rus
Issue #5/2024
S.А.Zhukova, D.Yu.Obizhaev, S.А.Ulyanov, М.А.Zinoviev, D.D.Riskin, S.Yu.Suzdaltsev, Y.N.Frolov, Yu.А.Gantseva
DEVELOPMENT OF MICROMECHANICAL LINEAR ACCELERATION SENSORS AND THEIR SERIAL INDUSTRIAL ENGINEERING
DEVELOPMENT OF MICROMECHANICAL LINEAR ACCELERATION SENSORS AND THEIR SERIAL INDUSTRIAL ENGINEERING
DOI: https://doi.org/10.22184/1993-8578.2024.17.5.282.290
In SRC RF FSUE "Central Research Institute of Chemistry and Mechanics" has been developed a line of micromechanical linear acceleration sensors. The line includes sensors of three versions MMA-2, MMA-10 and MMA-30 with conversion ranges of ±20 m/s2, ±100 m/s2 and ±300 m/s2 respectively. The sensors are intended for use as part of orientation, stabilisation and navigation systems in various products. The full range of tests confirming the declared technical characteristics and resistance to external influences has been carried out, and the operating design documentation for serial industrial engineering has been approved. The planned production value of these sensors is several thousand pieces per year.
In SRC RF FSUE "Central Research Institute of Chemistry and Mechanics" has been developed a line of micromechanical linear acceleration sensors. The line includes sensors of three versions MMA-2, MMA-10 and MMA-30 with conversion ranges of ±20 m/s2, ±100 m/s2 and ±300 m/s2 respectively. The sensors are intended for use as part of orientation, stabilisation and navigation systems in various products. The full range of tests confirming the declared technical characteristics and resistance to external influences has been carried out, and the operating design documentation for serial industrial engineering has been approved. The planned production value of these sensors is several thousand pieces per year.
Теги: accelerometer capacitive sensor mems sensor calibration sensor packaging sensor test акселерометр емкостной датчик испытания датчиков калибровка датчиков мэмс сборка датчиков
INTRODUCTION
Micromechanical linear acceleration sensors are widely used in platform-free navigation systems (PFNS). They can provide high sensitivity, time and temperature stability of parameters in combination with high resistance and robustness to external influences, small size and low power consumption. One of the most efficient designs is the micromechanical accelerometer, which uses an all-silicon miniature capacitive-type transducer with a pendulum suspension as a sensing element. This design has been used by accelerometer developers since the nineties of the last century and allows to provide low temperature and time drift, high resistance and durability to external influences. Examples of designs and methods of their manufacture are described in [1–5].
In the Russian Federation, in spite of considerable interest on the part of organisations-developers of inertial devices and products based on them, there is no serial production of micromechanical linear acceleration sensors. At the same time, precision sensors are not supplied due to export restrictions.
Thus, development of a line of precision miniature micromechanical linear acceleration sensors and organizing of their serial production is an urgent task. In addition, one of the most important tasks during developing was to exclude the use of foreign-made materials and purchased component parts (hereinafter – PCP) in the created design.
FEATURES AND KEY ELEMENTS OF SENSOR DESIGN AND MANUFACTURING TECHNOLOGY
Each sensor includes electronic subsystem of "capacitance-voltage" conversion, micromechanical pendulum sensing element (SE), mounted in hermetically sealed gas-filled metal-ceramic housing with information outputs.
Measurement of acceleration is provided as a result of formation of the output analogue signal proportional to the change in electrical capacitance of the SE due to the action of the inertia force along the sensing axis.
Sensors of all three versions have the same principle of operation, are designed using a single set of PCI and differ only in the characteristics of the SE.
The SE is made of low-resistance silicon wafers with a diameter of 100 mm and represents a micromechanical structure based on three hermetically connected silicon elements – the central movable electrode and the outermost fixed electrodes. An inertial mass is made in the central plate by liquid anisotropic etching, connected to the sealing frame by means of an elastic suspension [6]. The upper and lower plates are connected to the central electrode by direct splicing (without adhesive) through a silicon dioxide layer. On the surface of the upper and lower electrodes, four dielectric silicon dioxide-based inertial mass movement limiters are formed each. They provide electrical isolation of the inertial mass from the electrode surface in case of its large deviation from the equilibrium position. Aluminium contacts are formed on the non-sealed part of the each electrode structure. At the last stage of fabrication, the wafers are separated into crystals by disc cutting. Fig.1 shows images of the wafer containing the SE before separation into crystals and the SE prepared for sensor assembly.
At the next stage the sensors are assembled. In this case, due to the need to ensure low temperature drift in a wide temperature range (-60 ÷ +85 °C), the technological process of assembly is of crucial importance. The developed assembly technology provides a minimum level of deformations of the SE in the whole operating temperature range caused by deformation of the ceramic base of the housing. This is achieved by using a specialised elastic adhesive, methods of its application and SE installation. Fig.2 shows a microphotograph of the sensors at the assembly stage.
When sealing these sensors, special attention is paid to ensuring a minimum level of moisture in their underbody volume. The process is carried out in nitrogen atmosphere with moisture content not exceeding 1 ppm, using specialised equipment, which also provides possibility of long-term degassing of housing elements at elevated temperature before their sealing. Fig.3 shows a photo of the equipment for sensor sealing processes.
Once the sealing process is complete, all sensors are tested for leaks and submitted for the calibration process.
SENSOR CALIBRATION AND TESTING
The calibration process is performed using a hardware-software complex based on a laboratory centrifuge, which implements an automated algorithm for selecting the configuration parameters of the electronic subsystem that ensure the minimum level of nonlinearity of the sensor output signal. Fig.4 shows photos of a fragment of the hardware-software complex and a set of measuring equipment.
It should be noted that the product is also equipped with a built-in temperature sensor, the readings of which are transmitted as an analogue signal and can be used for thermal compensation. The characteristics of the built-in temperature sensor are not standardised by the manufacturer.
After calibration, these sensors are subjected to a set of acceptance tests. Each sensor undergoes control of fourteen parameters that fully characterise suitability of the product operation. The values of the parameters confirmed during the tests for each sensor version are presented in Table No. 1 [7, 8]. Fig.5 shows photos of sensors in preparation for the control of zero offset variation in the operating temperature range.
During developing of durability and resistance of manufactured sensors to external influences (mechanical and climatic) were confirmed. The obtained values are presented in Tables 2 and 3.
After acceptance, tested sensors are labelled, packed and sealed. Packaging consists of group consumer packaging in the form of a matrix-type spoon made of antistatic plastic and transport packaging in the form of a box made of corrugated cardboard. Fig.5 shows photos of MMA-2 sensors after labelling and during packing.
The sensors are manufactured under the QC. Within the framework of the development, the working design documentation was approved for organisation of serial production of sensors. The technological and testing base available in SRC RF FSUE "Central Research Institute of Chemistry and Mechanics" provides possibility of serial production of linear acceleration sensors with the production volume of several thousand pieces per year.
POSSIBLE DIRECTIONS FOR IMPROVING SENSOR PERFORMANCE
The analysis of the data obtained during development showed that further improvement of the sensor characteristics (output noise, parameter instability) is limited by the characteristics of the applied electronic subsystem. At the same time, as a result of mathematical modelling it has been established that in case of using the SE in the compensatory mode it is possible to reduce these parameters by one decimal order. Thus, implementation of an electronic subsystem providing a compensatory mode of operation of the SE is a priority direction for improving the characteristics of micromechanical linear acceleration sensors. In turn, the improvement of the SE can be aimed at increasing its resistance to shock impact by optimising the parameters of dielectric inertial mass displacement limiters.
CONCLUSIONS
SRC RF FSUE "Central Research Institute of Chemistry and Mechanics" has created a line of micromechanical linear acceleration sensors with conversion ranges of ±20 m/s2, ±100 m/s2 and ±300 m/s2 with the acceptance of the QC. The sensors are made on the basis of Russian-made materials and components. The created sensors combine small dimensions (the occupied area is less than 1 cm2) and power consumption (less than 1 mA at supply voltage of 3.3 V) with sufficiently high performance characteristics, wide range of operating temperatures (-60 ÷ +85 °C) and other external influences. The available technological and testing base in SRC RF FSUE "Central Research Institute of Chemistry and Mechanics" provides possibility of serial production of linear acceleration sensors with the production volume at the level of 1000 pieces per year.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Micromechanical linear acceleration sensors are widely used in platform-free navigation systems (PFNS). They can provide high sensitivity, time and temperature stability of parameters in combination with high resistance and robustness to external influences, small size and low power consumption. One of the most efficient designs is the micromechanical accelerometer, which uses an all-silicon miniature capacitive-type transducer with a pendulum suspension as a sensing element. This design has been used by accelerometer developers since the nineties of the last century and allows to provide low temperature and time drift, high resistance and durability to external influences. Examples of designs and methods of their manufacture are described in [1–5].
In the Russian Federation, in spite of considerable interest on the part of organisations-developers of inertial devices and products based on them, there is no serial production of micromechanical linear acceleration sensors. At the same time, precision sensors are not supplied due to export restrictions.
Thus, development of a line of precision miniature micromechanical linear acceleration sensors and organizing of their serial production is an urgent task. In addition, one of the most important tasks during developing was to exclude the use of foreign-made materials and purchased component parts (hereinafter – PCP) in the created design.
FEATURES AND KEY ELEMENTS OF SENSOR DESIGN AND MANUFACTURING TECHNOLOGY
Each sensor includes electronic subsystem of "capacitance-voltage" conversion, micromechanical pendulum sensing element (SE), mounted in hermetically sealed gas-filled metal-ceramic housing with information outputs.
Measurement of acceleration is provided as a result of formation of the output analogue signal proportional to the change in electrical capacitance of the SE due to the action of the inertia force along the sensing axis.
Sensors of all three versions have the same principle of operation, are designed using a single set of PCI and differ only in the characteristics of the SE.
The SE is made of low-resistance silicon wafers with a diameter of 100 mm and represents a micromechanical structure based on three hermetically connected silicon elements – the central movable electrode and the outermost fixed electrodes. An inertial mass is made in the central plate by liquid anisotropic etching, connected to the sealing frame by means of an elastic suspension [6]. The upper and lower plates are connected to the central electrode by direct splicing (without adhesive) through a silicon dioxide layer. On the surface of the upper and lower electrodes, four dielectric silicon dioxide-based inertial mass movement limiters are formed each. They provide electrical isolation of the inertial mass from the electrode surface in case of its large deviation from the equilibrium position. Aluminium contacts are formed on the non-sealed part of the each electrode structure. At the last stage of fabrication, the wafers are separated into crystals by disc cutting. Fig.1 shows images of the wafer containing the SE before separation into crystals and the SE prepared for sensor assembly.
At the next stage the sensors are assembled. In this case, due to the need to ensure low temperature drift in a wide temperature range (-60 ÷ +85 °C), the technological process of assembly is of crucial importance. The developed assembly technology provides a minimum level of deformations of the SE in the whole operating temperature range caused by deformation of the ceramic base of the housing. This is achieved by using a specialised elastic adhesive, methods of its application and SE installation. Fig.2 shows a microphotograph of the sensors at the assembly stage.
When sealing these sensors, special attention is paid to ensuring a minimum level of moisture in their underbody volume. The process is carried out in nitrogen atmosphere with moisture content not exceeding 1 ppm, using specialised equipment, which also provides possibility of long-term degassing of housing elements at elevated temperature before their sealing. Fig.3 shows a photo of the equipment for sensor sealing processes.
Once the sealing process is complete, all sensors are tested for leaks and submitted for the calibration process.
SENSOR CALIBRATION AND TESTING
The calibration process is performed using a hardware-software complex based on a laboratory centrifuge, which implements an automated algorithm for selecting the configuration parameters of the electronic subsystem that ensure the minimum level of nonlinearity of the sensor output signal. Fig.4 shows photos of a fragment of the hardware-software complex and a set of measuring equipment.
It should be noted that the product is also equipped with a built-in temperature sensor, the readings of which are transmitted as an analogue signal and can be used for thermal compensation. The characteristics of the built-in temperature sensor are not standardised by the manufacturer.
After calibration, these sensors are subjected to a set of acceptance tests. Each sensor undergoes control of fourteen parameters that fully characterise suitability of the product operation. The values of the parameters confirmed during the tests for each sensor version are presented in Table No. 1 [7, 8]. Fig.5 shows photos of sensors in preparation for the control of zero offset variation in the operating temperature range.
During developing of durability and resistance of manufactured sensors to external influences (mechanical and climatic) were confirmed. The obtained values are presented in Tables 2 and 3.
After acceptance, tested sensors are labelled, packed and sealed. Packaging consists of group consumer packaging in the form of a matrix-type spoon made of antistatic plastic and transport packaging in the form of a box made of corrugated cardboard. Fig.5 shows photos of MMA-2 sensors after labelling and during packing.
The sensors are manufactured under the QC. Within the framework of the development, the working design documentation was approved for organisation of serial production of sensors. The technological and testing base available in SRC RF FSUE "Central Research Institute of Chemistry and Mechanics" provides possibility of serial production of linear acceleration sensors with the production volume of several thousand pieces per year.
POSSIBLE DIRECTIONS FOR IMPROVING SENSOR PERFORMANCE
The analysis of the data obtained during development showed that further improvement of the sensor characteristics (output noise, parameter instability) is limited by the characteristics of the applied electronic subsystem. At the same time, as a result of mathematical modelling it has been established that in case of using the SE in the compensatory mode it is possible to reduce these parameters by one decimal order. Thus, implementation of an electronic subsystem providing a compensatory mode of operation of the SE is a priority direction for improving the characteristics of micromechanical linear acceleration sensors. In turn, the improvement of the SE can be aimed at increasing its resistance to shock impact by optimising the parameters of dielectric inertial mass displacement limiters.
CONCLUSIONS
SRC RF FSUE "Central Research Institute of Chemistry and Mechanics" has created a line of micromechanical linear acceleration sensors with conversion ranges of ±20 m/s2, ±100 m/s2 and ±300 m/s2 with the acceptance of the QC. The sensors are made on the basis of Russian-made materials and components. The created sensors combine small dimensions (the occupied area is less than 1 cm2) and power consumption (less than 1 mA at supply voltage of 3.3 V) with sufficiently high performance characteristics, wide range of operating temperatures (-60 ÷ +85 °C) and other external influences. The available technological and testing base in SRC RF FSUE "Central Research Institute of Chemistry and Mechanics" provides possibility of serial production of linear acceleration sensors with the production volume at the level of 1000 pieces per year.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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