A thin film hydrogen sensor and its preparation method

Abstract

The present invention discloses a thin film hydrogen sensor, which includes a substrate, a hydrogen measuring unit for detecting hydrogen concentration, and a bonding glass. The hydrogen measuring unit has a Wheatstone bridge structure with four bridge arms, and the Wheatstone bridge structure is composed of a plurality of hydrogen-sensitive resistor elements with the same electrochemical characteristics. The number of hydrogen-sensitive resistor elements on each bridge arm is the same, wherein two opposite bridge arms are hydrogen-sensitive resistor elements for hydrogen measurement, and the other two opposite bridge arms are reference hydrogen-sensitive resistor elements. A groove is provided at one end of the bonding glass close to the substrate, and the top of the groove wall is sealed and connected to the substrate to form a closed cavity in the groove, and the reference hydrogen-sensitive resistor is located in the closed cavity. The sensor has a simple and mature production process, high sensitivity and measurement accuracy of the sensor, and no heating element is required, thereby greatly reducing the power consumption of the sensor.

Description

Technical Field

[0001] The invention belongs to the field of hydrogen sensors, and in particular relates to a thin film hydrogen sensor. Background Art

[0002] Hydrogen is a major industrial raw material and the most important industrial gas and specialty gas. It is widely used in petrochemical, metallurgical, semiconductor and power industries.

[0003] Compared with conventional gases, hydrogen has many properties that are not conducive to safety. Hydrogen has a wider explosion range in the air (4% to 75% vol), lower ignition energy (0.019 mJ), is more likely to leak, and has a higher flame propagation speed. Therefore, hydrogen leakage and explosion are one of the important causes of safety accidents, and it is necessary to detect the hydrogen concentration in the hydrogen use environment and monitor its leakage.

[0004] The hydrogen sensor is a special sensor for measuring hydrogen concentration and monitoring hydrogen leakage.

[0005] Traditional prior art solutions, for example, H2SCAN introduced a thin film hydrogen sensor based on palladium-nickel alloy in the thin film gas sensor structure of the Chinese invention patent CN1947007B, which includes a MOS capacitor sensor for sensing low concentration hydrogen, a resistor sensor for sensing high concentration hydrogen, a nickel thin film temperature sensor and a thin film heating element. This thin film hydrogen sensor achieves geometric structure savings and reduces heat loss. However, the patent has the following disadvantages:

[0006] 1) The sensor structure design is relatively complex, including MOS capacitor detection elements, reference elements, palladium-nickel thin film resistor elements, nickel thin film temperature sensors and thin film heaters. The sensor production process is complicated, and the setting of the thin film heater greatly increases the power consumption of the sensor.

[0007] 2) The sensor uses a single palladium-nickel alloy resistor sensor to sense high concentration hydrogen. Since the palladium-nickel alloy film has inherent instability at working temperature, the sensor exhibits a fixed drift characteristic, which shortens the calibration cycle of the sensor.

[0008] 3) The sensor uses a single palladium-nickel alloy resistor sensor to sense high concentration hydrogen. Since the palladium-nickel alloy film has a large resistance temperature coefficient, in order to obtain higher measurement accuracy, it can often only be achieved by improving the temperature control accuracy of the sensor, which obviously increases the power consumption of the sensor.

[0009] 4) The sensor uses a single palladium-nickel alloy resistor sensor to sense high concentration hydrogen, but for low concentration hydrogen, the sensitivity of the palladium-nickel thin film resistor is relatively low, which affects the measurement accuracy of the hydrogen sensor.

[0010] In existing hydrogen sensors, hydrogen is generally isolated by stacking multiple layers of metal and oxide composite films on a reference hydrogen-sensitive resistor element using thin film preparation technology. This method is complex and the sensor is at risk of hydrogen penetration when it is in a hydrogen environment for a long time. Summary of the invention

[0011] The present invention aims to provide a thin film hydrogen sensor and a preparation method thereof to address the defects of the prior art hydrogen sensor, such as complex production process, low sensor measurement accuracy, and high power consumption. The sensor production process is simple and mature, which improves the sensitivity and measurement accuracy of the sensor, and does not require a heating element, thereby greatly reducing the power consumption of the sensor.

[0012] In order to achieve the above object, the technical solution adopted by the present invention is:

[0013] A thin film hydrogen sensor comprises a substrate, a hydrogen measurement unit for detecting hydrogen concentration, and bonding glass;

[0014] The hydrogen measurement unit is a Wheatstone bridge structure with four bridge arms, the Wheatstone bridge structure is composed of a plurality of hydrogen-sensitive resistor elements with the same electrochemical characteristics, the number of hydrogen-sensitive resistor elements on each bridge arm is the same, two opposite bridge arms are provided with hydrogen-sensitive resistor elements for hydrogen measurement, and the other two opposite bridge arms are provided with reference hydrogen-sensitive resistor elements;

[0015] The upper and lower surfaces of the substrate are provided with an upper oxide insulating layer and a lower oxide insulating layer respectively, the hydrogen-sensitive resistor element is located on the upper oxide insulating layer, and the reference hydrogen-sensitive resistor element is located on the lower oxide insulating layer;

[0016] A groove is provided at one end of the bonding glass close to the substrate, the top of the groove wall is sealed and connected to the substrate to form a closed cavity in the groove, and the reference hydrogen-sensitive resistor element is located in the closed cavity;

[0017] The reference hydrogen-sensitive resistor element is connected to a metal lead pin, one end of the metal lead pin is connected to the reference hydrogen-sensitive resistor element, and the other end extends out relative to an end of the bonding glass away from the substrate.

[0018] When working, the hydrogen-sensitive resistor element for hydrogen measurement in the Wheatstone bridge structure generates a resistance change after contacting hydrogen, thereby achieving the function of detecting hydrogen; the reference hydrogen-sensitive resistor element in the Wheatstone bridge structure is physically isolated from hydrogen through a closed cavity, and will not generate a resistance change after contacting hydrogen.

[0019] Furthermore, there are one or two hydrogen-sensitive resistor elements on each of the bridge arms. Preferably, there is one hydrogen-sensitive resistor element on each of the bridge arms.

[0020] Furthermore, a plurality of through holes are provided on the bonding glass, and the metal lead pins pass through the through holes. The number of the metal lead pins is twice the number of reference hydrogen-sensitive resistor elements, and the number of the through holes is the same as the number of the metal lead pins.

[0021] Furthermore, the metal lead pin is surrounded by a conductive silver paste layer, the end of the bonding glass facing away from the substrate is sprayed with sealant, one end of the metal lead pin is connected to a reference hydrogen-sensitive resistor element, and the other end extends relative to the sealant, forming a closed cavity between the bonding glass and the substrate.

[0022] Furthermore, metal electrode bumps are provided on the hydrogen measurement unit, and the metal bumps are used to connect metal lead pins.

[0023] Furthermore, the circumferential dimensions of the upper oxide insulating layer and the lower oxide insulating layer are smaller than those of the substrate.

[0024] Further, the oxide insulating layer is one or more layers of oxide thin film, and the oxide insulating layer is preferably a dielectric material with excellent insulating properties, preferably silicon dioxide, aluminum oxide. Further, the hydrogen-sensitive resistor element and the reference hydrogen-sensitive resistor element are preferably metal materials that have a catalytic effect on hydrogen, preferably palladium-chromium, palladium-gold, palladium-nickel alloy. Further, the bonding glass is preferably Schott BF33 glass or Corning 7740 glass.

[0025] Based on the same inventive concept, the present invention also provides a method for preparing a thin film hydrogen sensor, which comprises the following steps:

[0026] (1) forming an upper oxide insulating layer and a lower oxide insulating layer on the upper and lower surfaces of the substrate respectively;

[0027] (2) fabricating a hydrogen measurement unit with a Wheatstone bridge structure on the upper oxide insulating layer and the lower oxide insulating layer;

[0028] (3) using bonding glass with a pre-processed groove and a substrate for anodic bonding, installing a metal lead pin, and making the top of the groove wall sealed with the substrate to form a closed cavity in the groove;

[0029] (4) Thin film hydrogen sensor is obtained by slicing.

[0030] Preferably, in step (1), one or more oxide thin films are prepared on the upper and lower surfaces of the substrate respectively by photolithography and thin film deposition technology to form upper and lower oxide insulating layers to achieve electrical insulation.

[0031] Preferably, the step (2) uses photolithography technology to form a pattern structure of hydrogen-sensitive resistor elements on the surfaces of the upper and lower oxide insulating layers, and deposits a hydrogen-sensitive film by thermal evaporation and sputtering technology. After stripping and cleaning, a hydrogen measurement unit with a Wheatstone bridge structure can be obtained.

[0032] Preferably, in the step (3), a metal lead pin having a conductive silver paste layer on all sides is filled in the bonding glass through hole, and then sintered and solidified at low temperature in an inert gas atmosphere or a vacuum environment. After sintering, a sealant is sprayed on the surface of the end of the bonding glass away from the substrate to form the closed cavity.

[0033] Preferably, the oxide film thickness is 200nm to 2000nm; more preferably, the oxide film thickness is 400nm to 1500nm; more preferably, the oxide film thickness is 800nm ​​to 1000nm;

[0034] Preferably, the thickness of the hydrogen-sensitive film is 50nm to 200nm; further preferably, the thickness of the hydrogen-sensitive film is 80nm to 180nm; further preferably, the thickness of the hydrogen-sensitive film is 100nm to 150nm;

[0035] Preferably, the thickness of the metal electrode bump is 800nm ​​to 2000nm; further preferably, the thickness of the metal electrode bump is 1000nm to 1800nm; further preferably, the thickness of the metal electrode bump is 1200nm to 1500nm;

[0036] The thin film hydrogen sensor of the present invention can be used for hydrogen concentration detection and hydrogen leakage monitoring, etc. The measurable range of hydrogen concentration is from 0.005% to 100% (volume fraction).

[0037] The existing hydrogen sensor technology is to prepare a group of hydrogen-sensitive resistor elements, a group of heating resistor elements and a group of temperature-measuring resistor elements on the surface of the substrate. The temperature control of the sensor is achieved by the heating resistor elements and the temperature-measuring resistor elements. At a constant temperature, the resistance value of the resistor element is only related to the hydrogen concentration.

[0038] The present invention adopts the design concept of Wheatstone bridge, and utilizes two groups of hydrogen-sensitive resistor elements and two groups of reference hydrogen-sensitive resistor elements, which not only increases the sensitivity of the sensor, but also eliminates the need for a temperature control unit, thereby greatly reducing power consumption. The sensitivity of the hydrogen sensor using the present invention is twice that of a single hydrogen-sensitive resistor, and the improvement of the sensor sensitivity improves the stability of the hydrogen sensor and improves the measurement accuracy.

[0039] In addition, the present invention does not use thin film preparation technology to stack multiple layers of metal and oxide composite films on the reference hydrogen-sensitive resistor element to isolate hydrogen (this method has a complex process and the sensor is at risk of hydrogen penetration when in a hydrogen environment for a long time), but instead draws on the anodic bonding process of the piezoresistive pressure sensor to prepare a closed cavity to form a hydrogen-free environment.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] 1) The structure of the present invention is simple in design, and the hydrogen sensor does not require a heating element, which greatly reduces power consumption.

[0042] 2) The sensor of the present invention adopts a hydrogen measurement unit based on a Wheatstone bridge structure. The inherent instability and temperature drift between hydrogen-sensitive resistor elements can offset each other, thereby eliminating the measurement error caused by temperature fluctuations, increasing the stability of the sensor, and improving the measurement accuracy of the sensor.

[0043] 3) The present invention adopts an anodic bonding process to prepare a closed cavity to form a hydrogen-free environment, and the production process is simple and has high stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a schematic diagram of the cross-sectional structure of the thin film hydrogen sensor of the present invention;

[0045] Figure 2 is a top view schematic diagram of a thin film hydrogen sensor of the present invention;

[0046] Figure 3 It is the schematic diagram of the Whittons bridge structure;

[0047] Figure 4 This is a data graph obtained by measuring with the thin film hydrogen sensor.

[0048] In the figure: 1-substrate; 2-hydrogen measurement unit; 21-hydrogen sensitive resistor element for hydrogen measurement; 22-reference hydrogen sensitive resistor element; 3-bonding glass; 31-groove; 32-top of groove wall; 33-through hole; 34-metal lead pin; 35-sealant; 4-upper oxide insulating layer; 5-lower oxide insulating layer; 6-metal electrode bump. DETAILED DESCRIPTION

[0049] The present invention will be described in detail below in conjunction with the embodiments. It should be noted that the embodiments and features of the embodiments of the present invention can be combined with each other without conflict. For the convenience of description, if the words "upper", "lower", "left" and "right" appear in the following, they only indicate that the upper, lower, left and right directions are consistent with the drawings themselves, and do not limit the structure.

[0050] Example 1

[0051] See also Figure 1-3The thin film hydrogen sensor of this embodiment includes a substrate 1, an upper oxide insulating layer 4 and a lower oxide insulating layer 5 arranged on the substrate 1, a hydrogen measuring unit 2 arranged on the upper and lower oxide insulating layers, and an electrode bump 6 arranged on the hydrogen measuring unit 2. The hydrogen measuring unit 2 is a Wheatstone bridge structure composed of four hydrogen-sensitive resistor elements with the same electrochemical characteristics. The Wheatstone bridge structure is composed of two hydrogen-sensitive resistor elements 21 for hydrogen measurement and two reference hydrogen-sensitive resistor elements 22 in a hydrogen-free environment sealed cavity. The hydrogen-free environment sealed cavity is prepared by anode bonding of the substrate 1 and the bonding glass 3, curing of the metal lead pin 34, and spraying of the sealant 35.

[0052] The top 32 of the bonding glass groove wall is sealed and connected to the substrate 1 to form a closed cavity in the groove 31 .

[0053] The bonding glass 3 is provided with a plurality of through holes 33 , and a sealant 35 is sprayed on one end of the bonding glass 3 facing away from the substrate 1 . One end of the metal lead pin 34 having a conductive silver paste layer around it is connected to the reference hydrogen-sensitive resistor element 22 , and the other end passes through the through hole 33 and extends relative to the sealant 35 .

[0054] In a preferred embodiment of the thin film hydrogen sensor of the present invention, the substrate 1 is a double-sided polished silicon wafer.

[0055] The hydrogen-sensitive resistor element 21 and the reference hydrogen-sensitive resistor element 22 are preferably made of a metal material having a catalytic effect on hydrogen, preferably palladium-chromium, palladium-gold, or palladium-nickel alloy.

[0056] The upper oxide insulating layer 4 and the lower oxide insulating layer 5 are one or more layers of oxide thin films. The oxide thin films are preferably made of dielectric materials with excellent insulating properties, preferably silicon dioxide or aluminum oxide.

[0057] The bonding glass 3 is preferably Schott BF33 glass or Corning 7740 glass, and the bonding glass 3 is pre-processed with a groove 31 and a through hole 33 .

[0058] In a preferred embodiment of the thin film hydrogen sensor of the present invention, two hydrogen-sensitive resistors in the Wheatstone bridge structure produce resistance changes after contacting hydrogen, thereby achieving the function of detecting hydrogen; the other two hydrogen-sensitive resistor elements in the Wheatstone bridge structure achieve physical isolation from hydrogen through a closed cavity, and will not produce resistance changes after contacting hydrogen. The two hydrogen-sensitive resistors for hydrogen measurement in the Wheatstone bridge structure produce resistance changes after contacting hydrogen, and the resistance change is positively correlated with the hydrogen concentration. A constant voltage power supply is used to supply power, and the output voltage change of the hydrogen-sensitive resistor is measured to obtain the corresponding hydrogen concentration.

[0059] The thin film hydrogen sensor of the present invention can be used for hydrogen concentration detection and hydrogen leakage monitoring, etc. The measurable range of hydrogen concentration is from 0.005% to 100% (volume fraction).

[0060] Example 2

[0061] A method for preparing a thin film hydrogen sensor comprises the following steps:

[0062] (1) Clean the double-sided silicon substrate to remove oil and impurities from the polished surface of the substrate;

[0063] (2) forming a pattern structure of an oxide insulating layer on the upper and lower surfaces of the substrate by a photolithography process to form a photoresist mask;

[0064] (3) Using sputtering deposition technology, SiO2 and Al2O3 are deposited successively as oxide films with a film thickness of 800 nm to form upper and lower oxide insulating layers;

[0065] (4) forming a hydrogen sensitive unit pattern structure of a Wheatstone bridge structure on the upper and lower oxide insulating layers by a photolithography process to form a photoresist mask;

[0066] (5) using a thermal evaporation process to deposit a palladium-chromium alloy thin film with a designed film thickness of 80 nm, followed by stripping and cleaning to form four hydrogen-sensitive resistor elements;

[0067] (6) fabricating a metal electrode bump photoresist mask pattern by photolithography;

[0068] (7) Using thermal evaporation process, first deposit a Ti film as a transition layer with a thickness of 60 μm; then deposit an Al film as a metal electrode bump with a thickness of 1000 nm;

[0069] (8) Anodic bonding is performed using bonding glass with pre-processed grooves and through holes and silicon on one side of the substrate;

[0070] (9) Filling the bonding glass through hole with a metal lead pin surrounded by a conductive silver paste layer, and then sintering and curing at low temperature in an inert gas atmosphere or a vacuum environment, and spraying a UV-curing sealant on the surface after sintering to form a hydrogen-free environment closed cavity;

[0071] (10) A thin film hydrogen sensor is formed by a dicing machine.

[0072] Example 3

[0073] A method for preparing a thin film hydrogen sensor comprises the following steps:

[0074] (1) Clean the double-sided silicon substrate to remove oil and impurities from the polished surface of the substrate;

[0075] (2) forming a pattern structure of an oxide insulating layer on the upper and lower surfaces of the substrate by a photolithography process to form a photoresist mask;

[0076] (3) Using sputtering deposition technology, SiO2 and Al2O3 are deposited successively as oxide films with a film thickness of 1500nm to form upper and lower oxide insulating layers;

[0077] (4) forming a hydrogen sensitive unit pattern structure of a Wheatstone bridge structure on the upper and lower oxide insulating layers by a photolithography process to form a photoresist mask;

[0078] (5) using a thermal evaporation process to deposit a palladium-chromium alloy thin film with a designed film thickness of 150 nm, and then stripping and cleaning to form four hydrogen-sensitive resistor elements;

[0079] (6) fabricating a metal electrode bump photoresist mask pattern by photolithography;

[0080] (7) Using thermal evaporation process, first deposit a Ti film as a transition layer with a film thickness of 40 μm; then deposit an Al film as a metal electrode bump with a film thickness of 1500 nm;

[0081] (8) Anodic bonding is performed using bonding glass with pre-processed grooves and through holes and silicon on one side of the substrate;

[0082] (9) Filling the bonding glass through hole with a metal lead pin surrounded by a conductive silver paste layer, and then sintering and curing at low temperature in an inert gas atmosphere or a vacuum environment, and spraying a UV-curing sealant on the surface after sintering to form a hydrogen-free environment closed cavity;

[0083] (10) A thin film hydrogen sensor is formed by a dicing machine.

[0084] Example 4

[0085] See also Figure 4 The thin film hydrogen sensor of the present invention is used to measure the hydrogen concentration. Hydrogen with a concentration of 0.4% is introduced twice in succession, and the background gas is nitrogen. The output results of the two times are consistent, with almost no difference. Under a constant current power supply of 1mA, the sensor sensitivity reaches 6mV, and the change rate is 1.09%, which is more than twice that of the existing palladium alloy thin film hydrogen sensor.

[0086] The contents explained in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

Claims

1. A thin film hydrogen sensor, characterized in that: The invention comprises a substrate (1), a hydrogen measurement unit (2) for detecting hydrogen concentration, and bonding glass (3). The hydrogen measurement unit (2) is a Wheatstone bridge structure with four bridge arms, the Wheatstone bridge structure is composed of a plurality of hydrogen-sensitive resistor elements with the same electrochemical characteristics, the number of hydrogen-sensitive resistor elements on each bridge arm is the same, two opposite bridge arms are provided with hydrogen-sensitive resistor elements (21) for hydrogen measurement, and the other two opposite bridge arms are provided with reference hydrogen-sensitive resistor elements (22); An upper oxide insulating layer (4) and a lower oxide insulating layer (5) are provided on the upper and lower surfaces of the substrate (1) respectively, the hydrogen-sensitive resistor element (21) is located on the upper oxide insulating layer (4), and the reference hydrogen-sensitive resistor element (22) is located on the lower oxide insulating layer (5); A groove (31) is provided at one end of the bonding glass (3) close to the substrate (1), and a top portion (32) of the groove wall is sealed and connected to the substrate (1) to form a closed cavity in the groove (31), and the reference hydrogen-sensitive resistor element (22) is located in the closed cavity; The reference hydrogen-sensitive resistor element (22) is connected to a metal lead pin (34), one end of the metal lead pin (34) is connected to the reference hydrogen-sensitive resistor element (22), and the other end extends out from an end of the bonding glass (3) away from the substrate (1).

2. The thin film hydrogen sensor according to claim 1, characterized in that: The bonding glass (3) is provided with a plurality of through holes (33), the metal lead pins (34) pass through the through holes (33), the number of the metal lead pins (34) is twice the number of the reference hydrogen-sensitive resistor element (22), and the number of the through holes (33) is the same as the number of the metal lead pins (34).

3. The thin film hydrogen sensor according to claim 2, characterized in that: The metal lead pin (34) has a conductive silver paste layer around it, and a sealant (35) is sprayed on one end of the bonding glass (3) away from the substrate (1). One end of the metal lead pin (34) is connected to a reference hydrogen-sensitive resistor element (22), and the other end protrudes relative to the sealant (35).

4. The thin film hydrogen sensor according to claim 1, characterized in that: A metal electrode bump (6) is provided on the hydrogen measurement unit (2).

5. The thin film hydrogen sensor according to claim 1, characterized in that: The circumferential dimensions of the upper oxide insulating layer (4) and the lower oxide insulating layer (5) are smaller than those of the substrate (1).

6. The thin film hydrogen sensor according to claim 1, characterized in that: The upper oxide insulating layer (4) and the lower oxide insulating layer (5) are one or more layers of oxide thin films.

7. The thin film hydrogen sensor according to claim 6, characterized in that: The oxide film is made of silicon dioxide and / or aluminum oxide.

8. The thin film hydrogen sensor according to claim 1, characterized in that: The hydrogen-sensitive resistor element (21) and the reference hydrogen-sensitive resistor element (22) are made of palladium-chromium alloy, palladium-gold alloy or palladium-nickel alloy.

9. The method for preparing a thin film hydrogen sensor according to any one of claims 1 to 8, characterized in that: The following steps are involved: (1) preparing an upper oxide insulating layer (4) and a lower oxide insulating layer (5) on the upper and lower surfaces of a substrate (1), respectively; (2) manufacturing a hydrogen measurement unit (2) having a Wheatstone bridge structure on the upper oxide insulating layer (4) and the lower oxide insulating layer (5); (3) using a bonding glass (3) with a pre-processed groove (31) and a substrate (1) for anodic bonding, installing a metal lead pin (34), and making the top of the groove wall (32) sealedly connected to the substrate (1) to form a closed cavity in the groove (31); (4) Thin film hydrogen sensor is obtained by slicing.

10. The method for preparing a thin film hydrogen sensor according to claim 9, characterized in that: In step (3), a metal lead pin (34) having a conductive silver paste layer on all sides is filled in the bonding glass through hole (33), and then sintered and solidified at low temperature in an inert gas atmosphere or a vacuum environment. After sintering, a sealant (35) is sprayed on the surface of the end of the bonding glass (3) away from the substrate (1) to form the closed cavity.

Images