A microwave probe nanostructure for atomic force microscopy

An atomic force microscope (AFM) probe on a GaAs wafer was studied as a new microwave probe structure. A waveguide was created by evaporating an Au film on the top and bottom surfaces of the GaAs AFM probe. The fabricated AMF probe’s tip is 8 μm long and has a radius of curvature of about 50 nm. The open structure of the waveguide at the tip of the probe was generated by using focused ion beam (FIB) fabrication. AFM topography of a grating sample was created by using the fabricated microwave AFM probe. The fabricated probe exhibits nanometer-scale resolution, and microwave emission was successfully detected at the tip of the probe by approaching Cr–V steel and Au wire samples.     

Properties of M-AFM probe affected by nanostructural metal coatings

In order to develop a new structure microwave probe, the fabrication of the atomic force microscope (AFM) probe on a GaAs wafer was studied and characteristics of the AFM probe with different nanostructural metal coating were evaluated in order to understand the performance of the probe for the topography of materials and the propagation of microwave signals. A waveguide was introduced by the sputtering and the electron beam (EB) evaporation technique on the top and bottom surfaces of the GaAs AFM probe with Au or Al film. The open structure of the waveguide at the tip of the probe was introduced by using focused ion beam fabrication. It was found that the fabricated probes coated with the Au or Al film have nanometer order resolution. Moreover, using the Au-coating probe formed by the EB evaporation technique, microwave emission was detected successfully at the tip of the probe by approaching an Au film sample.     

Fabrication of a guide block for measuring a device with fine pitch area-arrayed solder bumps

This paper describes the design and fabrication of a guide block and micro probes, which were used for a vertical probe card to test a chip with area-arrayed solder bumps. The size of the fabricated guide block was 10 mm × 6 mm. The guide block consisted of 172 holes to insert micro probes, 2 guide holes for exact alignment, and 4 holes for bolting between the guide block and the housing of a PCB. Pitch and size of the inserting holes were 80 μm, and 90 μm × 30 μm, respectively. A silicon on insulator wafer was used as the substrate of the guide block to reduce micro probes insertion error. The micro probes were made of nickel–cobalt (Ni–Co) alloy using an electroplating method. The length and thickness of the micro probes were 910 and 20 μm, respectively. A vertical probe card assembled with the fabricated guide block and micro probes showed good x–y alignment and planarity errors within ±4 and ±3 μm, respectively. In addition, average leakage current and contact resistance were approximately 0.35 nA and 0.378 ohm, respectively. The proposed guide block and micro probes can be applied to a vertical probe card to test a chip with area-arrayed solder bumps.     

Structure modification of M-AFM probe for the measurement of local conductivity

In order to realize the evaluation of electrical properties of materials in nanometer scale, a method to measure the local conductivity of materials was demonstrated. A microwave atomic force microscope (M-AFM) probe which can propagate and emit microwave signals was fabricated. An open structure of a waveguide at the tip of the probe was introduced by focused ion beam fabrication. The M-AFM combined a network analyzer and an AFM was used to measure a sample. The amplitude and phase of the reflection coefficient of the microwave signals were measured, thereby the electrical conductivities of metallic materials were determined. The conductivity obtained by this method is agreement well with that measured by a high-frequency conductometry.     

Geometrical strengthening and tip-sharpening of a microneedle array fabricated by X-ray lithography

A novel fabrication method for LIGA (from the German “Lithographie”, “Galvanik”, and “Abformung”) microneedles with through holes is presented. Such microneedles are in demand by most bio-medical MEMS applications and in some fluidic MEMS applications. We propose a technique that combines conventional deep X-ray lithography, plane-pattern to cross-section transfer (PCT) process, and alignment X-ray lithography. The technique provides precise hole alignment with ± 3 μm tolerance. Finite-element simulations on various hole locations were performed to determine the optimum position. We previously fabricated a microneedle with a 100-μm base and a 300-μm height by a right-triangular mask. The resultant microneedle had a very sharp tip but was excessively steep, and thus resulted in a very low strength. Improved strength and tip sharpness was consequently achieved by changing the mask-pattern from a triangular pattern to a polygonal mask and changing the dimensions of the microneedle to have a 300-μm base with various heights between 350 and 800 μm. Using the proposed technique, we could produce a total of 100 hollow microneedles on a 5 × 5 mm² chip. Moreover, we successfully fabricated sharpened microneedles that were stronger than that we have fabricated so far. The molding process or electroplating and the cost list of the LIGA microneedle will also be included.     

A MEMS guide plate for a high temperature testing of a wafer level packaged die wafer

This paper describes the design and fabrication of a MEMS guide plate, which was used for a vertical probe card to test a wafer level packaged die wafer. The size of the fabricated MEMS guide plate was 10.6 × 10.6 cm. The MEMS guide plate consisted of 8,192 holes to insert pogo pins, and four holes for bolting between the guide plate and the housing. To insert pogo pins easily, an inclined plane was defined at the back of each hole. Pitch and diameter of the hole were 650 and 260 μm, respectively. In order to define inserting holes and inclined planes at an exact position, silicon MEMS technology was used such as anisotropic etching, deep reactive etching and more. Silicon was used as the material of the guide plate to reduce alignment mismatch between the pogo pins and solder bumps during a high temperature testing. A combined probe card with the fabricated MEMS guide plate showed good x–y alignment and planarity errors within ±9 and ±10 μm at room temperature, respectively. In addition, x–y alignment and planarity are ±20 and ±16 μm at 125°C, respectively. The proposed MEMS guide plate can be applied to a vertical probe card for burn-in testing of a wafer level packaged die wafer because the thermal expansion coefficient of the MEMS guide plate and die wafer is same.     

Integrated micro Pirani gauge based hermetical package monitoring for uncooled VO x bolometer FPAs

This paper presents the design and fabrication of a micro Pirani gauge using VO _x as the sensitive material for monitoring the pressure inside a hermetical package for micro bolometer focal plane arrays (FPAs). The designed Pirani gauge working in heat dissipating mode was intentionally fabricated using standard MEMS processing which is highly compatible with the FPAs fabrication. The functional layer of the micro Pirani gauge is a VO _x thin film designed as a 100 × 200 μm pixel, suspended 2 μm above the substrate. By modeling of rarefied gas heat conduction using the Extended Fourier’s law, finite element analysis is used to investigate the sensitivity of the pressure gauge. Also the thermal interactions between the micro Pirani gauge and bolometer FPAs are verified. From the fabricated prototype, the measured device TCR is about −0.8% K⁻¹ and the sensitivity about 1.84 × 10⁻³ W K⁻¹ mbar⁻¹.     

Novel U-shape gold nanoparticles-modified optical fiber for localized plasmon resonance chemical sensing

A novel fiber-optic localized plasma resonance (FO-LPR) sensor composed of a U-shape optical fiber was proposed and demonstrated in this study. The U-shape optical fiber was fabricated by a femtosecond laser micromachining system. The dimensions of the U-shape zone were 100 μm in depth measured from the surface of the polymer jacket layer, 80 μm in width in the jacket layer, 60 μm in width in the cladding layer. The total length is 5 mm. After laser annealing treatment, the average surface roughness was 205.8 nm as determined by Atom Force Microscope (AFM). The exposed surface of the U-shape fiber was modified with self-assembled gold nanoparticles to produce the FO-LPR sensor. The response of the sensor shows that the signal increases linearly with increasing refractive index. The sensor resolution of the sensor was determined to be 1.06 × 10⁻³ RIU.     

Fabrication of large-volume microfluidic chamber embedded in glass using three-dimensional femtosecond laser micromachining

We report on fabrication of large-volume, square-shaped microfluidic chamber embedded in glass by scanning a tightly focused femtosecond laser beam inside a porous glass immersed in water. After the hollow structure is created in the porous glass substrate, the fabricated glass sample is post-annealed at 1,050°C during which it can be sintered into a compact glass. By the use of this technique, a 1 mm × 1 mm × 100 μm microchamber connected to four microfluidic channels is created inside the transparent glass substrate, showing that our technique allows for fabrication of not only thin channel structures with arbitrary lengths and configurations, but also hollow structures with infinitely large sizes.     

Fabrication of AFM probe with CuO nanowire formed by stress-induced method

A novel method has been proposed to fabricate an atomic force microscope (AFM) probe using CuO nanowire and a stress-induced method that can form the nanowire easily. By heating a commercial AFM probe with a film coating of Ta and Cu, a Cu hillock with CuO nanowires on its surface could be formed at the end of the probe. The thickness of the coating films, the heating temperature, and the heating time were investigated to obtain CuO nanowires with a high aspect ratio for use as an AFM probe tip. It was found that a suitable probe tip can be fabricated using the a Cu film thickness of 700 nm, a heating temperature of 380 °C and a heating time of 6 h. Probe tips (~5 μm high) and nanowires of ~25 nm diameter were obtained successfully. In the range evaluated, the measurement resolution of the CuO nanowire probe was slightly worse than that of a commercial AFM probe. However, both probes had almost the same dimensional measurement precision.     

Thin-film sensor based tip-shaped split ring resonator metamaterial for microwave application

The artificially constructed materials based split ring resonators (SRRs) may have exotic electromagnetic properties and have received growing interest in recent years. Moreover, the resonance frequency shift of this material is extraordinarily sensitive to the changes in the capacitance of SRR, which makes SRR suit for microwave thin-film sensing applications. Based on such principle, the tip-shaped SRR metamaterial is presented as thin-film sensor in this paper to reduce device size and resonance frequency as well as to improve the Q-factor. The structure is placed inside an X-band waveguide with dimensions of 22.86 mm × 10.16 mm × 12.8 mm to investigate resonance frequency shift in different cases by numerical method. In contrast to the traditional structures, the tip-shaped design exhibits a miniaturization and sharper dip on resonance in their transmission spectra. Furthermore, the proposed sensor can deliver the sensitivity level of 16.2 MHz/μm and less than a 2 μm nonlinearity error when the uniform benezocyclobutene films from 100 nm to 50 μm thick are coated onto the fixed structure. These results indicate that the proposed thin-film sensor has high sensitivity and low nonlinearity error, and make it great promising application for wireless sensors in future.     

Device for oxide dots fabrication with copper wire as cathode probe

A device has been fabricated to perform large area local oxidation with copper wire (thickness 7 μm) as cathode probe. Ability of this device was studied, by silicon oxide (SiO₂) dots fabrication on silicon (Si) surface and patterning of model microorganism, Mycobacterium smegmatis on the predetermined positions (oxide dots) with preferable surface monolayer. Positive patterning of Mycobacterium smegmatis attained on the fabricated substrate due to the charge difference between SiO₂ dot and Si surface, which was confirmed by atomic force microscopy and scanning electron microscopy (SEM) analysis. This device shows possibilities of overcoming the inherent limitations of large area local oxidation by AFM.     

Super permeable nano-channel membranes defined with laser interferometric lithography

We report the design, fabrication, and testing of super permeable nano-channel membranes, characterized by the absolute control in the pore size at the nano-scale dimensions, large surface area, very high permeability, mechanical stability and durability. The membranes were fabricated using a unique nanotechnology process that combines laser interferometric lithography to define nano-channels (pores) and micro-machining to produce free-standing amorphous silicon membranes, allowing rapid and cost-effective mass production. The suspended membranes were defined as 50 nm thick a-Si, characterized by a very high porosity of approximately 20%, achieved by definition of large arrays of nano-channels. The dimensions of each individual nano-channel was 65 nm wide, 250 nm long. The measured apparent permeability was 0.14 ± 0.05 cm/min for each individual 70 μm × 70 μm membrane, representing one of the highest permeability values ever reported for this scale.     

Micro-electroforming metallic bipolar electrodes for mini-DMFC stacks

This paper describes the development of metallic bipolar plate fabrication using micro-electroforming process for mini-DMFC (direct methanol fuel cell) stacks. Ultraviolet (UV) lithography was used to define micro-fluidic channels using a photomask and exposure process. Micro-fluidic channels mold with 300 μm thick and 500 μm wide were firstly fabricated in a negative photoresist onto a stainless steel plate. Copper micro-electroforming was used to replicate the micro-fluidic channels mold. Following by sputtering silver (Ag) with 1.2 μm thick, the metallic bipolar plates were completed. The silver layer is used for corrosive resistance. The completed mini-DMFC stack is a 3.5 × 3.5 cm² fuel cell stack including a 1.5 × 1.5 cm² MEA (membrane electrode assembly). Several MEAs were assembly into mini-DMFC stacks using the completed metallic bipolar plates. All test results showed the metallic bipolar plates suitable for mini-DMFC stacks. The maximum output power density is 9.3 mW/cm² and current density is 100 mA/cm² when using 8 vol.% methanol as fuel and operated at temperature 30°C. The output power result is similar to other reports by using conventional graphite bipolar plates. However, conventional graphite bipolar plates have certain difficulty to be machined to such micro-fluidic channels. The proposed micro-electroforming metallic bipolar plates are feasible to miniaturize DMFC stacks for further portable 3C applications.     

Mechanical punching of 15 μm size hole

This study investigates the size limit of a hole produced by the conventional punching process. In the micron size hole punching, there are two main technical obstacles that complicate the miniaturization steps. One is the fabrication of the micro punch tools with high dimensional accuracy and the other is the accurate alignment of the tools within the die clearance of 1∼2 μm. In this study, we tried to mechanically punch a 15 μm size hole. For this, we fabricated and alignedthe punch tools. Micro punch tools made of tungsten carbide were fabricated by micro-electrical discharge machining (micro-EDM). The diameter of punch tip was 15 μm, and that of the die hole, 17 μm. With the developed micro punching system, tools were aligned, and then, 15 μm size holes were made on 13-μm-thick brass and stainless steel foil, respectively.     

Design, fabrication and testing of a high performance silicon piezoresistive Z-axis accelerometer with proof mass-edge-aligned-flexures

This paper presents design, fabrication and testing of a quad beam silicon piezoresistive Z-axis accelerometer with very low cross-axis sensitivity. The accelerometer device proposed in the present work consists of a thick proof mass supported by four thin beams (also called as flexures) that are connected to an outer supporting rim. Cross-axis sensitivity in piezoresistive accelerometers is an important issue particularly for high performance applications. In the present study, low cross-axis sensitivity is achieved by improving the device stability by placing the four flexures in line with the proof mass edges. Various modules of a finite element method based software called CoventorWare^™ was used for design optimization. Based on the simulation results, a flexure thickness of 30 μm and a diffused resistor doping concentration of 5 × 10¹⁸ atoms/cm³ were fixed to achieve a high prime-axis sensitivity of 122 μV/Vg, low cross-axis sensitivity of 27 ppm and a relatively higher bandwidth of 2.89 kHz. The designed accelerometer was realized by a complementary metal oxide semiconductor compatible bulk micromachining process using a dual doped tetra methyl ammonium hydroxide etching solution. The fabricated accelerometer devices were tested up to 13 g static acceleration using a rate table. Test results of fabricated devices with 30 μm flexure thickness show an average prime axis sensitivity of 111 μV/Vg with very low cross-axis sensitivities of 0.652 and 0.688 μV/Vg along X-axis and Y-axis, respectively.     

High-performance MEMS-based gas chromatography column with integrated micro heater

A high-performance MEMS-based gas chromatography (GC) device is proposed comprising a miniature serpentine column with dimensions of 3.2 m × 200 μm × 250 μm (length × width × depth) and with an integrated Pt micro heater. The column is fabricated on a Si die measuring 3.5 × 1.8 mm² using a wet etching process and is bonded to a Pyrex cover plate incorporating the Pt micro heater via a thermal fusion process. The experimental results reveal that an applied voltage of 9.7 V is sufficient to maintain a constant temperature of 85°C for elution purposes. In addition, it is shown that the proposed device successfully detects the concentrations of both pure and mixed samples of four volatile organic compound gases, namely acetone, toluene, methanol, and benzene. Finally, the theoretical plate number obtained by the proposed MEMS-based GC device is shown to be 2–3 times higher than that obtained from a conventional capillary-based GC system under the same injection conditions.     

A methodology for quantitative evaluation of local electrical conductivity: from micron to submicron

The local electrical conductivity of aluminum thin film with dimensions from micron to submicron was quantitatively measured by a four-point atomic force microscope (AFM) technique. The technique is a combination of the principles of four-point probe method and standard AFM. A silicon nitride based AFM probe with a V-shaped two-dimensional sliced structure tip was patterned by using conventional photolithography method. The probe was then etched to four parallel electrodes isolated from each other, for the purpose of performing current input and electrical potential drop measurement. The spacing between electrodes is smaller than 1.0 μm, which facilitates the quantitative electrical conductivity measurement of ultrathin film. The four-point AFM probe technique is capable of measuring surface topography together with local conductivity simultaneously. The technique was applied to a series of 99.999% aluminum thin films with thicknesses from micron to submicron. The repeatable measurements demonstrate the capability of this technique and its possible extension to be used for fast in situ electrical properties characterization of submicron interconnects that widely applied in nanosensors and nanodevices.     

Microfabrication of thick tungsten films for use as absorbers of deep X-ray lithography masks

 We fabricated thick (5 μm) tungsten (W) film patterns by sputtering and dry etching, and realized a new deep X-ray lithography mask. The X-ray mask with 5-μm-thick W absorbers could expose about 1-mm-thick resist structures. In the deposition process of W films, the column structure of about 0.2 μm grain size, from which pattern edge roughness originates, disappeared by adding nitrogen into the sputtering gas. W film etching was carried out by reducing gas pressure and cooling the substrate (−40 °C), and a side etch width of below 0.2 μm was obtained. From the results of the pattern edge roughness and the side etch width, a pattern fabrication accuracy below ±0.5 μm was achieved. Furthermore, film stress, which induces pattern distortion, was reduced to below 50 MPa by controlling the sputtering gas pressure. The obtained mask achieved a pattern distortion below ±0.3 μm. Received: 7 July 1999/Accepted: 29 May 2000     

In-situ fabrication of polymer microsieves for ��TAS by slanted angle holography

We present a simple, versatile method for the in-situ fabrication of membranes inside a microfluidic channel during a chip manufacturing process using only two extra slanted angle holographic exposure steps. This method combines the strengths of both inclined UV exposure and holographic lithography to produce micrometer-sized three-dimensional sieving structures. Using a common chip material, the photoresist material SU-8, together with this method, a leak-free membrane-channel connection is obtained. The resulting membranes are monodisperse, with a very well-defined pore geometry (i.e., microsieves with a pore diameter between 500 nm and 10 μm) that is easily controllable with the holographic set-up. The selectivity of in-situ fabricated microsieves with a pore diameter of 2 μm will be demonstrated using polystyrene beads of 1 and 3 μm.