JPH0577986B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a mounting structure for a semiconductor acceleration sensor.

[Conventional technology]

Conventionally, as a structure generally used to detect vibrations and acceleration, a thin diaphragm part 21 on which a semiconductor strain gauge is formed is formed on a semiconductor substrate 20, as shown in the perspective view of FIG. One thick part of the support body 22 is adhesively fixed to the pedestal 30, and the other thick part is used as a free end 23 to detect the force to be measured according to the change in the resistance value of the semiconductor strain gauge. Semiconductor type acceleration sensors and the like are known. In FIG. 4, a load 24 is bonded to the free end 23 in order to increase the mass of the free end 23 and increase its inertia. Further, the direction of the detected force is the direction of the arrow 40.

[Problem that the invention seeks to solve]

As shown in FIG. 4, when the semiconductor acceleration sensor described above is fixed so that its longitudinal direction is parallel to the direction in which gravity is applied (gravitational direction), that is, the vertical direction with respect to the earth, the diaphragm portion 21 Axis in the longitudinal direction passing through x ₁ and free end 2
There is a difference of distance l between the center of gravity of load 24 and the axis _x2 extending in the direction of gravity, and when vibration in the vertical direction relative to the ground is applied to the semiconductor acceleration sensor, a moment acts and the free The end 23 is displaced in the direction of the arrow 40, the diaphragm portion 21 is bent, an error is added to the true displacement due only to the detected force, and an electrical signal corresponding to the error is detected as noise, resulting in semiconductor acceleration. Sensor S
(Signal)/N (Noise) ratio deteriorates.

Therefore, the present invention has been made in view of the above points, and when vibration in the direction of gravity is applied to a semiconductor acceleration sensor, the influence of the vibration is reduced as much as possible,
The purpose is to improve the S/N ratio.

[Means for solving problems]

In order to achieve the above object, the present invention provides a semiconductor strain gauge that includes a thin-walled diaphragm portion disposed on the gauge placement surface, a thick-walled support portion formed at one end of the diaphragm portion, and a thick-walled support portion formed at one end of the diaphragm portion. a cantilever having a free end that is a thick wall portion formed at the other end of a diaphragm part, and an axis in the longitudinal direction of the cantilever passing through the diaphragm part;
The semiconductor acceleration sensor is formed such that a center of gravity at the free end is offset by a predetermined distance from an axis extending in a direction in which gravity is applied, and the longitudinal direction of the cantilever is perpendicular to the direction of gravity. The support part is fixed to the object to be detected so that the gauge arrangement surface of the diaphragm part is parallel to the direction of gravity, and the direction is perpendicular to the longitudinal direction of the cantilever and the direction of gravity is parallel to the direction of gravity. A semiconductor type acceleration sensor is used, which is characterized by detecting the acceleration of the object to be detected in a direction perpendicular to the direction.

〔Example〕

Hereinafter, the present invention will be explained using embodiments shown in the drawings.

FIG. 1 shows an embodiment of the present invention, and FIG. 1A shows a top view thereof, and FIG. 1B shows a cross-sectional view taken along the line B--B in FIG. In the figure, 100 is a thick film printed substrate, an electric element 200, which will be described later, and a cantilever 4.
A sensor element consisting of a and a pedestal 6 is installed on the substrate, and these are electrically wired. A ceramic cap 600 is airtightly adhered to the thick film printed circuit board 100 with an adhesive or the like, and inside the ceramic cap 600 are a sensor element, a terminal 500, a terminal 500 and a cantilever 4a installed on the thick film printed circuit board 100. A damping liquid 400 and a wire wire 300 to be wire-bonded are provided for electrical connection with a pad portion 11b2 which will be described later. Damping liquid 40
0 is made of silicone oil or the like, and is used as a mechanical high-cut filter by utilizing the damping effect of viscous resistance. Here, air 900 is enclosed in the ceramic cap 600 in order to absorb expansion and contraction of the damping liquid 400 due to temperature changes. A partition wall 601 is provided.

Next, regarding the sensor element consisting of the cantilever 4a and the pedestal 6, the top view shown in FIG. 2a and the A--A in FIG.
This will be explained using an A-line sectional view. In the figure, 4a
is a cantilever made of, for example, an N-type silicon single crystal substrate, and includes a thin diaphragm portion 7, a free end 1, a guard portion 4a1 arranged around the free end 1 to protect the free end 1, and a support member 8. Become.
Incidentally, the scribing for forming the gap 4a2 between the free end 1 and the guard portion 4a1 is performed by etching both sides of the cantilever 4a.
The formation of the diaphragm part 7 and the scribing are performed simultaneously by trenching and etching the upper surface (in FIG.

A base layer 3b in which a Ni layer or the like is plated or vapor-deposited is formed on the surface of a predetermined region of the support 8 and the guard portion 4a1, and the base layer 3b is formed on the base 6 on which the base layer 3b is also formed, via the solder layer 5b. It's glued.
Incidentally, a recess 6a of a predetermined depth is formed on the surface of the pedestal 6 facing the cantilever 4a so that the cantilever 4a can be displaced in accordance with the acceleration to be measured and to prevent damage due to excessive displacement. Ori,
Further, the recess 6a is formed from one end surface to the other end surface so that the damping liquid 400 can freely enter and exit the sensor element.

A base layer 3a is formed at multiple locations (seven locations in the figure) on one main surface (adhesive surface) 2 of the free end 1.
The solder layer 5a as a load is passed through the base layer 3a.
is glued. Here, as in this example, the solder layer 5
By forming a at multiple locations, solder dripping and misalignment can be suppressed. In addition, the base layer 3a and the solder layer 5
a can be formed at the same time and in the same process as the base layer 3b and solder layer 5b formed on the surface of the support 8 or the guard portion 4a1.

Inside the diaphragm part 7 or the diaphragm part 7
At the top (the former shown in the figure), there are four semiconductor strain gauges 9 formed by introducing a P-type impurity such as boron into the diaphragm part 7 by thermal diffusion or ion implantation using a known semiconductor processing technique. and P
Wiring layer 11 formed by introducing type impurities at high concentration
The semiconductor strain gauges 9 are electrically connected to each other by a wiring member 11b made of an Al vapor deposited film or the like, thereby forming a full bridge. The wiring layer 11a is formed to extend to the free end 1 so that an abnormal signal can be output as an output of the semiconductor acceleration sensor in the event that the diaphragm part 7 is damaged. A protective film such as an oxide film, 11b1 is a contact portion between the wiring layer 11a and the wiring member 11b, and 11b2 is a pad portion.

And the above sensor element has a free end 1
When acceleration is applied to the diaphragm section 7, the resistance value of the semiconductor strain gauge 9 changes depending on the magnitude of the acceleration. By applying a voltage to the bridge circuit in advance, an unbalanced voltage is generated as the bridge output. The acceleration to be detected is detected according to the voltage value, and the thick film printed circuit board 1 is
00 by gluing the pedestal 6 so that its longitudinal direction is perpendicular to the direction of the arrow in FIG.

In FIG. 1, 200 is an electric element, which constitutes a high gain amplification circuit that amplifies the electric signal from the sensor element, and is electrically connected to the terminal 500 and the pad portion 101 on the thick film printed circuit board 100. ing. 800 is a metal case that protects the sensor element, high gain amplifier circuit, etc. from EMI (electromagnetic interference). Further, a through hole is formed in the case 800, and the lead terminal 700 exists in the through hole with good airtightness while maintaining electrical insulation from the case 800 via glass or the like.
Further, the lead terminal 700 and the pad portion 101 are electrically connected by a wire line 300, and the electrical connection with the outside of the case 800 is made through the lead terminal 70.
It is done by 0. Then, it is assembled into a device such as an automobile, with the arrow direction in FIG. 1 pointing upward, that is, perpendicular to the ground, and the acceleration in the direction perpendicular to the plane of the paper in FIG. 1 is detected.

Therefore, according to the above embodiment, as shown in the enlarged perspective view of the main part of the cantilever 4a in FIG. 1 of FIG. 3, the longitudinal direction of the cantilever 4a is equal to the horizontal direction y with respect to the earth, and The cantilevers 4a are arranged so that the width direction of the cantilevers 4a is equal to the direction x. Note that the longitudinal direction in the present invention refers to the direction from the support body 8 to the diaphragm portion 7,
This refers to the direction toward the free end 1 or the opposite direction, and the width direction is the direction in which the long sides of the quadrilateral cross section face when the cantilever 4a is cut along a plane perpendicular to its longitudinal direction. In other words, the longitudinal direction of the cantilever 4a is the horizontal direction y, and the surface of the diaphragm portion 7 on which the semiconductor strain gauge 9 is formed is parallel to the vertical direction x. Further, the horizontal direction and vertical direction referred to in the present invention are considered with the earth as a reference.

By arranging the cantilever 4a as described above, for example, when a car passes through a bumpy road and the cantilever 4a receives vibration in the direction x perpendicular to the ground, the axis _y1 in the longitudinal direction passing through the diaphragm part 7, An axis x ₃ extending in the direction of gravity from the center of gravity between the free end 1 and the solder layer 5a as a load
and have a perpendicular relationship with a certain interval.
Therefore, the stress that the diaphragm portion 7 receives due to the vibration in the vertical direction x becomes a force due to the twisting of the free end 1 in the T direction. Here, when the same force is applied, the displacement in the Z direction in the figure (the direction in which the detected acceleration is applied) is naturally smaller in bending and twisting than in bending. It can be seen that even if vibration is received in the direction x, its influence is reduced.

Also, according to this embodiment, the same thick film printed substrate 10
The sensor element and high gain amplifier circuit are installed on the 0. Conventionally, they were installed on each board or case, and the connection between the two was made using a printed board. This eliminates the need for a compact semiconductor acceleration sensor.

Next, the experimental results of the present inventors will be shown using FIG. The perspective view of FIG. 5a shows the state in which the semiconductor acceleration sensor is attached to the pedestal 30. The semiconductor acceleration sensor is similar to the conventional one shown in Figure 4, and its mounting angle is
Assuming that the vertical direction x ₄ with respect to one principal surface 31 of 0 is 0°,
The deviation angle of the semiconductor acceleration sensor from the axis was set as θ°, and the magnitude of the output of the semiconductor acceleration sensor was detected when an acceleration of 1G was applied in the vertical direction x ₄ at that time. However, when θ゜=0゜, the arrow direction 41 in the figure
The magnitude of the output when 1G of acceleration is added to (corresponding to the direction of the measured acceleration) is taken as 100%.
Figure 5b is a graph showing the results.While the conventional method (θ゜=0゜) produces an output of approximately 18% (0.18G) (this value corresponds to noise), the present invention (θ° = 90°, 270°), the output is only about 3% (0.03G), indicating that the S/N ratio has improved six times.

Note that the present invention is not limited to the above embodiments,
Various modifications are possible as long as they do not deviate from the main idea.
For example, in the embodiment shown in FIG. 1, a solder layer 5a as a load is bonded to the free end 1, but a load other than solder may be bonded.

〔Effect of the invention〕

As described above, according to the present invention, the longitudinal direction of the semiconductor acceleration sensor is horizontal to the earth (direction perpendicular to the direction of gravity), and
Since the support is fixed so that its width direction is vertical (direction of gravity), the free end will be torsionally displaced when vibration is applied to the ground in the vertical direction (direction of gravity). Therefore, there is an effect that the influence can be reduced.

[Brief explanation of the drawing]

FIG. 1a is a top view of an embodiment of the present invention, FIG. 1b is a sectional view taken along line B-B in FIG.
Figure b is a sectional view taken along the line A-A in Figure a, Figure 3 is an enlarged perspective view of the main part of the cantilever in Figure 1,
Fig. 4 is a perspective view of a conventional semiconductor acceleration sensor, Fig. 5a is a perspective view of a semiconductor acceleration sensor for explaining the experiment conducted by the present inventors, and Fig. 5b shows the experimental results. It is a graph. DESCRIPTION OF SYMBOLS 1... Free end, 4a... Cantilever, 5a... Solder layer, 6... Pedestal, 7... Diaphragm part, 8... Support body, 9... Semiconductor strain gauge.

Claims (1)

[Scope of Claims] 1. A thin diaphragm portion on which a semiconductor strain gauge is disposed on the gauge placement surface, a support portion which is a thick portion formed at one end of the diaphragm portion, and the other end of the diaphragm portion. between an axis in the longitudinal direction of the cantilever passing through the diaphragm part and an axis extending in the direction in which gravity is applied from the center of gravity at the free end; The semiconductor acceleration sensor is formed to be deviated by a predetermined distance, and the longitudinal direction of the cantilever is perpendicular to the direction of gravity, and the gauge arrangement surface of the diaphragm portion is aligned with the direction of gravity. fixing the support part to the object to be detected so as to be parallel to the object, and detecting the acceleration of the object in a direction perpendicular to the longitudinal direction of the cantilever and perpendicular to the direction of gravity; A semiconductor acceleration sensor featuring: 2. The semiconductor acceleration sensor according to claim 1, wherein the free end has a load bonded to it.