JP2014115099A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To configure a pressure sensor capable of cost reduction without requiring a complex layer structure or wire routing structure.SOLUTION: The pressure sensor includes a substrate 1 and a diaphragm 2 formed on an upper part of the substrate. A conductor film 3 is formed on an inner surface of the diaphragm 2. Two electrodes 4,5 are formed on a surface facing the diaphragm 2 of the substrate 1. Terminals 6,7 which are electrically conducted with the electrodes 4,5 are formed on a lower surface of the substrate 1. When the diaphragm 2 is displaced in accordance with a pressure to be detected, a distance between the conductor film 3 and the electrodes 4,5 is changed. The conductor film 3 formed on the diaphragm 2 influences a fringe current generated between the electrodes 4,5, and the extent of the influence varies according to the distance between the conductor film 3 and the electrodes 4,5. In other words, electrostatic capacitance between the electrodes 4, 5 is changed according to an external force F, so that the external force F is detected on the basis of the electrostatic capacitance.

Description

  The present invention relates to a pressure sensor including a diaphragm that is displaced by a pressure to be detected.

  Currently, there is a growing market need for sensors that detect fluid pressure and force sensors that detect uniaxial pressing force. In the present invention, both the sensor for detecting the pressure of the fluid and the force sensor are sensors for detecting the pressure, and thus are treated as pressure sensors as a general concept.

  For example, Patent Documents 1 and 2 disclose a pressure sensor including a diaphragm that is displaced by a pressure to be detected.

  The pressure sensor of Patent Document 1 is a piezoresistive pressure sensor that detects a stress generated when a piezoresistor is arranged around a fixed portion of a diaphragm and the diaphragm is pressed by pressure.

  The pressure sensor disclosed in Patent Document 2 is a capacitive pressure sensor that detects a change in capacitance by arranging a diaphragm and an electrode at a position facing the diaphragm and changing the facing distance due to pressure.

  FIG. 8 is a cross-sectional view of the pressure sensor disclosed in Patent Document 2. As shown in FIG. In FIG. 8, the pressure sensor 30 has a structure in which a detection body 41 is joined to a plate-like base 32 having a relatively large thickness. A first electrode 44, a dielectric film 22, and the like are formed on the upper surface of the base 32. The detection body 41 is formed by forming a rectangular thin plate deformation region 42 at a substantially central portion of the crystal plate. A second electrode 46 is formed on the lower surface of the deformation region 42. Further, a conductive portion 37, a lead electrode 46a, and an electrode pad 46b are formed from the lower surface to the upper surface of the detection body 41. Bonding wires W1 and W2 are connected to the electrode pad 46b and the conductive portion 37, respectively.

JP 2009-180622 A JP 2007-278716 A

  In the piezoresistive pressure sensor shown in Patent Document 1, it is necessary to form a diaphragm structure and a piezoresistive element, which requires many processes and increases manufacturing costs.

  Moreover, in the capacitance-type pressure sensor shown in Patent Document 2, as shown in FIG. 8, wiring from the counter electrode becomes very complicated. Therefore, there are still many processes, and the manufacturing cost increases.

  Therefore, in view of these circumstances, an object of the present invention is to provide a pressure sensor that achieves cost reduction without requiring a complicated layer structure or wiring routing structure.

(1) The present invention is based on a fringe electric field that is formed on a same surface facing the diaphragm, and a diaphragm that is constituted by a conductor or has a conductor in part and is displaced by pressure to be detected. It is characterized by comprising at least two electrodes whose capacitance varies depending on the gap with the diaphragm.

(2) A diaphragm made of a dielectric material or having a dielectric material in part and displaced by a pressure to be detected, and a static electricity generated by a fringe electric field formed between the electrodes formed on the same surface facing the diaphragm. It is characterized by comprising at least two electrodes whose capacitance changes depending on the gap with the diaphragm.

  According to the present invention, since the electrodes are disposed only on the surface facing the diaphragm, a low-cost pressure sensor can be configured without requiring a complicated layer structure or wiring routing structure.

FIG. 1 is a cross-sectional view of the main part of the pressure sensor according to the first embodiment. FIG. 2 is a perspective view of the pressure sensor shown in FIG. 1 with the diaphragm removed. FIG. 3 shows an example of a capacitance detection circuit connected to the terminals 6 and 7 of the pressure sensor shown in FIG. FIG. 4A, FIG. 4B, and FIG. 4C are diagrams showing patterns of two electrodes that are formed on the surface of the pressure sensor according to the second embodiment on which the diaphragms face each other. FIG. 5 is a cross-sectional view of the main part of the pressure sensor according to the third embodiment. FIG. 6 is a cross-sectional view of the main part of the pressure sensor according to the fourth embodiment. FIG. 7 is a cross-sectional view of the main part of the pressure sensor according to the fifth embodiment. FIG. 8 is a cross-sectional view of the pressure sensor disclosed in Patent Document 2. As shown in FIG.

<< First Embodiment >>
FIG. 1 is a cross-sectional view of the main part of the pressure sensor according to the first embodiment. This pressure sensor includes a base material 1 and a diaphragm 2 formed thereon. A conductor film 3 is formed on the inner surface of the diaphragm 2. Two electrodes 4 and 5 are formed on the surface of the substrate 1 facing the diaphragm 2. Terminals 6 and 7 that are electrically connected to the electrodes 4 and 5 are formed on the lower surface of the substrate 1.

  FIG. 2 is a perspective view of the pressure sensor shown in FIG. 1 with the diaphragm removed. Each of the two electrodes 4 and 5 is a comb-like electrode and is alternately inserted. When a voltage is applied between the electrodes 4 and 5, a fringe electric field (around electric field) is generated in the gap where the electrodes 4 and 5 face each other and in the vicinity thereof. The wavy lines in FIG. 1 conceptually show the electric lines of force of the fringe electric field.

  The substrate 1 is, for example, a Si substrate, and the electrodes 4 and 5 and the conductor film 3 are, for example, an Al film. Although these are manufactured by a semiconductor process, the conductor film on the diaphragm side does not require the formation of a fine pattern, so the structure is simple. For example, there is no need to etch the Si substrate by deep RIE (Deep RIE). Cost can be reduced.

  The diaphragm 2 is curved and deformed (displaced) by an external force F (see FIG. 1). Since the conductor film 3 formed on the inner surface of the diaphragm 2 is deformed together with the diaphragm 2, the distance between the conductor film 3 and the electrodes 4 and 5 changes according to the displacement of the diaphragm 2.

  Although the conductor film 3 is in an electrically floating state, a part of the conductor film 3 exists in the fringe electric field generated between the electrodes 4 and 5, and therefore the conductor film 3 affects the fringe electric field. It varies depending on the distance between the film 3 and the electrodes 4 and 5. That is, the capacitance between the electrodes 4 and 5 is determined not only by the distance between the electrodes 4 and 5 but also by the distance between the electrodes 4 and 5 and the conductor film 3. Therefore, the capacitance between the electrodes 4 and 5 changes according to the external force F, and the external force F can be detected by this capacitance.

  FIG. 3 shows an example of a capacitance detection circuit connected to the terminals 6 and 7 of the pressure sensor shown in FIG. This capacitance detection circuit is composed of a switched capacitor circuit including an operational amplifier. In FIG. 3, one of capacitors Cw1 and Cw2 is a capacitance of the pressure sensor, and the other is a reference capacitance. The capacitor Cf is a feedback capacitance to the inverting input terminal of the operational amplifier OP, and the operational amplifier OP constitutes an integration circuit together with the capacitor Cf. Positive and negative constant voltages are applied to the power supply terminals + Vin and -Vin. The plurality of switches S1, S2 are alternately turned on / off. As a result, a voltage proportional to the capacitance ratio of the capacitors Cw1 and Cw2 is output to the Vout terminal.

<< Second Embodiment >>
FIG. 4A, FIG. 4B, and FIG. 4C are diagrams showing patterns of two electrodes that are formed on the surface of the pressure sensor according to the second embodiment on which the diaphragms face each other.

  In the example of FIG. 4A, electrodes 4a and 4b electrically connected to each other and electrodes 5a and 5b electrically connected to each other are provided. If the electrodes having the same potential are colored, a checkerboard pattern (checker pattern) is obtained.

  In the example of FIG. 4B, the adjacent positions of the electrodes 4a, 4b, 5a, and 5b shown in FIG.

  In the example of FIG. 4C, the two electrodes 4 and 5 are concentric arcs, and the two electrodes 4 and 5 are alternately inserted.

  As shown in these examples, by expanding the distribution range of the fringe electric field generated from the two electrodes facing each other, the rate of change of the interelectrode capacitance with respect to the displacement of the flange can be increased, and the pressure detection sensitivity can be increased.

<< Third Embodiment >>
FIG. 5 is a cross-sectional view of the main part of the pressure sensor according to the third embodiment. The pressure sensor includes a base material 1 and a diaphragm 23 formed on the base material 1. In this pressure sensor, the entire diaphragm is composed of a conductor film. Two electrodes 4 and 5 are formed on the surface of the substrate 1 facing the diaphragm 23. Terminals 6 and 7 that are electrically connected to the electrodes 4 and 5 are formed on the lower surface of the substrate 1.

  The diaphragm 23 is made of, for example, Si. Thus, the whole diaphragm may be comprised with the conductor.

<< Fourth Embodiment >>
FIG. 6 is a cross-sectional view of the main part of the pressure sensor according to the fourth embodiment. This pressure sensor includes a base material 1 and a diaphragm 2 formed thereon, and a dielectric film 8 is formed on the inner surface of the diaphragm 2. Two electrodes 4 and 5 are formed on the surface of the substrate 1 facing the diaphragm 2. Terminals 6 and 7 that are electrically connected to the electrodes 4 and 5 are formed on the lower surface of the substrate 1.

  Thus, when the dielectric film is opposed to the electrode formed on the base material, a part of the dielectric film 8 exists in the fringe electric field generated between the electrodes 4 and 5, and therefore the dielectric film 8 is The fringe electric field is affected, and the degree thereof varies depending on the distance between the dielectric film 8 and the electrodes 4 and 5. That is, the capacitance between the electrodes 4 and 5 is determined not only by the distance between the electrodes 4 and 5 but also by the distance between the electrodes 4 and 5 and the dielectric film 8. Therefore, the capacitance between the electrodes 4 and 5 changes according to the external force F, and the external force F can be detected by this capacitance.

  By configuring the dielectric film 8 with a high εr dielectric material, the required capacity can be configured in a space-saving manner. Unlike the metal film, since the surface of the dielectric film is uneven, the phenomenon that the dielectric film 8 sticks to the electrodes 4 and 5 (sticking) hardly occurs, and the gap between the substrate 1 and the diaphragm is designed to be narrow in advance. be able to.

<< Fifth Embodiment >>
FIG. 7 is a cross-sectional view of the main part of the pressure sensor according to the fifth embodiment. The pressure sensor includes a base material 1 and a diaphragm 28 formed on the base material 1. In this pressure sensor, the entire diaphragm 28 is formed of a dielectric film. Two electrodes 4 and 5 are formed on the surface of the substrate 1 facing the diaphragm 28. Terminals 6 and 7 that are electrically connected to the electrodes 4 and 5 are formed on the lower surface of the substrate 1.

  The diaphragm 28 is made of, for example, glass or PZT. Thus, the whole diaphragm may be comprised with the dielectric material.

  Even when the entire diaphragm is formed of a conductor film or a dielectric film, the electrodes 4 and 5 can have various shapes as shown in FIG.

  The pressure sensor described above can be configured as a single element, but can also be mounted on an IC that performs various signal processing. It is also possible to configure a module with a pressure sensor by configuring a diaphragm on a part of a semiconductor substrate on which a circuit other than the sensor is formed.

F ... External force 1 ... Base material 2 ... Diaphragm 3 ... Conductor films 4, 5 ... Electrodes 4a, 4b, 5a, 5b ... Electrodes 6, 7 ... Terminal 8 ... Dielectric film 23 ... Diaphragm 28 ... Diaphragm

Claims (2)

A diaphragm constituted by a conductor or having a conductor in part and displaced by the pressure to be detected;
A pressure sensor comprising at least two electrodes, which are formed on the same surface facing the diaphragm, and change in capacitance due to a fringe electric field generated between the electrodes depending on a gap with the diaphragm. A diaphragm constituted by a dielectric material or having a dielectric material in part and displaced by a pressure to be detected;
A pressure sensor comprising at least two electrodes, which are formed on the same surface facing the diaphragm, and change in capacitance due to a fringe electric field generated between the electrodes depending on a gap with the diaphragm.

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