Batch mode micro-electro-discharge machining

This paper describes a micro-electro-discharge machining (micro-EDM) technique that uses electrode arrays to achieve high parallelism and throughput in the machining. It explores constraints in the fabrication and usage of high aspect ratio LIGA-fabricated electrode arrays, as well as the limits imposed by the pulse discharge circuits on machining rates. An array of 400 Cu electrodes with 20 μm diameter was used to machine perforations in 50-μm-thick stainless steel. To increase the spatial and temporal multiplicity of discharge pulses, arrays of electrodes with lithographically fabricated interconnect and block-wise independent pulse control resistance-capacitance (RC) circuits are used, resulting in >100× improvement in throughput compared to single electrodes. However, it was found to compromise surface smoothness. A modified pulse generation scheme that exploits the parasitic capacitance of the interconnect offers similarly high machining rates and is more amenable to integration. Stainless steel workpieces of 100 μm thickness were machined by 100 μm×100 μm square cross-section electrodes using in 85 s using an 80-V power supply. Surface smoothness was unaffected by electrode multiplicity. Using electrode arrays with four circuits, batch production of 36 WC-Co gears with 300 μm outside diameter and 70 μm thickness in 15 min is demonstrated     

High aspect ratio meso-scale parts enabled by wire micro-EDM

Micro-electro discharge machining (EDM) is a subtractive meso-scale machining process. The Agie Excellence 2F wire micro EDM is capable of machining with a 25 micron diameter wire electrode and positioning the work piece to within ±1.5 microns. The over-burn gap can be controlled to within 3 microns to obtain a minimum feature radius of about 16 microns while achieving submicron surface finish and an imperceptible recast layer. For example, meso-scale gears that require vertical sidewalls and contour tolerances to within 3 microns can be wire EDMed into a variety of conductive materials. Material instabilities can affect the dimensional precision of machined meso-scale parts by material relaxation during the machining process. A study is done to investigate the machining performance of the wire micro EDM process by machining a high aspect ratio meso-scale part into a variety of metals (e.g. 304L stainless steel, Nitronic 60 Austentic Stainless, Beryllium Copper, and Titanium). Machining performance parameters such as, profile tolerance, perpendicularity, and repeatability are compared for the different materials. Pertinent inspection methods desirable for meso-scale quality assurance tasks are also evaluated. Sandia National Laboratories is developing meso-scale electro-mechanical components and has an interest in the assembly implications of piece parts fabricated by various meso-scale manufacturing processes. Although the wire EDM process is typically used to fabricate 2½ dimensional features, these features can be machined into a 3 dimensional part having other features such as hubs and chamfers to facilitate assembly.     

Design and fabrication of a micro Alvarez lens array with a variable focal length

A 5 × 5 micro Alvarez lens array mold was fabricated using a 5-axis ultraprecision diamond machine and an Alvarez lens array was manufactured by injection molding process. Unlike conventional processes for asymmetrical element fabrication such as small tool grinding, this research demonstrates slow tool servo broaching process that allows the entire Alvarez lens array to be accurately machined on a metal mold in a single operation. To further reduce manufacturing cost, injection molding was used to fabricate the Alvarez lens arrays. The mold and molded lenses were both measured using an optical profiler. All measured profiles showed a good agreement with design and surface roughness also indicated an optical surface finish. The functionality of the molded polymeric lens arrays was achieved when the focal lengths were varied by laterally translating the molded Alvarez lens array pair. This research is a demonstration of the capability of fabricating complex optics using the same approach.     

MEMS微探针及其在嗅粘膜神经递质检测中的研究

采用微探针电极阵列对大鼠嗅粘膜神经递质进行了在体检测.基于MEMS技术,制备了具有8通道电极阵列的微探针芯片.每一电极的传感器表面为16μm×120μm或0.3 μm×120 μm尺寸.采用循环伏安法,该探针可以检测到50 nM浓度的多巴胺.将探针固定于大鼠鼻腔嗅粘膜,对多巴胺等单胺类神经递质进行了在体检测.通过二氧化碳诱导的三叉神经刺激动物模型的研究,证明微探针适合于神经递质的多位点实时测量.     

A micromachining process for die-scale pattern transfer in ceramics and its application to bulk piezoelectric actuators

This paper reports on a batch mode planar pattern transfer process for bulk ceramics, glass, and other hard, brittle, nonconductive materials suitable for micromachined transducers and packages. The process is named LEEDUS, as it combines lithography, electroplating, batch mode micro electro-discharge machining (/spl mu/EDM) and batch mode micro ultrasonic machining (/spl mu/USM). An electroplating mold is first created on a silicon or metal wafer using standard lithography, then using the electroplated pattern as an electrode to /spl mu/EDM a hard metal (stainless steel or WC/Co) tool, which is finally used in the /spl mu/USM of the ceramic substrate. A related process (SEDUS) uses serial /spl mu/EDM and omits lithography for rapid prototyping of simple patterns. Feature sizes of 25 /spl mu/m within a 4.5/spl times/4.5 mm/sup 2/ die have been micromachined on glass-mica (Macor) ceramic plates with 34 /spl mu/m depth. The ultrasonic step achieves 18 /spl mu/m/min. machining rate, with a tool wear ratio of less than 6% for the stainless steel microtool. Other process characteristics are also described. As a demonstration, octagonal and circular spiral shaped in-plane actuators were fabricated from bulk lead zirconate titanate (PZT) plate using the LEEDUS/SEDUS process. A device of 20 /spl mu/m thickness and 450 /spl mu/m/spl times/420 /spl mu/m footprint produces a displacement of /spl ap/2/spl mu/m at 40 V.     

Wideband sequential feeding network for Ku‐band dual circularly polarized 4 × 4 antenna array

In this article the analysis and design of a dual circularly polarized 4 × 4 antenna array operating in Ku band are discussed with emphasis on its sequential feeding network. The proposed antenna element is composed of stacked circular patches fed by a branch line coupler to introduce dual circular polarization. These antenna elements are arranged into 2 × 2 sequential fed antenna arrays with two separate sequential feeding networks for LH and RH circular polarizations. These 2 × 2 sequential fed antenna arrays are arranged to compose the proposed 4 × 4 antenna array. The proposed feeding network is implements on a single layer. Due to the coupling between the lines of the complete feeding network, matching and axial ratio of the complete antenna are degraded. Matching stubs at appropriate points on the complete feeding network are used to adjust the total performance of the designed 4 × 4 antenna array. Simulation results by using both HFSS and CST are presented for comparison. In addition, experimental verifications are presented.     

Miniaturized 1D beam switching and 2D printed Yagi-Uda antenna arrays

This article presents a multi-board arrangement of printed Yagi-Uda antennas that can be configured into 1D and 2D arrays. First, a 1 × 4 collinear array is designed and fed with a metamaterial Butler matrix (BM) network to provide beam switching at four azimuthal directions. Slow-wave concept is used in designing the hybrid, crossover and delay sections of BM to achieve a footprint reduction of 67%. The 1 × 4 collinear array with the feed network achieves 8.42–11.7 dBi gain and 21.7–25.7 degrees half power beam width (HPBW) in horizontal plane for the four switched beam patterns at 5.8 GHz in simulations. Second, measurement results of the fabricated 1 × 4 collinear array with its miniaturized feed network confirm a range of 22–27 degrees in HPBW in the horizontal plane. Finally, parasitic structures are designed to reduce antenna coupling and a 3-shelf holder is proposed to stack the 1 × 2 printed Yagi antenna subarray boards in compact 2D planar array configurations. Simulations of the 2 × 4-array demonstrate achieving 13.09 dBi peak gain at 5.8 GHz along with reduction of the HPBW by 24.7 degrees in horizontal plane in comparison with the 1 × 4-array prototype.     

L3: An FPGA-based multilayer maze routing accelerator

This paper describes a multi-layer maze routing accelerator which uses a two-dimensional array of processing elements (PEs) implemented in an FPGA. Routing for an L-layer N×N grid is performed by an array of N×N PEs that time-multiplex each layer over the array. This accelerates the classic Lee Algorithm from O(L×d²) in software to O(L×d). Each PE can be implemented in 32 look up tables in a Xilinx Virtex-II FPGA, which makes possible routing arrays that are large enough to support detailed routing for VLSI. Cycle measurements show a speedup of 50–75× over a 2.54 GHz Pentium 4 for a 4-layer 8×8 array and 93× for a 4-layer 16×16 array.     

Circularly polarized 4 × 8 stacked patch antenna phased array with enhanced bandwidth for commercial drones

This paper demonstrates the design procedure of a 4 × 8 phased array antenna. Initially, a unit element in multilayer topology with orthogonal slots in the ground plane to couple electromagnetic energy is designed. Then, a stacked patch with truncated edges is placed on the top thick substrate layer to enhance the bandwidth to 600 MHz. This multilayered stacked patch unit element is then used to design a 1 × 4 and 4 × 8 slot coupled stacked patch array. On the bottom side, a novel feedline structure is designed to provide a 90 ^o phase difference at the antenna feed for the circular polarization. The phase difference is achieved in the feedline structure using a quarter wavelength ( λ_g/4 ) difference in the lengths. After the numerical validation, both 1 × 4 and 4 × 8 stacked patch antenna arrays are fabricated to validate the simulations. The final 4 × 8 array achieved the target specification of an active reflection of less than ?10 dB over 2.4 to 3.0 GHz, axial ratio of less than 3 dB, and stable radiation pattern over the complete band. In addition, beam scanning characteristics of the proposed stacked patch antenna arrays are also verified. The prototype resulted a peak gain of 19.5 dB at 2.7 GHz, 3‐dB beamwidth around 12 ^o in the xz‐plane, and scanning range of 90 ^o . Overall, good agreement between measured and simulated results showed that the proposed designed array capable of providing 600 MHz is an excellent candidate for the radar communication, small commercial drones, and synthetic aperture radar applications.     

Microstructuring of non-conductive silicon carbide by electrical discharge machining

The electrical discharge machining process is an established process for machining materials regardless of their mechanical properties. Thus this process is especially attractive for materials which are hard to machine with conventional machining methods. The only requirement a material has to fulfil is having a certain electrical conductivity. Ceramic materials, (e.g. zirconia, silicon nitride or silicon carbide) exhibit excellent mechanical properties but are mostly electrically non-conductive. This can be compensated by an applied, electrically conductive assisting electrode. With this modification, the electrical discharge machining of non-conductive ceramic material is enabled. In this study the micro electrical discharge machining of non-conductive sintered silicon carbide is investigated. The drilling process shows instabilities due to the excessive generation of carbon products. A stabilisation of the process up to the maximum depth of 420 μm is realized by two approaches: adapting process parameters and adapting the tool electrode geometry. An analysis of the amount of infeed used in a milling process shows that an infeed of 15 μm has the best material removal rate to tool wear rate ratio. A maximum material removal rate of 3.58 × 10^?3 mm³/min is achieved. Detached microstructures with an aspect ratio of 30 are machined. A conducted surface analysis indicates that the present removal mechanism is thermally induced spalling. Furthermore no heat affected zone is present in the machined near-surface area.     

Fabrication of high-aspect-ratio electrode array by combining UV-LIGA with micro electro-discharge machining

In this paper, the combination of UV-LIGA with the Micro electro-discharge machining (Micro-EDM) process was investigated to fabricate high-aspect-ratio electrode array, and an easy and rapid process for fabricating ultra-thick SU-8 microstructures up to millimeter depth was described. First, the modified UV-LIGA process was used to fabricate the copper hole array, and then the hole array electrode was employed as a tool in the Micro-EDM process to fabricate the multiple-tipped electrodes. Electrode array of various shapes have been fabricated by this technique. The aspect ratio is up to 17.65.     

High gain flexible liquid crystal polymer based 8‐element printed antenna for millimetric wave applications

In this article, an offset fed printed dipole antenna 2‐element, 4‐element, and 8‐element arrays are developed and analyzed for millimeter wave applications. The 8‐element array antenna is of compact size with dimensions 43.6 × 25.1 × 0.25 mm³. It achieved a broad impedance bandwidth (S₁₁ < ?10 dB) of 15.7 GHz from 24.7 to 40.4 GHz. The mutual coupling between array elements is less than ?35 dB in the operating band. The antenna achieved a gain of 12.62 to 13.1 dB. The 8‐element array antenna is fabricated on liquid crystal polymer material and tested. Impedance matching, far field radiation characteristics, co‐polarized and cross‐polarized patterns and group delay are analyzed in simulation and experimental measurement. The investigated results are in good agreement and hence, the developed array antenna is attractive for wideband millimeter wave applications.     

Chemical and electrical stabilities of organic thin‐film transistors for display application

Abstract— The chemical and electrical stabilities of pentacene organic thin‐film transistors (OTFTs) fabricated on plastic by a self‐organized process was studied. The degradation in on‐current, threshold voltage, and field‐effect mobility of the OTFT under air exposure can be expressed in exponential form in time and can be reduced by using multilayer passivation on the organic semiconductor, which reduces the penetration of H₂O and O₂ into the pentacene. The threshold voltage degrades during negative gate bias stress, which can be reduced significantly by optimizing the organic gate insulator used for the OTFT. A stable OTFT can be fabricated by using the proper organic gate insulator.     

High gain substrate integrated waveguide beam scanning antenna with sub‐array elements

A method to enhance the gain of substrate integrated waveguide (SIW) beam scanning antenna is proposed in this article. 2 × 2 SIW cavity‐backed sub‐arrays are employed in array design. The antenna is constructed on two layers. The top layer places four SIW cavity‐backed sub‐arrays as radiating elements and the bottom layer is an SIW transmission line to feed the sub‐arrays. Beam scanning feature can be obtained due to the frequency dispersion. Moreover, through separating radiators to the other layer and using 2 × 2 SIW cavity‐backed sub‐arrays as radiating parts, the antenna gain is improved significantly. For a linear array, 4.1 to 6.8 dB gain enhancement is achieved compared to a conventional SIW beam scanning antenna with the same length. Then, the linear array is expanded to form a planar array for further gain improvement. A 64‐element planar beam scanning array is designed, fabricated, and tested. Experimental results show that the proposed planar array has a bandwidth from 18.5 GHz to 21. 5 GHz with beam scanning angle from ?5° to 11.5° and gain in the range of 20.5 to 21.8 dBi. The proposed high gain beam scanning antennas have potential applications in radar detection and imaging.     

A 5‐in. flexible ferroelectric liquid‐crystal display driven by organic thin‐film transistors

Abstract— An organic thin‐film‐transistor (OTFT) driven color flexible ferroelectric‐liquid‐crystal (FLC) display with 160 × 120 pixels and a resolution of 50 ppi has been developed. The flexible FLC was fabricated on a pentacene‐OTFT array using printing and lamination techniques. To drive the display at a fast driving speed, an OTFT was developed with a short channel length having a large current output. The fabricated OTFT array with a channel length of 5 μm exhibits a carrier mobility of 0.3 cm²/V‐sec and an ON/OFF ratio of over 10⁷ at a low drain voltage of ?6 V. A field‐sequential‐color system with a flexible backlight unit was also developed and used to drive the display. Color moving images were successively shown on the 5‐in. display using an active‐matrix driving technique of the OTFT.     

GaN‐based emissive microdisplays: A very promising technology for compact,ultra‐high brightness display systems

High‐brightness GaN‐based emissive microdisplays can be fabricated with different approaches that are listed and described. They consist either of hybridizing a GaN LED array on a CMOS circuit or building a monolithic component on a single substrate. Using the hybridization approach, two types of 10‐μm pixel pitch GaN microdisplay prototypes were developed: (1) directly driven, 300 × 252 pixels and (2) active‐matrix, 873 × 500 pixels. Brightness as high as 1 × 10⁶ and 1 × 10⁷ cd/m² for blue and green arrays, respectively, were reached. GaN‐based emissive microdisplays are suitable for augmented reality systems or head‐up displays, but some challenges remain before they can be put in production.     

A wideband dielectric resonator antenna array using air‐bridgeless coplanar waveguide power divider

In this communication a 2 × 2 dielectric resonator antenna (DRA) array is proposed with a wideband frequency response. An air bridgeless coplanar waveguide (CPW) power divider network is first time used to feed the 2 × 2 DRA array. Four rectangular DRAs are used as array element and exited in TE₁₁₁ mode by four slots at the end of the CPW lines in the feed network. The straight CPW phase delay line in feed network is further meandered resulting an enhanced radiation performance. The proposed DRA array exhibits a wideband response with an impedance bandwidth of 16% while maintaining a stable broadside radiation pattern with the gain range from 8 to 9.4 dBi. The proposed design is fabricated and measured, reaching good agreement with simulation results.     

The micromilling process for high aspect ratio microstructures

 High aspect ratio microstructures are currently created by several processes which include lithography (X-ray, deep ultraviolet, etc.) and mechanical machining (diamond machining, microdrilling, etc.). The lithographic processes require more extensive processing equipment such as an energy source, mask/mask holder/mask aligner, photoresist and substrate, and chemical development capacity. In addition, these processes are serial in nature and each adds to the tolerances of the finished structure. The current mechanical processes provide for the direct removal of the substrate material in a single step but are more limited in the geometric patterns which can be created. In conventional machining, the process which provides the most versatility in geometric patterns is milling. The micromilling process has two basic components. The first is the fabrication of small milling cutters with very sharp cutting edges. The second is the actual removal of the workpiece material with a very precise and repeatable machine tool. Several basic cutter designs have been fabricated using focused ion beam micromachining and are undergoing testing. The cutter diameters are nominally 100 micrometers and 22 micrometers. Results have been obtained which show that this process can be very effective for the rapid fabrication of molds and mask structures. Received: 30 October 1995 / Accepted: 4 March 1996     

A TM03 mode reduced side lobe high‐gain printed antenna array in K band for UDN and IoT applications in 5G

A single layer simple feed reduced side lobe gain‐enhanced microstrip antenna array using higher‐order modes is analyzed and designed in this work. The relationship between the relative magnitude of equivalent magnetic currents and directivity are studied. Modal analysis for rectangular patch is considered for broadside and non‐broadside radiation. Comparative investigations on antenna radiation and impedance characteristics for fundamental and higher‐order modes are presented. It is observed that an array can be designed to operate in TM₀₃ mode for enhanced gain with broadside radiation. Parametric optimization is carried out to attain low side lobe level. The proposed theory is validated by designing and fabricating a single layer single feed 2 × 2 microstrip patch array in the K band operating in TM₀₃ mode. The simulated and measured realized gain of the fabricated TM₀₃ mode array is 16.1 and 15.5 dBi, respectively, at 22 GHz with consistent broadside radiation pattern and linear polarization.     

三维神经微电极阵列新制作技术研究

尝试了一种低成本的三维微电极阵列微加工的新方法.玻璃划片形成的柱状阵列,经掩膜腐蚀后形成阳模板,再利用PDMS的微复制技术形成阴模板.利用阴模板进行电镀,可以得到三维微电极阵列.制作的铜电极阵列高度约180 μm,为制作更长的神经微电极阵列打下了基础.