Pressure sensor, and mass flow meter, and mass flow controller using same

1. A pressure sensor comprising:

a diaphragm made of a first material and having an inside surface facing to a fluid-tight space, the diaphragm including

a diaphragm film deformable in response to a pressure application, the diaphragm film having an inside surface that is part of the inside surface of the diaphragm, and

a diaphragm film support having an inside surface that is part of the inside surface of the diaphragm and constitutes a periphery of the inside surface of the diaphragm film;

a strain sensor bonded to the inside surface of the diaphragm by a bonding material such that a part of the strain sensor lies on the inside surface of the diaphragm film support, the strain sensor being made of a second material;

a plurality of strain gauges provided on the strain sensor, wherein defining a direction oriented from a center of the inside surface of the diaphragm to a position bonded of the strain sensor as an x-direction and another direction perpendicular to the x-direction on the inside surface of the diaphragm as a y-direction, the strain sensor has, on a central region of its surface, a bridge circuit consisting of four strain gauges, one pair on two opposite sides of the four strain gauges being disposed in such a manner that current flows through them in the x-direction, and the other pair on two other opposite sides of the four strain gauges being disposed in such a manner that current flows through them in the y-direction; and

a depression formed on the inside surface of at least the diaphragm film, wherein the depression extends a certain length in the y-direction, and the depression is adjacent to or a certain distance apart from an edge of the strain sensor in the y-direction.

2. The pressure sensor according to claim 1 , wherein:

the plurality of strain gauges are provided around a central region of the strain sensor;

and the central region of the strain sensor is positioned at the periphery region of the inside surface of the diaphragm film.

3. The pressure sensor according to claim 1 , wherein:

the depression includes at least two depressions that are disposed so as to sandwich the strain sensor in the y-direction.

4. The pressure sensor according to claim 3 , wherein:

each of the at least two depressions does not penetrate the diaphragm film;

each of the at least two depressions overlaps with at least part of the diaphragm film;

each of the at least two depressions has almost the same length in the x-direction as the strain sensor;

each of the at least two depressions is disposed parallel to and at almost the same position as the strain sensor in the x-direction; and

each of the at least two depressions does not extend to an outer perimeter of the inside surface of the diaphragm.

5. The pressure sensor according to claim 3 , wherein:

each of the at least two depressions does not penetrate the diaphragm film;

each of the at least two depressions overlaps with at least part of the diaphragm film;

each of the at least two depressions is has a longer length in the x-direction than the strain sensor;

each of the at least two depressions is disposed parallel to the strain sensor in the x-direction and extends from an x-direction position of an outer edge of the strain sensor to a position on the opposite side in the x-direction across a central region of the inside surface of the diaphragm; and

each of the at least two depressions does not extend to an outer perimeter of the inside surface of the diaphragm.

6. The pressure sensor according to claim 3 , wherein:

each of the at least two depressions does not penetrate the diaphragm film;

each of the at least two depressions overlaps with at least part of the diaphragm film;

each of the at least two depressions is disposed parallel to the strain sensor in the x-direction and extends from an outer perimeter of the inside surface of the diaphragm across a central region of the inside surface of the diaphragm to the opposite side outer perimeter of the inside surface of the diaphragm in the x-direction; and

each of the at least two depressions does not extend to an outer perimeter of the inside surface of the diaphragm in the y-direction.

7. The pressure sensor according to claim 3 , wherein:

each of the at least two depressions does not penetrate the diaphragm film;

each of the at least two depressions is disposed parallel to the strain sensor in the x-direction and extends from an outer perimeter of the inside surface of the diaphragm across a central region of the inside surface of the diaphragm to the opposite side outer perimeter of the inside surface of the diaphragm in the x-direction; and

each of the at least two depressions extends to an outer perimeter of the inside surface of the diaphragm in the y-direction.

8. The pressure sensor according to claim 3 , wherein:

each of the at least two depressions does not penetrate the diaphragm film;

each of the at least two depressions is formed with a constant depth;

each of the at least two depressions is disposed parallel to the strain sensor in the x-direction and extends from an outer perimeter of the inside surface of the diaphragm across a central region of the inside surface of the diaphragm to the opposite side outer perimeter of the inside surface of the diaphragm in the x-direction; and

each of the at least two depressions extends from the edge of the strain sensor in the y-direction to an outer perimeter of the inside surface of the diaphragm in the y-direction.

9. The pressure sensor according to claim 3 , wherein:

each of the at least two depressions does not penetrate the diaphragm film;

each of the at least two depressions overlaps with at least part of the diaphragm film;

each of the at least two depressions is has a longer length in the x-direction than the strain sensor;

each of the at least two depressions is disposed parallel to the strain sensor in the x-direction and extends from an outer perimeter of the inside surface of the diaphragm to a central region of the inside surface of the diaphragm in the x-direction; and

each of the at least two depressions extends to an outer perimeter of the inside surface of the diaphragm in the y-direction.

10. The pressure sensor according to claim 3 , wherein:

each of the at least two depressions does not penetrate the diaphragm film;

each of the at least two depressions is formed on only the inside surface of the diaphragm film; and

each of the at least two depressions is disposed parallel to the strain sensor in the x-direction and extends from a border of the inside surface of the diaphragm film across a central region of the inside surface of the diaphragm film to the opposite side border of the inside surface of the diaphragm film in the x-direction.

11. The pressure sensor according to claim 1 , wherein:

the first material is a metal; and

the second material is silicon.

12. The pressure sensor according to claim 11 , wherein:

the metal of the diaphragm is a 316L stainless steel.

13. The pressure sensor according to claim 1 , wherein:

the bonding material is an Au/Sn eutectic alloy, an Au/Ge eutectic alloy, or a low melting-point vanadium-based glass.

14. The pressure sensor according to claim 1 further comprising:

a fluid-tight housing; and

a flange provided at bottom of the diaphragm for fixing another member for pressure measurement, wherein

the flange is secured to the fluid-tight housing in such a way that the fluid-tight space is formed by being surrounded by the fluid-tight housing and the diaphragm, and that the fluid-tight space maintains a constant pressure.

15. The pressure sensor according to claim 1 , wherein:

the diaphragm film support has a groove on a side surface exposed to a fluid-tight space, the groove being formed along a whole periphery of the side surface and disposed above the flange.

16. The pressure sensor according to claim 1 , further comprising:

an additional diaphragm layer having a linear expansion coefficient close to the linear expansion coefficient of the strain sensor, the strain sensor being bonded to the diaphragm via the additional diaphragm layer.

17. The pressure sensor according to claim 16 , wherein:

the depression is formed on a surface of the additional diaphragm layer.

18. The pressure sensor according to claim 16 , wherein:

the additional diaphragm layer is made of a predetermined Ni—Co—Fe alloy or 42Ni—Fe alloy.

19. A pressure sensor comprising:

a diaphragm made of a first material and having an inside surface facing to a fluid-tight space, the diaphragm including

a diaphragm film deformable in response to a pressure application, the diaphragm film having an inside surface that is part of the inside surface of the diaphragm, and

a diaphragm film support having an inside surface that is part of the inside surface of the diaphragm and constitutes a periphery of the inside surface of the diaphragm film;

a strain sensor bonded to the inside surface of the diaphragm by a bonding material such that a part of the strain sensor lies on the inside surface of the diaphragm film support,

the strain sensor being made of a second material;

a plurality of strain gauges provided on the strain sensor;

a depression formed on the inside surface of the diaphragm, wherein defining a direction oriented from center of the inside surface of the diaphragm to a position bonded of the strain sensor as an x-direction and another direction perpendicular to the x-direction on the inside surface of the diaphragm as a y-direction, the depression extends a certain length in the y-direction, and the depression is adjacent to or a certain distance apart from an edge of the strain sensor in the y-direction; and

an additional diaphragm layer having a linear expansion coefficient close to the linear expansion coefficient of the strain sensor, the strain sensor being bonded to the diaphragm via the additional diaphragm layer.