Microelectromechanical Systems Chip Research Articles

Waveguide‐integrated MEMS‐based phase shifter for phased array antenna

This study investigates a new concept of waveguide-based W-band phase shifters for applications in phased array antennas. The phase shifters are based on a tuneable bilateral finline bandpass filter with 22 microelectromechanical system (MEMS) switching elements, integrated into a custom-made WR-12 waveguide with a replaceable section, whose performance is also investigated in this study. The individual phase states are selected by changing the configuration of the switches bridging the finline slot in specific positions; this leads to four discrete phase states with an insertion loss predicted by simulations better than 1 dB, and a phase shift span of about 270°. MEMS chips have been fabricated in fixed positions, on a pair of bonded 300 µm high-resistivity silicon substrates, to prove the principle, that is, they are not fully functional, but contain all actuation and biasing-line elements. The measured phase states are 0, 56, 189 and 256°, resulting in an effective bit resolution of 1.78 bits of this nominal 2 bit phase shifter at 77 GHz. The measured insertion loss was significantly higher than the simulated value, which is assumed to be attributed to narrow-band design of the devices as the influences of fabrication and assembly tolerances are shown to be negligible from the measurement results.

Development of a high-precision calibration method for inertial measurement unit

MEMS (Micro-Electromechanical Systems) based IMU (Inertial Measurement Unit) including accelerometers and gyroscopes is widely used for various applications such as INS (Inertial Navigation System), pose estimation devices and others for many industries such as toy, medical, automotive and military industry. But MEMS sensor chip originally has bias and sensitivity errors from manufacturing, and there is also axis misalignment when mounting a MEMS chip on IMU PCB layer. These error factors cause inaccuracy measurement results and non-linear measurement characteristics of IMU. In this paper, accelerometers and gyroscopes are mathematically modeled based on these error factors including bias, sensitivity, coning angle and azimuth angle. Calibration procedures for accelerometers and gyroscopes are formulated using nonlinear Gauss-Newton regression logic. The effectiveness of the proposed calibration procedures are proven by simulation and experiment using high accuracy 2-axis rotational gimbal motion system.

Design and characterization of micromachined sensor array integrated with CMOS based optical readout

This paper reports a micro electro-mechanical system (MEMS) based sensor array integrated with CMOS-based optical readout. The integrated architecture has several unique features. MEMS devices are passive and there are no electrical connections to the MEMS sensor array. Thus, the architecture is scalable to large array formats for parallel measurement applications and can even be made as a disposable cartridge in the future using self-aligning features. A CMOS-based readout integrated circuit (ROIC) is integrated to the MEMS chip. Via holes are defined on ROIC by customized post-processing and MEMS chip is thinned down by a grinding process to enable integrated optical readout. A diffraction grating interferometer-based optical readout is realized by pixel-level illumination of the MEMS chip through the via holes and by capturing the reflected light using a photodetector array on the CMOS chip. A model for the optical readout principle has been developed using Fourier optics.

Nanofabrication, effects and sensors based on micro-electro-mechanical systems technology

In this paper, our investigation of nanofabrication, effects and sensors based on the traditional micro-electro-mechanical systems (MEMS) technology has been reviewed. Thanks to high selectivity in anisotropic etching and sacrificial layer processes, nanostructures such as nanobeams and nanowires have been fabricated in top-down batch process, in which beams with thickness of only 20 nm and nanowires whose width and thickness is only 20 nm were achieved. With the help of MEMS chip, the scale effect of Young's modulus in silicon has been studied and confirmed directly in a tensile experiment using electron microscopy. Because of their high surface-to-volume ratio and small size, silicon nanowire (SiNW)-based field-effect transistors (FETs) have been shown as one of the most promising electronic devices and ultrasensitive detectors in biological applications. We demonstrated that an SiNW-FET sensor can reveal ultrahigh sensitivity for rapid and reliable detection of 0.1 fM of target DNA with high specificity. All these indicate that the MEMS technology can pave the way to nanoapplications with its advantages of batch production, low cost and high performance.

Parallel C4 Packaging of MEMS Using Self-Alignment: Simulation and Experiments

Packaging is one of the major cost drivers for microelectromechanical systems (MEMS). Currently wire bonding is the dominant method for electrically connecting MEMS chips to the substrate. Using self-alignment, a method for packaging multiple MEMS at the same time has been developed. The presented process achieves high throughput and precise alignment at low cost. The controlled collapse chip connection (C4) process has been adapted to the specific requirements of MEMS. The combination of coarse robotics and liquid solder self-alignment guarantees precise positioning and alignment of the individual MEMS chips to the respective substrates. The new method has been implemented in a case study. In the study, force sensors were packaged. Precise angular alignment of the sensors is critical for making accurate measurements. Results of the case study are presented. The alignment motion is analyzed, compared with results in the literature, and simulated. These simulations, in combination with our experiments, indicate that the motion is dominated by solder-specific effects such as oxide removal, wetting, and flux solvent evaporation.

MEMS-based Universal Fatigue-Test Technique

We have developed a MEMS (micro electro mechanical systems)—based method for fatigue testing of micrometer— millimeter-sized specimens of any material (hence ‘universal’). The miniature, re-usable, stand-alone fatigue test frame is fabricated as a single MEMS chip. Specimens of any material can be manually mounted in the chip and fatigue-tested. We describe the design and construction of the MEMS device and specimens, the test protocol and data analysis procedure, and show stress versus number of cycles to failure (S-N) results for 25 μm thick Al 1145 H19 foil. The S-N results are in accord with expectations, and examination of the fracture surface by scanning electron microscopy shows distinct regions corresponding to slow and fast crack growth.

Design, Fabrication, and Characterization of Freestanding Mechanically Flexible Interconnects Using Curved Sacrificial Layer

Technologies that enable integration of microelectromechanical systems (MEMS) (and sensor) chip with a complementary metal-oxide semiconductor (CMOS) integrated circuit (IC) are becoming increasingly more important as the semiconductor industry explores and tries to encompass “More-than-Moore” solutions for future electronic systems. 3-D integration, stacking of dissimilar chips that have been independently fabricated and optimized, is a promising method to integrate MEMS and its signal processing electronics into a single miniaturized package. Unlike conventional methods of integration, 3-D integration can simultaneously provide high density and high performance interconnections without the added process complexity resulting from the CMOS and MEMS process reconciliation. Vital to the success of such integration are many novel interconnect technologies such as through-silicon vias, mechanically flexible interconnect (MFI) technology is another vital interconnect technology providing low stress, area array interconnections between a MEMS chip and a CMOS IC. MFIs are batch fabricated freestanding interconnect structures fabricated using two photolithography steps. The stand-off height of MFIs are 20 μm and the dimension can be as small as 100 by 50 μm. In this paper, design, fabrication, and characterization of MFIs are presented, this paper also demonstrates SU-8 ring structures that allow fabrication and confinement of solder ball, so that MFIs can be assembled using a conventional flipchip bonder. Critical technology that enables fabrication of MFIs is the technology that uses reflowed photoresist as a sacrificial layer, development of such process is also discussed.

Novel First-Level Interconnect Techniques for Flip Chip on MEMS Devices

Flip-chip packaging is desirable for microelectro-mechanical systems (MEMS) devices because it reduces the overall package size and allows scaling up the number of MEMS chips through 3-D stacks. In this report, we demonstrate three novel techniques to create first-level interconnect (FLI) on MEMS: 1) Dip and attach technology for Ag epoxy; 2) Dispense technology for solder paste; 3) Dispense, pull, and attach technology (DPAT) for solder paste. The above techniques required no additional microfabrication steps, produced no visible surface contamination on the MEMS active structures, and generated high-aspect-ratio interconnects. The developed FLIs were successfully tested on MEMS moveable microelectrodes microfabricated by SUMMiTVTM process producing no apparent detrimental effect due to outgassing. The bumping processes were successfully applied on Al-deposited bond pads of 100 μm × 100 μm with an average bump height of 101.3 μm for Ag and 184.8 μm for solder (63Sn, 37Pb). DPAT for solder paste produced bumps with the aspect ratio of 1.8 or more. The average shear strengths of Ag and solder bumps were 78 MPa and 689 kPa, respectively. The electrical test on Ag bumps at 794 A/cm2 demonstrated reliable electrical interconnects with negligible resistance. These scalable FLI technologies are potentially useful for MEMS flip-chip packaging and 3-D stacking.

MEMS-based high-frequency vibration sensors

We present the development of two vibration sensors, one designed for out-of-plane sensingand one designed for in-plane sensing. Both sensors, fabricated on a 5 mm square MEMS(microelectromechanical system) chip, are variable capacitors with one electrode of thecapacitor suspended by springs and the other electrode fixed to the chip. When a biasvoltage is placed across the capacitor and the sensor is excited, the spring-suspendedstructure vibrates with respect to the fixed structure and induces a time-varying signal.Both sensors have resonant frequencies near 200 kHz. The out-of-plane sensor employs anopen grill design rather than square etch holes to reduce the effects of squeeze film dampingand increase sensitivity. The in-plane sensor uses a finger-type design which attempts totake advantage of the relatively high damping effect of air in the out-of-plane directionin order to suppress unwanted out-of-plane motion. Finite element simulationsestimating the resonant frequency are presented and compared to characterizationmeasurements of the resonant frequency. Characterization measurements of thesensitivity of each device are also presented. In addition, we report on a laboratoryexperiment in which we measure the response of each sensor to steady-state excitation.

MEMSエレクトレット・コンデンサ・マイクロホンによる脈波測定

A micro Electret Condenser Microphone (ECM) fabricated by Micro Electro Mechanical System (MEMS) technology was employed as a novel apparatus for human pulse wave measurement. Since ECM frequency response characteristic, i.e. sensitivity, logically maintains a constant level at lower than the resonance frequency (stiffness control), the slightest pressure difference at around 1.0Hz generated by human pulse wave is expected to detect by MEMS-ECM. As a result of the verification of frequency response of MEMS-ECM, it was found that -20dB/dec of reduction in the sensitivity around 1.0Hz was engendered by a high input-impedance amplifier, i.e. the field effect transistor (FET), mounted near MEMS chip for amplifying tiny ECM signal. Therefore, MEMS-ECM is assumed to be equivalent with a differentiation circuit at around human pulse frequency. Introducing compensation circuit, human pulse wave was successfully obtained. In addition, the radial and ulnar artery tracing, and pulse wave velocity measurement at forearm were demonstrated; as illustrating a possible application of this micro device.

A Cavity Chip Interconnection Technology for Thick MEMS Chip Integration in MEMS-LSI Multichip Module

We develop a cavity chip interconnection technology for thick microelectromechanical systems (MEMS) chip integration. The cavity chip comprising Cu through-silicon via and Cu beam-lead wire was fabricated by micromachining processes. The cavity chip could easily connect a thick MEMS chip with a high step height of more than a few hundred micrometers without changing the circuit design of MEMS chip and complicated extra process. Fundamental characteristics are successfully obtained from a pressure-sensing MEMS chip of 360- thickness, where the MEMS chip was connected to a Si substrate by the cavity chip without degrading brittle sensing elements. This interconnection technology would provide a good solution for thick MEMS chip integration with high flexibility.

Miniaturization of a Laser Doppler Blood Flow Sensor by System‐in‐Package Technology: Fusion of an Optical Microelectromechanical Systems Chip and Integrated Circuits

AbstractWe have developed the first and the smallest blood flow sensor composed of integrated circuits (ICs) fused with an optical microelectromechanical systems (MEMS) chip using system‐in‐package (SiP) technologies for application in a healthcare monitoring system. The probe of this blood flow sensor consists of three layers, and the optical MEMS chip is stacked as the top layer. Through silicon via (TSV), vertical‐cavity surface‐emitting laser (VCSEL) and cavities enable wafer‐level packaging of the optical MEMS chip. The other two layers consisting of ICs are highly densified by SiP technology, and the volume of the probe is miniaturized to about one‐sixth of our previously reported integrated laser Doppler blood flowmeter, an MEMS blood flow sensor to which SiP technology was not applied. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Chirality assignment to carbon nanotubes integrated in MEMS by tilted-view transmission electron microscopy

Front side etching combined with sample tilting – instead of wafer through etching – allows for transmission electron microscopy (TEM) investigations on nanostructures integrated in microelectromechanical systems (MEMS). We present electron diffraction of an individual single-walled carbon nanotube (SWNT) suspended between sharp polycrystalline silicon tips as far as 165 μm away from the MEMS chip edge. This novel approach for transmission-beam characterization avoids complex wafer backside processing and facilitates alignment of the SWNTs to the focal plane using tips defined directly by photolithographic means. The demonstration of chirality assignment to the integrated SWNT paves the way for correlating experimentally measured response of the SWNT sensing element upon stimuli with the response predicted by theory.

Tilted-view transmission electron microscopy-access for chirality assignment to carbon nanotubes integrated in MEMS

Front side etching in combination with sample tilting – instead of wafer through etching – allows for transmission electron microscopy (TEM) investigations on nanostructures integrated in microelectromechanical systems (MEMS). We present electron diffraction (ED) of an individual single-walled carbon nanotube (SWNT) suspended between sharp polysilicon tips on the bulk of a MEMS chip. This novel approach for transmission beam characterization avoids complex wafer backside processing while allowing for chirality assignment to the integrated functional SWNT, as demonstrated here.

Characterization of a MEMS-based pulse-shaping device in the deep ultraviolet

We describe the implementation and characterization of a micro-mirror-array set-up based on Micro-Electro-Mechanical System (MEMS) technology for femtosecond pulse shaping in the deep UV. We demonstrate its capability of re-compressing spectrally broadened UV pulses with a closed-loop approach based on a genetic algorithm. A single-shot synchronization scheme, taking advantage of the limited duty cycle of the device and allowing on-line correction of the signal, is described. The second dimension of the MEMS chip can be used to partially reduce the spatial chirp of the beam.

Bump-less Wafer Level Bonding Experiment for Vertical Integration MEMS Device

In the future, it is desired that high performance sensing module in small volume is realized. However, conventional MEMS (Micro Electro Mechanical Systems) packaging technology is becoming difficult to meet its desire (Especially Bulk MEMS). Small and package-less 3D sensing module, which consist of MEMS and IC chips bonded by SAB (Surface Activated Bonding) solves this problem (Fig. 1). But we have many technological opportunities in small and package-less 3D sensing module; Low damage bonding, electrical contact, and bonding alignment. This paper reports 'Bump-less wafer level bonding' which is needed for vertical integration MEMS device and the 3 wafer bonding experiment results of bonding strength, electrical contact, and alignment.

FPGA-Based Decentralized Control of Arrayed MEMS for Microrobotic Application

In this paper, the authors have developed and implemented a decentralized decision-making strategy using field-programmable gate array (FPGA) technology as a prototype for an integrated controller of a microelectromechanical systems (MEMS) array for air-flow planar micromanipulation. The MEMS array was proposed to be integrated in a hybrid multichip module containing the FPGA-based controller. Algorithms and architectures, used for the decentralized control implementation and the hardware resource optimization, are described. A charge-coupled device camera was used to make each MEMS like an autonomous system when the distributed MEMS chip was tested. Finally, under air-flow condition, the FPGA-based decentralized control system successfully performed an object manipulation.

Low-Actuation-Voltage MEMS for 2-D Optical Switches

This paper discusses the design, fabrication, and test results of electromagnetically actuated two-dimensional (2-D) microelectromechanical systems (MEMS) optical switches. The switching element consists of a 20 mumtimes500 mumtimes1200 mum vertical micromirror, which is monolithically integrated with an actuation flap. The micromirror is made by anisotropic tetramethyl-ammonium-hydroxide wet etching with an optical insertion loss of about 0.2 dB. A maximum insertion loss of 2.1 dB has been experimentally demonstrated for a 10 times 10 2-D optical crossconnect switch. The actuation flap has double layers of spiral metal coils to generate a large actuation force with the permanent magnets placed at the bottom of the MEMS chip. The magnetic flux is created on the surface of a pair of opposite polarized magnets to precisely control the moving direction of the vertical mirror. The required voltage is less than 0.5 V, and the power consumption is about 3.5 mW for a switching element. Due to the center symmetric design and the stress-free characteristic of the micromirror, the temperature dependence loss is demonstrated to be as low as 0.05 dB. A switching time of 5 ms is achieved by applying the proper driving waveform

Micromechanical Optical Crossconnect With 4->tex<$F$>/tex<Relay Imaging Optics

We describe a novel optical configuration for a microelectromechanical system (MEMS)-based beam-steering optical crossconnect. It incorporates 4-F imaging optics to relay light to the MEMS chip. This makes the system more tolerant to fiber-microlens misalignment. The use of a relay plus Fourier lens and patterned mirror removes the skew angle on the MEMS array and reduces the maximum angle for the MEMS mirror. A prototype 110 /spl times/ 110 crossconnect employing imaging optics was constructed to validate the approach. This achieved a mean fiber-to-fiber insertion loss of 2.9 dB.

Fabrication of MEMS Devices with Macroporous Silicon Membrane Embedded with Modulated 3D Structures for Optimal Cell Sorting

Macroporous silicon is a type of porous silicon that has ordered arrays of channels with high aspect ratio. Macroporous silicon with ordered 3-D structures have a variety of applications such as filters for a particle separation, photonic crystals and optical shortpass filters because of their spatially periodic structures [1–3]. These structures can be prepared by the electrochemical etching (ECE) of silicon wafers in hydrofluoric acid (HF). We report here a way to fabricate macroporous silicon membranes with ordered 3D structures that have controlled periodicity and dimensions appropriate for cell sorting. The silicon 3D structures have pores with variable diameters to modulate the flow behavior and optimize cell sorting efficiency. The silicon membranes were fabricated by wet etching of n-type (100) silicon substrate (40–60 W cm) in potassium hydroxide (KOH) solution with isopropyl alcohol at 80 °C. The 3-D structures were prepared by the electrochemical etching (ECE) of the membranes in diluted HF using the backside illumination with modulated intensity. The thickness of the fabricated membrane has been varied from 20 to 200 mm to optimize filtration of the cells by MEMS (Micro-ElectroMechanical Systems) chips designed for biological cell sorting and cell positioning. The software packages IntelliSuite and ANSYS FLOWTRAN were used to study the mechanical strength of the membrane as well as the velocity profile and flow behavior of Newtonian fluids inside the macroporous silicon membrane.