We are developing a variety of microsystems for the separation and detection of biological samples. At the heart of these systems, inexpensive polymer microfluidic chips carry out sample preparation and analysis. Fabrication of polymer microfluidic chips involves the creation of a master in etched silicon or glass; plating of the master to produce a nickel stamp; large lot chip replication by injection molding; precision chip sealing; and chemical modification of channel surfaces. Separation chips rely on insulator-based dielectrophoresis for the separation of biological particles. Detection chips carry out capillary electrophoresis to detect fluorescent tags that identify specific biological samples. Since the performance and reliability of these microfluidic chips are very sensitive to fluidic impedance, electromagnetic flux, and zeta potential, the microchannel dimensions, shape, and surface chemistry have to be tightly controlled during chip fabrication and use. This paper will present an overview of chip design, fabrication, and testing. Dimensional metrology data, surface chemistry characterization, and chip performance data will be discussed in detail.

Needle shaped probes with a dual electrode system in submicron size have been developed for electrochemical analyses of living single cells. The probe system is designed for local probing of the cytosolic cell environment and cell organelles using amperometric, potentiometric and impedance spectroscopic methods. Silicon nitride cantilevers with an electrode metal layer system are fabricated on four-inch wafers using conventional micro fabrication techniques. The probe needle structures with a tip in sub micron scale are patterned using Focus Ion Beam (FIB) technology. A focused ion beam is utilized to write the probe needle shape into the pre-shaped cantilever and, for a dual electrode system, the probe is divided into two parts to create two separate electrodes. Subsequently, the needle structures are released from the supporting bulk silicon during a wet etching step, and a silicon nitride layer is deposited to isolate and embed the electrode metal layer. Finally, FIB milling is used for a precise exposure of the buried metal layer by cutting the top of the tip. Electrochemical characterization of nano-probes showed full functionality of Ag/AgCl as well as of platinum transducer systems. The sharpness of the probe tip with a radius of smaller than 50nm and the mechanical robustness of the needle structure allow for a reliable penetration of cell membranes. Initial measurements of cell membrane potentials and cell membrane impedances of rat fibroblast cells using Ag/AgCl transducer probes demonstrate the analytical capability of these probes in biological environments.

We report our progress on the fabrication of three-dimensional (3D) photonic crystals to operate at near-infrared (IR) wavelengths using conventional planar silicon micromachining. The method involves patterning a single layer of planar etch mask and a custom etch process to create a 3D array of spherical voids. The etch mask is patterned in polymethyl methacrylate (PMMA) using conventional deep-UV contact photolithography and then transferred to a silicon dioxide (SiO₂) hard mask. The 3D spherical voids are fabricated using a sequence of etching and passivation steps. In the etch step performed in a fluorine-based inductively coupled plasma-etching system, first a layer of spherical voids is created. Then, the spherical voids are passivated by dry silicon oxidation. A subsequent anisotropic removal of oxide at the bottom of the sphere is achieved by high-energy ion bombardment thus enabling the creation of etch mask for the successive layers. Plasma chemistry with high selectivity to oxide is utilized for opening the subsequent layer of spherical voids. By repeating these steps, buried 3D array of spherical voids is obtained. This way, a 3D structure with simple cubic symmetry can be obtained from an etch mask initially patterned with a square lattice of circular holes. Our fabrication method has numerous advantages over alternative approaches as it is based on the well-established CMOS mass fabrication technology, which is compatible with the next generation optoelectronic circuits.

Microassembly process plays a key role in building 3-dimensional heterogeneous microsystems. This paper presents a miniaturized Fourier transform spectrometer (FTS) implemented by combining silicon micromachining and microassembly techniques. The FTS is based on a Michelson interferometer where a scanning mirror mechanism creates an interferogram, and the recorded interferogram is converted to a spectrum by Fourier transform. The miniaturized Michelson interferometer is integrated on a microoptical bench, which is fabricated using Deep RIE (Reactive Ion Etching) process on a SOI (Silicon On Insulator) wafer. Key components of the FTS optical bench are a linear translation stage, mechanical assembly sockets, a beam splitter, and assembled mirrors. An electrothermal actuator with stroke amplification mechanisms provides the amplified scanning motion of a scanning mirror. The sockets are female mechanical flexure structures that allow a precise snap-fit assembly with micromachined silicon mirrors. The dimension of the FTS optical bench is 1cm², and its embedded thermal actuator has a couple of V-beam structures whose beam length is 1mm. The mirrors are Deep RIE micromachined structures with reflection area 500x450μm² and 750μm long flexure structures for pick & place assembly. The flexure structure allows large deflection so that a microgripper can pick up the mirror by inserting the gripper tip into the structure, and snap-fit assembles it into the mechanical socket of the bench. The linear translation stage generates up to 30μm scanning stroke at 22V input, which corresponds to a spectral resolution of 10nm at 775nm wavelength. While this microassembly method is designed to self-align the mirror in the socket, the mirror slightly tilts after assembly due to the slope of side wall of DRIE processed structures. The measured tilting angles of assembled mirrors range from -2.5° to 0.8° from several assembly trials. The tilting angle combined with beam divergence can cause the loss of power and resolution, spectrum shift and phase error. A He-Ne laser was used as a light source to create interferogram with the assembled microspectrometer. Formation of fringe patterns was successfully conducted with a prototype. Mirrors with a large tilting misalignment resulted in stripe pattern fringes, whereas an improved alignment generated circular pattern fringes. A detector was used to measure light power with respect to input voltage, and the displacement of a scanning mirror was measured and curve-fitted. The relationship between light power changes versus the displacement of a scanning mirror represents interferogram. Spectrum profiles showed a peak around 632nm with FWHM (Full Width Half Magnitude) 25nm approximately. While further research is on going to improve spectrum quality and microassembly technique for the integration of various components with heterogeneous materials and shapes, this approach is expected to facilitate the design and manufacturing of MOEMS from the constraints of micromachining processes.

Polymers have been considered as one of the most versatile materials in making optical devices for communication and sensor applications. They provide good optical transparency to form filters, lenses and many optical components with ease of fabrication. They are scalable and compatible in dimensions with requirements in optics and can be fabricated on inorganic substrates, such as silicon and quartz. Recent polymer synthesis also made great progresses on conductive and nonlinear polymers, opening opportunities for new applications. In this paper, we discussed hybrid-material integration of polymers on silicon-based microelectromechanical system (MEMS) devices. The motivation is to combine the advantages of demonstrated silicon-based MEMS actuators and excellent optical performance of polymers. We demonstrated the idea with a polymer-based out-of-plane Fabry-Perot filter that can be self-assembled by scratch drive actuators. We utilized a fabrication foundry service, MUMPS (Multi-User MEMS Process), to demonstrate the feasibility and flexibility of integration. The polysilicon, used as the structural material for construction of 3-D framework and actuators, has high absorption in the visible and near infrared ranges. Therefore, previous efforts using a polysilicon layer as optical interfaces suffer from high losses. We applied the organic compound materials on the silicon-based framework within the optical signal propagation path to form the optical interfaces. In this paper, we have shown low losses in the optical signal processing and feasibility of building a thin-film Fabry-Perot filter. We discussed the optical filter designs, mechanical design, actuation mechanism, fabrication issues, optical measurements, and results.

To meet the performance requirements for some applications, including small sizes, precise optics, low power consumption and non-electrical control in the devices, an optical fiber scanner using electromagnetic actuation has been developed. This paper acquaints a compact external magnetic field actuated fiber optic scanner, in which the main structure is an optical fiber coated with nickel magnetic gel. The advantages of device architecture are: (1) the scanner dimensions are in the same scales of an optical fiber diameter, (2) optical properties and information are well preserved in the fiber, and (3) the actuation control is external and requires no electrical wiring in scanner design and zero power consumption. In this work, magnetic properties of the nickel based ferromagnetic gel were measured in order to carry out the theoretical calculations of static response and resonant frequencies. With the dynamic waveforms of input and output signals from the position sensing device at both modes of resonant frequencies, we conclude that it is significant to operate at the resonant frequencies so that the scanner requires less power to reach large displacement and the oscillating motion of the scanner is purely sinusoidal. A simple and versatile rotary gel coating technique, static and dynamic performance characterization and potential applications of the fiber scanner will be discussed. Moreover, we will also discuss the practical issues in operation and possible waveform distortion that affects imaging and display quality.

Many optical applications require smooth micromirror reflective surfaces with large radius of curvature. Usually when using surface micromachining technology and as a result of residual stress and stress gradient in thin films, the control of residual curvature is a difficult task. In this work, two engineering approaches were developed to enhance structural stiffness of micromirrors. 1) By integrating stiffening structures and thermal annealing. The stiffening structures consist of U-shaped profiles integrated with the mirror (dimension 200×300 μm²). 2) By combining selective electroplating and flip-chip based technologies. Nickel was used as electroplated material with optimal stress values around ±10 MPa for layer thicknesses of about 10 μm. With the former approach, typical curvature radii of about 1.5 cm and 0.6 cm along mirror width and length were obtained, respectively. With the latter approach, an important improvement in the micromirror planarity and flatness was achieved with curvature radius up to 23 cm and roughness lower than 5 nm rms for typical 1000×1000 μm² micromirrors.

A MEMS process design, development and tracking system is presented. It allows the specification of processes for specific applications and the tracking of the development procedures. The system consists of several components. Based on a comprehensive database that is able to store and manage all process related design constraint data as well as development related data linked to the fabrication process itself. A design model representing the relations between application specific fabrication processes and the structural design flow will be presented. Subsequently the software environment, called PROMENADE, will be introduced meeting the requirements of this process approach.

A traditional LCD backlight system is consist of light sources, a light guiding plate and prism sheets, diffusive sheets and reflective sheet. Following the development of the thin LCD, modify the backlight system which has already become the trend. The light guiding plate is very important element in backlight unit which is usually made of Polymethyl methacrylate (PMMA). Generally, the light guiding plates is fabricated by injection molding. MEMS and hot embossing technologies are applied to fabricate the integrated light guiding plate in this research. The micro-prisms, the micro pyramids and Al thin film are based on the integrated light guiding plate which is guiding light to the LCD panel evenly. So the backlight system will be simplified to use only one integrated light guiding plate without using any optical sheets. The light guiding plate can reduce three optical sheets in backlight, so it can save the space and lower the process cost. Non-prism LGPs and integrated LGPs are presented in this paper.

This paper describes improvements that enable engineers to create three-dimensional MEMS in a variety of materials. It also provides a means for selectively adding three-dimensional, high aspect ratio features to pre-existing PMMA micro molds for subsequent LIGA processing. This complimentary method involves in situ construction of three-dimensional micro molds in a stand-alone configuration or directly adjacent to features formed by x-ray lithography. Three-dimensional micro molds are created by micro stereolithography (MSL), an additive rapid prototyping technology. Alternatively, three-dimensional features may be added by direct femtosecond laser micro machining. Parameters for optimal femtosecond laser micro machining of PMMA at 800 nanometers are presented. The technical discussion also includes strategies for enhancements in the context of material selection and post-process surface finish. This approach may lead to practical, cost-effective 3-D MEMS with the surface finish and throughput advantages of x-ray lithography. Accurate three-dimensional metal microstructures are demonstrated. Challenges remain in process planning for micro stereolithography and development of buried features following femtosecond laser micro machining.

The use of modern microstreolithography (MSL) technology gives optics developers the freedom to integrate mounting and positioning structures directly into an optical mask structure. We have created Hadamard spectrometer masks with increments of 150 μm and less using the Sony SCS-6000 microstereolithography apparatus (MSLA). Due to laser over cure and other parameters, adjustments were made iteration by iteration until appropriate mask tolerances were met. A mounting structure was integrated with the mask for testing and application. At the computer aided design (CAD) model level, the mounting geometry can be adjusted to fit any specific mounting apparatus. By using the MSLA, features as small as 75 μm and larger than 300 mm can be created in the same build. Additionally, the conceptual design of an entire positioning system constructed using layer additive MSLA microfabrication is underway. This positioning system may be built as an integrated assembly, encapsulating necessary components. Optical characterization results are presented.

Microstereolithography (MSL) is rapidly developing technique for micro-fabrication. Vector-by-vector scanning MSL has a potential to create true 3D micro-devices as compared to mostly planar (2D-2 1/2 D) devices fabricated by conventional MEMS techniques. Previous literature shows two different scanning methods:(1) Galvanomirror scanning, (2) Photoreactor tank scanning. Galvanomirror scanning technique has higher fabrication speed but poor resolution because of defocusing of laser spot on the resin surface. Photo-reactor tank scanning has higher resolution but produces a wavy structures and limited speed of fabrication. This paper proposes and develops an offaxis lens scanning technique for MSL and carries out optical analysis to compare its performance with the existing techniques mentioned above. The comparison clearly demonstrates improved performance with the proposed offaxis lens scanning technique.

Lead Zirconate Titanate (PZT) is a high energy density active material with good piezoelectric coefficient and electromechanical coupling constant making it highly suitable for microsystems applications. In this paper, we present a rapid anisotropic high aspect ratio etching process for defining micron size features in PZT. We used an inductively coupled plasma reactive ion etching (ICP-RIE) system employing sulfur hexafluoride (SF6) and argon (Ar) based chemistry. A seed layer of Au/Cr was lithographically patterned onto fine lap finished PZT-4 substrates followed by electrodeposition of a thick 2-5 μm nickel on the seed layer, which acts as a hard mask during the etching process. The demonstrated technique was used to etch bulk PZT ceramic substrates, thereby opening possibilities for integration of bulk PZT substrates and structures into microsystems. A maximum etch rate of 19 μm/hr on PZT-4 and 25 μm/hr for PZT-5A compositions was obtained using 2000 W of ICP power, 475 W of substrate power, 5 sccm of SF₆, and 50 sccm of Ar on PZT substrate. We have also demonstrated a high aspect ratio etch (>5:1) on a 3 μm feature size. Detailed analysis of the effects of ICP power, substrate power, and the etch gas composition on the etch rate of PZT are also presented in this article.

The presented work demonstrates that the ability of localized electro-deposition to fabricate truly three dimensional microstructures does not only require accurate control of the deposition electrode, but also demands a fabrication strategy that highly affects deposition resolution, characteristics, and the economical return of the technology. For this purpose, a synchronous deposition strategy is proposed utilizing two tip displacement algorithms. Both algorithms view three dimensional microstructures as stacks of lateral trajectories forming the structure's boundaries. In the first algorithm the synchronized tip positioning is implemented using tip stepped displacement, where the tip is moved from a point on a deposition trajectory to a neighboring location only upon sufficient deposition at the current location. The second algorithm, however, is implemented using continuous electrode displacement that allows deposition at all points along a trajectory while the tip is kept in continuous motion. The proposed synchronous deposition algorithms are demonstrated through the fabrication of micro-chambers and enclosures of arbitrary size and geometries. Comparison between both algorithms is concluded from SEM images of deposited structures in terms of deposit characteristics and strategy artifacts. The stepped displacement algorithm provides a shorter fabrication time but suffers from stepping artifacts. The continuous displacement algorithm, on the other hand, provides smooth boundaries but requires longer fabrication time that depends on the displacement speed of the deposition tip relative to the deposition growth rate.

Filling deep trenches and cavities is currently accomplished by copper electro-less plating technology utilizing super-conformal deposition methods. Unlike typical electrolyses processes, where an electric potential is applied between the anodes to activate the plating reaction, electro-less plating relies on chemical agents to activate deposition. To achieve super-conformal deposition, special electrolytic paths must be used. This poses a challenge to the fabrication of narrower trenches, and thus requires the development of other deposition schemes. This work proposes an alternative solution to the filling of deep trenches that avoids the difficulties outlined above, using a forced convection magneto-electroplating method. The technique operates as in typical electrolysis processes, however, with forcing the flow of the plating electrolyte, by hydro-dynamic means, in the presence of an externally applied magnetic field. This arrangement introduces a Lorentz type of force that enhances the transport of deposit species toward desired locations, such as deep regions in interconnect trenches. The proposed method is demonstrated by filling interconnect trenches with aspect ratio as high as 3:1. Quality of samples filled using the proposed magneto-electroplating method is compared with the quality of samples filled by typical electroplating method.

Microelectromechanical systems (MEMS) devices made of single crystalline silicon carbide (SiC) are attractive for applications in harsh environment, because SiC is chemically inert and semiconductor devices made of SiC can be operated at very high temperature. On the other hand, due to its chemical inertness, controllable etching of SiC has been difficult. Molten KOH etching has been widely used to detect crystalline defects in SiC as etch pit in crystal growth researchers. Some etch pits have hexagonal shape, indicating anisotropic etching nature. Therefore, molten KOH etching may have potential as a SiC MEMS fabrication process. In this study we have developed the anisotropic wet chemical etching of single crystalline hexagonal SiC using molten KOH for SiC bulk micromachining. 6H-SiC (0001)Si face and (000-1)C face substrates are used. Etching rates of (0001)Si and (000-1)C faces at 490 °C are evaluated to be 37 nm/min and 3.1 μm/min, respectively, indicating that the (0001)Si face is etched almost 100 times slower than the (000-1)C face is. Cross sectional analysis of etched structure of (000-1)C face revealed that inclined crystal plane was formed as a sidewall with some undercut. To assess in-plane etching anisotropy, ring shape mesa structures are formed on SiC (0001)Si face by RIE and then etched by molten KOH. Ring shape changed into hexagonal shape, clearly indicating etching rate along <11-20> direction is larger than <1-100> direction in (0001)Si face.

In this paper, a new visual force sensor is proposed to measure the microforces acting upon the jaws of passive, compliant microgrippers, used to construct out-of-plane 3-D microstructures. The vision-based force measurement technique is reduced to determining the deflections of the microgripper jaws during the microassembly process. A computer vision system is used to measure the deflections in the gripper's jaws during the joining and grasping processes. A mathematical model of the microgripper system was developed where a relation between the force and the jaw displacement was deduced. Image processing methods, such as Zero-crossing Laplacian of Gaussian edge detection and region-filling, are used. The relative positions of the microgripper jaws, with respect to the gripper's pad, are determined by means of object recognition. Performed experiments confirm the success of the proposed sensor and verify that the measured deflections comply with the profile variations of the microgripper.

During the fabrication of many MEMs devices it is required to etch a layer of material to completion stopping on the layer below (e.g. Silicon on Insulator (SOI) - clearing a Si layer stopping on an underlying silicon dioxide layer). Allowing the etch process to proceed beyond the time when the first layer has been removed can result in reduced thickness of the underlying stop layer, or feature profile degradation (known as "notching" for SOI applications). One method commonly used to detect plasma process termination times is optical emission spectrometry (OES). OES analyzes the light emitted from a plasma source to draw inferences about the chemical and physical state of the plasma process. In semiconductor processing this technique is commonly used to detect material interfaces during plasma etch processes. While this approach works well for single step processes or process with a limited number of discrete etch steps (such as an etch initiation followed by a main etch) it is difficult to apply OES techniques to plasma processes with rapid and periodic plasma perturbations such as time division multiplex (TDM) plasma etching processes for Si etching. At Unaxis USA, we have developed a proprietary optical emission end point algorithm in conjunction with OES to detect material transitions in TDM processes. This technique requires no synchronization of the algorithm to the TDM process and has been applied to silicon on insulator (SOI) structures. The mechanism and performance of the algorithm will be discussed. The sensitivity of the technique has been evaluated over a range of silicon etch loads. Signal to Noise (SNR) ratios of greater than 15:1 have been achieved for samples with less than 10% exposed silicon.

We propose novel tool employing both low coherence interferometer and spectrally resolved reflectometer sensor. We discuss application of this novel tool for measurements of the narrow high aspect ratio structures. We demonstrate that the visible reflectance spectrum of such structures allows us to extend range of interferometer to measure depth trenches with diameter from 2 μm to 1 mm, with reproducibility 10 nm - 100 nm depending on range of the thin film thickness. We also present of this novel tool for measurement of ultra-thin coated pressure sensor membranes. Application of an auxiliary spectral reflectometer allows correcting for systematic errors of low coherence interferometer which can be as large as 1.5 - 2 μm.

Micro-Rings have been widely used for measurement of residual tensile stress in thin films. This measurement approach provides a simple and convenient way to estimate the stress. However, it still lacks accuracy compared to other methods. In this study, we propose an alternative design, which arranges the central beam in the vertical orientation, shrinks the beam width, and widens the ring width to limit the undesired out-of-plane deformation of the ring portion and thus to improve the measurement results. The simulation result both has verified our design. The ring portion of conventional micro-ring is easily deformed in the out-of-plane direction when subjected to residual stress. In our design, such undesired out-of-plane buckling can be effectively prevented. Some suggestions for limiting the undesired out-of-plane deformation have been proposed. Following these suggestions, the more precise critical buckling length and the more accurate stress measurement will be obtained.

Micro-electroplating technology has an increasingly wider application in the fabrication of MEMS devices. In order to fabricate a double-width cantilever beam which has three different electroplated areas. The proper composition of the bath solution is obtained through experiments firstly in the paper. Then the effects of the peak of current density, duty cycle and pause time on the surface morphology of the electroplated nickel are studied experimentally to make sure the regulating range of pulsed parameters. And at last the double-width cantilever beam is fabricated using lithographic, micro-electroplating and sacrificial layer releasing processes. The results show that the surface of the beam is bright and smooth, and the nucleation rate increases steadily. But the thickness of the three parts with different width is different which can be modified by increasing the duty cycle and reducing the current density to some extent.

Most previous research on electroplating in LIGA has focused on electrodeposition of metal into high aspect ratio resist molds. In overplating process how the metal grows up across the top of resist molds has been relatively neglected. Typical defects like holes formation at the top of cavities of electroplated metal mold usually occur due to improper process control especially when the space/linewidth ratio of microstructure increases. To help understand these problems, overplating process has been investigated. A model is developed to compute current density distribution based on LIGA mold feature using electroplating simulation tools. Results show that it is almost an isotropic growing model at the first stage of overplating. As the deposited metal grows bigger the space between electrodes is shortened and the current density distribution along electrode may be modulated by neighbor electrode. It doesn't show an isotropic growing model any more. The deposition rate in inward lateral direction is smaller than in vertical direction. The growing model based on calculation shows that the trench feature aspect ratio can reach a considerable magnitude especially when the LIGA mold feature space/linewidth ratio increases. In poor transport situation, ion depletion becomes significant and a stopped deposition may occur thus holes can be formed at the bottom of overlapped neighbor electrodes. An optimized experiment has been performed using low overpotentials at the stage before the overlapping of neighbor electrodes and a rigorous stirring of electrolyte. A nickel mold insert without holes-formation defects can be obtained.

Optical second-order nonlinear thin film was developed by doping dye organic molecules in a UV curing epoxy host polymer system and followed by an electric field poling step. The nonlinear optical polymeric thin film fabrication will be described. Results from a systematic evaluation of the film physical and optical properties using AFM, ellipsometer and Maker Fringe will be presented. The film absorption spectrum shows a promising advantage for frequency doubling in the blue color window. Optical nonlinear constants extraction from the Maker Fringe raw data will also be discussed.

This paper presents a large displacement static-electricity curled-hinge comb micro-mirror made by a CMOS-MEMS process. A micro-spring is incorporated to reduce the stress effects and the process variation. A mirror with a size of 500um x 500um is made using three metal layers. The micro-spring made a metal layer and a poly layer with a size of 4um x 21um. The nature frequency is 727 Hz and the maximum displacement of the micro-mirror is 32um using a driving voltage of 25 volts. The process variation has been successfully reduced from 30% to 10%.

We show the SAW resonators and ladder type SAW resonator filters using high coupling SiO₂/5°Y-X LiNbO₃ with Zero Temperature Coefficients of Frequency (TCF). The theoretical analysis of 5~10GHz ladder type filters including the propagation attenuations and resistive loss of interdigital transducers are shown. Finally the experimental results below 2.0dB insertion loss with a wide band and zero TCF at 5 ~ 10GHz-range are shown.

In portable electronic equipments, miniaturisation, cost, multi-functionalities and reliability are the main factors driving the power electronics industry. In this context, the realisation of all integrated high performance DC-DC micro-converters working at high frequencies (few MHz) is necessary. The passive components such as inductors, transformers and capacitors, are for the moment the bulkiest components and their integration on silicon substrate would constitute a real improvement in term of compactness and reliability of power converters. This paper deals with the fabrication of integrated capacitors realised on silicon using MEMS-type techniques. High capacitance density, low series resistance and inductance are sought. Structures using deep cavities etched in silicon were realised in order to increase the effective area of the capacitor's electrodes while minimising the area on the substrate. The development of micro-fabrication techniques such as Deep Reactive Ion Etching (DRIE) and doped-polysilicon deep trenches filling are presented. Some preliminary measurement on the fabricated capacitors with the developed processes show that high capacitance density (36 nF/mm²) can be obtained.