Micromachining

This paper reports a review about microelectromechanical system (MEMS) microphones. The focus of this review is to identify the issues in MEMS microphone designs and thoroughly discuss the state-of-the-art solutions that have been presented by the researchers to improve performance. Considerable research work has been carried out in capacitive MEMS microphones, and this field has attracted the research community because these designs have high sensitivity, flat frequency response, and low noise level. A detailed overview of the omnidirectional microphones used in the applications of an audio frequency range has been presented. Since the microphone membrane is made of a thin film, it has residual stress that degrades the microphone performance. An in-depth detailed review of research articles containing solutions to relieve these stresses has been presented. The comparative analysis of fabrication processes of single-and dual-chip omnidirectional microphones, in which the membranes are made up of single-crystal silicon, polysilicon, and silicon nitride, has been done, and articles containing the improved performance in these two fabrication processes have been explained. This review will serve as a starting guide for new researchers in the field of capacitive MEMS microphones.

A high-order electromechanical ΣΔ modulator uses additional electronic filtering in the loop to eliminate excessive in-band quantization noise inherently present in second-order implementations. The interface is fabricated in a 0.5μm CMOS process and tested with a gyroscope and accelerometer achieving 1°/s/4Hz and 150μg/Hz of resolution, respectively. Active chip area is 0.9mm2 and the IC consumes a total of 18mW.

This paper reports a review about microelectromechanical system (MEMS) microphones. The focus of this review is to identify the issues in MEMS microphone designs and thoroughly discuss the state-of-the-art solutions that have been presented by the researchers to improve performance. Considerable research work has been carried out in capacitive MEMS microphones, and this field has attracted the research community because these designs have high sensitivity, flat frequency response, and low noise level. A detailed overview of the omnidirectional microphones used in the applications of an audio frequency range has been presented. Since the microphone membrane is made of a thin film, it has residual stress that degrades the microphone performance. An in-depth detailed review of research articles containing solutions to relieve these stresses has been presented. The comparative analysis of fabrication processes of single- and dual-chip omnidirectional microphones, in which the membranes ...

This paper reports the effects of machining parameters on surface roughness in cylindrical wire electrical discharge grinding (WEDG) process. In this research tungsten carbide is used as workpiece. A rotary axis spindle is set up in the electric discharge machine in a submerged dielectric environment so as to machine cylindrical parts. The speed of the spindle is maintained constant at 200 rpm. Experiments have been under different process conditions like peak current, voltage, pulse off time and number of passes. Number of passes in the wire electric discharge grinding decreases the surface roughness.

The recent success of additive manufacturing processes (also called, 3D printing) in the manufacturing sector has led to a shift in the focus from simple prototyping to real production-grade technology. The enhanced capabilities of 3D printing processes to build intricate geometric shapes with high precision and resolution have led to their increased use in the fabrication of microelectromechanical systems (MEMS). The 3D printing technology has offered tremendous flexibility to users for fabricating custom-built components. Over the past few decades, different types of 3D printing technologies have been developed. This article provides a comprehensive review of the recent developments and significant achievements in most widely used 3D printing technologies for MEMS fabrication, their working methodology, advantages, limitations, and potential applications. Furthermore, some of the emerging hybrid 3D printing technologies are discussed, and the current challenges associated with the 3D printing processes are addressed. Finally, future directions for process improvements in 3D printing techniques are presented.

Electrochemical machining is a relatively new technique, only being introduced as a commercial technique within the last 70 years. A lot of research was conducted in the 1960s and 1970s, but research on electrical discharge machining around the same time slowed electrochemical machining research. The main influence for the development of electrochemical machining came from the aerospace industry where very hard alloys were required to be machined without leaving a defective layer in order to produce a component which would behave reliably. Electrochemical machining was primarily used for the production of gas turbine blades or to machine materials into complex shapes that would be difficult to machine using conventional machining methods. Tool wear is high and the metal removal rate is slow when machining hard materials with conventional machining methods such as milling. This increases the cost of the machining process overall and this method creates a defective layer on the machined surface. Whereas with electrochemical machining there is virtually no tool wear even when machining hard materials and it does not leave a defective layer on the machined surface. This article reviews the application of electrochemical machining with regards to micro manufacturing and the present state of the art micro electro-chemical machining considering different machined materials, electrolytes and conditions used.

The recent advances of sensor technologies have been powered by high-speed and low-cost electronic circuits, novel signal processing methods and innovative advances in manufacturing technologies. The synergetic interaction of new developments in these fields allow completely novel approaches increasing the performance of technical products. Innovative sensor structures have been designed permitting self-monitoring or self-calibration. The rapid progress of sensor manufacturing

In this report, capacitive micro pressure sensor’s design and fabrication methods are
examined. For design step SolidWork are used and geometrical constraints are specified by
literature source. The Sensor is working based on capacitance phenomena. Depend on this
phenomena sensor is designed. Fabrication steps are separated by two part one of them is glass
part and second part is SOI Wafer. Steps are briefly explain in fabrication part. In the discussion
part challenging steps are defined.

This paper gives an overview of setting up a rotary axis to the existing WEDM machine to investigate the machining parameters in WEDG of harder materials. There are a number of hybrid machining processes (HMPs) seeking the combined advantage of EDM and other machining techniques. One such combination is wire electrical discharge grinding (WEDG), which is commonly used for micro-machining of fine and hard rods. WEDG employs a single wire guide to confine the wire tension within the discharge area between the rod and the front edge of the wire and also to minimize the wire vibration. Other advantages of WEDG include the ability to machine hard-to-machine materials with large aspect ratio.

This study presents a new suction-type, pneumatically driven microfluidic device for liquid delivery and mixing. The three major components, including two symmetrical, normally closed micro-valves and a sample transport/mixing unit, are integrated in this device. Liquid samples can be transported by the suction-type sample transport/mixing unit, which comprised a circular air chamber and a fluidic reservoir. Experimental results show that volume flow rates ranging from 50 to 300 μl/min can be precisely controlled during the sample transportation processes. Moreover, the transport/mixing unit can also be used as a micro-mixer to generate efficient mixing between two reaction chambers by regulating the time-phased deformation of the polydimethylsiloxane (PDMS) membranes. A mixing efficiency as high as 98.4% can be achieved within 5 s utilizing this prototype pneumatic microfluidic device. Consequently, the development of this new suction-type, pneumatic microfluidic device can be a promising tool for further biological applications and for chemical analysis when integrated into a micro-total analysis system (μ-TAS) device.

This paper presents a method to enhance both the sensitivity and bandwidth of in-plane capacitive micromachined accelerometers by using compliant mechanical amplifiers, and thus obviating the compromise between the sensitivity and bandwidth. Here, we compare one of the most sensitive single-axis capacitive accelerometers and another with large resonant frequency reported in the literature with the modified designs that include displacement-amplifying compliant mechanisms (DaCMs) occupying the same footprint and under identical conditions. We show that 62% improvement in sensitivity and 34% improvement in bandwidth in the former, and 27% and 25% in the latter can be achieved. Also presented here is a dualaxis accelerometer that uses a suspension that decouples and amplifies the displacements along the two in-plane orthogonal axes. The new design was microfabricated, packaged, and tested. The device is 25-μm thick with the interfinger gap as large as 4 μm. Despite the simplicity of the microfabrication process, the measured axial sensitivity (static) of about 0.58 V/g for both the axes was achieved with a cross-axis sensitivity of less than ±2%. The measured natural frequency along the two in-plane axes was 920 Hz. Displacement amplification of 6.2 was obtained using the DaCMs in the dual-axis accelerometer.

The packaging of a medical imaging or therapeutic ultrasound transducer should provide protective insulation while maintaining high performance. For a capacitive micromachined ultrasonic transducer (CMUT), an ideal encapsulation coating would therefore require a limited and predictable change on the static operation point and the dynamic performance, while insulating the high dc and dc actuation voltages from the environment. To fulfill these requirements, viscoelastic materials, such as polydimethylsiloxane (PDMS), were investigated for an encapsulation material. In addition, PDMS, with a glass-transition temperature below room temperature, provides a low Young's modulus that preserves the static behavior; at higher frequencies for ultrasonic operation, this material becomes stiffer and acoustically matches to water. In this paper, we demonstrate the modeling and implementation of the viscoelastic polymer as the encapsulation material. We introduce a finite element model (FEM) that addresses viscoelasticity. This enables us to correctly calculate both the static operation point and the dynamic behavior of the CMUT. CMUTs designed for medical imaging and therapeutic ultrasound were fabricated and encapsulated. Static and dynamic measurements were used to verify the FEM and show excellent agreement. This paper will help in the design process for optimizing the static and the dynamic behavior of viscoelastic-polymer-coated CMUTs.