JPH09185947A - Electric field type vacuum tube, pressure sensor and acceleration sensor using the same, and manufacture of them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric field type vacuum tube capable of using in severe environment such as high temperature, with no difference between individuals, and in which electron current varies by the outside force, and provide a pressure sensor and an acceleration sensor using this vacuum tube. SOLUTION: An electric field type vacuum tube is formed in such a way that an emitter made of a silicon thin film and having sharped tip, and a collector 13 are formed on a silicon substrate 11 through an oxide film 14, and a cap part comprising a second silicon thin film and an oxide film 18 are placed thereon through an oxide film 16. The silicon substrate 11 is used as a first gate and the second silicon thin film is used as a second gate, and voltage is applied between the emitter 12 and the silicon substrate 11 to emit electrons. When the outside force is applied to the cap part, current flowing to the collector 13 and the second gate varies, and therefore, the vacuum tube can be utilized as a pressure sensor. By using the whole current or the current to the first gate as reference, the individual difference can be erased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a silicon-based microsensor such as a pressure sensor for measuring gas pressure or an acceleration sensor for measuring acceleration applied to a moving object such as an automobile accelerometer. The present invention relates to a semiconductor-type small sensor that makes full use of machining technology.

[0002]

2. Description of the Related Art FIG. 15 (a) uses a silicon semiconductor,
It is sectional drawing of the semiconductor type pressure sensor which made full use of the micromachining technique. The silicon sensor chip 51 provided with the recess 52 is mounted on the base 53 so that the recess 52 is kept in a vacuum. A sensor portion 54 of a diffusion resistance layer formed by introducing impurities is formed on the back side of the recess 52 of the sensor chip 51 in the figure, and the sensor portion 54 is formed by the pressure difference between the gas pressure in the cap 58 and the vacuum of the recess 52. When a force is applied to the diffusion resistance layer, the diffusion resistance layer is distorted and the resistance changes. An electrode 55 provided on the surface of the sensor chip 51 and a lead 56 penetrating the base 53 are connected by a bonding wire 57, and the cap 5 is prevented from changing resistance between the leads 56.
The pressure inside 8 can be sensed.

FIG. 15B is a sectional view of an acceleration sensor also using a silicon semiconductor. Vertical stopper 60
A cantilever type sensor chip 61 in which the above is joined is attached to a ceramic case 63. The sensor chip 6
A diffusion resistance layer is formed in the first sensor unit 64 by introducing impurities into silicon, and when the weight 69 at the tip of the sensor unit 64 is accelerated and the sensor unit 64 is deformed, the resistance of the diffusion resistance layer changes. Although only one is shown in the figure, the acceleration change can be sensed by measuring the resistance change between the two electrodes 65 sandwiching the sensor section 64 through the bonding wire 67 and the lead 66. The ceramic case 63 may be filled with silicone oil for damping.

[0004]

Generally, semiconductor sensors have the following drawbacks. Sensors that utilize semiconductor properties are difficult to use at high temperatures. In particular, most commonly used silicon cannot be used above 150 ° C. There is a characteristic change due to temperature, and temperature compensation is necessary.

A method of reading the sensor output by an absolute value is generally used, and since the method of correcting the variation of the sensor by an external circuit is taken, it takes time and effort. Further, especially in a pressure sensor, vacuum sealing is necessary, and a post process such as a vacuum packaging process is troublesome.

There is also a drawback. In view of the above problems, an object of the present invention is to provide a sensor that can be used at high temperature, does not require temperature compensation, has no characteristic variation of individual elements, and is easy to manufacture, and a manufacturing method thereof.

[0007]

[Means for Solving the Problems]

(1) In general, a sensor using solid physical properties such as a semiconductor cannot ignore temperature characteristics, and it is inevitable that usable temperature is naturally limited. Therefore, in order to solve the above problems, it is necessary to find a material with excellent temperature resistance and a small temperature change,
Or it seems that there is no choice but to take a method that does not utilize the physical properties of solids.

In the present invention, in order to solve the above problem (1),
I chose the method. That is, the response inside the vacuum tube is used as a sensor. Inside the vacuum tube, the sensor part is completely shielded from the outside world, so that it can be expected to have excellent environmental resistance as well as temperature. In particular, if the structure is such that the collector current changes in the field-type electron-emitting device due to the pressure or acceleration from the outside world, some of the electrons running in the vacuum are the sensor response function, so it is ideally not affected by the environment. A sensor can be realized.

That is, the electric field type vacuum tube of the present invention is an electric field type vacuum tube which includes an emitter, a collector and first and second gates, and emits electrons from the emitter by a voltage applied between the emitter and the first gate. By applying an external force to the second gate, the second gate is deformed and the potential distribution created by the emitter, the second gate and the collector is changed, causing a change in the collector current.

In particular, the vacuum tube is formed by minutely processing silicon and a silicon oxide film, and the emitter and the collector are mounted on the insulating film on the substrate so as to face each other in parallel at regular intervals. Two gates are provided above and below the space between the emitter, the collector. Specifically, the structure is as shown in the conceptual cross-sectional views shown in FIGS. FIG. 12A shows a case applied to a pressure sensor, and FIG. 12B shows a case applied to an acceleration sensor.

In FIG. 12 (a), there is an emitter 2 and a collector 3 placed on an insulating film 4a on a first gate 1, and a second gate 5 on the emitter 2 and collector 3 via an insulating film 4b. Is provided. The space in which the tips of the emitter 2 and collector 3 are placed is a vacuum. A voltage V _G1 is applied between the emitter 2 and the first gate 1 to cause the emitter 2 to emit electrons. The emitted electron current flows through the first gate 1, the collector 3 and the second gate 5 according to the electric field inside the space. When an external force (pressure in this case) is applied to the second gate 5, the second gate 5 is deformed and a current I _CE (X) flowing through the collector 3 or a current I _G2 (current flowing through the second gate 5) If the structure of (X) changes, conversely I _CE (X)
Or the force applied to the second gate from the change of I _G2 (X)
(X) can be detected.

Also in FIG. 2B, only the external force is a force due to the mass and acceleration of the weight 6 on the second gate 5 ', and it is possible to utilize the change in the electron current due to the deformation of the second gate 5'. Is the same. (2) As a means for solving the problem of dispersion of individual sensors, not the absolute measurement but the difference or ratio with respect to the reference value is measured.

The emission current from the emitter is basically determined by the emitter material, the emitter geometry, the surface conditions and the electric field strength between the emitter and the first gate. The geometrical shape is set within a certain range by a photo process or the like, but individual differences may occur depending on the surface state of the emitter. Therefore, the individual difference is eliminated by keeping the total current constant or taking the ratio to the total current. That is, I = I _CE (X) + I _G1 (X) + I _G2 (X) = constant Therefore, I _G2 (X) = I−I _CE (X) −I _G1 (X) where I _G1 (X) is , Current flowing through the first gate 1 when an external force (pressure in this case) is applied to the second gate. When an external force (pressure in this case) is applied to the second gate, only the second gate is deformed by the external force (X). I _G1 (X) does not change.

Alternatively, by evaluating the values of I _CE (X) / I and I _G2 (X) / I, the magnitude of the externally applied force can be sensed irrespective of the variations of the individual sensors. For the above reason, the first gate current may be used as a reference. Specifically, as shown in FIG. 12A, the first gate 1 is provided below the emitter 2 and the second gate 5 is provided above the emitter 2. When an external force (pressure in this case) is applied to the second gate 5, a current I flowing to the second gate
_G2 (X) changes, but this can be evaluated with respect to the total current I or the current I _G1 flowing through the first gate to eliminate individual differences.

(3) An in-process vacuum sealing method was devised as a means for simplifying the vacuum packaging process. That is, of the upper and lower gates, one is the substrate, and the other is also the cap portion for sealing the space between the emitter and the collector in a vacuum. The covering cap is provided with a hole connected to the space in advance, and the space between the emitter and the collector is kept in vacuum by the metal embedded in the hole.

The sealing method will be described below. FIG. 13 is a view for explaining the sealing mechanism, and FIG.
13A and 13B are a perspective view and a cross-sectional view before sealing, and FIGS. 13C and 13D are cross-sectional views after sealing. The base portion 8 having a recess and the cap portion 9 having a hole (two holes in this case) are attached to each other [FIG. 13 (b)]. As a means thereof, for example, a bonded SOI (silicon on insulator) wafer can be bonded by heat treatment.

In this state, if the sealing metal 7 such as Al is vacuum-deposited to such an extent that the hole of the cap portion 9 is completely filled, a vacuum chamber 10 having a vacuum degree at least during vapor deposition can be formed [FIG. )]. The higher the aspect ratio (hole depth / hole size) of the holes of the cap portion 9, the less the wraparound of the sealing metal 7 into the vacuum chamber 10, and the better vacuum sealing becomes possible.

If the cap portion is provided with a groove connected to the sealing hole, the vacuum chamber 10 and the groove may be connected to each other, so that the position of the cap portion can be easily adjusted. In particular, it is preferable that at least a part of the metal embedded in the hole for keeping the space between the emitter and the collector in a vacuum getter the residual gas. By using the getter metal 7a for gettering such residual gas, the residual gas and the released gas are gettered, so that the degree of vacuum in the vacuum chamber 10 is not deteriorated and a high vacuum is maintained, and the reliability of the vacuum tube is improved. And the life is extended [(d) in the figure].

As getter metals for gettering residual gas, for example, zirconium-aluminum alloys and zirconium-iron alloys containing 7 to 30% by weight of aluminum are known. The vacuum tube having the above structure serves as a pressure sensor if the external force applied to the cap portion serving as the second gate is pressure, and serves as an acceleration sensor if the external force exerted on the weight on the cap is acceleration.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION As a measure to take the above means, a first gate is provided below a line connecting an emitter and a collector.
A second gate is provided above, and the second gate is deformed by an external force applied to the second gate, and the emitter and the second gate are
It is assumed that the potential distribution created by the collector and the collector changes, causing a change in the collector current.

In particular, silicon and a silicon oxide film are finely processed to be minutely formed, the first gate is a silicon substrate, and the emitter / collector is a silicon thin film formed on the silicon substrate via an oxide film. The two gates consist of another thin silicon film. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0022]

1 is a perspective sectional view of a chip of a pressure sensor according to a first embodiment of the present invention. On a silicon substrate 11, an emitter 12 made of a silicon thin film and having a comb-teeth-shaped tip is provided with an oxide film 14 partially lacking, and a collector 13 also made of a silicon thin film, which is opposed to the emitter 12. A second gate 15 made of a silicon thin film is provided on the emitter 12 and the collector 13 with an oxide film 16 interposed therebetween, and an oxide film 18 covers the second gate 15. The uppermost oxide film 18 is opened, and the upper gate electrode 25 made of Al alloy is in contact with the second gate 15 through the opening. Oxide film 1
8, the second gate 15 and the oxide film 16 are also provided with connection holes, and the emitter electrode 2 made of an Al alloy is passed through the connection holes.
2 is the emitter 12 and the collector electrode 23 is the collector 13
Are in contact with each. The side wall of the connection hole is covered with an oxide film and is insulated from the second gate 15. On the uppermost oxide film 18, a vacuum sealing pad 26 made of an Al alloy that seals the space between the emitter 12 and the collector 13, that is, the hole communicating with the vacuum chamber 27 is also seen. Emitter 1
2, oxide film 16 between collector 13 and second gate 15
Is partially removed, and the second gate 15 faces the vacuum chamber 27. The silicon substrate 11 is also the first gate,
A three-layer film of Ti / Ni / Au is formed on the back surface thereof and serves as the lower gate electrode 21. The vacuum chamber 27 between the emitter 12 and the collector 13 is kept at a vacuum of 4 × 10 ⁻⁴ Pa.

2 to 11 are cross-sectional views in order of steps of respective parts for explaining the method of manufacturing the pressure sensor of the embodiment of the present invention shown in FIG. 1. For convenience, three blocks, that is, an emitter-collector part are shown. Forming process of the formed base portion [FIGS. 2 (a) to (e), FIG. 3 (a) to (f), and FIG.
(C)], Groove forming process of cap portion [FIG.
(E)] and the vacuum sealing process [FIGS. 6 to 11] will be described below separately.

FIGS. 2A to 2D are sectional views showing the main manufacturing steps of the groove forming step for the scribe line of the base portion. Silicon substrate 11 (ρ = 10Ω-c
m, n type, 4 inchφ wafer) / oxide film 14 (thickness t = 1μ
m) / silicon thin film 17 (ρ = 10 Ω-cm, t = 2 μm) is used [FIG. 2 (a)]. In the present invention, a so-called bonded SOI wafer in which a silicon wafer and a thermally oxidized silicon wafer are stacked and bonded by heat treatment, and one surface is wrapped to a desired thickness is used. However, oxygen is ion-implanted into the silicon wafer. Alternatively, a so-called SIMOX wafer having an SOI layer formed by heat treatment may be used.

After this wafer is thermally oxidized to form an oxide film 16 having a thickness of 1 μm (FIG. 4B), photoresist patterning is performed using the photomask shown in FIG. 4A to scribe. The oxide film 16 in the groove forming portion for line and vacuum sealing and the silicon thin film 17 thereunder are etched out by immersion in a buffer hydrofluoric acid solution (hereinafter referred to as BHF) and reactive ion etching, and the underlying oxide film is oxidized. A groove reaching the film 14 is formed [FIG.

After that, the silicon thin film 17 exposed on the side surface of the groove is thermally oxidized to oxidize the oxide film 1 having a thickness of about 1 μm.
6'was formed [(d) in the figure]. This completes the process of forming the groove 37 for vacuum sealing and the scribe line in the base portion. FIG. 2 (e) is a perspective view of the completed product. The base portion on which the groove forming process for the vacuum sealing and the scribe line has been completed shifts to the next emitter-collector forming process.

FIGS. 3A to 3D are sectional views showing the main manufacturing steps of the step of forming the emitter-collector portion, which is subsequent to FIG. 2D. 2D, the base portion on which the groove forming process is completed is subjected to resist patterning using the mask shown in FIG. 4B and immersed in BHF to expose the vacuum chamber forming portion, and at the same time, the oxide film 16 is formed. An emitter electrode connection hole 28 and a collector electrode connection hole 29 are opened in the above [FIG. 3 (a)].

Subsequently, a photoresist 19a is applied,
Resist patterning is performed using the mask shown in FIG. 4C, and a silicon thin film 17 is formed by reactive ion etching.
Is processed into an emitter 12 and a collector 13 whose tips are processed into a comb shape [FIG. 3 (b)]. Then, the oxide film 14 under the emitter 12 and the collector 13 is immersed in a BHF solution.
By etching the emitter 12 and collector 1
After retreating by about [mu] m [(c) in the figure], the photoresist is removed and the process of forming the emitter-collector section is completed [(d) in the figure]. During this period, the tip of the comb-shaped emitter 12 may be sharpened by immersing it in a potassium hydroxide solution.

FIG. 3E is an enlarged perspective view of the emitter-collector portion after the formation of the emitter-collector portion, and it can be seen that the emitter 12 and the collector 13 face each other. The square holes of the oxide film 16 are an emitter electrode connecting hole 28 'and a collector electrode connecting hole 29'. FIG.
(A)-(d) shows the process for forming the SOI wafer with a groove used as a cap part in the cross section.

Another Si substrate 31 (ρ = 10 Ω-cm, n type, 3.
SOI consisting of 5 inch φ wafer) / SiO ₂ 18 (t = 1 μm) / silicon thin film 32 (ρ = 10 Ω-cm, t = 30 μm)
The silicon thin film 32 of the wafer is oxidized to form an oxide film 34 having a thickness of 1 μm [FIG. 5 (a)]. Next, the oxide film 34 in the groove forming portion is selectively removed by a normal photo process, and the silicon thin film 32 is etched by plasma etching using the oxide film 34 as a mask to form a desired groove [FIG. )].

Thereafter, the entire surface of this wafer is oxidized to form an oxide film 34 'having a thickness of 1 μm on the side surface of the groove [FIG. 7 (c)]. Finally, in order to remove the oxide film 34 other than the groove portion of the silicon thin film 32 and thin the silicon thin film 32, mechanically polishing is performed to finish the silicon thin film 32 flat enough to be bonded and bonded [ The same figure (d)].

FIG. 5E is a perspective view after the process of forming the grooved SOI wafer to be the cap portion is completed. A groove whose side surface is covered with an oxide film is formed. The square holes are the emitter electrode connecting hole 28 and the collector electrode connecting hole 29. However, these connection holes stop at the oxide film 18 at this stage. Next, with respect to the base portion on which the emitter-collector portion formation process of FIG. 3D has been completed, the grooved SOI wafer of the cap portion of FIG.
The surface having the groove is bonded as a joint surface.

Specifically, as shown in FIG. 6, the orientation flats provided on the wafer from the beginning (however, the length of the orientation flat is the same on all wafers) are aligned and superposed. And heat it. The diameter of the SOI wafer with a groove in the cap part is made slightly smaller because the S-type
This is because the alignment marker provided near the outer periphery of the OI wafer can be aligned when viewed from above.

FIGS. 7A to 7D and 8A to 8D.
(D) shows the vacuum sealing process after bonding the grooved cap SOI wafer and the base SOI wafer on which the emitter / collector is formed, along the line D-D 'in FIG. The cross-sectional views, FIGS. 9A to 9D, and FIGS. 10A to 10D are partial cross-sectional views along the line EE ′ shown in FIG.

The SOI wafer of the base portion on which the emitter-collector portion is formed and the SOI wafer of the cap portion are replaced with the oxide film 16 of the SOI wafer of the base portion and the SO wafer of the cap portion.
The silicon thin film 32 of the I wafer is put together and bonded [FIG. 7 (a)]. In this sectional view, the SO of the cap part
The portion of the I wafer that does not have the silicon thin film 32 is an emitter electrode connection hole 28 and a collector electrode connection hole 29, and an emitter electrode connection hole 28 'and a collector electrode connection hole 29' of the oxide film 16 of the SOI wafer of the base portion. Each is matched.

Si substrate 31 of the SOI wafer of the cap portion
Are removed by etching to expose the oxide film 18 [FIG. Next, a photoresist 19b is applied on the exposed oxide film 18 and patterned [FIG. 7 (c)].
The oxide film 18 on the emitter electrode connection hole 28, the collector electrode connection hole 29, the upper part of the upper gate electrode connection hole and the portion where the vacuum sealing hole 30 is formed is removed by dry etching [FIG. The emitter electrode connection hole 28, the collector electrode connection hole 29, and the upper gate electrode connection hole are penetrated.

FIGS. 9A to 9D are shown in FIGS.
It is sectional drawing in another cross section in the step corresponding to each of (d). S of the base portion where the emitter-collector portion is formed
The OI wafer and the SOI wafer of the cap portion are bonded together [FIG. 9 (a)]. In this cross-sectional view, the oxide film 16 and the silicon thin film 17 of the SOI wafer of the base portion are not present and are not bonded to the silicon thin film 32 of the SOI wafer of the cap portion. The portion of the SOI wafer of the cap portion where the silicon thin film 32 is not present is the formed groove. The emitter 12 located outside the cross section is indicated by a dotted line.

Si substrate 31 of the SOI wafer of the cap portion
Are removed by etching to expose the oxide film 18 [FIG. Next, a photoresist 19b is applied on the exposed oxide film 18 and patterned [FIG. 7 (c)].
The oxide film 18 in the vacuum sealing hole forming portion is removed by dry etching [FIG. The sealing hole 30 communicates with the vacuum chamber 27 having the emitter 12.

After removing the photoresist 19b by ashing, the photoresist 19b was set in a vacuum evaporation chamber of an electron beam evaporation apparatus, and the substrate was heated to 300 ° C. and evacuated for 4 hours. The ultimate vacuum was 7 × 10 ⁻⁶ Pa. Then, the substrate temperature is set to 200 ° C., and a Zr-15% Al alloy is deposited by argon sputter deposition. Sputter condition is 0.27Pa, DC3kW
It is. A getter film 20 of Zr-15% Al alloy is deposited on the bottom of the sealing hole 30 which reaches the groove for vacuum sealing [FIG.
0 (a)]. At this time, the getter film 20 is also deposited on the bottoms of the emitter electrode connecting hole 28, the collector electrode connecting hole 29, and the upper gate electrode connecting hole, and also on the S0I wafer [FIG. 8 (a)].

Subsequently, Al is vapor-deposited by 5 μm electron beam. Since the sealing hole 30 reaching the groove for vacuum sealing is filled with Al, the vacuum chamber (that is, the space where the emitter-collector is arranged) 27 is vacuum-sealed [FIG.
(B)]. At the same time, the emitter electrode connecting hole 28, the collector electrode connecting hole 29 and the upper gate electrode connecting hole are filled with Al [FIG. 8 (b)]. Getter film 20 on S0I wafer
The Al film 24 is also deposited on the upper surface.

Subsequently, the photoresist is patterned and the Al film 24 and the getter film 20 are etched to form the emitter electrode 22, the collector electrode 23, the upper gate electrode 25 and the vacuum sealing pad 26. 8 (c) and 10 (c)]. Finally, Ti / on the back
Ni / Au is vapor-deposited, and this is used as the lower gate electrode 21 to complete the process [FIG. 8 (d), FIG. 10 (d)]. A
Since the degree of vacuum during vapor deposition was 4 × 10 ⁻⁴ Pa, the degree of vacuum in the vacuum chamber 27 is estimated to be about the same as that at the beginning, but the degree of vacuum is improved by cooling and gettering by the getter film 20. To be kept for a period.

FIG. 11 shows the SOI wafer of the base portion 35 having the emitter-collector portion of FIG.
(D) is a perspective plan view of the SOI wafer of the cap portion 36 bonded to each other on the groove forming surface. In the figure, the solid line is the processing pattern of the SOI wafer of the base portion 35, and the dotted line is the processing pattern of the SOI wafer of the cap portion 36 Indicates. Vacuum chamber 27
Inside, a comb-shaped emitter 12 and collector 13 can be seen. 28 is an emitter electrode connection hole, and 29 is a collector electrode connection hole. The vacuum sealing hole 30 can be seen on the groove of the cap portion 36 lateral to the vacuum chamber 27.

FIG. 14A shows the state of pressure measurement using the sensor chip of FIG. The chip is placed in a container 40 having a vent, and the emitter electrode 22, collector electrode 23, lower gate electrode 21 and upper gate electrode 25 are connected to the E, C, G ₁ and G ₂ terminals, respectively. A voltage V _CE is applied between EC, a voltage V _G1 is applied between EG ₁ , and a voltage V _G2 is applied between EG ₂ , and respective currents I _CE , I _G1 , and I _G2 are measured.

The measured result of I _CE is shown in FIG. In the figure, the horizontal axis is the emitter-collector voltage (V _CE ) and the vertical axis is the current (I _CE ) flowing between the emitter and collector. V
_{As CE} increases, I _CE also increases. Also, 1 × 10
^It was observed that I _CE increased at a constant rate as the external pressure was reduced from ⁵ Pa (atmospheric pressure) to 1 Pa.

A voltage of 20 V is applied to each of the lower gate electrode and the upper gate electrode, and the currents flowing through the respective gate electrodes are measured as I _G1 and I _G2 . If the current flowing through the entire sensor is I,

[0046]

[Equation 1] I [V _CE = 70V, P = P (X)] = I _CE [V _CE = 70V, P = P
(X)] + I _G1 [V _CE = 70V, P = P (X)] + I _G2 [V _CE = 70V, P = P
(X)] Here, the current I _G1 flowing into the first gate electrode is not subject to pressure change,

[0047]

[Equation 2] I _G1 [V _CE = 70V, P = P (X)] = I _G1 [V _CE = 70V, P = P ₀ ]
= I _G1 [V _CE = 70V] If the change of I _CE , ΔI _CE / I, is taken as the evaluation function,

[0048]

(Equation 3) Therefore, changes in pressure and I _CE can be standardized, and individual differences of the sensor can be canceled. Table 1 shows the result of evaluation by incorporating the arithmetic circuit.

[0049]

[Table 1] Where V _CE = 70V, V _G1 = V _G2 = 20V, P ₀ = 1 × 10 ^-3
Pa. That is, by using the total current or the current of the first gate electrode as a reference, a pressure sensor without element variation can be obtained. Moreover, since this pressure sensor does not use semiconductor characteristics, there is no need for temperature compensation and it can be used in a high temperature environment of 150 ° C. or higher.

If a method of using two SOI wafers is used as a manufacturing method as described above, the manufacturing is easy. And if you take a vacuum sealing method that fills the small diameter sealing hole with evaporated metal, it can be done during the vacuum process,
No special vacuum sealing process is required. In particular, by using a metal film having a getter action as the sealing metal, it is easy to realize and maintain a high degree of vacuum and reliability is improved.

[Embodiment 2] When used as an acceleration sensor, photoresist patterning should be performed after the step of FIG. 8C to deposit a metal such as Pd and then lift off to become a weight on the second gate. It is obvious that it can be easily realized by selectively forming a metal.

[0052]

As described above, according to the present invention, two gates are provided, and a vacuum region between the two gates is provided with an electron current emitted from the emitter so that the second gate can receive the electron current. The following effects are achieved by using a vacuum tube that changes according to a change in the external force applied to the pressure sensor, a pressure sensor in which the external force is pressure, or an acceleration sensor in which the external force is applied to the second gate.

Basically, since it is a vacuum tube structure, it is unlikely to be affected by ambient temperature like a carrier flowing in a solid.
There is an effect that a sensor having excellent environment resistance can be realized. In addition, since a highly sensitive sensor is obtained and sensing is performed by a standardized method, the problem of individual difference, which has been a problem with conventional sensors, can be avoided. Further, in the manufacturing method, since the wafer having the SOI structure is used for manufacturing, the process can be greatly simplified, and the in-process vacuum sealing is realized, which is excellent in mass production such as simplification of the packaging process. And so on.

[Brief description of the drawings]

FIG. 1 is a perspective sectional view of a pressure sensor according to a first embodiment of the present invention.

2A to 2D are cross-sectional views of the pressure sensor of FIG. 1 for each main manufacturing process, and FIG. 2E is a perspective cross-sectional view thereof.

3 (a) to 3 (e) are cross-sectional views of the main manufacturing steps of the electron emitting portion of the pressure sensor of FIG. 1 following FIG. 2 (d).

4A to 4C are views of a photomask used in the manufacturing process of FIGS.

5A to 5D are cross-sectional views of the cap portion of the pressure sensor of FIG. 1 for each main manufacturing process, and FIG. 5E is a perspective cross-sectional view thereof.

FIG. 6 is a diagram showing a situation of a bonding process of the pressure sensor of FIG.

7 (a) to 7 (d) are cross-sectional views of each main manufacturing process of the bonding process of the pressure sensor of FIG.

8A to 8D are cross-sectional views of main manufacturing steps of a bonding step of the pressure sensor of FIG. 1 following FIG. 7D.

9A to 9D are cross-sectional views in different cross-sections in each main manufacturing process of the bonding process of the pressure sensor of FIG.

10 (a) to (d) is a diagram following FIG. 1 (d).
Cross-sectional view of each main manufacturing process of the pressure sensor bonding process

FIG. 11 is a perspective view showing a bonding state of the pressure sensor of FIG.

12A is an explanatory diagram of the operating principle of the pressure sensor of FIG. 1, and FIG. 12B is an explanatory diagram of the operating principle of the acceleration sensor.

13A is a perspective view of the pressure sensor of FIG. 1 before vacuum sealing, FIG. 13B is a sectional view taken along the line AA ′, and FIG.
Is a cross-sectional view after vacuum sealing, (d) is a cross-sectional view after another vacuum sealing method

14A is an explanatory diagram of the operating principle of the pressure sensor of FIG. 1, and FIG. 14B is a characteristic diagram of the pressure sensor.

15A is a cross-sectional view of a conventional pressure sensor, FIG.
Is a cross-sectional view of a conventional acceleration sensor

[Explanation of symbols]

 1 First Gate 2 Emitter 3 Collector 4a, 4b Insulation Film 5 Second Gate 6 Weight 7 Sealing Metal 7a Getter Metal 8 Base Part 9 Cap Part 10 Vacuum Region 11 Silicon Substrate 12 Emitter 13 Collector 14 Oxide Film 15 First Gate 16 , 16 'Oxide film 17 Silicon thin film 18 Oxide film 19a, 19b Photoresist 20 Getter metal 21 Lower gate electrode 22 Emitter electrode 23 Collector electrode 24 Al film 25 Upper gate electrode 26 Vacuum sealing pad 27 Vacuum chamber 28, 28' Emitter electrode Connection hole 29, 29 'Collector electrode connection hole 30 Vacuum sealing hole 31 Silicon substrate 32 Silicon thin film 34, 34' Oxide film 35 Base part 36 Cap part 37 Base part groove 38 Cap part groove 39 Scribe line 40 Container 51, 61 Sensor Tip 2 indentation 53 units 54 sensor unit 55, 65 electrode 56, 66 lead 57 and 67 bonding wire 58 cap 60 stopper 63 ceramic case 69 weight

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoichi Yoichi Tanabe Nitta 1-1 Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. (72) Masato Nishizawa 1 Nitta Tanabe, Kawasaki-ku, Kawasaki-shi, Kanagawa No. 1 in Fuji Electric Co., Ltd. (72) Inventor Akira Amano 1-1 No. Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd.

Claims (14)

[Claims] 1. An electric field type vacuum tube comprising an emitter, a collector and first and second gates, wherein electrons are emitted from the emitter by a voltage applied between the emitter and the first gate, and an external force is applied to the second gate. The electric field type vacuum tube characterized by deforming the second gate, changing the potential distribution created by the emitter, the second gate, and the collector, and causing a change in the collector current. 2. The electric field type vacuum tube according to claim 1, wherein the electric field type vacuum tube is formed by minutely processing silicon and a silicon oxide film. 3. An emitter and a collector are mounted on an insulating film on a substrate so as to face each other in parallel at a constant interval, and two gates are provided above and below a space between the emitter and the collector. The electric field type vacuum tube according to claim 1 or 2, which is characterized. 4. The first gate is a silicon substrate, and the second gate also serves as a cap portion for sealing a space between the emitter and the collector in a vacuum.
The electric field type vacuum tube according to 1. 5. The electric field type vacuum tube according to claim 4, wherein the current flowing through the second gate is evaluated with reference to the current flowing through the first gate. 6. A cap portion covering a space between the emitter and the collector is provided with a sealing hole which is connected to the space in advance, and the space between the emitter and the collector is kept vacuum by a metal embedded in the sealing hole. The electric field type vacuum tube according to claim 5, wherein: 7. The electric field type vacuum tube according to claim 6, wherein the cap portion is provided with a groove connected to the sealing hole. 8. The electric field according to claim 7, wherein at least a part of the metal embedded in the sealing hole for keeping the space between the emitter and the collector in a vacuum is a getter for the residual gas. Type vacuum tube. 9. The electric field type vacuum tube according to claim 8, wherein the metal for gettering the residual gas is an aluminum-zirconium alloy containing 7 to 30% by weight of aluminum. 10. The electric field type apparatus according to claim 5, wherein the distance between the upper and lower gate electrodes is changed by applying pressure to the cap portion. A pressure sensor using a vacuum tube. 11. A structure in which a weight is formed on the cap portion, and a force is applied to the cap portion by applying an acceleration to the weight, and a distance between two upper and lower gate electrodes is changed. An acceleration sensor using the electric field type vacuum tube according to any one of claims 5 to 9. 12. An electric field type vacuum tube according to claim 1, wherein two SOI (silicon on insulator) wafers are processed and bonded together.
A method for manufacturing a pressure sensor or an acceleration sensor. 13. A cap that covers a space between the emitter and the collector is provided with a sealing hole that is connected to the space in advance. After the cap is joined on the emitter and the collector, the sealing hole is vacuumed. 13. The method for manufacturing an electric field type vacuum tube, a pressure sensor or an acceleration sensor according to claim 12, wherein the space is kept in a vacuum by being filled with a vapor-deposited metal. 14. A method of manufacturing an electric field type vacuum tube, a pressure sensor or an acceleration sensor according to claim 13, wherein after depositing a metal having a getter action, an aluminum alloy is deposited to fill the sealing hole.