DE2630640A1 - Piezo-resistive absolute pressure transducer - has flexible silicon integrated circuit resistors mounted in pressure cell - Google Patents

Abstract

The piezo-resistive pressure transducer consists of an integrated circuit chip formed from N-type Silicon with P-type resistance elements. Connections to the resistors are made via the metallisation layer to gold wires (19). The underside of the chip is machined away to form a recess (23) so that the wafer becomes a flexible membrane. Mechanical distortion of the resistor elements due to pressure changes will produce a corresponding change in their resistance value. A ceramic back plate (7) is welded to the chip and an isolation layer of anodised ceramic or anodised aluminium separates the cell from a metal base plate (10). All seals for the connectors (12) and central tube (15) are of glass. For use as an absolute pressure transducer, the inner space (23) is evacuated and the tube sealed off.

Description

Piezoresistive pressure measuring cell The invention relates to a pressure measuring cell according to the preamble of claim 1. Such cells are used for measuring and Used to monitor hydraulic and pneumatic pressures.

Frequently, but without limitation to the present subject matter of the invention, piezoresistive pressure measuring cells consist of a semiconductor circuit board, in particular made of silicon, using mechanical or photochemical processes the circuit board on its back over the larger part of its surface is provided with a recess to the thickness of the circuit plate so far to reduce that its flexibility in terms of the formation of a platelet membrane is increased.

Covering the back of the circuit board and its recess a second plate is attached in a fluid-tight manner, creating an absolute pressure measuring cell is created.

If, on the other hand, the second plate has a hole, which makes a connection to the recess of the circuit board produces, so is one Can be used as a reference pressure measuring cell.

Absolute and reference pressure measuring cells produced in this way are now built into different transducer housings to get a pressure sensor. It is widely used in electronics (Zias et al. Low Gost Gransducers Dec 4, 1972), the pressure sensor described, the measuring cell built into a hybrid circuit. The contacts between the thin-film layers of the measuring cell and those from the pressure chamber The leading conductor tracks of the hybrid are produced by means of welded gold wires. The structure for the reference pressure measuring cell contains two pressure inlets.

A pressure inlet leads to the rear via a hole in the hybrid plate the membrane of the measuring cell, which is glued tightly over this hole. The second Pressure inlet leads directly to the front panel. The disadvantage here is that the measuring cell and with it the electrical connections are exposed to the pressurized fluid. A seperation of the pressure fluid by means of a separating membrane and a pressure-transmitting oil filling can only be done with an additional housing. This kind of separation requires large, very elastic racing membranes, which are disadvantageous in terms of enlargement of the pressure sensor and are unsuitable for negative pressure measurements.

In an article by il. W. Keller in Measuring + Testing (No. -2 and 3 1974) a piezoresistive pressure sensor has been described where an absolute pressure measuring cell is built into a measuring head housing with glass feedthroughs. The measuring head is with a welded membrane closed, with oil through a filler screw has introduced into the measuring head that the Neßdruck from the membrane to the silicon membrane transmits. This results in certain advantages, such as high low frequency thanks to the smallest Distance between pressurization as well as silicon membrane and a very small volume of oil thanks to the compact arrangement in the measuring head, which makes the installation of a Steel membrane allows the use of the exceptions in all non-toxic Media and also allowed for negative pressure measurements.

The object of the invention is to create a compared to the prior the technology-improved pressure measuring cell, which is both universal in a pressure sensor is applicable for absolute pressure measurements as well as reference pressure measurements, namely with the smallest space requirement and while maintaining a stable structure. Achieved this is indicated by the identification part of claim 1.

Through the subject matter of the invention, the desired universal Achieve applicability in pressure sensors of various types, so that for the most diverse Types of pressure sensors only a single universal pressure measuring cell is required, which can be easily exchanged if necessary.

This gives advantages in the production of large numbers and also for repairs.

Developments of the invention according to claims 3-8 relate to special designs of pressure sensors using an inventive Pressure measuring cell.

The invention is explained in more detail below with reference to the drawing. The figures show: FIG. 1 an exemplary embodiment of a pressure measuring cell according to the invention Axial section, Fig. 2 the pressure measuring cell of Fig. 1 in plan view, with a fluid-tight attached Schxatskappe is omitted for the sake of clarity, Fig. 3 shows an embodiment of a pressure sensor using a pressure measuring cell 1, 2 in axial section, FIG. 4 shows an embodiment that is modified from FIG example of a pressure sensor in detail during the manufacturing process, in an axial section, which is significantly enlarged compared to FIG. 3, FIG. 5 shows an exemplary embodiment a pressure sensor designed with respect to FIG. 3 with a built-in plug contact base, in axial section, FIG. 6 shows an exemplary embodiment which is modified from FIG. 5 of a pressure sensor with laterally led out plug contacts, in axial section, Bigo 7 is another embodiment of a pressure sensor with laterally led out Socket contacts, also in axial section, in the drawing are the various Embodiments for similar or equivalent components of the better The same reference numbers are always used for the sake of clarity.

According to Fig. 1, 2, a pressure measuring cell consists of two silicon wafers. One plate is a circuit plate 1, e.g. made of n-doped silicon, with an integrated circuit comprising p-type resistors 2, which by means of metal thin film layers 3 to be contacted. These thin film layers 3 lie on an insulating glass layer and are open at locations 5 of the contact.

Usually several such circuit chips 1 simultaneously produced in the wafer association and the circuit plate 1 after the manufacturing process for the integrated circuits separated from each other by diamond disks. the Circuit platelets 1 pre-machined in this way are shaped like a blind hole on the rear side worked out. Various methods can be used successfully for this process, as set, discharge using an ultrasonic drill bit with the addition of an abrasive or boring with a diamond cutter. Through this process becomes the middle one Part of the circuit board 1 is designed to form a board membrane 6. The circuit Plate 1 is now tightly joined to a second silicon plate, the back plate 7. A gold-silicon eutectic soldering process or a connection with low-melting glass solders is used. The back plate 7 is After use, provide a hole 8 in the whole or in the middle. The resulting Structure with a whole back plate 7 is an absolute pressure measuring cell, the one with one Hole 8 in the back plate 7 is a reference pressure measuring cell. With the absolute pressure measuring cell the outside space is tightly separated from the inside of the cell. A change in the External pressure causes a mechanical tension in the platelet membrane 6, on the the resistors 2 are arranged so that these mechanical stresses as possible cause large and easily assignable resistance changes. The reference pressure measuring cell is used to process pressures that change on both sides. The use the same requires pressure separating devices0 It is also known that the circuit chips 1 can be worked out in the wafer bond by etching methods on the back. on what the wafer thus processed is connected to a second silicon plate, and that only then are the finished cells separated from the wafer assembly using diamond saws will.

A completed pressure measuring cell comprises a pressed glass bushing Consists of a full metal base washer 10 into which the base pin will be 13 or a group of base pins 13, a hole 11 is punched in which the melted Glass 12 fixes the base pins 13 to the base washers 10 and isolates them in the center of the circular base washer 10, a hole 14 is provided into which a lead-through tube 15 is melted in isolation. At the outer edge of the base plate 10 is to Acceptance of an O-ring or a metallic ring or flat seal, a sealing groove 16 recessed in a ring. The measuring cell 17 is by means of an epoxy or solder connection 18 tacked to the feed-through tube 15. A tight epoxy connection is made in such a way that that viscous epoxy resin by applying a vacuum at the other end of the duct 15 is sucked against an interior 23 of the measuring cell 17.

With a gold wire ultrasonic welding system, thin gold wires are made 19 welded to the contacting locations 5 of the circuit board 1, which with a Tweezer welding to be welded to the base pins 13. To isolate the Measuring cell 17 from the plate 10, to the setting of the measuring cell 17 and to protect the gold wires 19 an insulating particle 20 is installed, which the measuring cell 17 on the sides, where there are no wires 13, and a bottom with a hole for the separation of the measuring cell 17 and base washer 10 contains. The lateral version of the insulating particle 20 protrudes about 0.2 mm beyond the surface of the measuring cell 17.

An insulating cap 21 surrounds the internal structure of the measuring cell 17 and is held both laterally and in depth by the insulating particle 20. The gold wires 19 are thus protected. The lateral socket through the insulating particle 20 prevents them from being pressed onto the front plate of the measuring cell 17 The insulating particle 20 is made of anodized Ceramic material or anodized aluminum manufactured.

A reference pressure measuring cell is required for use as an absolute pressure sensor 17 produced according to the preceding description, then the interior 23 of the measuring cell 17 evacuated through the duct 15 and the duct 15 tightly closed. Furthermore, the glass lead-through tube 15 is so short that the Hole 14 can be omitted. The measuring cell 17 is attached to the insulating particle with an adhesive 20 and this is glued to the base plate 10.

Compared to other mounts for pressure measuring cells, the one described has Construction especially the advantage of a simple and space-saving installation for many Types of pressure measurements. This is particularly evident from the dark version of the application in piezoresistive pressure sensors. In terms of manufacturing, the structure brings price advantages, since the base plate 10 can be made with a punching tool and thus suitable for mass production. Further technical advantages resulting from the Separation of the pressure measuring cell and transducer body are shown below in application examples set out. It should be understood that the invention also includes other methods of manufacture of the measuring cells, for example if the resistors are made with other semiconductor manufacturing processes, such as by epitaxial layers or by means of a vapor deposition or sputtering process, getting produced; or leave, for example, if the technology under development is lost Siliconon-Saphire (SOS) makes the production of sapphire measuring cells possible.

Bigo 3 shows the application of a pressure measuring cell in a pressure sensor. The pressure sensor comprises a measuring cell 17, a housing 31 and a threaded ring 32. The housing 31 is formed at the rear to form a hexagon 28 has an external thread 33 and a sealing ring 34 for screwing in and sealing a (not shown) pressure vessel and an internal thread for receiving the threaded ring 32. A membrane 35 is welded or sealed onto the end face of the housing 31 soldered on.

Since the membrane 35 must be very thin (about 0.05 mm), must be at a Membrane welding can be worked with a protective welding ring 37. Known is a weld in which the membrane 35 is between an annular end face of the housing 31 and the welding ring 37 is clamped and the weld laterally total circumference nt is. Such welded membranes have disadvantages. For one The membrane 35 must function properly, free of mechanical stresses with the Body, otherwise it changes it slightly under the influence of temperature. Such voltage changes cause pressure changes in the interior of the housing 31, which are registered by the pressure sensor as an error measurement. But now it is at such welded membranes inevitable that by the during the welding occurring high temperature differences in the welding piece during cooling mechanical Tensions are caused. Another unfavorable factor is the fact that the inside between the membrane 35 and the welding ring 37 is a thin gap arises in which dirt can accumulate, which reduces the stress state of the membrane 35 in turn can influence.

In contrast, a soldered connection according to FIG. 4 has the advantage that that the entire housing 31 has the same temperature during the process. aside from that the solder can be chosen so that the working temperature of the solder is at the annealing temperature the steel membrane lies. This teaches careful cooling Tension-free mounted membranes 35 during the soldering process. The housing 31 has a centering shoulder 42 in which the membrane 35 and a centering ring 43 are held will. The membrane 35 is held by the centering ring 43 by means of a steel band 45, which is welded to a second steel band 46 under mechanical pretension, pressed onto an approximately 0.3 mm wide and 0.2 mm high annular membrane shoulder 44.

Between the centering shoulder 42 and the membrane shoulder 43 there is a 0.2 mm wide and just as deep trench in which a solder ring 47 is inserted. While During the soldering process, the solder shoots between the membrane 35 and the membrane shoulder 4Z, the membrane 35 and the centering ring 43, as well as the centering ring 43 and the centering shoulder 42. This guarantees double tightness and a defined membrane holder between the membrane 35 and the centering ring 43. The solders are 30 / kl sp in protective gas as well as VH 950 have been successfully used in vacuum. As a material for the housing. 31 and the membrane 35 is made of stainless steel (German material standard no. 1.4306). After the soldering, the centering ring 43 is machined back to the level of the centering shoulder 42.

The assembly of the pressure sensor according to FIG. 3 proceeds as follows. The measuring cell 17 is provided with a copper seal 29 and is inserted into the housing 31 The tightening ring 32 is pushed using a special key, the four protruding Has rods that engage holes 27 of the tightening ring 32 until a full turn screwed in before the stop.

Now the housing 31 is placed in a vessel, which is evacuated and then is filled with degassed silicone oil. The vessel is placed in an ultrasonic bath for a few minutes placed, which on the one hand the residual degassing, on the other hand the oil inlet in a measuring cell room 26 between the membrane 35 and the measuring cell 17 accelerated. Eventually that will Vacuum flooded again, the vessel opened and the tightening ring with the special key so tight that between the Housing 31 and the measuring cell 17 a perfect seal is created. With a maximum roughness of the sealing surfaces one micrometer and with soft-annealed copper seals 29 can do this manage with small forces of attraction. Now the Neßzelleraum 26 is with the Oil 25 filled, which the measuring pressure, which acts on the membrane 35, from this the measuring cell 17 transmits.

This pressure sensor produced in this way can be installed in a pressure vessel and used to measure pressures, with the connection to the resistors 2 via the glass lead-through wires protruding from the back of the body using a simple Soldered or plug connections can be produced. However, such a pressure sensor will provided with a plug, the plug contacts become the socket pins 13 connected with flexible, insulated wires, which are soldered in the open state. Then the connector housing and housing are pushed into one another and welded.

In the structure of Fig. 5, a pressure sensor is through a plug body 92 taken, and the socket pins 13 are released directly from plug contacts 94. Of the Installation is carried out so that first the socket pins 13 are at the correct distance from the plug contacts 94 can be solved. An inner connector part 95 is separated from the connector body 92. This pre-assembly is pushed into the connector housing 92 and then in an enclosure 96 and a connector inner part socket 97 glued. The connector body 92 will eventually screwed into the housing 91, filled with oil and tightened.

A pressure sensor manufactured in this way with a plug is suitable especially for absolute pressure sensors. Should the same structure be used for reference pressure sensors the equalization pressure or reference pressure must be in the interior of the transducer 98 are performed, which is in a humid reference pressure atmosphere to Short circuits in the electrical connections. This problem would go through the structure according to FIG. 6 solved. The housing is divided into two parts here - namely an outer housing 50 and membrane housing 51. The outer housing 50 has a threaded connection at the front 57 to accommodate a pressure nipple. A shoulder 58 at the end of the thread prevents the nipple can press on the membrane 35. The membrane housing 51, consisting of a holder 51 and the membrane 35, with the measuring cell 17 in the outer housing 50 and fixed with a tightening ring 32 in the outer housing 50 after the oil has been filled. This fixation and a sealing ring 59 is both a seal between Outer housing 50 and membrane housing 51 as well as between the membrane housing 51 and the back plate 7 made. A plug 60 is laterally inserted into the outer housing 50 screwed into a threaded hole provided for this purpose. A connector housing 61 is against the outer housing 50 is sealed with a steel gasket 62.

The glass lead-through wires 13 are plugged into the plug contacts 94 and soldered to these. The wires 13 are to be guided so that they are not with a spacer ring 55 or a reference nipple 56 come into contact. Well will the spacer ring 55 pushed in; the connector 60 is milled out throughout. An O-ring 65 is inserted over the glass lead-through tube 15. Now the reference nipple 56 screwed in, which can be easily tightened via a hexagon socket 66. The reference nipple 56 presses on the tightening ring 32 via the spacer ring 55 and thus secures this screw connection. A pressure calibration tube 67 of the reference nipple 56 has a conical widening 68 at the bottom for receiving the O-ring 65. The length of the pressure equalization pipe 67 must be designed so that this does not the plate 53 of the built-in element pushes open and that still a perfect seal of the O-ring 65 is guaranteed. A flat seal 69 from one elastic Material lies between the reference nipple 56 and the outer housing 50. It seals the interior of the transducer from the reference pressure chamber.

In operation of the pressure sensor of Fig. 6, the reference pressure is through the pressure equalization tube 67 of the reference nipple 56 and through the glass duct 15 passed to the rear of the silicon membrane 6. Such a structure is suitable thus for pressure measurements in which the pressure fluid is the membrane 35 and the reference pressure fluid do not attack the platelet membrane 6. It can also be used for differential pressure measurements take place by a thread in the reference nipple 56 for receiving an ambient pressure different reference pressure is installed.

However, the structure described can be modified with simple changes can also be used for differential pressure measurements of fluids that attack silicon. Fig. 7 shows the formation of the rear part of the structure of FIG. 6 for the Differential pressure transducer. The reference pressure nipple 56 of FIG. 6 is divided into a differential diaphragm body 75 and a threaded nipple 76. The differential diaphragm body 75 forms with the inner part of the measuring cell and the glass lead-through tube 15 one with oil 81 filled space, which is tightly sealed by the O-ring 65. For assembly the outer housing 50 with the built-in pressure sensor connected to the plug and the differential diaphragm body 75 placed back in a vessel that evacuates and then filled with oil. The vessel is opened again and the differential membrane body in the oil 75 pushed into the outer housing 50, after which the threaded nipple 76 is firmly in the body 50 is screwed. The differential diaphragm body 75 presses over the spacer ring 55 on the tightening ring 32 and secures this screw connection. Between the threaded nipple 76 and the differential diaphragm body 75 a metallic flat seal 77 is inserted, the creates the seal of the reference printing medium when tightening. For sealing of the threaded nipple 76 opposite the outer space, a flat seal 78 is inserted, which is pressed between the outer housing and the threaded nipple 76 during the tightening will. The threaded nipple 76 is inserted laterally in the outer housing 50 Hexagon socket locking screw 80 fixed.

This is to prevent a pressure nipple from being unscrewed the threaded nipple 76 of this is released.

When manufacturing absolute pressure transducers according to the structure of 6, the outer housing 50 is sealed at the rear with a closed disk, which again presses on the tightening ring 32 via the spacer ring 55 and thus this Screw connection secures.

It is understood that in the interests of cheaper manufacture some or all of the components described above are also made of plastic material instead can be made of metal, in particular flat gaskets and sealing rings.

Claims (8)

Claims Piezoresistive pressure measuring cell consisting of at least one layered Resistance-containing circuit board, which has a cell wall in the form of a Platelet membrane, a mechanical cell support and several of each other insulated electrical connection cables and cable holder for production a connection to the resistor, characterized in that the cell and Line holder consists of a flat base plate (10), which is in axial Molded glass feedthroughs embedded base pins (13) with the necessary radial spacing and in the necessary number around the cell circumference, and that the circumferential area of the base washer is designed as a sealing surface. 2. Cell according to claim 1, characterized in that in the middle of the base plate (10), a feed-through tube (15) is melted and insulated with glass is. 3. Pressure sensor using a pressure measuring cell according to one of the Claims 1 or 2 with a housing which shields the pressure measuring cell from a measuring fluid, characterized in that the housing (31) is on the side facing the measuring pressure with a membrane (35) and on the opposite side through the base washer (10) is completed that the space formed here, in which the pressure measuring cell was added is filled with an insulating incompressible fluid and that the housing a fastening element (tightening ring 32) for connecting the base washer with the housing contains. 4. Pressure sensor according to claim 3, characterized in that the fastening element is a plug body (92). 5. Pressure sensor according to claim 3, characterized in that the housing consists of two parts, namely an outer housing (50) and a membrane housing (51). 6. Pressure sensor according to claim 5, characterized in that the outer housing (50) has a hole on the side that receives a mechanical holder through which isolated electrical connections are routed into the outer housing, where they are with the base pins (13) of the pressure measuring cell are connected. 7. Pressure sensor according to claim 6, characterized in that in the Outer housing (50) is attached to a reference nipple (56) with a pressure equalization tube (67) is, which is an interior of the outer housing along with the electrical connections of the Seals socket pins (13) from the external environment and an outer space of the outer housing connects to the back of the platelet membrane (6). 8. Pressure sensor according to claim 6, characterized in that in the Outer housing a threaded nipple (76) and a differential diaphragm body (75) for sealing the interior of the outer housing from the exterior and from a reference pressure fluid are attached and that the differential diaphragm body with the duct (15) as well as the platelet membrane (6) forms a tightly sealed space, which with a incompressible, insulating fluid is filled.