JP2553613B2 - Pressure sensitive element - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure-sensitive element that converts a mechanical quantity such as load, pressure, or strain into an electric quantity. More specifically, it relates to an epoch-making high-sensitivity pressure sensitive element using a tetrapod-shaped zinc oxide whisker.

The application range of the present invention is wide, and various pressure gauges, weight scales, accelerometers, barometers, sphygmomanometers, accelerometers, excellent switches that require almost no changes and have no electrical contacts, digitizers,
It can also be applied as a pressure sensitive device such as a microphone or pickup.

2. Description of the Related Art Conventionally, there have been the following pressure sensitive elements.

First, a metal resistance strain gauge using a metal resistance wire as a sensing element. Next, in the parallel plate electrode system, there is a parallel plate-capacitance type that evaluates the magnitude of pressure by the change in electrostatic capacity by utilizing the fact that the distance between electrodes becomes smaller when pressure (load) is applied. there were.

In addition, there are semiconductor piezoresistive strain gauges, pressure-sensitive diodes (pn junction diodes, Zener diodes, Esaki diodes, metal-semiconductor barrier diodes), pressure-sensitive transistors, etc. that utilize various characteristics of semiconductors.

The metal resistance strain gauge, the parallel plate-capacitance type, and the semiconductor piezo resistance strain gauge described above require a relatively large amplifier because of their particularly low sensitivity, while the elements using the remaining semiconductors are However, since it is necessary to manufacture it by making full use of advanced semiconductor technology, the manufacturing yield is low and the cost is high, and there are also problems in impact resistance and reliability in terms of characteristics. Further, in the conventional technique, the sensitivity and the pressure-sensitive range can be adjusted with a single voltage (bias) with high sensitivity, and it is easy to take an arbitrary pressure-sensitive portion shape in two dimensions or three dimensions. There was no inexpensive pressure sensitive element that was rich in properties.

Means for Solving the Problems According to the present invention, a zinc oxide whisker composed of a core portion and needle-shaped crystal portions extending in different four-axis directions from the core portion is assembled to form a pressure-sensitive element as a sensitive portion.

Here, the diameter of the base portion of the needle-shaped crystal portion is 0.7 to 14 μm, and the length from the base portion to the tip of the needle-shaped crystal portion is 3 to 20.
When it is 0 μm, a particularly remarkable effect is obtained.

Action The pressure-sensitive element of the present invention uses a tetrapod-shaped zinc oxide whisker aggregate as a sensing part, and the effect of the contact interface between zinc oxide whiskers (whisker-shaped crystals) and the piezoelectric effect of zinc oxide crystals are combined to enhance the effect. It is considered that a sensitive pressure-sensitive element has been obtained. In addition, the aggregate of tetrapod-like whiskers creates an extremely sparse aggregate state and is isotropically equivalent, so that a needle-like crystal that directly exerts a strong stress against pressure from any direction. Exists, and therefore high sensitivity is obtained.

In addition, since the tetrapod-shaped zinc oxide whiskers are inherently highly elastic, the aggregate has extremely high impact resistance, which completely overcomes the drawbacks of conventional pressure-sensitive elements using semiconductors, and has a high reliability. A high pressure sensitive element has been provided.

In addition, the manufacturing of tetrapod-shaped zinc oxide whiskers
For example, because it can be easily obtained by simply heating a metal zinc powder having an oxide film on the surface in an atmosphere containing oxygen,
It is possible to provide an inexpensive pressure-sensitive element with high manufacturing yield.

EXAMPLES Hereinafter, specific examples will be described using examples.

Example 1 Zinc metal powder was crushed with a mortar type crusher in the coexistence of water, allowed to stand in water for 3 days, then dried and placed in an alumina porcelain crucible, and placed in a furnace at 1000 ° C. And heat treated for 1 hour to obtain zinc oxide whiskers. The typical electron micrograph is shown in the figure.

The diameter of the base of the needle-shaped crystal part of this whisker is 8 μm on average.
The average length from the base to the tip was 100 μm.
Most of them showed a tetrapod shape in which needle-like crystals extended in different four-axis directions, but in some cases, tetrapod-shaped whiskers were thought to have broken, extending in the uniaxial, biaxial, and triaxial directions. Whiskers were mixed.

A small amount of this whisker was sandwiched between parallel plate electrodes and pressed at a pressing pressure (to the effective electrode portion) of 8 kg to form a sensitive element having a thickness of about 200 μm. At this time, the effective electrode diameter is 2
It was 8 mmφ. The electrode material is hard chrome plated iron.

The pressure-current characteristics were evaluated while applying a DC bias voltage between the electrodes while sandwiching the sensitive element between parallel plate electrodes. The results are shown in FIG. In addition, the digital multimeter (National VP-26
When measured at 60 A), the resistance value changed by 3 digits or more at 0 to 10 kg.

Example 2 When a test similar to that of Example 1 was carried out with a planar electrode configuration, high sensitivity results were obtained.

Example 3 The same tetrapod-shaped zinc oxide whiskers as in Example 1 were sintered by a general varistor sintering method, and a silver paste was baked to form a sandwich-shaped electrode.
When the current characteristics were evaluated, it was found to be a highly sensitive pressure sensitive element.

Example 4 The same evaluation as in Example 1 was carried out using a fine tetrapod-like whisker having an average diameter of the base portion of less than 0.7 μm and a length from the base portion to the tip of less than 3 μm. The sensitivity suddenly dropped, but the pressure sensitivity was clear.

Comparative Example The same evaluation as in Example 1 was carried out using zinc oxide powder (granular, average particle size: about 1 μm) of a general reagent (manufactured by Kanto Chemical Co., Inc.), but no pressure sensitivity was observed. Results are shown in FIG.

In the above embodiments, the tetrapod-like whiskers are shown to have relatively uniform dimensions, but it is natural that they can be intentionally distributed to obtain suitable pressure-sensitive elements.

Other electrode materials include aluminum, zinc, gold,
Silver, copper, iron, nickel, chloro, cobalt, lithium,
Beryllium, sodium, magnesium, titanium, vanadium, manganese, gallium, tin, antimony, indium, cadmium, palladium, rhodium, ruthenium, technetium, molybdenum, niobium, zirconium, yttrium, strontium, rubidium, scandium, potassium, calcium, astatine, Polonium, bismuth, lead, thallium, mercury, platinum, iridium, osmium, rhenium, tungsten, tantalum,
Hafnium, barium, cesium, francium, radium, lanthanum, and lanthanum-based elements, actinium, and actinium-based elements may be used alone or in a plurality of alloys or mixtures.

For sintering, Bi ₂ O ₃ , CoO, MnO, TiO ₂ , Sb ₂ O ₃ , Cr ₂ O ₃ , Fe ₂ O ₃ and P, which are commonly used for varistors and porcelain capacitors, are used.
bO, ZrO ₂ , SiO ₂ , Dy ₂ O ₃ , Y ₂ O ₃ , Sn ₂ O ₃ , SrO, Al ₂ O ₃ , MnO ₂ , Cu ₂ O,
One or more kinds of Ti ₂ O ₃ , Co ₃ O ₄ , La ₂ O ₃ , Pr ₆ O ₁₁ , BaO, the above-mentioned electrode materials alone or oxides thereof can be added in appropriate amounts.

In addition, in the case of sintering or not, it is possible to stabilize the characteristics by adding an appropriate amount of an inorganic substance or an organic substance. In particular, by doping various materials into the whiskers, the resistance value can be significantly changed, which is useful for appropriate design settings.

The electrode system may be any of sandwich type, planar type, comb type, laminated type and the like.

The electrode area is 28 mmφ in the embodiment, but it can be applied from a small area to an infinitely large area due to its structure, and a pressure-sensitive element having an arbitrary shape as well as an arbitrary three-dimensional unevenness can be used. Easily obtained.

Further, whiskers having a length from the base to the tip of the tetrapod-like needle crystal in the range of 3 to 200 μm exhibit highly sensitive and stable pressure-sensitive characteristics, but the range of length is not limited to this. Absent.

In particular, a tetrapod-like whisker having a length from the base to the tip of 50 to 150 μm is most preferable from the viewpoints of characteristics, breakage of the whisker, easy handling, and cost.

On the other hand, the diameter of the base of the tetrapod-shaped needle-shaped crystal part is 0.7 to 1
Whiskers in the range of 4 μm exhibit pressure-sensitive characteristics with high sensitivity and high stability, but the range of diameter size is not limited to this. In particular, the tetrapod-like whiskers with a diameter of 2 to 10 μm at the base are characterized by
It is most preferable in terms of ease of handling and cost.

The thickness of the sensitive portion is designed in consideration of sensitivity and pressure sensitive range. Also, the thickness of the sensitive part depends on the molding press pressure,
This is set in consideration of the size of the tetrapod-shaped whiskers and the like within a range in which the tetrapod-shaped whiskers are not completely broken.

Further, it is one of the notable points of the pressure-sensitive element of the present invention that the sensitivity and the pressure-sensitive range of the pressure-sensitive element can be easily changed largely only by the magnitude of the bias voltage.

EFFECTS OF THE INVENTION The present invention has high sensitivity and a single voltage (bias),
In addition to providing a pressure-sensitive element that can easily adjust the sensitivity and pressure-sensitive range, it is easy to take an arbitrary pressure-sensitive portion shape in two dimensions and three-dimensionally, and it is mass-produced and inexpensive. , There are some very industrial.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the structure of tetrapod-shaped zinc oxide whisker crystals, FIG. 2 is a pressure-current characteristic diagram of the whisker aggregate, and FIG. 3 is a pressure-current characteristic diagram of zinc oxide powder. .

Front Page Continuation (72) Inventor Moto Kitano 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor ▲ Hideyuki Yoshida, 1006 Kadoma, Kadoma City, Osaka In-house (56) Reference JP 50-6597 (JP, A) JP 1-252599 (JP, A) JP 1-252600 (JP, A)

Claims (2)

(57) [Claims] 1. A pressure-sensitive element comprising a core and a zinc oxide whisker consisting of a needle-shaped crystal part extending in different four-axis directions from the core to form a sensitive part. 2. The pressure-sensitive element according to claim 1, wherein the needle-shaped crystal part of the zinc oxide whisker has a diameter of 0.7 to 14 μm, and the length of the needle-shaped crystal from the base to the tip is 3 to 200 μm. .