Silicon-on-insulator microfluidic device with monolithic sensor integration for /spl mu/TAS applications

A novel concept for the integration of liquid phase charge sensors into microfluidic devices based on silicon-on-insulator (SOI) technology is reported. Utilizing standard silicon processing we fabricated basic microfluidic cross geometries comprising of 5-10-mm-long and 55-/spl mu/m-wide channels of 3 /spl mu/m depth by wet sacrificial etching of the buried oxide of an SOI substrate. To demonstrate the feasibility of fluid manipulation along the channel we performed electroosmotic pumping of a dye-labeled buffer solution. At selected positions along the channel we patterned the 205-nm thin top silicon layer into freely suspended, 10-/spl mu/m wide bars bridging the channel. We demonstrate how these monolithically integrated bars work as thin-film resistors that sensitively probe changes of the surface potential via the field effect. In this way, a combination of electrokinetic manipulation and separation of charged analytes together with an on-chip electronic detection can provide a new basis for the label-free analysis of, for example, biomolecular species as envisaged in the concept of micrototal analysis systems (/spl mu/TAS) or Lab-on-Chip (LOC).     

Surface micromachined metallic microneedles

In this paper, a method for fabricating surface micromachined, hollow, metallic microneedles is described. Single microneedle and multiple microneedle arrays with process enabled features such as complex tip geometries, micro barbs, mechanical penetration stops and multiple fluid output ports were fabricated, packaged and characterized. The microneedles were fabricated using electroplated metals including palladium, palladium-cobalt alloys and nickel as structural materials. The microneedles were 200 mm-2.0 cm in length with a cross-section of 70-200 /spl mu/m in width and 75-120 /spl mu/m in height, with a wall thickness of 30-35 /spl mu/m. The microneedle arrays were typically 9.0 mm in width and 3.0 mm in height with between 3 and 17 needles per array. Using water as the fluid medium, the average inlet pressure was found to be 30.0 KPa for a flow rate of 1000 /spl mu/L/h and 106 KPa for a flow rate 4000 /spl mu/L/h.     

Arrays of monocrystalline silicon micromirrors fabricated using CMOS compatible transfer bonding

In this paper, we present CMOS compatible fabrication of monocrystalline silicon micromirror arrays using membrane transfer bonding. To fabricate the micromirrors, a thin monocrystalline silicon device layer is transferred from a standard silicon-on-insulator (SOI) wafer to a target wafer (e.g., a CMOS wafer) using low-temperature adhesive wafer bonding. In this way, very flat, uniform and low-stress micromirror membranes made of monocrystalline silicon can be directly fabricated on top of CMOS circuits. The mirror fabrication does not contain any bond alignment between the wafers, thus, the mirror dimensions and alignment accuracies are only limited by the photolithographic steps. Micromirror arrays with 4/spl times/4 pixels and a pitch size of 16 /spl mu/m/spl times/16 /spl mu/m have been fabricated. The monocrystalline silicon micromirrors are 0.34 /spl mu/m thick and have feature sizes as small as 0.6 /spl mu/m. The distance between the addressing electrodes and the mirror membranes is 0.8 /spl mu/m. Torsional micromirror arrays are used as spatial light modulators, and have potential applications in projection display systems, pattern generators for maskless lithography systems, optical spectroscopy, and optical communication systems. In principle, the membrane transfer bonding technique can be applied for integration of CMOS circuits with any type of transducer that consists of membranes and that benefits from the use of high temperature annealed or monocrystalline materials. These types of devices include thermal infrared detectors, RF-MEMS devices, tuneable vertical cavity surface emitting lasers (VCSEL) and other optical transducers.     

Single mask, large force, and large displacement electrostatic linear inchworm motors

We have demonstrated a family of large force and large displacement electrostatic linear inchworm motors that operate with moderate to high voltages. The inchworm motor design decouples actuator force from total travel and allows the use of electrostatic gap-closing actuators to achieve large force and large displacement while consuming low power. A typical inchworm motor measures 3 mm /spl times/ 1 mm /spl times/ 50 /spl mu/m and can lift over 130 times its own weight. One motor has achieved a travel of 80 /spl mu/m and a calculated force of 260 /spl mu/N at 33 V. The force density of that motor was 87 /spl mu/N/mm/sup 2/ at 33 V and the energy efficiency was estimated at 8%. Another motor displaced the shuttle at an average velocity of almost 4 mm/s and achieved an estimated power density of 190 W/m/sup 3/. Motors were cycled 23.6 million times for over 13.5 h without stiction. This family of motors is fabricated in silicon-on-insulator (SOI) wafers using a single mask.     

Two-axis single-crystal silicon micromirror arrays

This work presents the design, fabrication, and testing of a two-axis 320 pixel micromirror array. The mirror platform is constructed entirely of single-crystal silicon (SCS) minimizing residual and thermal stresses. The 14-/spl mu/m-thick rectangular (750/spl times/800 /spl mu/m/sup 2/) silicon platform is coated with a 0.1-/spl mu/m-thick metallic (Au) reflector. The mirrors are actuated electrostatically with shaped parallel plate electrodes with 86 /spl mu/m gaps. Large area 320-mirror arrays with fabrication yields of 90% per array have been fabricated using a combination of bulk micromachining of SOI wafers, anodic bonding, deep reactive ion etching, and surface micromachining. Several type of micromirror devices have been fabricated with rectangular and triangular electrodes. Triangular electrode devices displayed stable operation within a (/spl plusmn/5/spl deg/, /spl plusmn/5/spl deg/) (mechanical) angular range with voltage drives as low as 60 V.     

Uncooled multimirror broad-band infrared microbolometers

A new generation of microbolometers were designed, fabricated and tested for the NASA CERES (Clouds and the Earth's Radiant Energy System) instrument to measure the radiation flux at the Earth's surface and the radiant energy now within the atmosphere. These detectors are designed to measure the earth radiances in three spectral channels consisting of a short wave channel of 0.3 to 5 /spl mu/m, a wide-band channel of 0.3 to 100 /spl mu/m and a window channel from 8 to 12 /spl mu/m each housing a 1.5 mm x 1.5 mm microbolometers or alternatively 400 /spl mu/m x 400 mm microbolometers in a 1 /spl times/ 4 array of detectors in each of the three wavelength bands, thus yielding a total of 12 channels. The microbolometers were fabricated by radio frequency (RF) magnetron sputtering at ambient temperature, using polyimide sacrificial layers and standard micromachining techniques. A semiconducting YBaCuO thermometer was employed. A double micromirror structure with multiple resonance cavities was designed to achieve a relatively uniform absorption from 0.3 to 100 /spl mu/m wavelength. Surface micromachining techniques in conjunction with a polyimide sacrificial layer were utilized to create a gap underneath the detector and the Si/sub 3/N/sub 4/ bridge layer. The temperature coefficient of resistance was measured to be -2.8%/K. The voltage responsivities were over 10/sup 3/ V/W, detectivities above 10/sup 8/ cm Hz/sup 1/2//W, noise equivalent power less than 4 /spl times/ 10/sup -10/W/Hz/sup 1/2/ and thermal time constant less than 15 ms.     

A micromachining process for die-scale pattern transfer in ceramics and its application to bulk piezoelectric actuators

This paper reports on a batch mode planar pattern transfer process for bulk ceramics, glass, and other hard, brittle, nonconductive materials suitable for micromachined transducers and packages. The process is named LEEDUS, as it combines lithography, electroplating, batch mode micro electro-discharge machining (/spl mu/EDM) and batch mode micro ultrasonic machining (/spl mu/USM). An electroplating mold is first created on a silicon or metal wafer using standard lithography, then using the electroplated pattern as an electrode to /spl mu/EDM a hard metal (stainless steel or WC/Co) tool, which is finally used in the /spl mu/USM of the ceramic substrate. A related process (SEDUS) uses serial /spl mu/EDM and omits lithography for rapid prototyping of simple patterns. Feature sizes of 25 /spl mu/m within a 4.5/spl times/4.5 mm/sup 2/ die have been micromachined on glass-mica (Macor) ceramic plates with 34 /spl mu/m depth. The ultrasonic step achieves 18 /spl mu/m/min. machining rate, with a tool wear ratio of less than 6% for the stainless steel microtool. Other process characteristics are also described. As a demonstration, octagonal and circular spiral shaped in-plane actuators were fabricated from bulk lead zirconate titanate (PZT) plate using the LEEDUS/SEDUS process. A device of 20 /spl mu/m thickness and 450 /spl mu/m/spl times/420 /spl mu/m footprint produces a displacement of /spl ap/2/spl mu/m at 40 V.     

Arrays of hollow out-of-plane microneedles for drug delivery

Drug delivery based on MEMS technology requires an invasive interface such as microneedles, which connects the microsystem with the biological environment. Two-dimensional arrays of rigid hollow microneedles have been fabricated from single-crystal silicon using a combination of deep reactive ion etching and isotropic etching techniques. The fabricated needles are typically 200 /spl mu/m long with a wide base and a channel diameter of 40 /spl mu/m. The fabrication process allows creating either blunt needles or needles with sharp tips. Their shape and size make these needles extremely suitable for minimally invasive painless epidermal drug delivery. MEMS technology allows for batch fabrication and integration with complex microsystems. Fluid has been successfully injected 100 /spl mu/m deep into sample tissue through arrays of microneedles. Needle breakage did not occur during this procedure. Experiments have shown that the modified Bernoulli equation is a good model for liquid flowing through the narrow microneedle lumen.     

Large-stroke MEMS deformable mirrors for adaptive optics

Surface-micromachined deformable mirrors that exhibit greater than 10 /spl mu/m of stroke are presented. The segmented arrays described here consist of 61 and 85 hexagonal, piston/tip/tilt mirrors (three actuators each) with diameters of 500 and 430 /spl mu/m, respectively, and fill a 4 mm circular aperture. Devices were packaged in 208 and 256 pin-grid arrays and driven by a compact control board designed for turn-key operation. After metallization and packaging mirror bow is /spl sim/680 nm (/spl lambda//1), but a heat-treatment procedure is proposed for controlling mirror curvature to better than /spl lambda//10. An optical test bed was used to demonstrate basic beam splitting and open-loop aberration correction, the results of which are also presented.     

Testing of "Venetian-Blind" silicon microstructures with optical methods

In this paper, we illustrate the design and testing of new silicon microstructures, fabricated by means of a conventional planar process. These "Venetian-blind" structures consist of arrays of narrow, rectangular suspended masses (width =31 /spl mu/m, length =400 /spl mu/m, thickness =15 /spl mu/m), which can be tilted using electrostatic actuation. Characterization of their static and dynamic behavior was performed with optical methods. The diffraction patterns in monochromatic light were analyzed and vibration measurements were performed by means of semiconductor laser feedback interferometry: experimental data on the tilt angle as a function of the applied voltage and on the resonance frequencies are reported. A maximum tilt angle of approximately 1.9/spl deg/ was obtained with a driving voltage in the range of 70-95 V. All the tested devices showed resonance frequencies higher than 80 kHz, which is fast enough (i.e., switching time in the millisecond range) for future use in optical interconnections. Numerical analyses were performed to evaluate the coupled electromechanical behavior of the microstructures, confirming the observed experimental behavior.     

Thermal annealing in hydrogen for 3-D profile transformation on silicon-on-insulator and sidewall roughness reduction

A fast, effective process using hydrogen annealing is introduced to perform profile transformation on silicon-on-insulator (SOI) and to reduce sidewall roughness on silicon surfaces. By controlling the dimensions of as-etched structures, microspheres with 1 /spl mu/m radii, submicron wires with 0.5 /spl mu/m radii, and a microdisk toroid with 0.2 /spl mu/m toroidal radius have been successfully demonstrated on SOI substrates. Utilizing this technique, we also observe the root-mean-square (rms) sidewall roughness dramatically reduced from 20 to 0.26 nm. A theoretical model is presented to analyze the profile transformation, and experimental results show this process can be engineered by several parameters including temperature, pressure, and time.     

Low-voltage, large-scan angle MEMS analog micromirror arrays with hidden vertical comb-drive actuators

This paper reports on novel polysilicon surface-micromachined one-dimensional (1-D) analog micromirror arrays fabricated using Sandia's ultraplanar multilevel MEMS technology-V (SUMMiT-V) process. Large continuous DC scan angle (23.6/spl deg/ optical) and low-operating voltage (6 V) have been achieved using vertical comb-drive actuators. The actuators and torsion springs are placed underneath the mirror (137/spl times/120 /spl mu/m/sup 2/) to achieve high fill-factor (91%). The measured resonant frequency of the mirror ranges from 3.4 to 8.1 kHz. The measured DC scanning characteristics and resonant frequencies agree well with theoretical values. The rise time is 120 /spl mu/s and the fall time is 380 /spl mu/s. The static scanning characteristics show good uniformity (相似文献   

VHF single crystal silicon capacitive elliptic bulk-mode disk resonators-part II: implementation and characterization

This work, the second of two parts, reports on the implementation and characterization of high-quality factor (Q) side-supported single crystal silicon (SCS) disk resonators. The resonators are fabricated on SOI substrates using a HARPSS-based fabrication process and are 3 to 18 /spl mu/m thick. They consist of a single crystal silicon resonant disk structure and trench-refilled polysilicon drive and sense electrodes. The fabricated resonators have self-aligned, ultra-narrow capacitive gaps in the order of 100 nm. Quality factors of up to 46 000 in 100 mTorr vacuum and 26000 at atmospheric pressure are exhibited by 18 /spl mu/m thick SCS disk resonators of 30 /spl mu/m in diameter, operating in their elliptical bulk-mode at /spl sim/150 MHz. Motional resistance as low as 43.3 k/spl Omega/ was measured for an 18-/spl mu/m-thick resonator with 160 nm capacitive gaps at 149.3 MHz. The measured electrostatic frequency tuning of a 3-/spl mu/m-thick device with 120 nm capacitive gaps shows a tuning slope of -2.6 ppm/V. The temperature coefficient of frequency for this resonator is also measured to be -26 ppm//spl deg/C in the temperature range from 20 to 150/spl deg/C. The measurement results coincide with the electromechanical modeling presented in Part I.     

A micromachined impact microactuator driven by electrostatic force

This paper presents a novel micromachined actuator which is developed to produce precise and unlimited displacement. The actuator is driven by impact force between a silicon micro-mass and a stopper. The suspended silicon micro-mass is encapsulated between two glass plates and driven by electrostatic force. When the mass hits the stopper which is fixed on glass plates, impact force is generated to drive the whole actuator in a nano size step (/spl sim/10 nm). The overall dimension of the device is 3 mm /spl times/3 mm. The driving voltage is 100 V and average speed is 2.7 /spl mu/m/s. The total thickness is 600 /spl mu/m.     

A micromechanical flow sensor for microfluidic applications

We fabricated a microfluidic flow meter and measured its response to fluid flow in a microfluidic channel. The flow meter consisted of a micromechanical plate, coupled to a laser deflection system to measure the deflection of the plate during fluid flow. The 100 /spl mu/m square plate was clamped on three sides and elevated 3 /spl mu/m above the bottom surface of the channel. The response of the flow meter was measured for flow rates, ranging from 2.1 to 41.7 /spl mu/L/min. Several fluids, with dynamic viscosities ranging from 0.8 to 4.5/spl times/10/sup -3/ N/m, were flowed through the channels. Flow was established in the microfluidic channel by means of a syringe pump, and the angular deflection of the plate monitored. The response of the plate to flow of a fluid with a viscosity of 4.5/spl times/10/sup -3/ N/m was linear for all flow rates, while the plate responded linearly to flow rates less than 4.2 /spl mu/L/min of solutions with lower dynamic viscosities. The sensitivity of the deflection of the plate to fluid flow was 12.5/spl plusmn/0.2 /spl mu/rad/(/spl mu/L/min), for a fluid with a viscosity of 4.5/spl times/10/sup -3/ N/m. The encapsulated plate provided local flow information along the length of a microfluidic channel.     

Novel fabrication method for surface micromachined thin single-crystal silicon cantilever beams

This paper describes a novel technique for the fabrication of surface micromachined thin silicon cantilever beams using merged epitaxial lateral overgrowth (MELO) of silicon and chemical-mechanical polishing (CMP). The objective is to demonstrate the feasibility of using this novel technique for the fabrication of arrays of ultrathin, low-stress, single-crystal silicon cantilever beams for use in ultrahigh sensitivity surface-stress or resonant-frequency-based chemical or biological detection schemes. The process flow used in this work is described in detail and the issues that were faced during the fabrication are discussed. Cantilever beams with thickness of 0.3-0.5 /spl mu/m that were 10-25-/spl mu/m wide and 75-130-/spl mu/m long were fabricated. Mechanical characterization of the cantilever beams were performed by measuring their spring constant using the "added mass" method, which also demonstrated the use of these initial structures to detect masses as low as 10-100 pg. Further work is underway to scale the thickness of these beams down to the sub-100-nm regime.     

Encapsulated submillimeter piezoresistive accelerometers

While micromachined accelerometers are widely available and used in various applications, some biomedical applications require extremely small dimensions (相似文献   

Design, fabrication, and characterization of thermally actuated probe arrays for dip pen nanolithography

In Dip Pen Nanolithography (DPN), arbitrary nanoscale chemical patterns can be created by the diffusion of chemicals from the tip of an atomic force microscope (AFM) probe to a surface. This paper describes the design, optimization, fabrication, and testing of an actuated multi-probe DPN array. The probe array consists of 10 thermal bimorph active probes made of silicon nitride and gold. The probes are 300 /spl mu/m long and the tips are spaced 100 /spl mu/m apart. An actuation current of 10 mA produces a tip deflection of 8 /spl mu/m, which is enough to remove individual tips from the surface independent of the adjacent probes. An analytical probe model is presented and used to optimize the design against several possible failure modes. The array is demonstrated by using it to simultaneously write 10 unique octadecanethiol patterns on a gold surface. Pattern linewidth as small as 80 nm has been created at a maximum write speed of 20 /spl mu/m/sec. By writing multiple, distinctly different patterns in parallel, this device provides a significant improvement in throughput and flexibility over conventional AFM probes in the DPN process.     

Piezoelectric unimorph microactuator arrays for single-crystal silicon continuous-membrane deformable mirror

Micromachined deformable mirror technology can boost the imaging performance of an otherwise nonrigid, lower-quality telescope structure. This paper describes the optimization of lead zirconium titanate (PZT) unimorph membrane microactuators for deformable mirrors. PZT unimorph actuators consisting of a variety of electrode designs, silicon-membrane thickness, and membrane sizes were fabricated and characterized. A mathematical model was developed to accurately simulate the membrane microactuator performance and to aid in the optimization of membrane thicknesses and electrode geometries. Excellent agreement was obtained between the model and the experimental results. Using the above approach, we have successfully demonstrated a 2.5-mm-diameter PZT unimorph actuator. A measured deflection of 5 /spl mu/m was obtained for 50 V applied voltage. Complete deformable mirror structures consisting of 10-/spl mu/m-thick single-crystal silicon mirror membranes mounted over the aforementioned 4/spl times/4 4 PZT unimorph membrane microactuator arrays were designed, fabricated, assembled, and optically characterized. The fully assembled deformable mirror showed an individual pixel stroke of 2.5 /spl mu/m at 50 V actuation voltage. The deformable mirror has a resonance frequency of 42 kHz and an influence function of approximately 25%.     

Electronically controllable microvalves based on smart hydrogels: magnitudes and potential applications

Electronically controllable microvalves based on temperature sensitive hydrogels as actuators are described. A thermal-electronic interface was used for electronic control of the liquid flow. The hydrogel actuators were directly placed in a flow channel. They used the process medium as the swelling agent. Because of the direct placement into the channel the elastic properties of the hydrogel actuator were utilized to improve the pressure insensitivity, to achieve high particle tolerance and to avoid a leakage flow. The microvalves show an extremely simple structure. They can be fabricated using conventional micro technology within a few technical steps. The microvalves can also be miniaturized to a currently unrivalled extent of about 4 /spl mu/m/spl times/4 /spl mu/m/spl times/1/spl mu/m. Valves for "laboratory on chip" applications can already be obtained. The switching times of the electronically controllable microvalves based on hydrogels are 0.3 s to 10 s.