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An improvement of micromechanical accelerometers (MMA) is relevant due to the constant expansion of their applications and the use of such devices in increasingly demanding conditions. In the paper the sandwich designs of the sensitive element (SE) of a capacitive micromechanical accelerometer (MMA) with folded springs have been studied from the point of view of ensuring the high sensitivity to acceleration, resistance to temperature change and the presence of residual mechanical stresses in the structures while providing the relative simplicity of their manufacturing technology. The modeling has been executed in ANSYS program. The gaps between the movable and stationary electrodes are increased compared to analogs up to 20 microns. It has been shown that the high sensitivity to changes of the acceleration is provided due to the optimization of the sensitive element design, using folded springs with lower values of stiffness coefficient. It has been determined that the capacity change under the action of acceleration along the working axis ( Z ) is almost 20 times more than changes in capacity along axes X and Y and the effect of temperature in the range of -40 ºC to 85 ºC on changes in capacitances along the working axis ( Z ) is small ±0.0025 - 0.003 pF. The mechanical stresses, which occur in constructive elements of the sensitive element under acceleration to 50 g, do not exceed 2.29 MPa, while silicon has strength 440 MPa. The natural frequency of oscillation of the second mode of the sensitive MMA does not affect the natural frequency of oscillation of the first mode of the sensitive element due to a significant difference of these frequencies approximately by 2 kHz. The analysis has shown that the studied sandwich constructions are characterized by high sensitivity and stability of parameters with relatively simple manufacturing.
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In micro-electromechanical systems the resonators are used in the construction of generators, sensors of inertial navigation systems, in RF transceivers, for increasing the sensitivity (acoustic, biological, mechanical, etc.). In this paper the change in the natural frequency of four characteristic resonators under the influence of mechanical force has been investigated and the simulation results in the ANSYS program have been presented. The effect of thermoplastic damping on the natural frequencies of the resonator, which occurs as a result of the mechanical oscillation of the resonator, as well as the residual stress, arising in the structure of the resonator due to the difference in manufacturing technique, has been investigated. The Q-factors of these resonators have been calculated using the COMSOL program and the optimum resonator design have been chosen to increase the sensitivity of the frequency microaccelerometer. The obtained results are assumed to be used in real constructions of the micro-electromechanical devices to be developed.
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The frequency micromechanical accelerometer (MMA) measures the acceleration, based on a change of the resonator frequency, when the acceleration is caused by the displacement of the inertial mass. Its sensitivity can be influenced by such factors as vibration noise, temperature, etc. In this study using the calculation and modeling in the ANSYS program the influence of the temperature on the natural oscillation frequency of resonators of various designs has been studied. It has been shown that in a number of studied designs of the frequency MMA resonators the frequency change ∆ f , caused by the temperature increase, is comparable and even exceeds a change of the frequency due to the acceleration effect. It has been determined that the known designs of the resonators, operating based on the oscillations of a two-fixed beam, do not ensure the stability of the oscillations natural frequency with the temperature change. The frequency, due to the temperature increase, of the resonators, working on the cantilever beam base, practically does not change. The best result from the point of view of the temperature stability has been shown by the resonator in the form of a cantilever beam with the beam resonator inside it, for which change ∆ f with an increase of temperature up to 70 °C. The study of the basic MMA construction, consisting of an inertial mass with a resonator made in the form of a cantilever beam with a beam resonator inside it has shown that the invariance of the natural oscillation frequency of this construction when the temperature increases up to 70 °C.
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In high-efficient MMA-accelerometers the capacitive principle of measurement is used. In addition, in this connection a low level of noises and energy consumption, economical efficiency and reliability are provided. The capacitive sensitive elements, based on changing the clearance, require, as a rule, the control with feedback, which increases the complexity of the measurement circuit and energy consumption. The capacitive sensitive elements with changing the area of the electrodes overlapping have a good linearity of the capacitance dependence on movement and large range of measurements, but their fabrication is more complicated. In the paper a model of a sensitive element of a microelectromechanical capacitive accelerometer with sandwich construction has been presented and analyzed. The operation of the sensitive element is based on using the changes in the relative permittivity of the dielectric capacitors due to the introduction of a moving inertial mass between the moving capacitor electrodes under the action of acceleration. As a result, there is a change of capacitance in the output measuring circuit. It has been shown that the model considered provides high sensitivity to acceleration, resistance to temperature changes and low residual mechanical stress in the sensitive element. Modeling and calculations have been performed with using the Ansys and SolidWorks programs. It has been obtained that the movement of movable mass along the axis of sensitivity X 5 times exceeds the movement of the movable mass along the non-working axes, and the capacitance changes between the electrodes along the X-axis is 2500 times greater than the capacitance changes between the electrodes on the non-working axes Z and Y. The calculations have shown that for all values of acting acceleration (up to 30 g) the mechanical stress in the sensitive element is significantly less than the strength limit of silicon, equal to 440 MPa. It has been determined that the temperature variations in the range from -40 to +85 C have led to insignificant changes of capacitance along the working axis (0.0025 - 0.003pF). This demonstrates the temperature stability of work of the sensitive element. The analysis has shown that the developed and studied model of the sensitive element sandwich construction provides the high sensitivity of MMA accelerometer and stability of its parameters.
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In microelectromechanical devices and systems (MEMS), capacitive micromechanical accelerometers (MMA) are used in airbag systems, machine vibration monitoring, navigation, seismology, microgravity measurements, etc. The most important structural elements of the sensing element are suspensions, through which the inertial mass is connected to a fixed frame. To ensure reliable operation and stability of sensor parameters, it is necessary to take into account the results of external factors already at the design stage of the sensor structure, especially its sensitive element, and at subsequent stages of the life cycle. In this work, the characteristic structures of suspension elements, which are made of silicon with different crystallographic orientations, are investigated and the results of modeling their most important parameters are presented. The simulation has been performed using the ANSYS program. The natural frequencies of inertial mass oscillations, residual mechanical stresses in the structural elements of silicon sensitive element with different crystallographic orientations have been calculated upon impact (up to 10 000 g). The natural vibration frequency changes and the dynamics of the change in the residual mechanical stress in the suspension elements with a temperature change in the range from +150 to -150 °C for a short time interval of 10 s, which corresponds to thermal shock, investigated. The results of studies of residual mechanical stresses arising upon impact and natural frequencies of inertial mass oscillations have been made it possible to develop recommendations on the choice of the design of suspension elements made of silicon, providing high sensitivity and stability of MMA parameters. It has been established that the use of folded springs with a rectangular or round cross-sectional shape with a suspension element thickness of 40 μm provides the highest temperature stability of the parameters. The results obtained are useful for developing real designs of MMA and other micromechanical devices
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In the context of increasing the electronic components integration level, growing functionality and packaging density, as well as reducing the electronics weight and size, an integrated approach to engineering calculations of parts and assemblies of modern functionally and technically complex microelectronic products is required. Of particular importance are engineering calculations and structural modeling using computer-aided engineering systems, and also assessment of structural, technological and operational factors’ impact on the products reliability and performance. This work presents an approach to engineering calculations and microelectronic products modeling based on the finite-element method providing a comprehensive account of various factors (material properties, external loading, temperature fields, and other parameters) impact on the stress-strain state, mechanical strength, thermal condition, and other characteristics of products. On the example of parts and assemblies of products of microelectronic technology, the approximation of structures was shown and computer finite-element models were developed to study various structural and technological options of products and the effects on them. Engineering calculations and modeling of parts and assemblies were performed, taking into account the impact of material properties, design parameters and external influences on the products’ characteristics. Scientific and technical recommendations for structure optimization and design and technology solutions ensuring the products resistance to diverse effects were developed. It has been shown that an integrated approach to engineering calculations and microelectronic products modeling based on the finite-element method provides for the determination of optimal solutions taking into account structural, technological, and operational factors and allows the development of products with high tactical, technical and operational characteristics.
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The parameters of the well-known MEMS have been investigated, the promising building the orientation systems based on MEMS has been shown. The influence of the total measurement system error on the accuracy of the motion parameter determination by an autonomous orientation system has been studied.
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For modern information, measuring and optoelectronic systems based on micro-and nanomechanical sensors of angular velocity and linear acceleration it is important to ensure their stable operation in presence of external factors. In the work the results of the study on the effect of random vibration on the characteristics experimental samples of micromechanical accelerometers (MMA), obtained using the LDS V455 vibration stand, have been presented. The dependence of the vibroacceleration on the frequency of one of the samples, intended for measurement of the acceleration in the range of up to ±1.2 g, has a noticeable shift from its given profile. Therefore, to determine the causes of the discrepancy, the design of the sensing element (CHE) MMA, the effect of random vibration on it, the calculations and simulation in the ANSYS program have been performed. The calculations and simulation have been executed in the ANSYS program. The deformation e of this MMA along the z axis of sensitivity and capacitance changes under the influence of acceleration and random vibration along the X , Y and Z axes have been determined taking into account the crystallographic orientation of the silicon-CHE material. When performing the calculations and modeling, the influence of the crystallographic orientation, used for manufacturing CHE MMA as a structural material of silicon, has been considered, since it affects the deformation (deviation) of the rotor, which should be taken into account by designers-developers of MEMS sensors. The results of the theoretical and experimental research and computer modeling have been presented.
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Various types of parasitic influences must be considered at the stage of designing sensitive element of a micromechanical capacitive accelerometer (MMA) and the whole MMA construction, and throughout its lifecycle stages, to ensure consistent performance and parameter stability of MMA. Due regard to actual operating conditions is a primary consideration for designers. In this work, the influence of random vibration on the functioning of a 2-electrode sensitive element of an MMA with a sandwich construction using the principle of operation based on a change in the relative dielectric constant of a capacitor dielectric under acceleration was investigated. In the structure of the investigated sensitive element with one axis of sensitivity, the inertial mass is suspended on folded springs and is located between two fixed electrodes. Using the Ansys program, the deformations of the inertial mass of the sensitive element and the change in the capacity in the sensitive element were calculated, which occur when it is exposed to acceleration up to 5 g along the working axis and up to 50 g along the non-working axes and random vibration along the working axis X and along the non-working axes Y and Z . The random vibration affecting the sensitive element had a profile, the frequency of which was 20 Hz at 0.01 g / Hz, the frequency from 80 to 350 Hz at 0.04 g / Hz, 2000 Hz at 0.01 g / Hz. The changes in the capacity in the sensitive element of MMA under the influence of random vibration on it were calculated. Results have been obtained that confirm the performance of the sensitive element of MMA under conditions of significant impacts along non-working axes. The investigated sensitive element model requires further refinement to be used under conditions of exposure to random vibration.
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ICP plasma-chemical reactor of ICP type has been investigated using the plasma diagnostics probe methods. The evaluation of the plasma density in the substrate area with the different process parameters has been performed. The potential self bias on the surface of glass substrates with different thickness, and the uniformity of the ion current density distribution over the plate diameter, have been measured. The recipe of the deep silicon etching with high uniformity on the whole substrate has been found.
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The results of investigation and development of the characteristics of the micromirror element, driven by a thermal microactuator, have been presented. It has been shown that for calculating the micromirror element deflection it is crucial to take into consideration the temperature distribution along the element length. The superheat temperature calculation has been executed, the effective superheat temperature has been determined, as well as the comparison with the experimental data has been performed.
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The gas damping influence on bandwidth of the pendulum microaccelerometers has been investigated. It has been found that to increase the bandwidth, it is necessary to provide residual pressure of not higher than 1-5ּ10-1 torr inside the packaged device. This condition can be reached by using the developed technology of the glass-to-metal encapsulation.
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The results of investigation and designing of the technological processes of assembling and mounting MEMS components used for manufacturing breadboard samples have been presented.
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The possibilities of adjusting the parameters of the MEMS angular rate ring sensors using the balancing, effected by changing the mass of individual segments of the ring and the optimization of in-situ pressure in the manufacturing process of these devices, have been investigated. The positive results for the test samples have been obtained. An algorithm for performing the balancing by changing the mass of the ring segments, permitting to reduce the difference between the resonance frequency of the ring in different directions, has been proposed.
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When designing MEMS accelerometers, it is necessary to provide the high sensitivity of the instrument, which is directly related to the amplitude of deflection of the inertial mass under the acceleration effect. The inertial mass increase results in the sensor sensitivity increase. The results of the calculation of the spring constant of the micro-mechanical accelerometer folded beam have been presented. The modeling using the ANSYS program, confirming the calculation results, has been performed. The use of the folded beams having compact sizes permits to increase the efficiency of the resonator operation, to achieve greater displacement in direction of the acceleration and stability of the inertial mass in other directions, taking into account the flexibility and rigidity in different directions.
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In microelectromechanical (MEMS) sensors the construction of a comb actuator is used for excitation of the resonator. In this article, we found a refined equation for the calculation of the electrostatic force of such an actuator. With the help of simulation in ANSYS program the effect of overlap amount between the teeth of the combs on the electrostatic force and the capacitance has been studied as well as the changes of the frequency of the resonator when it is exerted by the force. Similar studies have been implemented for a bar construction of the resonator, the usage of which, as comb design with small overlap of teeth, allows to decrease the parasitic electrostatic forces (along axes y , z ) and to increase the sensitivity of the frequency microaccelerometer due to a larger change in the frequency of the resonator oscillations when subjected to forces.
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On the samples of SEF wafers it has been shown that the thickness of oxide films and the surface oxidation conditions demonstrate strong effect upon the electron work function (EWF), measured under atmospheric conditions by technique of the static condenser with the ionized space. The EWF changes are connected with the water sorbed vapors, the quantity of which is determined by the oxide film structure and properties. It has been found that the EWF changes depending on the oxide film type can achieve ~ 20%.
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One of the plausible circuit engineering solutions for the capacitive accelerometers with the differential type sensing element has been considered. The test results of the prototype on a specialized stand have been presented.
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