An in-plane thermoelectric cooling MEMS flow sensor and a manufacturing method thereof

Abstract

The present invention discloses an in-plane thermoelectric cooling MEMS flow sensor and a manufacturing method thereof, wherein the structure mainly comprises: a substrate, a film, a temperature measuring element, an in-plane thermoelectric cooling element and a chip pin; the film is symmetrical about the center of the substrate; the temperature measuring element is symmetrically distributed in the film; the in-plane thermoelectric cooling element is symmetrically placed at the junction of the film and the substrate; the electrical signals of the in-plane thermoelectric cooling element and the temperature measuring element are connected to the outside world through the chip pins around the substrate; the passivation layer covers the upper surface of the structure; during the manufacturing process, the temperature measuring element and the in-plane thermoelectric cooling element are realized by MEMS technology. The back of the silicon substrate is subjected to deep silicon etching treatment, and the silicon dioxide material on the front of the silicon substrate is used as an etching stop layer to form a thin film structure with good mechanical properties. The present invention combines the advantages of high sensitivity and non-movable structure of the thermal flow meter, and effectively avoids the problems caused by heating the measured medium.

Description

Technical Field

[0001] The present invention belongs to the field of MEMS sensors, and relates to a semiconductor Peltier effect-based quantitatively cooled MEMS flow sensor, in particular to an in-plane thermoelectric cooling structure and a manufacturing method thereof. Background Art

[0002] With the rapid development of Internet information and integrated circuits, MEMS (micro-electromechanical system) sensors, as the core components for realizing intelligent perception, are becoming increasingly important. MEMS flow sensors manufactured based on micro-nano processing technology have been widely used in industrial production process control, energy metering, environmental monitoring, biomedicine and other fields due to their advantages of miniaturization, low cost and compatibility with CMOS (complementary metal oxide semiconductor). According to different measurement principles, MEMS flow sensors can be mainly divided into differential pressure type, thermal type, ultrasonic type and Coriolis type. Among them, thermal flow sensors have received widespread attention and application due to their advantages such as no movable structure and high sensitivity. However, traditional thermal flow sensors based on the Joule heat principle have many adverse effects in the measurement process, such as: heating of the measured medium may cause potential dangers, especially in the case of certain chemical gases, heating may cause explosions or fires; in liquid flow measurement, heating may cause the liquid to boil or generate bubbles, thereby affecting the accuracy of the measurement; in microfluidic applications, heating may cause undesirable chemical reactions or cause sample denaturation and other problems. In order to overcome the above defects, thermoelectric cooling elements based on the Peltier effect can replace conventional heating elements to build new flow sensors, thereby effectively avoiding the adverse effects of heating the measured medium. However, the current commercial vertical Peltier cooling elements are large in size, high in power consumption, and difficult to achieve effective integration with MEMS flow sensors. Therefore, designing a thermoelectric cooling structure suitable for MEMS flow sensors and ensuring that it is compatible with micro-nano processing technology has become a key issue that needs to be solved urgently. Summary of the invention

[0003] The object of the present invention is to provide an in-plane thermoelectric cooling MEMS flow sensor structure and a manufacturing method thereof, which not only retains the advantages of the thermal sensitive flow sensor such as no movable structure and high sensitivity, but also avoids the defect of heating the measured medium.

[0004] The technical solution to achieve the purpose of the present invention is:

[0005] An in-plane thermoelectric cooling MEMS flow sensor comprises a substrate, a film, a temperature measuring element, an in-plane thermoelectric cooling element and a chip pin;

[0006] The film is arranged at the center of the substrate, and has the same width as the fluid channel, and is used to block the heat transfer between the cold end and the hot end of the P-type thermoelectric arm and the N-type thermoelectric arm;

[0007] The in-plane thermoelectric cooling elements are arranged in two groups, symmetrically straddling the junction between the film and the substrate, and include a plurality of parallel P-type thermoelectric arms and N-type thermoelectric arms alternately arranged at equal intervals, the two ends of the two types of thermoelectric arms are located on the film and the substrate respectively, the cold end is located on the film, and the hot end is located on the substrate; the ends of the P-type thermoelectric arms and the N-type thermoelectric arms are connected by metal wires;

[0008] The temperature measuring elements are symmetrically distributed in the film, one is located at the inlet of the fluid channel, and the other is located at the outlet of the fluid channel, and are used to characterize the flow velocity and flow direction information of the fluid through temperature detection.

[0009] A method for manufacturing an in-plane thermoelectric cooling MEMS flow sensor, comprising:

[0010] Step 1, thin film deposition: growing a layer of silicon dioxide thin film on the front side of the substrate;

[0011] Step 2, processing the temperature measuring element: depositing platinum metal on the surface of the film, and then using a patterned photoresist as a mask to remove excess platinum by ion beam etching to form a platinum line pattern of the temperature measuring element;

[0012] Step 3, processing the metal wires and chip pins of the in-plane thermoelectric cooling element: after photolithography and development, a patterned photoresist structure is obtained, and then a layer of gold is deposited, and then placed in an acetone solution. The gold deposited on the surface of the photoresist is stripped off due to the dissolution of the photoresist, while the gold deposited in the area without the photoresist is retained, forming a pattern of the metal wires and chip pins of the in-plane thermoelectric cooling element;

[0013] Step 4, processing the P-type thermoelectric arm: after photolithography and development, a patterned photoresist structure is obtained, and then a layer of P-type thermoelectric material is deposited, and then placed in an acetone solution, and the P-type thermoelectric material deposited in the photoresist-free area is retained to form a pattern of the P-type thermoelectric arm of the in-plane thermoelectric cooling element;

[0014] Step 5, processing the N-type thermoelectric arm: after photolithography and development, a patterned photoresist structure is obtained, and then a layer of N-type thermoelectric material is deposited, and then placed in an acetone solution, and the N-type thermoelectric material deposited in the photoresist-free area is retained to form a pattern of the N-type thermoelectric arm of the in-plane thermoelectric cooling element;

[0015] Step 6, passivation layer protection: depositing a passivation layer thin film on the front side of the substrate, i.e., the side where the temperature measuring element and the in-plane thermoelectric cooling element are processed;

[0016] Step 7, releasing the silicon dioxide film structure: using the silicon dioxide film as an etching stop layer and the patterned photoresist as a mask, removing the material on the back of the substrate by deep reactive ion etching to release the silicon dioxide film structure;

[0017] Step 8, etching the passivation layer: Using the patterned photoresist as a mask, use reactive ion etching to remove the passivation layer material above the chip pins.

[0018] Compared with the prior art, the present invention has the following significant advantages:

[0019] 1) Refrigeration control avoids possible adverse effects such as explosion, bubbles, and deterioration caused by the temperature increase of the measured medium due to Joule heat; 2) The in-plane thermoelectric cooling element is placed across the junction of the film and the substrate, which makes the sensor have better refrigeration efficiency; 3) The in-plane thermoelectric cooling element adopts a multi-stage cooling method to increase the maximum cooling temperature, which is beneficial to improve the sensitivity of the flow sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a cross-sectional view of the axis position of the overall structure of the present invention;

[0021] Figure 2 yes Figure 1 Bottom view of

[0022] Figure 3 It is a processing flow chart of the sensor of the present invention;

[0023] Figure 4 is a top view of the sensor structure with multi-stage thermoelectric arms.

[0024] Among them: 1. Silicon substrate; 2. Silicon dioxide film; 3. Temperature measuring element; 4. P-type thermoelectric arm; 5. N-type thermoelectric arm; 6. Metal wire; 7. Chip pin; 8. First-level thermoelectric arm; 9. Second-level thermoelectric arm; 10. Third-level thermoelectric arm. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0026] like Figure 1 and Figure 2 As shown, the in-plane thermoelectric cooling MEMS flow sensor structure described in the present invention includes a silicon substrate 1, a silicon dioxide film 2, a temperature measuring element 3, a P-type thermoelectric arm 4, an N-type thermoelectric arm 5, a metal wire 6, and a chip pin 7.

[0027] The silicon dioxide film 2 is located on the front of the silicon substrate 1, symmetrical about the center of the silicon substrate 1, and has the same width as the fluid channel width. The temperature measuring element 3 is symmetrically distributed in the silicon dioxide film 2, one is located at the entrance of the fluid channel, and the other is located at the exit of the fluid channel. The in-plane thermoelectric cooling element is symmetrically placed at the junction of the silicon dioxide film and the silicon substrate 1, and includes a plurality of P-type thermoelectric arms 4 and a plurality of N-type thermoelectric arms 5. The P-type thermoelectric arms 4 and the N-type thermoelectric arms 5 are arranged alternately in parallel and at equal intervals. The two ends of the thermoelectric arms are respectively located on the silicon dioxide film 2 and the silicon substrate 1, and the ends of the P-type thermoelectric arms 4 and the N-type thermoelectric arms 5 are connected by metal wires 6. The electrical signals of the in-plane thermoelectric cooling element and the temperature measuring element 3 are connected to the interface circuit through the chip pins 7 around the substrate. The passivation layer covers the upper surface of the structure. The fluid channel is located above the sensor structure, and its width is the same as the film width.

[0028] The sensor reduces the temperature of the silicon dioxide film 2 through an in-plane thermoelectric cooling element. When the current flows from the N-type thermoelectric arm 5 to the P-type thermoelectric arm 4, the electrons need to absorb heat to move from a low energy level to a high energy level; when the current direction is opposite, the excess energy will be released. The in-plane thermoelectric cooling element with alternating P-type thermoelectric arms 4 and N-type thermoelectric arms 5 is macroscopically characterized by one end absorbing heat and the other end releasing heat. It is stipulated that the heat absorbing end (cold end) is located on the silicon dioxide film 2, and the heat releasing end (hot end) is located on the silicon substrate 1. The corresponding current direction is positive, realizing the cooling function of the fluid and the silicon dioxide film 2.

[0029] The sensor indirectly characterizes the flow velocity and flow direction information of the fluid by sensing the temperature at the left-right symmetrical position on the surface of the silica film 2 through the temperature measuring element 3. When the flow velocity of the measured medium in the flow channel is zero, due to the symmetry of the sensor structure, a centrally symmetrical temperature field will be formed on the surface of the silica film 2. The temperatures sensed by the two temperature measuring elements are the same at this time, and the difference in the output electrical signals of the two is zero. When the flow velocity is not zero, the fluid with a low temperature at the center is transmitted to the downstream, causing the temperature of the upstream silica film to be higher than that of the downstream silica film. The greater the flow velocity, the greater the temperature difference between the upstream and downstream.

[0030] The hot end of the in-plane thermoelectric cooling element is located on the silicon substrate 1. Since the silicon substrate 1 is about 400μm thick and is made of single crystal silicon, the thermal resistance is small, and heat is more easily dissipated to the surrounding environment through the silicon substrate 1, and the temperature of the hot end is closer to the ambient temperature. The cold end of the in-plane thermoelectric cooling element is located on the silicon dioxide film 2. Since the silicon dioxide film 2 is about 2μm thick and is made of silicon dioxide, the thermal resistance is large, and heat is difficult to transfer between the cold end and the hot end through the silicon dioxide film 2. It is easier to establish a larger temperature difference between the cold end and the hot end. Combining the above two points, the in-plane thermoelectric cooling element is placed across the junction of the silicon dioxide film 2 and the silicon substrate 1, so that the sensor has better cooling energy efficiency.

[0031] like Figure 4 As shown, in order to increase the maximum cooling temperature, the single-stage thermoelectric arm of the in-plane thermoelectric cooling element can be changed to a multi-stage thermoelectric arm. The cold ends of all thermoelectric arms are close to the inside of the chip, and the hot ends of all thermoelectric arms are close to the outside of the chip. The cold end of the first-stage thermoelectric arm 8 is located on the film 2, and the hot end of the first-stage thermoelectric arm 8 and the cold and hot ends of its second-stage thermoelectric arm 9 and third-stage thermoelectric arm 10 are all located on the substrate 1. The support between the hot and cold ends of the thermoelectric arms of the same level is a silicon dioxide film 2 (except for the silicon dioxide film 2 set at the center position, the corresponding positions of the remaining levels of in-plane thermoelectric cooling elements are also set with silicon dioxide films 2) to improve the cooling efficiency. The larger the number of stages, the more thermoelectric arms should be in the stage, because the Joule heat generated in a given stage has a heat load effect on all subsequent stages.

[0032] The two temperature measuring elements 3 are metal thermistors, which form a Wheatstone bridge with two off-chip resistors. The voltage between the bridges is proportional to the temperature difference signal between the upstream and downstream, realizing the conversion of flow velocity to heat and then to electrical signals. The aspect ratio of the metal thermistor line and the thickness of the metal film need to be reasonably set to ensure that the resistance value of the metal thermistor is large enough, the Joule heat generated is small enough, and the heating effect on the fluid can be ignored. An in-plane thermoelectric cooling MEMS flow sensor, and its manufacturing method, the specific steps are as follows:

[0033] Step 1, silicon dioxide deposition: a silicon dioxide film is grown on the front side of the silicon substrate 1 by thermal oxidation or chemical vapor deposition. Figure 3 As shown in a.

[0034] Step 2, processing the temperature measuring element 3: depositing platinum metal on the surface of the silicon dioxide film by sputtering or evaporation, and then removing excess platinum by ion beam etching using a patterned photoresist as a mask to form a platinum line pattern of the temperature measuring element 3, such as Figure 3 As shown in b.

[0035] Step 3, processing the metal wire 6 and chip pin 7 of the in-plane thermoelectric cooling element: after photolithography and development, a patterned photoresist structure is obtained (i.e., there is no photoresist in the area where metal needs to be deposited), and then a layer of gold is deposited by sputtering or evaporation. The sample is placed in an acetone solution, and the gold deposited on the surface of the photoresist is stripped off due to the dissolution of the photoresist, while the gold deposited in the area without the photoresist is retained on the sample, forming a pattern of the metal wire 6 and chip pin 7 of the in-plane thermoelectric cooling element, as shown in FIG. Figure 3 As shown in c.

[0036] Step 4, processing the P-type thermoelectric arm 4: After photolithography and development, a patterned photoresist structure is obtained, and then a layer of P-type thermoelectric material Bi is deposited by sputtering or evaporation. 0.5 Sb 1.5 Te 3, the sample is placed in an acetone solution, and the P-type thermoelectric material deposited in the photoresist-free area is retained on the sample, forming a pattern of the P-type thermoelectric arm 4 of the in-plane thermoelectric cooling element, such as Figure 3 As shown in d.

[0037] Step 5, processing the N-type thermoelectric arm 5: after photolithography and development, a patterned photoresist structure is obtained, and then a layer of N-type thermoelectric material Bi is deposited by sputtering or evaporation. 2 Te 2.7 Se 0.3 , the sample is placed in an acetone solution, and the N-type thermoelectric material deposited in the photoresist-free area is retained on the sample, forming a pattern of the N-type thermoelectric arm 5 of the in-plane thermoelectric cooling element, as shown in FIG. Figure 3 As shown in e.

[0038] Step 6, passivation layer protection: deposit a passivation layer film on the upper surface of the sample, i.e., on the side where the temperature measuring element 3 and the in-plane thermoelectric cooling element are processed, such as Figure 3 f.

[0039] Step 7, releasing the silicon dioxide film 2 structure: using silicon dioxide as an etching stop layer and a patterned photoresist as a mask, deep reactive ion etching is used to remove the material on the back of the silicon sample to release the silicon dioxide film 2 structure, such as Figure 3 As shown in g.

[0040] Step 8, etching the passivation layer: using the patterned photoresist as a mask, using reactive ion etching to remove the passivation layer material above the chip pin 7, such as Figure 3 h.

[0041] The above is the manufacturing process of the in-plane thermoelectric cooling MEMS flow sensor of the present invention.

[0042] The thermoelectric cooling MEMS flow sensor of the present invention combines the advantages of high sensitivity and non-movable structure of thermistor flowmeter, while effectively avoiding the problems caused by heating the measured medium. In addition, the in-plane thermoelectric cooling structure using multi-stage thermoelectric arms can significantly increase the maximum cooling temperature of the thermoelectric cooling element, thereby further improving the sensitivity of flow monitoring. The design of the present invention not only improves the measurement accuracy, but also helps to be widely used in industrial production, energy metering, environmental monitoring, biomedicine and other fields.

Claims

1. An in-plane thermoelectric cooling MEMS flow sensor, characterized in that: It includes a substrate, a film, a temperature measuring element, an in-plane thermoelectric cooling element and a chip pin; The film is arranged at the center of the substrate, and has the same width as the fluid channel, and is used to block the heat transfer between the cold end and the hot end of the P-type thermoelectric arm and the N-type thermoelectric arm; The in-plane thermoelectric cooling elements are arranged in two groups, symmetrically straddling the junction between the film and the substrate, and include a plurality of parallel P-type thermoelectric arms and N-type thermoelectric arms alternately arranged at equal intervals, the two ends of the two types of thermoelectric arms are located on the film and the substrate respectively, the cold end is located on the film, and the hot end is located on the substrate; the ends of the P-type thermoelectric arms and the N-type thermoelectric arms are connected by metal wires; The temperature measuring elements are symmetrically distributed in the film, one is located at the inlet of the fluid channel, and the other is located at the outlet of the fluid channel, and are used to characterize the flow velocity and flow direction information of the fluid through temperature detection; The electrical signals of the in-plane thermoelectric cooling element and the temperature measuring element are connected to the outside world through the chip pins on the substrate.

2. The in-plane thermoelectric cooling MEMS flow sensor according to claim 1, characterized in that: The two temperature measuring elements are metal thermistors, which form a Wheatstone bridge with two off-chip resistors. The voltage between the bridges is proportional to the temperature difference signal between the upstream and downstream of the fluid channel, realizing the conversion of flow velocity to heat and then to electrical signals.

3. The in-plane thermoelectric cooling MEMS flow sensor according to claim 1, characterized in that: The in-plane thermoelectric cooling element is provided with a multi-stage thermoelectric arm, the cold ends of all the thermoelectric arms are close to the inner side, and the hot ends of all the thermoelectric arms are close to the outer side; the cold end of the first-stage thermoelectric arm is located on the film, and the hot end of the first-stage thermoelectric arm and the cold ends and hot ends of the other-stage thermoelectric arms are all located on the substrate; the hot ends and cold ends of the other-stage thermoelectric arms are supported by additional films.

4. The in-plane thermoelectric cooling MEMS flow sensor according to claim 3, characterized in that: The larger the number of stages, the greater the number of thermoelectric arms within the stage.

5. The in-plane thermoelectric cooling MEMS flow sensor according to claim 1, characterized in that: The substrate material is silicon, and the film material is silicon dioxide.

6. A method for manufacturing an in-plane thermoelectric cooling MEMS flow sensor, characterized in that: include: Step 1, thin film deposition: growing a layer of silicon dioxide thin film on the front side of the substrate; Step 2, processing the temperature measuring element: depositing platinum metal on the surface of the film, and then using a patterned photoresist as a mask to remove excess platinum by ion beam etching to form a platinum line pattern of the temperature measuring element; Step 3, processing the metal wires and chip pins of the in-plane thermoelectric cooling element: after photolithography and development, a patterned photoresist structure is obtained, and then a layer of gold is deposited, and then placed in an acetone solution. The gold deposited on the surface of the photoresist is stripped off due to the dissolution of the photoresist, while the gold deposited in the area without the photoresist is retained, forming a pattern of the metal wires and chip pins of the in-plane thermoelectric cooling element; Step 4, processing the P-type thermoelectric arm: after photolithography and development, a patterned photoresist structure is obtained, and then a layer of P-type thermoelectric material is deposited, and then placed in an acetone solution, and the P-type thermoelectric material deposited in the photoresist-free area is retained to form a pattern of the P-type thermoelectric arm of the in-plane thermoelectric cooling element; Step 5, processing the N-type thermoelectric arm: after photolithography and development, a patterned photoresist structure is obtained, and then a layer of N-type thermoelectric material is deposited, and then placed in an acetone solution, and the N-type thermoelectric material deposited in the photoresist-free area is retained to form a pattern of the N-type thermoelectric arm of the in-plane thermoelectric cooling element; Step 6, passivation layer protection: depositing a passivation layer thin film on the front side of the substrate, i.e., the side where the temperature measuring element and the in-plane thermoelectric cooling element are processed; Step 7, releasing the silicon dioxide film structure: using the silicon dioxide film as an etching stop layer and the patterned photoresist as a mask, removing the material on the back of the substrate by deep reactive ion etching to release the silicon dioxide film structure; Step 8, etching the passivation layer: Using the patterned photoresist as a mask, use reactive ion etching to remove the passivation layer material above the chip pins.

7. The method for manufacturing the in-plane thermoelectric cooling MEMS flow sensor according to claim 6, characterized in that: The P-type thermoelectric material is Bi 0.5 Sb 1.5 Te3; the N-type thermoelectric material Bi2Te 2.7 Se 0.3 .

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