JP2016008953A - Physical quantity sensor, pressure sensor, altimeter, electronic apparatus, and moving body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a physical quantity sensor with high detection accuracy, and a pressure sensor, an altimeter, an electronic apparatus, and a moving body having the physical quantity sensor.SOLUTION: The physical quantity sensor includes a diaphragm part 64 bending and deforming under pressure and a plurality of piezoresistors 7 forming a bridge circuit in the diaphragm part 64. The diaphragm part 64 receives pressures of 30 kPa or more, which is the lower limit of the range of working pressures, when the output voltage of the bridge circuit is 0 V.

Description

  The present invention relates to a physical quantity sensor, a pressure sensor, an altimeter, an electronic device, and a moving object.

  A pressure sensor having a diaphragm that is bent and deformed by receiving pressure is widely used. As such a pressure sensor, there is known a sensor that detects a pressure applied to a diaphragm based on a change in resistance value of a piezoresistive element arranged on the diaphragm (see, for example, Patent Document 1).

  For example, in the pressure sensor according to Patent Document 1, four pressure-sensitive elements (piezoresistive elements) arranged in a diaphragm form a bridge circuit, and based on an output voltage (midpoint potential) from the bridge circuit. Detect the pressure.

  Conventionally, as disclosed in Patent Document 1, a resistance element for correction is provided in the bridge circuit, whereby the offset voltage of the bridge circuit (the output voltage when the pressure reception is 0 kPa) is set to 0V. Adjustments have been made.

  However, conventionally, when AD converting an analog signal based on the output voltage from the bridge circuit into a digital signal, not only the voltage range corresponding to the operating pressure range but also the pressure from 0 kPa to the lower limit value of the operating pressure range. The number of bits must be assigned over a wide range in the voltage range corresponding to. For this reason, the number of bits assigned to the voltage range corresponding to the working pressure range is reduced (that is, the resolution is lowered), and as a result, the detection accuracy is lowered.

JP 2011-27611 A

  An object of the present invention is to provide a physical quantity sensor having excellent detection accuracy, and to provide a pressure sensor, an altimeter, an electronic device, and a moving body including the physical quantity sensor.

Such an object is achieved by the present invention described below.
[Application Example 1]
The physical quantity sensor of the present invention includes a diaphragm portion that is bent and deformed by pressure,
A plurality of piezoresistive elements arranged in the diaphragm portion and constituting a bridge circuit;
With
The pressure applied to the diaphragm when the output voltage of the bridge circuit is 0 V is 2 kPa or more.

  According to such a physical quantity sensor, when an analog signal based on the output voltage of the bridge circuit is AD converted into a digital signal, the number of bits allocated to a voltage range corresponding to a pressure smaller than the lower limit value of the working pressure range is reduced. Alternatively, the number of bits allocated to the voltage range corresponding to the operating pressure range can be increased. Therefore, the resolution of AD conversion can be improved, and as a result, excellent detection accuracy can be realized.

[Application Example 2]
The physical quantity sensor of the present invention includes a diaphragm portion that is bent and deformed by pressure,
A plurality of piezoresistive elements arranged in the diaphragm portion and constituting a bridge circuit;
With
The pressure received by the diaphragm portion when the output voltage of the bridge circuit is 0 V is a lower limit value of a working pressure range.

  According to such a physical quantity sensor, when the analog signal based on the output voltage of the bridge circuit is AD-converted into a digital signal, the number of bits allocated to the voltage range corresponding to the pressure smaller than the lower limit value of the working pressure range is substantially reduced. Therefore, the number of bits allocated to the voltage range corresponding to the working pressure range can be increased as much as possible. Therefore, the resolution of AD conversion can be improved, and as a result, excellent detection accuracy can be realized.

[Application Example 3]
In the physical quantity sensor according to the present invention, it is preferable that a correction resistance element electrically connected to the bridge circuit is provided.

  Thereby, the offset amount of the output voltage of the bridge circuit can be adjusted with a relatively simple configuration.

[Application Example 4]
The physical quantity sensor of the present invention preferably includes an AD conversion circuit to which an analog signal based on the output voltage of the bridge circuit is input.

  Thereby, the digital signal according to the pressure which the diaphragm part received can be output from an AD conversion circuit.

[Application Example 5]
In the physical quantity sensor according to the aspect of the invention, it is preferable that the AD conversion circuit converts the analog signal into a digital signal within a pressure range of 2 kPa to 130 kPa.

  Thereby, a highly accurate atmospheric pressure sensor can be realized using the physical quantity sensor of the present invention.

[Application Example 6]
In the physical quantity sensor according to the aspect of the invention, it is preferable that the AD conversion circuit converts the analog signal into a digital signal within a pressure range of 80 kPa to 3000 kPa.

  Thereby, a highly accurate water pressure sensor can be realized using the physical quantity sensor of the present invention.

[Application Example 7]
In the physical quantity sensor of the present invention, it is preferable that a pressure reference chamber is formed together with the diaphragm part, and a wall part made of a material different from the diaphragm part is provided.

  Thereby, the offset amount of the output voltage of the bridge circuit can be adjusted with a relatively simple configuration.

[Application Example 8]
In the physical quantity sensor of the present invention, the number of the diaphragm portions is plural,
It is preferable that the bridge circuit includes a plurality of the piezoresistive elements arranged in different diaphragm portions.

  Thereby, an area can be increased by the sum total of the several piezoresistive element arrange | positioned at a mutually different diaphragm part. Therefore, pressure sensitivity can be increased while reducing 1 / f noise.

[Application Example 9]
The pressure sensor of the present invention includes the physical quantity sensor of the present invention.
Thereby, the pressure sensor which has the outstanding detection accuracy can be provided.

[Application Example 10]
The altimeter according to the present invention includes the physical quantity sensor according to the present invention.
Thereby, the altimeter which has the outstanding detection accuracy can be provided.

[Application Example 11]
An electronic apparatus according to the present invention includes the physical quantity sensor according to the present invention.

  Thereby, an electronic device including a physical quantity sensor having excellent detection accuracy can be provided.

[Application Example 12]
The moving body of the present invention includes the physical quantity sensor of the present invention.

  Thereby, a mobile body provided with a physical quantity sensor having excellent detection accuracy can be provided.

It is sectional drawing which shows the physical quantity sensor which concerns on 1st Embodiment of this invention. It is a top view which shows arrangement | positioning of the piezoresistive element of the physical quantity sensor shown in FIG. It is a figure which shows the circuit containing the piezoresistive element of the physical quantity sensor shown in FIG. It is a figure for demonstrating the effect | action of the physical quantity sensor shown in FIG. 1, Comprising: (a) is sectional drawing which shows a pressurization state, (b) is a top view which shows a pressurization state. (A) is a graph showing the relationship between the pressure received by the diaphragm and the resistance value of the piezoresistive element, and (b) shows the relationship between the pressure received by the diaphragm and the output voltage (midpoint potential) of the bridge circuit. It is a graph. It is a figure which shows the manufacturing process of the physical quantity sensor shown in FIG. It is a figure which shows the manufacturing process of the physical quantity sensor shown in FIG. It is a figure which shows the manufacturing process of the physical quantity sensor shown in FIG. It is sectional drawing which shows the physical quantity sensor which concerns on 2nd Embodiment of this invention. It is a top view which shows arrangement | positioning of the piezoresistive element of the physical quantity sensor shown in FIG. It is a figure which shows the bridge circuit containing the piezoresistive element of the physical quantity sensor shown in FIG. It is sectional drawing which shows an example of the pressure sensor of this invention. It is a perspective view which shows an example of the altimeter of this invention. It is a front view which shows an example of the electronic device of this invention. It is a perspective view which shows an example of the moving body of this invention.

  Hereinafter, a physical quantity sensor, a pressure sensor, an altimeter, an electronic device, and a moving body of the present invention will be described in detail based on each embodiment shown in the accompanying drawings.

<First Embodiment>
1. Physical Quantity Sensor FIG. 1 is a sectional view showing a physical quantity sensor according to the first embodiment of the present invention. 2 is a plan view showing the arrangement of the piezoresistive elements of the physical quantity sensor shown in FIG. 1, and FIG. 3 is a diagram showing a circuit including the piezoresistive elements of the physical quantity sensor shown in FIG. In the following, for convenience of explanation, the upper side in FIG. 1 is referred to as “upper” and the lower side is referred to as “lower”.

  A physical quantity sensor 1 shown in FIG. 1 includes a substrate 6 and a laminated structure 8 provided on the upper surface of the substrate 6. Here, the substrate 6 has a diaphragm portion 64, and a plurality of piezoresistive elements 7 are formed in the diaphragm portion 64. Further, in the laminated structure 8, a portion corresponding to the diaphragm portion 64 is separated from the substrate 6, whereby a cavity S (pressure reference chamber) is formed between the portion and the substrate 6. Has been.

Hereinafter, each part which comprises the physical quantity sensor 1 is demonstrated sequentially.
-Substrate 6
The substrate 6 includes a silicon layer 61 (handle layer) made of single crystal silicon, a silicon oxide layer 62 (box layer) made of a silicon oxide film, and a silicon layer 63 made of single crystal silicon. (Device layer) is an SOI substrate laminated in this order. The substrate 6 is not limited to the SOI substrate, and may be another semiconductor substrate such as a single crystal silicon substrate.

  Further, the substrate 6 is provided with a diaphragm portion 64 that is thinner than the surrounding portion and is bent and deformed by receiving pressure. The diaphragm portion 64 is formed by providing a bottomed recess 65 on the lower surface of the substrate 6. The lower surface of the diaphragm portion 64 is a pressure receiving surface 641. In the present embodiment, as shown in FIG. 2, the diaphragm portion 64 has a substantially square plan view shape.

  In the substrate 6 of the present embodiment, the concave portion 65 penetrates the silicon layer 61, and the diaphragm portion 64 is composed of two layers, a silicon oxide layer 62 and a silicon layer 63. Here, as will be described later, the silicon oxide layer 62 can be used as an etching stop layer when the recess 65 is formed by etching in the manufacturing process of the physical quantity sensor 1, and the thickness of the diaphragm portion 64 for each product. Variations can be reduced.

  The concave portion 65 may not penetrate the silicon layer 61, and the diaphragm portion 64 may be constituted by three layers, that is, a thin portion of the silicon layer 61, a silicon oxide layer 62, and a silicon layer 63.

-Piezoresistive element 7-
As shown in FIG. 1, the plurality of piezoresistive elements 7 are respectively formed on the surface of the diaphragm portion 64 on the cavity portion S side. Here, although not shown, a silicon oxide film and a silicon nitride film are stacked in this order on the piezoresistive element 7. Each of the silicon oxide film and the silicon nitride film functions as an insulating film. Further, the silicon nitride film also functions as an etching stop layer used when forming the cavity S in the manufacturing process of the physical quantity sensor 1 described later. The silicon oxide film and the silicon nitride film may be provided if necessary and may be omitted.

  As shown in FIG. 2, the plurality of piezoresistive elements 7 are composed of a plurality of piezoresistive elements 71a, 71b, 71c, 71d.

  Piezoresistive elements 71a, 71b, 71c, and 71d are arranged corresponding to the four sides of the diaphragm portion 64, which is substantially rectangular in plan view.

  A pair of piezoresistive elements 71 a are arranged on the outer periphery of the diaphragm portion 64, and each extend along a direction parallel to the corresponding side of the diaphragm portion 64. The pair of piezoresistive elements 71a are electrically connected in series by a wiring 92a, and are drawn to the outside by a pair of wirings 91a. In the pair of wirings 91a, one wiring 91a is electrically connected to the electrode 84b1, and the other wiring 91a is electrically connected to the electrode 84b2.

  Similarly, a pair of piezoresistive elements 71 b are arranged on the outer peripheral portion of the diaphragm portion 64, and each extend along a direction parallel to a corresponding side of the diaphragm portion 64. The pair of piezoresistive elements 71b are electrically connected in series by the wiring 92b, and are drawn to the outside by the pair of wirings 91b. In the pair of wirings 91b, one wiring 91b is electrically connected to the electrode 84b3, and the other wiring 91b is electrically connected to the electrode 84b4.

  On the other hand, a pair of piezoresistive elements 71 c are arranged on the outer peripheral portion of the diaphragm portion 64, and each extend along a direction perpendicular to the corresponding side of the diaphragm portion 64. The pair of piezoresistive elements 71c are electrically connected in series by the wiring 92c, and are drawn to the outside by the pair of wirings 91c. In the pair of wirings 91c, one wiring 91c is electrically connected to the electrode 84b1 through the correction resistance element 2a, and the other wiring 91c is electrically connected to the electrode 84b3 through the correction resistance element 2a. It is connected to the.

  Similarly, a pair of piezoresistive elements 71d are arranged on the outer peripheral portion of the diaphragm portion 64, and each extend along a direction perpendicular to the corresponding side of the diaphragm portion 64. The pair of piezoresistive elements 71d are electrically connected in series by a wiring 92d, and are drawn to the outside by a pair of wirings 91d. In the pair of wirings 91d, one wiring 91d is electrically connected to the electrode 84b2 via the correction resistance element 2b, and the other wiring 91d is electrically connected to the electrode 84b4 via the correction resistance element 2b. It is connected to the.

  Here, each of the resistance elements 2a and 2b is disposed outside the outer peripheral edge of the diaphragm portion 64 of the substrate 6 so as not to be affected by the stress change of the substrate 6 due to the bending deformation of the diaphragm portion 64. .

  In the following description, the pair of piezoresistive elements 71a are collectively referred to as “piezoresistive element 7a”, the pair of piezoresistive elements 71b are collectively referred to as “piezoresistive element 7b”, and the pair of piezoresistive elements 71c are combined. The “piezoresistive element 7c” and the pair of piezoresistive elements 71d are collectively referred to as “piezoresistive element 7d”. In addition, the wirings 91a, 91b, 91c, 91d, 92a, 92b, 92c, and 92d are collectively referred to as “wiring 9”.

  Such resistive elements 2a, 2b, piezoresistive elements 7a, 7b, 7c, 7d and wiring 9 are each composed of, for example, silicon (single crystal silicon) doped (diffused or implanted) with impurities such as phosphorus and boron. Has been. Here, the impurity doping concentration in the wiring 9 is higher than the impurity doping concentration in the resistance elements 2a, 2b and the piezoresistance elements 7a, 7b, 7c, 7d. The wiring 9 may be made of metal.

The piezoresistive elements 7a, 7b, 7c, 7d and the resistive elements 2a, 2b as described above constitute a bridge circuit 70 (Wheatstone bridge circuit) as shown in FIG. The bridge circuit 70 is connected to a drive circuit (not shown) that supplies a drive voltage AVDC between the pair of electrodes 84b1 and 84b4. In the bridge circuit 70, the potential difference (midpoint potential) between the pair of electrodes 84b2 and 84b3 is output as a signal (output voltage V _out ) corresponding to the resistance value change of the piezoresistive elements 7a, 7b, 7c, and 7d. The

The AD conversion circuit 32 is electrically connected to the bridge circuit 70 through the amplifier circuit 31. The amplifier circuit 31 has a function of amplifying the output voltage _Vout from the bridge circuit 70 and outputting an analog signal based on the output voltage _Vout . The AD conversion circuit 32 has a function of receiving the analog signal output from the amplifier circuit 31, AD converting the analog signal into a digital signal, and outputting the digital signal. Accordingly, a digital signal corresponding to the pressure received by the diaphragm unit 64 can be output from the AD conversion circuit 32.

-Laminated structure 8-
The laminated structure 8 is formed so as to define a cavity S where the piezoresistive element 7 is disposed. Here, the laminated structure 8 constitutes a “wall portion” which is disposed on one surface side of the silicon layer 61 and forms a cavity S together with the diaphragm portion 64.

  This laminated structure 8 includes an interlayer insulating film 81 formed on the substrate 6 so as to surround the piezoresistive element 7, a wiring layer 82 formed on the interlayer insulating film 81, a wiring layer 82 and an interlayer insulating film 81. An interlayer insulating film 83 formed thereon, a wiring layer 84 formed on the interlayer insulating film 83 and having a coating layer 841 having a plurality of pores (openings), and on the wiring layer 84 and the interlayer insulating film 83 And a sealing layer 86 provided on the covering layer 841.

  Here, the wiring layer 82 includes a wiring layer 82 a formed so as to surround the cavity S. The wiring layer 84 includes the wiring layer 84a formed so as to surround the cavity S and the electrodes 84b1 to 84b4 described above.

  Such a laminated structure 8 can be formed using a semiconductor process such as a CMOS process. A semiconductor circuit may be formed on and above the silicon layer 61. This semiconductor circuit has active elements such as MOS transistors, and other circuit elements such as capacitors, inductors, resistors, diodes, and wires (including wires connected to the piezoresistive element 7) formed as necessary. ing.

-Cavity S-
The cavity S defined by the substrate 6 and the laminated structure 8 is a sealed space. The cavity S functions as a pressure reference chamber that serves as a reference value for the pressure detected by the physical quantity sensor 1. In this embodiment, the cavity S is in a vacuum state (300 Pa or less). By making the cavity S into a vacuum state, the physical quantity sensor 1 can be used as an “absolute pressure sensor” that detects pressure based on the vacuum state, and the convenience is improved.

However, the cavity S may not be in a vacuum state, may be atmospheric pressure, may be in a reduced pressure state where the atmospheric pressure is lower than atmospheric pressure, or is a pressurized state where the atmospheric pressure is higher than atmospheric pressure. It may be. The cavity S may be filled with an inert gas such as nitrogen gas or a rare gas.
The configuration of the physical quantity sensor 1 has been briefly described above.

  4A and 4B are diagrams for explaining the operation of the physical quantity sensor shown in FIG. 1, in which FIG. 4A is a cross-sectional view showing a pressurized state, and FIG. 4B is a plan view showing the pressurized state. is there.

As shown in FIG. 4A, the physical quantity sensor 1 is deformed in accordance with the pressure P received by the pressure receiving surface 641 of the diaphragm part 64. As a result, as shown in FIG. The piezoresistive elements 7a, 7b, 7c, and 7d are distorted, and the resistance values of the piezoresistive elements 7a, 7b, 7c, and 7d are changed. Accordingly, the output voltage _{Vout of the} bridge circuit 70 (see FIG. 3) including the piezoresistive elements 7a, 7b, 7c, and 7d changes, and the pressure P received by the pressure receiving surface 641 based on the output voltage _Vout. Can be obtained.

  More specifically, when the deformation of the diaphragm portion 64 as described above occurs, as shown in FIG. 4B, the piezoresistive elements 71a and 71b are subjected to compressive strain along the width direction and in the longitudinal direction. The tensile strain along the width direction and the compressive strain along the longitudinal direction are generated in the piezoresistive elements 71c and 71d. Therefore, when the deformation of the diaphragm portion 64 as described above occurs, one of the resistance values of the piezoresistive elements 7a and 7b and the piezoresistive elements 7c and 7d increases, and the other resistance. The value decreases.

An output voltage V _out (potential difference) corresponding to such distortion of the piezoresistive elements 71 a, 71 b, 71 c, 71 d is output from the bridge circuit 70. Based on the output voltage _Vout from the bridge circuit 70, the magnitude (absolute pressure) of the pressure received by the pressure receiving surface 641 can be obtained. Note that the resistance values of the correction resistance elements 2 a and 2 b do not change due to the deformation of the diaphragm portion 64.

  FIG. 5A is a graph showing the relationship between the pressure received by the diaphragm and the resistance value of the piezoresistive element, and FIG. 5B shows the pressure received by the diaphragm and the output voltage (midpoint potential) of the bridge circuit. It is a graph which shows the relationship.

  As shown in FIG. 5A, the total resistance value of the piezoresistive element 7a and the piezoresistive element 7b increases as the pressure applied to the diaphragm section 64 (hereinafter also simply referred to as “pressure”) increases. On the other hand, the total resistance value of the piezoresistive element 7c and the piezoresistive element 7d becomes small.

Here, when the pressure is 0 kPa, a difference ΔR ₀ occurs between the total resistance value of the piezoresistive element 7a and the piezoresistive element 7b and the total resistance value of the piezoresistive element 7c and the piezoresistive element 7d. There is a case. This difference ΔR ₀ is caused by a dimensional error or initial stress of the piezoresistive elements 7a, 7b, 7c, 7d, and is usually relatively small.

As described above, the resistance elements 2a and 2b for correction are electrically connected to the piezoresistive elements 7c and 7d. By adjusting the resistance values of the resistance elements 2a and 2b, the difference ΔR ₀ is obtained. Can be adjusted.

Conventionally, the resistance value of the correcting resistance element is adjusted so that the difference ΔR ₀ becomes zero. Thus, conventionally, as shown in FIG. 5B, the output voltage V _out (hereinafter also referred to as “offset voltage”) when the pressure is 0 kPa is adjusted to 0 V. Conventionally, when the analog signal based on the output voltage _Vout is AD converted into a digital signal in the AD conversion circuit, the range of the output voltage _Vout corresponding to the pressure range from 0 kpa to the upper limit value P2 of the working pressure range ( The number of bits is assigned to a range of 0 to V ₂ [V] indicated by b in FIG. Here, the “operating pressure range” is a pressure range (measurement pressure range) that the physical quantity sensor 1 can detect.

However, since the number of bits is conventionally assigned to the range of the output voltage _Vout corresponding to the range where the pressure is smaller than the lower limit value P1 of the working pressure range during AD conversion, the number of bits assigned to the working pressure range As a result, there is a problem that the detection accuracy is lowered.

Therefore, in the present invention, as shown in FIG. 5A, the sum of the resistance values of the piezoresistive elements 7c and 7d and the resistance values of the correcting resistive elements 2a and 2b is near the lower limit value P1 of the working pressure range. Thus, the resistance values of the resistance elements 2a and 2b are adjusted to be equal to the resistance values of the piezoresistance elements 7a and 7b. Here, when the pressure is 0 kPa, the sum of the resistance values of the piezoresistive elements 7c and 7d and the resistance values of the correcting resistive elements 2a and 2b is larger than the resistance values of the piezoresistive elements 7a and 7b. When the pressure is 0 kPa, the difference ΔR between the sum of the resistance values of the piezoresistive elements 7c and 7d and the resistance values of the correcting resistive elements 2a and 2b and the resistance values of the piezoresistive elements 7a and 7b is , The difference ΔR ₀ is greater.

By adjusting the resistance values of the resistance elements 2a and 2b as described above, in the present invention, as shown in FIG. 5B, the output voltage _Vout becomes 0 V near the lower limit value P1 of the working pressure range. The offset voltage has been adjusted. Here, the offset voltage is shifted to the negative side.

The lower limit P1 of the working pressure range is usually set to 2 kPa or more (preferably 30 kPa or more). Therefore, the pressure received by the diaphragm section 64 when the output voltage _Vout of the bridge circuit 70 is 0 V is 2 kPa or more (preferably 30 kPa or more). As a result, in the AD conversion circuit 32, when an analog signal based on the output voltage _Vout of the bridge circuit 70 is AD converted into a digital signal, the analog signal is assigned to a voltage range corresponding to a pressure smaller than the lower limit value P1 of the working pressure range. By reducing or eliminating the number of bits, the number of bits allocated to the voltage range corresponding to the working pressure range (the range of 0 to V ₁ [V] of a shown in FIG. 5B) can be increased.

In particular, since the pressure received by the diaphragm section 64 when the output voltage _Vout of the bridge circuit 70 is 0 V is the lower limit value P1 of the operating pressure range, the voltage corresponding to the pressure smaller than the lower limit value P1 of the operating pressure range The number of bits assigned to the range can be substantially eliminated, and the number of bits assigned to the voltage range corresponding to the working pressure range can be increased as much as possible. “The pressure received by the diaphragm section 64 when the output voltage V _out of the bridge circuit 70 is 0V is the lower limit value P1 of the operating pressure range” means that the output voltage V _out of the bridge circuit 70 is 0V. The pressure received by the diaphragm 64 when the output voltage V _out of the bridge circuit 70 is 0 V is not only the case where the pressure received by the diaphragm 64 is equal to the lower limit P1 of the operating pressure range. In addition, a case where it is in a range of 0.8 times to 1.0 times (preferably 0.9 times to 1.0 times) is included.

  Thus, by increasing the number of bits allocated to the voltage range corresponding to the working pressure range, the resolution of AD conversion can be improved, and as a result, excellent detection accuracy can be realized.

Here, the AD conversion circuit 32 converts an analog signal based on the output voltage V _out of the bridge circuit 70 into a digital signal in the working pressure range. However, when the physical quantity sensor 1 is used as an atmospheric pressure sensor, the lower limit value of the working pressure range. It is preferable that P1 is 2 kPa or more and the upper limit value P2 is 130 kPa or less. In this case, the AD converter circuit 32 outputs the output of the bridge circuit 70 in a range where the pressure received by the diaphragm section 64 is 2 kPa or more and 130 kPa or less. An analog signal based on the voltage _Vout is converted into a digital signal. Thereby, a highly accurate barometric sensor can be realized using the physical quantity sensor 1. More preferably, when the AD conversion circuit 32 performs AD conversion in a range of 30 kPa or more and 120 kPa or less, a more accurate barometric sensor can be realized.

When the physical quantity sensor 1 is used as a water pressure sensor, it is preferable that the lower limit value P1 of the operating pressure range is 80 kPa or more and the upper limit value P2 is 3000 kPa or less. In this case, the AD conversion circuit 32 includes a diaphragm section. The analog signal based on the output voltage _Vout of the bridge circuit 70 is converted into a digital signal in a range where the pressure received by 64 is in the range of 80 kPa to 3000 kPa. Thereby, a highly accurate water pressure sensor can be realized using the physical quantity sensor 1.

The adjustment of the offset amount of the output voltage _Vout of the bridge circuit 70 as described above is performed with a relatively simple configuration by using the correction resistance elements 2a and 2b electrically connected to the bridge circuit 70. be able to.

  Further, the wiring layers 82 and 84 and the sealing layer 86 (wall portion) of the laminated structure 8 constituting the cavity portion S together with the diaphragm portion 64 are made of a material different from the diaphragm portion 64 (more specifically, the linear expansion coefficient is larger). Also, the offset amount of the output voltage of the bridge circuit 70 can be adjusted with a relatively simple configuration. Such adjustment can be performed in place of the resistance elements 2a and 2b or together with the resistance elements 2a and 2b. This point will be described in detail together with the description of the manufacturing method described later.

Next, a method for manufacturing the physical quantity sensor 1 will be briefly described.
6-8 is a figure which shows the manufacturing process of the physical quantity sensor shown in FIG. Hereinafter, description will be made based on these drawings.

[Sensor element formation process]
First, as shown in FIG. 6A, a substrate 6X which is an SOI substrate is prepared. The substrate 6X includes a silicon layer 61X (handle layer) made of single crystal silicon, a silicon oxide layer 62 (box layer) made of a silicon oxide film, and a silicon layer made of single crystal silicon. 63X are stacked in this order. Here, in a later step, the silicon layer 61X is thinned by polishing or the like as necessary, and then a recess 65 is formed to become the silicon layer 61.

  Next, the silicon layer 63X is doped (ion-implanted) with impurities such as phosphorus and boron, thereby forming the piezoresistive element 7 as shown in FIG. At this time, although not shown, the resistance elements 2a and 2b and the wiring 9 are also formed in the silicon layer 63X. Thereby, the silicon layer 63 in which the piezoresistive element 7 and the like are formed is obtained.

  In this ion implantation, the ion implantation conditions and the like are adjusted so that the doping amount of impurities into the wiring 9 is larger than that of the piezoresistive element 7 and the resistive elements 2a and 2b.

For example, when ion implantation of boron is performed at 17 keV, the ion implantation concentration into the piezoresistive element 7 and the resistive elements 2a and 2b is set to about 1 × 10 ¹³ atoms / cm ² or more and about 1 × 10 ¹⁵ atoms / cm ² or less. The ion implantation concentration to 9 is set to about 1 × 10 ¹⁵ atoms / cm ² or more and 5 × 10 ¹⁵ atoms / cm ² or less.

[Interlayer insulation film / wiring layer formation process]
Next, as illustrated in FIG. 6C, interlayer insulating films 81 </ b> X and 83 </ b> X, wiring layers 82 and 84, and a surface protective film 85 are formed on the silicon layer 63.

  The interlayer insulating films 81X and 83X are formed by forming a silicon oxide film by sputtering, CVD, or the like, and patterning the silicon oxide film by etching.

  Here, the thickness of each of the interlayer insulating films 81X and 83X is not particularly limited, but is, for example, about 1500 nm to 5000 nm.

  The wiring layers 82 and 84 are formed by forming a layer made of, for example, aluminum on the interlayer insulating films 81X and 83X by a sputtering method, a CVD method, or the like, and then performing a patterning process.

  Here, the thickness of each of the wiring layers 82 and 84 is not particularly limited, but is, for example, about 300 nm to 900 nm.

  Such a laminated structure of the interlayer insulating films 81X and 83X and the wiring layers 82 and 84 is formed by a normal CMOS process, and the number of laminated layers is appropriately set as necessary. In other words, more wiring layers may be stacked via an interlayer insulating film as necessary.

  After the formation of the interlayer insulating films 81X and 83X and the wiring layers 82 and 84, the surface protective film 85 is formed by a sputtering method, a CVD method, or the like. The constituent material of the surface protective film 85 is formed of a material having resistance for protecting the element from moisture, dust, scratches and the like, such as a silicon oxide film, a silicon nitride film, a polyimide film, and an epoxy resin film.

  Here, the thickness of the surface protective film 85 is not particularly limited, but is, for example, about 500 nm to 2000 nm.

[Cavity formation process]
Next, as shown in FIG. 7A, the cavity S is formed by etching. Thereby, part of the interlayer insulating films 81X and 83X is removed, and the interlayer insulating films 81 and 83 are formed.

  The cavity S is formed by removing a part of the interlayer insulating films 81X and 83X by etching through the plurality of pores 842 formed in the covering layer 841. Here, when wet etching is used as such etching, an etching solution such as hydrofluoric acid or buffered hydrofluoric acid is supplied from the plurality of pores 842, and when dry etching is used, hydrofluoric acid gas or the like is supplied from the plurality of pores 842. Etching gas is supplied.

[Sealing process]
Next, as shown in FIG. 7B, a sealing layer 86 made of a silicon oxide film, a silicon nitride film, a metal film such as AL, Cu, W, Ti, TiN or the like is formed on the coating layer 841 by a sputtering method. Then, the respective pores 842 are sealed by a CVD method or the like. Thus, the cavity S is sealed by the sealing layer 86, and the laminated structure 8 is obtained.

  Here, although the thickness of the sealing layer 86 is not specifically limited, For example, it is about 1000 nm or more and 5000 nm or less.

[Diaphragm formation process]
Next, after grinding the lower surface of the silicon layer 61X as necessary, a part of the lower surface of the silicon layer 61X is removed by etching to form a recess 65 as shown in FIG. Thereby, the diaphragm part 64 thinner than the periphery is formed.

  Here, when a part of the lower surface of the silicon layer 61X is removed, the silicon oxide layer 62 functions as an etching stop layer. Thereby, the thickness of the diaphragm part 64 can be prescribed | regulated with high precision.

  The method for removing a part of the lower surface of the silicon layer 61X may be dry etching or wet etching.

In the physical quantity sensor 1 thus obtained, the substrate 6 is mainly composed of silicon, but the sealing layer 86 is composed of a metal material having a linear expansion coefficient larger than that of silicon. In the sealing layer 86, a force for contracting in the direction indicated by the arrow in FIG. 8 is generated, and a tensile stress repelling the force remains. Further, the force that the sealing layer 86 tends to contract also acts on the diaphragm portion 64 so that the diaphragm portion 64 bends and deforms (initial deformation) as shown by a broken line in FIG. An initial stress is generated in the resistance element 7. This initial stress contributes to shifting the offset voltage to the negative side. Therefore, as described above, the offset amount of the output voltage of the bridge circuit 70 can be adjusted using the initial stress.
The physical quantity sensor 1 can be manufactured through the processes as described above.

Second Embodiment
Next, a second embodiment of the physical quantity sensor of the present invention will be described.

  FIG. 9 is a cross-sectional view showing a physical quantity sensor according to the second embodiment of the present invention. FIG. 10 is a plan view showing the arrangement of the piezoresistive elements of the physical quantity sensor shown in FIG. 9, and FIG. 11 is a diagram showing a bridge circuit including the piezoresistive elements of the physical quantity sensor shown in FIG.

  Hereinafter, the second embodiment of the physical quantity sensor of the present invention will be described. The description will focus on the differences from the above-described embodiment, and the description of the same matters will be omitted. 9 to 11, the same reference numerals are given to the same configurations as those in the above-described embodiment.

  The second embodiment is the same as the first embodiment described above except that a plurality of diaphragm portions are provided on the same substrate.

  The physical quantity sensor 1 </ b> A shown in FIG. 9 is provided with a plurality of diaphragm portions 64 on the same substrate 6. In the present embodiment, as shown in FIG. 10, four diaphragm portions 64 are arranged in a matrix, and piezoresistive elements 7 a, 7 b, 7 c, and 7 d are arranged in each diaphragm portion 64. It can be said that such a physical quantity sensor 1A includes four units 1a, 1b, 1c, and 1d for each diaphragm section 64.

  The piezoresistive elements 7a, 7b, 7c and 7d of the four units 1a, 1b, 1c and 1d constitute a bridge circuit 70A (Wheatstone bridge circuit) as shown in FIG.

  Specifically, as shown in FIG. 10, the piezoresistive elements 7a of the units 1a, 1b, 1c, and 1d are electrically connected in series to a pair of electrodes 84b1 and 84b2. The piezoresistive elements 7b of the units 1a, 1b, 1c, and 1d are electrically connected in series to the pair of electrodes 84b3 and 84b4. The piezoresistive element 7c and the resistive element 2a of the units 1a, 1b, 1c, and 1d are electrically connected in series to the pair of electrodes 84b1 and 84b3. The piezoresistive element 7d and the resistive element 2b of the units 1a, 1b, 1c, and 1d are electrically connected in series to the pair of electrodes 84b2 and 84b4.

As described above, the piezoresistive elements 7a, 7b, 7c and 7d and the resistive elements 2a and 2b of the units 1a, 1b, 1c and 1d constitute the bridge circuit 70A shown in FIG. The bridge circuit 70A is connected to a drive circuit (not shown) that supplies a drive voltage AVDC between the pair of electrodes 84b1 and 84b4. In the bridge circuit 70A, the potential difference (output voltage V _out ) between the pair of electrodes 84b2 and 84b3 is output as a signal (voltage) corresponding to the resistance value change of the piezoresistive elements 7a, 7b, 7c, and 7d.

  In addition, although the cavity S is arrange | positioned for every diaphragm in the illustration, it is not limited to this, For example, the one cavity S may respond | correspond to a some diaphragm.

  In the physical quantity sensor 1A as described above, a plurality of piezoresistive elements 7 are disposed in different diaphragm portions 64 and electrically connected in series, so that one piezoresistive element 7 is associated with downsizing. The area can be increased by the sum of a plurality of piezoresistive elements 7 connected in series. Therefore, pressure sensitivity can be increased while reducing 1 / f noise. Therefore, the S / N ratio can be improved even if the size is reduced.

  The physical quantity sensor 1A as described above can also exhibit excellent detection accuracy.

2. Next, a pressure sensor (a pressure sensor of the present invention) including the physical quantity sensor of the present invention will be described. FIG. 12 is a cross-sectional view showing an example of the pressure sensor of the present invention.

  As shown in FIG. 12, the pressure sensor 100 of the present invention includes a physical quantity sensor 1, a casing 101 that houses the physical quantity sensor 1, and a calculation unit 102 that calculates a signal obtained from the physical quantity sensor 1 to pressure data. ing. The physical quantity sensor 1 is electrically connected to the calculation unit 102 via the wiring 103.

  The physical quantity sensor 1 is fixed to the inside of the housing 101 by fixing means (not shown). In addition, the housing 101 has a through-hole 104 through which the diaphragm portion 64 of the physical quantity sensor 1 communicates with, for example, the atmosphere (outside the housing 101).

  According to such a pressure sensor 100, the diaphragm portion 64 receives pressure through the through hole 104. The pressure-received signal is transmitted to the calculation unit via the wiring 103 to calculate pressure data. The calculated pressure data can be displayed via a display unit (not shown) (for example, a monitor of a personal computer).

3. Next, an example of an altimeter (the altimeter of the present invention) including the physical quantity sensor of the present invention will be described. FIG. 13 is a perspective view showing an example of an altimeter according to the present invention.

  The altimeter 200 can be worn on the wrist like a wristwatch. In addition, the physical quantity sensor 1 (pressure sensor 100) is mounted inside the altimeter 200, and the altitude from the current location above sea level, the atmospheric pressure at the current location, or the like can be displayed on the display unit 201.

  The display unit 201 can display various information such as the current time, the user's heart rate, and weather.

4). Next, a navigation system to which an electronic device including the physical quantity sensor of the present invention is applied will be described. FIG. 14 is a front view showing an example of an electronic apparatus of the present invention.

  The navigation system 300 includes map information (not shown), position information acquisition means from GPS (Global Positioning System), self-contained navigation means using a gyro sensor, acceleration sensor, and vehicle speed data, physical quantity sensor 1, The display unit 301 displays predetermined position information or course information.

  According to this navigation system, altitude information can be acquired in addition to the acquired position information. By obtaining altitude information, for example, when traveling on an elevated road that shows approximately the same position as a general road, if you do not have altitude information, you are traveling on an ordinary road or on an elevated road The navigation system was unable to determine whether or not the vehicle was being used, and the general road information was provided to the user as priority information. Therefore, in the navigation system 300 according to the present embodiment, altitude information can be acquired by the physical quantity sensor 1, and a change in altitude due to entering from an ordinary road to an elevated road is detected, and navigation information in the traveling state of the elevated road is obtained. Can be provided to the user.

  The display unit 301 is configured to be small and thin, such as a liquid crystal panel display or an organic EL (Organic Electro-Luminescence) display.

  The electronic device provided with the physical quantity sensor of the present invention is not limited to the above-described ones. For example, a personal computer, a mobile phone, a medical device (for example, an electronic thermometer, a blood pressure meter, a blood glucose meter, an electrocardiogram measuring device, an ultrasonic diagnostic device , Electronic endoscope), various measuring instruments, instruments (for example, instruments for vehicles, aircraft, ships), flight simulators, and the like.

5. Next, the moving body (the moving body of the present invention) to which the physical quantity sensor of the present invention is applied will be described. FIG. 15 is a perspective view showing an example of the moving body of the present invention.

  As shown in FIG. 15, the moving body 400 has a vehicle body 401 and four wheels 402, and is configured to rotate the wheels 402 by a power source (engine) (not shown) provided in the vehicle body 401. ing. Such a moving body 400 incorporates a navigation system 300 (physical quantity sensor 1).

  As described above, the physical quantity sensor, pressure sensor, altimeter, electronic device, and moving body of the present invention have been described based on the illustrated embodiments, but the present invention is not limited thereto, and the configuration of each part is the same. Any structure having a function can be substituted. Moreover, other arbitrary structures and processes may be added.

  In the embodiment described above, the number of piezoresistive elements provided in one diaphragm portion is not limited to the embodiment described above, and may be one or more and three or less, or five or more. Also good. Further, the arrangement, shape, and the like of the piezoresistive element are not limited to the above-described embodiment. For example, in the above-described embodiment, the piezoresistive element may be arranged at the center of the diaphragm portion.

  In the above-described embodiment, the case where the number of resistance elements for correction per diaphragm section is four has been described as an example. However, the present invention is not limited to this, and the number of resistance elements may be one or more and three or less. It may be five or more. In the second embodiment, the number of resistance elements for correction may be different for each diaphragm portion.

  In the above-described embodiment, the number of diaphragms arranged in the physical quantity sensor is not limited to the above-described embodiment, and may be two or three, for example, or five or more. .

1. Physical quantity sensor 1A ... Physical quantity sensor 1a ... Unit 1b ... Unit 1c ... Unit 1d ... Unit 2a ... Resistance element 2b ... Resistance element 6 ... Substrate 6X ... Substrate 7 ... Piezoresistive element 7a ... Piezoresistive element 7b ... Piezoresistive element 7c ... Piezoresistive element 7d ... Piezoresistive element 8 ... Multilayer structure 9 ... Wiring 31 ... Amplifier circuit 32 ... AD converter circuit 61 ... Silicon layer 61X ... Silicon layer 62 ... Silicon oxide layer 63 ... Silicon layer 63X ... Silicon layer 64 ... Diaphragm part 65 ... Recess 70 ... Bridge circuit 70A ... Bridge circuit 71a ... Piezoresistive element 71b ... Piezo Resistive element 71c ... Piezoresistive element 71d ... Piezoresistive element 81 ... Interlayer insulating film 81X ... Interlayer insulating film 82 ... Wiring layer 82a ... Wiring 83 ... Interlayer insulating film 83X ... Interlayer insulating film 84 ... Wiring layer 84a ... Wiring layer 84b1 ... Electrode 84b2 ... Electrode 84b3 ... Electrode 84b4 ... Electrode 85 ... Surface protective film 86 ... Sealing layer 91a ... wiring 91b ... wiring 91c ... wiring 91d ... wiring 92a ... wiring 92b ... wiring 92c ... wiring 92d ... wiring 100 ... pressure sensor 101 ... casing 102 ... computing unit 103 ... Wiring 104 ... Through hole 200 ... Altimeter 201 ... Display unit 300 ... Navigation system 301 ... Display unit 400 ... Moving body 401 ... Car body 402 ... Wheel 641 ... Pressure receiving surface 841 ... Cover layer 842 ... ‥ pores P1 ‥‥ lower limit P2 ‥‥ upper limit S ‥‥ cavity _{V out} ‥‥ output voltage [Delta] R ‥‥ difference [Delta] R ₀ ‥‥ difference

Claims (12)

A diaphragm portion that bends and deforms by receiving pressure;
A plurality of piezoresistive elements arranged in the diaphragm portion and constituting a bridge circuit;
With
The physical quantity sensor, wherein the pressure received by the diaphragm portion when the output voltage of the bridge circuit is 0 V is 2 kPa or more. A diaphragm portion that bends and deforms by receiving pressure;
A plurality of piezoresistive elements arranged in the diaphragm portion and constituting a bridge circuit;
With
A physical quantity sensor characterized in that the pressure received by the diaphragm when the output voltage of the bridge circuit is 0 V is a lower limit value of a working pressure range.   The physical quantity sensor according to claim 1, further comprising a correction resistance element electrically connected to the bridge circuit.   The physical quantity sensor according to claim 1, further comprising an AD conversion circuit to which an analog signal based on an output voltage of the bridge circuit is input.   5. The physical quantity sensor according to claim 4, wherein the AD conversion circuit converts the analog signal into a digital signal within a range in which a pressure received by the diaphragm unit is in a range of 2 kPa to 130 kPa.   5. The physical quantity sensor according to claim 4, wherein the AD conversion circuit converts the analog signal into a digital signal within a range in which a pressure received by the diaphragm unit is in a range of 80 kPa to 3000 kPa.   The physical quantity sensor according to any one of claims 1 to 6, comprising a pressure reference chamber together with the diaphragm portion, and a wall portion made of a material different from that of the diaphragm portion. The number of the diaphragm portions is plural,
The physical quantity sensor according to any one of claims 1 to 7, wherein the bridge circuit includes a plurality of the piezoresistive elements arranged in different diaphragm portions.   A pressure sensor comprising the physical quantity sensor according to claim 1.   An altimeter comprising the physical quantity sensor according to any one of claims 1 to 8.   An electronic apparatus comprising the physical quantity sensor according to claim 1.   A moving body comprising the physical quantity sensor according to claim 1.

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