JPH04181170A - Semiconductor acceleration sensor - Google Patents

Abstract

PURPOSE:To use the title sensor even in the circumferential environment of a wide temp. range for a long period of time with high reliability by providing a means absorbing the volumetric increment due to the thermal expansion of oil. CONSTITUTION:A volume absorbing means is constituted of sponge 20 having elasticity and the sponge 20 is covered with an oil impermeable cover 20a so as not to absorb oil 14. A protective member 21 is fixed to a base 1 in order to hold the sponge 20. The oil 14 is injected from an injection hole 15 in such a state that the circumferential temp. is lowered to the min. use circumferential temp. permitted by an acceleration sensor and hermetically sealed by a seal material 18. When the sensor is set to a use state, the oil 14 always acts in an expanding direction. The increased volume due to expansion is absorbed by the sponge 20 and the pressure of the oil in the sensor rises by a slight value compressing the sponge 20. That is, the expansion increment of the oil 14 at the time of the change of the use circumferential temp. within a tolerant temp. range is entirely absorbed by the sponge 20 and the internal pressure of the oil is kept almost constant to be suppressed to a slight change.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor acceleration sensor, and more specifically, to a semiconductor acceleration sensor used as a sensor for controlling electronically controlled suspensions, anti-skid brakes, etc. of automobiles. It is.

[Prior Art] FIGS. 5 to 8 show conventional acceleration sensors, and FIGS.
In Figure 6, (1) is a base, (2) is a silicon pedestal fixed to this base (1), and (3) is made of n-type silicon, with one end fixed to the pedestal (2). Cantilever beam (4) is a weight provided on the tip of this cantilever beam (3) to increase sensitivity;
(5) is a resistance section consisting of four pieces provided as described later on a part of the cantilever beam (3) near the pedestal (2);
(6a) to (6d) are lead bins for drawing out the resistance part (5) to the outside, and (7) is a lead bin for drawing out the resistance part (5) to the outside, and (7) is a lead bin for each resistor of the resistance part (5) and four glue dowels (6a) to (6d). Wires for connection, (8) are grooves, and (10) have one end fixed to the base (1) and lead bins (6a) to (6d).
), (11) is a lead bin (
A shield for fixing and sealing 6a) to (6d) and the base (1), (12) a case that envelops the whole, (13) a joint that joins the base (1) and the case (12), (1
4) is oil for providing a damper to the cantilever beam (3), (15) is an injection hole for injecting oil, (
16) is a sealing material for sealing the injection hole (15), ^y
is the acceleration acting on the weight (4).

Figure 7 shows the details of the resistive part (5) provided on the cantilever beam (3), where R2+R3 is the cantilever beam (3).
Parallel to the longitudinal direction of the beam (3)/A resistor diffused on the silicon crystal, R,, R, is a resistor also provided perpendicularly, (8) is a resistor disposed on the cantilever beam (3). The groove (9) provided to increase sensitivity is the thin part of the cantilever beam (3) where the stress is greatest.

Moreover, FIG. 8 is a wiring diagram in which the resistors RI+Rt+R3+R provided on the cantilever beam (3) are pre-connected and di-connected.

Figures 9 (a), (b), and (c) show the input-output relationship; (a') input characteristics, (b) output characteristics when no tamper is present, and (c) appropriate tamper FIG.

Next, the operation will be explained.

When acceleration AV acts on the weight (4) in the direction shown by the arrow in Figure 5, the cantilever beam (3) including the weight (4)
) A force py-M-Ay acts on the center of gravity of M is the total weight of the weight (4) and the cantilever beam (3).

Due to this force FY, either the bending stress σ8 acts on the cantilever beam (3) or the stress σ on the thinly formed portion (9) becomes the largest. This stress σ.

The resistor Rl+R2 provided on the upper part of the thin wall part (9)
+R3+ R produces a resistance change proportional to stress σ due to the piezoresistance effect. This rate of change in resistance is expressed by the following equations.

R,R32 R,R,2 Here, α is a piezoresistance coefficient specific to NRICON single crystal.

Since the resistors Rl+R, , R3, and R are configured in a bridge circuit as shown in FIG. 8, the bridge output voltage is proportional to the input acceleration Ay as shown in the following equation.
. is obtained (R= R, = R, = R.

-R,).

△R Vo-Vs The above indicates a steady state, or in a transient state, the 9th
The output voltage when the impulse input shown in Figure (a) is input will converge to a steady value after causing vibration as shown in Figure (b) if oil (14) for the damper is not included. On the other hand, damper fluid of appropriate viscosity, oil (14
), it exhibits appropriate output characteristics as shown in FIG. 2(e).

Next, the state of the oil injected for the damper will be explained. The oil (14) injected into the space surrounded by the base (1) and the case (12) is filled at the temperature at the time of injection so that there are no cavities. When the ambient temperature rises above the temperature at the time of injection, the oil (14) expands in volume, the internal pressure increases significantly, and the case (12) deforms as shown by the dashed line in FIG. 10. On the other hand, when the ambient temperature decreases,
The oil (14) contracts in volume and creates a cavity inside.

[Problems to be Solved by the Invention] Since the conventional acceleration sensor is configured as described above, the enclosed oil (14) may be damaged due to changes in ambient temperature.
When the temperature rises, the internal pressure increases and a portion of the case (12) may be deformed as shown in FIG. 10, or the joint (13) may be damaged.

On the other hand, when the temperature drops, a cavity is formed inside and oil (14
) could cause damage to the cantilever beam (3) due to vibration.

This invention was made to solve the above-mentioned problems, and aims to provide a semiconductor acceleration sensor that can be used with long life and high reliability even in an ambient environment with a wide temperature range.

[Means for Solving the Problems] A semiconductor acceleration sensor according to the present invention is provided with volume absorption means for absorbing volume expansion and contraction of sealed oil either in the case or in the case.

[Function] The volume absorbing means in the present invention maintains the internal pressure substantially constant by absorbing the volumetric expansion and contraction of the enclosed oil.

[Embodiment 1] A first embodiment of the present invention will be described below with reference to FIG. In the figure, the same reference numerals as in FIGS. 5 and 6 indicate the same parts. The volume absorbing means is an elastic sponge. The sponge (20) is covered with an oil-impermeable cover (20a) so as not to absorb the oil (14). (21) is a holding member fixed to the base (1) to hold the sponge (20).

Next, the operation will be explained. However, the basic principle of acceleration measurement is the same as that of conventional equipment, so it will be omitted.
Only matters related to the present invention will be described.

With the ambient temperature lowered to the lowest operating ambient temperature allowed by this acceleration sensor, pour oil (14) into the injection hole (15).
and seal with a sealing material (16). Thereafter, when the device is put into use, the oil (14) always works in the direction of expansion.

The increased volume due to this expansion is absorbed by the sponge (20),
The internal oil pressure increases by a small amount that compresses the sponge (20).When the operating ambient temperature changes within the permissible temperature range due to 6 or more, the sponge (20) absorbs all of the increased expansion of the oil (14). However, the oil internal pressure can be kept to a small change.

FIG. 2 shows a second embodiment, in which a space (23) is formed by a shielding plate (22) provided on the earthen wall of the case (12). (24) is a fine hole provided in the shielding plate (22), (
25) is an air layer. The volume absorbing means is thus formed.

In addition, the same reference numerals as in FIG. 1 indicate the same parts.

With the above configuration, the oil (14) always acts in a contracted state in the usage state after being sealed, and the contracted oil container 4) forms the micropores (24) below the maximum usage temperature.
The air moves downward through the air, forming an air layer (25).

The shield plate (22) is provided so that the micropores (24) are immersed in an appropriate amount of oil even at the lowest operating temperature.

On the other hand, the micropores (24) are set to an extremely small size so that the oil (14) can move following the expansion and contraction of the oil (14).

As described above, even when the air layer (25) is formed and the acceleration sensor vibrates, the cantilever beam (3)
The oil (14) in this section hardly vibrates.

FIG. 3 shows a third embodiment, and in the figure, (26) is an absorbing plate fixed to the case (12) with a sealed space (27) made of a thin elastic plate.

In the volume absorption means having the above structure, after oil is injected, the oil (14) expanded within the operating environment temperature range is
Deform the absorbing plate (26) outward. Absorption plate (26)
Since it is made of a material that deforms with slight force, it absorbs the increased volume of expansion of the oil (14) with only a slight change in the oil internal pressure within the allowable operating ambient temperature range.

FIG. 4 shows a fourth embodiment, in which case (1
2), a bellows part processed into a so-called bellows shape (
28) is provided.

In this configuration, after oil is injected, the oil (14) expanded within the usage environment temperature range is transferred to the bellows part (28).
deform outward. Since the bellows part (28) is configured to deform with a slight force, the oil (14) can be deformed by only a slight change in oil internal pressure within the allowable operating ambient temperature range.
absorbs the increased volume of expansion.

[Effects of the Invention] As described above, according to the present invention, since a volume absorbing means is provided which absorbs the volume increase due to thermal expansion of oil injected into the case with a minute pressure change, long life and reliability can be achieved. can be improved.

[Brief explanation of drawings]

1 to 4 are front sectional views of first to fourth embodiments of the present invention, FIGS. 2 and 3 are sectional views of acceleration sensors showing other embodiments of the invention, and FIG. 6 is a bottom view of the conventional acceleration sensor, FIG. 7 is a plan view (a) and side view (b) of the cantilever beam in FIG. 5, and FIG. 8 is a front view of the cantilever beam in FIG. Wiring diagram of the resistor formed in the Cheer lever beam, Figure 9 (a), (b)
, (c) is the input-output characteristic diagram of the one in Figure 5, the first
FIG. 0 is a front sectional view for explaining the operation of the device shown in FIG. (1) Base, (3) Cantilever beam,
(4)... Weight, (12)... Case, (14)... Oil, (20)... Sponge, (22)... Shielding plate,
(24) - Micropore, (26)... Absorption plate, (27>
... Space, (28) - Bellows section. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] In a semiconductor acceleration sensor, a cantilever beam having a semiconductor that detects acceleration is fixed to a case, and the case is filled with oil for a damper. Volume absorption absorbs the volume increase due to thermal expansion of the oil. A semiconductor acceleration sensor comprising: means.