Fabrication

About: Fabrication is a research topic. Over the lifetime, 20475 publications have been published within this topic receiving 235676 citations.

A three-mask process for fabricating vacuum-sealed capacitive micromachined ultrasonic transducers using anodic bonding

Abstract: This paper introduces a simplified fabrication method for vacuum-sealed capacitive micromachined ultrasonic transducer (CMUT) arrays using anodic bonding. Anodic bonding provides the established advantages of wafer-bondingbased CMUT fabrication processes, including process simplicity, control over plate thickness and properties, high fill factor, and ability to implement large vibrating cells. In addition to these, compared with fusion bonding, anodic bonding can be performed at lower processing temperatures, i.e., 350°C as opposed to 1100°C; surface roughness requirement for anodic bonding is more than 10 times more relaxed, i.e., 5-nm rootmean- square (RMS) roughness as opposed to 0.5 nm for fusion bonding; anodic bonding can be performed on smaller contact area and hence improves the fill factor for CMUTs. Although anodic bonding has been previously used for CMUT fabrication, a CMUT with a vacuum cavity could not have been achieved, mainly because gas is trapped inside the cavities during anodic bonding. In the approach we present in this paper, the vacuum cavity is achieved by opening a channel in the plate structure to evacuate the trapped gas and subsequently sealing this channel by conformal silicon nitride deposition in the vacuum environment. The plate structure of the fabricated CMUT consists of the single-crystal silicon device layer of a silicon-on-insulator wafer and a thin silicon nitride insulation layer. The presented fabrication approach employs only three photolithographic steps and combines the advantages of anodic bonding with the advantages of a patterned metal bottom electrode on an insulating substrate, specifically low parasitic series resistance and low parasitic shunt capacitance. In this paper, the developed fabrication scheme is described in detail, including process recipes. The fabricated transducers are characterized using electrical input impedance measurements in air and hydrophone measurements in immersion. A representative design is used to demonstrate immersion operation in conventional, collapse-snapback, and collapse modes. In collapsemode operation, an output pressure of 1.67 MPa pp is shown at 7 MHz on the surface of the transducer for 60-Vpp, 3-cycle sinusoidal excitation at 30-V dc bias.

Organic and perovskite solar modules innovated by adhesive top electrode and depth-resolved laser patterning

Abstract: We demonstrate an innovative solution-processing fabrication route for organic and perovskite solar modules via depth-selective laser patterning of an adhesive top electrode. This yields unprecedented power conversion efficiencies of up to 5.3% and 9.8%, respectively. We employ a PEDOT:PSS–Ag nanowire composite electrode and depth-resolved post-patterning through beforehand laminated devices using ultra-fast laser scribing. This process affords low-loss interconnects of consecutive solar cells while overcoming typical alignment constraints. Our strategy informs a highly simplified and universal approach for solar module fabrication that could be extended to other thin-film photovoltaic technologies.

Fabricating Copper Components with Electron Beam Melting

Abstract: ADVANCED MATERIALS & PROCESSES • JULY 2014 20 Direct fabrication of fully dense metal structures using the electron beam melting (EBM) process developed by Arcam AB, Sweden, has been successfully demonstrated for a wide range of materials including Ti-6Al-4V[1,11,9], cobalt chromium[7,6], titanium-aluminide[4,8], H-13 steel[2], and nickelbase alloys[10]. A growing interest in additive manufacturing (AM) to build components from copper and copper alloys[5,13,12] is spurring a variety of applications including novel radio frequency (RF) accelerating structures. A critical issue for high average power, high brightness photoinjectors—the technology of choice for generating high brightness electron beams used in many of today’s linear accelerators—is efficient cooling. RadiaBeam Technologies is exploring the use of AM to fabricate complex RF photoinjectors with geometries optimized for thermal management: Spatially optimized internal cooling channels can be fabricated without the constraints typically associated with traditional manufacturing methods. However, several properties of pure copper present significant processing challenges for direct metal AM. For one, pure copper has a relatively high thermal conductivity (401 W•m−1•K−1 at 300K) which, while ideal for thermal management applications, rapidly conducts heat away from the melt area resulting in local thermal gradients. This can lead to layer curling, delamination, and ultimately, build and part failure. Additionally, copper’s high ductility hinders post-build powder removal and recovery. Particles also tend to agglomerate, reducing overall flowability and impeding powder deposition. Because Cu is sensitive to oxidation, great care must be taken in handling and storage before, during, and after part fabrication.

Micromotor fabrication

Abstract: Micromotor fabrication and related issues are discussed. The micromotors under study are of the variable-capacitance side-drive type with salient-pole and wobble (harmonic) designs. Polysilicon surface micromachining forms the basis of the micromotor fabrication process. In this process, LPCVD heavily phosphorus-doped polysilicon is used for the structural parts, LPCVD silicon nitride is used for electrical isolation, and CVD low-temperature oxide is used to as the sacrificial material. The fabrication process affects the performance characteristics of the micromotor through the reproduction accuracy of the design geometry and through the modification of the characteristics of contacting surfaces. Pattern definition and delineation are among the most critical steps of the micromotor fabrication process because of the increasing surface topography during fabrication and the large film thicknesses utilized. The release and testing process can affect the frictional characteristics of the micromotor significantly, determining success or failure of operation by dielectric excitation. >

A Review of Polymer-Based Materials for Fused Filament Fabrication (FFF): Focus on Sustainability and Recycled Materials

Abstract: Recently, Fused Filament Fabrication (FFF), one of the most encouraging additive manufacturing (AM) techniques, has fascinated great attention. Although FFF is growing into a manufacturing device with considerable technological and material innovations, there still is a challenge to convert FFF-printed prototypes into functional objects for industrial applications. Polymer components manufactured by FFF process possess, in fact, low and anisotropic mechanical properties, compared to the same parts, obtained by using traditional building methods. The poor mechanical properties of the FFF-printed objects could be attributed to the weak interlayer bond interface that develops during the layer deposition process and to the commercial thermoplastic materials used. In order to increase the final properties of the 3D printed models, several polymer-based composites and nanocomposites have been proposed for FFF process. However, even if the mechanical properties greatly increase, these materials are not all biodegradable. Consequently, their waste disposal represents an important issue that needs an urgent solution. Several scientific researchers have therefore moved towards the development of natural or recyclable materials for FFF techniques. This review details current progress on innovative green materials for FFF, referring to all kinds of possible industrial applications, and in particular to the field of Cultural Heritage.