MEMS Industry Research Articles

A Framework of Data Fusion Algorithm for Precision Measurement of Multiscale Surfaces

Multiscale surfaces enriched with different scales of features are becoming widely used in many fields such as MEMS and optics industries. Due to the complexity of the multiple scale geometries, a single sensor or a single measurement can hardly obtain the holistic information of these surfaces. Multiple measurement method can solve this problem while it will introduce a lot of challenges for multiscale data fusion for the measurement results. This paper presents a framework of a data fusion algorithm for precision measurement of multiscale surfaces. The method makes use of iterative closest point based method to precisely register the datasets obtained in multiple measurements, and a Gaussian zero-order regression filter is used to separate the geometric features in different scales. Hence, the datasets are fused based on an edge intensity data fusion algorithm within the same wavelength. Finally, the fused datasets of different wavelengths were merged and replaced to the corresponding area in the large scale measurement to form a new surface with holistic multiscale information. The effectiveness of the proposed method has been verified on a v-grooved surface through a series of simulation experiments

Pulse potential deposition of thick polyvinylpyridine-like film on the surface of titanium nitride

We achieved covalent attachment of a thick polyvinylpyridine-like polymeric film on a 200 mm diameter titanium nitride wafer (MEMS industry standard) using a simple electrochemical setup.

Effects of substrate temperature on structure, thermal stability and mechanical property of a Zr-based metallic glass thin film

The effect of substrate temperature on the structure and properties of magnetron sputtered Zr–Cu–Ni–Al–Hf–Ti thin films were systematically investigated. With increasing deposition temperature from 293K to 493K, the films remain amorphous but their thermal stability decreases. Crystallization occurs as the substrate temperature reaches 563K. It was demonstrated that the hardness and Young's modulus of glassy films were enhanced and fracture toughness was worsen by increasing the substrate temperature, along with generating a denser structure. Through the scaling analysis, it was revealed that all glassy films grow in an anomalous mode. These metallic glass films prepared herein exhibit extremely low roughness, less than 1nm, high thermal stability and excellent mechanical properties, which are useful properties for their potential use for MEMS and other industry applications.

Experimental investigation into the micro-EDM characteristics of conductive SiC

SiC is an advanced ceramic which finds wide range of industrial applications. Cutting of SiC is difficult using conventional machining methods due to its low fracture toughness. In the past few years, researchers have claimed successful machining of SiC using EDM process. Furthermore, increasing trend for miniaturization in MEMS and semiconductor industry has necessitated the development of micro-machining methods for advanced ceramics. Therefore, this research was focused on micro-EDM of SiC. In this work, the effect of voltage, capacitance and threshold on surface roughness, MRR, TWR, radial overcut (ROC) and residual stresses was studied through experiments. Signal to noise ratio analysis was used to determine the optimum machining parameters in conjunction with ANOVA. The surface condition of the machined surface was studied using SEM and EDX. The experimental observations revealed that during µEDM operation, all the process parameters (Voltage, Capacitance and Threshold) affect the Surface Roughness, MRR, TWR and ROC significantly. The process input parameters are directly related to micro discharge energy which affects the process performance. Experimental results and optimization attempts show that in micro-EDM of SiC, optimum machining conditions for good surface finish are 150V, 0.1µF and 60% threshold. For high MRR, the optimum conditions are 150V, 0.4µF and 80% threshold. Optimum parameters for low TWR are 110V, 0.4µF and 40% threshold and those for low ROC are 110V, 0.4µF and 60% threshold. Surface characterization revealed the presence of debris, resolidified material and craters on the µEDMed surface that were responsible for high surface roughness. XRD analysis revealed the presence of compressive residual stresses of the order of 1200N/mm2 on the µEDM surface and their magnitude varied slightly with the input parameters. EDX analysis revealed the bidirectional material migration phenomenon in µEDM of SiC.

Multi-objective optimisation for the micro-end milling process using principal component analysis technique

Nowadays, micro-machining processes are playing an important role because of the technological developments in the MEMS, electrical, medical and aerospace industries. In this research work, the principal component analysis (PCA) technique is used to examine and explains the influences of three process parameters (spindle speed, feed rate and depth of cut) on the output responses such as MRR and Ra in micro-end milling process. Also this approach is used for the optimisation of multiple responses in micro-end milling operation to achieve maximum metal removal rate (MRR) and minimum surface roughness (Ra). Further, the optimised machining parameters were determined considering the multiple response objective using multiple response performance index value. The predicted value of multiple response performance index (Z) is 0.6412 which is calculated by using additive model. The measured value of multiple response performance index is 0.707, which shows good prediction accuracy. From the experimental result, it was concluded that, the PCA technique is suitable for the optimisation of multi-response problem.

Microfabrication of stacks of acoustic matching layers for 15 MHz ultrasonic transducers

This paper presents a novel method used to manufacture stacks of multiple matching layers for 15MHz piezoelectric ultrasonic transducers, using fabrication technology derived from the MEMS industry. The acoustic matching layers were made on a silicon wafer substrate using micromachining techniques, i.e., lithography and etch, to design silicon and polymer layers with the desired acoustic properties. Two matching layer configurations were tested: a double layer structure consisting of a silicon–polymer composite and polymer and a triple layer structure consisting of silicon, composite, and polymer. The composite is a biphase material of silicon and polymer in 2-2 connectivity. The matching layers were manufactured by anisotropic wet etch of a (110)-oriented Silicon-on-Insulator wafer. The wafer was etched by KOH 40wt%, to form 83μm deep and 4.5mm long trenches that were subsequently filled with Spurr’s epoxy, which has acoustic impedance 2.4 MRayl. This resulted in a stack of three layers: The silicon substrate, a silicon–polymer composite intermediate layer, and a polymer layer on the top. The stacks were bonded to PZT disks to form acoustic transducers and the acoustic performance of the fabricated transducers was tested in a pulse-echo setup, where center frequency, −6dB relative bandwidth and insertion loss were measured. The transducer with two matching layers was measured to have a relative bandwidth of 70%, two-way insertion loss 18.4dB and pulse length 196ns. The transducers with three matching layers had fractional bandwidths from 90% to 93%, two-way insertion loss ranging from 18.3 to 25.4dB, and pulse lengths 326 and 446ns. The long pulse lengths of the transducers with three matching layers were attributed to ripple in the passband.

Experimental study of a novel Magneto Mercury Reciprocating (MMR) micropump, fabrication and operation

Today, MEMS have wide applications in modern technologies. Magneto hydro dynamic (MHD) micropumps play an important role in the MEMS industry and have been thoroughly studied in the recent years. In this study, the idea of classic reciprocating micropumps was combined with magneto hydro dynamics (MHD) to develop a novel Magneto Mercury Reciprocating (MMR) micropump. To attain this goal, the Lorentz force, as the actuation mechanism, was used to move a conductive liquid (mercury) slug in a reciprocating manner in order to suck the working fluid (air) from the inlet and pump it to the outlet. The performance of the fabricated MMR micropump was examined in terms of parameters such as pressure difference, pumping frequency, and magnetic flux density. The maximum flow rate was achieved at a minimum backpressure of 9.5mL/min. The maximum pressure head achieved in the experiments was 245Pa. Furthermore, the results of these experiments were compared with other micropumps, which showed an improvement of 153% over the next best MHD micropump presented to date.

Sealing dispensing requirements to meet MEMS packaging and throughput impact

The MEMS industry has gained big momentum recently with significant unit growth, especially in the consumer market. While traditional MEMS devices like automotive accelerators have established high-volume manufacturing processes and packages with high reliability, most MEMS devices have been fragmented in packaging because of their unique requirements and small volumes, resulting in high packaging costs. In the cost-sensitive consumer market, devices such as MEMS microphones, accelerometers, and gyroscopes in mobile devices have rapidly increased their production volume and chased lower packaging cost while accepting relatively less reliability than traditional devices. Sealing dispensing can be applied to device or cap wafer for wafer capping process. Wafer capping protects active MEMS from dicing process after release because the additional cavity wafer with sealing covers the MEMS structure. There are manufacturing challenges because wafer capping requires precise alignment and a variety of bonding methods have technical drawbacks. Printing is one way to deposit sealing lines to cap wafers, but consumes a relatively wide area and may not work if the sealing line must go onto the MEMS die wafer. Sealing line can also be applied to organic substrate that contains MEMS device and ASIC and then lid is attached for bonding in cavity packages. Previous paper covered technical requirements for dispensing sealant, volumetric accuracy, and motion systems to meet packaging trends and addressed manufacturing cost reductions. This paper will include investigating the impact on the throughput model due to size reduction efforts in packaging. More dies can be produced per given wafer size, which means there is more dispensing area per wafer. In addition, sealing line requirements will be more challenging, and so this paper will address these demands.

Low-temperature (≤200 °C) plasma enhanced atomic layer deposition of dense titanium nitride thin films

Titanium nitride (TiN) has been widely used in the semiconductor industry for its diffusion barrier and seed layer properties. However, it has seen limited adoption in other industries in which low temperature (<200 °C) deposition is a requirement. Examples of applications which require low temperature deposition are seed layers for magnetic materials in the data storage (DS) industry and seed and diffusion barrier layers for through-silicon-vias (TSV) in the MEMS industry. This paper describes a low temperature TiN process with appropriate electrical, chemical, and structural properties based on plasma enhanced atomic layer deposition method that is suitable for the DS and MEMS industries. It uses tetrakis-(dimethylamino)-titanium as an organometallic precursor and hydrogen (H2) as co-reactant. This process was developed in a Veeco NEXUS™ chemical vapor deposition tool. The tool uses a substrate rf-biased configuration with a grounded gas shower head. In this paper, the complimentary and self-limiting character of this process is demonstrated. The effects of key processing parameters including temperature, pulse time, and plasma power are investigated in terms of growth rate, stress, crystal morphology, chemical, electrical, and optical properties. Stoichiometric thin films with growth rates of 0.4–0.5 Å/cycle were achieved. Low electrical resistivity (<300 μΩ cm), high mass density (>4 g/cm3), low stress (<250 MPa), and >85% step coverage for aspect ratio of 10:1 were realized. Wet chemical etch data show robust chemical stability of the film. The properties of the film have been optimized to satisfy industrial viability as a Ruthenium (Ru) preseed liner in potential data storage and TSV applications.

Design and measurement of a piezoresistive triaxial accelerometer based on MEMS technology

With the springing up of the MEMS industry, research on accelerometers is focused on miniaturization, integration, high reliability, and high resolution, and shares extensive application prospects in military and civil fields. Comparing with the traditional single cantilever beam structure or “cantilever-mass" structure, the proposed structure of “8-beams/mass" with its varistor completely symmetric distribution in micro-silicon piezoresistive triaxial accelerometer in this paper has a higher axial sensitivity and smaller cross-axis sensitivity. Adopting ANSYS, the process of structural analysis and the manufacturing flow of sensing unit are showed. In dynamic testing conditions, it can be concluded that the axial sensitivity of x, y, and z are Sx = 48 μV/g, Sy = 54 μV/g and Sz = 217 μV/g respectively, and the nonlinearities are 0.4%, 0.6% and 0.4%.

MEMS Technology and Market Trends - Change of Supply Chain and Business Models, Focus on MEMS Microphone Market

Yole Développement now expects the sector to see 16% growth in 2011, to reach a $10.0 billion market this year. After three relatively flat years in 2007 to 2009, final figures indicate total MEMS sales jumped some 25% in 2010, to $8.6 billion, thanks largely to the surprisingly fast recovery of the automotive industry and its inventory restocking, as well as the boom in smart phones and tablets with motion sensing. But stronger than anticipated sales of optical MEMS for both telecommunications and consumer applications, and of inertial and RF devices for industrial applications also contributed to the outsize growth. Though growth will now settle down to more sustainable post-recovery rates, we now expect continued stronger demand across these multiple sectors to drive 14% compound annual growth for the MEMS industry for the next five years, to reach a $19.5 billion market by 2016.

New Dynamics of the MEMS Inertial Sensor Market

We will present our new market forecast 2010-2016 for MEMS inertial sensors. The consumer and automotive inertial sensors market saw a healthy 15% growth in 2011 to surpass a $2.7 billion business, thanks to the increasing penetration of more motion sensing into more mobile devices and more automotive safety systems in more cars across the globe. The market and technology trends will be detailed. We will focus on the development of sensor combos. The key drivers to integrate several MEMS sensors in a package are to provide cost / size decrease, or to provide new functionalities with sensor fusion. We will see that sensor fusion with specific software brings a lot of the value, because MEMS players are now trying to sell functions rather than sensors. Lastly we will focus on describing the leading players and the hot developments in this area. The development of MEMS combos implies new business models which are shaking the MEMS industry. The complexity of the inertial MEMS supply chain and the major evolutions will be highlighted in this presentation.

Predicting the Failure Probability of Device Features in MEMS

In the MEMS industry today, device reliability is commonly evaluated by simulating the loads applied to a device using finite element (FE) analysis and setting a threshold for the allowable first principal stress ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> ). This is a potentially misleading practice for the analysis of brittle structures, but it is used because better reliability tools have not been validated and adopted for MEMS design. In this paper, we detail and validate pragmatic FE-based MEMS analysis capabilities: local (device feature) failure probability prediction and surface-specific failure probability intensity (FPI, μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ) plotting, which quantitatively identify the most probable locations of fracture on a MEMS device and provide a more meaningful and higher contrast visualization versus corresponding plots of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> . To validate prediction effectiveness, fractographic analysis was completed on micromirrors (a representative MEMS device) loaded in two distinct complex stress states (primarily, tension or torsion) until failure, thus determining the locations of fracture initiation and their relative probabilities. Our method improves the simulation-driven design of brittle microstructures by providing not only the failure probability of the total structure but also probable failure locations as a function of load, all of which are essential for intelligent design iteration.

Analytical extraction of residual stresses and gradients in MEMS structures with application to CMOS-layered materials

Accurate thin-film characterization is a key requirement in the MEMS industry. Residual stresses determine both the final shape and the functionality of released micromachined structures, and should therefore be accurately assessed. To date, a number of techniques to characterize thin-film materials have been developed, from substrate curvature measurement to methods that exploit the post-release deformation of test structures. These techniques have some major drawbacks, from high implementation costs to accuracy limitations due to improper boundary condition modeling. Here, we present a new technique for the characterization of multilayered, composite MEMS structures that uses easily accessible experimental information on the post-release deformation of microbridges only, with no need for multiple beam lengths. The method is based on an analytical solution of the (post-)buckling problem of microbridges, including the effect of residual stresses (both mean and gradient) and non-ideal clamping (boundary flexibility). The method allows simultaneous characterization of both the mean and the gradient residual stress components, as well as the effective boundary condition associated with the fabrication process, yielding approximately one order of magnitude improvement in resolution compared to extant methods using the same type and number of test structures. The higher resolution is largely attributable to proper accounting for boundary flexibility by our method, with the boundary condition for the structures in this work being ∼90% as stiff in bending relative to the commonly assumed perfectly clamped condition. Additional enhancement can be achieved with post-release deformation measurements of simple cantilevers in addition to the microbridges. The method is useful as it ensures very low stress extraction uncertainty using a limited number of microbridge test structures, and it is transferrable to package-stress characterization. The analytical approach can also be extended to device design, quantifying the effect of residual stresses and boundary flexibility on a structure's post-release state.

Etching Rate of Machinable Glass Ceramic

Micromachining of advanced ceramics has been growing tremendously especially in the MEMs industry. All the time, researchers and industrial engineers have strived to achieve the lowest production cost at possible highest quality in micromachining operations. In this paper, the micromachining operation by means of chemical etching of ceramics is discussed. Machinable glass-ceramic (MGC) is used as the substrate and the influence of various input factors of the etching process is analyzed. These factors include etching temperature, etching period and, etching solution. The etching rate is then analyzed by calculating the weight loss per minutes. In order to establish the relationship between these factors, central composite design (CCD) and artificial neural network are used. Additionally, a prediction model that can be used with a high level of confidence in the industry is created at the end of the analysis.

The Investigation of the First Order Size Effect in Micro-Plastic Forming

With the rapid development of MEMS and electronic industry, the demands for micro-parts are increasing gradually. However, size effects make the traditional forming theories and deformation mechanism not suitable in micro forming field. In this paper, we introduced the classification of the size effects. It pointed out that the size effects can be divided into the first order and the second order size effects in the micro-forming. For the first order size effects, the theory model was established based on the surface layer model. It also clarified the phenomenon that flow stress of the blank reduced with the increase of the ratio of grain size and thickness (t decreases or d increases). Finally, the model was verified with the experimental results of the first order size effects in the references, confirming the effectiveness of the theoretical model. It provides a method to theoretically and experimentally study the micro-plastic forming.

Solutions for Wafer-Level Packaging of High Brightness LEDs

High brightness LEDs (HB-LEDs) carry a high prospect for general lighting applications. Competing with the cost/performance ratio of current light sources demands an increase of the overall efficiency as well as the reduction of the device cost. Since packaging accounts for 30%–50% of the cost of HB LED manufacturing, moving from die- level to wafer-level processes is one likely potential solution for reducing cost per lumen. Silicon-based WLP, using the established processing technology of the MEMS and IC industry, offers high fabrication reliability, high yield and the direct integration of the driver IC in the package. The already small form factor of WLP can be further reduced using Through-Silicon-Vias (TSV), increasing the maximum amount of chips per wafer. Silicon WLP also offers superior thermal management, with the relatively high thermal conductance of silicon. Redistributing LED dies on silicon wafer submounts, with metal bonding and copper TSVs, further improves the heat conductance away from the active region of the chip, resulting in increased device performance. Wafer-level optics can further improve performance and reduce packaging costs. Wafer-level lens molding based on imprint lithography is in high volume manufacture for cell phone camera modules. It allows creation of spherical and a-spherical lenses as well as lens stacks with minimized form factor. In contrast to the currently applied drop dispensing technique for LED lens fabrication, the shape of the lens can be accurately tailored and the decrease of the lens size results in lower absorption and higher light output. Most of these technologies are already in high volume production in other sectors. We will discuss the field proven solutions at each process step, from the formation of the silicon interposer, through the chip-to-wafer bonding, to the final imprinting of the wafer-level optics.

Patterning of soft polydimethylsiloxane elastomers using plasma etching

AbstractSoft polydimethylsiloxane (PDMS) elastomers spin coated on silicon wafers are patterned using plasma etching. The elastomers are formed by mixing vinyl‐terminated PDMS (prepolymer) and crosslinker containing hydride sites. The elastomers are made softer by adding either excess prepolymer, excess crosslinker, or swelling agent. The different elastomers were etched using reactive ion etching, an old and well established processing technology in the microelectronic and MEMS industry. The etch rate and profiles of the etched surfaces were dependent on the process pressure. The dependence was different for the different elastomers. It was found that at low pressure, the etch rate was dependent on the shear modulus. At high pressures, the etch rate was dependent on the chemical composition of the elastomer. The results for the swollen elastomers were different from those for the nonswollen elastomers. The etch rate was lower and the profiles of the etched cavities were different. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Internal profile measurement of GaAs microstructures based on near-infrared light phase-stepping interferometry

Internal profile nondestructive measurement of MEMS microstructures based on semiconductor materials is urgently demanded with the dramatic development of MEMS industry. A new attempt was made to extend the interferometric method and the thickness-profile measurement theory of transparent thin film layers from the visible light region (400–800 nm) to near-infrared light region (900–1700 nm). The measurement system based on Linnik interferometer using a near-infrared halogen light source with 1127 nm center wavelength was established for internal profile measurement. The measurement method for internal profile of GaAs microstructures was realized. From a comparison of reflection interferometry and transmission interferometry, it can be concluded that the latter measurement results were consistent with those of the former and internal profile was determined within an error range of 8%.

Commercial MEMS case studies: market drivers, designs, materials and processes

MEMS has finally become the “disruptive” technology that many predicted 30 years ago. Why did it take so long? The simple fact is that MEMS devices are seldom discrete products. Instead, they enable “disruptive” new functions in higher-level products. It takes time to recognize the value of these capabilities and to develop the higher-level products. Market maturation, technical expertise and a willingness to take financial risk fueled the recent MEMS industry growth. This paper uses examples from the past and present to identify technical and business characteristics that lead to successful high volume MEMS products. These lessons are then projected forward to identify emerging high volume MEMS opportunities.