JPH07198745A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To simplify the constitution of a voltage source so as to reduce the cost of the voltage source by electrically separating an overlapping section and beam section from each other by a P-N junction and applying an electrostatic driving voltage across the overlapping section and an electrode for self- diagnosis from an independent voltage source. CONSTITUTION:A P-type overlapping section 3 is electrically separated from a beam section 2 which is grounded and composed of an N-type epitaxial layer 8 by a P-N junction. Consequently, the electrostatic driving voltage applied across metallic electrodes 11 on a pedestal 5 from a voltage source 13 is applied across an air gap between the base of the section 3 and the electrodes 11 as it is and utilized as an electrostatic force generating voltage. When the minimum voltage value of a primary power source is 9 V and the voltage applied across the air gap required for electrostatic self-diagnosis is 15V, the voltage source 13 from which the voltage is applied across the electrodes 11 on the pedestal 5 can be obtained when the voltage of the primary power source is boosted double. Therefore, the constitution of the voltage source 13 can be simplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor,
In particular, it relates to improvement of a voltage applying structure for electric self-diagnosis.

[0002]

2. Description of the Related Art Conventional acceleration sensors include those shown in FIGS. 3 and 4, for example (Japanese Patent Application No. 5-278).
032). In these drawings, reference numeral 21 denotes a sensor chip, in which a thin beam portion 22 is formed by anisotropically etching a silicon substrate from the back surface side, and this is a so-called both-sided support for supporting a central weight portion 23 from both sides. It has a beam structure. A piezoresistor 26 is formed on the surface side of the beam portion 22 by an impurity diffusion layer, and when the weight portion 23 is displaced by the application of acceleration and stress is generated on the surface side of the beam portion 22, the resistance value changes to accelerate the acceleration. Is detected. In the illustrated example, the piezoresistor 26 is formed on the fixed side of the beam portion 22 and on the weight portion 23 side, and by configuring a bridge circuit (not shown), the stress on the beam portion 22 is converted into a voltage. It is designed to output. 27 is a silicon oxide film. A pedestal 25 made of Pyrex glass having a thermal expansion coefficient relatively close to that of silicon is anodically bonded to the lower portion of the sensor chip 21. The pedestal 25 extends outside the end of the sensor chip 21 in a predetermined area (right side in the drawing). On the surface of the pedestal 25, a recess 28 having a depth of several μm is formed in a region facing the weight portion 23 and a region from the weight portion 23 to the extension portion.
Is formed, and an insulating film 34 of SiO ₂ or the like is formed thereon. The connection terminal of the sensor chip 21 is electrically connected to the outside from the bonding pad 29 via the bonding wire 31. Pedestal 25
The upper metal electrode 30 is also connected to an external electrostatic drive voltage source 33 for self-diagnosis through a bonding wire 31 at the extension.

When an acceleration is applied from the outside in the direction perpendicular to the chip surface, the weight portion 23 is displaced, and the surface of the beam portion 22 receives a stress whose polarities are opposite on the fixed side and the weight portion 23 side and whose absolute values are substantially equal. Occur. Due to this stress, the resistance value of the piezoresistor 26 changes, and this change is converted into a voltage through a bridge circuit, an amplifier circuit, etc., and taken out as an electric signal.

Usually, a P-type diffusion layer is used for the piezoresistor 26 and is formed by diffusing P-type impurities in an N-type silicon substrate which will be a sensor chip, so that the N-type beam portion 22 and the weight portion 23 are formed. Is a positive voltage source 32 having a voltage higher than the bridge applied voltage in order to electrically isolate the piezoresistive 26 element.
Are connected and are positively biased to the voltage value _Vcc .
Therefore, when a voltage of V _d is applied from the electrostatic drive voltage source 33 to the metal electrode 30 for self-diagnosis, a voltage of V _b = V _d −V _cc is applied to the gap between the metal electrode 30 and the bottom surface of the weight portion 23. Now, when a predetermined voltage _Vb is applied between the weight portion 23 and the metal electrode 30, the electromotive force F acts between them and the beam portion 22 receives the same stress as when downward acceleration is applied.
The sensor function can be diagnosed or its sensitivity can be calibrated. Where the electric power F
_e is expressed by the following equation.

F _e = (1/2) ε · S (V _b / d) ² (1) where ε is the dielectric constant of the gap portion, S is the bottom area of the weight portion, and d is the gap length. . If a stabilizing voltage of 5 V is used as the value of V _cc , 20 V is required as V _{d in} order to apply a static driving voltage of V _b = 15V to the gap.

[0006]

In the conventional acceleration sensor, a beam / weight structure is formed by etching an N-type silicon substrate, and a positive voltage for separating a piezoresistive element composed of a P-type diffusion layer is formed therein. _Vcc is applied to positively bias the weighted portion, and a voltage is applied to the metal electrode facing the weighted portion to generate the nematic power for self-diagnosis, so that the required nematic power is generated. Therefore, there is a problem that the voltage applied to the metal electrode is increased by V _cc and a booster circuit is required, or the boosting coefficient becomes large and the cost for boosting increases.

The present invention has been made by paying attention to such a conventional problem, and it is possible to use the voltage for driving the static electricity from the voltage source as it is as the voltage for generating the static electric power, thereby simplifying the configuration of the voltage source. It is an object of the present invention to provide an acceleration sensor that can be realized at a reduced cost.

[0008]

In order to solve the above-mentioned problems, the present invention is, firstly, the present invention, which is formed by etching a semiconductor substrate, is supported by a beam portion on a fixed portion, and is displaced in accordance with a detected acceleration. A sensor chip having a piezoresistor formed on the surface portion of the beam portion, and the weight portion is joined to the lower portion of the sensor chip so as to have a required air gap. A pedestal having electrodes formed on the opposite surfaces thereof, and an acceleration sensor configured to self-diagnose the sensor function by the whiskers generated by the voltage applied between the weight portion and the electrodes, wherein the weight portion and the beam portion are provided. PN
The gist is that the electrodes are electrically separated by joining, and a voltage for driving electricity is applied between the weight portion and the electrode from an independent voltage source.

Secondly, in the above-mentioned first structure, the semiconductor substrate is formed by forming another conductivity type layered region on one main surface of one conductivity type semiconductor substrate, and the beam portion is formed by the layered region. The weight portion is mainly formed of the one conductivity type semiconductor substrate, and one conductivity type impurity diffusion region penetrating the layered region and reaching the one conductivity type semiconductor substrate is formed on one main surface side of the weight portion. The gist is that the voltage source is formed and is connected to the weight portion through the diffusion region.

Thirdly, in the first structure, the one conductivity type semiconductor substrate is P type, the other conductivity type layered region is an N type epitaxial layer, and the beam portion and the weight portion are the N type. The gist is that the epitaxial layer is formed by electro-chemical etching while biasing it to a positive voltage.

[0011]

In the above structure, firstly, since the weight portion and the beam portion are electrically separated by the PN junction, the electrostatic driving voltage applied between the weight portion and the electrode from the voltage source is directly applied to the weight portion. It is applied to the air gap between the bottom surface of the electrode and the electrode layer, and is used as a voltage for generating static electricity. Therefore, the configuration of the voltage source can be simplified.

Secondly, in the PN junction separation between the weight portion and the beam portion, the other conductive type layered region forming the beam portion is penetrated,
By forming the one-conductivity-type impurity diffusion region that reaches the one-conductivity-type semiconductor substrate portion forming the weight portion, it is easily and surely realized by using a normal semiconductor processing technique.

Thirdly, because of the PN junction isolation, specifically, since the semiconductor substrate is a P-type substrate on which an N-type epitaxial layer is formed, the beam portion and the weight portion are N-shaped. By forming the epitaxial layer by electro-chemical etching while biasing it to a positive voltage, it becomes possible to form a sensor chip easily and accurately.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of the present invention. First, the structure of the acceleration sensor will be described. 1 is a P-type silicon substrate, and 8 is a thin N-type epitaxial layer deposited on one main surface of the P-type silicon substrate 1. Reference numeral 2 denotes a beam portion composed of the N-type epitaxial layer 8 portion, and 3 and 4 are respectively a weight portion and a fixed portion mainly composed of the P-type silicon substrate 1 portion, which are biasing the N-type epitaxial layer 8 to a positive potential. The P-type silicon substrate 1 is formed by performing electro-chemical etching from the back surface using an alkaline anisotropic etching solution. The weight portion 3 is suspended and supported by the beam portion 2 from both sides on a fixed portion 4 surrounding the beam portion 2, and has a so-called double-supported beam structure. In order to electrically separate the weight portion 3 and the beam portion 2 by a PN junction on one main surface side of the weight portion 3, the P-type which forms the weight portion 3 through the N-type epitaxial layer 8 is formed. A P-type diffusion region 15 reaching the silicon substrate 1 is formed. Further, a plurality of piezoresistors 6 are formed on the surface of the beam portion 2 by a P-type diffusion layer, which are bridge-connected (not shown),
A change in the resistance value of the piezoresistor 6 due to the stress generated on the surface of the beam portion 2 when the acceleration is applied to the weight portion 3 is converted into a voltage, and a voltage signal corresponding to the acceleration is output.
Reference numeral 7 is a surface protective film such as SiO ₂ , and 9 is an electrode portion for electrically taking out the P-type diffusion region 15 to the outside. In this way, the sensor chip 10 is formed.

A pedestal 5 made of Pyrex glass is anodically bonded to the lower portion of the sensor chip 10 so as to face the weight portion 3 and have a recess 18 in a region wider than the weight portion 3. Recess 18
A metal electrode 11 for electric self-diagnosis is formed therein, and a protective film 14 is formed thereon. The pedestal 5 and the metal electrode 11 on the pedestal 5 extend to the outside of the end of the sensor chip 10 for electrical connection to the outside, and are connected to a wire (not shown) there to connect to an external voltage source for driving electricity. It is connected to 13. Reference numeral 19 is a lateral hole for taking out the electrode. The N-type epitaxial layer 8 has a piezoresistor 6
In order to electrically isolate the elements, the voltage source 12 biases them to a positive potential.
It is also grounded via the electrode portion 9 and is electrically separated from the beam portion 2 formed of the N-type epitaxial layer 8 by a PN junction.

Next, the operation of the acceleration sensor configured as described above will be described. Since the P-type weight portion 3 is grounded and electrically separated from the beam portion 2 formed of the N-type epitaxial layer 8 by the PN junction, the voltage source 13 applied to the metal electrode 11 on the pedestal 5 The electrostatic driving voltage is applied as it is to the air gap between the bottom surface of the weight portion 3 and the metal electrode 11, and is used as a voltage for generating electrostatic power. Assuming that the minimum voltage value of the original power supply is 9V and the voltage applied to the air gap required for the electrostatic self-diagnosis is 15V or more, the base 5
The voltage source 13 for applying a voltage to the upper metal electrode 11 can be realized by double boosting in this embodiment. On the other hand, in the above-mentioned conventional example, triple boosting is required, resulting in a large cost increase.

Next, FIG. 2 shows another embodiment of the present invention. In this embodiment, the structure of the sensor chip 10 is the same as that of the embodiment shown in FIG. 1, but the connection method of the metal electrode 11 on the pedestal 5 is different. The metal electrode 11 extends to the fixed portion 4 on the right side of the figure, where the P-type silicon substrate 1
Is electrically connected to the fixed portion 4 composed of a pedestal 5 so as to be pressed. Since the P-type silicon substrate 1 is grounded, the metal electrode 11 is also grounded.
On the other hand, the P-type weight portion 3 is connected to the negative voltage source 1 via the electrode portion 9.
6 is used, and the static electricity driving voltage from the voltage source 16 is directly used as the static electricity generating voltage.
According to the present embodiment, by adopting the above-described configuration, the electrode lead-out portion on the pedestal 5 is not required, so that the sensor size can be reduced, and further, the electrode lead-out lateral hole portion shown in FIG. Since water does not enter during dicing, reliability can be further improved.

Although the acceleration sensor having the double-supported beam structure has been described in the above embodiment, it is needless to say that the present invention can be applied to the acceleration sensor having the cantilever structure or the diaphragm structure. In the beam type, the method of leaving the N-type epitaxial layer by electro-chemical etching has been described, but a diffusion layer may be used instead of the N-type epitaxial layer, or a time-controlled etching method may be used.

[0019]

As described above, according to the present invention,
First, the weight portion and the beam portion are electrically separated by a PN junction,
Since the voltage for driving electric power is applied from an independent voltage source between the weight and the electrode for self-diagnosis, the voltage for driving electric power from the voltage source can be directly used as the voltage for generating electric power. The configuration of the voltage source can be simplified, and the cost can be reduced.

Secondly, the semiconductor substrate is formed by forming another conductive type layered region on one main surface of one conductive type semiconductor substrate, the beam portion is formed by the layered region, and the weight portion is mainly the above-mentioned. A one-conductivity type semiconductor substrate is formed, and a one-conductivity type impurity diffusion region penetrating the layered region and reaching the one-conductivity type semiconductor substrate is formed on one main surface side of the weight portion, and a voltage source is provided through the diffusion region. Since the weight portion and the beam portion are connected to each other, the PN junction separation between the weight portion and the beam portion can be easily and surely realized by using an ordinary semiconductor processing technique.

Third, in order to separate the PN junction between the weight portion and the beam portion, since the semiconductor substrate is specifically a P-type substrate on which an N-type epitaxial layer is formed, the beam portion is used. By forming the weight portion and the weight portion by the electro-chemical etching method while biasing the N-type epitaxial layer to a positive voltage, the sensor chip can be formed easily and highly accurately.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of an acceleration sensor according to the present invention.

FIG. 2 is a vertical sectional view showing another embodiment of the present invention.

FIG. 3 is a plan view showing a conventional acceleration sensor.

4 is a cross-sectional view taken along the line AA of FIG.

[Explanation of symbols]

 1 P-type silicon substrate 2 Beam part 3 Weight part 4 Fixing part 5 Pedestal 6 Piezoresistor 8 N-type epitaxial layer 10 Sensor chip 11 Metal electrode for self-diagnosis 12 Bias voltage source 13, 16 Electric drive voltage source 15 P type Diffusion area

Claims (3)

[Claims] 1. A semiconductor substrate is formed by etching, a fixed portion has a weight portion supported by a beam portion and displaced in accordance with a detected acceleration, and a piezoresistor is formed on a surface portion of the beam portion. A sensor chip and a pedestal that is joined to the lower portion of the sensor chip so as to have a required air gap and has an electrode formed on a surface facing the weight portion. In an acceleration sensor in which the sensor function is self-diagnosed by the static electricity generated by the voltage applied between the electrodes, the weight portion and the beam portion are electrically separated by a PN junction, and the weight portion and the electrode are independent. An acceleration sensor configured to apply a voltage for driving electric power from the voltage source. 2. The semiconductor substrate is a semiconductor substrate in which a layer of another conductivity type is formed on one main surface of a semiconductor substrate of one conductivity type.
The beam portion is formed by the layered region, the weight portion is mainly composed of the one conductivity type semiconductor substrate, and the one major surface side of the weight portion penetrates the layer region to the one conductivity type semiconductor substrate. 2. The acceleration sensor according to claim 1, wherein an impurity diffusion region of one conductivity type that reaches is formed, and the voltage source is connected to the weight portion through the diffusion region. 3. The one conductivity type semiconductor substrate is P type,
The other conductivity type layered region is an N type epitaxial layer,
The acceleration sensor according to claim 1, wherein the beam portion and the weight portion are formed by electro-chemical etching while biasing the N-type epitaxial layer to a positive voltage.