KR101703379B1 - Mems device having a membrane and method of manufacturing - Google Patents

Abstract

The present invention relates to a MEMS device including a micromachining bulk body (BB) and a membrane (MM) fixed thereto. Preferably, the film is cut by a laser from a flat metal sheet and bonded to the bulk body.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a MEMS device having a membrane,

To a MEMS device having a membrane and a method of manufacturing the same.

MEMS (Micro Electro Mechanical System) devices including membranes are used in various other applications. For example, flexible membranes in microphones, sensors, capacitors, switches, and other types of devices are used in a passive or active manner.

Usually MEMS devices are fabricated on silicon or ceramic substrates using planar processing and bulk micromachining techniques. Such techniques include physical and chemical etching steps, deposition of thin film layers, formation of conductor lines, formation of through-conducts, and also mechanical methods such as polishing or polishing. The microstructure formation may also include a bonding step in which two wafers are bonded by respective methods.

MEMS devices with membranes require a construction method in which a free space is formed on both sides of the membrane. The free space on the substrate side may be formed, for example, by etching a sacrificial layer deposited under the film. This technique causes problems in most film structures when the aspect ratio of the horizontal plane and the vertical plane becomes too large. Then, removal of the sacrificial layer becomes increasingly difficult. Moreover, the high selectivity between the sacrificial layer and the permanent layer can be difficult to obtain and potentially imposes additional constraints on the design. As a result, it will be difficult to produce a planar region for applying the film if the previous layers have a shape such as a protrusion or depression.

It is an object of the present invention to provide a MEMS device having a membrane that can skip the above-mentioned problems.

This problem is solved by the MEMS device according to claim 1. Other embodiments of the invention as well as a method of manufacturing a micro-mechanical device are given by other claims.

Figure 1 shows a cross-sectional view of a membrane mounted on top of a bulk body.
Figure 2 shows a top view of the membrane.
Figure 3 shows a cross-section of an apparatus with a membrane.
Figure 4 shows a processing frame.
Figure 5 shows a schematic cross-section of another apparatus with a membrane.
Figure 6 shows a membrane with suspension arms having different shapes in plan view.

A MEMS device is provided that includes a micro-machined bulk body and a membrane fixed thereon. The film is not deposited or sputtered, but is constructed from a flat metal foil. The metal foil that can be used as the membrane will be structured rather than cut directly to the surface of the MEMS device being discussed. This means that the process constituting the membrane is completely independent from the process constituting the bulk body. For this reason, problems arising during the processing of bulk bodies of microstructures have no effect on the process of forming the film. In addition, the membrane will be formed in one step in any two-dimensional shape without any problems and without having to consider the topography of the surface of the micromachined bulk body to which the membrane will be mounted in the next step.

The material of the membrane may be selected from any suitable metal foil. Thus, the choice of metal is not limited by the need to form etch selectivity as in known processes. Since there is no limitation on the thickness of the metal foil, the thickness of the film is not limited. Without any problems, the metal foil can be used having a thickness between 1 and 50 micrometers to meet the needs of most devices using such a film. In some cases, metal foils having smaller thicknesses or thicknesses in excess of a given range may also be used.

In one embodiment, the membrane comprises a planar member. In most applications of MEMS devices, the planar member provides a planar electrode of the device. Thus, the area of the planar member is important for defining the characteristics and electrical parameters of the MEMS device.

The second electrode of the MEMS device is generally a fixed electrode and is integrated or fixed in the bulk body.

In another embodiment, a suspension arm extending laterally from the planar member is provided. At the outermost end, the suspension arm widens to a suspension arm pad, which is used to secure the suspension arm to each contact pad on the bulk body.

Suspension arms may exist in any number. The three suspension arms are sufficient to secure the membrane parallel to the surface of the bulk body at a relatively stable location. Depending on the mode of operation of the micro-mechanical device, the number of suspension arms may be more than three and more than four.

Usually, the suspension arm has a small width sufficient to provide sufficient flexibility. The width is selected to provide a cross-sectional area of the suspension arm that is sufficient to provide sufficient mechanical strength to secure the membrane at the starting position.

In another embodiment, the suspension arm is bent so as to extend above / below the face of the planar member. Also, the suspension arm will bend or tilt in the plane of the planar member. Thus providing an additional length that can be used to compensate for translational movement of the film in the plane or to compensate for the pressure acting in the horizontal direction. The suspension arm includes a straight portion as well as a curved portion.

The cutting process is used to structure and separate a single film from a large area metal foil. The finished structure of the membrane, including the planar member, the suspension arm, and the suspension arm pad, is cut into a piece from the metal foil.

In an embodiment, the membrane is located between the anchor means formed on the top of the bulk body. The plane member itself or the suspension arm would instead be secured to the anchor means on the bulk body. In this embodiment, the membrane may be flat without extending over the face of the planar member.

The suspension of the membrane in the anchor means also includes mechanical fixation and electrical contact. The anchor means can be formed from a structured back-end layer and in this case is a part of the bulk body.

In all embodiments, if the film is not considered, the MEMS device will be formed as a known MEMS or CMOS device. The bulk body will include semiconductors with or without integrated circuits integrated within the semiconductor body. In an embodiment, the bulk body may be a ceramic body.

The trailing layer is deposited on top of the semiconductor or ceramic body to serve as a conductive layer arranged on the opposite side of the membrane or as a back electrode that cooperates with the first electrode formed by the membrane.

The integrated circuit is in electrical contact with the back electrode and in electrical contact with the membrane by respective through-contacts through the membrane. In addition to the through-contacts, the electrical connection lines will be part of each electrical connection.

Bulk bodies include semiconductors or ceramic bodies and end layers deposited thereon. The tailing layer comprises a stack of layers of the same or different materials. These materials will be selected mechanically from a stable layer, an electrically conductive layer and electrically isolating layers. A preferred layer for the trailing layer is known as a CMOS device, for example, silicon oxide or silicon nitride to electrically isolate and form a given three-dimensional shape, and aluminum and tungsten as the most preferred metals for micro- . Other insulators, polysilicon, and metals will also be used.

The through-contact through the tailing layer will also include other materials used to fill the hole produced for the through-contact in the isolated tailing layer. Tungsten can be deposited on the bottom and sidewalls of a hole with a large aspect ratio and is a preferred material for forming a through-contact.

In certain embodiments, the MEMS device is designed and used as a microphone. Thus, the membrane will be fixed to the bulk body and will be vibrated or reoriented by acoustic sound. For best operation, a back volume is provided in the device.

The back plate is hollowed with a back plate to reduce the damping between the membrane and the back plate. A back volume or cavity can be formed in the bulk body directly below the back plate. The back plate holes and cavities are structured by micromachining means. The back volume can be formed to go through a hole or recess near the bottom by the cover. In a bulk body, the integrated circuit (IC) at any location, except just below the back plate, can be integrated if a semiconductor bulk body is used. Membranes and backplanes can be electrically connected to the IC, creating a monolithic microphone design.

The air gap distance between the membrane and the backing plate can be defined by a stand-off structure on the top of the tailing layer. The standoff structure can form a circular closed or partially closed rim that forms a stand-off rim at the edge of the back plate. If one or more openings are made in the standoff rim, they can be used as ventilation holes to make the static pressure differential the same. Ventilation holes can also be structured in the membrane.

The method for manufacturing the above-described MEMS device will include the following steps:

Providing a metal foil;

Providing a laser;

Cutting the foil with a laser to obtain a film;

Providing a micromachined bulk body for the device; And

And transferring and fixing the foil having the designed membrane in a bulk body.

Instead, a roll-to-roll technique can be used to treat the foil while bonding the laser cut and film to the apparatus. The laser is guided along the periphery of the film to be cut from the metal foil. The control means controls the scanning of the laser across the surface of the foil.

The scan speed is selected according to the amount of power per area (W / cm ² ) required to cut the foil.

The spot diameter when the laser focuses on the metal foil is chosen according to the desired smoothness of the cutting edge at the later membrane. A spot diameter of 1 m to 30 m is suitable. The preferred diameter is between 5 탆 and 20 탆.

The metal foil will be selected from suitable metals that provide desirable properties such as mechanical strength, resilience and electrical conductivity. In most applications, aluminum is the preferred material for the metal foil. The metal foil preferably has a thickness between 1 [mu] m and 20 [mu] m, but thicker sheets can also be used.

The micromachined bulk body is preferably a semiconductor or ceramic body that may include integrated circuits such as CMOS devices. The integrated circuit may provide the electronic functions necessary for operation of the MEMS device. These functions may include detecting and measuring electrical parameters such as voltage, capacitance, resistance, current, or various other electrical parameters. In addition, the integrated circuit will provide a voltage across the membrane and backplate.

In other applications, the integrated circuit may provide a frequency selected from a frequency, an RF frequency, or an acoustic frequency applied to the electrodes of the device. Logic circuits can be integrated to control the operating mode of the micromachined device. An amplifier will be included to amplify the measured parameters as described above. Operations using other computers required for operation of the MEMS device or its surroundings may be performed in an IC in a bulk body.

In another embodiment, securing the membrane to the bulk body may be accomplished by ultrasonic bonding. By this step, the film is in electrical contact with the contact pads arranged on the upper surface of the bulk body. The adhesion position on the film may be on a suspension member extending from a planar member or a planar member, and preferably located on the suspension arm pad at the outermost end of the suspension arm.

In an embodiment, a method of manufacturing a MEMS device includes the following steps:

Fixing and pressing the foil to the processing frame before cutting;

Performing the cutting while the foil is fixed to the processing frame;

Moving the membrane to a bulk body with the aid of a treatment frame;

Fixing the membrane to the bulk body;

The process frame falls off the membrane and the membrane is cut and separated from any remaining foil that is not part of the membrane.

In this embodiment, the metal foil is fixed to the processing frame and pressed before cutting. Preferably, the fixing takes place in such a way that the film can easily fall off in the next step. The frame is used to process a single film as well as an array of structured films in one step from the metal foil.

The cutting is done while the foil is fixed to the processing frame. At this stage, the film is sequentially cut and the film is at least partially cut away from the remaining foil. The remaining anchoring structure is preferred to fix the cutting film to the remaining foil and then fix it with the treatment frame. This facilitates the transfer of the film to the bulk body with the aid of the processing frame. The membrane is secured to the bulk body while connected to the treatment frame.

In the final step, the film falls off the processing frame. At this stage, the connecting structure still present is cut or broken, so that the membrane is separated from any remaining foil that is not part of the membrane.

The processing frame includes a plate of a hard material such as glass or metal. The plate is preferably an array of openings, each opening providing a region that accommodates only one membrane. The openings may be cut-outs or have a limited depth.

According to the embodiment, the micromachined device is designed and used as a very small microphone with an integrated IC. In this application, the membrane is excited by acoustic vibrations due to incoming sound. The vibration is detected by measuring an electric parameter which is changed by the vibration of the film. This parameter will be the voltage or capacitance between the two electrodes, the first electrode being in the film and the second electrode being integrated in the backplate.

In another embodiment, the micromachined device is designed and used as a tunable capacitor. In this application, the membrane is configured to function as a movable electrode capable of moving along a direction perpendicular to the surface of the planar member and in a direction away from the second electrode integrated on the back plate. The movement of the film can be initiated by the electrostatic force generated by the voltage applied to the two electrodes.

The variable capacitor can be adjusted to have at least two different capacitances, one of which is a basic capacitance without the force affecting the film. The second capacitance will be in the position closest to the counter electrode on which the membrane is moving and is now integrated on the back plate. The variable capacitance is continuously adjusted so that any position between the two extreme positions may be used to provide the desired capacitance of the variable capacitance. One or more sets of standoff structures may be formed in the bulk body between the membrane and the backing plate. As the voltage between the membrane and the backplate increases, the membrane may collapse onto another set of standoffs, thereby obtaining several discrete capacitances.

In another embodiment, the device is designed and used as a switch. Here, movement of the film may also be used. At the end of the movement, contact is made between the membranes at the contact points on the bulk body.

In all applications, it is preferred that the second electrode integrated on the back plate be electrically separated from the film by at least one separation layer on the second electrode.

Hereinafter, the present invention will be described in detail with reference to the description of the embodiments and the accompanying drawings. The drawings are schematically shown for purposes of illustration only. Some dimensions can be distorted. Therefore, it is impossible to obtain a ratio of any dimension or size directly from the drawing.

Figure 1 shows a schematic cross-sectional view of a MEMS device including a bulk body (BB) and a membrane (MM) mounted thereon. In the figures, the bulk body BB has a flat surface but is not necessary in the apparatus according to the invention. The membrane (MM) is a metal foil laser-cut to the desired shape required for a given application. The membrane mainly comprises a planar member (PM) arranged in parallel on the surface of the bulk body (BB) with a large surface area.

In the peripheral region of the membrane (MM), the plane arm of the suspension arm pad or membrane itself is fixed to the bulk body at the membrane connection point (MCP).

In Fig. 1, the membrane connection point is located at the top of the anchor means AN projecting from the surface of the bulk body BB. The membrane connection point is at the same level as the surface of the bulk body (BB).

Figure 2 shows a schematic plan view at the top of the membrane showing the membrane structure in more detail. The planar member PM of the membrane MM is shown here as a circular region, but is not limited to this shape.

There is provided a suspension arm SA which is connected to the periphery of the planar member PM. The suspension arm may be formed of bends and / or strips located in the plane of the planar member PM. In Fig. 2, the suspension arm is formed of three linear portions and surrounds the angle between each two portions to form the letter "Z" by three portions. The suspension arm will also include rounded corners.

The suspension arm SA provides a flexible connection between the planar member PM and the suspension arm pad SP used to secure the suspension arm to the bulk body BB. The suspension arm SA will also function as a spring that provides a flexible connection of the planar member. The spring will apply and maintain the planar member PM at the base position relative to the surface of the bulk body.

The suspension arm SA is as short as possible but long enough to provide flexibility and can be made sufficiently to secure the planar member PM. At the ends of all suspension arms, the suspension arm pads SP have a width that provides a sufficient area to allow a reliable bonding of each suspension arm pad SP to the surface of the bulk body BB at each membrane connection point (MCP) It may be a widened portion of the arm.

Figure 3 shows a micromachined device implemented with a microphone. In this embodiment, the bulk body comprises a semiconductor body SB on top of which a stack of trailing layers BL is deposited to form a rigid structure. The termination layer BL will be a layer that is essentially present on top of the CMOS device integrated in the semiconductor body SB. Otherwise, the trailing layer BL is provided to form an appropriate mechanical stiff structure including only electrically conductive lines and regions.

In the semiconductor body SB, an integrated circuit (IC) is formed. The termination layer (BL) mainly comprises a layer of insulating material such as an oxide or nitride or any other insulating inorganic material, and a metal that can be deposited and structured by known methods. At least one through contact TC is formed through a terminal layer that provides electrical conductive connection from the terminals of the IC to the contact pads on the surface above the end layer BL. Other structures may be a conductive or insulative structure arranged and patterned in the trailing layer (BL).

The entire bulk body BB including the trailing layer and the semiconductor or ceramic body SB is structured to form a depression in the semiconductor body SB. The bottom of the depression is formed by a semiconductor or ceramic material or a cover member LM that closes or covers the depression from the opposite side of the bulk body as shown in the figure.

The back plate portion SP is formed by a plurality of end layers BL. This number will be smaller than the number of end layers in areas other than the back plate, which will make the thickness of the back plate smaller. The depth of the first recess in the upper surface of the tailing layer may depend on the number of layers missing in the backing portion.

In the back plate portion BP, the back plate holes VH are arranged to connect the second recesses of the semiconductor body with the free regions on the back plate portion. At the back plate portion, at least one electrically conductive layer (CL) is arranged and arranged to be separated from the surface of the back plate portion, preferably near the top surface of the back plate or by the insulating layer. The conductive layer CL forms the electrodes of the microphone and is preferably connected to the integrated circuit (IC) in the semiconductor body SB by respective electrical connections such as a conductive line and a through-contact TC.

The resonance space BV will be formed between the depressions of the end plates BL, back plate BP and semiconductor body SB and the bottom will be covered by the cover member LM.

The cutting film MM is fixed on the upper portion of the end layer BL so that the planar members PM of the film MM are arranged at a distance on the back plate portion. The membrane is secured by bonding each suspension pad (SP) to each metallic pad on the surface of the tailing layer. The membrane MM operating in the microphone as shown preferably includes a ventilation hole for equalizing the static pressure difference between the resonance space BV and the atmosphere above the plane member PM. However, this opening is omitted so that venting is performed in the region where the membrane is supported by the stand-off structure.

Figure 4 shows a top view of a processing frame (HF), viewed from above, holding a metal foil during cutting and transferring the cutting film to a wafer on which a plurality of MEMS devices are performed after cutting. The processing frame HF includes a plurality of openings OP, each opening having a diameter slightly larger than the diameter of the film. The diameter of the opening may be between 1 mm and 3 mm.

The metal foil MF can be fixed so that it can be loosened (HF) to the processing frame at the fixing point FP by bonding, for example using an adhesive. Laser cutting of the metal foil will be done while the metal foil is fixed to the processing frame, for example, using an adhesive. Alignment of the bulk body in the membrane may be facilitated by alignment protrusions FP if matching holes or recesses are structured in the bulk body bb.

Figure 5 shows a schematic cross section of a micromachined device designed for use as a switch. Here again, the MEMS device includes a bulk body BB and a membrane, the planar member PM shown in the figure. The planar member PM is fixed to the anchor means AN arranged on the surface of the bulk body BB by a spring element SE formed by a suspension arm (for example, see Fig. 2). In the bulk body BB, at least one conductive layer is electrically used to form the backplane BP connected to the terminal T2 arranged on the top or bottom surface of the backplane BP. The plane member PM is connected to any position of the apparatus, preferably to the top of the anchor means AN or to another terminal T1 arranged on top of the bulk body BB. Preferably, both the conductive layer CL and the planar member PM are electrically connected to the contact areas of the same surface of the bulk body BB by respective contact lines and through-contacts. The planar member PM and the conductive layer CL form two electrodes to which a voltage is applied.

The movement of the planar member PM, which is fixed to the surface of the bulk body flexibly, and the movement of the planar member PM thus fixed flexibly to the conductive layer CL, induce an electrostatic force. The contact point CP1 on each planar member and the contact point CP2 on the surface of the bulk body are brought into contact with each other when the planar member PM moves with respect to the bulk body BB so that the planar member PM and the bulk body BB And the third terminal T3 connected to the contact CP2, thereby closing the switch.

5, the contact point CP1 on the bottom surface of the planar member PM may be electrically separated from the planar member, but may be separate from the anchor means AN or each contact pad (not shown) on the surface of the bulk body As shown in FIG.

Figure 6 shows another embodiment of a membrane (MM) having suspension arms (SA) comprising straight and curved portions. The number of the suspension arms is not limited to three but may be more or less.

The MEMS device according to the present invention is not limited to any embodiment shown in the drawings or described therein. The inventive device may differ from the above-described embodiment in actual structure or actual dimension. With the exception of the cutting membrane, the micromachined device is any device known in the art and will be the same as known devices except for the membrane. The present invention can achieve the advantages described above by combining a micromanic structure and a cutting film.

AM: Anchor means
BB: Bulk body
BL: End layer
BP: back plate
BV: resonance space
CL: conductive layer
CP: contact point
FP :: array overhang
HF: Processing frame
IC: Integrated Circuit
MCP: Membrane contact point
MM: Just
OP: opening
FM: Planar member
SA: suspension arm
SB: Semiconductor body
SP: Suspension arm pad
T1 to T3: Terminals
TC: Through-contact
TL: Terminal line
VH: back plate hole

Claims (18)

Micromachining bulk body (BB); And
A membrane (MM) secured to the bulk body,
The film is laser cut from a flat sheet of metal and bonded to the bulk body,
The film may be,
A planar member (PM); And
And a suspension arm (SA) extending laterally from the plane member,
Wherein the suspension arm ends at a suspension arm pad (SP) associated with the bulk body. delete The method according to claim 1,
A semiconductor body or a ceramic body SB integrated with an integrated circuit (IC);
A stack of end layers (BL) deposited on top of the semiconductor body; And
Further comprising a conductive back electrode (CL) arranged on the opposite side of said membrane to one of said end layers,
Wherein the bulk body is formed by the tailing layer and the semiconductor body, and the integrated circuit is electrically connected to the rear electrode and the membrane through a through-contact TC through the tailing layer, respectively. The method of claim 3,
A first depression located on the top surface of the stack of end plates (BL) and covered by the membrane (MM);
A second depression located in the semiconductor body or the ceramic body (SB) side by side with the first depression and forming a resonance space (BV); And
Further comprising a micromachining backplane hole (VH) guided through the tailing layer and connecting the resonant space to a space above the micromachining backplane. ≪ RTI ID = 0.0 > 1 < / RTI > to a method for fabricating a MEMS device,
Providing a metal foil;
Laser cutting said foil to produce a flat film (MM);
Providing a micromachined bulk body (BB) for the apparatus; And
Transferring the membrane to the bulk body and securing the membrane to the bulk body,
The film may be,
A planar member (PM); And
And a suspension arm (SA) extending laterally from the plane member,
Wherein the suspension arm ends at a suspension arm pad SP coupled to the bulk body. 6. The method of claim 5,
Wherein the step of securing the membrane to the bulk body comprises ultrasonically bonding the membrane to a contact pad arranged on the upper surface of the bulk body (BB). The method according to claim 5 or 6,
The foil is fixed to the processing frame (HF) before cutting,
The cutting is performed while the foil is fixed to the processing frame,
The film is transferred to the bulk body with the aid of the processing frame,
The membrane is secured to the bulk body,
Wherein the processing frame is separated from the membrane such that the membrane is cut and separated from any remaining foil that is not part of the membrane. 8. The method of claim 7,
Wherein said processing frame (HF) comprises a plate of rigid material, said plate having an array of openings (OP) each providing an area for one film. 6. The method of claim 5,
Wherein the laser is focused on a surface of the metal foil with a spot diameter of 1 占 퐉 to 50 占 퐉. 6. The method of claim 5,
Wherein a metal foil having a thickness of 1 占 퐉 to 50 占 퐉 is used. The method according to claim 1,
Wherein the MEMS device is designed to be used as a micro-microphone together with an integrated IC. The method according to claim 1,
Wherein the MEMS device is designed for use as an adjustable capacitor. The method according to claim 1,
Wherein the MEMS device is designed to be used as a switch. The method according to claim 1,
A semiconductor body or a ceramic body SB having no integrated circuit (IC);
A stack of end layers (BL) deposited on top of the semiconductor body; And
Further comprising a conductive back electrode (CL) arranged on the opposite side of said membrane to one of said end layers,
Wherein the bulk body is formed by the terminal layer and the semiconductor body. Micromachining bulk body (BB); And
A membrane (MM) secured to the bulk body,
The film is laser cut from a flat sheet of metal and bonded to the bulk body,
A semiconductor body or a ceramic body SB integrated with an integrated circuit (IC);
A stack of end layers (BL) deposited on top of the semiconductor body; And
Further comprising a conductive back electrode (CL) arranged on the opposite side of said membrane to one of said end layers,
Wherein the bulk body is formed by the tailing layer and the semiconductor body, and the integrated circuit is electrically connected to the rear electrode and the membrane through a through-contact TC through the tailing layer, respectively. ≪ RTI ID = 0.0 > 1 < / RTI > to a method for fabricating a MEMS device,
Providing a metal foil;
Laser cutting said foil to produce a flat film (MM);
Providing a micromachined bulk body (BB) for the apparatus; And
Transferring the membrane to the bulk body and securing the membrane to the bulk body,
The foil is fixed to the processing frame (HF) before cutting,
The cutting is performed while the foil is fixed to the processing frame,
The film is transferred to the bulk body with the aid of the processing frame,
The membrane is secured to the bulk body,
Wherein the processing frame is separated from the membrane such that the membrane is cut and separated from any remaining foil that is not part of the membrane. ≪ RTI ID = 0.0 > 1 < / RTI > to a method for fabricating a MEMS device,
Providing a metal foil;
Laser cutting said foil to produce a flat film (MM);
Providing a micromachined bulk body (BB) for the apparatus; And
Transferring the membrane to the bulk body and securing the membrane to the bulk body,
Wherein the laser is focused on a surface of the metal foil with a spot diameter of 1 占 퐉 to 50 占 퐉. ≪ RTI ID = 0.0 > 1 < / RTI > to a method for fabricating a MEMS device,
Providing a metal foil;
Laser cutting said foil to produce a flat film (MM);
Providing a micromachined bulk body (BB) for the apparatus; And
Transferring the membrane to the bulk body and securing the membrane to the bulk body,
Wherein a metal foil having a thickness of 1 占 퐉 to 50 占 퐉 is used.

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