RU2526788C1 - High-temperature semiconductor pressure transducer - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: proposed transducer comprises membrane with bulged peripheral base. Said membrane has depth equal to that of strain gages made at the ply secured to said membrane. Strain gages are integrated by commutation buses with metalised contact sides to bridge measuring circuit. Membrane has section with mechanical strain concentrators at strain gage location points, said section being composed of the combination of thinned sections and stiff sections. Membrane and strain gages are made of polycrystalline diamond of one type of conductivity while ply secured at the membrane is composed of polycrystalline diamond of another type of conductivity.

EFFECT: expanded temperature range of measurements, reduced temperature error.

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Description

The proposed technical solution relates to the field of measurement technology, in particular to low-pressure transducers of high-temperature media, and can be used in the design and manufacture of small-sized semiconductor pressure transducers that are operable at elevated temperatures.

A known pressure transducer and method of its manufacture, characterized in that the membrane with a dielectric layer on which the strain gages are formed is doped with boron to the same concentration level as the strain gages, while the thickness of the membrane under the dielectric layer is equal to the thickness of the strain gages [1].

The disadvantages of this converter are its low sensitivity to measuring low pressures while maintaining its own resonant frequency, low membrane strength, high level of measurement errors in the temperature range from minus 100 to 850 ° C.

The closest in technical essence to the invention is a pressure transducer containing a silicon membrane with a thickened peripheral base made of n-type silicon and doped with boron to a concentration of at least 5 · 10 ¹⁹ cm ^-3 , and having a thickness equal to the height of the strain gauges formed on a silicon dioxide layer fixed on the membrane and made of silicon doped with boron to the same concentration level as the membrane, and connected by means of busbars in a bridge measuring circuit him, and having metallic pads connected to them. The membrane contains a profile with stress concentrators at the location of the strain gages, which is a combination of refined sections and rigid centers, and the surface of the strain gages is covered with a layer of silicon dioxide [2].

The disadvantages of the prototype are the impossibility of measuring high-temperature media, due to the low elasticity and high mobility of defects in the silicon lattice at temperatures above 500 ° C, as well as a high additional temperature measurement error caused by the difference in the physicochemical properties of silicon from which the strain gauges are made and the dioxide layer silicon isolating the strain gages from the membrane. In the design of the prototype, the strain gauges are made of silicon and placed on the surface of a layer made of silicon dioxide. The temperature coefficient of linear expansion (TEC) of silicon is 2.33 · 10 ^-6 / K, and the TEC of silicon dioxide is 0.55 · 10 ^-6 / K [3]. The temperature coefficient of resistance (TCR) of silicon is determined by the degree of doping, its typical value is 2 · 10 ^-3 / K [4]. In addition, in the prototype, due to the different structure of the layer of strain gauges made of silicon and the layer fixed on the membrane (silicon dioxide), additional mechanical stresses will arise at the interface due to defects and dislocations caused by the mismatch of the silicon lattice and the amorphous structure of dioxide silicon [5, 6]. These mechanical stresses caused by the difference in the thermal expansion coefficient of silicon and silicon dioxide, as well as defects and dislocations at the interface, will lead to the appearance of an additional temperature error of the converter.

The impossibility of measuring high-temperature media (more than 500 ° C) is explained by the fact that the silicon of which the membrane is made shows neither plastic deformation nor creep at temperatures up to 500 ° C, but at higher temperatures, this material exhibits a significant decrease in elasticity and an increase defect mobility in the crystal lattice, which ultimately leads to the destruction of structures made of silicon [4].

The invention is aimed at expanding the temperature range of measurements and reducing the additional temperature error of the Converter.

This goal is achieved by the fact that in a semiconductor pressure transducer containing a membrane with a thickened peripheral base having a thickness equal to the height of the strain gages formed on the membrane fixed to the membrane, combined by patch buses in a bridge measuring circuit having metallic contact pads connected to them, moreover, the membrane contains a profile with concentrators of mechanical stresses at the locations of the strain gages, which is a combination of ut nchennyh portions and hard centers, according to the invention the membrane and the strain gauges are made of polycrystalline diamond of one conductivity type, and fixed to the membrane layer is made of polycrystalline diamond other conductivity type.

Introduction of the proposed design containing

polycrystalline diamond allows you to expand the temperature range of measurements in terms of increasing the upper limit of measurements to 600 ° C due to the fact that polycrystalline diamond, which is a semiconductor wide-gap material, has a number of unique properties, including resistance to high temperatures.

Of all wide-gap semiconductors, diamond has the best combination of basic electrophysical parameters. Diamond has a high thermal conductivity among all known materials, which is 20-24 W / cm · K at room temperature. This is due to its high Debye temperature (1860 K), due to which the room temperature is “low” with respect to the dynamics of the diamond lattice, as a result of which it can serve as a heat-dissipating dielectric substrate, which contributes to better heat dissipation when operating products in the high temperature range. In diamond purified from isotopes (natural crystals contain 1.1% of the ¹³ C isotope), the thermal conductivity can reach 33 W / cm · K [7]. When doping a diamond, its resistivity can vary over a wide range, which turns it into a wide-gap semiconductor with a band gap of 5.4 eV, which is significantly higher than that of silicon. A large band gap, in comparison with silicon, means a wider range of operating temperatures (up to a temperature of 600 ° C, above which diamond graphitization begins in air) [8, 9].

And the introduction of the proposed design, containing a membrane and strain gauges made of polycrystalline diamond of one type of conductivity, and a layer fixed to the membrane made of polycrystalline diamond of another type of conductivity, can reduce the additional temperature error of the converter.

The change in the resistance of the bridge circuit caused by the influence of temperature is determined by the expression [3]:

$$\frac{\Delta R}{R}=\left[{\alpha }_R+K({\lambda }_s-{\lambda }_j)\right]\Delta T,\left(\mathrm{one}\right)$$

where α _R is the TCR of the material of the strain gages, λ _s is the temperature thermal expansion coefficient of the material of the strain gauges, λ _j is the thermal expansion coefficient of the material of the layer material fixed to the membrane. In the proposed design, the strain gauges and the layer fixed to the membrane are made of polycrystalline diamond so that in the expression (1) λ _s = λ _j , and the change in the resistance of the bridge circuit caused by the influence of temperature is determined by the expression:

$$\frac{\Delta R}{R}={\alpha }_R\Delta T.\left(2\right)$$

For example, when the TCS value of polycrystalline diamond is α _R = -4.4 · 10 ^-4 / K (which is achieved by selecting the appropriate concentration of the dopant), the change in the bridge resistance caused by the temperature effect determined for the prototype according to formula (1) will be 0 , 2002% / ° C ^-1 , and the change in the resistance of the bridge circuit caused by the influence of temperature for the proposed design, determined by formula (2), will be equal to 4.4 · 10 ^-2 % / ° C ^-1 . Thus, the introduction of the proposed design can reduce the change in resistance caused by the influence of temperature, and therefore reduce the additional temperature error.

In addition, in the proposed design, additional mechanical stresses will be absent, since the strain gauges and the layer fixed to the membrane are made of the same material (polycrystalline diamond), for which the crystal lattice parameters coincide [5, 6].

The proposed device is illustrated in figure 1.

Figure 1 shows a semiconductor pressure transducer containing a membrane (1) with a thickened peripheral base (2). The membrane has a thickness equal to the thickness of the strain gages (3) formed on the layer fixed to the membrane (4). Strain gages are combined with the help of switching buses (5), having metallized contact pads (6) connected to them, into a bridge measuring circuit. The membrane contains a profile with stress concentrators (7) at the locations of the strain gauges, which is a combination of sophisticated sections and rigid centers. The membrane and strain gauges are made of polycrystalline diamond of one type of conductivity, and the layer fixed to the membrane is made of polycrystalline diamond of another type of conductivity.

The principle of operation of the converter is as follows.

The measured pressure, acting on a membrane with a rigid center, deforms the strain gauges and increases the imbalance of the bridge circuit into which the strain gauges are closed. The choice of polycrystalline diamond as the material of the membrane and strain gauges makes it possible to expand the temperature range of measurements in terms of increasing the upper limit of measurements to 600 ° C through the use of a semiconductor wide-gap polycrystalline diamond material with a number of unique properties, including resistance to high temperatures. And the use of a design in which the membrane and strain gauges are made of polycrystalline diamond of one type of conductivity, and the layer fixed to the membrane is made of polycrystalline diamond of another type of conductivity, allows to reduce the additional temperature error of the converter caused by the difference in physicochemical properties of the materials of the membrane, strain gauges and fixed to membrane layer.

The technical and economic advantages of the proposed converter in comparison with the known are:

- expansion of the temperature range of measurements;

- reduction of additional temperature error of the Converter.

Information sources

1. Patent RU 1732199.

2. Patent RU 2271523.

3. Ash. J. et al. Sensors of measuring systems: In 2 books. Book 1. Per. with french - M.: Mir, 1992 .-- 480 s, ill.

4. Gridchin, V.A. Physics of microsystems: textbook. allowance; at 2 p. Part 1 / V.A. Gridchin V.P. Dragunov. - Novosibirsk: NSTU Publishing House, 2004 .-- 416 p.

5. Nakladan A., Sager K., Gerlach G. Influences of humidity and moisture on the long-term stability of piesoresistive pressure sensors // Measurement. 1995. V.16. No.1. P.21-29.

6. Gerlach G., Sager K., Zwiebber R. Der EinfluP Halbleiter technologist realisierbarer Passivierung - Konzepte auf dielectrische Stabilitet piesoresistiver Drucksensoren // VD - Ber. 1992. Bd. 960. N 1. S.281-294.

7. Ralchenko V. CVD-diamonds. Application in electronics / V.Ralchenko, V.Konov // Electronics: Science, Technology, Business. - 2007. - No. 4. - S. 58-67.

8.http: //www.intactive.rU/ru/info/articles/article/4/

9. Pleskov Yu.V. Electrochemistry of diamond. / Yu.V. Pleskov - Editorial URSS; 2003; 104 p.

Claims (1)

A semiconductor pressure transducer comprising a membrane with a thickened peripheral base having a thickness equal to the height of the strain gages formed on the membrane fixed to the membrane, combined by patch buses in a bridge measuring circuit having metallized contact pads connected to them, the membrane containing a profile with mechanical concentrators stresses at the locations of the strain gages, which is a combination of sophisticated sections and rigid centers, excel characterized in that in it the membrane and strain gauges are made of polycrystalline diamond of one type of conductivity, and the layer fixed to the membrane is made of polycrystalline diamond of another type of conductivity.