CN113124845A - Full-bridge double-push-pull flow z-axis film gyroscope and processing method thereof - Google Patents

Abstract

The invention discloses a full-bridge double-push-pull flow z-axis film gyroscope and a processing method thereof, wherein the z-axis film gyroscope comprises a sensitive layer and a cover plate, wherein the upper surface of the sensitive layer is provided with two pairs of heaters, two pairs of thermistors and an isolating resistor; the power-on mode of the heater is periodic push-pull power-on; the cover plate is etched with a groove and is hermetically connected with the upper surface of the sensitive layer. The invention adopts full-bridge and double push-pull heat flow, four bridge arms of the bridge all work, the sensitivity is 4 times of that of a single arm, the sensitivity is the highest one, and the power consumption is not large; the extraction circuit is an equal-arm bridge, the nonlinearity of the relationship between the resistance change of the bridge arms of the equal-arm bridge and the output unbalanced voltage of the bridge is minimum, and the linearity of the gyroscope is good.

Description

Full-bridge double-push-pull flow z-axis film gyroscope and processing method thereof

Technical Field

The invention relates to the technical field of detecting angular velocity attitude parameters of a moving body by utilizing a Coriolis force deflection heat flow sensitive body, in particular to a full-bridge type double push-pull flow z-axis film gyroscope and a processing method thereof, and belongs to the field of inertia measurement.

Background

The Micro inertial sensor manufactured by using Micro-Electro-Mechanical-System (MEMS) technology has the advantages of mass production, low cost, small volume, low power consumption and the like, and is an ideal product of the future medium and low precision Micro inertial sensors. The gyroscope and the accelerometer are core inertial sensors for measuring and controlling the motion attitude of the carrier, and the gyroscope is a sensor sensitive to angular velocity, angular acceleration and other angular parameters. The traditional micro gyroscope (micromechanical gyroscope) is a micro rate gyroscope based on the principle of the Coriolis effect existing when a high-frequency vibrating mass is driven to rotate by a base, and micro-electronics and a micro machine are combined. The solid mass block in the gyro sensitive element needs to be suspended and vibrated through a mechanical elastic body, is easy to damage under slightly high acceleration impact, and simultaneously needs vacuum packaging for reducing damping, has complex process and can generate fatigue damage and vibration noise when working for a long time. The micro fluid inertia device is a novel device for measuring input acceleration and angular velocity by detecting the flow field offset of fluid in a closed cavity. Because the movable part and the suspension system in the traditional miniature gyro are not provided, the high overload can be resisted; the sensitive mass of the gas sensor is gas, and the mass is almost zero, so the response time is short and the service life is long; due to the simple structure, the application requirement of low cost can be met. The micro fluid gyroscope is an angular velocity sensor which utilizes the deflection of an air flow sensitive body in a closed cavity under the action of Goldson force and senses the deflection quantity caused by angular velocity by a thermistor (hot wire). At present, the market has higher and higher requirements on the capability of the micro inertial gyroscope to adapt to severe and harsh environments, and compared with the traditional micro mechanical vibration gyroscope, the micro fluid gyroscope has higher market competitiveness and very wide application prospect due to the advantages of extremely high vibration resistance and impact resistance, low cost and the like.

At present, micro fluid gyroscopes based on MEMS technology can be roughly divided into four categories: micro fluidic gyroscopes, ECF (electro-coupled fluid) fluidic gyroscopes, micro thermal convection gyroscopes and micro thermal flow gyroscopes. The Chinese patent is a miniature four-channel circulating flow type three-axis silicon jet gyro (patent application number: 201510385582.4), which belongs to the miniature jet gyro, the piezoelectric sheet in the sensitive element of the miniature jet gyro increases the processing difficulty and the cost, and the volume of the miniature jet gyro is difficult to further reduce on the premise of keeping the flow rate. ECF fluid gyroscopes are relatively large (40mm x 60mm x 7mm) and are difficult to commercialize in large volumes and at low cost because of the high kilovoltage required to form the liquid jet. The miniature thermal convection gyro cannot work without a gravity field, and the sensitivity is low. The above-described microfluidic gyros have their own inherent disadvantages that make them difficult to be the low-cost choice for commercial microfluidic gyros. The micro heat flow gyro (also called thermal expansion gyro) is a new micro fluid gyro which is proposed in recent years, a voltage-free electric sheet is arranged in a sensitive element, high voltage is not needed, the micro fluid gyro can be used in a gravity-free environment, the sensitivity of the micro fluid gyro is moderate, the micro fluid gyro is between the micro fluid gyro and the micro heat convection gyro, and meanwhile, the micro fluid gyro has the advantages of simple structure and processing technology, extremely low cost, high reliability and excellent vibration and impact resistance, so that the micro fluid gyro can compete with a capacitive micro mechanical vibration gyro in the micro gyroscope market with low precision and low price.

The sensitive working principle of the micro heat flow gyroscope is that a heater is electrified to generate heat, gas around the heater is heated to form gas thermal diffusion, an air flow sensitive body moving along a certain direction is generated, and when an angular velocity is input, the air flow sensitive body deflects under the action of a Coriolis force to change a bridge arm resistor (generally composed of a thermistor) of a Wheatstone bridge, so that bridge unbalanced voltage in direct proportion to the input angular velocity is output. In chinese patents 201410140298.6 and 201210130318.2, the main components in the sensor sensing element, i.e., the heater and the thermistor, are both in a suspended cantilever beam structure, and first, since the heater and the thermistor are both suspended above the cavity, after the cavity releasing structure is etched, the heater and the thermistor may be deformed or even broken by stress, the yield is low, and the warp deformation may generate an asymmetric gas flow field under the condition of no angular velocity input, thereby causing an angular velocity detection error. Secondly, the extraction circuit and the sensitive element chip of the sensor are separated, the extraction circuit needs to be manufactured additionally, and the extraction circuit and the sensitive element are not integrated on one chip, so that the integration level is not high, and the sensor is large in size. Thirdly, if the resistors in the four-arm bridge in the discrete device are not in the same temperature field, the temperature coefficients of the resistors are different, which easily causes temperature drift and affects the accuracy of the sensor, thereby limiting the application field of the sensor. Therefore, how to overcome the above problems becomes a technical problem that needs to be solved urgently by those skilled in the art.

Disclosure of Invention

The invention aims to provide a full-bridge double-push-pull flow z-axis film gyroscope to solve the technical problems in the prior art.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides a full-bridge double-push-pull flow z-axis film gyroscope, which comprises a sensitive layer and a cover plate, wherein,

two pairs of heaters, two pairs of thermistors and an isolating resistor are arranged on the upper surface of the sensitive layer;

defining the placing direction of the upper surface isolation resistor as a Y direction, the direction vertical to the placing direction of the upper surface isolation resistor as an X direction, and the height direction of the sensitive layer as a Z direction; the heater is placed in the Y direction, the thermistor is placed in the X direction, namely the heater and the thermistor are perpendicular to each other and used for detecting the angular speed of the Z axis;

the four pairs of heaters are powered on in a periodic push-pull mode, namely one working period of the heaters comprises pulse voltage excitation time and power-off interval time;

and the cover plate is etched with a groove and is hermetically connected with the upper surface of the sensitive layer.

As a further technical scheme, each pair of heaters is driven by two square wave signals with the same frequency, the phase difference is 90 degrees, and the pulse duty ratio is 50%.

As a further technical scheme, the distance from the upper surface of the sensitive layer to the top of the groove on the cover plate is the height of the gas medium working cavity, and the height is 200-1000 μm.

As a further technical scheme, the height of the heater and the thermistor on the upper surface of the sensitive layer is 15-20 μm.

As a further technical scheme, the lengths of the heater and the thermistor are consistent and are 1/6-1/5 of the width of the whole sensitive layer.

As a further technical scheme, the heaters are all made of TaN material resistance wires with high temperature coefficients.

As a further technical scheme, the thermistors are all formed by n-type heavily doped GaAs material resistance wires.

As a further technical scheme, the isolation resistor is composed of Si with the height of 25-30 μm₃N₄A resistive line of material.

A method for processing a full-bridge double push-pull flow z-axis film gyroscope is characterized by comprising the following specific process flows of:

the method comprises the following steps: preparation of doping Density of 10 on GaAs wafer¹⁸cm^-3N of (A) to (B)⁺The GaAs epitaxial layer is etched to form an upper surface thermistor and a balance resistor;

step two: sputtering TaN (tantalum nitride) layer as upper surface heater;

step three: sputtering Ti/Au/Ti respectively to form

Thick pads and sensitive resistance lines;

step four: deposited by chemical vapor deposition (PECVD)

Thick Si₃N₄Preparing an isolation resistor;

step five: the upper cover plate and the sensitive layer are bonded through a bonding process, so that the working environment of the gas medium is sealed;

step six: and packaging the processed structure to form the full-bridge double-push-pull flow z-axis film gyroscope.

By adopting the technical scheme, the invention has the following beneficial effects:

1. the gyroscope inherits the advantages of no solid sensitive mass block, vibration and impact resistance and the like of the micro heat flow gyroscope, and the sensitive element of the gyroscope has no cantilever beam structure, simple process, high yield of the sensitive element and low cost.

2. The four-arm bridge in the extraction circuit in the sensitive element in the film type micro-mechanical heat flow gyroscope is realized on one chip, and the four-arm bridge is manufactured in the same structure and the same process, so that the dispersion degree of the resistance of the bridge arms of the bridge is small, the resistors with the same temperature coefficient are very easy to manufacture, and the temperature drift caused by the difference of the temperature coefficient and the temperature gradient can not be caused because each bridge arm of the bridge is in the same temperature field.

3. Four thermistors form an equal-arm bridge, four bridge arms as working arms all participate in the deflection of sensitive hot air flow, the sensitivity is four times that of a single working arm, and the sensitivity of the gyroscope is greatly improved.

4. The extraction circuit is an equal-arm bridge, the nonlinearity of the relationship between the resistance change of the bridge arms of the equal-arm bridge and the output unbalanced voltage of the bridge is minimum, and the nonlinearity of the gyroscope can be greatly reduced.

5. The process adopted by the invention is compatible with the integrated circuit process and has the potential of high integration level.

6. The push-pull type heat flow is adopted, the heat flow state is changed quickly, the heat flow velocity is large, the air flow state is stable, the corresponding speed is high, the sensitivity of the gyroscope is high, and the stability is good.

7. Because the sensitive mass of the sensor does not contain a solid mass block, compared with micro inertial sensors with other working principles, the sensor has the advantages of large impact resistance, simple structure, extremely low cost and high reliability.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a schematic three-dimensional structure diagram of a sensitive layer provided in an embodiment of the present invention;

fig. 2 is a schematic three-dimensional structure diagram of a cover plate according to an embodiment of the present invention;

FIG. 3 is a top view of a sensitive layer provided by an embodiment of the present invention;

FIG. 4 is a sectional view taken along line A-A of FIG. 3;

FIG. 5 is a schematic diagram of the operation of the present invention;

FIG. 6 is a schematic structural diagram of a heater according to an embodiment of the present invention;

FIG. 7 is a schematic structural diagram of a thermistor according to an embodiment of the present invention;

FIG. 8 is a flow chart of a process for manufacturing a full-bridge dual push-pull z-axis thin film gyroscope according to an embodiment of the present invention;

icon: 1-sensitive layer, 2-cover plate, 3-cover plate groove, 4-heater, 5-heater, 6-heater, 7-heater, 8-thermistor, 9-thermistor, 10-thermistor, 11-thermistor, 12-isolation resistor, 13-TaN material resistor block, 14-Si₃N₄A material resistance block, a 15-TaN material resistance block and a 16-n type heavily doped GaAs material resistance block.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.

As shown in fig. 1 to 5, the present embodiment provides a full-bridge dual push-pull z-axis thin film gyroscope, which includes a sensitive layer 1 and a cover plate 2, wherein,

two pairs of heaters, two pairs of thermistors and an isolating resistor are arranged on the upper surface of the sensitive layer 1;

defining the placing direction of the upper surface isolation resistor 12 as a Y direction, the direction vertical to the placing direction as an X direction, and the height direction of the sensitive layer 1 as a Z direction; the heater is placed in the Y direction, the thermistor is placed in the X direction, namely the heater and the thermistor are perpendicular to each other and used for detecting the angular speed of the Z axis;

a thermistor 8, a thermistor 9, a thermistor 10 and a thermistor 11 for detecting the angular velocity of the Z axis are arranged on two sides of the upper surface X direction of the sensitive layer, a heater 4, a heater 5, a heater 6 and a heater 7 are arranged on two sides of the upper surface Y direction of the sensitive layer, and the heaters are vertical to the thermistors;

the heater is powered on in a periodic push-pull mode, namely one working period of the heater comprises pulse voltage excitation time and power-off interval time;

the electrifying mode of the thermistor is constant current;

and a cover plate groove 3 is etched on the cover plate 2 and is hermetically connected with the upper surface of the sensitive layer 1.

In this embodiment, as a further technical solution, each pair of the heaters is driven by two square wave signals with the same frequency, the phase difference is 90 degrees, and the pulse duty ratio is 50%. The heater is alternately electrified to generate Joule heat, and releases heat to the surrounding gas to carry out heat diffusion and form heat flow. The square wave signals applied to the heaters heat alternately, thus forming a push-pull type heat flow between each pair of heaters. The push-pull type heat flow has the advantages of large flow rate, stable airflow state, high gyro sensitivity and good stability. The square wave signal drives the heater to work and is divided into two stages, in the first stage, the heater 5 and the heater 6 are electrified for heating, the heater 4 and the heater 7 are not electrified and are at the ambient temperature, and two hot air flows with the same direction as the orthogonal direction of the heater 5 and the heater 6 are generated between the two pairs of heaters. In the second stage, the heater 4 and the heater 7 are energized to heat, the heater 5 and the heater 6 are not energized, and hot air flow opposite to the direction of the first stage is generated between the two pairs of heaters. The continuous operation of the heaters in both stages will constitute a push-pull type of hot gas flow. The two pairs of thermistors 8 and 10 with the same resistance value and the thermistors 9 and 11 form an equiarm Wheatstone bridge, and both the thermistors are used as working bridge arms to participate in the deflection of sensitive airflow to form a full-bridge double-push-pull flow z-axis film gyroscope.

The working principle of the Z-axis heat flow gyroscope is explained by taking the first stage as an example. If an angular velocity Ω Z is input in the Z-axis direction, the heat flows generated by the heater 5 and the heater 6 reach the two relatively parallel thermistors 8 and 11 in opposite directions in the XOY plane due to the Coriolis force principle, and at this time, the temperature of the thermistors 8 and 11, to which the heat flows are biased, is higher than that of the thermistors 9 and 10 parallel thereto, and a temperature difference proportional to the input angular velocity Ω Z is generated between the two relatively parallel thermistors 8 and 11 and the thermistors 9 and 10. The changes of two adjacent bridge arm resistors R1 and R3 (thermistors 11 and 9) and R2 and R4 (thermistors 10 and 8) are increased and decreased, the resistance changes are equal in size and opposite in sign, and according to a formula (1), the full-bridge voltage output is four times that of a bridge with a single thermistor participating in the sensitive heat flow deflection. The temperature difference generated by the input angular velocity is converted into a voltage unbalance voltage delta Vout which is in direct proportion to the angular velocity omega Z through the change of the resistance value of the bridge arm of the Wheatstone bridge and is output, so that the angular velocity in the Z-axis direction is sensed. The two bridge arms as working arms participate in the deflection of the sensitive hot air flow, the sensitivity is twice of that of a single working arm, and the sensitivity of the gyroscope is greatly improved.

In this embodiment, as a further technical solution, the distance from the upper surface of the sensitive layer 1 to the top of the groove on the cover plate 2 is the height of the gas medium working cavity, and the height is 200 μm to 1000 μm.

In this embodiment, as a further technical solution, the height of the heater and the thermistor on the upper surface of the sensitive layer 1 is 15 μm to 20 μm.

In this embodiment, as a further technical solution, the lengths of the heater and the thermistor are the same, and are 1/6 to 1/5 of the width of the whole sensitive layer.

In this embodiment, as a further technical solution, the distance between the heater and the thermistor for detecting the angular velocity in the Z-axis direction is 1/4 to 1/3 of the length of the heater.

As a further technical scheme, the isolation resistor is composed of Si with the height of 25-30 μm₃N₄A resistive line of material.

In this embodiment, as a further technical solution, the heaters are made of resistive wires of TaN material with high temperature coefficient, as shown in fig. 6-7. The thermistors are all composed of n-type heavily doped GaAs material resistance wires. Wherein, the heater comprises 2 symmetrical TaN material resistance blocks 13, 15 and 1 Si₃N₄A resistive mass of material 14. The TaN material resistance block 13 is composed of 4 series-connected resistors, and each resistor is specifically realized in the form of 3 parallel TaN material resistance lines with high temperature coefficients. By designing the TaN material resistance wire in this way, the heater can generate more heat, thereby being beneficial to improving the sensitivity of gyro detection. The thermistor is a resistor block 16 of n-type heavily doped GaAs material. Wherein the n-type heavily doped GaAs material resistive block 16 is formed by 5 n-type heavily doped GaAs material resistive lines connected in series. By designing the GaAs material resistance wire in this way, the thermistor can obtain larger voltage signal output,thereby being beneficial to improving the sensitivity of gyro detection.

Referring to fig. 8, the full-bridge dual push-pull z-axis thin film gyroscope disclosed by the invention can be prepared by using a GaAs-MMIC technique, and the specific process flow is as follows:

step (a): preparation of doping Density of 10 on GaAs wafer¹⁸cm^-3N of (A) to (B)⁺And etching the GaAs epitaxial layer to form the upper surface thermistor and the balance resistor.

Step (b): a sputtered TaN (tantalum nitride) layer acts as the top surface heater.

Step (c): sputtering Ti/Au/Ti respectively to form

Thick pads and sensitive resistance lines.

Step (d): deposited by chemical vapor deposition (PECVD)

Thick Si₃N₄And preparing the isolation resistor.

A step (e): and the upper cover plate is bonded with the sensitive layer through a bonding process, so that the working environment of the gas medium is sealed.

Step (f): and packaging the processed structure to form the full-bridge double-push-pull flow z-axis film gyroscope.

In conclusion, the invention inherits the advantages of no solid sensitive mass block, vibration resistance, impact resistance and the like of the micro heat flow gyroscope, and the full-bridge double-push-pull flow z-axis film gyroscope sensitive element has no cantilever beam structure, simple process, high yield of the sensitive element and low actual cost. Four-arm electric bridges in an extraction circuit in a sensitive element in the film type micro-mechanical heat flow gyroscope are all realized on one chip, and the temperature drift caused by different temperature coefficients and temperature gradients can not be caused by the same structure and the same process manufacturing. Meanwhile, due to the adoption of the push-pull type heat flow moving in opposite directions, the heat flow state is changed quickly, the heat flow velocity is large, the air flow state is stable, the response speed is high, and the stability is good. Four thermistors form an equal-arm bridge, four bridge arms as working arms all participate in the deflection of sensitive hot air flow, the sensitivity is four times that of a single working arm, and the sensitivity of the gyroscope is greatly improved. Meanwhile, the extraction circuit is an equal-arm bridge, the nonlinearity of the relationship between the resistance change of the bridge arms of the equal-arm bridge and the output unbalanced voltage of the bridge is minimum, and the nonlinearity of the gyroscope can be greatly reduced. The process adopted by the invention is compatible with the integrated circuit process and has the potential of high integration level. Because the sensitive mass of the sensor does not contain a solid mass block, compared with micro inertial sensors with other working principles, the sensor has the advantages of large impact resistance, simple structure, extremely low cost and high reliability.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (9)

1. A full-bridge double push-pull flow z-axis film gyroscope is characterized by comprising a sensitive layer and a cover plate, wherein,

two pairs of heaters, two pairs of thermistors and an isolating resistor are arranged on the upper surface of the sensitive layer;

defining the placing direction of the upper surface isolation resistor as a Y direction, the direction vertical to the placing direction of the upper surface isolation resistor as an X direction, and the height direction of the sensitive layer as a Z direction; the heater is placed in the Y direction, the thermistor is placed in the X direction, namely the heater and the thermistor are perpendicular to each other and used for detecting the angular speed of the Z axis;

the heater is powered on in a periodic push-pull mode, namely one working period of the heater comprises pulse voltage excitation time and power-off interval time;

and the cover plate is etched with a groove and is hermetically connected with the upper surface of the sensitive layer.

2. The full-bridge dual push-pull z-axis membrane gyroscope of claim 1, wherein each pair of heaters is driven by two square wave signals of the same frequency, with a phase difference of 90 degrees and a pulse duty cycle of 50%.

3. The full-bridge dual push-pull z-axis thin film gyroscope of claim 1, wherein the distance from the upper surface of the sensing layer to the top of the groove on the cover plate is the height of the gas medium working cavity, and the height is 200 μm to 1000 μm 1.

4. The full-bridge dual push-pull z-axis thin film gyroscope of claim 1, wherein the heater and thermistor height at the top surface of the sensing layer is 15 μm to 20 μm.

5. The full bridge dual push-pull z-axis membrane gyroscope of claim 1, wherein the heater and the thermistor are of uniform length, each 1/6-1/5 of the width of the entire sensing layer.

6. The full-bridge dual push-pull z-axis thin film gyroscope of claim 1, wherein each heater comprises 4 series-connected "resistive blocks" each consisting of 3 parallel resistive lines of TaN material with high temperature coefficient.

7. The full-bridge double push-pull z-axis thin film gyroscope of claim 1, wherein the thermistors are each formed by 5 n-type heavily doped GaAs material resistor lines connected in series.

8. The full-bridge dual push-pull z-axis membrane gyroscope of claim 1, wherein the isolation resistors do not participate in the deflection of the sense airflow and are formed from 1 piece of Si₃N₄A resistive line of material.

9. A method for processing a full-bridge double push-pull flow z-axis film gyroscope according to any one of claims 1-8, characterized in that the specific process flow is as follows:

the method comprises the following steps: preparation of doping Density of 10 on GaAs wafer¹⁸cm^-3N of (A) to (B)⁺The GaAs epitaxial layer is etched to form an upper surface thermistor and a balance resistor;

step two: sputtering a TaN layer as an upper surface heater;

step three: sputtering Ti/Au/Ti respectively to form

Thick pads and sensitive resistance lines;

step four: deposited by chemical vapor deposition (PECVD)

Thick Si₃N₄Preparing an isolation resistor;

step five: the upper cover plate and the sensitive layer are bonded through a bonding process, so that the working environment of the gas medium is sealed;

step six: and packaging the processed structure to form the full-bridge double-push-pull flow z-axis film gyroscope.

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