the film here represents the film structure formed by the microheater and thermistor on the substrate, and the film based on the microheater and thermistor can be released after the Post-CMOS post-processing process). And k m , m , C m and δ t are all parameters related to temperature and humidity, and their corresponding values ​​can be obtained from the properties of related materials. Therefore, the solution of formula (3) is C 2 The analytical solution of the temperature distribution T(x) of the MCF sensor in the flow direction (x) can be used to obtain the upstream and downstream temperatures T based on the above thermal analysis information. u and T d , where T u is the temperature value of the upstream pair of thermistors, T d is the temperature value of the downstream pair of thermistors.

[0058] S130, constructing a first equivalent circuit model according to the thermoelectric coupling equivalent model and the circuit structure of the constant temperature difference control circuit.

[0059] According to the above formula (2) and the circuit structure of the constant temperature difference control circuit, the equivalent circuit model of the CTD feedback circuit can be established, that is, the first equivalent circuit model Dx1. Figure 2 As shown, VCCS is a voltage-controlled current source that converts the voltage and current signals of the microheater into thermal power. Its expression is P = I (Heat) × V h VCVS is a voltage-controlled voltage source, which sets the heating temperature T h Converted into voltage signal V h =I h ×R h .

[0060] S140, constructing a second equivalent circuit model corresponding to the two pairs of thermistors according to a preset resistance function and the thermal analysis information.

[0061] The equivalent circuit model of the thermistor can be expressed by formula (4), which is also the resistance function of the thermistor:

[0062] R=R0(1+α(T(x)+T a -T0)) (4);

[0063] Where R0 is the resistance of the thermistor at the reference ambient temperature T0 = 25°C, α is the temperature coefficient of linear resistance (TCR), and T(x) is the solution of formula (3). Therefore, by combining formula (3) and formula (4), the equivalent circuit model (ECM) of the thermistor can be constructed. The equivalent circuit model of the thermistor is Dx2. The specific circuit structure is as follows: Figure 2 shown.

[0064] S150. Perform force-heat-electric coupling on the first equivalent circuit model and the second equivalent circuit model according to the heat transfer analytical model to obtain a system-level equivalent circuit model corresponding to the sensor.

[0065] The first equivalent circuit model and the second equivalent circuit model are coupled according to the heat transfer analytical model. The specific structure of the coupling circuit O is as follows: Figure 2 As shown. By coupling the two equivalent circuit models, the system equivalent circuit model can be constructed. In the above method, the thermoelectric coupling equivalent model of the microheater is first established by using the modified King's law and the law of conservation of energy. The temperature expressions of the upstream and downstream thermistors are obtained by analyzing the heat transfer analytical model of the micro thermal flow sensor. Finally, the resistance values ​​of the upstream and downstream thermistors are calculated according to the temperature distribution T(x), thereby establishing C 2 System-level equivalent circuit model of the MCF sensor.

[0066] See also Figure 3 and Figure 4 , Figure 3 The manufacturing method of the micro flow sensor provided by the embodiment of the present invention can also be called a Post-CMOS post-processing process; Figure 3 As shown, the method includes steps S210 to S270.

[0067] S210. A flow sensor and an on-chip integrated interface circuit are manufactured on a substrate by complementary metal oxide semiconductor process; the substrate is composed of a silicon substrate and a silicon dioxide layer covering the surface of the silicon substrate, and the flow sensor is embedded in the bottom of the silicon dioxide layer.

[0068] The flow sensor (C in this embodiment) can be manufactured by using a 0.18 μm 1P6M complementary metal oxide semiconductor (CMOS) process. 2MTF flow sensor) and on-chip integrated interface circuit, the flow sensor includes microstrip line components and metal aluminum basic circuit structure, the basic circuit structure of the flow sensor includes polysilicon (such as p+ type polysilicon) embedded in the silicon dioxide layer in the form of microstrip lines, the polysilicon can form the above microstrip line components after Post-CMOS post-processing process, and metal aluminum embedded in the silicon dioxide layer in the form of metal microstrip lines, wherein the metal aluminum is arranged on the upper layer of the polysilicon, and there is a certain gap between the metal aluminum and the polysilicon, the width of the metal aluminum is slightly larger than the width of the polysilicon, and the hard mask layer determined by the metal aluminum pattern can provide self-aligned windowing for deep silicon etching, and the flow sensor obtained at this time does not yet have perfect functions. The basic structure of the obtained flow sensor and interface circuit is as follows Figure 4 and Figure 6 As shown, the basic structure of the flow sensor and interface circuit manufactured in step S210 is as follows Figure 4 (a) shown.

[0069] S220 , spraying photoresist to deposit a photoresist covering film on the top layer of the flow sensor.

[0070] Spray photoresist around the flow sensor to deposit a layer of photoresist covering film around the flow sensor, that is, no photoresist covering film is deposited on the flow sensor. At this time, the basic structure is as follows: Figure 4 (b) Wherein, the photoresist may be AZ9260 type photoresist, the thickness of the photoresist cover film is 2-8 μm, and the thickness of the photoresist cover film in the best embodiment is 4 μm.

[0071] S230, removing the silicon dioxide covering the upper layer of the flow sensor by silicon dioxide reactive ion etching.

[0072] The silicon dioxide on the substrate where no photoresist covering film is deposited is removed by oxide reactive ion etching. Since no photoresist covering film is deposited on the upper layer of the flow sensor, the silicon dioxide on the upper layer of the flow sensor is etched away. At this time, the basic structure is as follows: Figure 4 (c) as shown.

[0073] S240, removing the metal aluminum on the upper layer of the microstrip line component of the flow sensor for blocking oxide reactive ion etching by metal Al dry etching;

[0074] A layer of metal aluminum above the polysilicon in the flow sensor is used to block oxide reactive ion etching, and the polysilicon wrapped with silicon dioxide on the outside forms a microstrip line component. After oxide reactive ion etching, the metal aluminum is completely exposed, which is used to complete the thinning of the microstrip line component and the exposure of the bottom cavity silicon base; the hard mask layer determined by the high-precision metal Al can provide self-aligned windowing for subsequent deep reactive ion etching; at this time, the metal aluminum can be removed by dry etching, and the basic structure is as follows Figure 4 As shown in (d), since there is a certain gap between the metal aluminum and the polysilicon, and the width of the metal aluminum is greater than the width of the polysilicon, the silicon dioxide around the polysilicon is retained and wrapped in the outer layer of the polysilicon.

[0075] S250, etching the silicon substrate at the component gap of the microstrip line component by deep reactive ion etching to form a silicon groove; the component gap is a gap formed between microstrip lines arranged in parallel in the microstrip line component.

[0076] The microstrip line component is composed of multiple parallel microstrip lines with certain gaps between them. Deep reactive ion etching (DRIE) can be used to etch silicon grooves between the gaps of the components. This step is to etch the silicon substrate to a certain depth. The basic structure is as follows: Figure 4 (e) as shown.

[0077] S260, etching the silicon substrate at the bottom of the microstrip line by xenon difluoride isotropic silicon-based etching to form a micro-suspended bridge based on the microstrip line.

[0078] The micro-suspended bridges are released by isotropic silicon-based etching with xenon difluoride (XeF2), that is, the silicon substrate at the bottom of each microstrip line is etched by isotropic silicon-based etching with xenon difluoride, thereby forming micro-suspended bridges based on the microstrip line. At this time, a substrate bottom cavity is formed on the silicon substrate through isotropic silicon-based etching with xenon difluoride (XeF2), and multiple micro-suspended bridges are parallelly erected on the substrate bottom cavity; the suspension height between the microstrip line component and the silicon substrate can be set to 80-400μm, and in the optimal embodiment, the suspension height between the microstrip line component and the silicon substrate can be set to 80-150μm. The specific structure of each component of the final micro thermal flow sensor is as follows: Figures 5 to 7 As shown, the components are labeled as follows: substrate 10, microstrip line component 20, constant temperature difference control circuit 30, current feedback instrument amplifier 40, metal aluminum 23, polysilicon 22, silicon base 12, silicon dioxide layer 13, passivation layer 14, tungsten 53, photoresist 52, interface circuit 51, substrate bottom cavity 11.

[0079] S270, removing residual photoresist by O2 plasma etching and electrically connecting the circuit connection port of the micro suspension bridge to the constant temperature difference control circuit and the current feedback instrument amplifier in the interface circuit, respectively, to obtain a monolithic integrated CMOS-MEMS micro thermal flow sensor.

[0080] The residual photoresist can be removed by O2 plasma etching, that is, the previously deposited photoresist cover film is removed, and the basic structure obtained is as follows Figure 4 (f) As shown. Circuit connection ports are provided at both ends of the micro-suspended bridge, and the circuit connection ports of the micro-suspended bridge can be electrically connected to the constant temperature difference control circuit and the current feedback instrument amplifier in the interface circuit, thereby obtaining a micro thermal flow sensor. At this time, the micro thermal flow sensor can realize complete functions.

[0081] Through the above method, a small-sized thermal flow sensor microstructure can be integrated and manufactured on a single chip based on CMOS-MEMS technology, so that the manufactured thermal flow sensor microstructure has an extremely small footprint.

[0082] The embodiment of the present invention further provides a micro flow sensor with temperature compensation, which is manufactured by the aforementioned micro flow sensor manufacturing method, that is, manufactured by a Post-CMOS post-processing process. Figures 5 to 10 As shown in the figure, the sensor includes a microstrip line component 20, a constant temperature difference control circuit 30 and a current feedback instrument amplifier 40 arranged on the substrate 10; a substrate bottom cavity 11 is arranged on the substrate 10, and the microstrip line component 20 is provided with a microheater R h And two pairs of thermistors, one pair of thermistors R u The micro heater R is provided h Upstream of the other thermistor R d The micro heater R is provided h downstream, and the two pairs of thermistors and the microheater R h The spacing distances of the micro heaters R h The two pairs of thermistors are parallelly mounted on the substrate bottom cavity 11 in the form of micro-bridges. h The constant temperature difference control circuit 30 is electrically connected to control the micro heater R through the constant temperature difference control circuit 30. h Maintain constant temperature; the first pair of thermistors R u Including the first thermistor R u1 and the second thermistor R u2 , the second pair of thermistors R d Including the third thermistor R d1 And the fourth thermistor Rd2 , the first thermistor R u1 The fourth thermistor R d2 The second thermistor R u2 and the third thermistor R d1 The first thermistor R u1 With the fourth thermistor R d2 The connection point between the second thermistor R u2 With the third thermistor R d1 The connection points between them are electrically connected to the current feedback instrument amplifier 40, and the two pairs of thermistors sense the voltage changes caused by temperature changes and output electrical signals to the current feedback instrument amplifier 40; the current feedback instrument amplifier 40 is used to amplify the electrical signals to obtain the amplified signals and output them, and the substrate bottom cavity 11 can be obtained by Post-CMOS post-processing process.

[0083] The electrical connection relationship between the two pairs of thermistors and the current feedback instrument amplifier 40 is as follows: Fig. 9 As shown, the second thermistor R u2 With the fourth thermistor R d2 The connection point between them is connected to the power supply, and the output voltage of the power supply is V s , the first thermistor R u1 With the third thermistor R d1 The connection point between ground and the first thermistor R u1 With the fourth thermistor R d2 The connection point between the positive input terminal of the current feedback instrumentation amplifier 40 and the second thermistor R u2 With the third thermistor R d1 The connection point between is connected to the negative input terminal of the current feedback instrumentation amplifier 40 .

[0084] Microstrip line component 20 (also known as C 2 The MTF sensor consists of a polysilicon microheater R h , and parallel to the microheater R h Two pairs of thermistors R u and R d Composition, two pairs of thermistors R u and R d Symmetrically distributed on the micro heater R h The upstream and downstream, that is, the two pairs of thermistors and the micro heater R h The spacing distances of the micro heaters are equal. h The constant temperature difference control circuit 30 is used to control the temperature to be constant, such as 50°C. The two pairs of thermistors Ru and R d In the presence of fluid flow (such as air flow) (assuming the flow velocity is U), the microheater R h The surrounding temperature distribution is distorted by the fluid flow, and the heat transfer causes the upstream (upstream and downstream relative to the fluid flow) pair of thermistors R u The temperature of the downstream thermistor R d The temperature is low and there is a temperature difference output ΔT=T u -T d , T u For the first pair of thermistors R u The sensing temperature, T d For the second pair of thermistors R d The sensed temperature, ΔT, is the temperature difference between the thermistors. The Wheatstone bridge formed by the thermistors converts the thermal signal ΔT into an electrical signal ΔV, which is amplified by a low-noise current feedback instrumentation amplifier 40 and outputs an amplified signal V out , then the amplified signal V out The size of the signal V is related to the flow rate U. out The size of the flow velocity U sensed by the micro thermal flow sensor can be obtained.

[0085] In a more specific embodiment, the microheater R h The two pairs of thermistors are made of polysilicon coated with silicon oxide; wherein the microheater R h The polysilicon is arranged in a serpentine zigzag line, and silicon oxide is coated on the outer layer of the polysilicon arranged in the serpentine zigzag line. More specifically, the first thermistor R u1 and the second thermistor R u2 Fold the first pair of thermistors R in half u The corresponding micro-suspended bridge; the third thermistor R d1 and the fourth thermistor R d2 Fold the second pair in half to bisect the thermistor R d The first thermistor R u1 The second thermistor R u2 , the third thermistor R d1 and the fourth thermistor R d2 The polysilicon is arranged in a serpentine fold line, and the silicon oxide is coated on the outer layer of the polysilicon arranged in the serpentine fold line. h The arrangement of the two pairs of polysilicon in the thermistor is as follows: Figure 7 As shown, the micro heater R hThe width of the polysilicon in the microheater is greater than that of the polysilicon in the thermistor. The thickness of the polysilicon can be set to 0.2 μm, and the thickness of the silicon oxide coated on the outer layer of the polysilicon can be set to 2.5 μm. In this embodiment, the microheater R h The polysilicon in the microstrip line is folded three times based on the width of the substrate bottom cavity 11 to obtain the polysilicon arranged in a serpentine fold line; the polysilicon in the thermistor is folded four times based on half the width of the substrate bottom cavity 11 to obtain the polysilicon arranged in a serpentine fold line. In addition, the suspension height between the microstrip line component and the silicon substrate can be set to 80-400μm.

[0086] In a more specific embodiment, the constant temperature difference control circuit 30 includes a first resistor R1, a second resistor R2, a reference ambient temperature sensor resistor R r , Temperature regulating resistor R c and an operational amplifier OP-Amp; the first resistor R1, the second resistor R2, the micro heater R h , the reference ambient temperature sensor resistance R r And the temperature regulating resistor R c The first and the second resistor R2 are connected end to end to form a Wheatstone bridge, and the second resistor R2 and the micro heater R h The connection point between the first resistor R1 and the temperature regulating resistor R c The connection point between the first resistor R1 and the second resistor R2 is connected to the output end of the operational amplifier OP-Amp. r The microheater R is made of carrier polysilicon, such as hole carrier polysilicon or electron carrier polysilicon. In a more preferred embodiment, the microheater R h With reference to ambient temperature sensor resistor R r Specifically, the constant temperature difference control circuit 30 and the micro heater R h The electrical connection relationship between Figure 8 As shown, the first resistor R1, the second resistor R2, the micro heater R h , Reference ambient temperature sensor resistance R r And temperature regulating resistor R c The five resistors form a Wheatstone bridge, the second resistor R2 and the microheater R h The connection point between them is connected to the negative signal input terminal of the operational amplifier OP-Amp, and the first resistor R1 is connected to the temperature regulating resistor R c The connection point between them is connected to the positive signal input terminal of the operational amplifier OP-Amp, where the temperature adjustment resistor R cThe microheater R can be arranged on the substrate 10 or outside the substrate and connected to the constant temperature difference control circuit 30 through an external connection. h The specific method of constant temperature control is: when the flow passes through the micro heater R h When the flow rate increases, the microheater R h The resistance of the microheater decreases due to the influence of cooling. At this time, the voltage difference at the positive signal input end of the operational amplifier OP-Amp increases, so that the voltage amplified by the operational amplifier OP-Amp also increases; at this time, the output end of the operational amplifier OP-Amp outputs an increased voltage and performs feedback adjustment on the Wheatstone bridge. The input current of the Wheatstone bridge also increases accordingly, and the input power increases. As the input power of the bridge increases, the microheater R h The resistance value R h The bridge becomes balanced again after feedback adjustment. In the above constant temperature difference adjustment circuit, R1 / R2 and (R r +R c ) / R h The ratio is a to ensure that most of the power is supplied by the microheater R h Consumption, in this embodiment, the resistance value of each resistor can be adjusted so that a=5, and the corresponding proportional relationship can be expressed by formula (5):

[0087]

[0088] Specifically, the on-chip reference ambient temperature sensor resistor R r It can be made of hole carrier polysilicon (P+ polysilicon, that is, trivalent doped polysilicon). In addition, the microheater R h It can also be made of hole carrier polysilicon. The resistor manufactured based on hole carrier polysilicon in CMOS tape-out has a good linear temperature coefficient of resistance (TCR), α=0.003.

[0089] Further obtain the on-chip reference ambient temperature sensor resistance R r And micro heater R h The expression of is as follows:

[0090]

[0091] R r0 That is, when the temperature is T0, the reference ambient temperature sensor resistance R r The reference temperature resistance value (such as R r0 is the reference temperature T0 = 25°C R r resistance value), R h0 That is, when the temperature is T0, the micro heater R h The heating resistance value is adjusted by configuring the resistor Rc =αR r0 ΔT h (ΔT h YesR c Adjusted superheat temperature), further deduction can be obtained formula (7):

[0092]

[0093] T a is the ambient temperature, by configuring the reference ambient temperature sensor resistor R r And the temperature regulating resistor R c , which can make T h According to T a automatically regulates, thus ensuring that the microheater R h At different input flow rates with a constant ΔT h Work, not subject to T a In addition, to ensure the micro thermal flow sensor is sensitive to the micro heater R h By accurately controlling the temperature feedback regulation, the gain and phase of the operational amplifier OP-Amp can be tested at various frequencies. The test results are as follows: Fig.11 As shown, from Fig.11 It can be seen that the phase margin of the operational amplifier OP-Amp is 63 (when the gain is 0dB), the open-loop gain is as high as 97dB, and it has a strong current driving capability of more than 52.8mA.

[0094] In practical applications, due to the two pairs of thermistors R u and R d The voltage output ΔV of the Wheatstone bridge is usually in the mV level, so a current feedback instrument amplifier 40 is designed to amplify the output electrical signal ΔV sensed by the thermistor. The specific circuit structure of the current feedback instrument amplifier 40 is as follows: Fig.10 As shown. m,in and G m,fb They are input and feedback transconductance, converting the output and feedback voltage into current and sharing a node, which improves the power efficiency compared with the traditional three-stage amplifier. In order to reduce the current flowing into the Wheatstone bridge and avoid self-heating, we choose 0.5V as the power supply voltage of the bridge, that is, the voltage of the power supply Vs = 0.5V, and use PMOS tube as the folded common source common gate input pair tube ( Fig.10 In order to reduce low frequency noise, a chopper is added to the current feedback instrumentation amplifier (CFIA) circuit 40, and the chopper is output at 50Khz, as shown in FIG. Fig.10The three choppers Z1, Z2 and Z3 are set in the figure. The chopper first modulates the input and feedback signals to the chopping frequency and then demodulates them through the chopper. The input reference offset and flicker noise only pass through one chopper, which modulates them to the chopping frequency and odd harmonics. The chopping ripple at the output can be eliminated by modulating the signal twice and the noise once, and then connecting a low-pass filter at the output.

[0095] When configuring the current feedback instrumentation amplifier (CFIA) circuit 40, in order to achieve accurate matching of input and feedback transconductance and reduce gain error, it is necessary to configure G m,in =G m,fb , then the closed-loop gain of the current feedback instrumentation amplifier (CFIA) circuit 40 can be expressed by formula (8):

[0096]

[0097] Among them, R can be configured 21 =R 22 =99.5KΩ, R23=1KΩ, G m,in =G m,fb , so G=200. Fig.12 That is, the analysis result obtained by performing periodic noise analysis on the current feedback instrumentation amplifier (CFIA) circuit 40, Fig.12 The input-referred noise spectral density of the closed-loop CFIA is about 4.32nV / √Hz, which has good low-noise characteristics. In addition, the CMRR (Common Mode Rejection Ratio) of the amplifier is greater than 163dB, and the power consumption is as low as 1.49mW. The current feedback instrumentation amplifier (CFIA) can be used as the above C 2 Well-interfaced readout circuit for MTF sensors. Fig.12 The corner frequency of the flicker noise after chopping is around 300mHz, and the noise spectral density is about 4.32nV / √Hz.

[0098] In order to further improve the sensitivity of the sensor, the distance between the micro heater and the h Two pairs of thermistors are arranged at the same distance upstream and downstream, and the two pairs of thermistors form a Wheatstone bridge. The output electrical signal ΔV sensed by the thermistors is amplified by the current feedback instrumentation amplifier (CFIA) circuit 40, and the obtained full system voltage output V out It can be expressed by formula (9):

[0099]

[0100] For the above-mentioned micro thermal flow sensor (C 2MTF sensor), output test can be performed, Fig.13 This is the comparison between the output of the micro thermal flow sensor and the two-dimensional computational fluid dynamics (CFD) model. Fig.13 It can be seen that the output results of the micro thermal flow sensor produced by this scheme are very consistent with the output results of the CFD model (the fitting factor ε is 2.3). Fig.13 It can also be concluded that the above C 2 The sensitivity of the MTF sensor is 0.274V / (m / s), proving that C 2 The MTF sensor has high sensitivity in low flow areas. Fig.13 The test results also show that the greater the flow rate of the sensor input, the smaller the sensitivity, which also reflects the C 2 The trade-off relationship between the sensitivity and output voltage of the MTF sensor. Moreover, the integrated SoC flow sensor has an extremely low system power consumption of 3.04 to 3.6 mW in the flow range of 0 to 10 m / s.

[0101] By setting the microheater R h Working in constant temperature (CT) mode, the test was carried out when the ambient temperature changed from 0°C to 50°C and the flow range was 0-10m / s. The output results obtained without temperature compensation were as follows: Fig.14 shown. Fig.14 (a) The test results show that ΔT h Correspondingly, the temperature drops from 75℃ to 25℃. Fig.14 (b) shows the test results showing that the output voltage of the micro thermal flow sensor drops sharply, with a variation of up to 50%.

[0102] By configuring the micro heater in CTD mode and testing when the ambient temperature changes from 0°C to 50°C and the flow range is 0-10m / s, the corresponding output results are as follows: Fig.15 As shown, Fig.15 (a) shows that ΔT h Almost kept constant at 50°C (variation <0.53%). 2 The analog output of the MTF sensor system decreases only slightly (±7%) when the ambient temperature ranges from 0℃ to 50℃ (reference room temperature T0 = 25℃). Fig.15 (b) The test results show that the proposed interface circuit can effectively suppress temperature drift.

[0103] Further test the effect of ambient temperature on C 2 The MTF sensor performance is affected by adding an on-chip overheat temperature adjustment resistor R with a positive TCR. c , it can automatically adjust ΔT hIn order to reduce output drift, the test was carried out when the ambient temperature changed from 0°C to 50°C and the flow range was 0-10m / s. The results are as follows Fig.16 As shown. Fig.16 As shown in (a), by configuring a positive TCR R in the same CMOS chip c , when T a When the temperature changes from 0℃ to 50℃, ΔT h It rose slightly from 46.7℃ to 54.22℃. Fig.16 (b) shows the test results, the sensor output reduction can be increased by increasing ΔT h Automatic compensation. Therefore, the above C 2 The MTF sensor shows excellent temperature insensitivity, with output variations as small as 0.5%. Fig.16 (b) as shown.

[0104] The following table summarizes the C 2 The performance of the MTF sensor is compared with other sensors in the prior art, and the comparison results are shown in Table 1. 2 The MTF sensor is monolithically integrated, has a flow range of -10 to 10 m / s, a system power of less than 3.6 mW, and a high sensitivity of 274 mV / (m / s).

[0105] Table 1

[0106] serial number Flow rate range (m / s) Power consumption (mW) Sensitivity (V / (m / s)) Temperature compensation MI Comparative Example 1 0～26 <![CDATA[3 b ]]> 0.117 - - Comparative Example 2 -3.33～3.33 <![CDATA[4 b ]]> 0.0023 - - Comparative Example 3 0.5～40 <![CDATA[2~452.6 b ]]> 0.0079 - - Comparative Example 4 0.02-38 <![CDATA[400-600 a ]]> - - yes Comparative Example 5 -11～11 <![CDATA[2.36~2.77 b ]]> 0.543 0.5％ - This program -10～10 <![CDATA[3.04~3.6 a ]]> 0.274 ±0.5％ yes

[0107] Marking description, a sensor system power, b micro heater power, MI: Whether the MEMS flow sensor and interface circuit can be monolithically integrated on a single chip.

[0108] The embodiment of the present invention provides a monolithic integrated design method, manufacturing method and sensor for a micro flow sensor. A thermoelectric coupling equivalent model of a micro heater is constructed according to King's law of thermal effect and the law of conservation of energy; a heat transfer analysis of the microstrip line component is performed according to the heat transfer analysis model of the micro flow sensor to obtain thermal information; a first equivalent circuit model is constructed according to the thermoelectric coupling equivalent model and the circuit structure of the constant temperature difference control circuit; a second equivalent circuit model corresponding to two pairs of thermistors is constructed according to the resistance function and thermal analysis information; and the first equivalent circuit model and the second equivalent circuit model are subjected to force-heat-electric coupling according to the heat transfer analysis model to obtain a system equivalent circuit model corresponding to the sensor. Through the above method, a nonlinear system-level equivalent model associated with temperature and humidity can be established based on a heat transfer analysis model with thermophysical properties to achieve efficient simulation of the impact of temperature and humidity changes on sensor output, and the MEMS microstructure and CMOS interface circuit can be quickly collaboratively designed and optimized based on the system-level equivalent circuit model.

[0109] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A monolithic integrated design method for a micro flow sensor, characterized in that: The sensor comprises a microstrip line component, a constant temperature difference control circuit and a current feedback instrument amplifier arranged on a substrate; the microstrip line component is composed of a microheater and two pairs of thermistors, one pair of thermistors is arranged upstream of the microheater, and the other pair of thermistors is arranged downstream of the microheater; The method comprises: According to King's law of thermal effect and the law of conservation of energy, a thermoelectric coupling equivalent model of the microheater is constructed; the thermoelectric coupling equivalent model is: ; A is the heat loss due to conduction, radiation and natural heat, BU n is the strong convective heat transfer in the thermal boundary layer, T h and T a are the operating temperature and ambient temperature of the micro heater, is the density, is the heat capacity, is the volume, is time, R h is the resistance value of the microheater, I is the current value on the microheater; According to the heat transfer analysis model of the micro flow sensor, the microstrip line component is heat-analyzed to obtain thermal analysis information corresponding to the microstrip line component; a first equivalent circuit model is constructed according to the thermoelectric coupling equivalent model and the circuit structure of the constant temperature difference control circuit; the first equivalent circuit model is an equivalent circuit model of a feedback circuit; the feedback circuit is composed of the micro heater and the constant temperature difference control circuit; the thermal analysis information is: ;in , ,and are the thermal conductivity, density and heat capacity of moist air, respectively. is the thermal boundary layer, h is the height of the substrate bottom cavity, is the thermal conductivity of the film, t is the thickness of the film; the film is a film structure formed by the micro heater and thermistor on the substrate; A second equivalent circuit model corresponding to the two pairs of thermistors is constructed according to the preset resistance function and the thermal analysis information; the second equivalent circuit model is , R0 is the resistance of the thermistor at the reference ambient temperature T0 = 25°C, α is the linear resistance temperature coefficient, and T(x) is the solution in the thermal analysis information; The first equivalent circuit model and the second equivalent circuit model are subjected to force-heat-electric coupling according to the heat transfer analytical model to obtain a system-level equivalent circuit model corresponding to the sensor.

2. A monolithic integrated manufacturing method for a micro flow sensor, characterized in that: The method comprises: A flow sensor and an on-chip integrated interface circuit are manufactured on a substrate by complementary metal oxide semiconductor technology; the substrate is composed of a silicon substrate and a silicon dioxide layer covering the surface of the silicon substrate, and the flow sensor is embedded in the bottom of the silicon dioxide layer; spraying photoresist to deposit a photoresist cover film on the top layer of the flow sensor; Removing the silicon dioxide covering the upper layer of the flow sensor by silicon dioxide reactive ion etching; Remove the metal aluminum on the upper layer of the microstrip line component of the flow sensor for blocking oxide reactive ion etching by metal Al dry etching; The silicon substrate is etched at the component gap of the microstrip line component by deep reactive ion etching to form a silicon groove; the component gap is a gap formed between microstrip lines arranged in parallel in the microstrip line component; Etching the silicon substrate at the bottom of the microstrip line by xenon difluoride isotropic silicon-based etching to form a micro-suspended bridge based on the microstrip line; The residual photoresist is removed by O2 plasma etching and the circuit connection port of the micro suspension bridge is electrically connected to the constant temperature difference control circuit and the current feedback instrument amplifier in the interface circuit respectively, so as to obtain a monolithic integrated CMOS-MEMS micro flow sensor.

3. The monolithic integrated manufacturing method of a micro flow sensor according to claim 2, characterized in that: The complementary metal oxide semiconductor process is a 0.18 μm CMOS process.

4. A micro flow sensor, characterized in that: The sensor is manufactured by the monolithic integrated manufacturing method of the micro flow sensor according to any one of claims 2 to 3, and the sensor includes a microstrip line component, a constant temperature difference control circuit and a current feedback instrument amplifier arranged on the substrate; a substrate bottom cavity is arranged on the substrate, and the substrate bottom cavity is processed by a Post-CMOS post-processing process; The microstrip line assembly is composed of a microheater and two pairs of thermistors, one pair of thermistors is arranged upstream of the microheater, and the other pair of thermistors is arranged downstream of the microheater, and the two pairs of thermistors are equidistant from the microheater; the microheater and the two pairs of thermistors are parallelly mounted on the bottom cavity of the substrate in the form of micro-suspension bridges; The micro heater is electrically connected to the constant temperature difference control circuit so as to control the micro heater to maintain a constant temperature through the constant temperature difference control circuit; The first pair of thermistors includes a first thermistor and a second thermistor, and the second pair of thermistors includes a third thermistor and a fourth thermistor. The first thermistor, the fourth thermistor, the second thermistor and the third thermistor are connected end to end in sequence to form a Wheatstone bridge. The connection point between the first thermistor and the fourth thermistor and the connection point between the second thermistor and the third thermistor are both electrically connected to the current feedback instrument amplifier. The two pairs of thermistors sense voltage changes caused by temperature changes and output electrical signals to the current feedback instrument amplifier. The current feedback instrument amplifier is used to amplify the electrical signal to obtain an amplified signal and output it.

5. The micro flow sensor according to claim 4, characterized in that: The constant temperature difference control circuit includes a first resistor, a second resistor, a reference ambient temperature sensor resistor, a temperature adjustment resistor and an operational amplifier; The first resistor, the second resistor, the microheater, the reference ambient temperature sensor resistor and the temperature-adjusting resistor are connected end to end in sequence to form a Wheatstone bridge, the connection point between the second resistor and the microheater and the connection point between the first resistor and the temperature-adjusting resistor are respectively connected to the two signal input terminals of the operational amplifier, and the connection point between the first resistor and the second resistor is connected to the output terminal of the operational amplifier.

6. The micro flow sensor according to claim 5, characterized in that: The reference ambient temperature sensor resistor is made of carrier polysilicon.

7. The micro flow sensor according to claim 4, characterized in that: The micro heater and the two pairs of thermistors are both made of polysilicon coated with silicon dioxide.

8. The micro flow sensor according to claim 7, characterized in that: The polysilicon of the microheater is arranged in a serpentine shape, and silicon dioxide is coated on the outer layer of the polysilicon arranged in the serpentine shape.

9. The micro flow sensor according to claim 7, characterized in that: The first thermistor and the second thermistor fold in half to divide the micro-suspended bridges corresponding to the first pair of thermistors; the third thermistor and the fourth thermistor fold in half to divide the micro-suspended bridges corresponding to the second pair of thermistors.

10. The micro flow sensor according to claim 9, characterized in that: The polysilicon of the first thermistor, the second thermistor, the third thermistor and the fourth thermistor are arranged in a serpentine shape, and silicon dioxide is coated on the outer layer of the polysilicon arranged in the serpentine shape.

Images