Photonic crystal slabs with hexagonal air holes fabricated by selective area metal organic vapor phase epitaxy

It is shown that the photonic crystal slab (PCS) with hexagonal air holes has band gaps in the guided mode spectrum, which can be compared to that of the PCS with circular air holes, thus it is also a good candidate to be used for the PC devices. The PC with hexagonal air holes and a = 0.5 μm and r = 0.15 μm was fabricated successfully by selective area metal organic vapor phase epitaxy (SA-MOVPE). The vertical and smooth sidewalls are formed and the uniformity is very good. The same process was also used to fabricate a hexagonal air hole array with the width of 0.1 μm successfully. The air-bridge PCS with hexagonal air holes and a = 0.3 μm and r = 0.09 μm was also fabricated successfully by SA-MOVPE. Further optimization of the growth conditions for the sacrificial layer and the selective etching of the GaAs cap layer is also needed. Our experimental results indicate that SA-MOVPE is a promising method for fabricating PC devices and photonic nanostructures.     

Fabrication and characterization of a thermal switch

The development of a thermal switch based on arrays of liquid–metal micro-droplets is presented. Prototype thermal switches are assembled from a silicon substrate on which is deposited an array of 1600 30-μm liquid–metal micro-droplets. The liquid–metal micro-droplet array makes and breaks contact with a second bare silicon substrate. A gap between the two silicon substrates is filled with either air at 760 Torr, air at of 0.5 Torr or xenon at 760 Torr. Heat transfer and thermal resistance across the thermal switches are measured for “on” (make contact) and “off” (break contact) conditions using guard-heated calorimetry. The figure of merit for a thermal switch, the ratio of “off” state thermal resistance over “on” state thermal resistance, R_off/R_on, is 129 ± 43 for a xenon-filled thermal switch that opens 100 μm and 60 ± 17 for an 0.5 Torr air-filled thermal switch that opens 25 μm. These thermal resistance ratios are shown to be markedly higher than values of R_off/R_on for a thermal switch based on contact between polished silicon surfaces. Transient temperature measurements for the liquid–metal micro-droplet switches indicate thermal switching times of less than 100 ms. Switch lifetimes are found to exceed one-million cycles.     

An uncooled optically readable infrared imaging detector

This paper presents a design and fabrication of bi-material micro-cantilever array (focal plane array, FPA) made of silicon nitride (SiN_x) and gold (Au) for uncooled optical readout infrared (IR) imaging system, in which silicon (Si) substrate is removed. Compared with the conventional thermal imaging detectors where the FPA must be put in high vacuum, IR thermal images can be obtained even though the cantilever array is placed in the atmosphere. The reason is the elimination of air gap (∼2 μm) between the cantilever beam and substrate, which introduces the air conduction of high temperature gradient. The preliminary experimental results with the micro-cantilever array of 140 × 98 elements and a 12-bit charge-coupled device (CCD) indicate that objects at temperature of higher than 120 °C can be detected and the noise-equivalent temperature difference (NETD) is ∼7 K. Also, the experimental results are well accordant with the thermomechanical analysis of designed micro-cantilever array.     

Electrostatically actuated dip pen nanolithography probe arrays

Dip pen nanolithography (DPN) is a method of creating nanoscale chemical patterns on surfaces using an atomic force microscope (AFM) probe. Until now, efforts to increase the process throughput have focused on passive multi-probe arrays and active arrays based on thermal bimetallic actuation. This paper describes the first use of electrostatic actuation to create an active DPN probe array. Electrostatic actuation offers the benefit of actuation without the probe heating required for thermal bimetallic actuation. Actuator cross talk between neighboring probes is also reduced, permitting more densely spaced probe arrays. The array presented here consists of 10 cantilever probes, where each is 120 μm long and 20 μm wide. Each cantilever probe is actuated by the electrostatic force between the probe and a built-in counter electrode with a 20–25 μm gap. The tip-to-tip probe spacing, also called the array pitch, is 30 μm. Patterns of 1-octadecanethiol were created on gold surfaces to demonstrate single-probe actuation, simultaneous multi-probe actuation, and overlap of patterns from adjacent probes. The minimum line width was 25 nm with an average line width of 30–40 nm.     

Electroactive polymer based microfluidic pump

A planar, valveless, microfluidic pump using electrostrictive poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] based polymer as the actuator material is presented. P(VDF-TrFE) thick films having a large electrostrictive strain ∼5–7% and high elastic energy density of 1 J/cm³ have been used in a unimorph diaphragm actuator configuration. The microfluidic pump was realized by integrating a nozzle/diffuser type fluidic mechanical-diode structure with the polymer microactuator. The P(VDF-TrFE) unimorph diaphragm actuator, 80 μm thick and 2.2 mm × 2.2 mm in lateral dimensions, showed an actuation deflection of 80 μm for an applied electric field of 90 MV/m. The microfluidic pump could pump methanol at a flow rate of 25 μl/min at 63 Hz with a backpressure of 350 Pa. The flow rate of this pump could be easily controlled by external electrical field. Two different sizes of nozzle/diffuser elements were studied and the pumping efficiency of these structures is 11 and 16%, respectively.     

Slotted capacitive microphone with sputtered aluminum diaphragm and photoresist sacrificial layer

In this paper, we have fabricated a new microphone using aluminum (Al) slotted perforated diaphragm and back plate electrode, and photoresist (AZ1500) sacrificial layer on silicon wafer. The novelty of this method relies on aluminum diaphragm includes some slots to reduce the effect of residual stress and stiffness of diaphragm for increasing the microphone sensitivity. The acoustic holes are made on diaphragm to reduce the air damping, and avoid the disadvantages of non standard silicon processing for making back chamber and holes in back plate, which are more complex and expensive. Photoresist sacrificial layer is easy to deposition by spin coater and also easy to release by acetone. Moreover, acetone has a high selectivity to resist compared to silicon oxide and Al, thus it completely removes sacrificial resist without incurring significant damage silicon oxide and Al. The measured zero bias capacitance is 17.5 pF, and its pull-in voltage is 25 V. The microphone has been tested with external amplifier and speaker, the external amplifier was able to detect the sound waves from microphone on speaker and oscilloscope. The maximum amplitude of output speech signal of amplifier is 45 mV, and the maximum output of MEMS microphone is 1.125 μV.     

Mechanical design and characterization of a resonant magnetic field microsensor with linear response and high resolution

A resonant magnetic field microsensor based on Microelectromechanical Systems (MEMS) technology including a piezoresistive detection system has been designed, fabricated, and characterized. The mechanical design for the microsensor includes a symmetrical resonant structure integrated into a seesaw rectangular loop (700 μm × 450 μm) of 5 μm thick silicon beams. An analytical model for estimating the first resonant frequency and deflections of the resonant structure by means of Rayleigh and Macaulay's methods is developed. The microsensor exploits the Lorentz force and presents a linear response in the weak magnetic field range (40–2000 μT). It has a resonant frequency of 22.99 kHz, a sensitivity of 1.94 V T^?1, a quality factor of 96.6 at atmospheric pressure, and a resolution close to 43 nT for a frequency difference of 1 Hz. In addition, the microsensor has a compact structure, requires simple signal processing, has low power consumption (16 mW), as well as an uncomplicated fabrication process. This microsensor could be useful in applications such as the automotive sector, the telecommunications industry, in consumer electronic products, and in some medical applications.     

Design and performance of a microcantilever-based hydrogen sensor

This paper describes the design of, and the effects of basic environmental parameters on, a microelectromechanical (MEMS) hydrogen sensor. The sensor contains an array of 10 micromachined cantilever beams. Each cantilever is 500 μm wide×267 μm long×2 μm thick and has a capacitance readout capable of measuring cantilever deflection to within 1 nm. A 20-nm-thick coating of 90% palladium–10% nickel bends some of the cantilevers in the presence of hydrogen. The palladium–nickel coatings are deposited in ultra-high-vacuum (UHV) to ensure freedom from a “relaxation” artifact apparently caused by oxidation of the coatings. The sensor consumes 84 mW of power in continuous operation, and can detect hydrogen concentrations between 0.1 and 100% with a roughly linear response between 10 and 90% hydrogen. The response magnitude decreases with increasing temperature, humidity, and oxygen concentration, and the response time decreases with increasing temperature and hydrogen concentration. The 0–90% response time of an unheated cantilever to 1% hydrogen in air is about 90 s at 25 °C and 0% humidity.     

Characterization and optimization to improve uneven surface on MEMS bridge fabrication

This paper presents an optimized fabrication method for developing a freestanding bridge for RF MEMS switches. In this method, the sacrificial layer is patterned and hard baked a 220 °C for 3 min, after filling the gap between the slots of the coplanar waveguide. Measurement results by AFM and SEM demonstrate that this technique significantly improves the planarity of the sacrificial layer, reducing the uneven surface to less than 20 nm, and the homogeneity of the Aluminum thickness across the bridge. Moreover, a mixture of O₂, Ar and CF₄ was used and optimized for dry releasing of the bridge. A large membrane (200 × 100 μm²) was released without any surface bending. Therefore, this method not only simplifies the fabrication process, but also improves the surface flatness and edge smoothness of the bridge. This fabrication method is fully compatible with standard silicon IC technology.     

Thick film sensors based on laccases from different sources immobilized in polyaniline matrix

Thick film electrode based biosensors containing Trametes versicolor (TvL) and Aspergillus niger (AnL) laccases and Agaricus bisporus tissues (AbT) were developed for the determination of phenolic compounds and the measurement was based on oxygen consumption in relation to analyte oxidation. The electrodeposited organic polymer; polyaniline was used as a matrix for the immobilization in the preparation of thick film sensors. The systems were calibrated for different phenolic substances. A linearity was obtained in concentration range between 0.4 and 6.0 μM phenol, 0.2 and 1.0 μM catechol, 2.0 and 20.0 μM l-DOPA for TvL based biosensor; for AnL based enzyme electrode 0.4 and 4.0 μM phenol, 0.4 and 15 μM catechol, 0.4 and 6.0 μM l-DOPA; for AbT electrode 1.0 and 10 μM phenol, 0.4 and 1.6 μM catechol, 1.0 and 10 μM l-DOPA, respectively, in the response time of 300 s. Furthermore, as well as sample application and accuracy, optimum pH, temperature and thermal stabilities of the proposed systems were also detected.     

Development of a piezoelectric lead titanate thin film process on silicon substrates by high rate gas flow sputtering

Polycrystalline lead titanate (PT) thin films in the range of 3–6 μm were crack and void free deposited on silicon substrates in a high rate gas flow sputtering process. Gas flow sputtering uses the hollow cathode effect which results into high deposition rates of about 120 nm/min. (1 1 1) Textured platinum was used as bottom electrode to assist the nucleation of PT.Material properties of the PT thin films as well as the Pt bottom electrode like topography, morphology, chemical composition, and structure are evaluated. The sputtered PT layers show clearly Perovskite traces in XRD patterns, even the (1 1 1) texture of the Pt is partial transferred. The most difficult part is to fulfil the empirical formula PbTiO₃. This problem is solved by stabilising the process parameters. It was shown that the temperature has got enormous influence at the stoichiometry.     

Characteristics of a Pd–oxide–In0.49Ga0.51P high electron mobility transistor (HEMT)-based hydrogen sensor

An interesting hydrogen sensor based on a high electron mobility transistor (HEMT) device with a Pd–oxide–In_0.49Ga_0.51P gate structure is fabricated and demonstrated. The hydrogen sensing characteristics including hydrogen detection sensitivity and transient responses of the studied device under different hydrogen concentrations and temperature are measured and studied. The hydrogen detection sensitivity is related to a change in the contact potential at the Pd/insulator interface. The kinetic and thermodynamic properties of hydrogen adsorption are also studied. Experimentally, good hydrogen detection sensitivities, large magnitude of current variations (3.96 mA in 9970 ppm H₂/air gas at room temperature) and shorter absorption response time (22 s in 9970 ppm H₂/air gas at room temperature) are obtained for a 1.4 μm × 100 μm gate dimension device. Therefore, the studied device provides a promise for high-performance solid-state hydrogen sensor, integrated circuit (IC) and micro electro-mechanical system (MEMS) applications.     

Low-cost microelectrode array with integrated heater for extracellular recording of cardiomyocyte cultures using commercial flexible printed circuit technology

This article reports the use of commercial, flexible printed circuit technology for the fabrication of low-cost microelectrode arrays (MEAs) for recording extracellular electrical signals from cardiomyocyte cultures. A 36-electrode array has been designed and manufactured using standard, two-layer, polyimide-based flexible circuit technology, with electrode diameters of 75 and 100 μm. Copper structures defined on the backside of the array have been used for low-power thermal regulation of the culture. Electrical characterization of the gold-plated electrodes showed impedances below 250 kΩ at 1 kHz. Functional testing was conducted using HL-1 cardiac myocytes. The arrays proved biocompatible, and supported the formation of functional syncytia, as demonstrated by electrical recordings of depolarization waves across the array. A comparison with conventional, glass-based MEAs is presented, which reveals differences in signal strength (smaller for larger electrode) and variability (less for larger electrodes), but no effect of the substrate types on culture parameters such as beat rate or conduction velocity. The performance of the on-chip heating was evaluated, with typical temperature settling times (to ±0.1 °C) below 10 s, for a power consumption around 1 W (at 37 °C). Accuracy and stability are discussed. HL-1 cell responses to various temperature profiles enabled by the on-chip heating are presented, showing a remarkable correlation between temperature and beat rate.     

High-precision and ultrafast UV laser system for next-generation flexible PCB drilling

Since conventional mechanical punching technology for Flexible Printed Circuit Board (FPCB) drilling has restricted via-hole size and depth control for multi-layer circuit boards, CO₂ and Ultra Violet (UV) laser drilling technologies have been developed. However, the FPCBs for mobile phones and Personal Digital Assistants (PDAs) require smaller via-hole diameters, since the development of thinner and higher circuit density devices is demanded. Currently, UV laser systems are widely used for FPCB drilling of 75–105 μm diameter via-holes and inspectors performs quality test manually using microscopes. We developed a high-precision UV laser microfabrication system for next-generation FPCB drilling of 15 μm diameter via-holes. The degrees of the precision of the microfabricated via-holes of 15, 35, 50 and 85 μm were mean absolute error rate of 4.4, 2.2, 2.3, and 2.2 which was fully satisfied with industrial inspection specification ±10%. The drilling speed of the system of 2800 via-holes per second at stationary state was achieved. In addition, we applied modified Greedy 2-opt algorithm to find out optimal drilling path which reduced the total time of via-hole fabrication. We successfully reduced the production time by 25% compared with the result obtained in the normal Greedy 2-opt algorithm. Moreover, we designed very accurate inspection method using Canny edge detection and geometric pattern matching algorithms and successfully applied it to the Automated Optical Inspection (AOI) module for the inspections of 15 μm diameter via-hole which was required for the fabrication of high density FPCB.     

Fabrication of thermal microbridge actuators and characterization of their electrical and mechanical responses

This study presents thermal silicon microbridge actuators which have been made by a novel fabrication process utilizing dry processes for all critical steps. The fabrication process results in microbridges which are fully oxide covered, with excellent surface quality and dimensional control. The microbridges are made in the device layer of a silicon-on-insulator (SOI) wafer which ensures uniform doping profile and accurate thickness control. The electrical and mechanical responses of the bridges were measured upon rapid heating up to near the melting point of silicon. Up to 12 μm mechanical deflection due to thermal expansion was detected by white light interferometry (WLI) which allowed accurate measurement. Mechanical deflection has previously not been measured for silicon microlamps. Thermal conduction in the air gap between the actuator and the neighbouring solid silicon parts was analysed and shown to be more important than convection or radiation, even at very high operation temperatures.     

Development of a novel micromirror based on surface micromaching technology

A novel 3 × 3 micromirror array is designed and successfully fabricated with multi-layer silicon surface micromaching technology. It is composed of bottom electrode, support part and mirror plate, in which a T type beam structure is used to support the mirror plate. It can provide mirror with the vertical movement and the rotation about two horizontal axes, thus enabling phase modulation and amplitude modulation for the incident light. The test results show that the maximum deflection length along the vertical direction of the mirror plate is 2 μm, while the rotation angle about X- and Y-axis are ±2.3° and ±1.45°, respectively.     

Ultra high performance planar InGaAs PIN photodiodes for high speed optical fiber communication

This paper reports a front-illuminated planar InGaAs PIN photodiode with very low dark current, very low capacitance and very high responsivity on S-doped InP substrate. The presented device which has a thick absorption layer of 2.92 μm and a photosensitive area 73 μm in diameter exhibited the high performance of a very low capacitance of 0.47 pF, a very low dark current of 0.041 nA, a very high responsivity of 0.99 A/W (79% quantum efficiency) at λ = 1.55 μm, the 3 dB bandwidths of 6.89 GHz (−5 V), 7.48 GHz (−12 V) for bare chips and 4.48 GHz (−5 V), 5.02 GHz (−12 V) for the devices packaged in TO can, respectively. Furthermore, the developed PIN photodiodes possess high breakdown voltage of less than −25 V.     

Development of an automation system to evaluate the three-dimensional oxygen distribution in wastewater biofilms using microsensors

In this paper the authors describe the development of an automation system applicable to environmental biofilm studies. The automation system controls a combined oxygen microsensor to measure the three-dimensional dissolved oxygen distribution in a wastewater biofilm sample. The biofilm is sampled from a rotating biological contactor in a municipal wastewater treatment plant. The automation system consists of a data acquisition system, a motion control system, and a computer program. The combined oxygen microsensor consists of a sensing electrode, a reference electrode, a guard cathode, an oxygen permeable membrane, and an electrolyte solution. The automation system allows the acquisition and storage of data from 4000 measurements from the microsensor and the precise positioning of the microsensor in order to measure 100 dissolved oxygen profiles in a 1000 μm × 1000 μm biofilm area. The three-dimensional profile shows that the dissolved oxygen concentration in the biofilm sample is highly heterogeneous and it revealed “pockets” of dissolved oxygen in deep sections of the biofilm sample. The automation system and the combined oxygen microsensor were proven to be tools that improve the quantity and quality of experimental results needed to understand important functions in biofilms used in wastewater treatment.     

A passive through hole microvalve for capillary flow control in microfluidic systems

A passive through hole microvalve is proposed to stop the capillary-driven flow in microchannels with small static contact angle (θ_s < 45°). Its gating condition on regulating flow is derived based on contact line theory. Using numerical simulations in certain limits and some experiments, we investigated the valve performance of a few different valve designs. A kind of converging through hole microvalve is found which can stop the relative faster capillary flow and is easier to fabricate and integrate. It is shown that allowable flow velocity for DI water could reach 0.5 m/s, and the height of microvalve could be as short as to 20 μm.     

Perchlorate-selective polymeric membrane electrode based on a cobaloxime as a suitable carrier

A cobaloxime ([chlorobis(dimethylglyoximeato)(triphenylphosphine)] cobalt (III), [Co(dmgH)₂pph₃Cl]) incorporated in a plasticized poly(vinyl chloride) membrane was used to develop a perchlorate-selective electrode. The influence of membrane composition on the electrode response was studied. The electrode exhibits a Nernstian response over the perchlorate concentration range 1.0 × 10⁻⁶ to 1 × 10⁻¹ mol l⁻¹ with a slope of −56.8 ± 0.7 mV per decade of concentration, a detection limit of 8.3 × 10⁻⁷, a wide working pH range (3–10) and a fast response time (<15 s). The electrode shows excellent selectivity towards perchlorate with respect to many common anions. The electrode was used to determine perchlorate in water and human urine.