RU2555190C1 - Semiconductor pressure converter - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: semiconductor pressure converter comprises a membrane with a thickened peripheral base. The membrane has thickness equal to thickness of strain gauges formed on the dielectric layer fixed onto the membrane. Strain gauges are combined using conductors having metallised contact sites connected with them into a bridge measuring circuit. The membrane comprises a profile with concentrators of mechanical stresses in areas of strain gauges location, which represents a combination of thinned sections and stiff centres. Besides, the converter comprises an additionally formed layer of dielectric fixed at the membrane side opposite to the formed strain gauges, and equal in thickness and properties to the dielectric layer fixed on the membrane at the side of the strain gauges.

EFFECT: increased reliability of a converter, increased strength of a membrane, higher stability of parameters at higher temperatures.

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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.

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 600 ° C.

The closest in technical essence to the invention is a pressure transducer and a method for its manufacture, comprising a membrane with a thickened peripheral base made of silicon and doped with boron to a concentration of at least 5 · 10 ¹⁹ cm ^-3 , having a thickness equal to the thickness of the strain gauges formed on the fixed on the membrane a dielectric layer made of silicon doped with boron to the same concentration level as the membrane, connected by means of conductors into a bridge measuring circuit and having a connection related metallized contact pads, moreover, the bridge measuring circuit contains a thermistor made of silicon, and the membrane contains a profile with stress concentrators at the locations of the strain gages, which is a combination of refined sections and rigid centers, while the surfaces of the strain gages and the thermistor are coated with a layer of dioxide silicon [2].

, а кремния k_Si=4,5·10^-6K^-1 [3, 4]. То есть коэффициенты термического расширения двух слоев отличаются друг от друга приблизительно в 10 раз. Учитывая, что слои занимают эквивалентную площадь и непосредственно соприкасаются друг с другом, в данном преобразователе давления при работе в широком диапазоне температур (от минус 70 до 600°C) будут иметь место значительные механические напряжения, вызванные, помимо различия коэффициентов термического расширения двуокиси кремния и кремния, усадочными явлениями материалов этих слоев, несовершенством проведения технологических процессов, неоднородностью пластической деформации, несоответствием параметров решетки слоев и т.д. [5]. Возникающие высокие механические напряжения растяжения либо сжатия снижают надежность преобразователя и приводят к прогибу мембраны, появлению неинформативного сигнала и, как следствие, - к повышению дополнительной температурной погрешности.The disadvantages of the prototype are low reliability, low membrane strength, high additional temperature error of the transducer due to high mechanical stresses due to the difference in the properties of the silicon of which the membrane is made, and the dielectric layer that insulates the strain gauges from the membrane. For example, the coefficient of thermal expansion of silicon dioxide (as the most typical dielectric) is $$K_{Si{O}_2}=0.5\cdot {10}^{-6}{K}^{-\mathrm{one}}$$

and silicon k _Si = 4.5 · 10 ^-6 K ^-1 [3, 4]. That is, the thermal expansion coefficients of the two layers differ from each other by about 10 times. Considering that the layers occupy an equivalent area and are in direct contact with each other, in this pressure transducer, when operating in a wide temperature range (from minus 70 to 600 ° C), significant mechanical stresses will occur due to, in addition to the difference in the thermal expansion coefficients of silicon dioxide and silicon, the shrinkage phenomena of the materials of these layers, the imperfection of technological processes, the heterogeneity of plastic deformation, the mismatch of the lattice parameters of the layers, etc. [5]. The resulting high mechanical tensile or compression stresses reduce the reliability of the transducer and lead to deflection of the membrane, the appearance of an uninformative signal, and, as a result, to an increase in the additional temperature error.

The invention is aimed at improving the reliability of the Converter, increasing the strength of the membrane, increasing the stability of parameters at elevated temperatures.

This goal is achieved by the fact that in a semiconductor pressure transducer containing a membrane with a thickened peripheral base made of silicon, having a thickness equal to the thickness of the strain gauges formed on the dielectric layer fixed to the membrane, connected with the help of conductors in a bridge measuring circuit having connected to them metallized contact pads and containing a profile with stress concentrators in the locations of the strain gages, which represents bout combination thinned portions and hard centers, further dielectric layer is formed, fixed with respect to the opposite side of the membrane formed strain gages and equal in thickness and dielectric properties of the layer, fixed to the membrane by the strain gauges.

The introduction of the proposed design, containing an additionally formed dielectric layer, fixed on the opposite side of the membrane with respect to the strain gauges formed and equal in thickness and properties to the dielectric layer fixed on the membrane on the side of the strain gauges, allows to reduce the level of mechanical stresses caused by the difference in the properties of silicon and the dielectric.

The proposed design is a multilayer heterostructure, the thermal stresses of which are analytically determined from:

where E _f is the modulus of elasticity of the film, ν _f is the Poisson's ratio of the film, α _s and α _f are the temperature coefficients of the linear expansion of the layers, ΔT is the temperature range [6]. According to expression (1), a silicon membrane experiences a voltage of about 25 MPa when the temperature rises by 50 ° C compared to normal conditions, and an additionally formed dielectric layer fixed from the opposite side of the membrane relative to the formed strain gauges, as well as the dielectric layer fixed to to the membrane from the side of strain gauges, it experiences a voltage of the order of 9 MPa (the stresses of the layers of the dielectric are equal in value but opposite in sign), which means a decrease in the mechanical stress zheniya, the test membrane to the same value. More accurate results are provided by numerical modeling in a finite element analysis package of applied programs, according to which the average mechanical stress experienced by the prototype structure membrane at a temperature increase of 50 ° C is about 21 MPa, and in the proposed design is about 13 MPa. Thus, the proposed design reduces the additional mechanical stresses acting on the strain gauges by a value of about 62%, which means reducing the additional temperature error by the same value, as well as increasing the reliability of the converter, increasing the strength of the membrane. And considering that mechanical stresses cause deformation of the membrane, especially when the converter is operated at elevated temperatures, the proposed design also allows to increase the stability of parameters at elevated temperatures.

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 (1) has a thickness equal to the thickness of the strain gages (3) formed on the dielectric layer (4) fixed on the membrane. Strain gages (3) are combined using conductors (5) having metallized contact pads (6) connected to them into a bridge measuring circuit. The membrane (1) contains a profile with stress concentrators (7) at the locations of the strain gauges (3), which is a combination of refined sections and rigid centers. In addition, the transducer contains an additionally formed dielectric layer (8) fixed on the opposite side of the membrane (1) with respect to the strain gauges (3) and equal in thickness and properties to the dielectric layer (4) fixed to the membrane (1) on the side of the strain gauges (3) )

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 presence of an additionally formed dielectric layer fixed from the opposite side of the membrane with respect to the strain gauges formed and equal in thickness and properties to the dielectric layer fixed to the membrane from the side of the strain gauges provides mutual compensation of mechanical stresses, both tension and compression, taking into account the identical thickness and physical the mechanical properties of these layers, when deformations caused by mechanical stresses are equal in value but opposite in sign, when the silicon membrane experiences a voltage of about 25 MPa when the temperature rises by 50 ° C compared to normal conditions, and the additionally formed dielectric layer fixed on the opposite side of the membrane relative to the formed strain gauges, as well as the dielectric layer fixed on the membrane from the strain gauge side experiences a stress of the order of 9 MPa (the stresses of the layers of the dielectric are equal in value but opposite in sign), which means a decrease in mechanical stress, direct membrane to the same value. During operation of the transducer, mutual compensation of mechanical stresses, both tension and compression, takes into account the identity in thickness and physico-mechanical properties of these layers, when deformations caused by mechanical stresses will be equal in value but opposite in sign. Thus, the proposed technical solution allows to reduce the level of mechanical stresses, increase the reliability of the transducer, increase the strength of the membrane, increase the stability of parameters at elevated temperatures.

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

- improving the reliability of the Converter;

- increase the strength of the membrane;

- increasing the stability of parameters at elevated temperatures.

Information sources

1. A.S. (USSR) No. 1732199, MKI G01L 9/04, 1990.

2. Patent 2284613 RU. Semiconductor pressure transducer and method for its manufacture. Publ. 09/27/2006. Bull. Number 27.

3. Kontseva Yu.A., Litvinov Yu.M., Fattakhov E.A. Plasticity and strength of semiconductor materials and structures. M .: Radio and communications, 1982.- 240 p.

4. Palatnik L.S., Sorokin V.K. Materials science in microelectronics. M .: Energy, 1978.- 280 s.

5. V.S. Sergeev, O.A. Kuznetsov, N.P. Zakharov, V.A. Letagin. Stresses and strains in the elements of microcircuits. M .: Radio and communications, 1987. - 88 p.: Ill.

6. Allyson L. Hartzell, Mark G. da Silva, Herbert R. Shea. MEMS Reliability. - Springer London, Limited, 2013.

Claims (1)

A semiconductor pressure transducer containing a membrane with a thickened peripheral base made of silicon, having a thickness equal to the thickness of the strain gauges formed on the dielectric layer attached to the membrane, combined by means of conductors in a bridge measuring circuit, having metallized contact pads connected to them and containing a profile with stress concentrators in the locations of strain gages, which is a combination of sophisticated sections and FIR centers, characterized in that it further dielectric layer is formed, fixed with respect to the opposite side of the membrane formed strain gages and equal in thickness and dielectric properties of the layer, fixed to the membrane by the strain gauges.