JPH06201500A - Pressure sensor - Google Patents

Abstract

PURPOSE:To provide a pressure sensor capable of obtaining a stable output of high accuracy even at a high temperature. CONSTITUTION:The pressure sensor comprises a diaphragm 2 formed on the surface of a silicon substrate 1, an anode (or a cold cathode emitter) 4 formed on the diaphragm 2, and a cold cathode emitter (or an anode) 7 disposed facing on the anode (or the cold cathode emitter) 4. The space between the anode 4 and the emitter 7 is evacuated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon pressure sensor, and more particularly to a silicon pressure sensor having high sensitivity in a high temperature range (200 ° C. or higher).

[0002]

2. Description of the Related Art Conventionally, as a semiconductor type pressure sensor, a resistor is arranged on a Si diaphragm to utilize the piezoresistive effect. A device that processes silicon or glass to form a gap and detects capacitance changes. Etc. are known.

[0003]

However, in the case where the pn junction is formed in order to utilize the piezo effect, it is 120
There is a problem that the leak current is large and the sensitivity is low in the high temperature range above ℃. On the other hand, the capacitive pressure sensor has a problem that it is susceptible to stray capacitance although it has high sensitivity. That is, the capacitance type has a high output impedance, and when it is downsized, the sensor capacitance becomes small and the influence of the stray capacitance becomes relatively large.

The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a pressure sensor capable of obtaining a stable output with high sensitivity even at a high temperature.

[0005]

In order to solve the above-mentioned problems, the present invention provides a diaphragm formed on a silicon substrate,
An anode (or cold cathode emitter) formed on the diaphragm, and a cold cathode emitter (or anode) arranged to face the anode (or cold cathode emitter)
The space between the anode and the cold cathode emitter is made vacuum.

[0006]

[Operation] When a voltage is applied between the cold cathode emitter and the anode which are arranged opposite to the vacuum space, the electrons emitted from the emitter are proportional to the function of the electric field strength (inversely proportional to the distance between the electrodes).
And increase. Since the diaphragm is displaced in proportion to the applied pressure, the field emission current changes in association with the change in the distance between the emitter and the anode.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a cross sectional view showing an embodiment of the present invention, in which 1 is a first Si wafer having a rectangular diaphragm 2 formed by anisotropic etching. This first Si
On the diaphragm 2 of the wafer 1, a high-concentration diffusion portion 3 functioning as a lead wire and an electrode 4 functioning as an anode are formed. Reference numeral 5 is a second Si wafer having a recess 6, and a porous Si 7 functioning as an emitter is formed at the bottom of the recess 6 (above the anode 4 in the figure). A high-concentration diffusion portion 3'which functions as a lead wire is connected to the porous Si7. 8 is the second excluding the concave portion 6
An insulating film (SiO ₂ formed on the surface of the silicon wafer 5
And Si ₃ N ₄ ). Anode 4 of the first Si wafer 1
The side on which is formed and the side of the second Si wafer 5 on which the insulating film is formed are joined by direct joining, and the recess 6 serves as a vacuum chamber. Reference numerals 9 and 9'indicate contact portions made of heat-resistant wiring for connecting to the lead wires 3 and 3 '.

Reference numeral 10 is a mounting substrate made of, for example, Pyrex glass and having a through hole 11 formed therein, and the other surface of the first Si wafer 1 is bonded to the mounting substrate 10 to form a fluid introduction chamber 12. Reference numeral 13 is a pillar made of an insulator formed at a predetermined position on the anode 4. Next, a schematic manufacturing process of the pressure sensor will be described with reference to FIGS. In FIG. 2A, the first
Impurities 3 such as boron are diffused at a high concentration (about 10 ¹⁹ to 10 ²⁰ cm ⁻³ ) in a portion of the Si wafer 1 where the diaphragm 2 is formed and a portion to be a lead wire. Then (b)
In the figure, the T on the portion where the impurities are diffused on the diaphragm
An i film is formed by sputtering, and then heat treatment (annealing) is performed in an N ₂ atmosphere. By this annealing, the Ti film becomes the electrode 4 which functions as an anode made of TiSix and TiN. Next, a resist is coated on the substrate including the electrodes 4 and holes are formed at predetermined positions to expose the electrodes 4,
For example, SiO ₂ is sputtered to a thickness of several μm. Next, the resist is removed to form a plurality of columns 13.

Next, an electrode (for example, Au, Pt, T2 N, T2 Six, etc.) 9'as a heat resistant member is formed on the lead portion. Next, anisotropic etching is performed from the back surface of the Si wafer 1 to form the fluid introduction chamber 12 and the diaphragm 2. In FIG. 3A, one surface of the second Si wafer 5 is etched to be wider and shallower (for example, several μm) than the area of the diaphragm 2 of FIG. ´ is high concentration (1
0 ^{19-10 20} diffuses into cm approximately ^-3) electrodes and electrode Li -
Form a do. In this process, an insulating film (SiO ₂ or Si ₃ N ₄ ) 8 is formed on the portion where impurity diffusion is not performed,
The impurities 3'are removed after the formation. In FIG. 3 (b), the insulating film 8 is formed again, and only the electrode portion to be the emitter is opened and immersed in high-concentration HF (hydrofluoric acid). When the impurity diffusion layer 3'is used as an anode and electricity is applied, the following reaction occurs. Si + 2HF + 2h ⁺ → SiF2 + 2H ⁺

This SiF ₂ + 2H ⁺ produces amorphous Si ^* , but this amorphous Si ^* is deposited on the surface of the diffusion layer to form the porous Si layer 7. This porous Si (which functions as an emitter) is formed to a depth not exceeding 1 μm from the surface of the diffusion layer, but if the diffusion layer 3 ′ is formed to have a thickness of, for example, about 3 μm, it will be porous. The electrode layer (diffusion layer) is left in contact with the Si layer 7, and the remaining portion is extended to the lead portion. In FIG. 3 (c), electrodes (eg, Au, Pt, T) as heat-resistant members are attached to the ends of the lead wires.
2 N, T2 Six, etc.) 9 is formed after making a hole from the opposite side of the Si wafer 5.

The thickness of the diaphragm and the diffusion depth of boron and the sputtering film thickness of Ti in FIG. 2 and the etching depth and diffusion depth of the recess 6 in FIG. 3 are the basic values between the electrodes when field emission is performed. Although they are distances, these should be adjusted to the optimum conditions according to the pressure and temperature conditions to be measured. As a method of forming the recess 6 in a vacuum chamber, the Si wafers 1 and 5 are combined and degassed and bonded under reduced pressure. You may stop it. In this case, Ti is used as the anode electrode 4 to have heat resistance, but since Ti has a getter action for adsorbing unnecessary gas in the vacuum chamber, the effect of improving the degree of vacuum can be expected.

In FIG. 4, the side of the Si wafer 1 formed in FIG. 2 on which the anode 4 is formed and the side of the Si wafer 5 formed in FIG. 3 on which the emitter 7 is formed are combined and heated to about 1100.degree. 2 is a cross-sectional view showing a state of being bonded by direct bonding, and then a mounting substrate 10 formed of Pyrex glass or the like is bonded to complete the Si pressure sensor shown in FIG.

In the structure of FIG. 1, when the fluid is introduced from the through hole 11 into the pressure introducing chamber 12 and the pressure applied to the diaphragm 2 changes, the diaphragm 2 is deformed and the electrode spacing between the anode 4 and the emitter 7 is changed. Changes. When excessive pressure is applied to the diaphragm, the tip of the support column contacts the emitter and prevents contact between the anode and the emitter. FIG. 5 shows an embodiment of claim 2 in which the emitter 7 portion 7'is formed into a protrusion (cone) shape. The step shown in FIG. 1 is a step of forming a porous silicon portion into a cone shape. Only is different. Other reference numerals are the same as those in FIG.

As a method for producing a cone on a silicon wafer, for example, a known method described in NIKKEI ELECTRONICS issued on October 29, 1990 and US Pat. No. 3,789,471 can be used. Generally, the displacement (ω ₀ ) of the center of the diaphragm when pressure p is applied to the diaphragm.
Can be expressed by the following equation. (Ω ₀ ) = 1.710 ^-13 [{(2a) ⁴ / h ³ }]
p a: Length of one side of diaphragm h: Thickness of diaphragm

That is, the displacement of the diaphragm is proportional to the pressure. When the emitter (7, 7 ') is silicon, the emission current density j from the valence band is expressed by the following equation. j = AT ² {exp (−b) / (ckT) ² · (rp / 1 + rp) ... b = {U ^1/2 (x + Eg) ^3/2 / ψi ² } φ {ψi / (x + Eg)} c = 3 {U (x + Eg)} ^1/2 / 2ψi ² where A; coefficient, U; energy, mp; effective mass of holes m; rest mass of electron k; Boltzmann constant,
T; absolute temperature ψi (potential); 3.8 × 10 ^-4 Φ [F ^1/2 ] F; electric field, Φ; coefficient rp; mp / mx; electron affinity Eg; energy gap Note that the above formula is an electron. Technical Research Institute Vocabulary 53
No. 10, pp. 1171-1182.

FIG. 6 shows the radiation current density calculated as a function of the reciprocal of the electric field F using the above equation. The figure shows that the current increases in proportion to the reciprocal of the distance between the electrodes, and that the output is not affected even if the absolute temperature T changes to 200 to 400K. Further, according to FIG. 6, it can be seen that when the electric field is doubled, the current density is increased by 2-3 digits. Since this is detected as the displacement of the diaphragm in the present invention, a minute change in the displacement can be taken out as a large change in the output current.
FIG. 7 shows an embodiment in which the Si pressure sensor of the present invention is applied as a differential pressure gauge, and in this example, FIGS. 3 (a) to 3 (c) are provided on both sides of the second silicon wafer 5 shown in FIG.
Si wafer 1 manufactured by the process shown in FIG.
Is joined to both sides. A similar voltage is applied to the emitters 7, 7 of this differential pressure gauge from a common power source (not shown), and the potentials of the nodes 4, 4 are also connected to the common potential (14 is the contact portion 9 ', 9'is a connecting member). In this differential pressure gauge, the respective outputs applied to both diaphragms 2 and 2 are measured separately and the output difference is detected as a signal.

In this embodiment, the anode 4 is formed on the diaphragm 2 of the first Si wafer 1 and the second S
Although the emitter 7 is formed on the i-wafer 5, the emitter 7 is formed on the first Si wafer 1 side and the anode 7 is formed on the second Si wafer 5.
The cord 4 may be formed. Further, a pillar for preventing excessive pressure may be formed on the emitter side. Further, although an example in which the present invention is applied to a pressure gauge has been described in the present embodiment, the present invention is not limited to this embodiment and may be used in an accelerometer or the like.

[0018]

As described above in detail, according to the present invention, since a material having high heat resistance is used as the electrode material, it can be used up to a high region. Since a small amount of diaphragm displacement can be detected as a large current change, high sensitivity can be achieved and minute pressure measurement is also possible. Since the emission from the valence band is used, it is less dependent on temperature and has good temperature characteristics. Strong against overpressure. Since the emitter and anode are placed in the vacuum chamber, they are not easily affected by the external environment. And so on.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a pressure sensor of the present invention.

2A to 2C are cross-sectional views showing an outline of a manufacturing process.

3A to 3C are cross-sectional views showing an outline of a manufacturing process.

FIG. 4 is a cross-sectional view showing an outline of a manufacturing process.

FIG. 5 is a perspective view showing an embodiment of claim 2 of the pressure sensor of the present invention.

FIG. 6 is a diagram showing a radiation current density calculated by using Si as an emitter and a distance from the anode as a function of an electric field.

FIG. 7 is a sectional view showing another embodiment of the present invention.

[Explanation of symbols]

 1 First Si Wafer 2 Diaphragm 3,3 'High Concentration Diffusion Part 4 Electrode (Anode) 5 Second Si Wafer 6 Vacuum Chamber 7 Porous Si (Emitter) 8 Insulation Film 9,9' Heat Resistant Wiring (Contact Part) 10 Attachment Substrate 11 Through hole 12 Fluid introduction chamber 13 Support

Claims (3)

[Claims] 1. A diaphragm formed on a silicon substrate, an anode (or a cold cathode emitter) formed on the diaphragm, and a cold cathode arranged to face the anode (or cold cathode emitter). A pressure sensor comprising a cathode emitter (or an anode), wherein the space between the anode and the cold cathode emitter is evacuated. 2. The pressure sensor according to claim 1, wherein silicon subjected to a porous treatment is used as the cold cathode emitter. 3. The pressure sensor according to claim 1, wherein a plurality of emitters having protrusion tips are used as the cold cathode emitters.