Composition of a high sensitivity sensor for detecting mechanical quantity

A composition of a high sensitivity sensor for detecting mechanical quantity including: an insulating matrix material; and a conductive path formed by discontinuously dispersing second phase particles of a conductor or a semiconductor into the insulating matrix material at an interparticle distance from 0.001 to 1 .mu.m, thereby imparting the high sensitivity in the mechanical quantity to the composition.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a composition of a high sensitivity sensor
 for detecting mechanical quantity of force, pressure, torque, speed,
 acceleration, position, displacement, impact force, weight mass, vacuum
 degree, rotating force, vibration, noise, etc. with high sensitivity.
 2. Description of Related Art
 An electrical resistance strain gauge, silicon of a semiconductor, etc. are
 conventionally used as a component of a sensor for detecting mechanical
 changing amounts of force, pressure, torque, speed, acceleration,
 position, displacement, impact force, weight mass, vacuum degree, rotating
 force, vibration, noise, etc. through strain (stress).
 In particular, the semiconductor silicon is applied to an impact tester, a
 displacement gauge, a pressure converter, an accelerometer, a compact
 pressure gauge for an organism, a flow meter, a gas pressure gauge, etc.
 as a strain gauge element of high sensitivity in various fields such as
 general industry, automobiles, medical care, etc.
 Silicon (Si) is generally used as a sensor for detecting mechanical
 quantity using the semiconductor. A phenomenon in which an electrical
 resistance value of the semiconductor is changed by strain caused by
 applying external force to the silicon is used.
 However, because of the lower sensitivity of the sensor constituted of a
 conventional material, it is difficult to obtain a sensor for detecting
 mechanical quantity having a required accuracy and high sensitivity which
 are used as a micro pressure sensor of an organismic system, etc., a
 combustion pressure sensor and a pressure sensor for a hydraulic device.
 SUMMARY OF THE INVENTION
 In consideration of such problems, the object and an aspect of the present
 invention is to provide a composition of a high sensitivity sensor for
 detecting mechanical quantity in which a sensor capable of detecting a
 mechanical quantity can be constructed with a high sensitivity (high gauge
 ratio).
 Next, a second aspect of the invention is a composition of a high
 sensitivity sensor for detecting mechanical quantity comprising:
 an insulating matrix material;
 a conductive path formed by discontinuously dispersing second phase
 particles of a conductor or a semiconductor into the insulating matrix
 material at an interparticle distance from 0.001 to 1 .mu.m;
 wherein an average distance A between the second phase particles parallel
 to a loading direction of mechanical quantity to be detected is smaller
 than an average distance B between the second phase particles
 perpendicular to the loading direction;
 thereby imparting the high sensitivity in the mechanical quantity to the
 composition.
 The composition of a high sensitivity sensor for detecting mechanical
 quantity in the second aspect of the invention comprises the insulating
 matrix material and the conductive path which is constituted of
 discontinuously dispersing the second phase particles into this insulating
 matrix material at the interparticle distance from 0.001 to 1 .mu.m.
 In this composition of a high sensitivity sensor for detecting mechanical
 quantity, the average distance A between the second phase particles in the
 loading direction of the detected mechanical quantity is smaller than the
 average distance B between the second phase particles in the direction
 perpendicular to the loading direction. Accordingly, a large electrical
 resistance changing rate can be also obtained with respect to a small
 strain although its detailed mechanism is yet unclear. Therefore,
 strain-electrical resistance effects with high sensitivity can be
 obtained. Therefore, it has become clear that a gauge ratio is greatly
 increased in comparison with the conventional material.
 Therefore, sensitivity of the sensor for detecting mechanical quantity
 manufactured by the composition of the sensor in the second aspect of the
 invention is greatly improved. Accordingly, a sensor for detecting
 mechanical quantity with a high accuracy can be obtained.
 As mentioned above, in accordance with the second aspect of the invention,
 it is possible to provide a composition of a high sensitivity sensor for
 detecting mechanical quantity capable of constituting a sensor capable of
 detecting the mechanical quantity with high sensitivity.
 Next, a third aspect of the invention is a composition of a high
 sensitivity sensor for detecting mechanical quantity comprising:
 an insulating matrix material;
 a conductive path formed by discontinuously dispersing second phase
 particles of a conductor or a semiconductor into the insulating matrix
 material at an interparticle distance from 0.001 to 1 .mu.m;
 wherein the insulating matrix comprises crystal particles which are
 oriented and aligned in a loading direction of mechanical quantity to be
 detected;
 thereby imparting the high sensitivity in the mechanical quantity to the
 composition.
 The composition of a high sensitivity sensor for detecting mechanical
 quantity in the third aspect of the invention comprises the insulating
 matrix material and the conductive path which is constituted of
 discontinuously dispersing the second phase particles into this insulating
 matrix material at the interparticle distance from 0.001 to 1 .mu.m.
 This composition of a high sensitivity sensor for detecting mechanical
 quantity is in a state in which the crystal particles constituting the
 above insulating matrix are oriented along the loading direction of the
 detected mechanical quantity. In other words, an anisotropic property is
 given to a dispersion mode of the second phase particles.
 Accordingly, the distance between the second phase particles in the loading
 direction of the detected mechanical quantity can be set to be smaller
 than that in a direction perpendicular to the loading direction although
 its detailed mechanism is unclear.
 Further, a change in the interparticle distance in the loading direction
 caused by a stress load can be increased in comparison with that in the
 direction perpendicular to the loading direction. Namely, a change in
 electrical resistance value in the stress loading direction can be set to
 be larger than that in the direction perpendicular to the stress loading
 direction.
 Thus, a large electrical resistance changing rate can be also obtained with
 respect to a small strain and strain-electrical resistance effects with a
 high sensitivity can be obtained. Accordingly, it has become clear that a
 gauge ratio is greatly increased in comparison with the conventional
 material.
 Therefore, sensitivity of the sensor for detecting mechanical quantity
 manufactured by the composition of the sensor in the third aspect of the
 invention is greatly improved. Accordingly, a sensor for detecting
 mechanical quantity with a high accuracy can be obtained.
 As mentioned above, in accordance with the third aspect of the invention,
 it is possible to provide a composition of a high sensitivity sensor for
 detecting mechanical quantity capable of constituting a sensor capable of
 detecting the mechanical quantity with a high sensitivity.

DETAILED DESCRIPTION OF THE INVENTION
 (First Aspect of the Invention)
 A sensor for detecting mechanical quantity constituted of a composition of
 a high sensitivity sensor for detecting mechanical quantity of a first
 aspect of the invention is a sensor for measuring and detecting a
 mechanical quantity. Here, the mechanical quantity is preferably
 constituted of one or more kinds selected from a quantity of strain,
 displacement, stress, pressure and weight (load).
 The quantity of strain, stress and pressure mechanical quantity are more
 preferable.
 The above insulating matrix material becomes a base material in the
 composition of a high sensitivity sensor for detecting mechanical
 quantity. This insulating matrix material is constituted of a metal oxide,
 a metal nitride, or their composite compound.
 For example, the insulating matrix material can include an oxide or a
 nitride and their composite compound or a solid solution formed by one or
 more kinds of elements selected from aluminum, silicon, magnesium,
 calcium, chromium, zirconium, yttrium, ytterbium, lanthanum, vanadium,
 barium, strontium, scandium, boron, hafnium, bismuth, titanium, iron,
 zinc, niobium, tungsten, cerium, dysprosium, rhenium, lithium, samarium,
 tantalum, etc.
 The insulating matrix material can also include a composite oxide, a
 composite compound and a solid solution of the above elements. Further,
 the insulating matrix material can be also constituted of a ceramics
 material such as sialon, cordierite, mullite, zircon, forsterite, ferrite,
 spinet, etc.
 This insulating matrix material preferably includes a material of higher
 strength, higher toughness and higher impact resistance in comparison with
 second phase particles. In this case, it is possible to obtain a
 composition of a high sensitivity sensor for detecting mechanical quantity
 having a high strength and an excellent impact resistance.
 Usable kinds of a material as the above second phase particles depend on a
 kind of the insulating matrix material.
 For example, when a nitride of silicon, aluminum and boron is utilized as
 the insulating matrix material, particles formed by one kind or more of a
 metal carbide, a nitride, a silicide, a sulfide, and a boride, including
 B, Si, Ti, W, V, Hf, Zr, Zn, Nb, Ta, Cr, Ru, Au, Sn, In, Tl, Ag, Mo, etc.,
 can be used as the second phase particles.
 When the insulating matrix material is formed by Al.sub.2 O.sub.3,
 particles including one or more kinds of WC, Mo.sub.3 C, ZrC, W,
 TiB.sub.2, B.sub.4 C, SiC, Sn.sub.2 O.sub.3, RuO and Cu.sub.2 O can be
 used as the second phase particles.
 When the insulating matrix material is formed by AIN, particles including
 one or more kinds of TiB.sub.2, VB, ZrB.sub.2, CrB.sub.2, TiN, ZrN,
 Cr.sub.2 N, WSi.sub.2, NbSi.sub.2, TaSi.sub.2, etc. can be used as the
 second phase particles.
 The interparticle distance between the second phase particles dispersed
 into the insulating matrix material ranges from 0.001 to 1 .mu.m. When the
 interparticle distance is smaller than 0.001 .mu.m, it is close to a case
 in which the second phase particles are continuously dispersed. Therefore,
 linear strain resistance effects with a high sensitivity may not be
 obtained. In contrast with this, when the interparticle distance is
 greater than 1 .mu.m, the electric conductivity of the composition of a
 high sensitivity sensor for detecting mechanical quantity is reduced so
 that the function of the sensor for detecting mechanical quantity may not
 be obtained.
 The above interparticle distance means the distance of a clearance between
 a certain second phase particle and another second phase particle.
 The above interparticle distance can be measured by cutting the composition
 of a high sensitivity sensor for detecting mechanical quantity and etching
 a cross section of the composition of this sensor by ECR plasma to observe
 this cross section by SEM. Otherwise, the above interparticle distance can
 be measured by TEM-observing a thin piece of the composition of a high
 sensitivity sensor for detecting mechanical quantity.
 (First Aspect of the Invention)
 Next, in a first aspect of the invention, the above interparticle distance
 A is preferably equal to or smaller than half of an interparticle distance
 B. In this case, effects of the first aspect of the invention can be more
 reliably obtained.
 An insulating matrix material in a composition of a high sensitivity sensor
 for detecting mechanical quantity in the first aspect of the invention can
 be constituted of various kinds of substances previously shown as
 examples. Further, second phase particles can be also constituted of
 various kinds of substances previously shown as examples.
 These details are similar to those in the above-mentioned first aspect of
 the invention.
 (Second Aspect of the Invention)
 An insulating matrix material in a composition of a high sensitivity sensor
 for detecting mechanical quantity in a second aspect of the invention can
 be constituted of various kinds of substances previously shown as
 examples. Further, second phase particles can be also constituted of
 various kinds of substances previously shown as examples.
 These details are similar to those in the above-mentioned first aspect of
 the invention.
 (First and Second Aspects of the Invention)
 In the above first and second aspects of the invention, it is preferable to
 set a structure in which a third phase of an insulating property having an
 elastic modulus smaller than that of the above insulating matrix material
 is dispersed into the above insulating matrix material and the second
 phase particles are discontinuously dispersed into this third phase.
 As shown in FIG. 2 described later, effects of the first aspect of the
 invention can be obtained when the second phase particles are dispersed
 into crystal particles and/or an intercrystalline phase constituting the
 insulating matrix material. However, it is more preferable to disperse the
 second phase particles such that a conductive path is formed in at least
 the intercrystalline phase of the insulating matrix material.
 In each of these cases, the effects of the present invention can be more
 reliably obtained.
 It is also preferable that the above insulating matrix material is porous
 and has a high porosity in a direction perpendicular to a loading
 direction of the detected mechanical quantity. In this case, the Poisson's
 ratio in the perpendicular direction is reduced so that a change in
 resistance in the perpendicular direction can be reduced. Accordingly,
 since an electrical resistance changing rate in the loading direction is
 increased, it is possible to obtain a composition of a high sensitivity
 sensor for detecting mechanical quantity capable of constituting a sensor
 with higher sensitivity.
 The conductivity path formed by the above second phase particles may be set
 to be in an isotropic state. However, it is more preferable that the
 conductive path is in a state in which the conductive path is formed prior
 to the loading direction of the detected mechanical quantity. In this
 case, it is possible to obtain a composition capable of efficiently
 detecting the electrical resistance changing rate by a load of the
 detected mechanical quantity so that the effects of the present invention
 can be more reliably obtained.
 Various kinds of producing methods of the composition of a high sensitivity
 sensor for detecting mechanical quantity s in the first and second aspects
 of the invention will next be shown as examples.
 (Producing Method 1)
 There is a producing method of a composition of a high sensitivity sensor
 for detecting mechanical quantity comprising the steps of:
 preparing a matrix powder constituted of an insulating material, and second
 phase particles having a particle diameter ratio equal to or smaller than
 1/2 with respect to this matrix powder and constituted of a conductor or a
 semiconductor by wet or dry grinding and mixing;
 pressurizing the mixing powder from a predetermined direction and molding
 this mixing powder by using a die so that a molded body is obtained;
 obtaining a sintering body by sintering the above molded body while the
 molded body is pressurized in the same direction as the pressurizing
 direction to the above mixing powder; and
 cutting a cutting piece out of the sintering body such that a loading
 direction of a detected mechanical quantity is parallel to the
 pressurizing direction in the sintering.
 The above matrix powder may be constituted of a raw material powder itself
 or the granular powder of the raw material powder.
 As shown in FIGS. 1A-1C, described later, the cutting piece is cut out of
 this sintering body such that the loading direction of the detected
 mechanical quantity is parallel to the pressurizing direction in the
 sintering. Thus, it is possible to obtain a composition of a high
 sensitivity sensor for detecting mechanical quantity in the present
 invention (the cutting piece cut out of the, sintering body becomes the
 composition of a high sensitivity sensor for detecting mechanical
 quantity).
 A device such as a hot press, a HIP (Hot Isostatic Press), etc. can be used
 to sinter the molded body while the molded body is pressurized.
 (Producing Method 2)
 There is a producing method of a composition of a high sensitivity sensor
 for detecting mechanical quantity comprising the steps of:
 making a laminating molded body in which an insulating sheet molded body
 formed by molding a matrix powder constituted of an insulating material in
 a sheet shape, and mixing powder formed by mixing second phase particles
 constituted of a conductor or a semiconductor with the above insulating
 material, or a second sheet molded body formed by molding the above second
 phase particles in a sheet shape are laminated with each other;
 obtaining a laminating sintering body in which an internal stress is given
 to the laminating sintering body by sintering the laminating molded body
 while the laminating molded body is pressurized in a direction
 perpendicular to a laminating direction; and
 cutting a cutting piece out of the laminating sintering body such that a
 loading direction of a detected mechanical quantity is parallel to a
 pressurizing direction.
 For example, the mixing powder constituted of the above second phase
 particles and the above insulating material is printed to the above
 insulating sheet molded body by screen printing, etc. while patterns of a
 stripe and a grid are formed. Thus, a printing body is produced. The
 laminating molded body can be produced by overlapping a plurality of such
 printing bodies.
 The others are similar to those in the above producing method 1.
 (Producing Method 3)
 There is a producing method of a composition of a high sensitivity sensor
 for detecting mechanical quantity comprising the steps of:
 preparing a matrix powder constituted of an insulating material, and second
 phase particles having a particle diameter ratio equal to or smaller than
 1/2 with respect to this matrix powder and constituted of a conductor or a
 semiconductor;
 kneading the above matrix powder and the above second phase particles after
 adding a binder to the matrix powder and the second phase particles;
 making a core-shaped molded body having a conductive path discontinuously
 dispersing the second phase particles thereinto by extrusion-molding the
 kneading substance;
 making a columnar molded body having a cylindrical shape, a rectangular
 parallelepiped shape, etc. by again applying a uniaxial press pressure to
 the core-shaped molded body in its longitudinal direction together with
 the matrix powder constituted of the insulating material;
 a process for obtaining a columnar sintering body by sintering the columnar
 molded body while the columnar molded body is pressurized in its
 longitudinal direction; and
 a process for cutting a cutting piece out of the columnar sintering body in
 a direction parallel to the longitudinal direction of the columnar
 sintering body.
 In accordance with each of the above producing methods 1 to 3, the
 composition of a high sensitivity sensor for detecting mechanical quantity
 in the present invention comprises an insulating matrix material and a
 conductive path constituted of discontinuously dispersing the second phase
 particles into this insulating matrix material at an interparticle
 distance from 0.001 to 1 .mu.m.
 Further, it is similarly possible to easily obtain a composition of a high
 sensitivity sensor for detecting mechanical quantity in which the distance
 A between the second phase particles in the loading direction of the
 detected mechanical quantity is shorter than the distance B between the
 second phase particles in a direction perpendicular to this loading
 direction.
 Further, it is possible to easily obtain a composition of a high
 sensitivity sensor for detecting mechanical quantity in which crystal
 particles constituting the above insulating matrix are oriented or aligned
 in the loading direction of the detected mechanical quantity.
 The composition of a high sensitivity sensor for detecting mechanical
 quantity in the present invention can be also obtained by a producing
 method other than the above producing methods.
 In the above producing methods crystal particles constituting the
 insulating matrix material can be oriented or aligned in one or two
 directions by adopting a method in which columnar crystal particles are
 used as matrix powder, etc.. In embodiments, axes of columnar crystal
 particles can be oriented substantially parallel to a loading direction of
 a mechanical quantity.
 Thus, the distance between the second phase particles can be changed so
 that the sensitivity of a sensor made by this material can be adjusted.
 EMBODIMENTS
 Embodiment 1
 A composition of a high sensitivity sensor for detecting mechanical
 quantity in an embodiment of the present invention and its producing
 method will next be explained with reference to FIGS. 1A-3. Samples 1-6 in
 this embodiment will be also explained together with Comparative Samples
 C1-C2 with respect to performance of this composition of a high
 sensitivity sensor for detecting mechanical quantity.
 The composition of a high sensitivity sensor for detecting mechanical
 quantity in this Embodiment is also constituted of an insulating matrix
 material and a conductive path constituted of discontinuously dispersing
 second phase particles formed by a conductor or a semiconductor into the
 insulating matrix material at an interparticle distance from 0.001 to 1
 .mu.m. Further, in the composition of a high sensitivity sensor for
 detecting mechanical quantity, the distance A between the second phase
 particles in a loading direction of a detected mechanical quantity is
 smaller than the distance B between the second phase particles in a
 direction perpendicular to this loading direction. This composition of a
 high sensitivity sensor for detecting mechanical quantity functions as a
 high sensitivity sensor for detecting mechanical quantity capable of
 detecting the loaded detected mechanical quantity (Sample 6 Described
 Later).
 The composition of a high sensitivity sensor for detecting mechanical
 quantity in this example is also constituted of an insulating matrix
 material and a conductive path constituted of discontinuously dispersing
 second phase particles formed by a conductor or a semiconductor into the
 insulating matrix material at an interparticle distance from 0.001 to 1
 .mu.m. Further, in the composition of a high sensitivity sensor for
 detecting mechanical quantity, crystal particles constituting the above
 insulating matrix are oriented in a loading direction of a detected
 mechanical quantity. This composition of a high sensitivity sensor for
 detecting mechanical quantity functions as a high sensitivity sensor for
 detecting mechanical quantity capable of detecting the loaded detected
 mechanical quantity (Sample 7 described later).
 Producing methods of Samples 1-7 in this embodiment and Comparative Samples
 C1-C2 will be explained.
 &lt;Sample 1&gt;
 94 wt % of Si.sub.3 N.sub.4 (average particle diameter: 0.2 Mm), 6 wt % of
 Y.sub.2 O.sub.3, PVA (polyvinyl alcohol) as a binder, and a dispersion
 stabilizer are mixed by wet grinding and mixing in a ball mill and
 granular powder having about 100 .mu.m in particle diameter is made by a
 spray dryer. Here, Si.sub.3 N, is matrix powder for an insulating matrix
 material and Y.sub.2 O.sub.3 is a sintering assistant agent.
 90 wt % of the above granular powder and 10 wt % of SiC (average particle
 diameter: 0.4 .mu.m) are mixed by wet mixing and grinding and are set to
 100 wt %. This mixed material is dried, degreased and molded. Here, SiC is
 second powder constituting second phase particles.
 As shown in FIG. 1A, a molded body 11 having a disc shape and 60 mm in
 diameter and 10 mm in thickness is obtained by the above molding. This
 molded body 11 is hot-pressed for one hour in a condition of 1850 .mu.C in
 temperature and 20 MPa in press pressure.
 As shown in FIG. 1B, a cutting piece 1 is cut out of the obtained hot
 pressed body 12 such that the direction of a detected mechanical quantity
 is parallel to a direction of the press pressure applied in the hot press
 as shown in FIG. 1C. As shown in FIG. 1C, this cutting piece 1 is a
 composition of a high sensitivity sensor for detecting mechanical quantity
 1 in this embodiment (Sample 1).
 A cutting cross section 120 of the hot pressed body 12 provided by cutting
 the above sample 1 is ECR-plasma-etched and its etching portion is
 SEM-observed. As a result, as shown in FIG. 2, it is confirmed that a cell
 wall stricture is formed in the above hot pressed body 12 such that
 peripheral portions of plural Si.sub.3 N.sub.4 crystal particles 21 are
 surrounded by SiC particles 22. In this figure, reference numeral 23
 designates an intercrystalline phase.
 Thus, it has become clear that the above Sample 1 has a structure in which
 SiC as the second phase particles is discontinuously dispersed into
 Si.sub.3 N.sub.4 as the insulating matrix material at an interparticle
 distance from 0.001 to 1 .mu.m.
 &lt;Samples 2 and 3&gt;
 64 wt % of Si.sub.3 N.sub.4 (average particle diameter: 0.2 .mu.m), 6 Wt %
 Of Y.sub.2 O.sub.3, 30 wt % of SiC (average particle diameter: 0.01 to
 0.03 .mu.m, specific surface area: 48 m.sup.2 /g) are mixed by wet
 grinding and mixing in a ball mill and are dried so that mixing raw
 material powder is obtained.
 This mixing raw material powder is uniaxial pressed and molded at a
 pressure of 20 MPa. Thereafter, these molded materials are hot-pressed for
 one hour at a press pressure of 20 mPa or 30 MPa and at a temperature of
 1850.degree. C. (in N.sub.2)
 Cutting pieces are cut out of these obtained hot pressed bodies such that a
 loading direction of a detected mechanical quantity is parallel to a hot
 pressing direction (see FIG. 1B). These cutting pieces become a
 composition of a high sensitivity sensor for detecting mechanical quantity
 of each of Sample 2 (press pressure 20 MPa) and Sample 3 (press pressure
 30 MPa).
 A cross section of the hot pressed body is ECR-plasma-etched by a method
 similar to that with respect to Sample 1 and its etching portion is
 SEM-observed. As a result, as shown in FIG. 2, it is confirmed that a cell
 wall structure is formed in the above hot pressed body 12 such that
 peripheral portions of plural Si.sub.3 N.sub.4 crystal particles are
 surrounded by SiC particles.
 &lt;Sample 4&gt;
 64 wt % of Si.sub.3 N.sub.4 (average particle diameter: 0.8 .mu.m), 6 wt %
 of Y.sub.2 O.sub.3, 30 wt % of TiN (average particle diameter: 0.4 .mu.m,
 specific surface area: 18 m.sup.2 /g ) are mixed by wet grinding and
 mixing in a ball mill and are dried so that mixing raw material powder is
 obtained. Here, TiN constitutes second phase particles.
 This mixing raw material powder is uniaxial pressed and molded at a
 pressure of 20 MPa. Thereafter, this molded material is hot-pressed for
 one hour at a press pressure of 20 MPa and a temperature of 1850.degree.
 C. (N.sub.2) as a condition.
 A cutting piece is cut out of this obtained hot pressed body such that a
 loading direction of a detected mechanical quantity is parallel to a hot
 press direction (see FIG. 1B). This cutting piece becomes a composition of
 a high sensitivity sensor for detecting mechanical quantity of Sample 4.
 A cross section of this hot pressed body is ECR-plasma-etched by a method
 similar to that of Sample 1 and its etching portion is SEM-observed. As a
 result, it is confirmed that a cell wall structure is formed in the above
 hot pressed body such that peripheral portions of plural Si.sub.3 N.sub.4
 crystal particles are surrounded by TiN particles (see FIG. 2).
 &lt;Sample 5&gt;
 54 wt % of Si.sub.3 N.sub.4 raw material powder having 0.2 .mu.m in
 particle diameter, 6 wt % of Y.sub.2 O.sub.3 raw material powder, and 40
 wt % of SiC raw material powder having an average particle diameter from
 0.01 to 0.03 .mu.m (specific surface area is 48 m.sup.2 /g) are mixed by
 wet grinding and mixing in a ball mill and are then dried so that mixing
 powder is obtained.
 This mixing powder is molded by a die and is then hot-pressed for one hour
 at a temperature of 1850.degree. C. and a press pressure of 20 MPa as a
 condition. A cutting piece is cut out of this hot pressed body such that a
 loading direction of a detected mechanical quantity is parallel to a hot
 press direction (see FIG. 1B). This cutting piece becomes a composition of
 a high sensitivity sensor for detecting mechanical quantity of Sample 5.
 A cross section of this hot pressed body is ECR-plasma-etched by a method
 similar to that of Sample 1 and its etching portion is SEM-observed. As a
 result, it is confirmed that a cell wall structure is formed in the above
 hot pressed body such that peripheral portions of plural Si.sub.3 N.sub.4
 crystal particles are surrounded by SiC particles (see FIG. 2).
 &lt;Sample 6&gt;
 60 wt % of Si.sub.3 N.sub.4 raw material powder having 1 .mu.m in particle
 diameter (specific surface area: 4 m.sup.2 /g), 5 wt % of Y.sub.2 O.sub.3
 raw material powder, 5 wt % of MgAlO.sub.2 raw material powder and 30 wt %
 of SiC raw material powder having 0.3 .mu.m in average particle diameter
 (specific surface area is 21 m.sup.2 /g) are mixed by wet grinding and
 mixing in a ball mill and are then dried so that mixing powder is
 obtained.
 This mixing powder is molded by a die and is precalcinated for one hour at
 a temperature of 1600.degree. C and a pressure of 20 MPa as a condition.
 Thereafter, this calcinated material is hot-pressed for one hour at a
 temperature of 1850.degree. C and a pressure of 20 MPa as a condition. A
 cutting piece is cut out of this hot pressed body such that a loading
 direction of a detected mechanical quantity is parallel to a hot press
 direction (see FIG. 1B). This cutting piece becomes a composition of a
 high sensitivity sensor for detecting mechanical quantity of Sample 6.
 A cross section of this hot pressed body is ECR-plasma-etched by a method
 similar to that of Sample 1 and its etching portion is SEM-observed. As a
 result, it has become clear that a cell wall structure is formed in the
 above hot pressed body such that peripheral portions of plural Si.sub.3
 N.sub.4 crystal particles having a large aspect ratio are surrounded by
 SiC particles (see FIG. 2). Further, it is confirmed that the distance
 between the SiC particles in the press direction is smaller than that in a
 direction perpendicular to the press direction.
 &lt;Sample 7&gt;
 6 wt % of Y.sub.2 O.sub.3 and 30 wt % of SiC particles are mixed by wet
 grinding and mixing with 74 wt % of columnar crystal Si.sub.3 N.sub.4
 powder in a ball mill so that a slurry is made. This slurry is formed in
 the shape of a thick film having about 50 .mu.m in thickness by using a
 doctor bladend is dried.
 The dried thick film body is laminated and hot-pressed for one hour at a
 temperature of 1850.degree. C and a pressure of 20 MPa as a condition.
 Then, similar to the sample 6, a cutting piece is cut out of the film body
 and is set to a composition of a high sensitivity sensor for detecting
 mechanical quantity of Sample 7.
 &lt;Comparative Sample C1&gt;
 74 wt % of Si.sub.3 N.sub.4 (average particle diameter; 0.5 .mu.m), 6 wt %
 of Y.sub.2 O.sub.3 and 20 wt % of SiC (average particle diameter; 0.7
 .mu.m) are mixed by wet grinding and mixing with each other in a ball mill
 and are dried and molded. Further, the molded material is hot-pressed so
 that a hot pressed body is obtained. A cutting piece is cut out of this
 hot pressed body and is set to Comparative Sample C1.
 A cross section of this hot pressed body is ECR-plasma-etched by a method
 similar to that of Sample 1 and its etching portion is SEM-observed. As a
 result, in this hot pressed body, SiC particles are uniformly dispersed
 into crystal particles of Si.sub.3 N.sub.4.
 &lt;Comparative Sample C2&gt;
 Comparative Sample C2 is produced by molding and sintering semiconductor
 silicon. This Comparative Sample C2 is conventionally used as a
 composition of a sensor for detecting mechanical quantity.
 &lt;Performance Evaluating Test&gt;
 With respect to composition of a high sensitivity sensor for detecting
 mechanical quantity s in Samples 1-7 and Comparative Samples C1-C2, gold
 (Au) is evaporated on both end faces of these composition of a high
 sensitivity sensor for detecting mechanical quantity s and these
 comparative samples. Further, a change in electrical resistance value is
 examined by using a two-terminal method when compression stress is loaded
 to these materials and samples. From these results, a specific resistance
 value are derived and described in Table 1.
 TABLE 1

Specific Resistance (.OMEGA.cm)
 Samplc 1 20
 Sample 2 9 .times. 10.sup.2
 Sample 3 4 .times. 10.sup.2
 Sample 4 3 .times. 10.sup.-3
 Sample 5 2 .times. 10.sup.2
 Sample 6 5
 Sample 7 2
 Comparative Sample C1 4 .times. 10.sup.8
 Comparative Sample C2 0.1
 Further, with respect to Sample 5 and Comparative Sample C2, a graphic
 representation showing the relation of strain and a resistance changing
 rate is described in FIG. 3.
 As can be clearly seen from FIG. 3, Sample 5 has resistance of strain
 effects in which the resistance changing rate is linearly changed from
 small strain to large strain.
 In contrast to the Samples 1-7 in this example, the Comparative Sample C1
 having SiC as the second phase particles uniformly dispersed into the
 insulating matrix material has a very large specific resistance value and
 no electric conductivity of the Comparative Sample C1 is recognized as
 shown in the Table 1. Therefore, Comparative Sample C1 can not be used as
 a composition of a high sensitivity sensor for detecting mechanical
 quantity.
 In contrast to this, it is recognized that Comparative Sample C2
 constituted of the silicon semiconductor has linear strain resistance
 effects. Accordingly, this Comparative Sample C2 functions as a
 composition of a sensor for detecting mechanical quantity. However, it has
 become clear that Comparative Sample C2 is not preferable as a material
 for obtaining a high sensitivity sensor for detecting mechanical quantity.
 Having thus described the invention in detail, it will be understood that
 these details need not be strictly adhered to, but that various changes or
 modifications may suggest themselves to those skilled in the art, all
 falling within the scope of the invention as defined by the claims.
 The disclosure of the priority document Application No. 10-020275, which
 was filed in Japan on Jan. 16, 1998, is incorporated by reference herein
 in its entirety.