Pressure sensor

A pressure sensor has a thin plate diaphragm having a strain detecting section thereon, and a support member for receiving and properly positioning the diaphragm within a stepped bore structure. The pressure sensor with which the strain detecting section is formed on the diaphragm surface is formed by the use of semiconductor manufacture technology by making the diaphragm of the pressure sensor in the form of a thin plate member. The diaphragm and the support member are joined together by diffusion bonding, and heat treatment for this diffusion bonding is also utilized to crystallize the semiconductor strain gauges.

Description 
1. Technical Field 
The present invention relates to a pressure sensor which has a structure 
suitable for mounting to components of hydraulic machines, i.e., hydraulic 
equipment such as hydraulic pipes and couplings (joints) for the hydraulic 
pipes, and which has a diaphragm positioned such that strain gauges in a 
strain detecting section provided on the diaphragm take an optimum 
location for high measurement accuracy, a pressure sensor manufacturing 
method by which the pressure sensor can simply be manufactured in a mass 
quantity by utilizing semiconductor manufacture technology, and to 
hydraulic equipment which is produced with the structure allowing the 
pressure sensor to be incorporated therein in advance for high 
practicability. 
2. Background Art 
Pressure sensors are one sort of sensors contained in the category of 
stress sensors in a broad sense that conceptually includes strain sensors, 
torque sensors, load sensors, etc., and are employed for measuring a 
pressure of a liquid, gas, etc. Such pressure sensors are often used as 
detector means for detecting working hydraulic pressures at various 
mechnical components in hydraulic machines for civil engineering and 
construction, for example. Pressure sensors may have various types of the 
structure. A pressure sensor of the diaphragm type will be described 
below. 
The structure of a conventional diaphragm type pressure sensor is shown in 
FIG. 39. The pressure sensor comprises a metal-made diaphragm base 300 
which is directly subjected to a pressure P, e.g., a hydraulic pressure, 
an insulting film 301 formed by a film forming technique, such as CVD, 
using silane gas or the like, four strain gauges 302 each of which has a 
resistance value changed dependent on a strain of the diaphragm caused by 
the pressure P, thin film conductors 302 serving as terminals for electric 
wiring, and a passivation film 304 which functions as a hermetic 
protection film. The metal-made diaphragm base 300 is functionally divided 
into to two parts. One part is a diaphragm section 305 subjected to the 
pressure P for developing a strain dependent on the magnitude of the 
pressure, and another part is a tubular support section 306 which 
functions to support the diaphragm section 305 and fix the pressure sensor 
at a certain mounting location. The diaphragm section 305 is formed at a 
top position of the tubular support section 306 so as to close one end 
face thereof. The strain gauge 302 and the thin film conductors 303 are 
covered by the passivation film 304 such as a SiN.sub.x or SiO.sub.2 film. 
Wires 307, 307 are connected at their lower ends to the thin film 
conductors 303, 303, respectively, as viewed on the drawing. The other 
ends of the wires 307 are connected to an electrical measuring unit such 
as a voltage meter or ampere meter via lead wires (not shown) for 
electrically measuring a strain developed in the diaphragm section 305. 
More specifically, in the no-load condition where the pressure P does not 
act on the diaphragm section 305, the specific resistances of the strain 
gauges 302 remain unchanged so that no potential difference occurs between 
the wires 307 and 307 and no current flows into the measuring unit. On the 
other hand, when a strain is developed in the diaphragm section 305 upon 
being subjected to the pressure P, the specific resistances of the strain 
gauges 302 are changed to produce a potential difference between the wires 
307 and 307, whereby the measuring unit can determine the pressure applied 
to the diaphragm section 305. 
In the pressure sensor having the structure shown in FIG. 39, the diaphragm 
section 305 and the support section 306 are integrally structured into the 
metal-made diaphragm base 300. Conventionally, however, there has also 
been proposed a pressure sensor in which the diaphragm section 305 and the 
support section 306 are structured as separate members, are disclosed in 
Japanese Utility Model Laid-Open 61(1986)-137242 by way of example. In 
this type pressure sensor, the diaphragm section 305 is formed into a 
metal-made thin plate diaphragm as an independent member by itself, and 
then welded to a metal-made tubular body as a support member. Taking into 
account the situation where the pressure sensor is practically used, the 
support section 306 is required to relate to the object to which the 
pressure sensor is mounted. Accordingly, even in the pressure sensor of 
the type where the diaphragm section 305 and the support section 306 are 
structured as separate members, a support element for supporting a 
diaphragm is indispensable. A separate support member is necessarily added 
to the pressure sensor to finally provide substantially the same structure 
as that of the pressure sensor shown in FIG. 39. Then, the semiconductor 
manufacture technology is applied to a combined assembly of the thin plate 
diaphragm and the tubular member for forming semiconductor strain gauges 
on the upper surface of the diaphragm. 
The strain gauges 302 may be each a metallic strain gauge or semiconductor 
strain gauge. In particular, use of the semiconductor strain gauge has 
recently become widespread because it has a higher gauge rate, develops a 
larger change in the resistance value dependent on small mechanical 
strain, and hence provides higher accuracy in pressure measurement than 
the metallic strain gauge. The strain gauge 302 shown in FIG. 39 is a thin 
film semiconductor strain gauge formed on the upper surface of the 
insulating film 301. The strain gauge disclosed in Japanese Utility Model 
Laid-Open 61(1986)-137242 is also a semiconductor strain gauge, as 
mentioned above. The strain gauge is fabricated, for example, by forming a 
silicon thin film for the gauge, which includes an impurity such as 
phosphor or boron, on the insulating film 301 with the plasma CVD, and 
then patterning the silicon thin film with the photolithography, thereby 
to produce a piezo resistance element of which specific resistance is 
changed when strained upon receiving an external force. The thin film 
conductors as the terminals 303 are fabricated, for example, by forming 
thin films made of a high conductive material, such as gold, copper or 
aluminum, with the vacuum vapor deposition, and then forming patterns 
interconnecting the respective strain gauges 302 with the 
photolithography, thereby to constitute a Wheatstone bridge circuit. As 
described above, the insulting film 301, the strain gauges 302, the thin 
film conductors 303, and the passivation film 304 are all fabricated by 
application of the semiconductor manufacture technology. Thus, the 
semiconductor manufacture technology is utilized in producing pressure 
sensors equipped with semiconductor strain gauges. 
Notwithstanding the above state of art, the pressure sensor having the 
structure of FIG. 39 has faced a problem when directly forming the strain 
gauges 302 or the like on the upper surface of the mental-made diaphragm 
base 300. Specifically, while the mental-made diaphragm base 300 has a 
thickness of about 3-6 mm, the strain detecting section including the 
strain gauges 302 and others is formed on the thin plate with a thickness 
less than 2 mm. Therefore, the thickness of the metal-made diaphragm base 
300 imposes an obstacle to impede sufficient use of the semiconductor 
manufacture technology. Such a problem also occurs in the pressure sensor 
as disclosed in the above-cited Japanese Utility Model Laid-Open 
61(1986)-137242 in which the diaphragm and the tubular body are fabricated 
as separate members. Specifically, when the semiconductor manufacture 
technology is applied to fabricate the strain gauges, the diaphragm and 
the tubular body are combined into the integral structure. As with the 
above-mentioned prior art, therefore, the disclosed pressure sensor has a 
certain substantial thickness, resulting in a similar problem that the 
semiconductor manufacture technology cannot sufficiently be utilized in 
fabricating the pressure sensor. 
There will now be explained another problem wherein the conventional 
pressure sensors have difficulties in keeping high strain detecting 
sensitivity of the strain gauges in the diaphragm due to the specific 
structure thereof and the manufacture method restricted by that structure, 
as well as in positioning the strain gauges, which leads to the reduced 
positioning accuracy. 
In the pressure sensor shown in FIG. 39, the metal-made diaphragm base 300 
is fabricated by machining into a substantially channel-like shape in 
cross section, and the four strain gauges 302 are formed on a strain 
causing area of the diaphragm section 305. Since the strain gauges 302 are 
each formed by the semiconductor film forming technology as a very thin 
film less than/or equal to 2 .mu.m, the diaphragm section 305, require to 
be formed to have a uniform thickness with high accuracy, in order to 
maintain capability of the semiconductor strain gauges 302 which are 
intrinsically endowed with high strain detecting sensitivity. But, it is 
difficult to meet such a requirement by the machining technique currently 
used. 
Further, for the purpose of effectively developing specific high strain 
detecting sensitivity, it is desired that the four strain gauges 302 are 
arranged with possibly maximum distances therebetween in the strain 
causing area presumably defined by the inner diameter of the tubular 
support section 306 on the upper surface of the pressure diaphragm section 
305. With the conventional machining technique, however, round edges 
remain at the ceiling corners of a bore when the diaphragm base 300 is 
bored from the lower side in the drawing, as a result of which machining 
accuracy cannot be enhanced. Therefore, the strain causing area of the 
diaphragm section 305 cannot strictly be defined by only a dimension of 
the inner diameter of the support section 306, making it hard to position 
the strain gauges 302 with high accuracy. This necessarily results in that 
the strain gauges of the pressure sensor manufactured with the 
above-mentioned structure are lowered in positioning accuracy. 
In the pressure sensor as disclosed in the above-cited Japanese Utility 
Model Laid-Open 61(1986)-137242, the thin plates as a diaphragm and the 
tubular body as a support member are fabricated separately, followed by 
welding the thin plate and the tubular body to each other. The strain 
gauges are then formed on the upper surface of the thin plate. The thin 
plate can be machined so as to have a uniform thickness because it is 
singly fabricated from a thin plate member having a strain causing area. 
However, the thin plate is then joined by welding to the tubular body 
fabricated as a separate member, whereupon the strain causing area of the 
thin plate is deformed due to, e.g., heat applied in the welding step. The 
resulting error makes it impossible to strictly define a dimension of the 
strain causing area in the final pressure sensor. Therefore, the strain 
gauges formed on the strain causing area are difficult to position with 
high accuracy, and lowered in the positioning accuracy. 
Considering pressure sensors from the standpoint of the user with much 
importance paid to use of the pressure sensors, there are problems as 
follow. In any case, the structure of a pressure sensor must be 
determined, taking into account circumstances of the location where it is 
to be mounted. In the normal mounted condition of the pressure sensor, the 
support member for supporting the diaphragm section is required to serve a 
double purpose of installing the diaphragm section and protecting it from 
any disturbance, i.e., a deforming force. Taking the conventional pressure 
sensor shown in FIG. 39 from such a viewpoint, since the diaphragm section 
305 and the support section 306 are fabricated integrally into the 
mental-made diaphragm base 300 in advance by manufacturers without 
considering circumstances in which the pressure sensor is to be employed, 
it cannot be said that this type pressure sensor is convenient for users 
who attempt to utilize it. Furthermore, the form of the support section 
306 of the mental-made diaphragm base 300 and the structure of the 
pressure sensor itself are generally standardized by manufacturers and not 
always optimum for circumstances in which the pressure sensor is to be 
employed by the user. 
SUMMARY OF THE INVENTION 
A first object of the present invention is to provide a pressure sensor and 
a manufacture method for the pressure sensor, which sensor has the 
structure that allows a strain causing area to be definitely defined on a 
diaphragm subjected to a pressure, and allows a plurality of semiconductor 
strain gauges each having high detecting sensitivity to be formed on the 
strain causing area with positioning accuracy high enough to fully develop 
their own capability, and by which method the pressure sensor adopting 
that structure can be manufactured in a mass quantity through a simple 
film forming process by effective use of the semiconductor manufacture 
technology. 
A second object of the present invention is to provide a pressure sensor 
which is structured such that a thin plate diaphragm is installed into a 
stepped bore of a metal-made support member to position the diaphragm by 
the stepped bore with high accuracy. The diaphragm is firmly supported by 
the support member in mounting the pressure sensor to hydraulic equipment 
or the like, thereby to make the pressure sensor adaptable for detection 
of a high pressure, and hence which has the optimum structure for mounting 
to a wall of the hydraulic equipment because a fixing force is not 
directly applied to the diaphragm even when the pressure sensor is fixed 
to the equipment wall. 
A third object of the present invention is to provide a pressure sensor 
which is structured such that the pressure sensor has a single thin plate 
diaphragm including a strain detecting section formed of strain gauges and 
others, and different pressures are applied to the opposite sides of the 
diaphragm, and hence which can achieve a differential pressure sensor 
having good response and simple construction with the single diaphragm. 
A fourth object of the present invention is to provide a manufacture method 
for a pressure sensor with which the semiconductor manufacture technology 
is effectively applied to a diaphragm singly fabricated in the form of a 
thin plate, thereby permitting manufacture of a pressure sensor that a 
strain detecting section including semiconductor strain gauges and others 
is formed on a strain causing area of the diaphragm with high positioning 
accuracy, and which can simply manufacture such a pressure sensor having 
high positioning accuracy in a mass quantity. 
A fifth object of the present invention is to provide a manufacture method 
for a pressure sensor with which the pressure sensor can be produced 
through the simplified manufacture process by utilizing the semiconductor 
manufacture technology while also permitting diffusion bonding and 
crystallization of amorphous strain gauges to be performed with single 
heat treatment. 
A sixth object of the present invention is to provide hydraulic equipment 
with a pressure sensor which can be mounted with a simple construction 
that is fabricated into the form presenting no problem in appearance, 
which makes it possible to freely select the position of measuring a 
hydraulic pressure, etc., and which can perform pressure measurement with 
high reliability at the reduced cost. 
A first pressure sensor according to the present invention is constructed 
such that the pressure sensor comprises a diaphragm shaped into the form 
of a thin plate, having a strain detecting section provided on one 
surface, and using at least one surface as a pressure receiving surface, 
and a support member having a larger-diameter bore and a smaller-diameter 
bore formed in continuous and coaxial relation to the larger-diameter 
bore, wherein the larger-diameter bore receives the diaphragm, the inner 
wall surface of the larger-diameter bore determines an installed position 
of the diaphragm relative to the smaller-diameter bore in accordance with 
the positional relationship of limiting a position of the outer edge of 
the diaphragm, the smaller-diameter bore defines a dimension of a strain 
causing area of the diaphragm, a stepped portion formed between the 
larger- diameter bore and the smaller-diameter bore provides a bonding 
surface to be bonded to the diaphragm, and a pressure medium is introduced 
to the pressure receiving surface of the diaphragm placed in the 
larger-diameter bore. 
A second pressure sensor according to the present invention is constructed, 
in addition to the above first construction, such that the diaphragm is 
positioned relative to the smaller-diameter bore by bringing the outer 
edge of the diaphragm into contact with the inner wall surface of the 
larger-diameter bore. 
A third pressure sensor according to the present invention is constructed, 
in addition to the above first construction, such that the diaphragm is 
shaped into the form of a rectangular thin plate, and the diaphragm is 
positioned in accordance with the positional relationship that the inner 
wall surface of the larger-diameter bore limits positions of respective 
apexes of the diaphragm. 
A fourth pressure sensor according to the present invention is constructed, 
in addition to the above first construction, such that the diaphragm is 
joined to the support member by an adhesive. 
A fifth pressure sensor according to the present invention is constructed, 
in addition to the above first construction, such that the diaphragm and 
the support member are both made of a metallic material, and the diaphragm 
is joined to the support member by diffusion bonding the peripheral 
surface of the diaphragm around the outer circumference of the strain 
detecting section to the surface of the stepped portion of the support 
member. 
A sixth pressure sensor according to the present invention is constructed 
such that the pressure sensor comprises two diaphragms each shaped into 
the form of a thin plate, having a strain detecting section provided on 
one surface, and using the other surface as a pressure receiving surface, 
and a support member having two pairs of larger-diameter bores and 
smaller-diameter bores formed in continuous and coaxial relation to the 
larger-diameter bores, wherein each of the two pairs of larger-diameter 
bores receives one of the two diaphragms, the inner wall surface of each 
larger-diameter bore determines an installed position of each diaphragm 
relative to each smaller-diameter bore in accordance with the positional 
relationship of limiting a position of the outer edge of each diaphragm, 
each smaller-diameter bore defines a dimension of a strain causing area of 
each diaphragm, a stepped portion formed between each larger-diameter bore 
and each smaller-diameter bore provides a bonding surface to be bonded to 
each diaphragm, and pressure media under different levels of pressure are 
introduced to the pressure receiving surfaces of the diaphragms placed in 
the larger-diameter bores, whereby the pressure sensor is constituted as a 
differential pressure sensor. 
A seventh pressure sensor according to the present invention is constructed 
such that the pressure sensor comprises a diaphragm shaped into the form 
of a thin plate, having a strain detecting section provided on one 
surface, and using both one surface and the other surface as pressure 
receiving surfaces, and a support member having a larger-diameter bore and 
a smaller-diameter bore formed in continuous and coaxial relation to the 
larger-diameter bore, wherein the larger-diameter bore receives the 
diaphragm, the inner wall surface of the larger-diameter bore determines 
an installed position of the diaphragm relative to the smaller-diameter 
bore in accordance with the positional relationship of limiting a position 
of the outer edge of the diaphragm, the smaller-diameter bore defines a 
dimension of a strain causing area of the diaphragm, a stepped portion 
formed between the larger-diameter bore and the smaller-diameter bore 
provides a bonding surface to be bonded to the diaphragm, and pressure 
media under different levels of pressure are introduced to one surface and 
the other surface of the diaphragm placed in the larger-diameter bores, 
whereby the pressure sensor is constituted as a differential pressure 
sensor. 
A first manufacture method for a pressure sensor according to the present 
invention comprises a diaphragm forming step to form a thin plate 
diaphragm of a metallic material, an insulating film forming step to form 
an insulating film on one surface of the diaphragm near the center 
thereof, a silicon thin film forming step to form a silicon thin film in 
an amorphous state on the upper surface of the insulating film, a heat 
treating step to heat treat the amorphous silicon thin film for 
crystallization, a gauge pattern forming step to pattern the crystallized 
silicon thin film into strain gauges, and a joining step to join the 
diaphragm and a support member for receiving and positioning the diaphragm 
to each other. 
A second manufacture method for a pressure sensor according to the present 
invention is provided by reversing the process sequence of the heat 
treating step and the gauge pattern forming step in the above manufacture 
method for the pressure sensor. 
A third manufacture method for a pressure sensor according to the present 
invention comprises a diaphragm forming step to form a thin plate 
diaphragm of a metallic material, an insulating film forming step to form 
an insulating film over one surface of the diaphragm, a silicon thin film 
forming step to form a silicon thin film in an amorphous state on the 
upper surface of the insulating film, a heat treating step to heat treat 
the amorphous silicon thin film for crystallization, a gauge pattern 
forming step to pattern the crystallized silicon thin film into strain 
gauges, and a joining step to join the diaphragm and a support member for 
receiving and positioning the diaphragm. 
A fourth manufacture method for a pressure sensor according to the present 
invention is provided by reversing the process sequence of the heat 
treating step and the gauge pattern forming step in the above manufacture 
method for the pressure sensor. 
A fifth manufacture method for a pressure sensor according to the present 
invention comprises a substrate fabricating step to fabricate a thin plate 
substrate of a metallic material, the substrate having any desired area 
enough to form a plurality of diaphragms, a mask placing step to place a 
mask on the thin plate substrate for defining spaces in each of which a 
strain detecting section of each diaphragm is to be formed, an insulating 
film forming step to form an insulating film in each of the spaces defined 
by the mask on the upper surface of the thin plate substrate, a silicon 
thin film forming step to form a silicon thin film in an amorphous state 
on the upper surface of each insulating film, a mask removing step to 
remove the mask from the thin plate substrate, a heat treating step to 
heat treat each amorphous silicon thin film for crystallization, a gauge 
pattern forming step to pattern each crystallized silicon thin film into a 
plurality of strain gauges, a severing step to sever the thin plate 
substrate for each set of the plural strain gauges for forming a plurality 
of diaphragms each provided with a strain detecting section, and a joining 
step to join the diaphragm and a support member for receiving and 
positioning the diaphragm. 
A sixth manufacture method for a pressure sensor according to the present 
invention is provided by reversing the process sequence of the heat 
treating step and the gauge pattern forming step in the above manufacture 
method for the pressure sensor. 
A seventh manufacture method for a pressure sensor according to the present 
invention comprises a substrate fabricating step to fabricate a thin plate 
substrate of a metallic material, the substrate having any desired area 
enough to form a plurality of diaphragms, an insulating film forming step 
to form an insulating film on the upper surface of the thin plate 
substrate, a silicon thin film forming step to form a silicon thin film in 
an amorphous state on the upper surface of the insulating film, a heat 
treating step to heat treat the amorphous silicon thin film for 
crystallization, a gauge pattern forming step to pattern the crystallized 
silicon thin film into a plurality of strain gauges, a severing step to 
sever the thin plate substrate for each set of the plural strain gauges 
for forming a plurality of diaphragms each provided with a strain 
detecting section, and a joining step to join the diaphragm and a support 
member for receiving and positioning the diaphragm. 
An eight manufacture method for a pressure sensor according to the present 
invention is provided by reversing the process sequence of the heat 
treating step and the gauge pattern forming step in the above manufacture 
method for the pressure sensor. 
A ninth manufacture method for a pressure sensor according to the present 
invention comprises a diaphragm forming step to form a thin plate 
diaphragm of a metallic material, an isulating film forming step to form 
an insulating film on one surface of the thin plate diaphragm near the 
center thereof, a silicon thin film forming step to form a silicon thin 
film in an amorphous state on the upper surface of the insulating film, a 
gauge pattern forming step to pattern the silicon thin film into a 
plurality of amorphous strain gauges, and a heat treating step to 
concurrently heat treat a support member, the diaphragm and amorphous 
strain gauges for joining the diaphragm having the amorphous strain gauges 
patterned thereon and the support member for receiving and positioning the 
diaphragm to each other by diffusion bonding, as well as crystallizing the 
amorphous strain gauges on the diaphragm. 
A tenth manufacture method for a pressure sensor according to the present 
invention comprises a substrate fabricating step to fabricate a thin plate 
substrate of a metallic material, the substrate having any desired area 
enough to form a plurality of diaphragms, a mask placing step to place a 
mask on the thin plate substrate for defining spaces in each of which a 
strain detecting section of each diaphragm is to be formed, an insulating 
film forming step to form an insulating film in each of the spaces defined 
by the mask on the upper surface of the thin plate substrate, a silicon 
thin film forming step to form a silicon thin film in an amorphous state 
on the upper surface face of each insulating film, a mask removing step to 
remove the mask from the thin plate substrate, a gauge pattern forming 
step to pattern each silicon thin film into a plurality of strain gauges, 
a severing step to sever the thin plate substrate for each set of the 
plural amorphous strain gauges for forming a plurality of diaphragms each 
provided with a strain detecting section, and a heat treating step to 
concurrently heat treat each support member, each diaphragm and the 
amorphous strain gauges for joining each diaphragm having the amorphous 
strain gauges patterned thereon and each support member for receiving and 
positioning each diaphragm to each other by diffusion bonding, as well as 
crystallizing the amorphous strain gauges on each diaphragm. 
A hydraulic equipment with a pressure sensor according to the present 
invention is constructed, in a hydraulic equipment having a wall of which 
inner surface is in contact with a hydraulic fluid, such that a pressure 
sensor installing bore formed to extend from the outer wall surface to the 
inner wall surface of the wall, and a hydraulic fluid introducing bore 
formed in the wall to communicate the pressure sensor installing bore with 
the hydraulic fluid contact surface, wherein a pressure sensor comprising 
a diaphragm provided with a strain detecting section and a support member 
for receiving and positioning the diaphragm is disposed in the pressure 
sensor installing bore, and the support member is fixedly held by a 
retainer member to fix the pressure sensor in the pressure sensor 
installing bore of the wall.

BEST MODE FOR CARRYING OUT THE INVENTION 
Hereinafter, embodiments of the present invention will be described with 
reference to the accompanying drawings. 
In FIG. 1, designated by reference numeral 1 is a pressure sensor unit 
according to a first embodiment of the present invention. The pressure 
sensor unit 1 comprises a metal-made diaphragm 2 having a strain causing 
area at the center thereof, a metal-made support member 3 for holding the 
metal-made diaphragm 2 placed and installed in a lower portion of the 
support member 3, and an electric circuit section 4 disposed in an upper 
portion of the support member 3. Thus, the pressure sensor unit 1 is 
comprised of the metal-made diaphragm 2, the metal-made support member 3 
and the electric circuit section 4 as mentioned above, thereby 
constituting a pressure sensor in a broad sense. In the pressure sensor 
unit 1, a strain detecting section 2A comprised of semiconductor strain 
gauges and others is provided on the upper surface of the metal-made 
diaphragm 2. Thus, the metal-made diaphragm 2 and the strain detecting 
section 2A jointly constitute a pressure sensor 1A in a narrow sense. The 
support member 3 is substantially cylindrical in its external shape with a 
short axial length, and is formed in its portion along the central axis 
with a circular stepped bore 5 partially different in diameter. The 
support member 3 is generally made of a metal. The bore 5 comprises three 
portions; a circular recessed larger-diameter bore 5a formed in the lower 
side, a smaller-diameter bore 5b formed at the center, and a circular 
recessed larger-diameter bore 5c formed in the upper side, as viewed on 
the drawing, these three bore portions 5a, 5c, 5b being formed in coaxial 
positional relationship. The larger-diameter bore 5a provides a space in 
which the metal-made diaphragm 2 is placed and installed, the 
larger-diameter bore 5c provides a space in which the electric circuit 
section 4 is placed, and the smaller-diameter bore 5b provides a space in 
which an electric wiring is inserted. Also, a circular ring-like groove 6 
is formed to surround the larger-diameter bore 5a in the lower surface of 
the support member 3 as shown in FIGS. 1 and 2. 
The diaphragm 2 is disposed in the larger-diameter bore 5a of the support 
member 3, and formed of a metal-made thin plate which is about 0.05-2 mm 
thick and has a square plan shape as shown in FIG. 2 by way of example. 
The diaphragm 2 may be, for example, of a metal such as SUS630 or any 
other rigid plate material. In this example, the diaphragm 2 is fabricated 
such that the diagonal of the diaphragm 2 has a length almost equal to the 
diameter of the larger-diameter bore 5a, whereby the diaphragm 2 is 
tightly fitted to be placed and installed in the larger-diameter bore 5a. 
Furthermore, the diaphragm 2 is firmly fixed at a peripheral portion of 
the upper surface thereof to the step surface of the larger-diameter bore 
5a via a joined portion 7 by diffusion bonding. The diaphragm 2 and the 
larger-diameter bore 5a have their axes aligned with each other in a state 
where the former is installed in the latter. 
With the above construction, the thin plate diaphragm 2 is placed in the 
larger-diameter bore 5a of the support member 3 and, in this state, the 
outer corner edges, i.e., four apexes, of the diaphragm 2 contact the 
inner wall surface of the larger-diameter bore 5a, causing the diaphragm 2 
to be positioned in the larger-diameter bore 5a. As a result, the 
diaphragm 2 is high-accurately positioned in the support member 3 with 
respect to the smaller-diameter bore 5b formed in coaxial relation to the 
larger-diameter bore 5a. With the diaphragm 2 fixedly joined to the step 
surface of the larger-diameter bore 5a, as mentioned before, the remaining 
area of the diaphragm 2 which is not joined to the step surface serves as 
a strain causing area. Since that step surface is determined by the 
smaller-diameter bore 5b, high positioning accuracy of the diaphragm 2 
with respect to the smaller-diameter bore 5b allows the strain causing 
area of the diaphragm 2 to be strictly defined in its dimension by the 
smaller-diameter bore 5b with high accuracy. Thus, the construction of the 
pressure sensor unit 1 according to the present invention makes it 
possible to strictly determined a dimension of the strain causing area in 
the diaphragm 2 by their own structures of the diaphragm 2 and the support 
member 3 which are designed to be adapted for the manufacture process of 
mounting the diaphragm 2 to the support member 3 and the accurate mounting 
thereof. 
In the foregoing, the apexes of the diaphragm 2 are not all necessarily 
brought into contact with the inner wall surface of the larger-diameter 
bore 5a in positioning the diaphragm 2 in the support member 3. Even in a 
state where one or more apexes do not make contact, the strain causing 
area can be defined from the positional relationship relative to the 
smaller-diameter bore 5b, if the apexes of the diaphragm 2 are restricted 
in their positions by the inner wall surface based on the positional 
relationship between the respective apexes and the inner wall surface of 
the larger-diameter bore 5a so that the diaphragm 2 is placed within a 
given region in the larger-diameter bore 5a. Note that the plan form of 
the diaphragm 2 is not limited to a square shape, and may have any other 
circular or polygonal shape. In the case of a circular shape, the 
diaphragm has the circumferential edge. Although the diaphragm 2 has a 
thickness smaller than a depth of the larger-diameter bore 5a in the 
illustration of FIG. 1, both the dimensions can be made equal to each 
other. 
FIG. 3 shows in enlarged scale the structure of the strain detecting 
section 2A formed on the upper surface of the diaphragm 2. As mentioned 
before, the diaphragm 2 and the strain detecting section 2A jointly 
constitute the pressure sensor 1A in a narrow sense. The strain detecting 
section 2A comprises an insulating film 8 formed on the upper surface of 
the diaphragm 2, four semiconductor strain gauges 9 (only two of which are 
shown) formed on the insulating film 8, thin film conductors 10 for 
terminals each associated with the strain gauge 9, wires 11 led out from 
the thin film conductors 10, and a passivation film 12 to cover the strain 
gauges 9, the thin film conductors 10 and others for protection. These 
components are all formed based on the semiconductor manufacture 
technology, as described later. The insulating film 8 is formed not all 
over the upper surface of the diaphragm, but over the region corresponding 
to the strain causing area so that a diaphragm surface 2a is exposed in 
the peripheral portion of the diaphragm 2. This diaphragm surface 2a 
serves as a bonding surface to be joined to the step surface of the 
larger-diameter bore 5a by diffusion bonding as mentioned above. The other 
construction and characteristics of the insulating film 8, the strain 
gauges 9, the thin film conductors 10, the wires 11 and the passivation 
film 12 are utterly the same as those of the prior art explained before in 
connection with FIG. 39, and hence not described here. With such structure 
of the pressure sensor, when a pressure P such as a hydraulic pressure is 
applied to the lower surface of the diaphragm 2 as shown in FIG. 1, a 
hydraulic fluid as a pressure medium produces a strain in the region 
corresponding to the strain causing area of the diaphragm 2. And the four 
strain gauges 9 disposed in the optimum positional relationship with 
respect to the strain causing area detect the strain and generate a 
voltage between the paired wires 11 and 11 dependent on the strain. It is 
to be noted that since the strain detecting section 2A thus constructed 
has a thickness on the order of microns much thinner than that of the 
diaphragm 2, the structure of the strain detecting section 2A is not shown 
in FIG. 1. 
In FIG. 1, the electric circuit section 4 is disposed on a circuit 
substrate 13. The circuit substrate 13 is disposed in the larger-diameter 
bore 5c formed on the upper side of the support member 3, whereby the 
electric circuit section 4 is in itself substantially placed and installed 
in the larger-diameter bore 5c. The electric circuit section 4 includes an 
amplifier circuit section, adjusting resistors and other components. FIG. 
4 shows one example of the circuit configuration which comprises the 
strain gauges 9 and the electric circuit section 4. Referring to FIG. 4, 
four resistors 9a, 9b, 9c, 9d represent the four strain gauges 9 in the 
form of electric circuit elements, and are interconnected so as to form a 
Wheatstone bridge circuit. A power source terminal 14 is connected to a 
node between the resistors 9a and 9b, while a ground terminal 16 is 
connected to a node between the resistors 9c and 9d. A variable resistor 
R.sub.1 between the resistors 9a and 9c and a variable resistor R.sub.2 
between the resistors 9b and 9c are each of a resistor for adjustment of 
zero point compensation. Output voltages of the Wheatstone bridge circuit 
are taken out from the respective terminals of the resistors R.sub.1 and 
R.sub.2. An operational amplifier 17 is associated with resistors 18-21 
and variable resistors R.sub.3, R.sub.4, R.sub.5 to constitute a 
differential amplifier. The output voltages of the Wheatstone bridge 
circuit are divided by the associated resistors on the input side, and 
applied to a non-inverted input terminal and an inverted input terminal of 
the operational amplifier 17, respectively, so that a voltage 
corresponding to the differential voltage on the input side is amplified 
and issued from an output terminal 15 of the operational amplifier 17. 
Among the variable resistors R.sub.3, R.sub.4 and R.sub.5, R.sub.3 is of a 
resistor for offset adjustment, and R.sub.4, R.sub.5 are of resistors for 
gain adjustment. Thus, the electric circuit section 4 includes the 
amplifier circuit section, the plurality of adjusting resistors, and the 
three connection terminals; i.e., the source terminal 14, the output 
terminal 15 and the ground terminal 16. As shown in FIG. 1, wiring leads 
14a, 15a, 16a are connected to these connection terminals 14, 15, 16, 
respectively, and further led out to the exterior. The adjusting resistors 
are arranged in such a manner as to be easily adjusted from above the 
electric circuit section 4. The wires 11, 11 led out from the strain 
detecting section 2A formed on the diaphragm 2 are inserted through the 
smaller-diameter bore 5b and then connected to the electric circuit 
section 4 on the circuit substrate 13 after passing through a small bore 
formed in the circuit substrate 13. 
FIG. 5 is a vertical sectional view showing a state where the pressure 
sensor unit 1 having the structure shown in FIG. 1 is mounted onto a wall 
22 of an equipment such as a hydraulic pipe. Referring to FIG. 5, 
designated by reference numeral 22a is an outer surface of the wall 22 and 
22b is an inner surface thereof. The wall 22 is in the outer surface 22a 
with a circular recess 23 in which the support member 3 of the pressure 
sensor unit 1 is placed and installed, with a bore 24 circular in cross 
section, for example, bored from the bottom surface of the recess 23 to 
the inner surface 22b. Accordingly, the side of the recess 23 is 
communicated with the fluid (oil) passage side via the bore 24. The depth 
of the recess 23 is greater than the thickness of the support member 3. 
The support member 3 on which the diaphragm 2, the electric circuit 
section 4 and others have been mounted in accordance with the structure of 
the pressure sensor unit shown in FIG. 1 is fitted in the recess 23 of the 
wall 22 for installation. A seal ring 25 for oil sealing is arranged in 
the ring-like groove 6 formed in the lower surface of the support member 
3. The support member 3 is then disposed in the recess 23 by contacting 
the lower surface of the support member 3 with the bottom surface of the 
recess 23, while making the seal ring 25 abutted with the bottom surface 
of the recess 23. In a state where the pressure sensor unit 1 is mounted 
onto the wall 22, as shown in FIG. 5, the lower surface, i.e., the 
pressure receiving surface, of the diaphragm 2 faces the fluid passage via 
the bore 24 to be subjected to the pressure P. In FIG. 5, since the 
diaphragm 2 receiving the pressure from below is supported by the stepped 
portion of the larger-diameter bore 5a of the support member 3 and fixedly 
joined to the step surface by diffusion bonding, pressure detection can be 
performed even for a higher pressure. FIG. 6 is a sectional view taken 
along the line VI--VI in FIG. 5, and shows the arrangement on the upper 
surface of the diaphragm 2 square in a plan view. Referring to FIG. 6, 
designated by 26 is an outline of the inner wall surface of the 
larger-diameter bore 5a, and 24 is the above-mentioned bore formed through 
the wall 22 in a position below the diaphragm 2. Four small rectangles 9 
indicate one example of the arranged configuration of the strain gauges. 
Returning to FIG. 5, 27 is a retainer member for pressing and fixing the 
pressure sensor unit 1 installed in the recess 23 from the side of the 
outer surface 22a. The retainer member 27 is a circular plate-like member 
having a projection 27a to be fitted in the recess 23. The retainer member 
27 is fixed to the wall 22 by at least two bolts 28 while making the 
projection 27a pressed against the support member 3. 29 is a threaded hole 
formed in the wall and 30 is a bolt insertion hole formed through the 
retainer member 27. The bolt insertion hole 30 includes a larger-diameter 
portion which receives a bolt head such that the head of a bolt 28 will 
not protrude from the hole 30 when it is screwed therein. Further, a 
stepped bore 31 is formed at the center of the retainer member 27, and the 
wiring leads 14a, 15a, 16a led out from the electric circuit section 4 of 
the pressure sensor unit 1 are taken out to the exterior through the bore 
31. With the retaining structure effected by use of the retainer member 
27, the pressing force produced by the retainer member 27 is directly 
applied to the support member 3 of high strength and the diaphragm 2 is 
hence subjected to no adverse deforming forces, whereby pressure measuring 
accuracy can be maintained high. 
Next, a manufacture method for a structural subassembly comprising the 
diaphragm 2, the support member 3, the insulating film 8 and the strain 
gauges 9 will be described in detail in relation to the pressure sensor 
unit 1 shown in FIG. 1. 
On the upper surface of the metal-made diaphragm 2 fabricated into a thin 
plate shape as mentioned above, the insulating film 8 is formed as a thin 
film having a thickness of about 1-20 .mu.m by application of the film 
forming technique such as CVD, vacuum vapor deposition or sputtering, 
using SiO.sub.2, SiC, SiN.sub.x or the like, for example, as with the 
prior art. In this case, the insulating film 8 is formed on the region 
corresponding to the strain causing area of the diaphragm 2 which has been 
known to a maker or manufacturer, so that the peripheral portion of the 
diaphragm 2 remains free of the insulating film 8 for later use as the 
bonding surface 2a. The semiconductor strain gauges 9 are formed on the 
upper surface of the insulating film 8 as follows. First, a silicon thin 
film in an amorphous state is formed on the upper surface of the 
insulating film 8 by plasma CVD, for example, while doping an impurity 
such as phosphor or boron. Then, the photolithography is applied to the 
silicon thin film to form patterns of the amorphous strain gauges. 
Afterward, heat treatment is applied so as to provide crystalline strain 
gauges. It is to be noted that although the strain gauges in an amorphous 
state cannot function as strain gauges, the term "strain gauge(s)" is used 
regardless of an amorphous or crystalline state in this description and 
the attached claims for convenience of explanation and unification of 
terms. In the foregoing manufacture method, the patterning step and the 
heat treating step may be reversed in the process sequence. 
In the pressure sensor unit 1 of the foregoing embodiment, heat treatment 
for diffusion bonding between the diaphragm 2 and the support member 3, 
and heat treatment for converting the strain gauges 9 on the upper surface 
of the diaphragm 2 from an amorphous state to a crystalline state can 
concurrently be performed by single heat treatment. The diffusion bonding 
is a technique to effect atomic bonding between the diaphragm 2 and the 
support member 3 both made of the same metallic material, for example, by 
abutting the bonding surface 2a of the diaphragm 2 against the step 
surface of the larger-diameter bore 5a of the support member 3 with an 
insert of aluminum or the like interposed therebetween, and then heating 
the assembly for a certain period of time at a temperature not lower than 
550.degree. C., while being held in a pressurized state under the 
atmosphere of vacuum or argon. This technique can provide a very high bond 
force. The diffusion bonding can also be made in the case where the 
diaphragm 2 and the support member 3 are formed not of the same material, 
but of different or inhomogeneous materials. Meanwhile, the strain gauges 
9 in an amorphous state is crystallized at a temperature of 
500.degree.-650.degree. C. Accordingly, the strain gauges 9 can 
concurrently be crystallized and bonded in a single step by utilizing the 
heat treatment of the diffusion bonding for crystallization as well. 
As described above, the diaphragm 2 is formed in advance in conformity with 
the bonding surface of the recess (larger-diameter bore) 5a in a state 
where the diaphragm 2 is placed and installed in the recess 5a of the 
support member 3 (diaphragm forming step); the insulating film 8 is formed 
on the upper surface of this diaphragm 2 at a predetermined location 
(insulating film forming step); an amorphous silicon thin film is formed 
on the upper surface of the insulating film 8 (silicon thin film forming 
step); and then amorphous strain gauges 9 are formed in patterns on this 
silicon thin film (gauge pattern forming step). Afterward, in order that 
the diaphragm 2 having the patterns of the amorphous strain gauges 9 
formed thereon is fixedly joined to the support member 3 by diffusion 
bonding and the amorphous strain gauges 9 are crystallized, the support 
member 3, the diaphragm 2 and the amorphous strain gauge 9 are heat 
treated together (heat treating step), thereby fabricating the aforesaid 
structural subassembly of the pressure sensor unit 1. 
It is to be noted that the foregoing manner of heat treatment for 
crystallizing the amorphous silicon thin film has been proposed by the 
present inventors in Japanese Patent Application No. 63(1988)-241995. As 
detailed in the specification of this patent application, by heating an 
amorphous silicon film with a resistance value nearly close to that of an 
insulator, a crystalline silicon thin film having the reduced resistance 
value and providing a piezo-resistance effect can be formed by the heat as 
treatment mentioned above. 
Next, another embodiment of the manufacture method for the aforesaid 
structural subassembly of the pressure sensor unit 1 will be described 
with reference to FIGS. 7 through 16. This manufacture method is directed 
to produce the structural subassembly comprising the diaphragm 2, the 
insulating film 8 and the strain gauge 9. 
First, a metal-made thin plate substrate 32 shown in FIG. 7 is fabricated 
in a substrate fabricating step. This metal-made thin plate substrate 32 
becomes the diaphragm 2 later. The thin plate substrate 32 is formed into 
a thin plate shape with a thickness t.sub.1 of about 0.05-2 mm using a 
metal material such as SUS630, for example. As described later, the 
substrate 32 has such a planar dimension as enough to fabricate a 
multiplicity of diaphragms 2 at the same time. A metallic mask 33 is then 
fixedly placed on the upper surface of the thin plate substrate 32 as 
shown in a mask placing step of FIG. 8. Placing the metallic mask 33 
defines a multiplicity of circular spaces on the upper surface of the thin 
plate substrate 32, each circular space corresponding to a region where 
the strain detecting section 2A is formed. 
FIG. 9 shows an insulating film forming step. In this step, the insulating 
film 8 having a thickness t.sub.2 of about 1-20 .mu.m is formed in each of 
circular spaces defined by the metallic mask 33 on the upper surface of 
the thin plate substrate 32 by an appropriate film forming technique such 
as vacuum vapor deposition or sputtering, using SiO.sub.2, SiC, SiN.sub.x 
or the like. 
FIG. 10 shows a silicon thin film forming step. In this step, a silicon 
thin film 34 in an amorphous state of low crystallinity is formed on each 
upper surface of the multiple insulating films 8 by doping phosphor or 
boron with plasma CVD, for example. After forming the silicon thin films, 
the metallic mask 33 is removed as shown in a mask removing step of FIG. 
11. Then, a gauge pattern forming step is carried out to form or pattern 
the four amorphous strain gauges 9 on each silicon thin film 34 by 
photolithography as shown in FIGS. 12 and 13. 
FIGS. 13 and 14 show a severing step. In this step, the thin plate 
substrate 32 is severed as indicated by broken lines in FIG. 13 into 
pieces for every four amorphous strain gauges 9 formed in the gauge 
pattern forming step, thereby fabricating the multiplicity of pressure 
sensors 1A each of which includes the diaphragm 2, the insulating film 8 
and the four amorphous strain gauges 9. 
Then, FIGS. 15 and 16 show a heat treating step for diffusion bonding the 
support member 3 and the diaphragm 2 and crystallizing the amorphous 
strain gauges 9. To prepare for the diffusion bonding, as shown in FIG. 
15, an insert material such as aluminum is first disposed or coated on 
either the step bonding surface of the large-diameter bore 5a of the 
support member 3 and the bonding surface 2a of the diaphragm 2, followed 
by closely contacting the support member 3 and the diaphragm 2 inclusive 
of the strain detecting section with each other. At this time, the 
diaphragm 2 is placed and installed into the larger-diameter bore 5a of 
the support member 3 while being guided by the inner wall surface of the 
larger-diameter bore 5a for positioning. In a state where the diaphragm 2 
is installed in the larger-diameter bore 5a, the strain detecting section 
faces the smaller-diameter bore 5b in the optimum positional relationship. 
While keeping the support member 3 and the diaphragm 2 in a closely 
contacted state, they are put in an electric furnace 36 equipped with a 
heater 35 and then heated for a certain period of time at a temperature 
not lower than 550.degree. C. necessary for the diffusion bonding. This 
allows the support member 3 and the diaphragm 2 to be fixedly joined by 
atomic bonding, and the amorphous strain gauges 9 to be crystallized for 
conversion to the semiconductor strain gauges which have a 
piezo-resistance effect. Thus, the diffusion bonding between the support 
member 3 and the diaphragm 2 and the crystallization of the semiconductor 
strain gauges 9 can be performed by single heat treatment, which leads to 
a reduction in both the number of manufacture steps and the production 
cost. It is also possible to fabricate a multiplicity of strain detecting 
sections at the same time using a thin plate substrate of large area, and 
hence to manufacture pressure sensors with the same quality in a mass 
quantity. 
FIG. 17 shows a modified embodiment of the structure of the pressure sensor 
1A which comprises the diaphragm 2 and the strain detecting section 2A 
comprised of an insulating film 37, the semiconductor strain gauges 9, the 
thin film conductors 10 and the passivation film 12. In this embodiment, 
the insulating film is formed all over the upper surface of the diaphragm 
2. The remaining construction is identical to that shown in FIG. 3. The 
pressure sensor thus constructed is fixed to the stepped portion of the 
circular large-diameter bore 5a of the support member 3 using an adhesive. 
This type pressure sensor is adopted in the case where the pressure to be 
detected is relatively low, because the bond force between the support 
member 3 and the diaphragm 2 is weaker than in the case where they are 
fixedly joined by diffusion bonding. 
A manufacture method for the pressure sensor having that structure will be 
described with reference to FIGS. 18 through 23. This manufacture method 
is basically the same as that explained above in connection with FIGS. 7 
through 14. First, the circular metal-made thin plate substrate 32 is 
fabricated in a substrate fabricating step (FIG. 18), and the insulating 
film 37 is formed all over the upper surface of the thin plate substrate 
32 by the film forming technique in an insulating film forming step (FIG. 
19). Then, an amorphous silicon thin film 38 is formed all over the upper 
surface of the insulating film 37 in a silicon thin film forming step 
(FIG. 20). Afterward, a gauge pattern forming step is carried out to form 
the silicon thin film 38 into patterns of the multiple amorphous strain 
gauges 9 by photolithography (FIGS. 21 and 22). Each set of the gauge 
patterns is formed in a predetermined region which turns out to be the 
strain causing area of the diaphragm 2 later. In a severing step, the thin 
plate substrate 32 and the insulating film 37 are severed as indicated by 
broken lines in FIG. 22 into pieces for every four amorphous strain gauges 
9, thereby finally fabricating the multiplicity of pressure sensors 1A 
each of which includes the diaphragm 2, the insulating film 37 and the 
amorphous strain gauges 9 (FIG. 23). Afterward, the thus-fabricated 
pressure sensors 1A shown in FIG. 23 are subjected to the above-mentioned 
heat treatment for crystallizing the amorphous strain gauges 9. An 
adhesive is then applied to the upper surface of the insulating film 37 at 
a predetermined location for fixing each of pressure sensors 1A to the 
support member 3. With the structure of the pressure sensor according to 
this embodiment, the manufacture process is simplified owing to no need of 
using a metallic mask. Also, the bonding method is easier because the 
support member 3 and the diaphragm 2 are bonded to each other using an 
adhesive. 
Other modified embodiments of the pressure sensor unit 1 will be described 
with reference to FIGS. 24 through 26. 
FIG. 24 shows a part of the pressure sensor unit 1. The pressure sensor 
unit 1 comprises a flat plate base 39 which has a lower surface 39a as a 
fluid contact surface brought into contact with the hydraulic fluid, as 
viewed on the drawing, and which is formed with a larger-diameter stepped 
portion 39c and a smaller-diameter bore portion 39d formed concentrically 
ranging from the fluid contact surface 39a to the opposite surface 39b, 
and a diaphragm 2 which is circular, for example, and fitted in the 
larger-diameter stepped portion 39c of the base 39. The base 39 may be of, 
for example, a wall of types of hydraulic equipment such as hydraulic 
pipes, couplings, hydraulic pumps and hydraulic motors, the wall being 
brought into contact with the hydraulic fluid. After a strain detecting 
section 2A has been formed on the upper surface of the diaphragm 2, as 
viewed on the drawing, the diaphragm 2 is fixed to the larger-diameter 
stepped portion 39c of the base 39 by diffusion bonding or an adhesive, 
for example, such that the strain detecting section 2A is received in the 
smaller-diameter bore portion 39d of the base 39. Thus, in this 
embodiment, the base 39 serving as a support member is substituted by a 
wall of hydraulic equipment contacting the hydraulic fluid. 
Further, in this embodiment, while the structure of the strain detecting 
section 2A comprising an insulating film 8, semiconductor strain gauges 9, 
thin film conductors 10, a passivation film 12 and wires 11 is the same as 
that of the embodiment shown in FIG. 3, the surrounding structure is 
different from that of the foregoing embodiment. More specifically, 
designated by 40 is a cover made of synthetic resin and formed into a 
tubular shape equipped with a lid. The cover 40 is fixed to the insulating 
film 8 so as to cover the strain detecting section 2A, and has a plurality 
of wire insertion bores 41, 41 (two shown in the illustrated embodiment) 
formed through a top wall 40a thereof. 42, 42 are connection terminal 
fixed to the upper surface of the top wall 40a for respective connections 
with a plurality of lead wires 44, 44. Connected to each of the plural 
connection terminals 42 is one end of the corresponding wire 11. An 
electric circuit section, a measuring unit and others (not shown) are 
connected to the distal ends of the lead wires 44, 44. 
With the pressure sensor unit 1 having the above construction, it is 
possible to enhance the strength of the diaphragm as an important part of 
the pressure sensor 1A, and to precisely and easily position the strain 
detecting section 2A formed on the diaphragm 2 simply by fitting the 
diaphragm 2 in the larger-diameter stepped portion 39c of the base 39 to 
be placed and installed therein, like the foregoing embodiment. In 
addition, since the base 39 as a support member is directly constituted by 
a wall of hydraulic equipment, the pressure sensor unit 1 can be mounted 
in compact fashion. 
FIG. 25 is a view similar to FIG. 24, showing still another embodiment. In 
this embodiment, a snap ring 48 is interposed between the inner peripheral 
surface of the larger-diameter stepped portion 46c of the base 46 and the 
outer peripheral surface of a diaphragm 47 fabricated into a circular 
shape. Also, an O-seal ring 49 for oil sealing is disposed at the contact 
surface between the diaphragm 47 and the base 46 to prevent the hydraulic 
fluid, etc. from entering the side of the strain detecting section 2A. The 
remaining construction is the same as that of the embodiment explained 
above by referring to FIG. 24. With this embodiment, in addition to the 
effect of improving the positioning accuracy as described in connection 
with the foregoing embodiments, the work of mounting the diaphragm 47 onto 
the base 46 can be facilitated and the diaphragm 47 can be removed for 
replacement of the strain detection section 2A, resulting in excellent 
operability for assembly, maintenance and other works. 
FIG. 26 shows a pressure sensor unit 1 fabricated into the more compact 
structure. Referring to FIG. 26, designated at 50 is a small-sized support 
member, 2 is a diaphragm placed and installed in a larger-diameter bore 
50a of the support member 50 and fixedly joined to the support member 50 
by diffusion bonding or other means, and 4 is an electric circuit section 
disposed on the upper surface of the support member 50. In this pressure 
sensor unit 1, a projected rim or flange 50b is formed all over the 
peripheral side face of the support member 50, By utilizing the projected 
rim 50b, a cover member 51 doubling as a cover and a retainer member is 
held on the support member 50 by fitting or other means, while a seal ring 
52 is disposed in a space under the projected rim 50b as indicated by 
imaginary lines. The pressure sensor unit 1 according to this embodiment 
can facilitate storage and handling, prevent damage of the electric 
circuit section, and can be attached to hydraulic equipment by easy 
mounting work. 
FIG. 27 is a view similar to FIG. 5, but showing a pressure sensor unit 100 
basically different in the construction. The pressure sensor unit 100 of 
this embodiment is constructed such that it includes two pressure sensors 
1A, and the output difference between the two pressure sensors 1A is taken 
to produce an intended pressure signal. In other words, the pressure 
sensor unit 100 is constituted as a differential pressure sensor. In FIG. 
27, the same elements as those shown in FIG. 5 are designated by the same 
reference numerals. Specifically, 22 is a wall, 23 is a larger-diameter 
circular recess for receiving the pressure sensor unit 100, 27 is a 
retainer member for fixing the pressure sensor unit 100 in the recess 23 
of the wall 22, and 28 is a bolt for fixing the retainer member 27 to the 
outer surface of the wall 22. 53 is a support member for the pressure 
sensor unit 100 according to this embodiment. The support member 53 has a 
larger diameter than that of the support member 3 in the foregoing 
embodiment, and is structured so as to include the two pressure sensors 
1A. Accordingly, the above-mentioned larger-diameter bore 5a for receiving 
and fixing a diaphragm 2 of each pressure sensor 1A is formed two in 
number in the lower surface of the support member 53, as viewed on the 
drawing. The surrounding structures of the two pressure sensors 1A are 
identical to each other, and designed as shown in FIG. 5. Therefore, the 
support member 53 is provided with two smaller-diameter bores 5b, two 
ring-like grooves 6, and two seal rings 25. Thus, the pressure sensor unit 
100 is constructed to provide the function of detecting a pressure at two 
locations. Meanwhile, corresponding to such structure of the pressure 
sensor unit 100, the wall 22 is formed with two bores 24 for introducing a 
pressure such as a hydraulic pressure therethrough. Pressure levels 
introduced to the bores 24, 24 are different from each other. The 
surrounding structure of a mount location for the electric circuit section 
4, disposed in an upper portion of the support member 53, is substantially 
the same as that of the support member 3 in the foregoing embodiment, just 
except that the size is increased to some extent. However, the electric 
circuit section 4 is arranged so as to receive detection signals from the 
two pressure sensors 1A corresponding to the different levels of pressure, 
and output a signal dependent on the differential pressure. 
FIG. 28 shows a modified embodiment of the differential pressure sensor 
which is constructed in accordance with the present invention. With the 
structure of a pressure sensor unit 200 constituted into a differential 
pressure sensor, a single pressure sensor 1A is employed to achieve the 
differential pressure sensor. In FIG. 28, designated by 54 is a part of a 
wall of hydraulic equipment or the like, the wall 54 having inner wall 
surfaces 54a and 54b subjected to different levels of hydraulic pressure. 
The inner wall surfaces 54a, 54b of the wall 54 are formed with bores 24, 
24a through which the hydraulic fluid is introduced, respectively. A 
larger-diameter bore 55 formed with female threads on its inner surface is 
bored in an outer wall surface 54c of the wall 54, and this bore 55 is 
formed in its bottom with a smaller-diameter bore 57 in which a support 
member 56 for holding the pressure sensor 1A is to be placed and 
installed. The support member 56 has a substantially columnar shape, and 
is formed with a larger-diameter bore 5a in its lower portion for 
receiving and fixing a diaphragm 2 of the pressure sensor 1A, a groove 58 
in the peripheral side face for defining a fluid passage, and a bore 59 
for a fluid passage in communication with the upper surface side of the 
diaphragm 2 and the groove 58, as viewed on the drawing. The aforesaid 
bore 24 is communicated with the lower surface side of the diaphragm 2, 
and the bore 24a has an opening its left end positioned to face the groove 
58, as viewed on the drawing. Accordingly, the hydraulic fluid contacting 
the inner wall surface 54a is introduced to the lower surface side of the 
diaphragm 2 via the bore 24, while the hydraulic fluid contacting the 
inner wall surface 54b is introduced to the upper surface side of the 
diaphragm 2 via the bore 24a, the groove 58 and the bore 59. Further, an 
electric circuit section 4 is placed and installed in a recess 60 formed 
in the upper surface of the support member 56. Designated by 61, 62, 63 
are seal rings. Specifically, 61 is an O-seal ring disposed in a ring-like 
groove formed in the lower surface of the support member 56, and 62, 63 
are seal rings disposed in circumferential grooves formed in the 
peripheral side face of the support member. 
The structure of the pressure sensor 1A is basically identical to that 
explained before in connection with the foregoing embodiments. However, 
since the hydraulic fluid is also introduced to the upper surface side of 
the diaphragm 2, a protective film 64 formed of SiNx or a molding film is 
provided to protect the strain detecting section formed on the upper 
surface of the diaphragm 2. With this embodiment thus constructed, the 
structure allowing different levels of pressure to exert on the upper and 
lower surfaces of the diaphragm 2 of the pressure sensor 1A makes it 
possible to directly detect the differential pressure therebetween. In 
other words, a differential pressure sensor excellent in response can be 
achieved by the single pressure sensor 1A by making the opposite surfaces 
of the metal-made diaphragm 2 subjected to pressures. A differential 
pressure signal detected by the strain detecting section on the upper 
surface of the diaphragm 2 is led by a plurality of wiring leads 65 to the 
electric circuit section 4 through a hermetic seal 66, and then processed 
by an amplifier and others in the electric circuit section 4. The hermetic 
seal 66 serves to prevent the hydraulic fluid from entering the side of 
the electric circuit section 4. 
FIG. 29 shows one example of the structure for fixing each wiring lead 65 
to the upper surface of the diaphragm 2. The wiring lead 65 has its lower 
end fixed to the upper peripheral surface of the diaphragm 2, and its 
lower portion coated by the protective film 64. The wiring lead 65 is 
connected with the pin erecting structure, for example, such that a female 
pin receiver 68 is provided on the upper peripheral surface of the 
diaphragm 2 by soldering at 67, and the lower end of the wiring lead 65 is 
inserted into an opening of the female pin receiver 68 being exposed to 
the outside from the protective film 64. Accordingly, assembly is much 
simplified. Alternatively, the wiring lead 65 may simply be soldered. Note 
that 69 in FIG. 29 designates a thin film for the wiring. 
With the structure shown in FIG. 28, the following advantageous effect is 
provided in addition to that of the present invention explained before in 
connection with the foregoing embodiments. Since the metal-made diaphragm 
2 of the pressure sensor 1A is tightly held between the housing portion of 
the wall 54 for the support member 56 and the PG,53 stepped portion of the 
larger-diameter bore 5a of the support member 56, the support structure 
becomes very rigid and strong, making it possible to arbitrarily select a 
higher or lower pressure of the hydraulic fluid in application. Also, 
since this embodiment can constitute the differential pressure sensor by a 
single diaphragm, the number of parts is reduced to enable manufacture of 
the differential pressure sensor unit with the smaller size and the 
simplified structure. Note that on the upper side of the support member 
56, a retainer member (not shown) is disposed to be meshed with the female 
threads of the bore 55 and fixed therein for holding the support member 
56. 
FIG. 30 shows an embodiment obtained by partially modifying the structure 
of the differential pressure sensor shown in FIG. 28. In this embodiment, 
the diaphragm subjected to pressures is modified in its shape. In FIG. 30, 
the same elements as those shown in FIG. 28 are designated by the same 
reference numerals. Specifically, in FIG. 30, designated by 54 is a wall, 
54a is an inner wall surface, 24 is a bore for introducing the hydraulic 
fluid, 56 is a support member, 59 is a bore for a fluid passage, 65 is a 
wiring lead, and 66 is a hermetic seal. The peripheral portion not shown 
in FIG. 30 is constructed similarly to that shown in FIG. 28 except that 
the seal ring 61 is not used in the former as describer later. Referring 
to FIG. 30, 102 is a diaphragm according to this embodiment. The diaphragm 
102 is of a metal-made diaphragm fabricated by machining. The diaphragm 
102 has a strain causing portion 102a in its top plate part, and a strain 
detection section provided on the strain causing portion 102a while being 
protected by a protective film 64, the upper and lower surfaces of the 
strain causing portion 102a being employed as pressure receiving surfaces. 
The part of the diaphragm 102 extending downward from the periphery of the 
strain causing portion 102a is formed into a tubular portion 102b 
continuous to and integral with the strain causing portion 102a. The 
tubular portion 102b supports the strain causing portion 102a. The upper 
surface of the tubular portion 102b is constituted as a strain not-causing 
area, and the wiring leads 65 are connected to the strain not-causing 
area. A stepped portion 102c is formed in the lower and outer peripheral 
surface of the tubular portion 102b, as viewed on the drawing. The 
diaphragm 102 having such configuration is fitted in a larger-diameter 
bore 5a of the support member 56 to be placed and installed therein for 
fixing to the step surface by diffusion bonding or an adhesive. In 
assembly, as shown in FIG. 30, the diaphragm 102 is set such that the fore 
ends of the tubular portion 102b are located in a larger-diameter bore 24a 
of the bore 24 of the wall 54, and an annular space is defined by the 
aforesaid stepped portion 102c and the stepped portion given by the 
larger-diameter bore 24a. An O-ring-seal 103 is disposed in the annular 
space. With such assembled structure, the bore 24 for introducing the 
hydraulic fluid is communicated with an inner side space of the diaphragm, 
and the hydraulic fluid is applied to the lower surface of the strain 
causing portion 102a. On the other hand, the hydraulic fluid at a 
different pressure is introduced via the fluid passage 59 to a space 
defined above the strain causing portion 102a and applied to the upper 
surface of the strain causing portion 102a. By thus applying different 
levels of pressure to the upper and lower surfaces of the metal-made 
diaphragm 102, the differential pressure therebetween can be detected by 
the strain detecting section. Note that since the seal ring 103 is 
disposed in the distal peripheral end of the tubular portion 102b of the 
diaphragm 102 as mentioned above, there is no need of providing the seal 
ring 61 shown in FIG. 28. The differential pressure sensor according to 
this embodiment also makes it possible to constitute a differential 
pressure sensor using a single diaphragm, as with the embodiment shown in 
FIG. 28. 
Next, a coupling for a hydraulic pipe and a hydraulic pipe itself which 
have previously had mounted thereon any of the pressure sensor units 
explained in the foregoing embodiments, will be described. 
FIG. 31 shows a first embodiment of such a coupling, and FIG. 32 is a plan 
view of a part of the coupling. Illustrated in this embodiment is the 
coupling which mounts thereon the pressure sensor unit 1 having the 
structure shown in FIG. 5. In FIGS. 31 and 32, the essentially same 
elements as those shown in FIG. 5 are designated by the same reference 
numerals. 70 is a bushing adapted to couple a pair of hydraulic pipes 
different in diameter. The inner circumference of the bushing 70 gives a 
fluid contact surface 70a in the form of a flat circumferential surface, 
thereby defining a fluid passage 71. Furthermore, larger-diameter female 
threads 72, 73 are formed on the inner circumferential surface of the 
bushing 70 at the axially opposite end portions thereof. 
Designated by 23 is a circular bore formed in an outer circumferential 
surface 70b of the bushing 70 for installing the pressure sensor unit 1 
therein, 74 is a circular bore for installing the aforesaid retainer 
member 27 therein, 28, 28 are bolts for fixing the retainer member 27 in 
place, 29, 29 are threaded bores in which the bolts 28, 28 are screwed for 
fastening, and 24 is a bore open to the fluid contact surface 70a for 
introducing the hydraulic fluid. As shown in FIG. 32, each bolt 28 has a 
hexagonal slot 28a formed in its top surface. A diaphragm 2 set in the 
pressure sensor unit 1 is subjected to a hydraulic pressure via the bore 
24 for introducing hydraulic fluid. In this way, the pressure sensor unit 
1 is mounted or assembled into the wall of the bushing 70 from the outer 
circumference side and fixed by the retainer member 27. In the drawings, a 
measuring unit and so on are not illustrated. 
The bushing 70 thus constructed provides the structure in which the 
pressure sensor capable of detecting a pressure of the hydraulic fluid 
passing through the fluid passage 71 is incorporated into the bushing 70 
in advance, and the pressure sensor unit 1 and the retainer member 27 are 
completely buried in the wall of the bushing 70, thereby enabling to 
surely prevent rocks, earth and sand, etc. from damaging the pressure 
sensor. Further, only by replacing the conventional bushing equipped with 
no pressure sensor by the bushing 70 of this embodiment, the pressure 
sensor can be mounted without changing the entire length of hydraulic 
pipes, and the mounting work is very simple. In addition, the measuring 
point of a hydraulic pressure can be selected freely and easily by 
modifying a position at which the bushing 70 is connected to the hydraulic 
pipes. 
FIGS. 33 and 34 show another embodiment of the coupling. In this 
embodiment, the same elements as those shown in FIG. 31 are designated by 
the same reference numerals and not described here. This embodiment is 
different from the foregoing embodiment in a retainer member for holding 
the support member 3 of the pressure sensor unit 1. More specifically, a 
bore 75 for installing the retainer member therein is formed as a 
larger-diameter female threaded bore in an upper portion of the 
installation bore 23 for the pressure sensor unit 1, as viewed on the 
drawing, and a retainer member 76 having made threads formed in its outer 
circumferential surface is screwed into the threaded bore 75 for mounting. 
In the outer end face of the retainer member 76, as shown in FIG. 34, 
there are provided two bores 76a for rotating the retainer member 76. 
Further, a penetration bore 76b is formed through a shaft portion of the 
retainer member 76, and lead wires of the electric circuit section 4 
disposed in an upper portion of the pressure sensor unit 1 are drawn via 
the bore 76b. Afterward, the bore 76b is sealed off. 
FIGS. 35 and 36 show an embodiment in which the pressure sensor unit 
according to the present invention is mounted to a flange portion of a 
hydraulic pipe. The mounted pressure sensor is assumed to have the 
structure shown in FIG. 5. Designated by 77 is a hydraulic pipe with a 
flange, which comprises a pipe portion 77a and a flange portion 77b and 
has the inner circumference serving as a fluid contact surface 77c. 23 is 
a bore formed radially from the outer circumferential surface of the pipe 
portion 77a inward and employed for installing the pressure sensor unit 1 
therein. 24 is a bore for introducing the hydraulic fluid. 78 is a holder 
vertically provided in concentrical relation to the installation bore 23, 
and formed with female threads 78a in an upper-half portion of its inner 
circumferential surface. A retainer member 79 for holding and fixing the 
pressure sensor unit 1 is screwed into the female threads 78a. 
With the above embodiment, the hydraulic pressure can be measured at an 
arbitrary position by mounting the flange equipped hydraulic pipe 77 
including the pressure sensor unit 1 at any desired location of hydraulic 
pipes. 
FIGS. 37 and 38 show an embodiment in which the pressure sensor unit 
according to the present invention is mounted to a flange portion 80b of a 
flange equipped hydraulic pipe 80 which comprises a hydraulic pipe 80a and 
the flange portion 80b. In this embodiment, the flange portion 80b is 
formed with a bore 23 for installing the pressure sensor unit 1 therein, 
and a female threaded bore 82 coaxially formed with the bore 23 for 
receiving a retainer member 81 adapted to fix the pressure sensor unit 1 
installed. Note that 24 is a bore for introducing the hydraulic fluid and 
80c is a fluid contact surface. 
Although the pressure sensors according to the foregoing embodiments have 
been explained as mainly measuring a hydraulic pressure, it should be 
understood that the present invention is also similarly applicable to a 
pressure of other liquid or gas. 
INDUSTRIAL APPLICABILITY 
The pressure sensor and the hydraulic equipment with the pressure sensor 
according to the present invention have the structure optimum to be 
mounted on or incorporated in or assembled with hydraulic equipments and 
the like for civil engineering and construction machines, and make it 
possible to improve positioning accuracy of respective components such as 
a diaphragm, facilitate mounting or assembly, and improve accuracy of 
measuring a pressure. With the manufacture method for the pressure sensor 
according to the present invention, the semiconductor manufacture 
technology can be utilized effectively.