RU89240U1 - DIAMOND PRESSURE SENSOR - Google Patents

Abstract

A diamond pressure sensor comprising a first silicon wafer on which shrink columns are located, and a polycrystalline CVD diamond sensing element bonded to said columns, characterized in that the heat shrink columns are made of polyurethane and the sides of the first silicon wafer and the sensing element face each other covered with a metallization layer, while the sensitive element is made by applying a film of polycrystalline CVD diamond on the surface of the second silicon wafer and making holes in the latter by etching it from the opposite side.

Description

The utility model relates to the design of a diamond pressure sensor in the field of electronics and can be used in various industries for measuring pressure when exposed to elevated temperature, ionizing radiation, and chemical aggressive environments.

Known designs of capacitive pressure sensors. The principle of operation of these sensors is based on a change in the capacitance of the capacitor from the applied load on one of the capacitor plates (1).

A known design of a capacitive pressure sensor (2). The pressure sensor contains a lower capacitor electrode, consisting of a silicon substrate, in which a membrane is formed with a sequentially located epitaxial layer of calcium fluoride, over which a metallization layer is located through the air gap, which is the upper capacitor electrode deposited on a silicon plate welded to the silicon epitaxial layer.

The sensor operates as follows.

When pressure is applied to the membrane formed in the highly doped silicon substrate and which is the lower electrode of the capacitor, it bends, changing the distance between the lower electrode and the upper one, which is the metallization layer of the second silicon wafer, and thus changes the capacitance. In this case, in proportion to the change in capacitance, the output signal changes in a special measuring circuit in which the sensor is included. A change in the output electrical signal is proportional to the movement of the membrane, which, in turn, is proportional to the pressure causing this movement.

The disadvantages of the known designs (2) are:

- a relatively limited temperature range of performance;

- low radiation resistance;

- not significant chemical resistance.

The expansion of the measurement ranges of the pressure sensor can be achieved by making the membrane in the form of a diamond film.

The use of diamond films with specially introduced impurities as semiconductor materials is described in (3).

The closest analogue of the claimed utility model is a diamond pressure sensor containing a first silicon wafer on which heat-shrink elements are located, and a sensitive element made of polycrystalline CVD diamond, bonded to these heat-shrink elements (4).

Polycrystalline CVD (Chemical Vapor Deposition) diamond is widely known (see, for example, (4).

The specified diamond sensor has a wide range of measurements, it is universal. However, the breadth of the range and the versatility of the specified diamond pressure sensor adversely affects the accuracy of the measurements. Moreover, in some cases, it is required to carry out accurate measurements of any one parameter.

The technical result, the achievement of which is aimed at creating a utility model, is to increase the accuracy of measurements while maintaining a wide range of measurements.

The technical result is achieved by the fact that in a diamond pressure sensor containing a first silicon wafer on which heat-shrink elements are located, and a sensitive element made of polycrystalline CVD diamond, bonded with the heat-shrink elements, according to the utility model, the heat-shrink elements are made of polyurethane, and facing each other to each other, the sides of the first silicon wafer and the sensitive element are coated with a metallization layer, while the sensitive element is made by applying a polycr film -crystal CVD diamond on the surface of the second silicon plate and the openings in the final etching it from the opposite side.

The utility model is illustrated in the drawing.

Figure 1 shows a diamond pressure sensor disassembled, a General view, a perspective view;

Figure 2 shows in the manufacturing process of the diamond pressure sensor the first silicon wafer before applying the metallization layer, side view;

Figure 3 shows in the manufacturing process of the diamond pressure sensor the first silicon wafer after applying a layer of metallization (aluminum), side view;

Figure 4 shows in the manufacturing process of the diamond pressure sensor the first silicon wafer after applying a layer of metallization (aluminum) and welding of an aluminum electrode, side view;

Figure 5 shows in the manufacturing process of the diamond pressure sensor a second silicon wafer before applying a metallization layer (aluminum), side view;

6 shows a second silicon wafer during manufacturing of a diamond pressure sensor after applying a layer of polycrystalline CVD diamond on one side of it with a thickness of 12 μm, and on the other side of it a layer of polycrystalline CVD diamond with a thickness of 3 μm (etching mask), side view ;

Figure 7 shows in the process of manufacturing a diamond pressure sensor a second silicon wafer after the laser beam forms a sensing element in the form of a cantilever of polycrystalline CVD diamond and conducting silicon etching mask, top view;

In Fig.8 is the same, section aa of Fig.7;

Figure 9 is the same section AA after the laser beam is formed of a sensing element in the form of a cantilever of polycrystalline CVD diamond, conducting a silicon etching mask and applying a metallization layer (aluminum) to the cantilever of polycrystalline CVD diamond, 12 μm thick;

Figure 10 is the same section aa after welding the aluminum electrode;

11 shows a manufactured diamond pressure sensor, parts of which are connected by heat-shrinkable polyurethane elements (columns) (cross section).

12 shows an assembly of a diamond pressure sensor, a perspective view;

On Fig depicts a structural diagram of a system for recording parameters of a diamond pressure sensor.

The diamond pressure sensor 1 contains a first silicon wafer 2, a metallization layer 3 of the first silicon wafer 2, for example of aluminum, with an electrode 4, in particular also made of aluminum, heat-shrinkable elements (columns) 5 made of polyurethane (figure 1) . In addition, the diamond pressure sensor contains a second silicon wafer 6 with an opening 7 therein, a polycrystalline CVD diamond sensing element 8 in the form of a polycrystalline CVD diamond film. The sensor element 8 in the form of a polycrystalline CVD diamond film is coated with a metallization layer 9 of the sensor element, for example, aluminum. An electrode 10 is connected to the metallization layer 9 of the sensing element, in particular also made of aluminum (Fig. 1). All of the above elements are interconnected during the manufacturing process, which is carried out in the following order.

First, take the first silicon wafer 2 (figure 2) and put on it a layer of metallization 3 (aluminum) (figure 3).

After that, the second silicon wafer 6 (Fig. 5) is coated with a polycrystalline CVD diamond sensing element 8 in the form of a 12 μm thick polycrystalline CVD diamond film, and on the other side of the second silicon wafer 6, a polycrystalline film 11 (or layer) (mask) is applied CVD diamond with a thickness of 3 μm (Fig.6). Next, a sensing element 8 is formed with a laser beam and silicon etching of the second silicon wafer 6 from the reverse side thereof is carried out on a film 11 (mask) of polycrystalline CVD diamond 3 μm thick). After that, a metallization layer 9 (aluminum) is applied to the sensitive element 8, which is a film of polycrystalline CVD diamond with a thickness of 12 μm (Fig. 9).

For the final assembly of the diamond pressure sensor, the electrode 4 is first welded to the metallization layer 3 (Fig. 4), and the electrode 10 to the metallization layer 9 (Fig. 10), and then fastened together using heat-shrinkable elements 5 made of polyurethane (in more detail, the manufacturing process diamond pressure sensor is described below).

12 shows an assembly of a diamond pressure sensor in a perspective view. The fluid, the pressure of which must be measured, is supplied to the hole 7 using the tube 12 with the outlet 13. The diamond pressure sensor has a cover 14.

On the indicated Fig.12 shows the first silicon wafer 2, on which the metallization layer 3, which is the conductive lining of the capacitor, and the heat-shrinkable elements 5 (columns), designed to separate the lining of the capacitor shrink polyurethane film). This part of the diamond sensor plays the role of the base (otherwise this part can be called the “lower base”, “the lower part of the diamond pressure sensor). On the second silicon wafer 6 there is an active sensing element 8 in the form of a membrane with a metallization layer 9, which is the second lining of the capacitor (otherwise this part can be called the “upper plate”, “the upper part of the diamond pressure sensor).

The principle of operation of the diamond pressure sensor is based on a change in the capacitance of the capacitor formed by the metallization layer 3, which is stationary on the first silicon wafer 2, and a movable metallization layer 9, located on the sensing element 8 when the pressure of the fluid, for example, gas or liquid, changes through the opening 7 acts on the sensing element 8, bending it. Metallization layers 3 and 9 form the capacitor plates.

In the absence of fluid pressure on the sensing element 8, the metallization layer 9 located on it is parallel to the stationary metallization layer 3. When the fluid is supplied through the tube 12 from the action of the pressure of the fluid on the sensing element 8, it will bend. Along with it, the metallization layer 9 located on the sensitive element 8 will bend. The distance between it and the fixed metallization layer 3 will change, which leads to a change in the capacitance between the movable metallization layer 9 and the fixed metallization layer 3.

This change will be recorded and converted into code in the converter capacity-code 15 (Fig.13). After that, the code will be sent to the device 16 for managing and collecting information, and from there to the personal computer 17.

Polycrystalline CVD diamond film is the main elastic element in the diamond pressure sensor from which the sensitive element 8 is made. Due to its unique properties such as extremely high hardness, high thermal conductivity, transparency in a wide optical range, large resistivity, an increase in measurement accuracy is achieved while maintaining wide range of measurements.

The applicant considers it necessary to pay attention to the following feature of the claimed device.

The use of an elastic sensing element 8 made of a CVD polycrystalline diamond film deposited on a silicon wafer made it possible to use standard technological equipment for the manufacture of microelectronics products when developing the manufacturing technology.

A deep anisotropic etching process of silicon was developed to fabricate the sensitive element 8 from a polycrystalline CVD diamond film. The uniqueness of the properties of a synthetic diamond film, namely, high chemical resistance to any acids and alkalis, made it possible to use it as an elastic element, as a stop for deep etching, and as a mask for deep etching of silicon.

Further, the applicant considers it necessary to dwell in more detail on the manufacturing technology of the diamond pressure sensor, in particular, on the installation of gas-phase deposition of diamond films.

The source of microwave power is magnetron 1, generating at a frequency of 2.45 GHz. Energy is fed through the waveguide to the reactor, where a discharge is ignited in the region above the substrate 5, on which the diamond film is deposited. The deposition process is monitored using optical electron microscopy 6 and other equipment. The estimated duration of the process is 4 hours.

This information is beyond the scope of the utility model, is not its subject and therefore is not disclosed in detail.

An important step in obtaining and using diamond materials was made with the development of technology for the growth of diamond materials from the gas phase, which does not require high pressure. It is plasma "thin-film" technology that allows you to get high-quality films. In this process, carbon atoms formed in the plasma volume during the dissociation of hydrocarbon molecules, most often methane CH4, under certain conditions, condense on the surface of the substrate into a diamond crystal lattice. An environment with a high content of chemically active radicals and ions will be created by excitation in the gas mixture of any type of discharge - glow, microwave, arc or others. An important role in this method is also played by the interaction of the generated gas-discharge plasma with the surface on which the material is deposited.

In the tasks of creating microelectronic devices based on diamond, the most interesting are diamond films of a sufficiently high quality, obtained in a microwave plasma. The diamond film is deposited during a chemical reaction on polished silicon substrates in a direct current discharge plasma initiated in a mixture of hydrogen and methane. The pressure of the gas mixture is 10 kPa, the discharge voltage is 700 V, the substrate temperature is determined by the discharge current and ranges from 700 to 1100 ° C.

The polycrystalline CVD diamond film used to make the diamond pressure transducer was obtained in a similar manner.

Specific example.

A CVD diamond film 12-14 μm thick was deposited on the front side of a KEF silicon wafer (4, 5) with a diameter of 76 mm. This film is strong enough to make a round membrane for a diamond pressure transducer.

A polycrystalline CVD diamond film of a thickness of 2-3 μm was deposited on the reverse side of the silicon wafer. This film was used as a mask during the process of deep anisotropic etching of silicon.

The synthetic diamond film was deposited on a diamond synthesis unit at low pressures. The synthesis process is based on the decomposition of methane in a mixture of hydrogen and the subsequent deposition of diamond on a heated substrate. The deposition rate of a polycrystalline diamond film was 2-3 μm / h.

As noted earlier, the principle of operation of a diamond pressure sensor is based on a change in the capacitance of the capacitor formed by a fixed plate (a fixed metallization layer) and a "moving metallization layer on the sensitive element of the diamond sensor, when the pressure of the fluid changes.

The sensor can be manufactured as a result of the following basic technological operations:

- chemical treatment of semiconductor and diamond wafers;

- applying a synthetic diamond film to a silicon wafer;

- formation of topology on the surface of a diamond film by a laser method;

- deep etching of silicon;

- application of metallization layers;

- assembly of diamond pressure sensor elements.

In the manufacture of the SE (sensitive element) of a diamond pressure sensor from a diamond film deposited on a silicon wafer, a combination of planar technology with other technologies was used, consisting in the use of deep etching of silicon, to obtain the main sensitive element of the diamond sensor: sensitive element 8 (membrane).

As noted earlier, the use of elastic CE from a polycrystalline CVD diamond film deposited on a silicon wafer made it possible to use standard technological equipment for the manufacture of microelectronics products when developing the manufacturing technology.

To obtain a membrane from a CVD diamond film, a process of deep anisotropic etching of silicon was developed. The uniqueness of the properties of a synthetic diamond film, namely, high chemical resistance to any acids and alkalis, made it possible to use it as an elastic element, as a stop for deep etching, and as a mask for deep etching of silicon.

In developing the technological route for manufacturing diamond pressure sensors, the physical and chemical properties of diamond, such as:

- high hardness and chemical resistance (taken into account during the operations of topology formation and chemical etching);

- diamond graphitization during high-temperature treatments (used in the development of chemical treatment);

- low adhesion to diamonds of various materials (taken into account when developing the technology of deposition of metals and insulating materials on the surface of diamond plates).

Elements of the diamond pressure sensor were created on the fabricated structure: diamond film-silicon-diamond film.

The laser beam was formed from two sides of the structure; the problem of combining the topology of the upper and lower sides of the plate was solved by calculation and reference to the zero point.

Since a synthetic diamond film has unique properties, namely, it is chemically stable in almost all acids and alkalis, the formation of a topology is possible only using ion etching processes or laser "drawing" of diamond sensor elements.

As repeatedly noted earlier, the sensitive element of the diamond pressure sensor is a diamond film equipped with a metallization layer with a thickness of the order of 12 μm, located on a fixed base of monolithic silicon.

The second part of the sensitive element, which plays the role of the second lining of the capacitor, is a silicon base with a metallization layer in the form of an aluminum film sprayed over the surface with a wire contact removed beyond its limits.

Thus, the diagram of the diamond pressure sensor assembly is a sandwich of two plates, articulated by polyurethane gaskets, polymerized under conditions of elevated temperature and pressure.

Obviously, the nominal capacitance values in such structures depend on the overall dimensions of the constituent parts, the overlapped metallized areas and the physico-mechanical properties of the applied dielectric materials.

In this case, the upper plate has dimensions of 7.0 × 7.0 × 0.4 mm, and the lower 7.0 × 8.0 × 0.4 mm.

The formation of the lower plates begins with the application of metallized coatings on the working surfaces of standard silicon wafers, the manufacture of topological patterns on the front sides of future crystals and reference marks for separation. The following is the separation of the plates into crystals on a diamond scraper "Almaz-M" followed by the separation of the plate into individual crystals breaking. After attaching the external leads by welding, by means of ultrasonic microwelding, segments of a gold wire ø25 μm to an aluminum film with a thickness of the order of 0.8 μm with further amplification by the conductive composition of the silver-containing contact K-12B, the lower plates are ready.

The manufacture of the upper parts of the sensitive elements begins with the cutting of silicon wafers on the original workpiece. For example, 18 crystals with a size of 7 × 7 mm are placed on a blank of 21 × 42 mm in three rows of six pieces each. This is important because in the manufacturing process there is a two-way alignment operation without end-to-end alignment marks. Those. Snap must be made to one corner of a symmetrical rectangle. Thus, a silicon wafer with “thick” and “thin” layers of a diamond film deposited on its surface enters the laser cutting operation in the form of a rectangle. It is fixed on the stage of the laser technological installation in a strictly fixed position. To the source of laser radiation, i.e. a thin layer of diamond coating should face the output lens. The control unit (coordinate-moving device) of the installation ensures the accuracy of movements along two horizontal axes by means of step motors with a resolution of 2 μm, and vertically with a resolution of 1 μm. In this case, the vertical feed tracks the depth and speed of penetration, focused at a point ø50 microns, of laser radiation deep into the material being processed. The reference point or zero point is activated by a single laser pulse and is subsequently tracked automatically by the control unit. The outline of the contour is set by software methods and reproduced by laser radiation, starting from the point of zero point. Further, using reference to the reference point, in concentric circles with a maximum diameter of 2.0 mm, the masking coating of all 18 elements is destroyed at the sites of subsequent etching of the silicon base. The next transition, the plate is contoured around the entire perimeter and cut through the laser through the required number of passes. If you turn the plate upside down with a thick layer of diamond coating and combine the zero point using the binding, you can divide the plate into crystals in a single cycle. The plates go to the deep etching operation in a mixture of hydrofluoric and nitric acids with the addition of sulfuric acid and heated solution, if necessary, and then, after the silicon diaphragm is completely cleaned of silicon residues, they are transferred to the operation of vacuum deposition of metal layers and the formation of contact pads . On the operation of attaching the wire leads by ultrasonic microwelding methods and conductive glue, the process of forming the main element of the diamond pressure sensor ends.

By deep chemical etching of silicon, an elastic sensitive element of a diamond pressure sensor was obtained. Etching was carried out over the entire thickness of the silicon wafer, in our case it is 380 ... 450 microns. The mask was a thin (2 ... 3 μm) film of polycrystalline CVD diamond deposited on the back of a silicon wafer. The etching was carried out through round holes in a thin film made with a laser. The diamond film on the front side of the plate played the role of a “stopper” for deep etching.

Upon completion of the formation and manufacture of parts of the sensitive elements of diamond pressure sensors, including the processes of vacuum metallization of surfaces, the assembly of diamond pressure sensor assemblies follows. The first preparatory operation is to equip the components of the nodes of the diamond pressure sensors with external wire leads. Considering the fact that the upper metallization layer, on silicon bases with a diamond film, consists of aluminum and has a total thickness of about 0.8 microns, the most reliable way to connect at the contact points is ultrasonic microwelding of well-welded metals. In this case, it is an aluminum wire along an aluminum film or a gold wire along an aluminum film. To assemble the first prototype models, the gold annealed wire Zl 999.9 ø25 μm in accordance with GOST 7222-75 was chosen as conductors. Welding was carried out on a subject two-coordinate micro-table with a rotation device mounted on the pantograph of a semiautomatic device UZSM 2.5 ultrasonic microwelding. The plate is placed on a micro table and is fixed with a clamp in a position convenient for work. With a special clamp on the table, a piece of gold wire of the required length is attached, and, by means of the moving mechanism of the table, it is oriented with a needle-tool fixed in a magnetostrictor concentrator. Welding modes are set within: power level (on the UZG block 2.5) of 6-8 divisions in the toggle switch position “more”, which corresponds to 1.6 W; welding duration 45-55 ms (type on the keyboard UZG 2,5); electrode loading of the order of 120-150 g (control by GS 0-150 gramometer); Max. pulse current 7-8 × 10 μA (microammeter “control pulse” when a button is pressed). By manipulating the pantograph of the UZSM 2.5 semiautomatic table, the object stage and the alignment mechanism, and observing all this through a binocular microscope, the working end of the instrument and the attached end of the wire lead are combined with the contact area on the crystal. Then welding is performed, for which the button on the pantograph control handle is clamped (in this case, the hub with the needle - the tool is lowered to the alignment position), the exact alignment is made, and when the button is released, the tool is automatically lowered and ultrasonic welding is performed. Welding of wire conductors to all plates of diamond pressure sensors intended for assembly takes place in the same way. In order to improve the contact, and, first of all, its mechanical strength, the contact point with the weld point is closed with a drop of Kontolol K-12B conductive adhesive based on dispersion silver. To do this, a wooden technological needle is applied to the contact points with a sample of carefully mixed multicomponent glue, after which it is polymerized in a temperature-controlled cabinet type SNOL 3.5 × 3.5 × 3.5 at a temperature of about 80 ° C for 4 hours. At the next stage of assembly, alternately, the lower plates are laid on the base of the device for mounting sensitive elements in an amount convenient for operation. Samples of rectangular polyurethane gaskets with approximate dimensions of 1 * b * h = 2.0 × 1.0 × 0.3 mm are placed on the peripheral areas of the plates that are free of metallization. From above, in accordance with the connection diagram, a second plate with a sensitive zone is laid and a constant clamping force is created through a common platform. A device with loaded elements is placed in a thermostat and at a temperature of 120-135 ° C, it settles within 3.5-4 hours. After extraction from the thermostat, cooling and visual control, including the strength of the connection of the terminals of the nodes of the diamond sensors are transferred to the certification and measurement of nominal capacities.

The sensor assembly is mounted on the table by gluing “Super EPOXY” glue or aquasint, which provides reliable fastening of both the table in the case and the diamond sensor on the table.

After the adhesive composition has completely dried, the free ends of the wire leads should be combined with the corresponding external leads of the housing and contacted. This operation can be carried out on a semiautomatic device of thermocompression microwelding type EM-429M. The modes of welding the gold wire leads to nickel gilt contacts with split electrodes with the following parameters were developed: loading on the electrode 250-300 g, decay and rise time of the pulse 5 ms, welding 20 ms, output voltage 1.3 V. Welding can be done without heating the subject table.

To perform welding, it is necessary to fix the case with the sensitive element located in it on the semiautomatic object table, so that it is most comfortable to observe the process along the visualization channel. Using the pantograph movement mechanism and the lever of the mechanism of combination, the desired arrangement of articulated parts is set. In accordance with the pre-established sequence diagram, when you press the button located on the pantograph handle, the tool lowers to its original position, and then, after the buttons are aligned and released, microwelding occurs in one of the two welding channels in the above modes. At the end of the connection process, visual inspection and marking, the output parameters of the diamond sensors should be checked by measuring the capacitance, but when in contact with the output legs of the housing. Further, the hulls are transferred for sealing.

As a basic design for diamond pressure sensors, metal-glass cases 3301.8 according to KYUYAL 431433.023-02 TU (TO-8) manufactured by the MARS plant (Torzhok) were selected. The overall dimensions of the cases: weight 13.6 g and external ø12.75 with a total height of 15 mm (together with the KYUYAL433684.001-05 cylinder), are optimal. At the same time, the completion of the buildings was required by the introduction of a table for the most rational use of the internal volume.

The design of the selected type of TO-8 provides two output air tubes, one of them is a pumping ram, by which, when an overpressure is applied, the detectors are certified. Tightness in the volume of the body is ensured by landing the balloon on the base of the body and by gluing with epoxy or K-400 glue. The tightness test is carried out by pumping through a plug on a helium leak detector of the type PTI-10. The plug must be soldered and closed with a protective cap after using the cold deflection mechanism.

Manufactured diamond pressure sensors according to the results of measurements on a digital meter L.C.R. E7-8s have a capacitance without load of 12 pF.

In the proposed design of the diamond sensor, the membrane sensitive element is made of a polycrystalline CVD diamond film. In diamond, the coefficient of thermal expansion is 4-6 times lower than in silicon, radiation resistance is 100 times higher, and chemical resistance is the highest, which allows you to expand the measurement range of the diamond pressure sensor, improve the accuracy of measurements while maintaining a wide range of measurements.

Sources of information taken into account when preparing the application:

1. J. Ash and others. Sensors of measuring systems, translation, ed. A.S. Obukhova, vol. 1, M., Mir, 1992, p. 383;

2. Patent of the Russian Federation No. 2251087, class G01L 9/12, published. 04/27/2005;

3. Ralchenko V., Konov V., CVD-diamonds. Application in electronics. Electronics. Issue 4/2007;

4. US Patent No. 6,613,601, cl. 438/50, published. 09/02/2003 (prototype).

Claims (1)

A diamond pressure sensor comprising a first silicon wafer on which shrink columns are located, and a polycrystalline CVD diamond sensing element bonded to said columns, characterized in that the heat shrink columns are made of polyurethane and the sides of the first silicon wafer and the sensing element face each other covered with a metallization layer, while the sensitive element is made by applying a film of polycrystalline CVD diamond on the surface of the second silicon wafer and making holes in the latter by etching it from the opposite side.