Pressure detector

Abstract: A good quality passive-state film is formed on a gas-contact face of a diaphragm of a pressure detector using a sensor chip to prevent corrosion on, or water content emission from, or catalytic action at a gas-contact face, thereby improving production quality in a semiconductor manufacturing process and providing high accuracy pressure detection. The passive-state film is formed on the gas-contact face of the diaphragm when the diaphragm is mounted on a diaphragm base. The diaphragm base is then fixedly secured to a sensor base in which a sensor chip is housed and a pressure transmitting medium is sealed in a gap between the sensor base and the diaphragm base.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to pressure detectors of a type utilising a sensor chip as a sensor element or a strain gauge; such pressure detectors being mainly used to detect pressures of highly corrosive gas lines, and the like, in semiconductor manufacturing processes. Heretofore, pressure detectors using sensor chips (as pressure-sensor elements) or strain gauges have been widely utilized to detect fluid pressures inside pipe lines, and the like. US-A-548868 discloses a pressure sensor for use at high temperatures, for instance in a cylinder of an internal combustion engine. The pressure, sensor comprises a hollow cylindrical female base member which is open at one end to receive hollow cylindrical male insert member. Said male insert member accommodates a pressure sensor and is closed at its outer end, that protrudes from the base member, by an integral pressure-sensitive diaphragm. US-A-4303903 discloses a pressure transducer comprising a base member that is formed with a fluid-filled recess in one end. Said recess accommodates pressure sensing means and is closed by a thin, flexible diaphragm that is welded at its edge to the base member. DE-A-4435909 discloses a pressure measuring device comprising a body portion that defines two opposed fluid filled recesses. Each recess is closed by a flexible diaphragm that is welded to the body portion, and the body portion accommodates pressure sensing means that communicate with the recesses via fluid-filled passageways formed in the body portion. US-A-5144843 discloses a pressure sensor suitable for use in hydraulic machines which comprises a flexible, pressure-sensitive diaphragm that is mounted in a retracted portion of a bore formed in a base member. Said diaphragm is adapted to be exposed to hydraulic fluid at its outwardly facing surface and carries pressure sensing means on its internal surface within the bore. US-A-5212989 discloses a pressure sensor suitable for use in a automotive internal combustion engine, which sensor comprises a generally cylindrical body portion that is formed with two opposed recesses that are interconnected by an axial passageway. One of said recesses is closed by a flexible, pressure-sensitive diaphragm which is welded at its edges to the body portion and the other is closed by a sensor base that carries pressure sensing means within the recess. Both recesses on said passageways are filled with a pressure-transmitting fluid. Fig. 5 shows an example of a pressure detector for detecting fluid pressures inside a pipe line, which includes a stainless-steel (SUS 316L) sensor base 1, a sensor chip (a pressure sensor or a semiconductor strain gauge) 2, a diaphragm (SUS 316L) 3, silicone oil 5, a ball 6, a lead pin 7, and the like. In the pressure detector in Fig. 5, an outer peripheral edge of the diaphragm 3 (formed of stainless-steel (SUS 316L), having a thickness of about 50 µm, has been welded to a lower end face of the sensor base 1 by means of laser welding, and, when a fluid pressure B applied to a gas-contact face 3a of the diaphragm 3 is transmitted through the silicon oil 5 to the sensor chip 2, values of four strain resistors formed on the sensor chip 2 are changed to cause a signal proportional to the received pressure B. This signal is output at an output terminal of a bridge circuit composed of the four strain resistors. Further, reference number 16 designates a weld of the diaphragm; and reference number 10 designates a weld of the ball 6. The above-mentioned pressure detector of Fig. 5 can detect fluid pressure inside a pipe line with a high accuracy and a relatively high sensitivity, thus having excellent and practical usefulness. However, many problems which must be solved have remained in this pressure detector, the most important of which is corrosion, such as catalytic activity, or the like, on the gas-contact face 3a of the diaphragm 3. That is, in the pressure detector of Fig. 5, the diaphragm 3 is formed of a stainless-steel (SUS 316L), and a mixed oxide layer of Fe and Cr. having a thickness of about 3nm (30Å), is formed on an electropolished outer face layer of the gas-contact face 3a. However, for a highly corrosive gas such as a halogen based gas including hydrogen chloride (HCl) and hydrogen bromide (HBr) and a fluorine based gas including fluorine gas (F 2 ) and hydrogen fluoride (HF), which are used for semiconductor manufacturing processes, corrosion significantly progresses due to water, and the like, contained in the gas itself, thereby causing a, so-called, metallic contamination. Further, in a pipe line for semiconductor manufacturing, an outgas from the contact face 3a and catalytic activation as well as the corrosiveness of the gas-contact face 3a of the above-mentioned diaphragm are also serious problems, so that the gas-contact face 3a is required to be free of gasout, non-catalytic, and non-corrosive. However, the mixed oxide layer of Fe and Cr formed on the outer face layer of the gas-contact face 3a of the above-mentioned diaphragm 3 is not sufficiently effective to prevent the outgas, causing a large amount of outgas to be released; and, in addition, due to its catalytic action, a self-decomposition of special gases for semiconductor manufacturing is accelerated, whereby various problems arise such as deteriorated product quality. For this reason, where a pressure detector having a construction as shown in Fig. 5 is used to detect pressure in a pipe line handling a highly corrosive gas, such as the above-mentioned halogen based and fluorine based gases, it is required that the diaphragm 3 have on its gas-contact face 3a a so-called chrome oxide passive-state film (Cr 2 O 3 , for halogen based gases) composed of only Cr not containing Fe, having a thickness of tens of nm (hundreds of Å), or a fluoride passive-state film (CrF 3 ,CrF 2 , FeF 2 , FeF 3 , and the like, for fluorine based gases), or a mixed-oxide passive-state film (Al 2 O 3 /Cr 2 O 3 , for ozone gas) composed of mainly aluminum oxide and chrome oxide, thereby protecting the gas-contact face 3a. This is because: the above-mentioned chrome oxide passive-state film is excellent in corrosion resistance to a halogen-based, highly corrosive gas, in prevention of outgas, and in non-catalyst properties; the fluoride passive-state film has a high corrosion resistance to a fluorine based, highly corrosive gas and ozone and is excellent in prevention of outgas, and in non-catalyst properties; and further, the mixed-oxide passive state film composed of mainly aluminum oxide and chrome oxide is excellent in corrosion resistance to an ozone gas having a very strong oxidising ability. In order to form the above-mentioned passive state film composed of 100% chrome oxide, for the diaphragm 3 made of austinitic stainless steel (for example, SUS 316L), it is necessary: (1) to polish the diaphragm 3 using a lapping-polishing method, or the like, so as to allow the outer face to have a microcrystalline structure (a so-called veilubi layer); and (2) heat treat (at 400°C to 500°C for one to ten hours) the diaphragm 3 with oxidising species containing a very small amount of water in a highly reducing atmosphere. In the same manner, in order to form the fluoride passive-state film, it is necessary: (1) to perform a treatment for forming the passive-state film at 200°C to 250°C for one to ten hours in a fluorine gas atmosphere; and (2) to perform a treatment for annealing the passive-state film at 350°C to 400°C for one to ten hours. To form the mixed-oxide passive-state film composed of aluminum oxide and chrome oxide, it is necessary to heat treat (at 400°C to 600°C for one to ten hours) the diaphragm 3 of stainless steel containing about 4% of aluminum with oxidising species containing a very small amount of water in a highly reducing atmosphere. However, because a sensor chip (a pressure sensor) has a heat resisting temperature of about 150°C for the conventional pressure detector shown in Fig. 5, the pressure detector cannot be heat treated at these otherwise desirable, high temperatures. Further, the sensor base 1 and the diaphragm 3 have already been welded in the conventional pressure detector, so that it is difficult to uniformly polish the gas-contact face 3a of the diaphragm 3 at a surface smoothness that a maximum projection value is about 0.7 µm or less, and thus the degree of polishing of the gas-contact face 3a of the diaphragm 3 is hardly uniform. Still further, for the conventional pressure detector, the weld 16 is positioned on the gas-contact face 3a of the diaphragm 3, so that polishing of the weld 16 brings about a state different from that of non-welded portions, and thus a uniform polished-finish of the weld 16 becomes difficult to achieve. As a result, for the conventional pressure detector, it is difficult to form the passive-state film, composed of 100% chrome oxide, or the fluoride passive-state film on the gas-contact face 3a of the diaphragm 3, so that as a degree of integration of semiconductors increases, various problems arise such as generation of metallic particles caused by corrosion of the gas-contact face 3a of the pressure detector and/or water content release from the diaphragm face; or troubles caused by catalytic action of the diaphragm face, and thus an improvement of product quality becomes difficult to achieve. Problems Solved By The Invention It is an object of this invention to solve the problems described above for conventional pressure detectors; that is, because passive-state films cannot be formed on gas-contact faces of diaphragms of pressure detectors, it is impossible to prevent corrosion of the gas-contact faces of the diaphragms, catalytic action of the diaphragm faces, and water content release from the diaphragm faces. It is a further object of this invention to provide a pressure detector which will not compromise product quality, even when it is used in a semiconductor manufacturing process, in that it provides a diaphragm of a pressure detector with a chrome oxide passive-state film, or a fluoride passive-state film, or a mixed-oxide passive-state film composed mainly of aluminum oxide and chrome oxide on its gas-contact face. SUMMARY OF THE INVENTION According to one aspect of the invention therefore there is provided a pressure detector comprising; a diaphragm base having an end face that defines an opening and a peripheral side wall which extends away from said end face; a diaphragm mounted on said diaphragm base across said opening, said diaphragm having a gas-contacting surface that is coated with a passive-state film; a sensor base that is assembled with said diaphragm base to define a space between the sensor base and the diaphragm; sensor means disposed within said space for detecting deflection of said diaphragm which sensor means comprise (i) a strain gauge member secured to said diaphragm, or (ii) a sensor chip mounted on said sensor base with pressure transmitting means sealed in said space between said diaphragm and said sensor chip; said sensor base and said diaphragm base being configured such that they can be assembled together after attachment of the diaphragm to the diaphragm base to enclose said sensor means; and characterised in that; said diaphragm is dish-shaped, having a peripheral upstanding rim which extends from an outer edge of said gas-contacting surface to provide a diaphragm side wall; and said diaphragm is brazed to the end surface of said diaphragm base and said diaphragm side wall is welded to the side wall of said diaphragm base. The passive state film may be composed of a layer of chrome oxide, fluoride or mixed oxide, the mixed oxide layer being mainly composed of aluminum oxide and chrome oxide. Preferably, when the sensor means of the pressure detector comprise a sensor chip, the diaphragm is about 50µm in thickness. Alternatively, when the sensor means of the pressure detector comprise a strain gauge it is preferred that the diaphragm be about 200µm in thickness. According to another aspect of the invention there is provided a method of making a pressure detector comprising; a) mounting a diaphragm having a gas-contacting surface on a diaphragm base such that said diaphragm extends across an opening formed in an end face of said diaphragm base; b) after step (a), assembling said diaphragm base with a sensor base to define a sensor space between the sensor base and the diaphragm ; and c) mounting sensor means for detecting deflection of said diaphragm within said sensor space, said sensor means comprising (i) a strain gauge attached to an inner surface of said diaphragm or (ii) a sensor chip mounted on said sensor base and a pressure transmitting means sealed in said sensor space; characterised by; d) prior to steps (b) and (c) forming a passive-state film on the gas-contacting surface of said diaphragm; e) brazing said diaphragm to said end face of the diaphragm base; f) after step (e), welding a side wall of said diaphragm defined by an upstanding peripheral rim to a peripheral side wall of said diaphragm base that extends away from said end face. In a pressure detector of the present invention, a desired passive-state film has already formed, in advance, on the gas-contact face of the diaphragm when the diaphragm base (having the diaphragm whose gas-contact face has the passive state film welded thereon) is combined with, and fixed to, the sensor base in which the sensor chip is housed and fixed; so that even where the diaphragm base and the sensor base are welded and fixed at their side wall faces, the desired passive-state film can be formed on the gas-contact face of the diaphragm without adversely affecting, by heating, the sensor chip or the strain gauge member of the strain gauge. As a result, a corrosion of the gas-contact face, water content release from the diaphragm face, and catalytic action of the gas-contact face are prevented, thereby allowing product quality in a semiconductor manufacturing process to be significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS The invention is described and explained in more detail in the drawings. The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating principles of the invention in a clear manner. Fig. 1 is a plan view of a pressure detector of the present invention; Fig. 2 is a vertical sectional view of Fig. 1 viewed along the line II-II; Fig. 3 is an illustrative cross-sectional view showing a pressure detector of the present invention mounted to a gas line; Fig. 4 is a schematic vertical sectional view of a pressure detector comprising strain gauge means; and Fig. 5 is a vertical sectional view of a prior art pressure detector utilising a conventional sensor chip. DETAILED DESCRIPTION OF THE INVENTION With reference to the drawings, the invention will be explained hereinafter. In drawings 1 through 4, corresponding members (members having similar functions) as those shown in the above mentioned prior-art device of Fig. 5 are designated by the same, or similar, reference numbers, although in some cases the members are somewhat different in structure. Fig. 1 is a plan view of a pressure detector of the present invention; and Fig. 2 is a vertical sectional view of Fig. 1 in which a sensor chip is provided as the means for detecting a change in fluid pressure. In the figures: reference number 1 designates a sensor base; reference number 2, a sensor chip (a pressure sensor); reference number 3, a dish-shaped diaphragm; reference number 4, a diaphragm base; reference number 5, silicon oil forming a pressure transmitting medium; reference number 6, a ball of a sealing member; reference number 7, lead pins; reference number 8, a portion where the sensor base and the diaphragm base are welded together; and reference number 9, a portion where the diaphragm and diaphragm base are welded together. The sensor base 1 of Fig. 1 is made of stainless steel, has a chip storage section 1a at a center of a lower face thereof and defines an oil injection hole 1b, a lead pin inserting hole 1c, and the like. A known diffusion type semiconductor pressure transducer is used as the above-mentioned sensor chip (the pressure sensor) 2, wherein a piezoresistance value of the semiconductor changes when subjected to a pressure. That is, the sensor chip 2 has a diaphragm structure and deforms when subjected to the pressure, four resistances being formed thereon by a manufacturing method like that of integrated circuits (IC), so that, when the resistance values of the four resistances, which are connected in a bridge, are changed by the application of the pressure, a voltage signal proportional to the pressure is output to output terminals of the bridge. Although, in this embodiment, a diffusion type semiconductor pressure transducer is used as the sensor chip 2, it should be pointed out that a pressure detecting sensor chip 2 having another structure may be used instead. The diaphragm 3 is made, in a shape of a dish, of stainless steel (SUS 316L) having a thickness about 50 µm. When the pressure detector is assembled, first the diaphragm base 4 and the diaphragm 3 are combined as shown in Fig. 2, and thereafter opposing faces of these two members are welded at the weld portion 9, by a laser welding method, at the side of the diaphragm base 11. The thickness of the diaphragm 3 can be changed according to a range of pressures to be detected by the pressure detector, but a pressure detector of this embodiment for measuring absolute pressures from about 250 N.m -2 to 1.08 x 10 6 N.m -2 (several torrs to 11 kfg/cm 2 ), it is desirable to make the diaphragm 3 with the diameter of 10 mm and being about 50 µm thick. On a gas-contact face 3a of the diaphragm 3 is formed a so-called passive-state film by a known method; and that is, as the outer face layer of the gas-contact face 3a is formed a passive-state film 3b composed of about 100% chrome oxide and having a thickness about 0.02µm (200Å), or a fluoride passive-state film 3b having a thickness about 0.1-0.3µm (1000 through 3000Å), or a mixed-oxide passive-state film mainly composed of aluminum oxide and chrome oxide and having a thickness of about 0.02µm (200Å). That is, for forming the chrome oxide passive state film 3b, first the gas-contact face 3a of the diaphragm is lapping polished to allow the outer face to be of a microcrystalline structure, thereby facilitating transfer of Cr from an inner layer part. Thereafter, the gas-contact face 3a of the diaphragm is heat treated at a temperature 400° to 500° for several hours in a mixture of H 2 of about 3% and Ar, with H 2 O of about 100ppm. Thus, the passive-state film 3b composed of about 100% chrome oxide and having a thickness of about 0.02µm (200Å) is formed. Where the stainless steel which forms the diaphragm 3 is a ferritic stainless steel having a high content of Cr, the above-mentioned polishing treatment may be omitted in some cases. This is because in ferritic stainless steels, a transfer of Cr from an inner layer part takes place relatively easily. For forming a fluoride passive-state film 3b on the gas-contact face 3a of the diaphragm, first the gas-contact face 3a is heat treated at a temperature 200° to 250°C for several hours in a diluted fluorine gas atmosphere to form the fluoride passive-state film. Then, the above-mentioned fluoride passive-state film is annealed at a temperature 350° to 400°C for several hours to stabilise the fluoride passive-state film. The above-mentioned silicone oil 5 of the pressure transmitting medium transmits pressure applied to the diaphragm 3 to the sensor chip 2. A silicone oil which has a low temperature expansion coefficient and a low compression coefficient, and is chemically stable, is normally used. Of course, different pressure transmitting mediums can be used. The above-mentioned ball 6 is used as a sealing member to seal the silicone oil 5 in the oil injection hole 1b, and a bearing steel ball is used for this purpose. A manner of assembling the pressure detector of the present invention, in which a sensor chip is provided as the sensor means, will be explained hereinafter. First a brazing material is interposed between an outer peripheral edge of the diaphragm 3 and a corresponding face of the diaphragm base 4 so that these two members are fixedly secured to each other by brazing. Having interposed the brazing material between these two members, the brazing material is then heated to melt so that the outer peripheral edge of the diaphragm 3 is brazed to the base 4. As a result, the oil 5 does not enter the gap between the two and thus the pressure applied to the sensor chip 2 never varies, but rather is uniform. The diaphragm 3 is then welded to the diaphragm base 4, and, thereafter, a chrome-oxide passive-state film, or a fluoride passive-state film, or a mixed-oxide passive-state film composed mainly of aluminum oxide and chrome oxide is formed on the gas-contact face 3a of the diaphragm 3. Of course the passive-state film 3b could first be formed on the gas-contact face 3a of the diaphragm 3, and then the diaphragm 3 could be welded to the diaphragm base 4. The sensor base 1 is formed, and the sensor chip 2 is inserted thereinto and fixedly secured within the chip inserting hole 1a. Then, the diaphragm base 4, whose diaphragm gas-contact face 3a is covered with the passive-state film 3b, and the sensor base 1 are placed opposite each other, as shown in Fig. 2, and the full circumferences of their side wall faces are welded at the weld portion 8 by a TIG welding method. When the above-mentioned welding 8 is completed, the oil injection hole 1b is used to fill the chip storage section 1a with the pressure transmitting medium (the silicone oil) 5, and thereafter the sealing member (the ball) 6 is welded at 10 to the sensor base 1 to seal in the oil 5. The weld 8 is not on the gas-contact face 3a of the diaphragm 3, so that the gas-contact face 3a can be very uniformly polished, with the result that the oxide passive-state film of 100% chrome can be formed. The pressure detector of the present invention is constructed such that the diaphragm 3 is formed as a separated member. Consequently, the diaphragm is easily formed. The present invention also provides a pressure detector using a so-called metallic strain gauge 16 in place of the sensor chip (the pressure sensor or semiconductor strain gauge) 2. An example of the type of strain gauge used is shown in Fig. 4. That is, to an inside upper face of the diaphragm 3, which has a thickness about 200 µm, is secured a strain gauge member 16a which is made by covering a metallic fine wire, or a metallic-foil resistance wire, with an insulator and forming this in a shape of a film. Mounted to an inside of the sensor base 1 is a bridge circuit (a transducer) 16b for detecting a change in resistance. An inner space of the diaphragm base 4 is not filled with silicone oil or the like. Although in Fig. 4 a metallic strain gage 16 is used in which the strain gage member 16a is separated from the transducer 16b, a strain gauge having a structure which integrates the two into one-piece may also be fixedly secured to the inside, upper face of the diaphragm 3. In assembling a pressure detector of the present invention using a metallic strain gauge 16, of the type shown in Fig. 4, for example, first the diaphragm 3 and diaphragm base 4 are brazed together, as described above. The diaphragm 3 is then welded to the diaphragm base 4 before it is combined with a strain gauge. However, prior to combining the diaphragm 3 with the strain gauge a passive-state film 3b is formed on the gas-contact face 3a of the diaphragm 3; then the strain gauge 16a is fixedly secured to the inside upper face of the diaphragm 3; and finally the diaphragm base 4 and the sensor base 1 are combined with one another and secured together by the welding 8 at their side wall faces. Fig. 3 shows a state in which a pressure detector of this invention is connected to a gas line to detect a fluid pressure, wherein the pressure detector is affixedly and air-tightly secured, via a holding member 12 and a bearing 13, into a mounting hole 15a of a body 15 by screwing a fixture 14 into the body 15. Reference number 17 designates a metallic gasket whose gas-contact face is treated to form thereon a chrome-oxide passive-state film, or a fluoride passive-state film, or a mixed-oxide passive-state film mainly composed of aluminum oxide and chrome oxide. Thus, a fluid pressure B at a flow passage hole 15b is applied through a hole 15c to the gas-contact face 3a of the diaphragm 3, and then transmitted through the silicone oil 5 to the sensor chip 2. The pressure detector of the present invention is constructed such that the diaphragm is formed in a dish shape, with a right-angle cylindrical rim. The diaphragm base and the outer peripheral edge of the diaphragm are brazed to each other. The diaphragm is then welded to the diaphragm base at the side wall face of the diaphragm base, and the passive-state film is formed on the gas-contact face, and then both the sensor base and the diaphragm base are welded together at the side wall face of the diaphragm base. As a result, manufacture of the diaphragm becomes remarkably easy, and at the same time, a good quality passive-state film can be formed on the gas-contact face of the diaphragm without adversely affecting the sensor chip by a high temperature, thereby allowing product quality in semiconductor manufacturing processes to be further improved. Also, because the diaphragm base and the outer peripheral edge of the diaphragm are brazed by a brazing material, so that a variation in pressure detected values due to oil entering to a gap, and the like, become nil, thereby causing labor, for calibration of pressure detector for example, to be significantly reduced. The present invention exhibits an excellent practical usefulness as described above.

Claims: A pressure detector comprising; a diaphragm base (4) having an end face that defines an opening and a peripheral side wall (11) which extends away from said end face; a diaphragm (3) mounted on said diaphragm base (4) across said opening, said diaphragm having a gas-contacting surface (3a) that is coated with a passive-state film (3b); a sensor base (1) that is assembled with said diaphragm base (4) to define a space between the sensor base (1) and the diaphragm (3); sensor means disposed within said space for detecting deflection of said diaphragm (3), which sensor means comprise (i) a strain gauge member (16a) secured to said diaphragm (3), or (ii) a sensor chip (2) mounted on said sensor base (1) with pressure transmitting means sealed in said space between said diaphragm (3) and said sensor chip (2); said sensor base (2) and said diaphragm base (4) being configured such that they can be assembled together after attachment of the diaphragm (3) to the diaphragm base (4) to enclose said sensor means; and characterised in that ; said diaphragm (3) is dish-shaped, having a peripheral upstanding rim which extends from an outer edge of said gas-contacting surface (3a) to provide a diaphragm side wall (11); and said diaphragm (3) is brazed to the end surface of said diaphragm base (4) and said diaphragm side wall (11) is welded to the side wall of said diaphragm base (4). A pressure detector as claimed in claim 1, wherein said passive state film (3b) is composed of a layer of chrome oxide, fluoride, or mixed oxide, the mixed oxide layer being mainly composed of aluminum oxide and chrome oxide. A pressure detector as claimed in claim 1 or claim 2, wherein said sensor means comprise a strain gauge member (16a) and said diaphragm (3) is about 200µm in thickness. A pressure detector as claimed in claim 1 or claim 2, wherein said sensor means comprise a sensor chip (2) and said diaphragm (3) is about 50µm in thickness. A method of making a pressure detector comprising; a) mounting a diaphragm (3) having a gas-contacting surface (3a) on a diaphragm base (4) such that said diaphragm (1) extends across an opening formed in an end face of said diaphragm base; b) after step (a), assembling said diaphragm base (4) with a sensor base (1) to define a sensor space between the sensor base (1) and the diaphragm; c) mounting sensor means for detecting deflection of said diaphragm within said sensor space, said sensor means comprising (i) a strain gauge (16a) attached to an inner surface of said diaphragm (3), or (ii) a sensor chip (2) mounted on said sensor base (1) and a pressure transmitting means sealed in said sensor space; characterised by ; d) prior to steps (b) and (c) forming a passive-state film (3b) on the gas-contacting surface (3a) of said diaphragm (3); e) brazing said diaphragm (3) to said end face of the diaphragm base (4); f) after step (e), welding a side wall of said diaphragm (3) defined by an upstanding peripheral rim to a peripheral side wall of said diaphragm base (4) that extends away from said end face.

Inventors: DOHI RYOSUKE, IKEDA NOBUKAZU, NISHINO KOJU, OHMI TADAHIRO, DOHI, RYOSUKE, IKEDA, NOBUKAZU, NISHINO, KOJU, OHMI, TADAHIRO
Applicants: FUJIKIN KK, OHMI TADAHIRO, FUJIKIN INC., OHMI, TADAHIRO
Application year: 1997
Main classification: G01L9
IPC codes: G01L9, G01L19