Showing papers on "Surface micromachining published in 2005"

An electromechanical material testing system for in situ electron microscopy and applications

Abstract: We report the development of a material testing system for in situ electron microscopy (EM) mechanical testing of nanostructures. The testing system consists of an actuator and a load sensor fabricated by means of surface micromachining. This previously undescribed nanoscale material testing system makes possible continuous observation of the specimen deformation and failure with subnanometer resolution, while simultaneously measuring the applied load electronically with nanonewton resolution. This achievement was made possible by the integration of electromechanical and thermomechanical components based on microelectromechanical system technology. The system capabilities are demonstrated by the in situ EM testing of free-standing polysilicon films, metallic nanowires, and carbon nanotubes. In particular, a previously undescribed real-time instrumented in situ transmission EM observation of carbon nanotubes failure under tensile load is presented here.

Capacitive micromachined ultrasonic transducers: fabrication technology

Abstract: Capacitive micromachined ultrasonic transducer (MUT) technology is a prime candidate for next generation imaging systems. Medical and underwater imaging and the nondestructive evaluation (NDE) societies have expressed growing interest in cMUTs over the years. Capacitive micromachined ultrasonic transducer technology is expected to make a strong impact on imaging technologies, especially volumetric imaging, and to appear in commercial products in the near future. This paper focuses on fabrication technologies for cMUTs and reviews and compares variations in the production processes. We have developed two main approaches to the fabrication of cMUTs: the sacrificial release process and the recently introduced wafer-bonding method. This paper gives a thorough review of the sacrificial release processes, and it describes the new wafer-bonding method in detail. Process variations are compared qualitatively and quantitatively whenever possible. Through these comparisons, it was concluded that wafer-bonded cMUT technology was superior in terms of process control, yield, and uniformity. Because the number of steps and consequent process time were reduced (from six-mask process to four-mask process), turn-around time was improved significantly.

Water‐Soluble Sacrificial Layers for Surface Micromachining

Abstract: This manuscript describes the use of water-soluble polymers for use as sacrificial layers in surface micromachining. Water-soluble polymers have two attractive characteristics for this application: 1) They can be deposited conveniently by spin-coating, and the solvent removed at a low temperature (95-150 degrees C), and 2) the resulting layer can be dissolved in water; no corrosive reagents or organic solvents are required. This technique is therefore compatible with a number of fragile materials, such as organic polymers, metal oxides and metals-materials that might be damaged during typical surface micromachining processes. The carboxylic acid groups of one polymer-poly(acrylic acid) (PAA)-can be transformed by reversible ion-exchange from water-soluble (Na+ counterion) to water-insoluble (Ca2+ counterion) forms. The use of PAA and dextran polymers as sacrificial materials is a useful technique for the fabrication of microstructures: Examples include metallic structures formed by the electrodeposition of nickel, and freestanding, polymeric structures formed by photolithography.

Micromachined acoustic resonant mass sensor

Abstract: This paper describes a highly sensitive, film bulk acoustic resonator (FBAR) mass sensor (built on a micromachined silicon-nitride diaphragm with a piezoelectric thin film and Al electrodes) that can operate in vapor and liquid. The sensitivity of the device to mass change on its surface has been investigated by having various thicknesses of silicon-nitride support layer and also of Al layer. The sensor is measured to have a mass sensitivity of 726 cm/sup 2//g, which is about 50 times that of a typical quartz crystal microbalance (QCM). In vapor, the sensor (operating at around 1 GHz and having a relatively high quality (Q) factor of 200-300) shows a minimum detectable frequency shift of about 400 Hz, which corresponds to a mass change of 10/sup -9/ g/cm/sup 2/ on the sensor surface, comparable with that detectable by a QCM. In liquid, though the Q usually drops more than an order of magnitude, we obtain a Q of 40 at 2 GHz by using a second harmonic resonance of the resonator. And with the Q, a minimum 5 ppm resonant frequency shift can be detected, which corresponds to 10/sup -8/ g/cm/sup 2/ change on the sensor surface.

A monolithic three-axis micro-g micromachined silicon capacitive accelerometer

Abstract: A monolithic three-axis micro-g resolution silicon capacitive accelerometer system utilizing a combined surface and bulk micromachining technology is demonstrated. The accelerometer system consists of three individual single-axis accelerometers fabricated in a single substrate using a common fabrication process. All three devices have 475-/spl mu/m-thick silicon proof-mass, large area polysilicon sense/drive electrodes, and small sensing gap ( /spl sim/5 pF/g measured sensitivity and calculated sub-/spl mu/g//spl radic/Hz mechanical noise floor for all three axes. The total measured noise floor of the hybrid accelerometer assembled with a CMOS interface circuit is 1.60 /spl mu/g//spl radic/Hz (>1.5 kHz) and 1.08 /spl mu/g//spl radic/Hz (>600 Hz) for in-plane and out-of-plane devices, respectively.

Ion-Beam-Assisted Lift-Off Technique for Three-Dimensional Micromachining of Freestanding Single-Crystal Diamond

Abstract: Diamond is a very attractive material for micromachining: it has high mechanical hardness, high Young’s modulus, a low coefficient of friction, high thermal conductivity, and a low thermal expansion coefficient. It is chemically inert and biocompatible. Optically, it is transparent over the widest range of the electromagnetic spectrum (from 220 nm to the far infrared), has a high refractive index, and exhibits a vast inventory of luminescent centers (> 500 electronic, > 150 vibrational), many of which are related to impurities or defects in the crystalline structure. [1] Some of these can therefore be controlled and engineered. Of particular interest is the nitrogen vacancy (NV – ) center that possesses very promising quantum properties. [2]

Three-dimensional micromachining of glass using femtosecond laser for lab-on-a-chip device manufacture

Abstract: Three-dimensional (3D) micromachining of photosensitive glass is demonstrated by photochemical reaction using femtosecond (fs) laser for lab-on-a-chip application. True 3D hollow microstructures embedded in the glass are fabricated by fs laser direct writing followed by heat treatment and successive wet etching. The modification mechanism of the photosensitive glass by the fs laser and advantage of this process are discussed. Various microcomponents for the lab-on-a-chip devices such as microfluidics, microvalves, microoptics, microlasers, etc. are fabricated by using this technique and their performance is examined .

Microfabrication of 3D silicon MEMS structures using gray-scale lithography and deep reactive ion etching

Abstract: Micromachining arbitrary 3D silicon structures for micro-electromechanical systems can be accomplished using gray-scale lithography along with dry anisotropic etching. In this study, we have investigated the use of deep reactive ion etching (DRIE) and the tailoring of etch selectivity for precise fabrication. Silicon loading, the introduction of an O 2 step, wafer electrode power, and wafer temperature are evaluated and determined to be effective for coarsely controlling etch selectivity in DRIE. The non-uniformity and surface roughness characteristics are evaluated and found to be scaled by the etch selectivity when the 3D profile is transferred into the silicon. A micro-compressor is demonstrated using gray-scale lithography and DRIE showing that etch selectivity can be successfully tailored for a specific application. © 2004 Elsevier B.V. All rights reserved.

Multiple-stage microfabricated preconcentrator-focuser for micro gas chromatography system

Abstract: The design, fabrication, and characterization of a multiple-stage Si microfabricated preconcentrator-focuser (/spl mu/PCF) for a micro gas chromatography (/spl mu/GC) system that can provide real-time quantification and identification of complex organic vapor mixtures are presented. The /spl mu/PCF consists of a Si microheater loaded with Carbopack B, Carbopack X, and Carboxen 1000 carbon adsorbent granules, and a Si micromachined cover plate. Deep reactive ion etching is utilized to produce mechanically robust fluidic interconnection adapters hermetically sealed to fused silica capillary tubing for connection to the other components in the /spl mu/GC. This three-stage device is designed to capture compounds spanning up to 4 orders of magnitude in volatility. The dead volume, thermal mass, heating efficiency, and pressure drop of the three-stage /spl mu/PCF are improved significantly over its single-stage /spl mu/PCF predecessor. We demonstrate the successful capture, desorption, and high-resolution chromatographic separation of a mixture of 30 common organic vapors using our three-stage /spl mu/PCF in a conventional GC system. The peak width at half height is <2.05 s for all compounds after elution from the GC column.

High-speed microfabricated silicon turbomachinery and fluid film bearings

Abstract: A single-crystal silicon micromachined air turbine supported on gas-lubricated bearings has been operated in a controlled and sustained manner at rotational speeds greater than 1 million revolutions per minute, with mechanical power levels approaching 5 W. The device is formed from a fusion bonded stack of five silicon wafers individually patterned on both sides using deep reactive ion etching (DRIE). It consists of a single stage radial inflow turbine on a 4.2-mm diameter rotor that is supported on externally pressurized hydrostatic journal and thrust bearings. This work presents the design, fabrication, and testing of the first microfabricated rotors to operate at circumferential tip speeds up to 300 m/s, on the order of conventional high performance turbomachinery. Successful operation of this device motivates the use of silicon micromachined high-speed rotating machinery for power microelectromechanical systems (MEMS) applications such as portable energy conversion, micropropulsion, and microfluidic pumping and cooling.

A resonant accelerometer with two-stage microleverage mechanisms fabricated by SOI-MEMS technology

Abstract: We present the design, fabrication, and testing of a push-pull differential resonant accelerometer with double-ended-tuning-fork (DETF) as the inertial force sensor. The accelerometer is fabricated with the silicon-on-insulator microelectromechanical systems (MEMS) technology that bridges surface micromachining and bulk micromachining by integrating the 50-/spl mu/m-thick high-aspect ratio MEMS structure with the standard circuit foundry process. Two DETF resonators serve as the force sensor measuring the acceleration through a frequency shift caused by the inertial force acting as axial loading. Two-stage microleverage mechanisms with an amplification factor of 80 are designed for force amplification to increase the overall sensitivity to 160 Hz/g, which is confirmed by the experimental value of 158 Hz/g. Trans-resistance amplifiers are designed and integrated on the same chip for output signal amplification and processing. The 50-/spl mu/m thickness of the high-aspect ratio MEMS structure has no effect on the amplification factor of the mechanism but contributes to a greater capacitance force; therefore, the resonator can be actuated by a much lower ac voltage comparing to the 2-/spl mu/m-thick DETF resonators. The testing results agree with the designed sensitivity for static acceleration.

Plastic micropump with ferrofluidic actuation

Abstract: We present the realization and characterization of a new type of plastic micropump based on the magnetic actuation of a magnetic liquid. The pump consists of two serial check-valves that convert the periodic motion of a ferrofluidic plug into a pulsed quasi-continuous flow. The ferrofluid is actuated by the mechanical motion of an external NdFeB permanent magnet. The water-based ferrofluid is synthesized in-house using a coprecipitation method and has a saturation magnetization of 32 mT. The micropump consists of various layers of polymethylmethacrylate (PMMA), which are microstructured by powder blasting or by standard mechanical micromachining techniques, and are assembled in a single plastic structure using a monomer gluing solution. Two soft silicone membranes are integrated in the microfluidic structure to form two check-valves. Water has been successfully pumped at flow rates of up to 30 /spl mu/L/min and pumping is achieved at backpressures of up to 25 mbar.

Microfluidic Lab-on-a-Chip for Chemical and Biological Analysis and Discovery

Abstract: Introduction Micromachining Methods Micromachining of Silicon Micromachining of Glass Micromachining of Fused Quartz (or Fused Silica) Micromachining of Polymeric Chips Metal Patterning World-to-Chip Interface Microfluidic Flow Liquid Pumping Methods Microfluidic Flow Control Sample Introduction Electrokinetic Injection Hydrodynamic Injection Other Sample Injection Methods Sample Pre-concentration Sample Stacking Extraction Porous Membrane Other Pre-concentration Methods Separation Gas Chromatography (GC) Capillary Electrophoresis (CE) Chromatographic Separations Coupled Separations Detection Methods Optical Detection Methods Electrochemical (EC) Detection Mass Spectrometry (MS) Other Detection Methods Applications to Cellular/Particle Analysis Retention of Cells and Particles Studies of Cells in a Flow Other Cell Operations Applications to Nucleic Acids Analysis Nucleic Acids Extraction and Purification Nucleic Acids Amplification DNA Hybridization Other Nucleic Acid Applications Applications to Protein Analysis Immunoassay Protein Separation Enzymatic Assays Appendix Problem Sets Introduction Micromachining Microfluidic Flow Sample Introduction Sample Preconcentration Separation Detection Cellular Analysis Nucleic Acid Analysis Protein Analysis References Glossary

Measurement of the mechanical properties of electroplated gold thin films using micromachined beam structures

Abstract: We have measured the Young’s modulus, residual stress, and stress gradient of electroplated gold thin films using surface micromachined beam structures. Cantilever and bridge beam structures of different lengths were fabricated using UV-LIGA surface micromachining and dry-release methods. The Young’s modulus and residual stress of the fabricated beams were determined from the resonance frequencies of electrostatically excited beams, and the stress gradient was evaluated from the self-deformation of released cantilevers. The observed Young’s modulus was smaller than the bulk Young’s modulus, and showed small changes depending on the deposition current density. The average residual stress was found to be tensile in nature, and the observed residual stresses showed no differences, regardless of the current density. However, the stress gradient increased with increasing current density. The deformation of the cantilever beam after release was dependent on the plasma ashing time used. This result implies that additional thermal effects from the post-deposition process may have an influence on the final performance of fabricated micro electro mechanical systems (MEMS) devices.

Miniature fiber-optic pressure sensor with a polymer diaphragm

Abstract: The fabrication and experimental investigation of a miniature optical fiber pressure sensor for biomedical and industrial applications are described. The sensor measures only 125 µm in diameter. The essential element is a thin polymer diaphragm that is positioned inside the hollow end of an optical fiber. The cavity at the fiber end is made by a simple and effective micromachining process based on wet etching in diluted HF acid. Thus a Fabry–Perot interferometer is formed between the inner fiber–cavity interface and the diaphragm. The fabrication technique is described in detail. Different sensor prototypes were fabricated upon 125 µm-diameter optical fiber that demonstrated pressure ranges from 0 to 40 and from 0 to 1200 kPa. A resolution of less than 10 Pa was demonstrated in practice. The fabrication technique presented facilitates production of simple and low-cost disposable pressure sensors by use of materials with that ensure the required biocompatibility.

Localized induction heating solder bonding for wafer level MEMS packaging

Abstract: This paper reports a new solder bonding method for the wafer level packaging of MEMS devices. Electroplated magnetic film was heated using induction heating causing the solder to reflow. The experiment results show that it took less than 1 min to complete the bonding process. In addition, the MEMS devices experienced a temperature of only 110 °C during bonding, thus thin film materials would not be damaged. Moreover, the bond strength between silicon and silicon wafer was higher than 18 MPa. The step height of the feed-through wire (acting as the electrical feed-through of the bonded region) is sealed by the electroplated film. Thus, the flatness and roughness of the electroplated surface are recovered by the solder reflow, and the package for preventing water leakage can be achieved. The integration of the surface micromachined devices with the proposed packaging techniques was demonstrated.

Femtosecond laser-drilled capillary integrated into a microfluidic device

Abstract: Recent growth in microfluidic technology is, to a large extent, driven by soft lithography, a high-throughput fabrication technique where polymer materials, such as poly(dimethyl) siloxane (PDMS), are molded to form microscopic channel networks. Nevertheless, the channel architectures that can be obtained by molding are limited. We address this limitation by using femtosecond laser micromachining to add unmoldable features to the microfluidic devices. We apply laser ablation to drill microcapillaries, with diameters as small as 0.5μm and aspect ratios as high as 800:1, in the walls of molded PDMS channels. Finally, we use a laser-drilled microcapillary to trap a polystyrene bead by suction and hold it against a shear flow.

Electrostatically actuated resonant microcantilever beam in CMOS technology for the detection of chemical weapons

Abstract: The design, fabrication, and testing of a resonant cantilever beam in complementary metal-oxide semiconductor (CMOS) technology is presented in this paper. The resonant cantilever beam is a gas-sensing device capable of monitoring hazardous vapors and gases at trace concentrations. The new design of the cantilever beam described here includes interdigitated fingers for electrostatic actuation and a piezoresistive Wheatstone bridge design to read out the deflection signal. The reference resistors of the Wheatstone bridge are fabricated on auxiliary beams that are immediately adjacent to the actuated device. The whole device is fabricated using a 0.6-/spl mu/m, three-metal, double-poly CMOS process, combined with subsequent micromachining steps. A custom polymer layer is applied to the surface of the microcantilever beam to enhance its sorptivity to a chemical nerve agent. Exposing the sensor with the nerve agent simulant dimethylmethylphosphonate (DMMP), provided a demonstrated detection at a concentration of 20 ppb or 0.1 mg/m/sup 3/. These initial promising results were attained with a relatively simple design, fabricated in standard CMOS, which could offer an inexpensive option for mass production of a miniature chemical detector, which contains on chip electronics integrated to the cantilever beam.

Frequency-dependent electrostatic actuation in microfluidic MEMS

Abstract: Electrostatic actuators exhibit fast response times and are easily integrated into microsystems because they can be fabricated with standard IC micromachining processes and materials. Although electrostatic actuators have been used extensively in "dry" MEMS, they have received less attention in microfluidic systems probably because of challenges such as electrolysis, anodization, and electrode polarization. Here we demonstrate that ac drive signals can be used to prevent electrode polarization, and thus enable electrostatic actuation in many liquids, at potentials low enough to avoid electrochemistry. We measure the frequency response of an interdigitated silicon comb-drive actuator in liquids spanning a decade of dielectric permittivities and four decades of conductivity, and present a simple theory that predicts the characteristic actuation frequency. The analysis demonstrates the importance of the native oxide on silicon actuator response, and suggests that the actuation frequency can be shifted by controlling the thickness of the oxide. For native silicon devices, actuation is predicted at frequencies less than 10 MHz, in electrolytes of ionic strength up to 100 mmol/L, and thus electrostatic actuation may be feasible in many bioMEMS and other microfluidic applications.

A microchip-based PCR device using flexible printed circuit technology

Abstract: Rapid heat transfer is crucial for an efficient polymerase chain reaction (PCR), and this makes temperature control one of the most essential features in a micro-PCR system, which always includes a heater and a sensor composing a closed-loop. Yet, the fabrication of the heater and the sensor often prevented micro-PCR systems from achieving both cost-effectiveness and fabrication-easiness. For most of the early researches micromachining techniques were used to allow sensors and heaters be integrated on a silicon or glass chip. However, the cost prevented them from wide applications. The work described in this paper is part of our effort to solve the cost/fabrication dilemma. An innovative digital temperature control system was developed by introducing a heater/sensor switching procedure. Only one temperature controlling element fabricated by flexible printed circuit technology was utilized in the constructed PCR device with minimum fabrication steps. The glass chip-based device was made from low cost materials and assembled with adhesive bonding. Through seemingly simple steps, we obtained both disposability and portability at the same time. Temperature stability within ±0.3 °C and a transitional rate of 8 °C/s during heating/cooling was achieved. A 244 bp DNA fragment of hepatitis C virus was successfully amplified in our device by a three-stage thermal cycling process. Further improvement was assisted by finite element analysis, and demonstrated by experiment.

The role of Triton surfactant in anisotropic etching of {1 1 0} reflective planes on (1 0 0) silicon

Abstract: Etching characteristics and properties of {1 1 0} silicon crystal planes used as 45° optical mirrors for deflecting optical beams from/to optical fibers were investigated. Fiber aligning grooves and passive mirror-like planes were realized by wet micromachining of (1 0 0) silicon in KOH–IPA and TMAH–IPA systems. Implementation of Triton-x-100 surfactant as an additive to 25% TMAH in anisotropic etching of {1 1 0} silicon passive mirror planes is reported and discussed. It was found that Triton-x-100 contents in the range of 10–200 ppm to the 25% TMAH–water etchant significantly increase the anisotropy mostly by decreasing the {1 1 0} etch rate and retaining the {1 0 0} etch rate. It is also shown that {1 1 0} surface roughness is substantially improved compared to two other etching systems. Furthermore, efficient convex corner underetching reduction is demonstrated. The results of optical characterization of passive mirrors with 632 nm incident light show reduced scattering of reflected optical beam due to improved microroughness for mirrors made by TMAH–Triton. For the reflection of the optical beam with 1.33 µm and 1.54 µm wavelengths, sputtered layer of gold is used as reflective coating on silicon mirrors thus increasing the reflected optical beam intensity by an additional 8%.

Surface- and bulk- micromachined two-dimensional scanner driven by angular vertical comb actuators

Abstract: In this paper, we present the design, fabrication, and measurements of a two-dimensional (2-D) optical scanner with electrostatic angular vertical comb (AVC) actuators. The scanner is realized by combining a foundry-based surface-micromachining process (Multi-User MEMS Processes-MUMPs) with a three-mask deep-reactive ion-etching (DRIE) postfabrication process. The surface-micromachining provides versatile mechanical design and electrical interconnect while the bulk micromachining offers high-aspect ratio structures leading to flat mirrors and high-force, large-displacement actuators. The scanner achieves dc mechanical scanning ranges of /spl plusmn/6.2/spl deg/ (at 55 Vdc) and /spl plusmn/4.1/spl deg/ (at 50 Vdc) for the inner and outer gimbals, respectively. The resonant frequencies are 315 and 144 Hz for the inner and the outer axes, respectively. The 1-mm-diameter mirror has a radius of curvature of over 50 cm. [1454].

Micromachined 2-D scanner for 3-D optical coherence tomography

Abstract: With the inherent advantages of micromachining technologies such as small size, small mass, low cost, low power consumption and high reliability, there will be radical changes to biomedical devices and how clinical diagnoses are made. One of the most promising applications of microtechnologies is in the field of medical science. This paper presents a potentially low voltage high electrostatic torque micromachined mirror capable of two-dimensional (2-D) scans (simultaneous transverse and longitudinal scans) for optical coherence tomographic imaging. When the micro-mirror is integrated with an optical coherence tomography (OCT) system, three-dimensional (3-D) sample images can be obtained in one longitudinal scan period. 3-D images of internal-organs of fruit fly ( Drosophila melanogaster ) and its larva are acquired using the micromachined-based OCT system. The dimension of the micromachined mirror is 1000 um × 1000 um. The entire MEMS scanner is made of single-silicon crystal, to act as mechanical reinforcement counteracting the inherent stresses of the deposited thin films on the mirror. The scanning mirror is actuated electrostatically.

A thermal bimorph micromirror with large bi-directional and vertical actuation

Abstract: This paper reports a novel large vertical displacement (LVD) microactuator that can generate large piston motion and bi-directional scanning at low driving voltage. A LVD micromirror device has been fabricated by using a unique deep reactive ion etch (DRIE) post-CMOS micromachining process that simultaneously provides thin-film and single-crystal silicon microstructures. The bimorph actuation structure is composed of aluminum and silicon dioxide with an embedded polysilicon thermal resistor. With a size of only 0.7 mm × 0.32 mm, the LVD micromirror demonstrated a vertical displacement of 0.2 mm at 6 V dc. This device can also be used to perform bi-directional rotational scanning through the use of two bimorph actuators. The micromirror rotates over ±15 ◦ at less than 6 V dc, and over ±43 ◦ (i.e., >170 ◦ optical scan angle) at its resonant frequency of 2.6 kHz.

Femtosecond laser micromachining of grooves in silicon with 800 nm pulses

Abstract: Femtosecond laser micromachining of grooves in silicon is investigated using 150 fs pulses with a center wavelength of 800 nm. Ablation rates are investigated as a function of pulse energy, translation speed, and the number of consecutive passes. The effect of the laser polarization relative to the translation direction is observed, and the morphologies of the groove walls are examined. In addition, the uniformity of the groove depth is investigated as a function of the number of passes of the sample under the beam.