JP3158825B2 - Acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor utilizing the electron emission phenomenon of a cold cathode.

[0002]

2. Description of the Related Art FIG. 4 is a structural sectional view showing a semiconductor acceleration sensor formed by a micromachining technique. This semiconductor acceleration sensor has a semiconductor chip 2 fixed in a ceramic package 1, which is immersed in silicon oil 1a. Semiconductor chip 2
Is a base 3 and a sensor chip 4 connected to one end thereof.
And a stopper 5 connected to the other end of the base 3. A weight film 4b such as a gold film is attached on the tip thick portion 4a of the sensor chip 4, and a plurality of independent semiconductor gauge layers (Wheatstone bridge circuits) are formed on the main surface of the sensor chip 4. Have been. Reference numeral 6 denotes a bonding wire. In such a semiconductor acceleration sensor,
When acceleration is applied, the tip thick portion 4a moves due to inertial force, so that the semiconductor gauge layer on the main surface of the sensor chip 4 is distorted, and a detection voltage corresponding to the amount of distortion (change in resistance) is output. Thereby, the magnitude of the acceleration and the direction of the acceleration (acceleration vector) can be measured.

[0003]

However, the above-described semiconductor acceleration sensor has the following problems. That is, in general, a semiconductor acceleration sensor has a high temperature (150 °).
C or more), and the temperature characteristics of the semiconductor greatly change even in a temperature range below the temperature range. Therefore, it is necessary to provide a temperature compensation circuit and the like. There was a problem that it was inferior in environmental resistance, especially in temperature resistance.

[0004] In view of the above problems, a first object of the present invention is to provide an acceleration sensor having excellent temperature resistance, and a second object is to provide an acceleration sensor having good miniaturization and good mass productivity. To provide.

[0005]

In order to solve the above-mentioned problems, it is necessary to find a material having a high temperature resistance and a small temperature change, or to use an acceleration detecting method which does not use the physical properties of a solid. In the present invention, the latter method is adopted.
That is, the present invention provides a vacuum tube having a field-effect type electron emitting portion capable of controlling emission of electrons from a cold cathode by an electric field of a control electrode, and a collector electrode for capturing the emitted electrons via a vacuum space path. The field effect type electron emitting portion is an inter-electrode distance variable mechanism in which a distance between an electron emitting portion of the cold cathode and the control electrode can be monotonously changed by applying an acceleration , and the cold cathode is cantilevered. It is characterized by a beam structure .

The vacuum tube itself can be a micro vacuum tube formed by finely processing silicon.

[0007]

In the acceleration sensor using such a vacuum tube, since the cathode is not a hot cathode but a cold cathode, electron emission characteristics having almost no temperature dependency can be obtained. Since the distance between the cold cathode and the control electrode changes depending on the acceleration, if the voltage between the cold cathode and the control electrode is constant, the electric field intensity at the cold cathode interface (electron emission site) changes depending on the magnitude and direction of the acceleration. The value of the electron flow (anode current) extracted by the effect changes. Therefore, the acceleration vector can be detected by measuring the anode current. As described above, the acceleration detection principle of the present invention is based on the field emission phenomenon (electron emission due to the Schottky effect (tunnel effect)) and the change in the anode current due to the change in the cold cathode-anode distance due to the inertial force (acceleration). Are organically combined, so that an acceleration sensor having excellent temperature resistance characteristics can be realized.

[0008] In particular, a cold cathode is used as the inter-electrode distance variable mechanism.
Because There is a cantilever structure, since the amount of deflection come into play in the fourth power of the length of the beam, is greater freedom of acceleration detection range and sensitivity settings.

Further, when the vacuum tube itself is a micro vacuum tube using micromachining technology, not only miniaturization but also mass productivity and cost reduction can be achieved.

[0010]

Next, an embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a front view showing an acceleration sensor according to a first embodiment of the present invention. This acceleration sensor is a small triode vacuum tube. That is, the small triode vacuum tube of the present embodiment has a field effect type electron emitting portion capable of controlling the emission of electrons from the cold cathode (cathode) 11 by the electric field of the control electrode (gate electrode) 10, Collector electrode (anode, anode) 1 captured via vacuum space path 13
And 2. The field-effect-type electron-emitting portion is configured such that the electron-emitting portion 11a of the cold cathode 11 and the control electrode 1
This is an inter-electrode distance variable mechanism in which the distance to 0 can be changed monotonically. The control electrode 10 of this example is a fixed electrode, and the cold cathode 1
Reference numeral 1 denotes a cantilever structure that protrudes right above the control electrode 10.

Since the combined electric field width of the electric field of the electron emission portion 11a of the cold cathode 11 and its work function is narrowed by the electric field of the control electrode 10, electrons are extracted from the cold cathode 11 by the Schottky effect (tunnel effect). The emitted electrons are captured by the collector electrode 12 and an anode current flows. However, when acceleration is applied, the tip side of the cold cathode 11 bends due to its inertial force, and the distance between the electron emission site 11a of the cold cathode 11 and the control electrode 10 is increased. Changes, the electric field applied to the electron emission portion 11a of the cold cathode 11 also changes, so that the anode current value also increases and decreases. Therefore, the magnitude and direction (acceleration vector) of the acceleration can be measured from the change amount.

Here, when acceleration G is applied in the direction of the arrow in FIG. 1, the cold cathode 11 bends downward due to its inertial force. If the length of the beam of the cold cathode 11 is L, the bending rigidity is EI _z , the thickness of the cold cathode is t, the Young's modulus is E, the section modulus of the beam is I _z , and the Poisson's ratio is ν, the deflection of the cold cathode 11 is given. The quantity y _A (y _A > 0 when the acceleration is upward, y _A <
0) is given by the following equation.

Y _A = GL ⁴ / (8EI _z ) = 3G (1−ν ² ) L ⁴ / (2Et ³ ) (1) Here, the electron emission portion 11 a of the cold cathode 11 when the acceleration G = 0. the distance of the control electrode 10 and a y _0. Acceleration G
There the work pleasure, the distance between the electron-emitting portion 11a and the control electrode 10 of the cold cathode 11 becomes (y ₀ -y _A).

On the other hand, the emission current (anode current) from the electron emission portion 11a of the cold cathode 11 is _{IE, which} is Fowler-Nor
It is given by the following formula from dheim's theory.

_IE = (sAF ² / φ) exp [−Bφ ^3/2 / F] (2) A = 1.54 × 10 ⁻⁸ , B = 6.83 × 10 ⁷ (3) where S is emission area (cm ^2), phi is a cold cathode material work function (emitter electrode material) (eV), the electric field strength F at the interface voltage V _G and the following relationship between the control electrode 10 and the cold cathode 11 It is in.

F = βV _G (4) where β is the tip shape of the electron emitting portion 11a and the cold cathode
It is a geometric quantity coefficient depending on the distance between control electrodes. For example, when the electron emitting portion 11a is a hemisphere having a radius of curvature r and the control electrode 10 is a flat plate separated from the tip by a distance d (Reference: The Institute of Television Engineers of Japan Vol.45 No.5).
612 (1991)), β = 2 / [r · ln (2d / r)] = k / ln (kd) (5) where k = 2 / r Therefore, the acceleration is obtained when the voltage of the control electrode 10 is constant. When G works, the emission current will show the following current changes.

[0018] ^{_{I E = (sAV G 2 /}} φ) [k / ln (kd)] ² × exp ^{[-Bφ 3/2 ln (kd) / kV} G ] ~K [ln (y ₀ -y _A)] ⁻² · (y ₀ −y _A ) ⁻¹ (6) where K is a constant excluding the dependent part of the distance d.

[0019] (6) As is apparent from the equation, the change in emission current I _E is seen to be sensitive to changes in deflection amount y _A. The bending amount y _A is a function of the electrode material (E, ν) and the shape (L, t) from the equation (1), and increases or decreases linearly with the acceleration G. In particular, since the amount of deflection y _A is effective in the fourth power of the length L of the beam, the sensing range (range) and sensitivity of the acceleration G can be selected arbitrarily to enable sensing over a wide range. is there.

According to the acceleration sensor using such a small vacuum tube, the electron emission mechanism is hardly affected by a temperature change, and a constant anode current value can be obtained even when the temperature changes.

[Second Embodiment] FIG. 2A shows a second embodiment of the present invention.
FIG. 2 is a longitudinal sectional view showing the acceleration sensor according to the embodiment, and FIG.
(B) is a plan view of the acceleration sensor. This acceleration sensor is a micro vacuum tube formed by micromachining technology (Kanemaru, Ito; Semiconductor World, March 1992)
21) (see Technical Report p62). Micro vacuum tube 21
A niobium control electrode 28 formed on the silicon substrate 22, a tungsten cold cathode 23 formed on one end of the silicon substrate 22 via the silicon oxide film 23 a, A tungsten collector electrode 24 formed on the end via the silicon oxide film 24a and facing the cold cathode 23 via the electrode facing space C of the internal vacuum space 25, and sealing for sealing the internal vacuum space 25 Material 26
Consisting of Reference numeral 27 denotes a bonding wire.

The micro vacuum tube 21 has a thickness of 600 μm, a width of 1 mm,
The length of the cold cathode 23 is as small as 1 mm, and the cold cathode 23 is made of a tungsten thin film (0.2 μm in thickness), and its tip is formed in a comb-like shape as shown in FIG. 20 comb teeth
0, the value corresponding to the beam length L in the above equation (1) is 5 μm
It is. In this example, the design is such that the amount of deflection y _A is 0.023 μm per G. The collector electrode 24 is a rectangle of a tungsten thin film (0.2 μm thick), and the tip is a uniform surface. The tip of the cold cathode 23 projects from the side surface of the silicon oxide film 23a in an eaves-like manner.
4 also protrudes like an eaves from the side surface of the silicon oxide film 24a.

FIG. 3 shows a change in anode current by applying an acceleration in the direction of the arrow shown in the drawing while applying 100 V between the cold cathode and the control electrode of the micro vacuum tube 21 and setting the anode voltage to +300 V. FIG. 3 shows a change characteristic of the anode current when the micro vacuum tube 21 is gradually accelerated to a certain acceleration (maximum acceleration), and then gradually decelerated and stopped. Is the maximum acceleration 10G, is the maximum acceleration 20G,
Is the maximum acceleration of 30G. As shown in FIG. 3, when the acceleration is gradually increased, the anode current (solid line) increases upward and monotonically increases. This is because, when the acceleration becomes extremely large, the rate of change of the amount of deflection does not increase so much, so that the curve becomes an upwardly convex monotonically increasing curve. When the current gradually decreases from the maximum acceleration, the anode current monotonously decreases as shown by the broken line in the figure.

As described above, the micro vacuum tube formed by the micromachining technique does not use a semiconductor gauge or the like, and has a field emission mechanism of an electron which is hardly affected by a temperature change, and a cantilever structure of a cold cathode by acceleration. The magnitude and direction of the acceleration can be detected by measuring the change in the anode current based on the change in the electric field intensity due to the change in the amount of deflection of the acceleration.
Since the electron emission mechanism is hardly affected by a change in temperature, a sensor having excellent temperature resistance can be realized. In addition, since the electron emission mechanism can be manufactured by the micromachining technology, miniaturization and cost reduction of the acceleration sensor can be achieved. Furthermore, since a plurality of electron-emitting portions and anode portions can be simultaneously formed on the same substrate,
It is significant to use a silicon substrate or the like to form a micro vacuum tube.

In addition, according to the acceleration sensor in which two micro vacuum tubes 21 of this embodiment are used and they are orthogonally arranged, the magnitude and direction of the three-dimensional acceleration can be detected. The cold cathode is common, and a plurality of anodes (collector electrodes) are independently
The structure may be arranged in a three-dimensional or three-dimensional manner, or a plurality of cold cathodes and control electrodes may be formed on the same substrate.

[0026]

As described above, the present invention relates to the field emission phenomenon (electron emission due to the Schottky effect (tunnel effect)) and the anodic current caused by the change in the distance between the cold cathode and the anode due to the inertial force (acceleration). The following effects can be obtained since the change is organically combined.

Since the cathode is not a hot cathode but a cold cathode, electron emission characteristics having almost no temperature dependence can be obtained. Therefore, an acceleration sensor having excellent temperature resistance characteristics can be realized.

As the inter-electrode distance variable mechanism, since the cold cathode has a cantilever structure , the amount of deflection is effective by the fourth power of the length of the beam, so that the acceleration detection range and sensitivity can be freely set. Great degree.

When the micro-vacuum tube itself is a micro-vacuum tube using the micromachining technology, not only miniaturization but also mass productivity and cost reduction can be achieved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an acceleration sensor according to a first embodiment of the present invention.

FIG. 2A is a longitudinal sectional view showing an acceleration sensor according to a second embodiment of the present invention, and FIG. 2B is a plan view of the acceleration sensor.

FIG. 3 is a characteristic diagram showing a value of an anode current with respect to a change in acceleration in a second embodiment.

FIG. 4 is a structural sectional view showing a conventional semiconductor acceleration sensor formed by a micromachining technique.

[Explanation of symbols]

 10, 28 control electrode 11, 23 cold cathode (cathode) 11a electron emission site 12, 24 collector electrode (anode, anode) 13 vacuum space path 20 ceramic package 21 micro vacuum tube 22 silicon substrate 23a Silicon oxide film 25 Internal vacuum space 26 Sealing material 27 Bonding wire C Electrode facing space.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-6-34652 (JP, A) JP-A-6-288843 (JP, A) JP-A-7-63780 (JP, A) JP-A-6-63780 235733 (JP, A) JP-A-6-11517 (JP, A) JP-A-63-186114 (JP, A) EP 619494 (EP, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01P 15/02 G01P 15/08 G01P 15/12

Claims (2)

(57) [Claims] 1. A vacuum tube having a field effect type electron emitting portion capable of controlling emission of electrons from a cold cathode by an electric field of a control electrode, and a collector electrode for capturing the emitted electrons via a vacuum space path. The field-effect-type electron-emitting portion is an inter-electrode distance variable mechanism in which the distance between the electron-emitting portion of the cold cathode and the control electrode can be monotonously changed by applying acceleration , and the cold cathode is cantilevered. An acceleration sensor having a beam structure . 2. The acceleration sensor according to claim 1, wherein said vacuum tube is a micro vacuum tube formed by finely processing silicon.