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.     

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.     

Reliability study of hermetic wafer level MEMS packaging with through-wafer interconnect

In this paper, we developed a hermetic wafer level packaging for MEMS devices. Au–Sn eutectic bonding technology in a relatively low temperature is used to achieve hermetic sealing, and the vertical through-hole via filled with electroplated copper for the electrical connection is also used. The MEMS package has the size of 1 mm × 1 mm × 700 μm, and a square loop Au–Sn metallization of 70 μm in width for hermetic sealing. The robustness of the package is confirmed by several tests such as shear strength test, reliability tests, and hermeticity test. The reliability issues of Au–Sn bonding technology, and copper through-wafer interconnection are discussed, and design considerations to improve the reliability are also presented. By applying O₂ plasma ashing and fabrication process optimization, we can achieve the void-free structure within the bonding interface. The mechanical effects of copper through-vias are also investigated numerically and experimentally. Several factors which could induce via hole cracking failure are investigated such as thermal expansion mismatch, via etch profile, copper diffusion phenomenon, and cleaning process. Alternative electroplating process is suggested for preventing Cu diffusion and increasing the adhesion performance of the electroplating process.     

MEMS micro fluxgate sensors with mutual vertical excitation coils and detection coils

As a classic Earth magnetic field sensor, fluxgate magnetic sensors have great potential applications in many fields. This paper presents a new 3D micro-solenoid fluxgate magnetic sensor based on the MEMS technique. The excitation coils were placed vertically to the detection coils on the chip plane, around a rectangular shaped magnetic core. Polyimide was used to insulate coils and magnetic core. Width of copper conductor lines is 50 μm, and line space is 50 μm. The design of such fluxgate magnetic sensor followed second harmonic signal selecting method. Phase-lock amplifier was used to get second harmonic signal output by detection coils. The linear range of 0–80 μT with sensitivity of 6.7 V/T was achieved from the fabricated sensor with excitation current of 430 mA and the operational frequency of 40 KHz. As the excitation current was 470 mA, linear range of 0–50 μT with sensitivity of 21.7 V/T was achieved.     

Design and fabrication of a flexible three-axial tactile sensor array based on polyimide micromachining

This paper describes the design and fabrication of a flexible three-axial tactile sensor array using advanced polyimide micromachining technologies. The tactile sensor array is comprised of sixteen micro force sensors and it measures 13 mm × 18 mm. Each micro force sensor has a square membrane and four strain gauges, and its force capacity is 0.6 N in the three-axial directions. The optimal positions of the strain gauges are determined by the strain distribution obtained form finite element analysis (FEA). The normal and shear forces are detected by combining responses from four thin-film metal strain gauges embedded in a polyimide membrane. In order to acquire force signals from individual micro force sensors, we fabricated a PCB based on a multiplexer, operational amplifier and microprocessor with CAN network function. The sensor array is tested from the evaluation system with a three-component load cell. The developed sensor array can be applied in robots’ fingertips, as well as to other electronic applications with three-axial force measurement and flexibility keyword requirements.     

Rapid quantification of bio-particles based on image visualisation in a dielectrophoretic microfluidic chip

We studied an imaging-based technique for the rapid quantification of bio-particles in a dielectrophoretic (DEP) microfluidic chip. Label-free particles could be successively sorted and trapped in a continuous flow manner under the applied alternating current (AC) conditions. Both 2 and 3 μm polystyrene beads at a concentration of 1.0 × 10⁷ particles ml⁻¹ could be rapidly quantified within 5 min in our DEP system. Capturing efficiencies higher than 95% could be 2 μm polystyrene beads with a linear flow speed, applied voltage and frequency of 0.89 mm s⁻¹, 20 V_p-p and 5 MHz. Yeast cells (Candida glabrata and Candida albicans) could also be captured even at a lower concentration of 2.5 × 10⁵ cells ml⁻¹. Images of aggregative particles taken from the designed trapping area were further processed based on the intensity of relative greyscale followed by correction of the particle numbers. The imaging-based quantification method showed higher agreement than that of the conventional counting chamber method and proved the stability and feasibility of our AC DEP system.     

A piezoelectric micro-cantilever bio-sensor using the mass-micro-balancing technique with self-excitation

A biosensor was developed for using in a Lab-On-a-Chip (LOC). The sensor detects the change in the resonance frequency of a micro-cantilever with a piezoelectric film. This is the mass micro-balancing technique, which has been successfully used for detecting bio-materials in the quartz crystal microbalance (QCM). The PZT film, a piezoelectric film, is designed to act as both sensor and actuator. The geometry of the micro cantilever is optimized to maximize the sensitivity and minimize the environmental effects such as viscous damping and added mass effect in liquid. The fabricated sensor is composed of a 100 μm long, 30 μm wide, and 5 μm thick cantilever with a 2.5 μm thick piezoelectric (PZT) layer on it. The ratio of thickness to length of the micro cantilever is very high compared to others in micro cantilever-based studies. This high aspect ratio is the key to maximize the sensitivity and minimize the environmental effects. The fabricated micro sensor was tested by detecting the mussel gluing protein, the insulin-anti insulin binding protein and the poly T-sequence DNA.     

A micro roller embossing process for structuring large-area substrates of laminated ceramic green tapes

This paper presents a micro roller embossing process for patterning large-area substrates of laminated green ceramic tapes. The aim of this research is to develop a large-area microstructure formation technique for green ceramic substrates using a thermal roller laminator, which is compatible with screen printing apparatus. A thin film nickel mold was developed via photolithographic patterning and nickel electroplating on a 75-μm-thick nickel film. The mold had an effective panel size of 150 mm × 150 mm with the height of plated protrusive patterns being about 38 μm. Formation of micro patterns was successfully demonstrated over the whole panel area on laminated green ceramic tapes using roller embossing. Micro patterns for inductors, heaters as well as interconnection with 50 μm line-width were embossed on green ceramic substrates. By means of tuning process parameters including roller temperature, applied pressure and feeding speed, we have demonstrated that micro roller embossing is a promising method for patterning large-area green ceramic substrates.     

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.     

Effect of dispersed phase viscosity on maximum droplet generation frequency in microchannel emulsification using asymmetric straight-through channels

Uniformly sized droplets of soybean oil, MCT (medium-chain fatty acid triglyceride) oil and n-tetradecane with a Sauter mean diameter of d _3,2 = 26–35 μm and a distribution span of 0.21–0.25 have been produced at high throughputs using a 24 × 24 mm silicon microchannel plate consisting of 23,348 asymmetric channels fabricated by photolithography and deep reactive ion etching. Each channel consisted of a 10-μm diameter straight-through micro-hole with a length of 70 μm and a 50 × 10 μm micro-slot with a depth of 30 μm at the outlet of each channel. The maximum dispersed phase flux for monodisperse emulsion generation increased with decreasing dispersed phase viscosity and ranged from over 120 L m⁻² h⁻¹ for soybean oil to 2,700 L m⁻² h⁻¹ for n-tetradecane. The droplet generation frequency showed significant channel to channel variations and increased with decreasing viscosity of the dispersed phase. For n-tetradecane, the maximum mean droplet generation frequency was 250 Hz per single active channel, corresponding to the overall throughput in the device of 3.2 million droplets per second. The proportion of active channels at high throughputs approached 100% for soybean oil and MCT oil, and 50% for n-tetradecane. The agreement between the experimental and CFD (Computational Fluid Dynamics) results was excellent for soybean oil and the poorest for n-tetradecane.     

Miniaturization limits of field-effect based MEMS accelerometers

Accelerometers are increasingly gaining in importance in the consumer electronics sector. To estimate whether field-effect based accelerometers have an advantage over sensor types common today, we analyze their scaling performance in this paper. Within the scope of this research, firstly we create an analytical model and subsequently verify it by numerical simulation. Based thereon, a numerical–analytical study of the scaling performance follows. The requirements are based on a commercially available capacitive accelerometer. We identify the main miniaturization limits of field-effect based accelerometers, which are total noise and pull-in effect. Those limits lead to a total area estimation for a triaxial MEMS accelerometer core of only 410 μm × 300 μm.     

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.     

Nano-structured solid oxide fuel cell design with superior power output at high and intermediate operation temperatures

A solid oxide fuel cell (SOFC) with a thin-film yttria-stabilized zirconia (YSZ) electrolyte was developed and tested. This novel SOFC shows a similar multilayer set-up as other current anode-supported SOFCs and is composed of a Ni/8YSZ anode, a gas-tight 8YSZ electrolyte layer, a dense Sr-diffusion barrier layer and a LSCF cathode. To increase the power density and lower the SOFC operating temperature, the thickness of the electrolyte layer was reduced from around 10 μm in current cells to 1 μm, using a nanoparticle deposition method. By using the novel 1 μm electrolyte layer, the current density of our SOFC progressed to 2.7, 2.1 and 1.6 A/cm² at operation temperatures of 800, 700 and 650°C, respectively, and out-performs all similar cells reported to date in the literature. An important consideration is also that cost-effective dip-coating and spin-coating methods are applied for the fabrication of the thin-film electrolyte. Processing of 1 μm layers on the very porous anode substrate material was initially experienced as very difficult and therefore 8YSZ nanoparticle coatings were developed and optimized on porous 8YSZ model substrates and transferred afterwards to regular anode substrates. In this paper, the preparation of the novel SOFC is shown and its morphology is illustrated with high resolution SEM pictures. Further, the performance in a standard SOFC test is demonstrated.     

Miniaturization limits of piezoresistive MEMS accelerometers

We present the miniaturization limits of axially loaded piezoresistive MEMS accelerometers. Therefore we identify limiting factors on the basis of FEM-verified analytical models. To ensure a broad discussion we compare two different axially loaded topologies: first a conventional topology, which can be manufactured already today, and second a future-oriented topology utilizing nanowires. To enable a realistic comparison of the different topologies we shrink the sensor while maintaining a specific performance (e.g. sensitivity and noise) considering design limitations such as fracture of silicon and buckling. To find the minimum total sensor area under certain constraints and therefore the optimal geometric and material parameters we apply optimization techniques to our analytical models. It will be seen that the piezoresistive transducer principle for MEMS accelerometers has a promising shrink potential with minimum total sensor dimensions as low as 150 × 150 × 10 μm³ achievable by use of currently available manufacturing processes.     

Replication of precise polymeric microlens arrays combining ultra-precision diamond ball-end milling and micro injection molding

A simple and novel combination of ultra-precision diamond ball-end milling and micro injection molding technique is described to produce precise microlens arrays out of polycarbonate (PC), polymethylmethacrylate (PMMA) as well as polystyrene (PS). The microlens arrays consist of 100 lenses in a 10 × 10 array with a lens radius of 273 μm, a lens diameter of 300 μm and a lens depth of 45 μm. Pitch between the lenses is fixed at 800 μm. The injection molding parameters were optimized to get precise microlens geometries with low surface roughness. The results show a precise diamond milled mold insert and injection molded microlens arrays with minor deviations in radius and surface roughness of the microlenses, particularly for microlens arrays out of PMMA.     

Cross-axis sensitivity reduction of a silicon MEMS piezoresistive accelerometer

This paper presents realization of a MEMS piezoresistive single axis accelerometer using dual doped TMAH solution. The silicon micromachined structure consists of a heavy proofmass supported by four thin flexures and sandwiched between top and bottom glass plates. Boron diffused piezoresistors located near fixed points of the flexure are used for sensing the developed stress due to applied acceleration. Based on the initial results an improved design has also been considered to achieve reduced cross-axis sensitivity and nonlinearity. The fabricated sensor tested upto 13 g acceleration shows average sensitivity of 0.556 mV/g along normal to the proofmass plane. The measured cross-axis sensitivity was 3.272 μV/g for X-axis and 3.442 μV/g for Y-axis which is less than 1% of Z-axis sensitivity. Comparing two designs there was an improvement of 63% sensitivity along Y-axis for the design with flexures placed along the proofmass edges.     

A hybrid capacitive pressure and temperature sensor fabricated by adhesive bonding technique for harsh environment of kraft pulp digesters

We have developed a compensated capacitive pressure and temperature sensor for kraft pulp digesters (pH 13.5, temperatures 25–175°C reaching a local maximum of 180°C and pressures up to 2 MPa). The gauge capacitive pressure sensor was fabricated by bonding silicon and Pyrex chips using a high temperature, low viscosity UV (ultraviolent) adhesive as the gap-controlling layer and heat curing adhesive as the bonding agent. A simple chip bonding technique, involving insertion of the adhesive into the gap between two chips was developed. A platinum thin-film wire was patterned on top of a silicon chip to form a resistance temperature detector (RTD) with a nominal resistance of 1,500 Ω. A silicon dioxide layer and a thin layer of Parylene were deposited to passivate the pressure sensor diaphragm and the sensors were embedded into epoxy for protection against the caustic environment in kraft digesters. The sensors were tested up to 2 MPa and 170°C in an environment chamber. The maximum thermal error of ±1% (absolute value of ±20 kPa) full scale output (FSO) and an average sensitivity of 0.554 fF/kPa were measured. Parylene-coated silicon chips were tested for a full kraft pulping cycle with no signs of corrosion.     

Design, fabrication and analysis of micromachined high sensitivity and 0% cross-axis sensitivity capacitive accelerometers

This paper presents the design and fabrication of three MEMS based capacitive accelerometers. The first design illustrates the achievement of an accelerometer with 0% cross-axis sensitivity and has been fabricated using PolyMUMPs, a multi-user surface-micromachining process. A unidirectional parallel plate configuration is utilized in this design to illustrate the achievement of 0% cross-axis sensitivity and an acceptable performance range. In addition, a method is introduced to improve the sensitivity of a capacitive sensor employing a transverse configuration based on the relationship of initial gaps setup in comb-finger arrangements. A design based on this technique and the PolyMUMPs fabrication process is illustrated which demonstrates a sensitivity value of 4.07 fF/μm, with a nonlinearity of 2.05% for a ±3 μm sensor operating range. The last design based on this method and the SOIMUMPs fabrication process exhibits a sensitivity of 3.45 pF/μm for ±1 μm operating range of the sensor.     

Advancements in technology and design of NEMS vector hydrophone

This paper reports on recent developments to improve the performance of hair vector hydrophone by means of several technological advancements in the fabrication procedures and corresponding sensor design. With fish’s lateral line organs as prototypes, NEMS (Nano-Electromechanical System) vector hydrophone with directivity has been designed. This paper describes the meso-piezoresistance effect of resonant tunneling thin-film, and the NEMS hydrophone based on this effect is highly sensitive and small size. The application of bionics structure may improve the low-frequency sensitivity of hydrophone. The calibration test shows that NEMS vector hydrophone’s receiving sensitivity is up to −170 dB (0dB = 1 V/μPa), has a good directional pattern in the form of “8” shape. The sea test shows that the direction of target can be detected by single NEMS vector hydrophone. In the anechoic tank, it has been verified that NEMS vector hydrophone can track the trajectory of the moving target.