Pulse wave detecting apparatus

A pulse wave detecting apparatus for detecting a pulse wave produced from an arterial vessel in a body portion of a subject, including a semiconductor substrate having a press surface at which the semiconductor substrate is adapted to be pressed against the body portion, the semiconductor substrate having a recess in a surface thereof opposite to the press surface and thereby including a diaphragm portion having a thin wall, and a pressure sensing device provided on the diaphragm portion, for converting a pressure transmitted from the arterial vessel to the diaphragm portion, into an electric signal.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates in general to an apparatus for detecting a 
pulse wave produced from an arterial vessel of a living body, and in 
particular to such an apparatus which is free from temperature effects. 
2. Related Art Statement 
An arterial pulse wave that is an oscillatory pressure wave produced from 
an arterial vessel in synchronization with heartbeat of a living body, 
provides information about not only intra-arterial blood pressure but also 
other conditions of the circulatory system of the living body. Thus, it is 
clinically needed to non-invasively detect a pulse wave produced from an 
arterial vessel, for measuring a blood pressure or making a diagnosis on 
pathology of the circulatory system of a patient. 
There has been known a pulse wave detecting device for non-invasively 
detecting a pulse wave produced from an arterial vessel via the skin of a 
subject overlying the artery, by pressing the skin directly above the 
artery. The pulse wave detecting device of this type is disclosed by U.S. 
Pat. No. 4,423,738. This device includes a semiconductor substrate which 
is adapted to be pressed at one of opposite surfaces thereof (hereinafter 
referred to as the "press surface") against the skin of the subject. The 
press surface has a plurality of independent cavities formed therein, and 
the thus formed diaphragms of the semiconductor substrate have a thin 
wall. Each of the diaphragms is provided with a piezoresistor which serves 
for converting a strain produced in the diaphragm into an electric signal, 
namely, a pressure transmitted from the artery to the diaphragm. 
Meanwhile, each cavity is filled with a soft filler, such as a silicone 
rubber, which serves for transmitting a pulse wave from the skin of the 
subject to the corresponding diaphragm. This device is adapted to press 
the semiconductor substrate against the underlying artery via the skin and 
thereby obtain an electric signal representing a pulse wave produced from 
the artery. 
However, the pulse wave detecting device of the above type suffers from a 
problem that an undesirable strain is produced in the diaphragm because of 
a temperature change, differently stated, a difference in thermal 
expansion between the semiconductor substrate and the soft filler. In the 
event that the difference in thermal expansion between the two members is 
large, an electric signal representing a pulse wave, generated by the 
device, may contain a temperature drift, therefore the pulse wave detected 
may not be accurate. If the output signal contains a temperature drift and 
the pulse wave represented by the output signal is not accurate, then the 
accuracy of measurement of blood pressure based on the pulse wave would 
not be satisfactory. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a pulse wave 
detecting apparatus which is free from the conventionally encountered 
problem that the accuracy of detection of pulse wave is lowered due to 
difference in thermal expansion between a semiconductor substrate and a 
soft filler. 
The above object may be achieved by the present invention, which provides a 
pulse wave detecting apparatus for detecting a pulse wave produced from an 
arterial vessel in a body portion of a subject, comprising a semiconductor 
substrate having a press surface at which the semiconductor substrate is 
adapted to be pressed against the body portion, the semiconductor 
substrate having a recess in a surface thereof opposite to the press 
surface and thereby including a diaphragm portion having a thin wall, and 
pressure sensing means provided on the diaphragm portion, for converting a 
pressure transmitted from the arterial vessel to the diaphragm portion, 
into an electric signal. 
In the pulse wave detecting apparatus constructed as described above, the 
press surface of the semiconductor substrate has no recess, and the 
pressure sensing means detects an arterial pulse wave transmitted directly 
from a body portion of a subject to the diaphragm portion of the 
semiconductor substrate, namely, not indirectly via an intervening object 
such as a soft filler. Thus, the present apparatus is free from the 
problem of insufficient accuracy of detection of pulse wave due to 
difference in thermal expansion between the semiconductor substrate and 
the soft filler. 
In a preferred embodiment of the present invention, the semiconductor 
substrate has an elongate recess in the surface opposite to the press 
surface, and a plurality of ridges extending transversely of the elongate 
recess, the ridges having a height smaller than a thickness of the 
semiconductor substrate, the pressure sensing means comprising a plurality 
of pressure sensing elements each of which is provided between a 
corresponding one pair of adjacent ridges of the plurality of ridges. 
In another embodiment of the present invention, the semiconductor substrate 
has an elongate recess in the surface opposite to the press surface, and a 
plurality of slits formed through the diaphragm portion and extending 
transversely of the elongate recess, the pressure sensing means comprising 
a plurality of pressure sensing elements each of which is provided between 
a corresponding one pair of adjacent slits of the plurality of slits. 
According to a feature of the present invention, the apparatus further 
comprises a back-up plate to which the semiconductor substrate is adhered. 
The back-up plate may be formed of a same material as a material of the 
semiconductor substrate, and adhered to the semiconductor substrate with a 
silicone rubber. Optionally, the back-up plate may be formed of a glass. 
According to another feature of the present invention, the apparatus 
further comprises an electric circuit supplying an electricity to the 
pressure sensing means and receiving the electric signal from the pressure 
sensing means. 
According to yet another feature of the present invention, the apparatus 
further comprises an insulator spacer interposed between the semiconductor 
and back-up plate, and the electric circuit. 
According to yet another feature of the present invention, the apparatus 
further comprises connection means for electrically connecting the 
pressure sensing means and the electric circuit for supplying the 
electricity to the pressure sensing means and transmitting the electric 
signal to the electric circuit. 
According to a further feature of the present invention, the back-up plate 
has a central hole communicating the recess of the semiconductor substrate 
with ambient air. 
According to a further feature of the present invention, the pressure 
sensing means comprises a Wheatstone bridge including four resistors and 
four conductors. 
In another embodiment of the present invention, the apparatus further 
comprises pressing means for pressing the semiconductor substrate against 
the body portion of the subject, the pressing means including a support 
member, and an elastic diaphragm secured to the support member, the 
elastic diaphragm cooperating with the support member to define a pressure 
chamber inside the support member, the semiconductor substrate being 
secured to the elastic diaphragm, so that the substrate is displaced 
toward the body portion together with the elastic diaphragm when the 
diaphragm is expanded due to an increased pressure in the pressure 
chamber. 
In the above-indicated embodiment, the apparatus may further comprise 
feeding means for moving the pressing means over the body portion in a 
direction generally perpendicular to the arterial vessel, the feeding 
means including an externally threaded feed screw engaging an internally 
threaded portion of the support member of the pressing means, a drive 
motor, and a reduction gear unit operatively connecting the feed screw and 
the drive motor, so that when the drive motor is driven the feed screw is 
rotated and the support member of the pressing means is moved over the 
body portion. 
In addition, the apparatus may comprise a housing accommodating the feeding 
means, and a cylindrical bearing fitted in a hole formed through a wall of 
the housing, the cylindrical bearing having an eccentric hole formed 
therethrough, one of opposite axial ends of the feed screw of the feeding 
means being fitted in the eccentric hole of the cylindrical bearing, while 
the other axial end of the feed screw being supported by the housing such 
that the other axial end is not displaceable relative to the housing, so 
that when the cylindrical bearing is rotated in the hole of the housing 
the feed screw is rotated slightly about the other axial end thereof 
supported by the housing. In this case, the reduction gear unit may 
include a first wheel fixed to the other axial end of the feed screw such 
that the first wheel is rotatable about an axis thereof together with the 
feed screw, and a second wheel engaging the first wheel, the second wheel 
being secured to the housing such that the second wheel is rotatable about 
an axis thereof and not displaceable relative to the housing, a distance 
between the axes of the first and second wheels being adjusted by rotating 
the cylindrical bearing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIG. 1, there is shown a pulse wave detecting apparatus 
embodying the present invention. In the figure, reference numeral 10 
designates a housing formed of resin and having a container-like 
configuration. Lengthwise side walls 18, 20 (also see FIG. 2) of the 
housing 10 have a crescent shape, while a widthwise intermediate portion 
of the housing 10 has an outwardly protruded shape. The housing 10 is 
detachably held on a wrist of a subject by bands 14, 14 such that an open 
end of the housing 10 contacts a body surface 12 (see FIG. 3) of the 
subject. 
As shown in FIG. 3, a reduction gear unit 22 is secured with a screw 23 to 
a support plate 24 formed of resin and having an L-shaped cross section. A 
pair of brackets 26 (only one shown) extending from the support plate 24 
are secured with screws 25 to the parallel longitudinal side walls 18, 20. 
Thus, the reduction gear unit 22 is secured to the housing 10. 
The reduction gear unit 22 includes six wheels 30, 32, 34, 36, 38, 44. The 
first wheel 30 meshes with the second wheel 32, while the second wheel 32 
is coaxial with the third wheel 34. The third wheel 34 meshes with the 
fourth wheel 36, while the fourth wheel 36 is coaxial with the fifth wheel 
38. The fifth wheel 38 meshes with the sixth wheel 44, which is connected 
to an output shaft 42 of a drive motor 40. Each of the second to fifth 
wheels 32, 34, 36, 38 is supported by a frame 28 of metal such that each 
wheel is rotatable about an axis thereof. The first wheel 30 is connected 
to one of opposite axial ends of a feed screw 48. This axial end of the 
feed screw 48 is supported by the frame 28 via a bearing 46 of resin 
fitted in a hole formed through the frame 28, such that the feed screw 48 
is rotatable with the first wheel 30. Thus, the feed screw 48 is 
operatively connected to the drive motor 40, that is, the feed screw 48 is 
driven or rotated by the drive motor 40. The drive motor 40 is fixed to 
the frame 28. 
A hole 52 is formed through a widthwise side wall 21 of the housing 10. A 
cylindrical bearing 50 is fitted in the hole 52. The other axial end of 
the feed screw 48 opposite to the one axial end thereof fitted in the 
bearing 46, is rotatably supported by the side wall 21 via the cylindrical 
bearing 50. The feed screw 48 is located at a widthwise middle position in 
the housing 10, and extends lengthwise of the housing 10. 
As shown in FIG. 4, the cylindrical bearing 50 has a small diameter portion 
54 at which the bearing 50 is fitted in the hole 52, and a large-diameter 
portion 56 concentric with the small-diameter portion 54. The cylindrical 
bearing 50 has an eccentric hole 58 which is formed through the small- and 
large-diameter portions 54, 56 such that the eccentric hole 58 is 
eccentric with the portions 54, 56. The large-diameter portion 56 has a 
groove 60 which is formed in an end face thereof such that the groove 60 
extends diametrically of the end face. If an adjusting tool is engaged 
with the groove 60 and the bearing 50 is rotated by the tool to an 
appropriate angular position, then the axial end of the feed screw 48 
fitted in the eccentric hole 58 of the bearing 50 is displaced upward, 
downward, leftward or rightward along a predetermined circle to an 
appropriate position. 
As shown in FIGS. 2 and 3, the present apparatus has a pressing device 66. 
The pressing device 66 includes an internally threaded, engage member 68 
engaging the externally threaded feed screw 48, and a rectangular hollow 
member 72 secured to a lower end of the engage member 68 via an elastic 
diaphragm 70 of rubber. A pulse wave sensor 74 is secured to a central 
area of a lower surface of the elastic diaphragm 70. The engage member 68 
and the elastic diaphragm 70 cooperate with each other to define a 
pressure chamber 76 connected to a pressure regulating device (not shown). 
If the pressure chamber 76 is supplied with a pressurized fluid from a 
supply device (not shown) via the pressure regulating device, the pulse 
wave sensor 74 is pressed against the body surface 12 with a pressing 
force corresponding to a fluid pressure in the pressure chamber 76. The 
pulse wave sensor 74 has a press surface 78 at which the pulse wave sensor 
74 is pressed against the body surface 12. The press surface 78 is defined 
by one of opposite surfaces of a semiconductor substrate 98 (see FIG. 5) 
on which are provided a plurality of pressure sensing elements 100 (see 
FIG. 6) such as semiconductor resistors or pressure sensing diodes 
(described later in detail). The pulse wave sensor 74 is pressed against 
the body surface 12 to such an extent that an underlying arterial vessel 
80 is partially flattened, that is, is deformed to have a flattened 
portion. In this situation, the pulse wave sensor 74 detects a pressure 
pulse wave (hereinafter, referred to as the "pulse wave") produced from 
the arterial vessel 80 in synchronization with heartbeat of the subject. 
As shown in FIG. 2, the rectangular hollow member 72 has a pair of straight 
guide grooves 82, 82 formed in outer surfaces of the side walls thereof 
parallel to the longitudinal side walls 18, 20 of the housing 10, while a 
pair of straight guide rails 84, 84 are formed on inner surfaces of the 
longitudinal side walls 18, 20. The guide rails 84, 84 engage the guide 
grooves 82, 82, respectively. When the feed screw 48 is rotated by the 
drive motor 40 with the present apparatus held on the wrist of the 
subject, the pressing device 66 is guided, without any rattle, over a 
predetermined stroke or distance by the guide grooves and rails 82, 84 in 
a direction generally perpendicular to the arterial vessel 80. 
As described above, the feed screw 48 is connected at one axial end thereof 
to the first wheel 30, and is supported at the other axial end thereof by 
the "eccentric" bearing 50. Therefore, if the angular position of the 
eccentric bearing 50 is changed as a result of being rotated by an 
adjusting tool, the other axial end of the feed screw 48 is displaced with 
the eccentric bearing 50. Consequently, the feed screw 48 is rotated 
slightly about the other axial end thereof or bearing 46, and the axis of 
the first wheel 30 fixed to the one axial end of the feed screw 48 is 
correspondingly displaced. While the present pulse wave detecting 
apparatus is fabricated, the distance between the axis of the first wheel 
30 on the side of the feed screw 48, and the axis of the second wheel 32 
on the side of the drive motor 40, is adjusted to an appropriate value by 
rotating the eccentric bearing 50 so as to establish a desirable 
engagement between the first and second wheels 30, 32. Thus, the present 
apparatus is free from a problem that the pulse wave sensor 74 is not 
moved smoothly due to a dimensional error with respect to the distance 
between the axes of the first and second wheels 30, 32, and a problem that 
the durability of the first or second wheel 30, 32 is lowered due to 
extraordinary wear thereof. Furthermore, since dimensional errors with 
respect to the first and second wheels 30, 32 are easily eliminated by 
adjusting the eccentric bearing 50, tolerances required with respect to 
parts used for fabricating the present apparatus may not be restrictive, 
whereby the cost of manufacture of the apparatus is reduced. 
As shown in FIG. 5, the pulse wave sensor 74 includes a ceramic substrate 
90, an insulator spacer 92 and a presser plate 94. The ceramic substrate 
90 is provided with conductor patterns superposed on each other. The 
insulator spacer 92, formed of an insulating material such as ceramics or 
resin, is fixed to a central area of the ceramic substrate 90. The presser 
plate 94 is supported by the insulator spacer 92. The pulse wave sensor 74 
is adapted to be pressed at the presser plate 94 (or the press surface 78 
thereof) on the body surface 12 of the subject. The presser plate 94 
includes a back-up plate 96 formed of a rigid material, and a 
semiconductor substrate 98 adhered to one of opposite surfaces of the 
back-up plate 96. The adhesion of the semiconductor plate 98 to the 
back-up plate 96 is carried out by using an epoxy resin, a silicone rubber 
or the like. The back-up plate 96 is constituted by a glass plate, or a 
thick plate formed of the same material as that of the semiconductor 
substrate 98. It is preferred to use the silicone-rubber adhesive to the 
epoxy-resin adhesive, for avoiding adverse influences due to possible 
difference in thermal expansion between the back-up plate 96 and the 
semiconductor plate 98. For the same reason it is preferred to use the 
thick semiconductor plate to the glass plate for the back-up plate 96. 
Therefore, it is the most recommendable manner that the semiconductor 
substrate 98 is adhered to the semiconductor back-up plate 96 with the 
silicone-rubber adhesive. In the present embodiment, the semiconductor 
plate 98 is constituted by a single crystal silicon. 
As shown in FIG. 6, an array of pressure sensing elements 100 each for 
detecting a pressure applied thereto are arranged along a straight line in 
a middle area of one of opposite surfaces of the semiconductor substrate 
98. In the present apparatus, the pulse wave sensor 74 is pressed on the 
body surface 12 such that the array of pressure sensing elements 100 
generally normally crosses over the underlying arterial vessel 80. 
Referring next to FIG. 7, there is shown the structure of the semiconductor 
substrate 98 and back-up plate 96. The semiconductor substrate 98 has the 
press surface 78, and a recessed surface 103 opposite to the press surface 
78. The recessed surface 103 has an elongate recess 104 formed therein and 
thereby includes a diaphragm portion 106 having a thin wall. The thickness 
(e.g., several to ten and several microns (.mu.m)) of the diaphragm 
portion 106 is smaller than the thickness (e.g., about 300 .mu.m) of the 
remainder (or non-recessed portion) 107 of the semiconductor substrate 98. 
A plurality of ridges 108 are provided on the diaphragm portion 106 at 
regular intervals of distance, and extend transversely of the elongate 
recess 104. The ridges 108 have a height smaller than the thickness of the 
non-recessed portion 107 (more precisely, a value obtained by subtracting 
the thickness of the diaphragm portion 106 from the thickness of the 
non-recessed portion 107). Each of the pressure sensing elements 100 is 
formed, on the diaphragm portion 106, between a corresponding one pair of 
adjacent ridges of the plurality of ridges 108. In the present embodiment, 
it is recommended that the above-indicated regular intervals between the 
individual ridges 108 fall within the range of 200 to 250 .mu.m and that 
the ridges 108 have a width of several tens of microns (.mu.m). The height 
of the ridges 108 is determined at an appropriate value for sufficiently 
protecting each pressure sensing element 108 against crosstalk, that is, 
interferance due to strains produced in the adjacent pressure sensing 
elements 100. Each pressure sensing element 100 converts into an electric 
signal a strain produced at a corresponding region in the diaphragm 
portion 106 as a result of transmission thereto of a pressure due to the 
pulse wave produced from the arterial vessel 80. 
The back-up plate 96 has a high rigidity because of a great thickness of 
500-1500 .mu.m, and has two holes 102, 102 formed therethrough for 
communicating the elongate recess 104 of the semiconductor substrate 98 
with ambient air under atmospheric pressure via central holes formed 
through the insulator spacer 92 and ceramic substrate 90. 
In FIG. 8, there is illustratively shown the press surface 78 of the 
semiconductor substrate 98, in particular the arrangement of one of the 
pressure sensing elements 100, and the corresponding pair of adjacent 
ridges 108 formed in the recess 104 are indicated in phantom line. The 
pressure sensing element 100 includes four semiconductor resistors 110a, 
110b, 110c, 110d, and four semiconductor conductors 112a, 112b, 112c, 112d 
which cooperate with the four resistors 110 to provide a Wheatstone 
bridge. The resistors 110 are formed by a known semiconductor 
manufacturing process, for example by diffusion or injection of a suitable 
impurity into the substrate 98. The conductors 112 are also formed by a 
similar process. The Wheatstone bridge constituted by the resistors and 
conductors 110, 112 serves for generating an electric signal representing 
a strain produced at the corresponding region in the diaphragm portion 106 
of the semiconductor plate 98 at which position the bridge is provided. 
This strain is caused by a pressure transmitted from the arterial vessel 
80 to the region of the diaphragm portion 106. Thus, this bridge serves as 
the pressure sensing element 110. In this connection, it is noted that the 
resistors or conductors 110, 112 are not visible on the diaphragm portion 
106 since those elements are formed by locally providing or increasing the 
concentration of the impurity in the diaphragm portion 106 of the 
substrate 98. 
The semiconductor substrate 98 is manufactured by the following manner, for 
example: A silicon wafer 98 is prepared as shown in FIG. 9. A resist 114 
is applied to the wafer 98 for a first etching, as shown in FIG. 10. After 
the first etching is carried out and then the resist 114 is removed, a 
shallow recess 116 is produced in the wafer 98, as shown in FIG. 11. The 
lengthwise and widthwise dimensions of the recess 116 are equal to those 
of the final, elongate recess 104 shown in FIG. 7. Subsequently, resists 
118 are applied to the wafer 98 for a second etching, as shown in FIG. 12. 
After the second etching is performed and then the resists 118 are 
removed, the elongate recess 104 is available in the wafer (semiconductor 
substrate) 98, as shown in FIG. 13. 
As described above, the ceramic substrate 90 is provided with an electric 
circuit. The electric circuit includes semiconductor devices such as 
multiplexers and preamplifiers, and superposed conductor patterns 
connecting those devices. Meanwhile, each of the pressure sensing elements 
100 formed on the diaphragm portion 106 is coupled to a common power 
supply via two supply terminals thereof, and is coupled to the electric 
circuit via two output terminals thereof. Thus, a number of terminals (or 
pads thereof) are arranged along a pair of opposite edge lines of the 
press surface 78. These terminals or pads are connected to corresponding 
terminals of the electric circuit provided on the ceramic substrate 90 via 
a flat cable 120 as shown in FIG. 5. The flat cable 120 includes a 
conductor pattern consisting of lead wires formed at regular intervals of 
distance, for example 100 .mu.m. The flat cable 120 is obtained by, for 
example, etching a copper foil adhered to one surface of a polyimide-resin 
film and plating ends (or terminals) of the thus obtained lead wires using 
gold or its alloy. One end of the flat cable 120 is connected, by thermal 
compression bonding or supersonic compression bonding, to the pads (or 
terminals) arranged on the press surface 78 of the semiconductor substrate 
98. The press surface 78 is coated with a suitable material, as needed. 
In the pulse wave detecting apparatus constructed as described above, the 
press surface 78 of the semiconductor substrate 98 has no recess, and each 
pressure sensing element 100 formed on the diaphragm portion 106 of the 
semiconductor substrate 98 detects a pulse wave transmitted directly from 
the arterial vessel 80 to the diaphragm portion 106, that is, not 
indirectly through an intervening object such as a soft filler. Thus, the 
present apparatus is free from the problem that the accuracy of detection 
of pulse wave is lowered due to a difference in thermal expansion between 
the semiconductor substrate 98 and the soft filler. 
In addition, since in the present apparatus the plurality of pressure 
sensing elements 100 are formed on the elongate diaphragm portion 106 at 
the bottom of the elongate recess 104 of the semiconductor substrate 98, 
the intervals between the pressure sensing elements 100 can be reduced as 
opposed to the event that a plurality of independent cavities or 
depressions are formed in a semiconductor substrate and each independent 
cavity is used for fabricating a pressure sensing element in an associated 
diaphragm portion thereof. 
Furthermore, the ridges 108 provided on the diaphragm portion 106 at the 
bottom of the elongate recess 104 serve for protecting the pressure 
sensing elements 100 against crosstalk, namely, interferance due to 
strains produced in the adjacent pressure sensing elements 100. Thus, the 
detection of pulse wave is carried out by the pressure sensing elements 
100 at the corresponding regions of the extremely small intervals, such 
that each element 100 is sufficiently independent of the other elements 
100. 
Referring next to FIGS. 14-16 there are shown other embodiments of the 
present invention. The same reference numerals as used in the preceding 
embodiment are used to designate the corresponding parts or portions of 
these embodiments, and no description of those parts or portions is 
provided. 
In the embodiment of FIGS. 14 and 15, a semiconductor substrate 98 has a 
plurality of slits 122 in place of the plurality of ridges 108 used in the 
preceding embodiment. The slits 122 are formed through an elongate 
diaphragm portion 106 of a small thickness by irradiation thereof of laser 
beam. A plurality of pressure sensing elements 100 are formed between the 
slits 122 in a manner similar to the preceding embodiment. Each of the 
slits 122 has a length and a width equal to those of the ridges 108. In 
the present embodiment, too, crosstalk between the adjacent pressure 
sensing elements 100 is effectively prevented. The slits 122 exhibit an 
appreciable effect even if the length of the slits 122 is smaller than the 
width of the elongate diaphragm portion 106. 
In the embodiment of FIG. 16, a back-up plate 126 formed of a glass is used 
in place of the insulator spacer 92 and back-up plate 96 of FIG. 5. The 
glass back-up plate 126 has a thickness greater than that of the back-up 
plate 96. In addition, a semiconductor substrate 98 is coupled to a 
ceramic substrate 90 through a gold wire pattern 128. In order to 
fabricate the present embodiment, first, ball-like ends of the gold wires 
128 are bonded to the ceramic substrate 90 and subsequently the other ends 
of the gold wires 128 are bonded to the semiconductor plate 98. In this 
case, the ball-like ends of the gold wires 128 are not located on the 
press surface of the semiconductor substrate 98, therefore the height of 
the bonding portions on the press surface is lowered to an advantage as 
compared with the other case in which the ball-like ends are bonded to the 
press surface of the semiconductor substrate 98. The gold wires 128 and 
the bonding portions are covered by a protect resin 130. 
While the present invention has been described in its presently preferred 
embodiments, it is to be understood that the present invention is by no 
means limited to the particularities of the illustrated embodiments but 
may otherwise be embodied. 
Although in the illustrated embodiments a plurality of pressure sensing 
elements 100 are provided at regular intervals of distance on the elongate 
diaphragm portion 106, it is possible to form a plurality of cavities or 
depressions in a surface opposite to a press surface of a semiconductor 
substrate, such that each cavity (or associated diaphragm) is provided 
with a pressure sensing element. According to the principle of the present 
invention, it is essentially required that a recess be formed in one 
surface of a semiconductor substrate (98) different from a press surface 
(78) at which the substrate (98) contacts a body portion (12) of a subject 
and that a diaphragm portion (106) of the substrate (98) serve for 
supporting pressure sensing means (100). The pressure sensing means may be 
constituted by a single pressure sensing element. 
In addition, the conductors 112a, 112b, 112c, 112d serving as parts of the 
Wheatstone bridge of the pressure sensing means 100 may be formed by vapor 
deposition of aluminum to the diaphragm portion 106 of the semiconductor 
substrate 98. 
Furthermore, while the illustrated embodiments utilize a single crystal 
silicon for the semiconductor substrate 98, it is possible to use as the 
semiconductor substrate 98 a single crystal of a compound such as gallium 
arsenide. 
It is to be understood that the present invention may be embodied with 
other modifications, changes and improvements that may occur to those 
skilled in the art without departing from the scope and spirit of the 
present invention as defined in the appended claims.