RU2547291C1 - Method to manufacture thin-film nano and microelectromechanical system of high temperature sensor of mechanical values - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: in the method to manufacture a thin-film nano and microelectromechanical system of a high temperature sensor of mechanical values on a planar side of an elastic element by methods of vacuum sputtering they produce a heterogeneous structure from nano and microsized films of materials, containing thin-film dielectric, resistive strain and contact layers. Strain elements (resistive strain sensors) are formed, as well as contact conductors and contact sites to them. A resistive strain layer is formed by the method of magnetron sputtering in a vacuum chamber with simultaneous use of two targets from nickel and titanium. The elastic element with a dielectric layer formed on it is installed on a carousel, heated, argon pressure is pulled, and then the carousel is rotated, at the same time current densities are set in areas of sputtering of the first and second targets, based on their certain ratio. Afterwards the elastic element is maintained in vacuum at higher temperature for several hours.

EFFECT: expansion of temperature range of sensor operation, increased reproducibility of such parameters of resistive strain sensors as electric resistance and temperature coefficient of resistance, reduced temperature sensitivity of sensors.

5 dwg

Description

The invention relates to measuring technique and can be used in the manufacture of thin-film strain gauge sensors of mechanical quantities designed to operate at elevated temperatures.

The nano- and microelectromechanical system (NIMEMS) of a thin-film strain gauge pressure sensor (TTDD) is an elastic element (RE) with a heterogeneous structure deposited on it, consisting of thin nano- and micro-sized layers of conductive, dielectric, resistive films of materials [1]. The heterogeneous structure of the NiMEMS pressure sensor usually consists of four nano- and micro-sized layers formed on an elastic element (36NXTJ steel may be the UE material) with a microroughness height of not more than 50-100 nm (when the microroughness of the membrane is more than 100 nm, it becomes essentially impossible to obtain stable thin-film structures, and, consequently, new qualitative indicators characteristic of the sensor).

A known method of manufacturing a high-temperature thin-film resistor for NIMEMS pressure sensor based on alloy X20N75YU [2]. It consists in the formation in vacuum of resistive monolayers with negative and positive temperature coefficients of resistance (TCS). Layer-by-layer formation of resistive monolayers is carried out in a single technological cycle, moreover, the resistive layer with negative TCS is formed by electron beam evaporation, and the resistive layer with positive TCS is formed by thermal evaporation.

The disadvantage of this method is the narrow temperature range of the pressure sensor - (from minus 196 to 150 ° C) and the impossibility of reproducibility of the exact composition of the strain gauge film, because when using thermal evaporation of thin-film strain gauges they are structured in the form of thinner layers of chromium, nickel, aluminum and t .d. The deposition of films from a single evaporator is possible when the substance passes into vapor in the form of molecules of stoichiometric composition, or when the alloy materials have the same volatility. The components of the X20H75Y alloy have different volatilities during evaporation, which leads to an uncontrolled composition of a thin tensoresistive film. As a result, the reproducibility of the strain gauges of the bridge measuring circuit is not high, the values of the TCS of the strain gauges are significantly different for NiMEMS manufactured at different times (in different lots, in different vacuum cycles). Because of this, NIMEMS and pressure sensors based on them have a large variation in temperature sensitivity, do not always meet the technical requirements, and are unsuitable for operation at elevated temperatures (above 150 ° C).

The closest in technical essence to the proposed solution is a method of manufacturing a nano- and microelectromechanical system of a sensor of mechanical quantities - a pressure sensor using thin-film nano- and microelectronic technology [3]. It consists in the fact that on the planar side of the elastic element by vacuum spraying methods they form a heterogeneous structure of nano- and micro-sized films of materials containing thin-film dielectric, strain gauge and contact layers, after which, using photolithography and etching, strain gauges (strain gauges), contact conductors and contact pads to them. Moreover, thermal evaporation is used as a vacuum spraying method for all layers. In this method, strain gages are formed on the flat side of the membrane. As the starting material for the formation of the strain-resistant layer using alloy X20N75YU. The strain gauges obtained as a result of its use have a positive TCR from 10 ^-4 to 10 ^-5 ° C ^-1 .

The disadvantage of this method is the narrow temperature range of the pressure sensor - (from minus 196 to 150 ° C), the low reproducibility of the parameters of the strain gages (electrical resistance, TCS), the relatively high temperature sensitivity (due to the insufficiently small values of the TCS strain gages) and how consequence, high temperature error. NiMEMS and mechanical value sensors manufactured by the method selected as a prototype also prove to be unsuitable for operation at elevated temperatures (above 150 ° C).

The technical result of the invention is the expansion of the temperature range of the sensor of mechanical quantities (up to 200 ° C), for example, a pressure sensor based on thin-film NiMEMS due to the fact that after applying the dielectric layer, the resistive layer is formed from nickel (Ni) and titanium (Ti). In addition, the technical result is a higher reproducibility of the parameters of the strain gages (electrical resistance, TCS), due to the fact that the resistive layer of Ni and Ti is formed by magnetron sputtering in a vacuum chamber with the simultaneous use of a carousel and two targets made of nickel and titanium, with a certain ratio of the current density of the magnetron discharge on targets of Ni and Ti. The technical result is also a lower temperature sensitivity of the sensor of mechanical values based on thin-film NiMEMS due to the fact that under the established spraying conditions, lower values of the TCS of the strain gauges are obtained. In this regard, the sensor manufactured by the proposed method has a lower temperature error in a wide temperature range.

, при этом упругий элемент со сформированным на нем диэлектрическим слоем устанавливают на карусель, расположенную на расстоянии 0,05 м от мишеней, нагревают до температуры 180-200°C, создают давление аргона 6,5·10^-3 мм рт.ст., а затем вращают карусель с упругим элементом со скоростью 50-60 об/мин в течение 10 минут, после чего упругий элемент с нанесенным на него тензорезистивным слоем выдерживают в вакууме при температуре 370°C в течение 5-6 часов.This is achieved by the fact that in the known method of manufacturing a thin-film nano- and microelectromechanical system of a sensor of mechanical quantities, which consists in the fact that on the planar side of the elastic element by vacuum spraying methods they form a heterogeneous structure of nano- and micro-sized films of materials containing thin-film dielectric, tensoresistive and contact layers, after which using photolithography and etching form strain cells (strain gauges), contact conductors and contact pads to them, according to the present invention, the thin-layer is formed by magnetron sputtering in the vacuum chamber, simultaneously from two separate sources, magnetron discharge current densities j _Ni and j _Ti on targets of Ni and Ti, which before it is determined by the ratio

wherein the elastic element with the dielectric layer formed on it is mounted on a carousel located at a distance of 0.05 m from the targets, heated to a temperature of 180-200 ° C, create an argon pressure of 6.5 · 10 ^-3 mm Hg, and then a carousel with an elastic element is rotated at a speed of 50-60 rpm for 10 minutes, after which the elastic element with a tensoresistive layer deposited on it is kept in vacuum at a temperature of 370 ° C for 5-6 hours.

мм рт.ст., карусель с упругим элементом вращают со скоростью 50-60 об/мин в течение 10 минут, упругий элемент с нанесенным на него тензорезистивным слоем выдерживают в вакууме при температуре 370°C в течение 5-6 часов.In this method of manufacturing a thin-film nano- and microelectromechanical system of a mechanical quantity sensor, in accordance with the invention, the carousel is placed at a distance of 0.05 m from targets of nickel (Ni) and titanium (Ti), an elastic element with a dielectric layer formed on it, mounted on a carousel, heated to a temperature of 180-200 ° C, create argon pressure of 6.5 · 10 ^-3

mm Hg, a carousel with an elastic element is rotated at a speed of 50-60 rpm for 10 minutes, the elastic element with a strain-resistant layer deposited on it is kept in vacuum at a temperature of 370 ° C for 5-6 hours.

Figure 1, 2 shows the design of the sensor of mechanical quantities - pressure sensor, which is manufactured by the proposed method. The sensor contains a housing 1 with a fitting 2 (Fig. 1), a thin-film nano- and microelectromechanical system (NIMEMS) 3 installed in it, output conductors 4, a cable jumper 5. The thin-film NIMEMS 3 is a structurally complete module that provides high manufacturability of the sensor assembly.

Figure 2 separately shows a thin-film nano- and microelectromechanical system (NIMEMS) sensor. It consists of an elastic element - a round membrane 6 with a rigid center 7, rigidly sealed along the contour, with a peripheral base 8 outside the border of 9 of a rigid center membrane, a heterogeneous structure 10, a contact block 11, a sealing sleeve 12, connecting conductors 13, output rings 14 dielectric bushings 15.

Figure 3 shows a diagram of an installation for magnetron sputtering of a resistive layer. The installation contains a magnetron atomizer 16 of the Ni target, a magnetron atomizer 17 of the Ti target, a heater 18, a carousel 19, located on the base plate 20 of the vacuum chamber. A holder of substrates 21, a thermocouple 22 for measuring temperature are mounted on the carousel 19. The carousel 19 is connected to the rotation drive 23.

Figure 4 separately presents a heterogeneous structure 10 on the elastic element - the membrane 6.

A method of manufacturing a thin film nano- and microelectromechanical system of a high temperature sensor of mechanical quantities, for example, a strain gauge pressure sensor (figure 1), is implemented as follows. On the planar side of the elastic element - the membrane 6 (Fig.2) by vacuum spraying methods form a heterogeneous structure 10 of nano- and micro-sized films of materials containing thin-film dielectric, strain-resisting and contact layers. So, for example, figure 4 presents a heterogeneous structure 10 formed on the flat surface of the membrane 6, which serves as a substrate. It was applied by vacuum spraying on a chromium sublayer (Cr) 24, a first dielectric layer (SiO) 25, a second dielectric layer (SiO ₂ ,) 26, a resistive layer (Ni-Ti) 27, and a contact layer (V-Au) 28.

The first layer, the chromium sublayer (Cr) 24, serves, firstly, as a buffer between the elastic element and the dielectric to relieve temperature stresses arising during the deposition process, and, secondly, ensures the adhesion of the dielectric film with the material of the elastic element. The thickness of the sublayer is 150-300 nm.

The second and third layers (25 and 26) are dielectric (SiO-SiO ₂ ). A dielectric film of dielectric layers must have insulation resistance at voltages up to 100 V - at least 1000 MΩ, have a dielectric loss tangent at a frequency of 1 kHz of not more than 80 · 10 ^-4 ; adhesion to a metal substrate, characterized by a peel force, must be at least 80 g / mm.

The fourth is the strain gauge layer. Its thickness is 40 ... 100 nm. Strict requirements are imposed on it: maximum coefficient of strain sensitivity; good adhesion with the dielectric layer and the material of the contact groups; high mechanical characteristics. The output parameters of the strain gauge pressure sensor directly depend on changes in the resistance of the strain gauges in the bridge circuit [3]. To ensure stable operation of the pressure sensor, the material of the strain gauges must maintain its properties under the influence of elevated temperatures and unsteady heat fluxes. Therefore, the value of the temperature coefficient of resistance (TCR) of the material used strain gauges should be close to zero in a wide temperature range. As the material of the strain gauge layer, an alloy X20H75YU is usually used. However, the best results can be obtained by the proposed method using an amorphous Ni-Ti compound.

The fifth layer is the contact group (pads, jumpers, conductors). The following requirements are imposed on it: low resistivity; good adhesion and low transition resistance with a strain gauge material; low level of heat and electromigration; good weldability with lead-out conductors with a minimum thickness; wide range of operating temperatures; low oxidation when exposed to operating temperatures and over time. As the contact group may be the structure of V-Au.

After the heterostructure is formed using photolithography and etching, a bridge measuring circuit of a thin-film NiMEMS strain gauge pressure sensor is formed, as, for example, in [3].

, где j_Ni и j_Ti - плотности токов магнетронного разряда на мишенях из Ni и Ti. После этого упругий элемент 6 с нанесенным на него тензорезистивным слоем выдерживают в вакууме при температуре 370°C в течение 5-6 часов.A distinctive feature of the proposed method is that the resistive layer is formed by magnetron sputtering in a vacuum chamber while using a carousel 19 and two targets 16 and 17 of nickel (Ni) and titanium (Ti) in an argon working gas medium. As materials of targets 16 and 17, nickel of 99.99% purity and titanium of 99.9% purity can be used. According to this method, the elastic element - the membrane 6 (figure 2) with a dielectric layer formed on it - layers 25 and 26 (figure 4) is installed on the carousel 19 (figure 3). The carousel 19 with the elastic element 6 installed on it is heated to a temperature of 180-200 ° C, an argon pressure of 6.5 · 10 ^-3 mm Hg is created, and then the carousel 19 (FIG. 3) is rotated with the elastic element 6 (FIG. .2) at a speed of 50-60 rpm for 10 minutes. At the same time, the current densities in the spray zones of the first 16 and second 17 targets are set (Fig. 3), based on the ratio

, where j _Ni and j _Ti are the current densities of a magnetron discharge on targets from Ni and Ti. After that, the elastic element 6 with the applied strain gauge layer is kept in vacuum at a temperature of 370 ° C for 5-6 hours.

Targets 16 and 17 (figure 3) perform the same thickness (for example, 6 mm) and the same radius (for example, r _Ti = r _Ni = 6 cm). The elastic element - the membrane 6 with the dielectric layers 25 and 26 formed on it (FIG. 4) is conveniently placed in the holders of the substrates 21, after which they are mounted on the carousel 19. The distance from the magnetron sputtering sources - targets 16 and 17 to the holders of the substrates 21 with elastic element 6 is set equal to h = 0.05 m. Before the argon is introduced into the vacuum chamber and the working gas (argon) medium is created, the chamber is evacuated to a residual gas pressure of no more than 2 · 10 ^-5 mm Hg.

The current densities j _Ni and j _Ti in the spray zones of the first 16 and second 17 targets (Fig. 3) are set by the magnetron sputtering mode control unit. After the magnetron sputtering regime is established, the carousel 19 (FIG. 3) is rotated with the elastic element 6 (FIG. 2) at a given speed and time. The elastic element 6 with the applied strain gauge layer is kept in vacuum at a temperature of 370 ° C for 5-6 hours to stabilize the parameters (TCS and resistance).

. При этом температурный коэффициент сопротивления (ТКС) принимает отрицательные значения от минус 10^-5 °C^-1 до минус 5·10^-6 °C^-1 (в диапазоне температур от минус 70°C до 200°C). Удельные поверхностные сопротивления ρ_S образцов с тензорезистивными слоями Ni-Ti составили ~30 Ом/квадрат. Эксперимент проводился при плотности тока на мишени из Ti, j_Ti=1·10^-3 [А/см²] и плотности тока на мишени из Ni: j_Ni=0,3j_Ti=0,3·10^-3 [А/см²].It has been experimentally established that Ni-Ti films (strain-resistant layers) of a thickness of ~ 70 nm are obtained by arranging a carousel at a distance of 0.05 m from nickel (Ni) and titanium (Ti) targets, heating an elastic element with a dielectric layer formed on it to a temperature 180-200 ° C, creating argon pressure of 6.5 · 10 ^-3 mm Hg, rotating the carousel at a speed of 50-60 rpm for 10 minutes, and then holding the elastic element coated with a strain gauge layer in vacuum at a temperature of 370 ° C for 5-6 hours. For this, it is necessary to set the current densities in the spray zones based on the ratio

. In this case, the temperature coefficient of resistance (TCS) takes negative values from minus 10 ^-5 ° C ^-1 to minus 5 · 10 ^-6 ° C ^-1 (in the temperature range from minus 70 ° C to 200 ° C). The specific surface resistances ρ _{S of} samples with strain-resistant Ni-Ti layers were ~ 30 Ω / square. The experiment was carried out at a current density on a target of Ti, j _Ti = 1 · 10 ^-3 [A / cm ² ] and a current density on a target of _Ti : j _Ni = 0.3j _Ti = 0.3 · 10 ^-3 [A / cm ² ].

The current densities j _Ni and j _Ti , on targets of Ni and Ti (the density of ion currents on targets in a cross section perpendicular to the direction of incidence of ions), were determined by the formula:

where I is the magnetron discharge current, A; S is the area of the sprayed surface of the target, cm ² .

The area of the sprayed surface of the target was determined from the expression (figure 5):

In a specific case, the sputtering areas had the following values: for a target of titanium (Ti) - 83.7 cm ² for a target of nickel (Ni) - 52.8 cm ² .

The obtained low value of TCS is explained as follows. Bicomponent films, such as Ni-Ti, obtained by simultaneous spraying of pure metals, have an amorphous dispersed structure. The presence of dispersion in the structure of the films makes it possible to consider, to a first approximation, their electrical resistance as the total resistance of individual granules and the barriers between them (Matisen rule [4]), in which the nature of the total resistance determines the value of the TCS. In a pure nickel (Ni) film, the resistance of the grains themselves is predominant, the conductivity of the film is metallic and the TCR is therefore positive. On the other hand, in a pure titanium (Ti) film, the resistance is due to the passage of electrons through the gaps between the grains, the conductivity is semiconductor in nature and the TCS is therefore reduced to values from minus 10 ^-5 ° C ^-1 to minus 5 · 10 ^-6 ° C ^-1 .

на мишенях из Ni и Ti получается отрицательное значение ТКС менее минус 10^-5 °C^-1 (величины поверхностного сопротивления пленок Ni-Ti получаются ~30 Ом/квадрат), что лучше, чем у аналогов и прототипа. При соблюдении указанного отношения представляется возможным изготавливать тензорезистивные слои Ni-Ti с низким отрицательным значением ТКС, а следовательно и тензорезисторы, с низкой температурной чувствительностью. Благодаря отрицательным значениям ТКС тензорезисторов, получаемых по предлагаемому способу из пленки Ni-Ti, представляется возможным осуществлять компенсацию температурной погрешности мостовой измерительной цепи, в которой имеются навесные элементы с положительными значениями ТКС.Thus, with respect to current densities

on targets from Ni and Ti, a negative TCS value of less than minus 10 ^-5 ° C ^{-1 is} obtained (the surface resistance of Ni-Ti films is ~ 30 Ohm / square), which is better than that of analogues and prototype. Subject to the indicated relationship, it seems possible to produce Ni-Ti strain gauge layers with a low negative TCR value, and hence strain gauge resistors, with low temperature sensitivity. Due to the negative values of the TCS of the strain gages obtained by the proposed method from the Ni-Ti film, it seems possible to compensate for the temperature error of the bridge measuring circuit, in which there are mounted elements with positive values of the TCS.

The proposed method of manufacturing a thin-film nano- and microelectromechanical system of a high-temperature sensor of mechanical quantities compares favorably with those previously known. With its help, it seems possible to expand the temperature range of the sensor, increase the reproducibility of such parameters of strain gauges as electrical resistance and temperature coefficient of resistance (TCS), reduce the temperature sensitivity of the sensors. And in the end - to produce mechanical value sensors based on thin-film NiMEMS with a lower temperature error in a wide temperature range. This method can be widely used for the manufacture of thin-film NiMEMS sensors of mechanical quantities (pressure, force, acceleration, etc.).

Information sources

1. Belozubov E.M., Vasil′ev V.A., Gromkov N.V. Thin-film nano- and micro-electromechanical systems - the basis of contemporary and future pressure sensors for rocket and aviation engineering // Measurement Techniques. - USA, New York: Springer, 2009 .-- V. 52. - N7 - P.739-744.

2. Volokhov IV, Peskov E.B., Popchenkov D.V. RF patent No. 2326460 H01C 17/00, G01L 7/08. A method of manufacturing a high temperature thin film resistor. Publ. 06/10/2008. Bull. No. 16.

3. Belozubov EM, Vasiliev V.A., Chernov P.S. RF patent No. 2398195 G01L 9/04, B82B 3/00. A method of manufacturing a nano- and microelectromechanical system of a pressure sensor and a pressure sensor based on it. Publ. 08/27/2010. Bull. Number 24.

4. Pasynkov V.V., Sorokin B.C. Materials of electronic technology Textbook. for stud. universities for special. electronic technology. 3rd ed. - St. Petersburg: Publishing House "Lan", 2001. - 368 p.

Claims (1)

1. A method of manufacturing a thin-film nano- and microelectromechanical system of a high-temperature sensor of mechanical quantities, which consists in the fact that on the planar side of the elastic element by vacuum spraying methods form a heterogeneous structure of nano- and micro-sized films of materials containing thin-film dielectric, strain-resisting and contact layers, after which using photolithography and etching form strain cells (strain gauges), contact conductors and contact pads to them, different This is because the strain-resisting layer is formed by magnetron sputtering in a vacuum chamber simultaneously from two separate sources at magnetron discharge current densities j _Ni and j _Ti on targets from Ni and Ti, which are previously determined by the ratio

wherein the elastic element with the dielectric layer formed on it is mounted on a carousel located at a distance of 0.05 m from the targets, heated to a temperature of 180-200 ° C, create an argon pressure of 6.5 · 10 ^-3 mm Hg, and then a carousel with an elastic element is rotated at a speed of 50-60 rpm for 10 minutes, after which the elastic element with a tensoresistive layer deposited on it is kept in vacuum at a temperature of 370 ° C for 5-6 hours.

Images