JP2016053508A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensor with which it is possible to reduce the non-linearity of sensor output against pressure.SOLUTION: The thickness of a diaphragm part 14 provided in a sensor chip 10 is defined to be t. The distance between the position of an outer circumferential end 15 of the diaphragm part 14 in a direction at right angles to the outer circumferential end 15 of the diaphragm part 14 among the plane directions of the surface 11 of the sensor chip 10 and the center position of strain gauges 20-23 is defined to be d. The strain gauges 20-23 are provided at the position of the distance d calculated by d=-6.16 t+83.5 [μm], where the position of the outer circumferential end 15 of the diaphragm part 14 is assumed to be d=0, the center area 16 side of the diaphragm part 14, with the outer circumferential end 15 serving as a point of reference, is assumed to be an area of d<0, and the outer circumferential area 17 side of the diaphragm part 14 is assumed to be d>0.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pressure sensor including a strain gauge whose resistance value changes in accordance with displacement of a diaphragm portion.

  Conventionally, for example, Patent Document 1 proposes a pressure sensor in which a plurality of strain detection elements are provided in a diaphragm portion. One of the strain detection elements is disposed across the inside and the outside of the diaphragm portion. Thereby, the sensitivity of the sensor output with respect to pressure improves.

Japanese Patent No. 4035519

  However, when the pressure increases, the sensor output changes so as to increase, but the change includes non-linearity. In addition, the non-linearity increases as the sensitivity of the sensor output increases. For this reason, there is a problem that non-linearity of the sensor output increases when an attempt is made to obtain a highly sensitive sensor output as in the prior art.

  An object of this invention is to provide the pressure sensor which can make the nonlinearity of the sensor output with respect to a pressure small in view of the said point.

  The inventors have determined that the non-linear component of the sensor output with respect to the pressure is a quadratic function according to the distance between the position of the outer peripheral end (15) of the diaphragm (14) and the center of each strain gauge (20-23). I found it to change. Further, it has been found that the inflection point of the quadratic function, that is, the distance at which the nonlinear component of the sensor output becomes the smallest varies depending on the thickness of the diaphragm portion (14).

  Therefore, in the invention described in claim 1, a part of the semiconductor substrate (13) having the front surface (11) and the back surface (12) is a thin wall shape removed from the back surface (12) side and is displaced by receiving pressure. The sensor chip (10) which has the diaphragm part (14) to be provided is provided.

  Further, a first strain gauge (20), a second strain gauge (21), which are formed on the surface (11) side of the sensor chip (10) and whose resistance value changes according to the displacement of the diaphragm portion (14), A third strain gauge (22) and a fourth strain gauge (23) are provided.

  The thickness of the diaphragm part (14) is defined as t, and the diaphragm part (14) in the direction perpendicular to the outer peripheral end part (15) of the diaphragm part (14) in the surface direction of the surface (11) of the sensor chip (10). The distance between the position of the outer peripheral end (15) and the center position of each strain gauge (20-23) is defined as d.

  Further, the position of the outer peripheral end portion (15) of the diaphragm portion (14) is d = 0, and the central region (16) side of the diaphragm portion (14) is d <0 with the outer peripheral end portion (15) as a reference position. In addition to the region, d> 0 is set on the outer peripheral region (17) side of the diaphragm (14).

  And at least 1 of each strain gauge (20-23) is provided in the position of the distance d calculated by d = -6.16t + 83.5 [micrometer], It is characterized by the above-mentioned.

  Thus, since the distance d of each strain gauge (20-23) on the basis of the outer peripheral end part (15) of the diaphragm part (14) is prescribed according to the thickness t of the diaphragm part (14), the pressure The non-linearity of the sensor output with respect to can be reduced.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

It is a top view of the pressure sensor concerning a 1st embodiment of the present invention. It is II-II sectional drawing of FIG. It is a figure for demonstrating the distance d of the position of the outer peripheral edge part of a diaphragm part, and the center position of each strain gauge. It is the figure which showed the calculation formula of the sensor output with respect to a pressure, and NLP. It is the figure which showed the relationship between the distance d and NLP. It is the figure which showed the relationship between the thickness t of a diaphragm part, and the distance d. It is a top view of a diaphragm part of a pressure sensor concerning a 2nd embodiment of the present invention. In other embodiment, it is the top view which showed an example of the shape of the outer peripheral end part of a diaphragm part. In other embodiment, it is the top view which showed an example of the shape of the outer peripheral end part of a diaphragm part.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the pressure sensor includes a sensor chip 10, a first strain gauge 20, a second strain gauge 21, a third strain gauge 22, and a fourth strain gauge 23.

  As shown in FIG. 2, the sensor chip 10 is composed of a plate-like semiconductor substrate 13 having a front surface 11 and a back surface 12. The sensor chip 10 has a diaphragm portion 14. The diaphragm portion 14 is a thin-walled portion in which a part of the semiconductor substrate 13 is removed from the back surface 12 side. The diaphragm portion 14 is displaced by receiving the pressure of the pressure medium on the pressure receiving surface on the back surface 12 side of the semiconductor substrate 13, for example. The front surface 11 of the semiconductor substrate 13 corresponds to the front surface of the sensor chip 10, and the back surface 12 of the semiconductor substrate 13 corresponds to the back surface of the sensor chip 10.

  The diaphragm portion 14 is formed on the sensor chip 10 so that the outer peripheral end portion 15 on the surface 11 of the semiconductor substrate 13 is an octagon. Such a shape of the diaphragm portion 14 can be formed by etching the semiconductor substrate 13 with the opening shape of the mask formed on the back surface 12 of the semiconductor substrate 13 being an octagon. For example, a silicon substrate is used as the semiconductor substrate 13.

  Each of the strain gauges 20 to 23 is a sensing means whose resistance value changes according to the displacement of the diaphragm portion 14. In the present embodiment, the strain gauges 20 to 23 are formed at four locations on the semiconductor substrate 13 so as to correspond to the respective sides of the diaphragm portion 14.

  And each strain gauge 20-23 is electrically connected so that a Wheatstone bridge circuit may be comprised. Thereby, the voltage according to the distortion of the diaphragm part 14 is detectable as a pressure using the piezoresistive effect of each strain gauge 20-23.

  Each strain gauge 20 to 23 is a diffusion resistor formed by ion implantation into the semiconductor substrate 13. That is, the strain gauges 20 to 23 are formed on the surface 11 side of the semiconductor substrate 13.

  Here, in FIG. 1, the strain gauges 20 to 23 are shown as squares, but in actuality, they are laid out in a wavy shape, and a region in which a straight portion is provided instead of a bent portion corresponds to the square. ing.

In addition, an insulating film 30 is formed on the surface 11 of the semiconductor substrate 13 so as to cover the strain gauges 20 to 23. The insulating film 30 is, for example, a silicon oxide film (SiO ₂ ). In FIG. 1, the insulating film 30 is omitted. Further, on the insulating film 30, wiring portions such as wirings for electrically connecting the strain gauges 20 to 23 and pads to which bonding wires are bonded are formed.

  In said structure, the position of each strain gauge 20-23 is prescribed | regulated as follows. First, the definition of length will be described. The thickness of the diaphragm part 14 is defined as t. That is, in the direction perpendicular to the front surface 11 of the semiconductor substrate 13, the length from the front surface 11 to the back surface 12 of the diaphragm portion 14 of the semiconductor substrate 13 corresponds to the thickness of the diaphragm portion 14.

  Further, the distance between the position of the outer peripheral end 15 of the diaphragm portion 14 and the center position of each strain gauge 20 to 23 in the direction perpendicular to the outer peripheral end 15 of the diaphragm portion 14 in the surface direction of the surface 11 of the sensor chip 10. d.

  Further, as shown in FIG. 3, the position of the outer peripheral end 15 of the diaphragm 14 is d = 0. The position of the outer peripheral end 15 of the diaphragm portion 14 is set as a reference position, and the central region 16 side of the diaphragm portion 14 is defined as a region of d <0. On the other hand, the outer peripheral region 17 side of the diaphragm portion 14 is set as a region where d> 0.

  In the above definition, at least one of the strain gauges 20 to 23 is provided at the position of the distance d calculated by d = −6.16t + 83.5 [μm]. In the present embodiment, all the strain gauges 20 to 23 are provided at positions of the distance d calculated by d = −6.16t + 83.5 [μm].

  Next, the basis for obtaining the above formula will be described. As described above, there is a problem that the nonlinearity of the sensor output increases as the pressure increases. Specifically, as shown in FIG. 4, the sensor output with respect to pressure ideally changes linearly as indicated by a broken line, but actually the sensor output changes nonlinearly as indicated by a solid line. This is due to the stress generated in the strain gauges 20-23.

  The inventors examined the relationship between the distance d between the strain gauges 20 to 23 and the outer peripheral end 15 of the diaphragm portion 14 and the NLP by changing the thickness t of the diaphragm portion 14. Here, NLP is the ratio of the nonlinear component to the ideal sensor output (full scale), and is represented by the equation shown in FIG. The smaller the NLP, the smaller the ratio of the nonlinear component to the ideal sensor output.

  As shown in FIG. 5, the inventors have found that NLP changes along a curve of a quadratic function with respect to the distance d. Moreover, it turned out that it shifts according to the thickness t of the diaphragm part 14. FIG. Furthermore, in each curve, it was found that NLP is closest to zero at the inflection point of the curve of the quadratic function.

  When the inventors approximated the relationship between the thickness t of the diaphragm portion 14 and the position of the inflection point (distance d) from the result of FIG. 5 by a linear function, d = −6.16t + 83 as shown in FIG. .5 [μm] was obtained. That is, the nonlinearity of the sensor output can be minimized by disposing the strain gauges 20 to 23 at the distance d obtained from the equation.

  As described above, the present embodiment is characterized in that each of the strain gauges 20 to 23 is determined by the distance d that changes according to the thickness t of the diaphragm portion 14. Thereby, the nonlinearity of the sensor output with respect to a pressure can be made small.

  In particular, since the thickness t of the diaphragm portion 14 is as thin as several tens of μm, each of the strain gauges 20 to 23 is easily affected by stress from the diaphragm portion 14. However, by determining the positions of the strain gauges 20 to 23 in accordance with the above formula, the influence of stress from the diaphragm portion 14 can be reduced, and the nonlinearity of the sensor output can be reduced.

(Second Embodiment)
In the present embodiment, parts different from the first embodiment will be described. In the present embodiment, the diaphragm portion 14 is formed on the sensor chip 10 such that the outer peripheral end portion 15 on the surface 11 is a quadrangle.

  Specifically, as shown in FIG. 7A, there is one in which the outer peripheral end portion 15 of the diaphragm portion 14 is formed in a square shape. On the other hand, as shown in FIG. 7B, there is a case where the outer peripheral end 15 of the diaphragm 14 is formed to be rectangular. In the case of a rectangular shape, one strain gauge 20 and one strain gauge 22 among the strain gauges 20 to 23 are arranged one by one corresponding to the two long sides of the rectangle. Further, the two strain gauges 21 and 23 are arranged between the two strain gauges 20 and 22, that is, in the central region 16 along the long side. Then, a distance d is set for the strain gauges 20 and 22 corresponding to the two long sides of the diaphragm portion 14.

  As described above, even in the structure in which the outer peripheral end portion 15 of the diaphragm portion 14 is formed to be a quadrangle (square and rectangle), the positions of the strain gauges 20 to 23 can be defined from the above-described formula of the distance d. it can.

(Other embodiments)
The configuration of the pressure sensor shown in each of the above embodiments is an example, and the present invention is not limited to the configuration shown above, and may be another configuration that can realize the present invention. For example, the above-described pressure sensor is configured as a back pressure-receiving type, but this is an example of how to use the pressure sensor. Therefore, the pressure sensor may be configured as a double-sided pressure receiving type or a surface pressure receiving type.

  In each of the above embodiments, the shape of the outer peripheral end 15 of the diaphragm portion 14 is shown as an octagon and a quadrangle, but the shape of the outer peripheral end 15 may be another even-numbered polygon. For example, as shown in FIG. 8A, the outer peripheral end 15 of the diaphragm 14 may be hexagonal. In this case, each of the strain gauges 20 to 23 is disposed so as to face each other.

  Further, as shown in FIG. 8B, the outer peripheral end 15 of the diaphragm 14 may be a dodecagon. In this case, the strain gauges 20 to 23 are arranged so as to correspond to four of the twelve sides. Thus, by making the outer peripheral end 15 of the diaphragm portion 14 into a polygonal shape, the stress transmitted to the strain gauges 20 to 23 from the outside, such as thermal stress, can be reduced, so the accuracy of sensor output is improved. can do.

  Further, as shown in FIG. 9, the outer peripheral end 15 of the diaphragm 14 on the surface 11 of the sensor chip 10 may be formed in a circular shape. In this case, each of the strain gauges 20 to 23 is set to have a distance d along the direction perpendicular to the outer peripheral end 15, that is, along the radial direction.

  In each of the above embodiments, all the strain gauges 20 to 23 are provided at the position of the distance d calculated by d = −6.16t + 83.5 [μm], but this is the arrangement of the strain gauges 20 to 23. It is an example. Therefore, at least one of the strain gauges 20 to 23 may be provided at the position of the distance d calculated by d = −6.16t + 83.5 [μm]. As described above, by arranging at least one of the strain gauges 20 to 23 at the position calculated by the equation, the nonlinearity of the sensor output with respect to the pressure can be reduced.

DESCRIPTION OF SYMBOLS 10 Sensor chip 11 Front surface 12 Back surface 13 Semiconductor substrate 14 Diaphragm part 15 Outer peripheral edge 16 Central area | region 17 Outer peripheral area 20-23 Strain gauge

Claims (4)

A semiconductor chip (13) having a front surface (11) and a back surface (12) is partially removed from the back surface (12) side, and has a diaphragm portion (14) that is displaced by pressure. (10) and
A first strain gauge (20) and a second strain gauge (21) which are formed on the surface (11) side of the sensor chip (10) and whose resistance value changes according to the displacement of the diaphragm portion (14). A third strain gauge (22) and a fourth strain gauge (23);
With
The thickness of the diaphragm portion (14) is defined as t, and the surface direction of the surface (11) of the sensor chip (10) is perpendicular to the outer peripheral end portion (15) of the diaphragm portion (14). The distance between the position of the outer peripheral end (15) of the diaphragm (14) and the center position of each strain gauge (20-23) is defined as d,
Further, the position of the outer peripheral end portion (15) of the diaphragm portion (14) is set to d = 0, and the outer peripheral end portion (15) is set as a reference position so that the central region (16) side of the diaphragm portion (14) is d. <0 and when the outer peripheral area (17) side of the diaphragm (14) is d> 0,
At least one of the strain gauges (20 to 23) is provided at a position of a distance d calculated by d = −6.16t + 83.5 [μm].   The pressure according to claim 1, wherein the diaphragm part (14) is formed on the sensor chip (10) so that the outer peripheral end part (15) of the surface (11) is a quadrangle. Sensor.   The said diaphragm part (14) is formed in the said sensor chip (10) so that the said outer peripheral edge part (15) in the said surface (11) may become an octagon. Pressure sensor.   The pressure according to claim 1, wherein the diaphragm part (14) is formed on the sensor chip (10) such that the outer peripheral end part (15) of the surface (11) is circular. Sensor.

Images