Silicon Micromachining Technology Research Articles

PLATINUM-BASED CONE MICROELECTRODES FOR IMPLANTABLE NEURAL RECORDING APPLICATIONS

There have been significant advances in fabrication of high-density microelectrode arrays using silicon micromachining technology in neural signal recording systems. The interface between microelectrodes and chemical environment is of great interest to researchers, working on extracellular stimulation. This interface is quite complex and must be modeled carefully to match experimental results. Computer simulation is a method to increase the knowledge about these arrays and to this end the finite element method (FEM) provides a strong environment for investigation of relative changes of the electrical field extension surrounding an electrode positioned in chemical environment. In this paper FEM simulation environment is used for modeling the metal–chemical interface, which provides helpful information about noise, impedance, and bandwidth for circuit designers to design the front-end electronics of these systems, more efficiently and reliable.

Piezo-electrically Actuated Micro Corner Cube Retroreflector (CCR) for Free-space Optical Communication Applications

In this paper, an extremely low voltage operated micro corner cube retroreflector (CCR) was fabricated for free-space optical communication applications by using bulk silicon micromachining technologies. The CCR was comprised of an orthogonal vertical mirror and a horizontal actuated mirror. For low voltage operation, the horizontal actuated mirror was designed with two PZT cantilever actuators, torsional bars, hinges, and a mirror plate with a size of <TEX>$400{\mu}m{\times}400{\mu}m$</TEX>. In particular, the torsional bars and hinges were carefully simulated and designed to secure the flatness of the mirror plate by using a finite element method (FEM) simulator. The measured tilting angle was approximately <TEX>$2^{\circ}$</TEX> at the applied voltage of 5 V. An orthogonal vertical mirror with an extremely smooth surface texture was fabricated using KOH wet etching and a double-SOI (silicon-on-insulator) wafer with a (110) silicon wafer. The fabricated orthogonal vertical mirror was comprised of four pairs of two mutually orthogonal flat mirrors with <TEX>$400{\mu}m4</TEX> (length) <TEX>$\times400{\mu}m$</TEX> (height) <TEX>$\times30{\mu}m$</TEX> (thickness). The cross angles and surface roughness of the orthogonal vertical mirror were orthogonal, almost <TEX>$90^{\circ}$</TEX> and 3.523 nm rms, respectively. The proposed CCR was completed by combining the orthogonal vertical and horizontal actuated mirrors. Data transmission and modulation at a frequency of 10 Hz was successfully demonstrated using the fabricated CCR at a distance of approximately 50 cm.

A CMOS Compatible Micromachined Thermopile IR Sensor with High Sensitivity

Micromachined thermal IR sensors are of major importance to IR radiation related applications. In this article, a thermopile IR sensor with high sensitivity was fabricated using the complementary metal-oxide-semiconductor (CMOS) process and silicon micromachining technology. As a result, the entire bulk silicon under the thermopile structure was removed and the thermopile structure was released from the front side; both the solid thermal loss of the support membrane and gas convection loss decreased. Without additional IR absorption material in the absorber area, the sensor shows a sensitivity of ∼ 131 V/W and a noise equivalent power of 0.21 nW/Hz 1/2 in air at room temperature.

Force-sensitive Sensor Based on Single-walled Carbon Nanotube Array

Traditional silicon micro-machining technology is utilized to produce parallel micro-electrodes on silicon chips,and silicon chips are deeply etched to wear a rectangular hole between the parallel micro-electrodes.Next,ultra-long single-walled carbon nanotube(SWCNT) array is grown across micro-electrodes and rectangular hole to suspend well aligned between the parallel micro-electrodes by the method of large gas flow directional chemical vapor deposition(CVD).The Si chip attached with SWCNTs is then mounted onto a thin PVC base and the connections of Si island are cut by laser technology,so that the force acting on the PVC base can directly transfer to SWCNT array.After extraction of wires,the fabrication of micro-nano-force-sensing unit is finished.Later,the research is carried out mainly on strain sensing of suspended SWCNT array.High gauge factor and linearity are obtained.The experimental results show that this sensor unit is simple and low in cost,thus providing a new way of thinking upon the preparation for micro-nano integrated sensor unit based on carbon nanotubes.

DRIE based technology for 3D silicon barcodes fabrication

Microworld barcoding has become a promising tool for cell biology. Individual and subpopulation cell tracking is of great interest to evaluate cell behaviour. Nowadays, many micrometer and even nanometer size silicon structures can be fabricated using microelectronics techniques. In this work we report for first time the development of 3D barcodes based on silicon substrate. The proposed silicon micromachining technology based on deep reactive ion etching (DRIE) allows to obtain micrometer-sized cylindrical structures with vertical etch profile that defines a bit = 1 and non-vertical etch profile that defines a bit = 0. Although this technology will allow more than 15 bits representation, only 4–8 bits are necessary for cell labelling. The results of this work show that DRIE has become a versatile technique to produce high aspect 3D biocompatible silicon-based barcodes structures for cell studies.

Resonant frequency sensitive MEMS bandpass filter using capacitive sensing scheme

This paper presents the theoretical and experimental behaviour of microelectromechanical bandpass filters. The proposed bandpass filter can detect frequencies of monitoring structures with high sensitivity using the resonant frequency of micro-resonator of sensor. The micro-resonator contains a proof mass and four supported beams fabricated using a bulk silicon micromachining technology on a silicon-on-insulator wafer. When applying an external force to the system, the device generates a capacitance change, which is converted into a voltage by an electrical circuitry. In good agreement with finite element simulations of the device, experimental results validate that the filter has a center frequency of about 3.3 kHz, a 3 dB bandwidth of 0.562 kHz and a quality factor Q of 5.9 in atmospheric pressure. This paper demonstrates a parallel-resonator filter to increase a monitoring bandwidth. A 3 dB bandwidth of the parallel filter is measured to be 1.25 kHz at atmospheric pressure.

A Varifocal Convex Micromirror Driven by a Bending Moment

A varifocal micromirror is designed and fabricated using silicon micromachining technology. A spherical convex surface of mirror is generated by applying a bending moment to the circumference of micromirror. This method is different from the conventional technique in which a distributed force is exerted on the central area of mirror. On the basis of the theory of materials strength, the deformation of a plate is purely spherical if only a bending moment is applied to the circumference. Spherical surface is well approximated to be a parabola if deflection is small. In order to generate only a bending moment, a force is applied to the plate in the region outside the fulcrum, by which the plate is supported freely in rotation. The proposed mirror was fabricated from a silicon on insulator wafer and a glass plate, which were connected by anodic bonding. The deviation in surface profile of mirror from a parabola was measured with an optical interferometer to be less than 4.7 nm rms in the mirror region inside the 400-mum-diameter fulcrum at the voltage lower than 215 V. The focal length of the fabricated mirror was varied from approximate infinity to 24 mm.

A Low-Loss Substrate-Independent Approach for 60-GHz Transceiver Front-End Integration Using Micromachining Technologies

This paper presents a low-loss, substrate-independent approach to integrate transceiver front-ends for 60-GHz wireless applications. Dielectric loss is eliminated by using polymer and bulk silicon micromachining technologies to create a cavity-based duplexer and a horn antenna in the air, above the substrate. A coplanar waveguide input is used for easy integration of the low-noise amplifier and power amplifier of the receiver and transmitter, respectively, with the micromachined passive module. A prototype is designed, fabricated, and characterized, with the transmit band (TX) set between 58.7-59.5 GHz and the receive band (RX) as 60.6-61.4 GHz. The proposed method offers an easy integration of both planar components and 3-D integrated modules on top of the substrate.

Silicon-based micro-reactor for preferential CO oxidation

Abstract A silicon-based micro-reactor was fabricated using a micro-electromechanical system (MEMS) process and silicon micromachining technology (SMT) to allow preferential CO oxidation (PrOx) to be applied to compact portable devices. To design the micro-PrOx reactor, the effects of channel length, channel width, channel array, and O2 content in the reactant gas on the CO conversion and selectivity for CO were investigated. The single micro-PrOx reactor required an O2 concentration four times higher than the theoretical quantity for a complete conversion of 1% CO into CO2. The optimum operating temperature to obtain high CO conversion, by suppressing the reverse water–gas shift (r-WGS) reaction, depended considerably on the channel lengths of the micro-reactor rather than on the channel widths or the channel arrays. The micro-PrOx reactor showed 99.4% conversion of CO and 44.14% selectivity for CO at 260 °C when operating with 1% CO, 50% H2, 35% CO2, N2 (balance), and 2% O2.

Design and fabrication of silicon-based 8×8 MEMS optical switch array

Silicon-based torsion-beam 8×8 optical switch array are designed and fabricated with bulk silicon micromachining technology. Torsion beams and cantilever beams with reflective micromirror situated on the same wafer are fabricated on (110) silicon. During fabricating the torsion beam actuating structure, the etched hillocks on (110) plane are obstacles to achieve smooth torsion beam. It is put forward the reasonable ratios mixtures of HF, HNO3 and CH3COOH to improve the processes of fabricating torsion beam actuating structure. The slanted under electrodes that can reduce the actuating voltage are designed and fabricated on tilting (111) plane by wet chemical etching. According to the etching characteristics of (111) silicon in KOH solution, two designed photomask patterns are proposed in this paper. According to the experimental results, for the 180μm displacement of mirrors, the device presents the switching time less than 6ms and the actuating voltage about 65V. It shows that this optical switch array can make the meet of the optical communication network.

Optimization of a wafer-level process for the fabrication of highly reproducible thin-film MOX sensors

Abstract Thin-film metal oxide semiconductor (MOX) gas sensors are characterized by high sensitivity and fast response. Those characteristics make them very promising among the several existing technologies for the production of solid state gas sensors. Furthermore, by means of silicon micro-machining technology, MOX sensors can be made on micro hotplates, allowing to reach very low-power consumption, and the batch production guaranties a high yield. However, reproducibility and reliability are still major issues preventing the use of thin-film MOX sensors in mass-market applications. In this work, a wafer-level fabrication process for micro-machined low-power consumption thin-film MOX sensor arrays is reported. Different solutions for the optimization of the fabrication process are investigated, aiming to increase the reproducibility. The critical technological steps related to signal generation and acquisition, like the thin-film definition and positioning and the definition of the sensing layer electrodes, have been optimized. The devices considered are 4-sensor arrays based on thin films of SnO2 deposited by a modified rheotaxial growth and thermal oxidation (M-RGTO) technique on micro-machined low-power hotplates. The different fabrication techniques are described in detail. 45 sensors from 3 wafers, made using the different fabrication techniques, are comparatively characterized. The spread of the main sensor functional parameters values shows an evident decrease when the optimized fabrication process is used.

Ultra-high-resolution monolithic thermal bubble inkjet print head

A monolithic inkjet print head, fabricated with silicon micromachining technology and capable of generating microscale liquid droplets, is developed and shown to function successfully. The print head uses a dense array of thermal bubble inkjet devices, made on a single silicon wafer. Each device is made of a Pt heater stack, a small, shallow fluid chamber, and a refilling channel formed by a Ge-sacrificial etching process, a deep-etched through-wafer feeding hole, and a micron-scale nozzle opened in a thin nitride membrane by plasma etching. Experimental results with a high resolution video imaging system show that this print head is capable of generating water droplets as small as 3 µm in diameter (0.014 pL), about 1/70th the volume of the droplets produced by existing inkjet systems. The printing process is also found to be stable, uniform in droplet size and velocity, and free of satellite droplets at optimum operation conditions. At small distances between the print head and substrate, droplet spreading is also small. This print head is then a capable tool for ultra-high-resolution inkjet printing and can be used in research areas where delivery of micron-scale fluid droplets is desired.

Proximity electron lithography using permeable electron windows

This letter reports on an electron source consisting of thin electron-permeable windows and a carbon nanocoil emitter. Electron windows with diameters of 250nm were fabricated using silicon micromachining technology. Carbon nanocoils that are selectively grown from silicon were used as emitters. Field-emitted electrons from the emitters are transmitted through the thin silicon electron windows with thicknesses in the range of 15–50nm. The electron transmittance of the electron windows was evaluated and it was demonstrated that transmittances higher than 60% are achievable for the case of electron energies higher than 5keV. Proximity electron lithography is demonstrated using 1.5×1.5μm2 electron windows with a thickness of 50nm.

Multiplexed electrospray deposition for protein microarray with micromachined silicon device

Multiplexed electrospray deposition device capable of delivering picoliter volumes made by silicon micromachining technology has been developed as a deposition tool for making protein microarrays in a noncontact mode. Upon application of potential difference in the range of 7–9kV, biomolecules dissolved in suitable buffer with nonionic surfactant and loaded on the electrospray tips were dispensed on the substrate with microfabricated hydrogel features (1–10μm) in cone-jet mode. Schiff base chemistry followed by reductive amination was utilized for covalent immobilization.

Resonator combined with a piezoelectric actuator for chemical analysis by force microscopy

A high frequency silicon resonator for dynamic scanning force microscopy is combined with an integrated piezoelectric actuation element for large displacements. A high resonance frequency is required for imaging on the nanometer scale, and a large displacement is needed for the chemical analysis of the material at the end of the probe. The small piezoelectric resonator is formed at the end of a long piezoelectric actuator using a silicon micromachining technology. The resonator can be oscillated at 96.4 kHz, and the actuator generates a maximum displacement of 15 microm at the end of the probe. The dynamic-mode scanning force microscopy capability, using the integrated piezoelectric resonator, is demonstrated on a 2 microm pitch Au grating.

Effects of environmental temperature on the performance of a micromachined gyroscope

This paper presents the modeling of the detection capacitance analysis for a tuning fork vibratory microgyroscope fabricated by the bulk silicon micromachining technology. The dynamic characteristics of the detection capacitance of the microgyroscope are calculated based on the model. Then the effects of environmental thermal fluctuations on the microgyroscope are considered. Non-linear analysis and numerical simulations show that the frequencies and output of the microgyroscope have slight deviations when the microgyroscope works at different environmental temperature. The deviations of the frequencies and dynamic characteristics are calculated accurately, which provides a reference for the design of temperature compensation method and robust structural design for the microgyroscope.

Self-organizing optimization method of structural shape of micromachined gyroscope

A tuning fork vibratory micromachined gyroscope fabricated by the bulk silicon micromachining technology is studied.The self-organizing method of shape optimization is presented based on cellular automata(CA).The local rule and performance evaluation function are derived for the self-organ-izing shape optimization.The shape of the micromachined gy-roscope is optimized.The substructuring model of the micro-machined gyroscope is established to conduct analysis with a reasonable accuracy and a reduced computational cost.The validity of the method is tested by a numerical example.The optimization result shows that the performance of micro-machined gyroscope is promoted greatly without change in the high Q-qualify factors.Based on promotion of analysis accu-racy and efficiency,the method and results of self-organizing shape optimization for micromachined gyroscope have impor-tant reference value to the analysis,design and evaluation of performance of the tuning fork vibratory micromachined gyro-scope in coupled multiphysics fields environment.

Multi-layer microstructure fabrication by combining bulk silicon micromachining and UV-LIGA technology

A novel method for fabrication of multi-layer microstructures of microelectro-mechanical system (MEMS) devices is described. This technique, which combines bulk silicon micromachining technique and UV-LIGA technique can overcome some shape limitations of single technique on complex microstructures. To demonstrate this combination, the SU-8 microstructure fabricated in the etched silicon grooves is presented. In this fabrication process, a SU-8 removal method by fuming sulfuric acid was introduced and a novel type of plastics PETG was tried in microhot embossing process. The proposed fabrication process can be applied to fabricating a high-aspect-ratio microstructure for a large displacement actuator and precision sensors. Moreover, this combined process enables the fabrication of more complex structures, which cannot be fabricated by bulk micromachining or UV-LIGA alone.

Analytical modeling for bulk-micromachined condenser microphones

The advent of silicon micromachining technology has opened up numerous opportunities for the commercialization of many miniaturized sensors and one of the beneficiaries is the silicon condenser microphone. Simple analytical expressions, such as those formulated by Škvor/Starr for mechanical-thermal noise calculation, are used to describe the mechanical performance of a microelectromechanical system (MEMS) microphone. However, the location effect of acoustic holes is usually not considered on both frequency response and mechanical-thermal noise. In this paper, the theory of a condenser microphone is reviewed and a new analytical modeling method for the MEMS condenser microphones is proposed based on Zuckerwar’s model. With reference to a B&amp;K MEMS microphone, the theoretical results obtained by the modeling method are in very good agreements with those experimental ones reported. It is also concluded that there is an optimum location for acoustic holes in the backplate. Finally, a new design for MEMS microphone with a polarization voltage of 10V is proposed, which has an open-circuit sensitivity of 2.1mV∕Pa (or −54dB ref. 1V∕Pa), a bandwidth of 18kHz, an A-weighted mechanical-thermal noise of 22dBA, and a signal-to-noise ratio of 60dB. This proposed microphone can be easily micromachined by using MEMS technology such as the deep reactive ion etching and wafer bonding technology.

Channeling-based collimators for generation of microbeams produced by silicon micromachining technology

The growing interest on micro-beams in recent years and the combined development of channeling technology in high-energy physics have opened the way to new concepts for micro-beams devices. Silicon micromachining technology is here applied to manufacture micro-collimators in inexpensive and feasible ways. Both dry and wet etchings can be employed for the purpose, though the latter technique appears to be cheaper and easier. Two designs for micro-collimator devices have been considered and preliminary samples have been produced accordingly.