A Novel MEMS Capacitive Microphone with Semiconstrained Diaphragm Supported with Center and Peripheral Backplate Protrusions

Audio applications such as mobile phones, hearing aids, true wireless stereo earphones, and Internet of Things devices demand small size, high performance, and reduced cost. Microelectromechanical system (MEMS) capacitive microphones fulfill these requirements with improved reliability and specifications related to sensitivity, signal-to-noise ratio (SNR), distortion, and dynamic range when compared to their electret condenser microphone counterparts. We present the design and modeling of a semiconstrained polysilicon diaphragm with flexible springs that are simply supported under bias voltage with a center and eight peripheral protrusions extending from the backplate. The flexible springs attached to the diaphragm reduce the residual film stress effect more effectively compared to constrained diaphragms. The center and peripheral protrusions from the backplate further increase the effective area, linearity, and sensitivity of the diaphragm when the diaphragm engages with these protrusions under an applied bias voltage. Finite element modeling approaches have been implemented to estimate deflection, compliance, and resonance. We report an 85% increase in the effective area of the diaphragm in this configuration with respect to a constrained diaphragm and a 48% increase with respect to a simply supported diaphragm without the center protrusion. Under the applied bias, the effective area further increases by an additional 15% as compared to the unbiased diaphragm effective area. A lumped element model has been also developed to predict the mechanical and electrical behavior of the microphone. With an applied bias, the microphone has a sensitivity of −38 dB (ref. 1 V/Pa at 1 kHz) and an SNR of 67 dBA measured in a 3.25 mm ´ 1.9 mm ´ 0.9 mm package including an analog ASIC.

Microstructural control of ZnO films deposited by RF magnetron sputtering for ultrasound transducers

<p>The aim of this study was to develop a deposition process using RF magnetron sputtering for the production of zinc oxide (ZnO) thin films on glass substrates. These ZnO films were to be used as the active piezoelectric element in very high frequency ultrasound transducers (> 300 MHz). In order to achieve piezoelectric activity the films had to be oriented with the c-axis of the ZnO grains perpendicular to the substrate surface. At the same time, a moderately high, at least 1 m=hr (17 nm=min) deposition rate was required for the production of practical devices. Prior to a full investigation into the sputtering parameters, an initial evaluation of the HHV Auto500 RF magnetron sputter coater system was performed. Using the original chamber configuration it was not possible to deposit ZnO at the required deposition rates. A modification of the growth chamber to allow a reduced target-substrate distance was successful in producing ZnO films at the required deposition rates. A systematic study into the deposition parameters and their effect on the ZnO film quality and deposition rates was then performed and it was found that strong c-axis oriented films could be deposited only when depositing at rates below 15 nm=min at a low substrate temperature (< 50 C). Depositions above this rate resulted in the growth of polycrystalline films. A two-step deposition process was designed to preserve c-axis orientation at high deposition rates up to 28 nm=min. The ZnO films were found to be highly strained due to inherent stress from the sputtering process. The deposition pressure was identified as the most critical deposition parameter for stress control. It was found that deposition above a critical pressure of 1:2 x10-² mbar was essential to prevent mechanical failure of the films. Post growth annealing was investigated and determined to be a viable technique to relax stress and improve the crystalline quality of the films. Finally a four-step deposition process was proposed to facilitate the growth of c-axis oriented ZnO films at relatively high deposition rates whilst minimising film stress.</p>

Microstructural control of ZnO films deposited by RF magnetron sputtering for ultrasound transducers

<p>The aim of this study was to develop a deposition process using RF magnetron sputtering for the production of zinc oxide (ZnO) thin films on glass substrates. These ZnO films were to be used as the active piezoelectric element in very high frequency ultrasound transducers (> 300 MHz). In order to achieve piezoelectric activity the films had to be oriented with the c-axis of the ZnO grains perpendicular to the substrate surface. At the same time, a moderately high, at least 1 m=hr (17 nm=min) deposition rate was required for the production of practical devices. Prior to a full investigation into the sputtering parameters, an initial evaluation of the HHV Auto500 RF magnetron sputter coater system was performed. Using the original chamber configuration it was not possible to deposit ZnO at the required deposition rates. A modification of the growth chamber to allow a reduced target-substrate distance was successful in producing ZnO films at the required deposition rates. A systematic study into the deposition parameters and their effect on the ZnO film quality and deposition rates was then performed and it was found that strong c-axis oriented films could be deposited only when depositing at rates below 15 nm=min at a low substrate temperature (< 50 C). Depositions above this rate resulted in the growth of polycrystalline films. A two-step deposition process was designed to preserve c-axis orientation at high deposition rates up to 28 nm=min. The ZnO films were found to be highly strained due to inherent stress from the sputtering process. The deposition pressure was identified as the most critical deposition parameter for stress control. It was found that deposition above a critical pressure of 1:2 x10-² mbar was essential to prevent mechanical failure of the films. Post growth annealing was investigated and determined to be a viable technique to relax stress and improve the crystalline quality of the films. Finally a four-step deposition process was proposed to facilitate the growth of c-axis oriented ZnO films at relatively high deposition rates whilst minimising film stress.</p>

The effect of material anisotropy on the mechanics of a thin-film/substrate system under mechanical and thermal loads

In this study, the stress analysis for an orthotropic thin film bonded to an orthotropic elastic substrate is addressed using both the analytical and finite element methods. The analytical method employs the integrodifferential formulation with the aid of membrane assumption. Utilizing the finite element method, the effect of orientation of the material principal directions are studied. The loading scenarios include a temperature gradient imposed on the film and a far-field uniaxial tension on the substrate. The results of current study indicate that the ratio of the film to the substrate stiffness plays a leading role in the film stress distribution. For the mechanical loading applied to the substrate, a soft thin film attached to a relatively stiffer substrate is preferred. The film can tolerate the induced thermal stresses as it is bonded to a softer host structure. The rotation angle of material orthotropy directions significantly affects the stress singularity near the film edges up to a certain extent.

Stress Calculations Adopted Finite Element Method of Pressure Steam Pipeline Containing Defects

The stress behavior of defects is the key factor in the safety assessment of pressure steam pipeline containing defects. For achieving carbon peaking and carbon neutrality, high-parameter pressure steam pipelines are widely designed in the recent years. It makes the safety assessment based on defect stresses become significantly important. A combined FEA method of stress calculations was proposed in the present study for calculating film stress and bend stress of defects located in a pressure steam pipeline from a certain power plant. An efficient program code with graphical user interface was designed to automatically generate FEA models of defect part pipelines. It is truly an innovative highlight of the present work attributed to convenient operation and outstanding efficiency. This paper provides an available way to obtain the stress state of defects in the safety assessment of pressure steam pipeline containing defects.