Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Physical deformation
Reexamination Certificate
1997-08-08
2002-09-10
Saadat, Mahshid (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Physical deformation
C257S414000, C257S415000, C257S416000, C257S418000, C257S419000, C257S420000, C438S050000
Reexamination Certificate
active
06448624
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims priority from Japanese Patent Applications No. 8-211086 filed Aug. 9, 1996, No. 8-211088 filed Aug. 9, 1996, No. 8-211089 filed Aug. 9, 1996, No. 8-230731 filed Aug. 30, 1996, No. 8-230732 filed Aug. 30, 1997, and No. 9-86331 filed Apr. 4, 1997, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor acceleration sensor for detecting acceleration by utilizing a semiconductor material having a large piezoresistance coefficient, particularly to a semiconductor acceleration sensor that is constituted to be able to detect acceleration at a comparatively low level of substantially ±1 G or smaller.
2. Description of Related Art
There is a semiconductor acceleration sensor that is formed into a shape where a weight portion dislocated by receiving acceleration is supported by an outer frame via beams at which diffused resistors are formed, by etching a silicon substrate. According to this sensor, when acceleration is applied thereon, the weight portion is dislocated by receiving a force proportional to the acceleration and therefore, the beams supporting the weight portion are distorted by which resistance values of the diffused resistors are changed through a piezoresistance effect in response to stresses caused by the distortion. The change of the resistance value can be detected as a voltage signal by forming a detecting circuit where the diffused resistors are connected in a bridge connection and the applied acceleration can be detected based on the voltage signal.
Meanwhile, such a semiconductor acceleration sensor is used for detecting, for example, a vehement impact that occurs in a case of an automobile collide. Because this semiconductor acceleration sensor detects the degree of impact received by a detected portion as a magnitude of acceleration, acceleration to be detected has a large acceleration value which exceeds 10 G (G is a gravitational acceleration of 9.8 m/sec
2
).
Meanwhile, it has been requested in recent years for an automobile or the like to achieve promotion of safety by carrying out braking control or the like by detecting a very small acceleration to a degree of level of acceleration or deceleration caused in a normal running state, which is far smaller than the acceleration caused by impact as described above. Accordingly, an acceleration sensor capable of accurately detecting an acceleration having a range from substantially ±1 G to at least substantially ±2 G as a range of acceleration to be detected has been requested.
However, such a semiconductor acceleration sensor for detecting a very small acceleration has the following technological problem. That is, a very small force which the weight portion of the sensor chip receives by acceleration, is caused as strain of the beams and accordingly, when the beams receives a force even slightly through the frame portion to which a sensor chip per se is fixed, stresses are caused in the beams supporting the weight portion and the diffused resistors on the beams are applied with stresses by which adverse influence may be effected on the detecting operation, such as variation of the sensitivity of detection.
In order to deal with such a drawback, according to a semiconductor acceleration sensor having a small detection range of from ±1 G to ±2 G as the detection range of acceleration, a structure for reducing as less as possible stresses received from a substrate, is adopted and an outline of the structure is shown, for example, in FIG.
44
and FIG.
45
. That is, a semiconductor sensor chip
1
made of silicon is formed in a state where a sensor element
3
is supported by a cantilever
4
in a first frame
2
which constitutes an outer frame.
The sensor element
3
is constituted by a second frame in an U-like shape, four beams
6
a
through
6
d
extended from the second frame
5
and a weight portion
7
supported by the four beams
6
a
through
6
d.
Diffused resistors are previously formed at the four beams
6
a
through
6
d
where resistances thereof are varied by the piezoresistance effect when they receive distortion. Further, the diffused resistors are wired in a bridge connection whereby a change in the resistance can be outputted as a voltage signal.
According to the semiconductor sensor chip
1
, the first frame
2
is fixed to a seat
8
made of glass by anodic bonding. A recess
8
a
is formed in the seat
8
on a side thereof more inner than a portion thereof facing to the first frame
2
by which even if the weight portion
7
is deformed it is not brought into contact with the recess
8
a.
The seat
8
made of glass is bonded and fixed to a substrate
9
made of ceramic. An IC chip
10
for carrying out signal processing of an output from the sensor is attached to the substrate
9
by die bonding and the IC chip
10
and the semiconductor sensor chip
1
are electrically connected by a bonding wire
11
.
The substrate
9
to which the semiconductor sensor chip
1
is fixedly adhered via the seat
8
, is arranged in a case
12
comprising a base
12
a
and a cap
12
b.
Oil
13
is filled in the case
12
as a damper material for preventing the device from destructing when an excessive acceleration is applied thereon. A lead, not shown, electrically connected to the semiconductor sensor chip
1
or the IC chip
10
is extended from the case
12
to outside by which a detection signal is outputted.
According to the above-described constitution, when the semiconductor sensor chip
1
receives an acceleration orthogonal to a face thereof, the weight portion
7
is dislocated in a direction opposed to the acceleration by a force at that moment, whereby the diffused resistors formed at the beam
6
a
through
6
d
are applied with a distortion in accordance with the acceleration. Then, an output voltage of a circuit in a bridge connection is varied by the piezoresistance effect of the diffused resistors and accordingly, the applied acceleration can be detected.
However, by adopting such a structure, the portion of the first frame
2
needs to be constituted extraneously in addition to essential portions for detecting acceleration according to the semiconductor acceleration sensor
1
and therefore, it is inevitable to increase the chip size by the first frame
2
. As a result, the portion of the first frame
2
becomes a hindrance for downsizing a total size of the sensor.
Further, according to the above-described sensor, a seal mechanism for preventing leakage of the oil
13
is needed and the like, which gives rise to general complication of the structure.
Moreover, there has been in recent years an increase in needs for detecting acceleration at a comparatively low level of substantially 1 G or lower in the usage of ABS (Antilock Braking System) or a device for preventing transverse skidding in curving operation of an automobile, however, according to the conventional acceleration sensor utilizing oil damping as mentioned above, it is difficult to sufficiently lower the detectable acceleration.
That is, the conventional sensor has a drawback where stable detecting operation may not be carried out due to the oil
13
filled in the case
12
as a damper material whereby the temperature range in use may be limited or detection error may be enlarged.
For example, according to a result of actual measurement of a degree of varying sensitivity (which indicates as a value of percentage a degree of varying sensitivity in a case where the sensitivity is defined as a value of a difference between output voltages when acceleration is 0 G and when it is 1 G) in the above-described structure in the case where the temperature range for use is as wide as from substantially −30° C. to 85° C., a dispersion of about −2.5% as a minimum value and about '1% as a maximum value is caused. Therefore, since the degree of varying sensitivity that is practically necessary in accurately
Ao Kenichi
Ishio Seiichiro
Kitao Norio
Kunda Tomohito
Murata Minoru
Denso Corporation
Ortiz Edgardo
Pillsbury Madison & Sutro LLP
Saadat Mahshid
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