JPH0664085B2 - Semiconductor acceleration detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention forms a strain detecting element, that is, a semiconductor strain gauge on or in a semiconductor substrate, and detects a change in resistance value of the semiconductor strain gauge that occurs when elasticity changes. The present invention relates to a semiconductor type acceleration detection device that outputs an electric signal.

[Conventional technology]

As a structure generally used to detect vibration, acceleration, etc., a thin diaphragm part on which a semiconductor strain gauge is formed is formed on a semiconductor substrate and one thick part of the support is fixed. However, there is known a cantilever-type semiconductor acceleration sensor that detects a force to be measured according to a change in resistance value of a semiconductor strain gauge with the other thick portion as a free end.

Since the diaphragm portion on which the semiconductor strain gauge is formed is thin as described above, its mechanical strength is naturally lower than that of the thick support and the free end. Then, for some reason, a strong shock is applied to the semiconductor type acceleration sensor to break the diaphragm part, and the sensing part formed by the semiconductor strain gauge may be broken.

Therefore, at least a part of the wiring portion electrically connected to the semiconductor strain gauge is formed so as to extend to the thick portion that is the free end, and for example, by applying a potential to the wiring and monitoring the potential, the sensing portion Some have been designed to detect abnormalities. FIG. 5 (a) is a plan view of such an acceleration sensor, and FIG. 5 (b) is a sectional view taken along line XX thereof. In the figure, reference numeral 500 denotes a silicon single crystal substrate, a thick-walled free end 500a, a thin-walled diaphragm portion 500b, and a thick-walled support 500c that is fixed to the pedestal 400 by soldering or the like.
Consists of. Further, four semiconductor strain gauges 100 are formed on the diaphragm portion 500b, and each semiconductor strain gauge 100 is formed by the wiring layer 200 formed by introducing impurities at a high concentration and the wiring member 300 formed of an Al vapor deposition film or the like. Are electrically connected to each other to form a full bridge. The wiring layer 200 extends to the thick free end 500a as described above. Incidentally, 300a is a contact portion between the wiring layer 200 and the wiring member 300, and 300b is a pad portion.

In this case, when acceleration is applied to the free end 500a, distortion occurs in the diaphragm portion 500b, the resistance value of the semiconductor strain gauge 100 changes according to the magnitude of acceleration, and voltage is applied to the bridge circuit in advance. An unbalanced voltage is generated as a bridge output, and the detected acceleration is detected according to the voltage value.

If the thin diaphragm 500b is broken,
The semiconductor strain gauge 100 or the wiring layer 200 is always damaged, and in this case, an abnormal signal appears in the output signal, so that the abnormal state of the semiconductor acceleration sensor can be confirmed.

[Problems to be Solved by the Invention]

However, conventionally, although the detection signal processing circuit in this type of acceleration sensor has been considered to detect an abnormality such as breakage of the diaphragm portion, it has not been considered to detect an abnormality due to another factor. That is, as an abnormality of the semiconductor type acceleration detection device, there is another abnormality such as fluctuation of the reference resistance value of the semiconductor strain gauge.

The present invention has been made in view of the above points, and an object of the present invention is to provide a semiconductor type acceleration detection device capable of detecting an abnormality in a semiconductor strain gauge.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present invention includes a detection element in which a strain detection element forming a bridge circuit is set in a detection section made of a semiconductor chip, and the detection section receives an acceleration so that an electrical response corresponding to the acceleration is obtained. An acceleration sensor for generating an output signal, a processing unit for detecting the output signal from the acceleration sensor, a timing circuit for generating a predetermined timing signal for instructing detection of an abnormal state of the acceleration sensor, and the timing circuit From the pseudo acceleration generation circuit for adding a pseudo acceleration signal to the detection element according to the generation of the predetermined timing signal to shift the balance of the bridge circuit and forcibly output an electrical output signal from the acceleration sensor, According to the output signal generated by the acceleration sensor by the pseudo acceleration signal from the pseudo acceleration generation circuit, Adopt the technical means of and an abnormality detection circuit for detecting an abnormal state of the serial acceleration sensor.

[Action]

 The operation of the above configuration will be described.

In an acceleration sensor, when acceleration is applied to a detection unit formed of a semiconductor chip, an electric output signal corresponding to the acceleration is generated by a strain detection element which is set in the detection unit and which constitutes a bridge circuit. The processing means detects and processes the acceleration based on the output signal from the acceleration sensor.

On the other hand, the timing circuit allows the operation of the pseudo acceleration generation circuit in response to the generation of a predetermined timing signal for instructing detection of an abnormal state of the acceleration sensor. That is, when the pseudo acceleration signal is added to the detection element, the balance of the bridge circuit is deviated, so that the acceleration sensor generates an electrical output signal as if the acceleration is applied to the detection portion formed of the semiconductor chip. Based on this output signal, the abnormality detection circuit detects an abnormal state of the acceleration sensor.

〔Example〕

 The present invention will be described below with reference to the embodiments shown in the drawings.

FIG. 1 is an electric circuit diagram showing the configuration of an embodiment of the present invention. In this embodiment, the structure of the acceleration sensor 11 is the same as that shown in FIGS. 5 (a) and 5 (b) described above. In FIG. 1, the acceleration sensor 11 is composed of a bridge circuit using a semiconductor strain gauge as described above, and points A, B, C, and D in the drawing are points A, B of the pad portion 300b in FIG. 5 (a).
It corresponds to B, C, D. This bridge circuit has amplifier A1
The constant current power supply from the constant current circuit 12 configured by is set to be supplied.

From such an acceleration sensor 11, a voltage signal having a value corresponding to the amount of acceleration used is output, and this detection signal is output by the amplifier circuit 13 to, for example, an in-vehicle airbag control EC.
Input to U3. Note that 3 is not limited to the airbag control ECU, but may be, for example, an anti-skid control ECU. More specifically, a signal of a potential difference corresponding to the amount of acceleration is generated between the output points A and D of the bridge circuit that constitutes the acceleration sensor 11, and this detection is performed by the instrument A3 and A4. It is amplified by the differential differential amplifier circuit 13 and output to the output terminal 1 as an acceleration detection signal. The amplifier A2 is an input buffer amplifier for supplying a reference voltage to the (-) side terminal of the amplifier A3.

In addition, the bridge circuit includes the pseudo acceleration generation circuit 14
Is provided. In this embodiment, a constant current power source is connected to the A terminal of the bridge circuit, and the action of this constant current power source is switched.
By turning on / off by SW, the balance of the bridge circuit is shifted, and the state is as if acceleration was applied. In the detection signal from the acceleration sensor 11 at that time, the pseudo acceleration appears as a variation ΔV as shown in FIG. Then, the detection signal from the acceleration sensor 11 is monitored by an abnormality detection circuit 15 which will be described later, and in the abnormality detection circuit 15, the switch SW is turned on to generate a pseudo acceleration by the pseudo acceleration generation circuit 14. When an abnormality is detected by the detection signal from the acceleration sensor 11 when applied, that is, the magnitude of the change ΔV, the sensor abnormality is notified. The switch SW is
For example, when the vehicle is traveling normally, it is set to the off state, the operation of the pseudo acceleration generating circuit 14 is prohibited, and the on / off control is performed only when the vehicle engine is started.

Further, while the pseudo acceleration generation circuit 14 is operating by the switch SW, the notification ECU 4 described later does not process the detection signal from the amplification circuit 13 in the airbag control ECU 3.

Next, a detection signal from the acceleration sensor 11 by the pseudo acceleration generation circuit 14 will be described.

(When the sensor bridge is broken) In FIG. 5 (a), the cantilever is normally bent in the χ direction and is unlikely to be bent in the y direction. When it is bent in the χ direction, the wiring is at points a and d in FIGS. 1 and 5 (a).
It will break at the point. Therefore, even if the pseudo acceleration generation circuit 14 is actuated, the variation ΔV due to the switch SW on / off control does not appear in the output signal from the amplification circuit 13, and it takes a constant value as shown in FIG. 3 (a). It becomes a waveform.
Incidentally, FIG. 3B shows a pseudo acceleration signal waveform generated by the pseudo acceleration generation circuit 14.

(If there is a disconnection or short circuit in the amplifier circuit 13 section) If there is an abnormal point in the amplifier circuit section, the amplifiers A3 and A4 will not operate properly. The change ΔV corresponding to the operation of the acceleration generation circuit does not appear.

(When the reference resistance of the semiconductor strain gauge changes) The output signal from the amplifier circuit 13 (see FIG. 4 (a)) includes
The pseudo acceleration signal (see FIG. 4 (b)) from the pseudo acceleration generating circuit 14 causes a variation ΔV due to the application of the pseudo acceleration. At this time, when the reference resistance value Rs of the semiconductor strain gauge is used, the magnitude of the variation ΔV is given by the following equation.

However, Av has an amplification degree determined by the amplifiers A3 and A4.

Therefore, the reference resistance value Rs of the semiconductor strain gauge changes and Rs'
In this case, the variation ΔV ′ determined by Rs ′ instead of Rs in the equation (1) becomes as shown in FIG. 4 (a).
It will appear in the output signal from 13.

Next, the configuration and operation of the abnormality detection circuit 15 that detects the above-described various abnormalities will be described. In FIG. 1, the abnormality detection circuit 15 includes a first and a second comparator.
It is composed of C1 and C2. This comparator C1
The first and second reference voltages V _TH 1 and V _TH 2 set by the resistors R1 to R3 are supplied and set to C2 and C2, respectively. The first (+) terminal of the first comparator C1 is connected to the first and second reference voltages V TH1 and V TH2. Reference voltage V _TH 1
Is supplied, and the second reference voltage V _TH 2 is supplied to the second comparator C2 (−) terminal. Then, the detection signal from the above-mentioned amplifier circuit 13 is supplied to the (−) terminal and (+) terminal of the first and second comparators C1 and C2, and the output signals from the comparators C1 and C2. Is collectively output from the output terminal 2 via the AND gate, and is processed by the notification ECU 4 provided later so as to notify the sensor abnormality when it is determined to be abnormal, for example.

In this embodiment, the notification ECU 4 sends a signal to the switch SW to perform on / off control.

That is, in the first comparator C1, the amplifier circuit
When the potential of the detection signal from 13 is higher than the first reference voltage V _TH 1, the output becomes low level. In the second comparator C2, the potential of the detection signal from the amplifier circuit 13 is The output becomes low level when the voltage is lower than the second reference voltage V _TH 2. Therefore, the amplifier circuit 13
The potential of the detection signal from the first and second reference voltages V _TH 1
When it does not exist between V _TH 2 and V _TH 2, either of the first and second comparators C1 and C2 is at a low level.

That is, the first and second reference voltages V _TH 1 and V _TH 2 are optimally set depending on the size of a predetermined pseudo circuit provided by the pseudo acceleration generation circuit 14, that is, the size of the above-mentioned change ΔV. By doing so, the sensor abnormality can be determined. The optimum setting of the first and second reference voltages V _TH 1 and V _TH 2 is the semiconductor strain gauge reference resistance value described above.
Offset error of Rs and switch SW are in OFF state,
The output potential when the pseudo acceleration generation circuit 14 does not act, that is, the reference output potential in the acceleration OG is taken into consideration, and when the sensor is normal, the potential of the detection signal from the amplification circuit 13 is the first and second reference voltages. It has been determined to exist between V _TH 1 and V _TH 2.

That is, when there is some abnormality in the acceleration sensor 11 and the amplification circuit 13 that constitute the semiconductor acceleration detection device, the potential of the detection signal from the amplification circuit 13 is the first reference voltage.
The level becomes higher than V _TH 1 or lower than the second reference voltage V _TH 2, and the output signal output from the abnormality detection circuit 15 to the output terminal 2 becomes low level.

Therefore, if any abnormality occurs, the output signal from the abnormality detection circuit 15 becomes low level, and the notification EC
The sensor abnormality is recognized by U4, and the output signal from this acceleration detection device is set in the abnormal voltage region.

In the above embodiment, the abnormality is detected when the engine is started, but this may be performed whenever the semiconductor strain gauge is not actually subjected to acceleration, for example, when the vehicle is stopped.

In addition, assuming that the cantilever breaks due to some factor when the vehicle is running or during sudden braking, as is well known, an abnormality detection circuit that constantly monitors the detection signal from the amplification circuit 13 may be provided. May be.

〔The invention's effect〕

As described above, according to the present invention, when the detection unit formed of the semiconductor chip in which the strain detection element forming the bridge circuit is set does not receive acceleration, an acceleration of a predetermined level is simulated according to a predetermined timing signal. Since the abnormality detection instruction of the semiconductor type acceleration detection device is performed by giving the abnormality to the detection element, it is possible to give an instruction to detect the abnormal state when an abnormality occurs in the strain detection element. There is an effect.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an acceleration detection device according to an embodiment of the present invention, FIG. 2 is a diagram for explaining a state of detection output when the pseudo acceleration generation circuit of the detection device is operating, FIG. 3, and FIG. FIG. 5 is a diagram for explaining the state of detection output when an abnormality occurs in the detection device, FIG. 5 is a diagram showing the structure of the acceleration sensor 11 of FIG. 1, and FIG. (B) is XX
FIG. 1 ... Output terminal, 2 ... Abnormality notification output terminal, 4 ... Notification ECU forming a timing circuit, 11 ... Acceleration sensor, 12 ... Constant current circuit, 13 ... Amplification circuit, 14 ... Pseudo acceleration generation Circuit 1
5 …… Abnormality detection circuit, 100 …… Semiconductor strain gauge, SW …… Switch, C1, C2 …… Comparator.

Claims (1)

[Claims] 1. A detection section comprising a semiconductor chip is provided with a detection element in which a strain detection element forming a bridge circuit is set, and when the detection section receives acceleration, an electrical output signal corresponding to this acceleration is generated. An acceleration sensor, processing means for detecting and processing the output signal from the acceleration sensor, a timing circuit for generating a predetermined timing signal for instructing detection of an abnormal state of the acceleration sensor, and the predetermined timing signal from the timing circuit. A pseudo acceleration generation circuit for adding a pseudo acceleration signal to the detection element to shift the balance of the bridge circuit and forcibly outputting an electrical output signal from the acceleration sensor, and the pseudo acceleration generation circuit. According to the output signal generated by the acceleration sensor due to the pseudo acceleration signal of An anomaly detection circuit for detecting a condition.