JPS60186725A - Pressure sensor - Google Patents

Abstract

PURPOSE:To obtain a pressure sensor of simple constitution by providing a pressure receiving diaphragm made of an elastic semiconductor plate material, an oscillation beam which is formed on the pressure receiving diaphragm while having both ends fixed, and an exciting means for the oscillation beam and an oscillation detecting means. CONSTITUTION:When the pressure receiving diaphragm 2 of the pressure sensor is applied with pressure from the inside as shown by an arrow P, the diaphragms 2 flexes owing to the pressure to apply tensile force to an oscillation beams 3 formed in the center and compressive force to an oscillation beam 4 formed at the peripheral edge part of the diaphragm 2. Consequently, natural oscillations frequencies f1 and f2 of the oscillation beams 3 and 4 vary differentially; with the pressure P and, for example, the value (f1-f2) is calculated to measure the pressure P.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a pressure sensor that outputs a force corresponding to the pressure generated in a pressure receiving diaphragm as a frequency signal. Specifically, the present invention relates to a pressure sensor having a structure in which a semiconductor substrate such as silicon is used as a pressure receiving diaphragm, and a vibrating beam is formed on this substrate.

[Prior art]

The measured pressure is received by a diaphragm, and the force generated on the diaphragm is detected by a strain gauge installed on the diaphragm.
Pressure sensors that convert into electrical signals are well known and have already been widely put into practical use.

In such a pressure sensor, the strain gauge exhibits an analog resistance value change according to the force to be measured, and its output value is also small. For this reason, when the output signal is processed by a computer or the like, it must be amplified or A/b converted.

There are also pressure sensors that obtain frequency signals corresponding to pressure.
This is known, for example, as seen in Japanese Unexamined Patent Publication No. 54-56880. This device applies a force generated in a pressure receiving diaphragm to a vibration wire coupled to the diaphragm, and obtains a change in the natural frequency related to the tension of the vibration wire as a frequency signal output.

In this device, it is necessary to connect the two so that the force generated in the diaphragm can be accurately transmitted to the vibration line, and the configuration must be such that changes in the environment around the vibration line do not cause changes in the natural frequency of the vibration line. The configuration is complicated, as it requires some ingenuity.

[Object of the present invention]

The present invention has been made in view of these problems in the prior art, and is intended to realize a pressure sensor with a simple configuration that outputs a frequency signal corresponding to pressure.

[Summary of the invention]

The device according to the present invention includes a pressure receiving diaphragm made of an elastic semiconductor, a vibrating beam fixed at both ends formed on the pressure receiving diaphragm, and vibration beam excitation means and vibration detection means provided on the pressure receiving diaphragm. It is characterized by the fact that it is

〔Example〕

FIG. 1 is a grooved perspective view of a pressure sensor according to the present invention, FIG. 2 is a sectional view taken along line XX in FIG. 1, and FIG. 3 is a partially omitted plan view.

In these figures, reference numeral 1 denotes a substrate made of an elastic semiconductor, such as a silicon substrate.

Reference numeral 2 denotes a pressure-receiving diaphragm constructed using a part of this semiconductor substrate 1, for example, by etching the semiconductor substrate 1.

5 and 4 are minute vibrating beams fixed at both ends formed on the pressure receiving diaphragm 2-F, with the vibrating beam 3 being located approximately at the center of the pressure receiving diaphragm 2, and the vibrating beam 4 being located at the periphery of the pressure receiving diaphragm 2, respectively. There is. These vibrating beams 5 and 4 are formed, for example, by undulating or undercutting the peripheral portions of the portions corresponding to the vibrating beams on the semiconductor substrate 1, for example.

FIG. 4 is an enlarged sectional view showing the vicinity of the vibrating beam surrounded by the broken line in FIG. 2. FIG. Here, an example is shown in which an n-type silicon substrate is used as the diaphragm 2. In this diagram,
21a and 21b are P layers, and 21a and 21b are electrically separated by a notch 20. 22 has n-type epitaxial layers, 23 has 2 layers, and 24 has 810 layers. A cavity 25 is formed in a part of the epitaxial layer 22, for example by under-etching, and the vibration beam 5 (4)
is the p ftl and 81 fixed at both ends spanning the cavity 25.
0° layer.

Here, an example of the size of the vibrating beam 6 is as follows.

Thickness h = 114m.

Length], = 1100p.

Width (1=5pm In FIG. 4, the first layer 23 constituting the vibrating beam 3 (4) and the p-layers 21a and 21b facing each other via the cavity 25
constitutes electrostatic [tfj, and here, the vibrating piece 5
(4) is excited using the electrostatic force acting between the second layer 21 and the first layer 23, and the vibration beam 3 (four ) is designed to detect vibrations.

O20 is an oscillation circuit, and this circuit is configured using an external device or a semiconductor substrate 1 (7), and has an input terminal p1!
21b is connected, and a signal related to the vibration of the vibrating beam 3 (4) is applied. The output end is still connected to the second layer 21a, and provides an output signal between the second layer 21 and P1ψ23. Accordingly, the oscillation circuit O8C and the vibrating beam 3 (4) constitute a self-excited excavation circuit that oscillates with the natural vibration meter of the vibrating beam.

In the pressure sensor configured in this way, if pressure is applied to the pressure receiving diaphragm 2 from the inside as shown by arrow P in FIG.
is deflected, and a tensile force is applied to the vibrating beam 5 formed in the center.
A compressive force is applied to each of the vibrating beams 4 formed at the peripheral edge of the diaphragm 2. As a result, the natural frequency f1 of each vibrating beam 5, 4. f2 changes differentially with respect to pressure P, and for example, pressure P can be measured by calculating the difference between f and -f7.

In the above explanation, two vibrating beams are formed on the pressure-receiving diaphragm 2, but pressure measurement cannot be performed even with one vibrating beam because its natural frequency corresponds to pressure. , this invention also includes cases such as this.

According to the device configured in this way, since the vibrating beam fixed at both ends is formed on the pressure receiving diaphragm, there is no need for any special configuration for coupling between the diaphragm and the vibrating beam, and the overall configuration is simple. Become.

'It is still possible to create a pressure sensor with extremely high detection sensitivity.

Incidentally, the strain sensitivity S-Δf/fo of the vibrating beam 3 (4) is expressed as follows. The dimensions of the vibrating beam are h = i pm, l =
If it is 10011 m, then S = O, 118xlO'·6.

Here, if a = 1100pp, Δf /fo=
0.1.2 (12X). Furthermore, when calculating f knee f2 using two vibrating beams, the sensitivity is doubled.

FIG. 5 is a sectional view showing another example of the pressure cell according to the present invention. In this example, the periphery of the vibrating beam 3 formed on the pressure receiving diaphragm 2 is covered with a cover 5 made of silicon, for example, on the pressure receiving diaphragm 2, and the inside 25 (around the vibrating beam 5) is kept in a vacuum state. It was designed to be retained. In order to maintain the inside of the cover 5 in a vacuum state, for example, 1J is applied to the pressure receiving diaphragm 2.
Attached by Th bonding method.

According to this embodiment, the vibrating beam is placed in a vacuum, so that the Q of the vibrating beam can be increased. Further, the vacuum chamber inside the cover 5 is minute, and a structure can be obtained that can withstand static pressure as high as, for example, several hundred kg/am2.

In addition, in each embodiment of the queen, the pressure receiving teraphram 2
The shape of the vibration beam 5 may be other than circular, and the vibration beam 5 may have a shape other than a circle.
For the excitation means and vibration detection means (4), other means than electrostatic force, static force, or capacitance may be used.

[Effects of the present invention]

As described above, according to the present invention, a pressure sensor with a simple configuration that outputs a frequency signal corresponding to pressure can be realized.

[Brief explanation of drawings]

FIG. 1 is a perspective view of the configuration of a pressure sensor according to the present invention, FIG. 2 is a sectional view taken along line X-X in FIG. 1, FIG. 3 is a partially omitted plan view, and FIG. 4 is a vibration diagram in FIG. FIG. 5 is an enlarged cross-sectional view showing the vicinity of the beam, and FIG. 5 is a structural cross-sectional view showing another example of the pressure sensor according to the present invention. 1... Semiconductor substrate, 2... Pressure receiving diaphragm, 3,
4... Vibration beam, 21a, 21b, 23... P layer, O20... Oscillation circuit. Chest 1

Claims (3)

[Claims] (1) A pressure sensor comprising a pressure receiving diaphragm made of an elastic semiconductor material, a vibrating beam fixed at both ends formed on the pressure receiving diaphragm, and means for exciting the vibrating beam and vibration detecting means provided on the pressure diaphragm. . (2) The pressure sensor according to claim 1, wherein the pressure receiving diaphragm has a cover that covers the vibrating beam over the pressure receiving diaphragm, and the area around the vibrating beam is maintained in a vacuum state. (3) The pressure sensor according to claim 1, wherein a vibrating beam fixed at both ends is formed on the pressure receiving diaphragm by the Andani and Tengu technique.