JPH01225382A - Pressure sensitive element - Google Patents

Abstract

PURPOSE:To obtain a highly sensitive pressure-sensitive-element which easily adjusts sensitivity and a pressure sensitive range by one bias voltage, by causing core parts as well as tetrapodlike zinc oxide whisker aggregates consisting of needlelike crystal parts which extend in different axis directions from the core parts to act as sensitive parts. CONSTITUTION:After crushing a metallic zinc powder with water, its powder is left in water for three days and oxide zinc whiskers are obtained by heating the above powder at a temperature 1000 deg.C. The base part diameters of needlelike crystal parts are 8mum on an average and the lengths up to tip are 100mum on the average. Most of whiskers indicate that each needlelike crystal extending in different four-directions shows a tetrapodlike shape. They are molded by a press pressure 8kg and a sensitive element having the thickness about 200mum are put in between parallel flat electrodes. While applying a bias d.c. voltage, voltage-current characteristics are evaluated. Thus, sensitivity and a pressure sensitive range can be varied exceedingly only according to the capacity of bias voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a pressure sensitive element that converts mechanical quantities such as load, pressure, strain, etc. into electrical quantities. More specifically, the present invention relates to a highly sensitive and innovative pressure-sensitive element using tetrabod-like zinc oxide whiskers.

The present invention has a wide range of applications, including various pressure gauges, weight gauges, accelerometers, barometers, blood pressure needles, accelerometers, and is an excellent switch that does not require any changes and has no electrical contacts.

It can be applied to digitizers, microphones, pickups, and other pressure-sensitive devices.

Conventional technology Conventionally, there have been the following types of pressure sensitive elements.

First, it is a metal resistance strain gauge that uses a metal resistance wire as a sensing element. Next is the parallel plate electrode system, which uses the fact that the distance between the electrodes becomes smaller when pressure (load) is applied to evaluate the magnitude of pressure by changes in capacitance. there were.

In addition, semiconductor piezoresistive strain gauges, pressure-sensitive diodes (p-n junction diodes,
These included Zener diodes, Esaki diodes, metal-semiconductor barrier diodes), and pressure-sensitive transistors.

Problems that the invention aims to solve The above-mentioned metal resistance strain gauge is a parallel plate capacitive type.

Semiconductor piezoresistive strain gauges require relatively large amplifiers due to their particularly low sensitivity.On the other hand, devices using other semiconductors are naturally difficult to manufacture because they need to be created using advanced semiconductor technology. It had a low yield, was expensive, and had problems with impact resistance and reliability. Also,
Conventional technology has high sensitivity, the sensitivity and pressure sensitive range can be adjusted with a single voltage (bias), it is easy to take any shape of the pressure sensitive part in two dimensions and S dimensions, and it is also easy to mass produce. There were no plentiful and inexpensive pressure-sensitive elements.

Means for Solving the Problems In the present invention, a pressure-sensitive element is constructed by assembling zinc oxide whiskers consisting of a core and needle-like crystal parts different from the core and extending in the axial direction as a sensing part.

Here, the diameter of the base of the needle crystal part is 0.7 to 17 μm, and the length from the base to the tip of the needle crystal is 3 to 20 μm.
Particularly remarkable effects can be obtained when the thickness is 0 μm.

Function The pressure-sensitive element of the present invention uses an aggregate of tetrabod-like zinc oxide whiskers as the sensing part, and the effect of the contact interface between the zinc oxide whiskers (whiskers-like crystals) and the piezoelectric effect of the zinc oxide crystals combine. It is considered that a pressure-sensitive element with high sensitivity has been obtained. In addition, an aggregate of tetrabod-like whiskers forms an extremely sparse aggregated state and is isotropic under equal constraints, so that the needle-like crystals that directly exert strong stress will react to pressure from any direction. Therefore, high sensitivity can be obtained.

In addition, since tetrabod-shaped zinc oxide whiskers are inherently highly elastic, their aggregates have extremely high impact resistance, completely overcoming the drawbacks of conventional pressure-sensitive elements using semiconductors, and improving reliability. A high pressure sensitive element has now been provided.

In addition, tetrabod-shaped zinc oxide whiskers can be easily produced by, for example, heating metallic zinc powder with an oxide film on the surface in an oxygen-containing atmosphere, resulting in a high production yield and an inexpensive pressure-sensitive element. can be provided.

Example This will be specifically explained below using examples.

Example 1 Metallic zinc powder was soaked in a mortar-type crusher in the presence of water, then left in water for 3 days, then dried, placed in an alumina porcelain crucible, and placed in a furnace at 1000°C. After heat treatment for 1 hour, zinc oxide whiskers were obtained. A typical electron micrograph is shown in the figure.

The diameter of the base of the needle-like crystal part of this whisker was 8 μm on average, and the length from the base to the tip was 10 μm on average.

Most of the specimens showed a tetrabod shape with needle-like crystals extending in four different axes, but some of them were thought to be broken tetrabod-like whiskers, with whiskers extending in one, two, and three axes. was mixed in.

A small amount of this whisker was sandwiched between parallel plate electrodes and pressed and molded at a pressing pressure (relative to the effective electrode portion) of 8 KP to obtain a sensing element with a thickness of approximately 200 μm.

At this time, the effective electrode diameter was 28flφ. The electrode material is hard chromed iron.

With this sensing element sandwiched between parallel plate electrodes, the pressure-current characteristics were evaluated while applying a DC bias voltage between the electrodes. The results are shown in FIG. Furthermore, the change in resistance value of the same sample was measured using a digital multimeter (Nashituna/L/vP).
-266OA), the resistance value changed by more than three orders of magnitude at 0710Kp.

Example 2 When a test similar to Example 1 was conducted using a planar type 5 electrode configuration, highly sensitive results were obtained.

Example 3 The same tetrabod-shaped zinc oxide whiskers as in Example 1 were sintered using a general varistor sintering method, silver paste was baked on to form a sandwich-shaped electrode, and the pressure-current characteristics were evaluated. It turned out to be a highly sensitive pressure-sensitive element.

Example 4 The same evaluation as in Example 1 was conducted using fine tetrabod-like 4 scars with an average diameter of the base as small as 0.7 μm and a length from the base to the tip as small as 3 μm. Due to this size, the sensitivity suddenly deteriorated, but the pressure sensitivity was excellent.

Comparative Example The same evaluation as in Example 1 was carried out using zinc oxide powder (granular, average particle diameter of about 1 μm) of General Reagent (manufactured by Kanto Kagaku Co., Ltd.), but no pressure sensitivity was observed. The results are shown in Figure 3.

In the above embodiments, the dimensions of the tetrabod-like whiskers are relatively uniform, but it goes without saying that an appropriate pressure-sensitive element can be obtained by intentionally distributing the whiskers.

Other electrode materials include aluminum and zinc.

Gold, silver, copper, iron, nickel IV, chromium, cobalt.

Lithium, beryllium, sodium, magnesium, titanium, vanadium, manganese, gallium.

Tin, antimony, indium 1. Cadmium, palladium, rhodium, /I/thenium, technetium.

Molybdenum, niobium, zirconium, yttrium, strontium, /L/vidium, scandium.

Potassium, calcium, astatine, boronium.

Bismuth, lead, thallium, mercury, platinum, iridium, osmium, rhenium, tungsten, tantalum, hafnium, barium, cesium, francium, radium,
Lanthanum, a lanthanum-based element, actinium, an actinium-based element, and the like can be used alone, or an alloy or a mixture of a plurality of them can be used.

In addition, for sintering, metals commonly used for varistors and ceramic capacitors, B i 203, Co O+ M n
O, T i O2tSb203. Cr2O3, Fe2
O3,,PbO,ZrO2,s,to2°D7203.
Y2O3,5n203. SrO, A6203. MnO□
.

Cu2O, Tl2O3, Co3O4, La2O3, Pr
6o1. .

BaO, a single substance of the electrode material, or its oxide can be added in an appropriate amount in one or more types.

In addition, even when sintering or not, it is possible to stabilize the properties by adding an appropriate amount of inorganic or organic matter. In particular, by doping various materials into the whisker, the resistance value can be greatly changed.
Useful for proper design settings.

The electrode system may be of any type, such as sandwich type, planar type, comb type, and laminated type.

The electrode area was also shown as an example of 2B111φ in the example, but
Due to its structure, it can be applied to any area ranging from a small area to a large area without limitation, and a pressure sensitive element having an arbitrary shape as well as an arbitrary three-dimensional unevenness can be easily obtained.

Furthermore, whiskers with a length ranging from 3 to 200 μm from the base to the tip of the tetofpod-like needle crystals exhibit high sensitivity and highly stable pressure-sensitive characteristics, but the length range is not limited to this. .

In particular, the length from the base to the tip is 60 to 150 μm.
Tetrabod-like whiskers are most preferable from the viewpoint of characteristics, whisker resistance to breakage, ease of handling, and cost.

On the other hand, the diameter of the base of the tetrabod-like needle crystal part is 0.7~
Whiskers in the range of 14 μm exhibit high sensitivity and stable pressure-sensitive characteristics, but the diameter size range is not limited to this. Especially at the base.

Tetrabod-shaped whiskers with a diameter of 2 to 10 μm are characterized by their characteristics, whisker resistance to breakage, ease of handling,
This is the most preferable in terms of cost and the like.

The thickness of the sensitive part is designed taking into consideration the sensitivity and pressure sensitive range. Further, the thickness of the sensing portion depends on the molding press pressure, but this is set within a range that does not completely break the tetrabod-like whiskers, taking into consideration the size of the tetrabod-like whiskers.

Furthermore, one of the noteworthy features of the pressure-sensitive element of the present invention is that the sensitivity and pressure-sensitive range of the pressure-sensitive element can be easily and largely changed only by the magnitude of the bias voltage.

Effects of the Invention The present invention provides a pressure-sensitive element that is highly sensitive and can easily adjust the sensitivity and pressure-sensitive range with a single voltage (bias), and also provides an arbitrary pressure-sensitive element in two or three dimensions. It is easy to take a shape, can be mass-produced, and is inexpensive, making it extremely industrially viable.

[Brief explanation of the drawing]

FIG. 1 is an electron micrograph of tetrabod-like zinc oxide whiskers, FIG. 2 is a pressure-current characteristic diagram of the same whisker aggregate, and FIG. 3 is a pressure-current characteristic diagram of zinc oxide powder. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 1: Figure 2: Total pressure (Niu) Figure 3: Total pressure (Niu) Procedural amendment (method) June 1985 To the Commissioner of the Japan Patent Office Indication of case No. 1 Patent application No. 1988 51893 No. 2 Name of the invention Pressure-sensitive element 3 Relationship to the amended case Patent application Address 1006 Oaza Kadoma, Kadoma City, Osaka Name
(582) Matsushita Electric Industrial Co., Ltd. Representative
Akio Tanii 4 Agent 571 Address 7, Matsushita Electric Industrial Co., Ltd., 1006 Kadoma, Kadoma City, Osaka Prefecture. Insert j to indicate structure.

Claims (2)

[Claims] (1) A pressure-sensitive element in which zinc oxide whiskers consisting of a core and needle-shaped crystal parts extending from the core in different axial directions are assembled to form a sensing part. (2) The diameter of the base of the needle-like crystal part of the zinc oxide whisker is 0
．． 2. The pressure-sensitive element according to claim 1, wherein the needle crystal has a length of 7 to 14 μm and a length from the base to the tip of the needle crystal is 3 to 200 μm.