Vacuum microcavity interferometer chip, manufacturing method and low-drift optical pressure sensor

Abstract

A vacuum microcavity interferometer chip, a manufacturing method and a low-drift optical pressure sensor, wherein a film island structure is formed on the upper surface of a first substrate, the film island structure comprises a protrusion and a pressure-sensitive film surrounding the protrusion, the lower surface of the first substrate is sequentially provided with a first side wall portion, a getter cavity, a second side wall portion and an F-P interference cavity located at the center in a radial direction, a first reflection surface is deposited on the lower surface of the first substrate in the F-P interference cavity, a second reflection surface is deposited on the upper surface of the second substrate in the F-P interference cavity, a first optical anti-reflection film is deposited on the surface of the protrusion, and the first optical anti-reflection film, the protrusion, the pressure-sensitive film, the first reflection surface and the second reflection surface have the same center; and further comprising an air vent, the air vent is provided on the second side wall portion for connecting the getter cavity and the F-P interference cavity.

Description

Technical Field

[0001] The present invention relates to sensors in the field of optoelectronic technology, and specifically to a wide-range vacuum microcavity interferometer chip, a manufacturing method and a low-drift optical pressure sensor based on the principle of a vacuum microcavity multi-beam interferometer. The sensor is mainly used to measure pressure signals of fluid media such as gas and liquid, and can also be used to measure and control flow, flow velocity, density, liquid level, altitude, contact force between objects, etc. Background Art

[0002] Pressure sensor refers to a device or apparatus that can sense the pressure signal of fluid media such as gas and liquid, and can convert the pressure signal into a usable output electrical signal or optical signal according to certain rules. Pressure sensor is the most commonly used sensor in industrial practice. It is widely used in various industrial automatic control environments such as water conservancy and hydropower, railway transportation, intelligent buildings, production automation, aerospace, military industry, petrochemical, oil wells, electricity, ships, machine tools, pipelines, etc., and is also increasingly widely used in consumer electronics fields such as medical equipment, robots and automotive electronics, smart phones, smart home appliances and wearable electronic products.

[0003] The price of pressure sensor products mainly depends on the applicable use conditions and the measurement accuracy that can be maintained for a long time. The price of industrial-grade pressure sensors that meet 0.01% accuracy in the working temperature range of -55℃~85℃ and pressure sensors that are temperature-resistant over 200℃ and meet 0.1% accuracy in the full temperature range are several thousand yuan or even tens of thousands of yuan. Pressure sensors with wide temperature range, high accuracy, high reliability and low drift have huge application demands in many fields such as nuclear power, aerospace, rail transportation, semiconductor equipment and process industry. Pressure sensors can be classified according to the detection method, such as electrical detection and optical detection pressure sensors. At present, among the electrical detection pressure sensors, resonant pressure sensors have a series of advantages such as high temperature stability, high long-term stability and high comprehensive accuracy and are widely recognized by the market. However, their use in high temperature, or radiation, electromagnetic interference and other occasions will be limited, while optical fiber pressure sensors can meet the use requirements of the above occasions. Optical fiber sensing technology is a new technology that has developed rapidly in the late 1970s. It is the application of fiber optics in non-communication fields. Fiber optic sensing technology can measure more than one hundred physical quantities. Its advantages are: wide range of applications, high sensitivity, anti-electromagnetic interference, good insulation, corrosion resistance, flexibility, small size, low cost, and good compatibility with fiber optic transmission lines, etc.

[0004] The fiber FP (Fabry-Perot) pressure sensor is a type of fiber optic pressure sensor. It usually consists of a fiber end face and a diaphragm end face to form a Fabry-Perot micro-resonant cavity. When pressure acts on the pressure-sensitive membrane, it deforms, causing the length of the Fabry-Perot cavity to change, thereby achieving sensing measurement. The fiber optic Fabry-Perot pressure sensor has a simple structure and is relatively easy to implement. It is currently the most commonly used interference fiber optic pressure sensor. The pressure-sensitive membrane of some sensors is made using the micro-electromechanical (MEMS) bulk silicon process and the surface sacrificial layer process; the pressure-sensitive membrane of some sensors is made using the fiber optic corrosion fusion process. In recent years, some design schemes have emerged. For example, in 2001, Jie Zhou, Samhita Dasgupta, et al. Optically interrogated MEMS pressure sensors for propulsion applications, Optical Engineering, 2001, 40: 598-604. of Cincinnati University used bulk silicon technology to make a fiber optic Fabry-Perot pressure sensor: a single-crystal silicon film was used as a pressure-sensitive film, and a shallow cylindrical cavity was etched on the glass with HF buffer solution. The silicon film and the glass were tightly bonded together using an electrostatic bonding process to form a Fabry-Perot cavity. Finally, the optical fiber and the sensor chip were aligned and bonded with epoxy resin. Since epoxy resin creeps under the influence of the external environment, the coupling angle between the optical fiber and the sensor chip will change, causing the zero-point output of the sensor to drift.

[0005] MEMS fiber optic pressure sensors combine the advantages of MEMS technology in miniaturization, high reliability and high consistency with the advantages of fiber optic signal readout technology, greatly expanding the scope of use of high-precision pressure sensors. High-precision MEMS fiber optic sensors usually use wavelength demodulation, especially FP optical interference cavity (Fabry-Perot) interference. Its working principle is to integrate the pressure-sensitive film with the optical FP optical interference cavity. The external pressure causes the pressure-sensitive film to produce a translational displacement, and the cavity length of the FP optical interference cavity changes synchronously, and its interference wavelength also changes. The change in wavelength is read out through the optical fiber, thereby measuring the external pressure. For details, please refer to the Chinese patent application CN201410728291.6 in the prior art, which discloses the use of an FP optical interference cavity to measure pressure. The sensor has a membrane island structure arranged in the FP optical interference cavity. The membrane island structure arranged inwardly increases the volume of the FP optical interference cavity, further increasing the layout area of ​​the getter film. At the same time, due to the limitation of the FP optical interference cavity, the height of the membrane island structure arranged inwardly is limited, resulting in the need for the optical anti-reflection film arranged thereon to have a high transmittance, which increases the cost of the vacuum microcavity interferometer chip. In addition, the membrane island structure arranged inwardly cannot be further processed after the sensitive chip is bonded and connected, and the parameters of the vacuum microcavity interferometer chip cannot be adjusted.

[0006] Since the dynamic detection resolution of the cavity length of the multi-beam FP interferometer can reach 1pm to 10pm, while the dynamic detection resolution of the cavity length of the dual-beam FP interferometer can only reach the order of 100pm to 1nm, the sensitivity of the pressure sensor can be greatly improved by constructing a multi-beam FP interferometer inside the vacuum microcavity interferometer chip. However, the construction of the multi-beam FP interferometer requires the deposition of optical films to increase the optical reflectivity of the two reflection surfaces of the FP interferometer, and there are very high requirements for the parallelism and cleanliness of the two reflection surfaces in order to maintain the laser signal incident into the cavity to form hundreds of reflections between the two reflection surfaces to meet the basic conditions of multi-wavelength interference. Limited by the temperature resistance range of 500℃~600℃ of the optical film, only the silicon-glass bonding process with a temperature range of 300℃~400℃ can ensure that the optical film on the reflective surface of the multi-beam FP interferometer inside the MEMS chip remains intact. However, the gas released by the silicon-glass bonding will cause the vacuum degree of the interference cavity inside the multi-beam FP interferometer to decrease and form an unstable refractive index, which affects the low-pressure measurement range and zero-point stability of the MEMS pressure-sensitive chip, and will also increase the temperature coefficient and reduce the measurement repeatability. In order to perform high-precision pressure measurements, this type of sensor usually needs to evacuate the inside of the FP optical interference cavity, and its vacuum degree needs to be kept stable. Usually, some residual gas will remain in the cavity during the manufacturing process. Therefore, it is necessary to seal a getter in the vacuum cavity, and activate the getter during the sensor manufacturing process to absorb the residual gas in the FP optical interference cavity to achieve a high vacuum inside the pressure sensor. Chinese patent application CN20121017590.0 discloses a MEMS chip packaging structure. Usually, the getter is deposited inside the FP optical interference cavity by PVD (physical vapor deposition). To ensure that the residual gas is absorbed cleanly, the getter usually occupies a large area. Therefore, when the sensor range is increased by reducing the area of ​​the pressure sensitive membrane, it will be limited by the getter area; on the other hand, the getter is a porous structure with poor density. The getter will produce particles when heated or vibrated by the outside world, polluting the FP optical interference cavity, potentially causing spectral degradation, and having a greater impact on the measurement of optical sensors, especially, and causing device failure in severe cases. Chinese patent application CN201410264998.6 relates to a hybrid wafer-level vacuum packaging method, in which a getter cavity is provided on the side of the chip packaging cavity and is connected through a vent hole. After the getter is fixed in the getter cavity, a cover plate is fixed. This structure and method also have the potential possibility of the getter contaminating the FP optical interference cavity. In this method, the getter cavity and the getter are superimposed after the chip is formed, and the manufacturing process is complicated; and there is a certain possibility that the getter particles enter the working cavity through the vent hole channel. The getter particles have a certain insulation property, and have little effect on electrical detection sensors.

[0007] In addition, after the MEMS pressure sensitive chip and the optical fiber coupling package form a MEMS optical pressure module, it is usually necessary to perform secondary packaging and fix it on the pressure sensor housing to achieve isolation and protection from sealing pressure taking, module measurement to lead-out cable, so as to become a MEMS optical pressure sensor that can be installed and used independently. During the secondary packaging process, whether the external mechanical force on the housing is transmitted to the MEMS pressure sensitive chip or to the welding and packaging part between the MEMS pressure sensitive chip and the optical fiber, the multi-beam FP interferometer will be subjected to uneven stress, causing the interference spectrum to deteriorate, resulting in abnormal changes in the measured value, and also causing the sensor zero point output to drift.

[0008] For industrial pressure sensors, in addition to high accuracy requirements, due to the difficulty or high cost of maintenance and calibration, pressure sensors are usually required to have low drift characteristics, including long-term high stability of zero point and low temperature drift. Compared with traditional electric pressure sensors (such as piezoresistive), MEMS fiber sensors have naturally higher zero point stability due to the lack of resistance thermal noise and other influences. In the present invention, the welding of the sensor chip and the shell is achieved by welding the second substrate and the shell, which greatly reduces the influence of the residual stress of the shell and solder and thermal expansion and contraction on the sensitive film of the pressure sensor and the optical fiber collimator, and can effectively improve the zero point stability of the pressure sensor. The first substrate and the third substrate are roughly symmetrical with respect to the second substrate, which also greatly reduces the sensor output change caused by temperature change, that is, low temperature drift. Without adding additional digital temperature compensation of the temperature measuring element, the thermal drift output change in the full temperature range of -55℃ to 125℃ can reach less than 1% of the full-scale pressure output change of the sensor. Summary of the invention

[0009] In order to overcome the technical deficiencies of optical fiber pressure sensors in the prior art, the present invention proposes a vacuum microcavity interferometer chip, a manufacturing method and a low drift optical pressure sensor. The vacuum microcavity interferometer chip includes a first substrate, a second substrate and a third substrate. The first substrate and the third substrate can be other substrates with similar functions such as silicon wafers or silicon nitride wafers. The second substrate can be other substrates with similar functions such as glass wafers or sapphire. The three substrates are fixedly connected by silicon-glass-silicon bonding or by bonding with corresponding dielectric layers such as BCB glue, gold layer or glass slurry. A membrane island structure is formed on the upper surface of the first substrate. The membrane island structure includes a protrusion formed by a countersunk hole and a pressure-sensitive film surrounding the protrusion. The lower surface of the first substrate is sequentially provided with a first side wall portion, a getter cavity, a second side wall portion and a FP interference cavity located in the center along the radial direction, a first reflection surface is deposited on the lower surface of the first substrate in the FP interference cavity, a second reflection surface is deposited on the upper surface of the second substrate in the FP interference cavity, a first optical anti-reflection film is deposited on the surface of the protruding portion, and the first optical anti-reflection film, the protruding portion, the pressure sensitive film, the first reflection surface and the second reflection surface have the same center; a mounting hole for the optical fiber collimator is provided at the center of the third substrate, and a getter film is provided on at least one surface in the getter cavity; and an air vent is also provided, and the air vent is provided on the second side wall portion for connecting the getter cavity and the FP interference cavity. The upper surface of the first substrate is the pressure-facing side. Through the membrane island structure facing the pressure-facing side, the thickness of the protrusion can be increased, and the high refractive index of silicon in the protrusion can be used to increase the optical path, so that the light passing through the first reflecting surface is attenuated, thereby reducing the process difficulty of depositing the optical anti-reflection film on the surface of the protrusion and the transmittance of the optical anti-reflection film, and better eliminating the interference effect of multi-interface reflected light on the FP interference cavity, so that the multi-beam FP interference cavity has more excellent spectral characteristics, and reduces the pressure monitoring interference of the vacuum microcavity interferometer chip; when using a semi-reflection demodulation method, the reflectivity of the first reflecting surface is set to non-total reflection, with a reflectivity of less than 50% and greater than 50%. The light will be transmitted from the first reflecting surface into the protrusion. When the thickness of the protrusion is small, the attenuation of this part of the transmitted light is small. Therefore, it is necessary to set a first optical anti-reflection film with higher transmittance, or even a first optical anti-reflection film with 99% transmittance, which has high requirements on the process and cost of the first optical anti-reflection film. At the same time, the membrane island structure facing the pressure side is not only conducive to reducing the total volume of the FP interference cavity, thereby reducing the area of ​​the required getter film, but also can selectively process the geometric dimensions of the protrusion of the membrane island structure, the pressure sensitive film and the frame located outside the pressure sensitive film after the three-layer substrate is completed by bonding, so as to flexibly adjust the sensitivity of the vacuum microcavity interferometer chip.Through the above structure, the getter cavity and the FP interference cavity are connected through the vent hole, and the getter cavity can be set separately, which ensures that the getter cavity has sufficient surface area to absorb the residual gas in the FP optical interference cavity, and also ensures that the area of ​​the pressure sensitive film can be flexibly adjusted. For example, the pressure sensitive film can be reduced to the minimum area when measuring a large range of pressure.

[0010] In a preferred embodiment, the vent hole is arranged on the second side wall portion, and the second side wall portion has a first height. Preferably, the vent hole is arranged at a middle height position of the second side wall portion, connecting the getter cavity and the FP interference cavity; the getter film will produce a small amount of particles after activation. By setting the vent hole at a middle height position of the second side wall portion, the particles cannot pass through the vent hole to reach the FP interference cavity as the sensor vibrates, thereby preventing the optical film in the FP interference cavity from being contaminated and causing chip failure.

[0011] In a further preferred embodiment, the getter cavity is an annular cavity, thereby providing a maximum getter cavity area and increasing the area of ​​the getter film.

[0012] In a further preferred embodiment, the vent hole is arranged at the bottom of the second side wall portion, and the vent hole can be processed by etching, and can be formed in the same step as the getter cavity and the FP interference cavity.

[0013] In a preferred embodiment, the protruding portion of the first substrate is a cylindrical structure, and the pressure-sensitive film has a circular area. This structure is conducive to achieving uniform force in fluid media such as gas and liquid, thereby improving the chip's ability to withstand high pressure and improving the interference spectrum stability between the two reflecting surfaces of the FP interference cavity inside the vacuum microcavity interferometer chip under pressure.

[0014] In a preferred embodiment, the first substrate and the third substrate have the same diameter, and the first substrate and the third substrate have the same thickness, and the same thickness and diameter form a roughly symmetrical structure about the second substrate. Since the first substrate and the third substrate are both silicon wafers, silicon nitride or other substrates, and have the same temperature coefficient, the three-layer substrate has good stress matching characteristics, which can achieve an extremely low temperature coefficient of the vacuum microcavity interferometer chip as a whole, reduce the bending deformation of the center of the vacuum microcavity interferometer chip, and ensure that the two reflecting surfaces of the FP optical interference cavity remain relatively parallel under the full-scale pressure, which is conducive to achieving high stability of the zero-point output of the vacuum microcavity interferometer chip through good stress matching, forming high zero-point long-term stability (maintained at 0.1% of the full-scale for 15 years) and low temperature drift characteristics (without adding additional digital temperature compensation of temperature measuring elements, the thermal drift output change in the full temperature range of -55°C to 125°C can reach less than 1% of the full-scale pressure output change of the sensor).

[0015] In a preferred embodiment, the size of the second substrate is larger than that of the first substrate and the third substrate. Therefore, when the vacuum microcavity interferometer chip is used to make a sensor, the second substrate is larger than the first substrate and the third substrate to form an exposed surface for bonding or welding to the sensor housing, so that the first substrate, the third substrate and the optical fiber collimator are not in contact with the sensor housing; stress isolation is achieved between the membrane island structure of the vacuum microcavity interferometer chip, the optical fiber collimator on the third substrate and the sensor housing. When the sensor housing is subjected to force or vibration, it will be directly transmitted to the second substrate. Since the first substrate and the third substrate are arranged on both sides of the second substrate and have a roughly symmetrical structure, the first substrate and the third substrate will vibrate as a whole, and will not apply stress to the membrane island structure and the optical fiber collimator on the third substrate, thereby ensuring that the zero-point output of the vacuum microcavity interferometer chip does not change before and after mechanical fastening and installation on site or when impacted by external force, thereby forming high zero-point long-term stability and low temperature drift characteristics.

[0016] In a preferred embodiment, the getter film is deposited on the surface of the second substrate in the getter cavity, that is, the lower surface, and / or the surface of the first substrate, that is, the upper surface, and a notch is provided on the first side wall and the second side wall, the notch is located at the position where the first side wall and the second side wall are bonded to the second substrate, and the notch is connected to the getter cavity, the notch is an annular groove, and when the getter film generates a small amount of particles after activation, the particles can be stored in the notch when the sensor is tilted or vibrated. The free movement of particles in the getter cavity is further reduced, and the possibility of particles entering the FP interference cavity through the vent is reduced.

[0017] The present application also relates to a low drift optical pressure sensor, comprising a sensor housing and a sensitive chip mounting seat arranged in the sensor housing, wherein the vacuum microcavity interferometer chip is fixed in contact with the sensitive chip mounting seat only through the second substrate. This structure can achieve stress isolation between the membrane island structure of the vacuum microcavity interferometer chip, the optical fiber collimator on the third substrate and the sensor housing. When the sensor housing is subjected to force or vibration, it will be directly transmitted to the second substrate. Since the first substrate and the third substrate are arranged on both sides of the second substrate and have a roughly symmetrical structure, the first substrate and the third substrate will vibrate as a whole, and will not apply stress to the membrane island structure and the optical fiber collimator on the third substrate, thereby ensuring that the zero-point output of the vacuum microcavity interferometer chip does not change before and after mechanical fastening and installation on site or when subjected to external force impact.

[0018] The present application also relates to a method for manufacturing a MEMS vacuum microcavity interferometer chip, wherein the first substrate is selected to be an SOI silicon wafer (a three-layer structure of top silicon-buried oxide layer-bottom silicon); S1, a getter cavity, an FP interference cavity and an air vent connecting the getter cavity and the FP interference cavity are formed on one surface of the first substrate by etching and / or KOH etching process, and a first reflection surface is deposited on the surface of the FP interference cavity; the membrane island structure is formed by etching and / or KOH etching on another surface of the first substrate, the surface of the protruding portion is an original polished surface with the same thickness as the frame, and a first optical anti-reflection film is deposited on the protruding portion; S2, the second substrate is a double-sided polished glass sheet, and a second reflection surface is deposited on the surface of the second substrate at a position corresponding to the FP interference cavity and a getter film is deposited at a position corresponding to the getter cavity; the getter film and the second reflection surface are located on the same side of the second substrate; A second optical anti-reflection film is deposited at the position; S3 selects the third substrate as an ultra-flat double-polished silicon wafer, on which the mounting hole of the optical fiber collimator is made; a countersunk hole is arranged on the surface of the third substrate facing the second substrate, and the area of ​​the countersunk hole is larger than the area of ​​the second optical anti-reflection film, so as to avoid the second optical anti-reflection film affecting the bonding quality of the second substrate and the third substrate; S4 bonds the first substrate, the second substrate and the third substrate through a three-layer bonding technology, and the bonding temperature is 300℃~400℃. Since the getter usually needs to be thermally activated after deposition, and the activation temperature is usually above 300℃, the activation of the getter film can be completed at the same time as bonding, and there is no need to activate the getter film after the device is manufactured; the bonding temperature of silicon-glass-silicon is usually lower than 400℃, or the corresponding dielectric layer is selected to be bonded at a temperature lower than 400℃, which can ensure that the optical film with a temperature resistance of more than 500℃ made by depositing optical dielectric materials inside the chip is not affected.

[0019] A further preferred embodiment further includes step S5, after the three-layer substrate is bonded, the thickness of the single crystal silicon of the protruding portion of the membrane island structure and the pressure sensitive film is measured in real time and selectively processed and controlled. The geometric dimensions of the protruding portion of the membrane island structure, the pressure sensitive film and the frame outside the pressure sensitive film are selectively processed, so as to flexibly adjust the sensitivity of the vacuum microcavity interferometer chip.

[0020] The present invention aims to provide a vacuum microcavity interferometer chip, a manufacturing method and a low drift optical pressure sensor. By separating a multi-beam FP interference cavity for pressure sensitivity and detection from a getter cavity in a vacuum microcavity interferometer chip and connecting the two through a vent hole, this structure can independently adjust the pressure sensitive film area and the getter area according to needs, and prevent activated getter particles from entering the FP interference cavity through a corresponding structure, thereby affecting the reliability of the vacuum microcavity interferometer chip; the second substrate of the MEMS vacuum microcavity interferometer chip has an outer size larger than the exposed surface formed by the first substrate and the third substrate, or is bonded or welded to a sensor housing through a glass protective tube, and the first substrate and the third substrate as well as the optical fiber collimator are not connected to the sensor housing with solder or adhesive, thereby realizing MEMS vacuum microcavity interferometer chip. The sensitive structure of the cavity interferometer chip, the fiber collimator and the chip packaging part and the pressure sensor housing are stress isolated; the chip adopts a three-layer bonding structure, and various structures and materials such as pressure sensitive film, optical FP optical interference cavity and getter are integrated and miniaturized, and the getter film is activated during the bonding process, which simplifies the manufacturing process of the sensor and does not need to consume energy to activate the getter film separately; the membrane island structure facing the pressure side is not only conducive to reducing the thickness of the FP interference cavity, thereby reducing its volume and the air inside it, and reducing the area of ​​the getter film; after the three-layer substrate is completed by bonding, the geometric dimensions of the raised part of the membrane island structure, the pressure sensitive film and the frame located outside the pressure sensitive film can be selectively processed, so as to flexibly adjust the sensitivity of the vacuum microcavity interferometer chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the structure of the MEMS vacuum microcavity interferometer chip of this application;

[0022] Figure 2 is a schematic diagram of the top surface structure of the first substrate;

[0023] Figure 3 is a structural schematic diagram of another embodiment;

[0024] Figure 4 for Figure 3 A schematic diagram of the bottom structure of the first substrate;

[0025] Figure 5It is a schematic diagram of the pressure sensor structure;

[0026] Figure 6 for Figure 5 Schematic diagram of some structures in .

[0027] Description of reference numerals:

[0028] 1-first substrate; 11-protrusion; 111-first optical anti-reflection film; 112-first reflection surface, 113-second reflection surface, 114-second optical anti-reflection film; 12-pressure sensitive film; 13-first side wall; 14-getter cavity; 141-notch groove; 142-vent; 15-second side wall; 16-FP interference cavity; 2-second substrate; 3-third substrate; 31-fiber collimator; 32-mounting hole; 4-sensor housing; 5-sensitive chip mounting seat. DETAILED DESCRIPTION

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] In order to simplify the drawings, only the parts related to the present invention are schematically shown in each figure, and they do not represent the actual structure of the product. In addition, in order to simplify the drawings and facilitate understanding, in some figures, only one of the parts with the same structure or function is schematically drawn or marked. In this article, "one" not only means "only one", but also means "more than one".

[0031] It should be further understood that the term “and / or” used in the specification and appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0032] In this document, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0033] In order to overcome the technical deficiencies of optical fiber pressure sensors in the prior art, the present invention proposes a vacuum microcavity interferometer chip, a manufacturing method and a low drift optical pressure sensor. The vacuum microcavity interferometer chip includes a first substrate 1, a second substrate 2 and a third substrate 3. The first substrate 1 and the third substrate 3 are silicon wafers, and the second substrate 2 is a glass wafer. The three substrates are connected by bonding. A membrane island structure is formed on the upper surface of the first substrate 1. Figure 1 As shown, the membrane island structure includes a protrusion 11 formed by a countersunk hole and a pressure-sensitive film 12 surrounding the protrusion 11, the lower surface of the first substrate 1 is sequentially provided with a first side wall portion 13, a getter cavity 14, a second side wall portion 15 and a FP interference cavity 16 located in the center in the radial direction, the lower surface of the first substrate 1 in the FP interference cavity 16 is deposited with a first reflection surface 112, the upper surface of the second substrate 2 in the FP interference cavity 16 is deposited with a second reflection surface 113, the surface of the protrusion 11 is deposited with a first optical anti-reflection film 111, the first optical anti-reflection film 111, the protrusion 11, the pressure-sensitive film 12, the first reflection surface 112 and the second reflection surface 113 have the same center; the mounting hole 32 of the optical fiber collimator 31 is provided at the center of the third substrate 3, and at least one surface of the getter cavity 14 is provided with a getter film; and further includes a vent hole 142, which is provided in the second side wall portion 15 for connecting the getter cavity 14 and the FP interference cavity 16. The upper surface of the first substrate 1 is the pressure-facing side. Through the membrane island structure facing the pressure-facing side, the thickness of the protrusion 11 can be increased, and the optical path can be increased by utilizing the high refractive index of silicon in the protrusion 11 to attenuate the light passing through the first reflecting surface 112, thereby reducing the process difficulty of depositing the optical anti-reflection film on the surface of the protrusion 11 and the transmittance requirement of the optical anti-reflection film, and better eliminating the interference effect of multi-interface reflected light on the FP interference cavity 16, so that the multi-beam FP interference cavity 16 has more excellent spectral characteristics, and improves the pressure monitoring sensitivity of the vacuum microcavity interferometer chip; for example, when a semi-reflection demodulation method is adopted, the reflectivity of the first reflecting surface 112 is set to be non-total reflection, with a reflectivity less than 50% and greater than 50% of the light will be transmitted from the first reflective surface 112 into the protrusion 11. When the thickness of the protrusion 11 is small, the attenuation of this part of the transmitted light is small. Therefore, it is necessary to set a first optical anti-reflection film 111 with a higher transmittance, or even a first optical anti-reflection film 111 with a transmittance of 99%. The process and cost requirements of the first optical anti-reflection film 111 are high. At the same time, the film island structure facing the pressure side is not only conducive to reducing the thickness of the FP interference cavity 16, thereby reducing its volume and the air inside it, and reducing the area of ​​the getter film; after the three-layer substrate is bonded, the geometric dimensions of the protrusion of the film island structure, the pressure sensitive film 12 and the frame located outside the pressure sensitive film 12 can be selectively processed, see Figure 2 As shown in , the sensitivity of the vacuum microcavity interferometer chip can be flexibly adjusted. Through the above structure, the getter cavity 14 is connected to the FP interferometer cavity 16 through the vent hole 142, and the getter cavity 14 can be set separately, which ensures that the getter cavity 14 has enough surface area to absorb the residual gas in the FP optical interferometer cavity, and also ensures that the area of ​​the pressure sensitive film 12 is small enough when measuring large pressure to meet the requirements of corresponding measurement sensitivity.

[0034] In a preferred embodiment, the at least one vent hole 142 is arranged on the second side wall portion 15, and the second side wall portion 15 has a first height. Preferably, the vent hole 142 is arranged at the middle height position of the second side wall portion 15, connecting the getter cavity 14 and the FP interference cavity 16; the getter film will produce a small amount of particles after activation. By setting the vent hole 142 at the middle height position of the second side wall portion 15, the particles cannot pass through the vent hole 142 to reach the FP interference cavity 16 as the sensor vibrates, thereby preventing the FP interference cavity 16 from being affected and causing inaccurate measurement.

[0035] In a further preferred embodiment, the vent hole 142 may also be provided at the bottom of the second side wall portion 15, see Figure 3 and 4 As shown in , the vent hole 142 can be processed by etching, and can be formed in the same processing step as the getter cavity and the FP interference cavity 16, thereby improving the vent hole processing efficiency.

[0036] In a further preferred embodiment, the getter cavity 14 is an annular cavity, thereby providing a maximum getter cavity 14 area and increasing the area of ​​the getter film.

[0037] In a preferred embodiment, the protrusion 11 is a cylindrical structure, and the pressure sensitive film 12 has a circular area. This structure is conducive to achieving uniform force in fluid media such as gas and liquid, thereby improving the chip's ability to withstand high pressure and improving the interference spectrum stability between the two reflecting surfaces of the FP interference cavity 16 inside the vacuum microcavity interferometer chip under pressure.

[0038] In a preferred embodiment, the first substrate 1 and the third substrate 3 have the same thickness, and the first substrate 1 and the third substrate 3 have the same diameter, and the same thickness and diameter form a roughly symmetrical structure about the second substrate 2. Since the first substrate 1 and the third substrate 3 are both silicon wafers and have the same temperature coefficient, the three-layer substrate has good stress matching characteristics, which can achieve an extremely low temperature coefficient for the entire vacuum microcavity interferometer chip, reduce the bending deformation of the center of the vacuum microcavity interferometer chip, and ensure that the two reflection surfaces of the FP optical interference cavity remain relatively parallel under the full-scale pressure, which is conducive to achieving high stability of the zero-point output of the vacuum microcavity interferometer chip through good stress matching.

[0039] In a preferred embodiment, the size of the second substrate 2 is larger than that of the first substrate 1 and the third substrate 3. The size may be a parameter such as length or diameter, depending on the shape of the second substrate. Therefore, when the vacuum microcavity interferometer chip is used to make a low drift optical pressure sensor, the second substrate 2 is larger than the first substrate 1 and the third substrate 3 to form an exposed surface for bonding or welding with the sensor housing, so that the first substrate 1 and the third substrate 3 and the optical fiber collimator 31 are not in contact with the sensor housing; stress isolation is achieved between the membrane island structure of the vacuum microcavity interferometer chip, the optical fiber collimator 31 on the third substrate 3 and the sensor housing. When the sensor housing is subjected to force or vibration, it will be directly transmitted to the second substrate 2. Since the first substrate 1 and the third substrate 3 are arranged on both sides of the second substrate 2 and have a roughly symmetrical structure, the first substrate 1 and the third substrate 3 will vibrate as a whole, and stress will not be applied to the membrane island structure and the optical fiber collimator 31 on the third substrate 3, thereby ensuring that the zero-point output of the vacuum microcavity interferometer chip does not change before and after mechanical fastening and installation on site or when subjected to external force impact.

[0040] In a preferred embodiment, the getter film is deposited on the surface of the second substrate 2, i.e., the lower surface, and / or the surface of the first substrate 1, i.e., the upper surface, in the getter cavity 14, and a notch 141 is provided on the first side wall portion 13 and the second side wall portion 15, the notch 141 is located at the position where the first side wall portion 13 and the second side wall portion 15 are bonded to the second substrate 2, and the notch 141 is connected to the getter cavity 14, when the getter film generates a small amount of particles after activation, when the sensor is tilted or vibrated, the particles can be received in the notch 141. The free movement of particles in the getter cavity 14 is further reduced, and the possibility of particles entering the FP interference cavity 16 through the vent 142 is reduced.

[0041] The present application also relates to a low drift optical pressure sensor, comprising a sensor housing 4 and a sensitive chip mounting seat 5 arranged in the sensor housing, such as Figure 4-5As shown in Figure 5 and 6 As shown, the vacuum microcavity interferometer chip is fixed in contact with the sensitive chip mounting seat 5 only through the second substrate 2. This structure can achieve stress isolation between the membrane island structure of the vacuum microcavity interferometer chip, the optical fiber collimator 31 on the third substrate 3 and the sensor housing. When the sensor housing is subjected to force or vibration, it will be directly transmitted to the second substrate 2. Since the first substrate 1 and the third substrate 3 are arranged on both sides of the second substrate 2 and have a roughly symmetrical structure, the first substrate 1 and the third substrate 3 will vibrate as a whole, and will not apply stress to the membrane island structure and the optical fiber collimator 31 on the third substrate 3, ensuring that the zero-point output of the vacuum microcavity interferometer chip does not change before and after mechanical fastening and installation on site or when subjected to external force impact.

[0042] The present application also relates to a method for manufacturing a MEMS vacuum microcavity interferometer chip, wherein the first substrate 1 is selected as an SOI silicon wafer (a three-layer structure of top silicon-buried oxide layer-bottom silicon); S1 forms a getter cavity 14, an FP interference cavity 16 and a vent hole 142 connecting the getter cavity 14 and the FP interference cavity 16 on one surface of the first substrate 1 by etching and / or KOH etching process, and deposits a first reflection surface 112 on the surface of the FP interference cavity 16; and the membrane island structure is formed by etching and / or KOH etching on another surface of the first substrate 1. The surface of the protruding portion 11 is an original polished surface with the same thickness as the frame, and a first optical anti-reflection film 111 is deposited on the protruding portion 11. Etching the film island structure on the other surface of the first substrate is not a necessary step and can be omitted and completed in subsequent steps; S2 The second substrate 2 is a double-sided polished glass sheet, and a second reflecting surface 113 is deposited on the surface of the second substrate 2 at a position corresponding to the FP interference cavity 16 and a getter film is deposited at a position corresponding to the getter cavity 14; The getter film and the second reflecting surface 113 are located at on the same side of the second substrate 2; a second optical anti-reflection film 114 is deposited at a position corresponding to the mounting hole 32 on the other surface of the second substrate 2; S3 selects the third substrate 3 to be an ultra-flat double-polished silicon wafer, on which the mounting hole 32 of the optical fiber collimator 31 is made; a countersunk hole is arranged on the surface of the third substrate 3 facing the second substrate 2, and the area of ​​the countersunk hole is larger than the area of ​​the second optical anti-reflection film 114, so as to prevent the second optical anti-reflection film 114 from affecting the bonding quality between the second substrate 2 and the third substrate 3; S4 uses a three-layer bonding technology to bond the first substrate 1. The second substrate 2 and the third substrate 3 are bonded at a bonding temperature of 300°C to 400°C. Since the getter usually needs to be thermally activated after deposition, and the activation temperature is usually above 300°C, the activation of the getter film can be completed at the same time as bonding, and there is no need to activate the getter film after the device is manufactured; the bonding temperature of silicon-glass-silicon is usually lower than 400°C, or the corresponding dielectric layer is selected to be bonded at a temperature lower than 400°C, which can ensure that the optical film with a temperature resistance of more than 500°C made by depositing optical dielectric materials inside the chip is not affected.

[0043] A further preferred embodiment further includes step S5, after the three-layer substrate is bonded, the thickness of the single crystal silicon of the protruding portion 11 of the membrane island structure and the pressure sensitive film 12 is measured in real time and selectively processed and controlled. The geometric dimensions of the protruding portion of the membrane island structure, the pressure sensitive film 12 and the frame outside the pressure sensitive film 12 are selectively processed, so as to flexibly adjust the sensitivity of the vacuum microcavity interferometer chip.

Claims

1. A vacuum microcavity interferometer chip, comprising a first substrate, a second substrate and a third substrate, wherein the three substrates are connected by bonding, characterized in that: A film island structure is formed on the upper surface of the first substrate, the film island structure includes a protrusion and a pressure-sensitive film surrounding the protrusion; a first side wall portion, a getter cavity, a second side wall portion and a FP interference cavity located in the center are sequentially arranged on the lower surface of the first substrate in a radial direction; a first reflection surface is deposited on the lower surface of the first substrate in the FP interference cavity; a second reflection surface is deposited on the upper surface of the second substrate in the FP interference cavity; a first optical anti-reflection film is deposited on the surface of the protrusion; the first optical anti-reflection film, the protrusion, the pressure-sensitive film, the first reflection surface and the second reflection surface have the same center; a mounting hole for an optical fiber collimator is arranged at the center of the third substrate, and a getter film is arranged on at least one surface in the getter cavity; and at least one vent hole is also included, the vent hole is arranged on the second side wall portion for connecting the getter cavity and the FP interference cavity; the diameter of the second substrate is larger than that of the first substrate and the third substrate, and the exposed surface of the second substrate is formed by bonding or welding with the sensor housing by utilizing the outer dimensions of the second substrate being larger than those of the first substrate and the third substrate, so that the first substrate and the third substrate and the optical fiber collimator are not in contact with the sensor housing.

2. The vacuum microcavity interferometer chip according to claim 1, characterized in that: The vent hole is arranged on the second side wall portion, the second side wall portion has a first height, and the vent hole is arranged at a middle position of the first height of the second side wall portion.

3. The vacuum microcavity interferometer chip according to claim 1 or 2, characterized in that: The getter cavity is an annular cavity.

4. The vacuum microcavity interferometer chip according to claim 1 or 2, characterized in that: The vent hole is disposed at the bottom of the second side wall portion and is formed in the same processing step as the getter cavity and the FP interference cavity.

5. The vacuum microcavity interferometer chip according to claim 1 or 2, characterized in that: The protrusion is a cylindrical structure, and the pressure sensitive film has a circular area.

6. The vacuum microcavity interferometer chip according to claim 1 or 2, characterized in that: The first substrate and the third substrate have the same diameter, and the first substrate and the third substrate have the same thickness, and the same thickness and diameter form a substantially symmetrical structure with respect to the second substrate.

7. The vacuum microcavity interferometer chip according to claim 1 or 2, characterized in that: The getter film is arranged to be deposited on the surface of the second substrate and / or the surface of the first substrate in the getter cavity, and a notch groove is arranged on the first side wall portion and the second side wall portion, the notch groove is located at the position where the first side wall portion and the second side wall portion are bonded to the second substrate, and the notch groove is connected to the getter cavity.

8. A low drift optical pressure sensor, comprising a sensor housing and a sensitive chip mounting seat arranged in the sensor housing, wherein the vacuum microcavity interferometer chip according to any one of claims 1 to 7 is fixed in contact with the sensitive chip mounting seat only through the second substrate.

9. The method for manufacturing a vacuum microcavity interferometer chip according to any one of claims 1 to 7, characterized in that: The steps include: S1. forming a getter cavity, an FP interference cavity and a vent hole connecting the getter cavity and the FP interference cavity on a surface of a first substrate, and depositing a first reflective surface on the surface of the FP interference cavity; S2. A second reflecting surface is deposited on the surface of the second substrate at a position corresponding to the FP interference cavity, and a getter film is deposited at a position corresponding to the getter cavity; the getter film and the second reflecting surface are located on the same side of the second substrate; a second optical anti-reflection film is deposited on the other surface of the second substrate at a position corresponding to the mounting hole; S3. A mounting hole for the optical fiber collimator is made on the third substrate; a countersunk hole is provided on the surface of the third substrate facing the second substrate, and the area of ​​the countersunk hole is larger than the area of ​​the second optical anti-reflection film; S4. Bond the first substrate, the second substrate, and the third substrate by three-layer bonding technology, and control the bonding temperature to be 300° C.-400° C.

10. The manufacturing method according to claim 9, characterized in that: The method further includes step S5. After the three-layer substrate bonding is completed, the thickness of the protruding portion of the membrane island structure and the pressure sensitive film are measured in real time and selectively processed and controlled.

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