Microelectromechanical Systems and Devices

The advances of microelectromechanical systems (MEMS) and devices have been instrumental in the demonstration of new devices and applications, and even in the creation of new fields of research and development: bioMEMS, actuators, microfluidic devices, RF and optical MEMS. Experience indicates a need for MEMS book covering these materials as well as the most important process steps in bulk micro-machining and modeling. We are very pleased to present this book that contains 18 chapters, written by the experts in the field of MEMS. These chapters are groups into four broad sections of BioMEMS Devices, MEMS characterization and micromachining, RF and Optical MEMS, and MEMS based Actuators. The book starts with the emerging field of bioMEMS, including MEMS coil for retinal prostheses, DNA extraction by micro/bio-fluidics devices and acoustic biosensors. MEMS characterization, micromachining, macromodels, RF and Optical MEMS switches are discussed in next sections. The book concludes with the emphasis on MEMS based actuators

Standalone Tensile Testing of Thin Film Materials for MEMS/NEMS Applications

The microelectronics industry has been consistently driven by the scaling roadmap, colloquially referred to as the Moore’s law. Consequently, during the past decades, integrated circuits have scaled down further. This shrinkage could have never been possible without the efficient integration and exploitation of thin film materials. Thin film materials, on the other hand, are the essential building blocks of the micro- and nano-electromechanical systems (MEMS and NEMS). Utilization of thin film materials provides a unique capability of further miniaturizing electromechanical devices in micro- and nano-scale. These devices are the main components of many sensors and actuators that perform electrical, mechanical, chemical, and biological functions. In addition to the wide application of thin film materials in micro- and nano-systems, this class of materials has been historically utilized in optical components, wear resistant coatings, protective and decorative coatings, as well as thermal barrier coatings on gas turbine blades. In some applications, thin film materials are used mainly as the load-bearing component of the device. Microelectromechanical systems (MEMS) are the example of these applications. Thin film materials carry mechanical loads in thermal actuators, switches and capacitors in RF MEMS, optical switches, micro-mirror hinges, micro-motors, and many other miniaturized devices. In these applications, one of the main criteria to choose a specific material is its ability to perform the mechanical requirements. Therefore, a clear understanding of the mechanical behavior of thin film materials is of great importance in these applications. This understanding helps better analyze the creep in thermal actuators (Tuck et al., 2005; Paryab et al., 2006), to investigate the fatigue of polysilicon (Mulhstein et al., 2001; Shrotriya et al., 2004) and metallic micro-structures (Eberl et al., 2006; Larsen et al., 2003), to scrutinize the relaxation and creep behavior of switches made of aluminum (Park et al., 2006; Modlinski et al., 2004) and gold films (Gall et al., 2004), to study the hinge memory effect (creep) in micro-mirrors (Sontheimer, 2002), and to address the wear issues in micro-motors. (van Spengen, 2003) In some other applications, the thin film material is not necessarily performing a mechanical function. However, during the fabrication process or over the normal life, the device experiences mechanical loads and hence may suffer from any of the mechanical failure issues. Examples of these cases are the thermal fatigue in IC interconnects (Gudmundson & Wikstrom, 2002), strain ratcheting in passivated films (Huang et al., 2002; He et al., 2000), the fracture and delamination of thin films on flexible substrates (Li & Suo, 2006), the fracture of porous low-k dielectrics (Tsui et al., 2005), electromigration (He et al., 2004), the chip-package-interaction (CPI) (Wang & Ho, 2005), and thin film buckling and delamination (Sridhar et al., 2001). In order to address the above-mentioned failure issues and to design a device that has mechanical integrity and material reliability, an in-depth knowledge of the mechanical behavior of thin film materials is required. This information will help engineers integrate materials and design devices that are mechanically reliable and can perform their specific functions during their life-time without any mechanical failure. In addition to the tremendous industrial and technological driving force that was mentioned earlier, there is a strong scientific motivation to study the mechanical behavior of thin film materials. The mechanical behavior of thin film structures have been known to drastically differ from their bulk counterparts. (Xiang, 2005) This discrepancy that has been referred to as the length-scale effect has been one of the main motivations in the scientific society to study the mechanical behavior of thin film materials. In order to provide fundamental mechanistic understanding of this class of materials, old problems and many of the known physical laws in materials science and mechanical engineering have to be revisited from a different and multidisciplinary prospective. These investigations will not be possible unless a concrete understanding of the mechanical behavior of thin film materials is achieved through rigorous experimental and theoretical research in this area.Natural Sciences and Engineering Research Council (NSERC) of Canad

Investigation into Contact Resistance and Damage of Metal Contacts Used in RF-MEMS Switches

This research examines the physical and electrical processes involved in lifecycle failure of Microelectromechanical (MEMS) Radio-Frequency (RF) cantilever beam ohmic contact switches. Failures of these switches generally occur at the contact, but complete details of performance of microcontacts are difficult to measure and have not been previously reported. This study investigated the mechanics of microcontact behavior by designing and constructing a novel experimental setup. Three representative contact materials of varying microstructure (Au, Au5%Ru, Au4%V2O5) were tested and parameters of contact during cycling were measured. The Au4%V2O5, a dispersion strengthened material developed at Lehigh University, showed the most promise of the materials tested with the longest-life contact lasting more than 15.5 x 106 cycles. Evidence of time-dependent deformation and contact heating during cycling was noted in all materials tested. Material hardness was not proportional to contact lifetime or adhesive forces measured during testing. Surfaces of post-cycling contact surfaces were evaluated and failures were categorized by ductile or brittle separation characteristics. Separation characteristics were correlated by contact lifetime

High Speed Test Interface Module Using MEMS Technology

With the transient frequency of available CMOS technologies exceeding hundreds of gigahertz and the increasing complexity of Integrated Circuit (IC) designs, it is now apparent that the architecture of current testers needs to be greatly improved to keep up with the formidable challenges ahead. Test requirements for modern integrated circuits are becoming more stringent, complex and costly. These requirements include an increasing number of test channels, higher test-speeds and enhanced measurement accuracy and resolution. In a conventional test configuration, the signal path from Automatic Test Equipment (ATE) to the Device-Under-Test (DUT) includes long traces of wires. At frequencies above a few gigahertz, testing integrated circuits becomes a challenging task. The effects on transmission lines become critical requiring impedance matching to minimize signal reflection. AC resistance due to the skin effect and electromagnetic coupling caused by radiation can also become important factors affecting the test results. In the design of a Device Interface Board (DIB), the greater the physical separation of the DUT and the ATE pin electronics, the greater the distortion and signal degradation. In this work, a new Test Interface Module (TIM) based on MEMS technology is proposed to reduce the distance between the tester and device-under-test by orders of magnitude. The proposed solution increases the bandwidth of test channels and reduces the undesired effects of transmission lines on the test results. The MEMS test interface includes a fixed socket and a removable socket. The removable socket incorporates MEMS contact springs to provide temporary with the DUT pads and the fixed socket contains a bed of micro-pins to establish electrical connections with the ATE pin electronics. The MEMS based contact springs have been modified to implement a high-density wafer level test probes for Through Silicon Vias (TSVs) in three dimensional integrated circuits (3D-IC). Prototypes have been fabricated using Silicon On Insulator SOI wafer. Experimental results indicate that the proposed architectures can operate up to 50 GHz without much loss or distortion. The MEMS probes can also maintain a good elastic performance without any damage or deformation in the test phase

Nematic Liquid Crystal Carbon Nanotube Composite Materials for Designing RF Switching Devices

Radio frequency microelectromechanical systems (RF MEMS) devices are microdevices used to switch or modify signals from the RF to millimeter wave (mmWave) frequency range. Liquid crystals (LCs) are widely used as electro-optic modulators for display devices. An electric field-induced electrical conductivity modulation of pure LC media is quite low which makes it difficult to use for RF MEMS switching applications. Currently, RF MEMS devices are characterized as an excellent option between solid-state and electromechanical RF switches to provide high isolation, low insertion loss, low power usage, excellent return loss, and large frequency band. However, commercial usage is low due to their lower switching speed, reliability, and repeatability. This research presents an electrical conductivity enhancement through the use of carbon nanotube (CNT) doping of LCs to realize a high-performance RF LC-CNT switching device. This thesis presents simulations of an RF switch using a coplanar waveguide (CPW) with a LC-CNT composite called 4-Cyano-4’-pentylbiphenyl multi-walled nanotube (5CB-MWNT) that is suitable for RF applications. The electrical conductivity modulation and RF switch performance of the 5CB-MWNT composite is determined using Finite Element Analysis (FEA). The simulations will present data on the coplanar waveguide’s s-parameters at the input and output ports S11 and S21 to measure return and insertion loss respectively, two key parameters for determining any RF switch’s performance. Furthermore, this thesis presents applications for improving tunable phased antenna arrays using the LC-CNT composite to allow for beam steering with high-gain and directivity to provide a broad 3D scannable coverage of an area. Tunable antennas are an important characteristic for 5G applications to achieve an optimal telecommunication system to prevent overcrowding of antennas and reduce overall system costs. This research investigates various device geometries with 5CB-MWNT to realize the best performing RF device for RF applications and 5G telecommunication systems. This research presents return and insertion loss data for three waveguide device configurations: CPW, coplanar waveguide grounded (CPWG), and finite ground coplanar waveguide grounded (FG-CPWG). The best results are shown using the CPW configuration. The return loss for the LC-CNT device showed a 5 dB improvement from -7.5 dB to -12.5 dB when using the LC-CNT signal line device. The insertion loss for this configuration showed a much more consistent 0 to -0.3 dB insertion loss value with much less noise when using the LC-CNT device compared to the -0.3 to -1 dB insertion loss value with heavy noise when using the Au signal line device. For the other two configurations the return loss and insertion loss value stayed the same indicating there is no loss in performance when using the LC-CNT switching mechanism. This is ideal due to the benefits that the LC-CNT switching mechanism provides like device reliability and increased switching speeds

National MEMS Technology Roadmap - Markets, Applications and Devices

MEMS teknologiaa on jo pitkään käytetty lukuisien eri laitteiden valmistamiseen. Osa näistä laitteista on ollut markkinoilla jo useita vuosia, kun taas osa on vasta kehitysvaiheessa. Jotta tutkimus ja kehitystyötä osattaisiin jatkossa kohdistaa oikeille painopistealueille, on tärkeää tietää mihin suuntaan kehitys on menossa. Tämä työ on osa kansallista MEMS teknologioiden tiekartta -projektia ja sen tavoitteena oli selvittää MEMS laitteiden kehityksen suuntaa. Työ toteutettiin laajana kirjallisuustutkimuksena. Lisäksi tulosten tueksi haastateltiin asiantuntijoita Suomen MEMS teollisuudesta. Työssä tarkasteltiin lukuisia jo markkinoilta löytyviä ja vasta kehitteillä olevia MEMS laitteita ja analysoitiin niitä sekä teknisestä että kaupallisesta näkökulmasta. Tutkimuksen perusteella kävi ilmi, että MEMS markkinat ovat pitkään muodostuneet vakiintuneista laitteista kuten mustesuihkupäistä, kiihtyvyysantureista, paineantureista sekä RF suotimista. Lisäksi mikrofonit, gyroskoopit ja optiset laitteet ovat olleet kaupallisesti saatavilla jo pitkään. Markkinat ovat hiljattain alkaneet tehdä tilaa myös uusille MEMS laitteille, joita tulee ulos nopeaa vauhtia. Viimeisimpänä markkinoille tulleita laitteita ovat erilaiset mikrofluidistiikka laitteet, mikrobolometrit sekä yhdistelmäanturit. Pian kaupallisesti saatavia laitteita ovat magnetometrit, automaattitarkennuslaitteet sekä MEMS oskillaattorit. Näiden laitteiden lisäksi kehitteillä on monia uusia MEMS laitteita, jotka saattavat tarjota merkittäviä mahdollisuuksia tulevaisuudessa. Kehitteillä olevia laitteita ovat erilaiset lääketieteelliset laitteet, atomikellot, mikrojäähdyttimet, mikrokaiuttimet, energiantuottolaitteet sekä RFID-laitteet. Kaikki kehitteillä olevista laitteista eivät välttämättä tule menestymään kaupallisesti, mutta jatkuva tutkimustyö osoittaa, että monilla MEMS laitteilla on potentiaalia useissa eri sovelluksissa. Markkinanäkökulmasta tarkasteltuna suurin potentiaali piilee kuluttajaelektroniikka markkinoilla. Muita tulevaisuuden kannalta potentiaalisia markkinoita ovat lääketieteelliset ja teollisuusmarkkinat. Tutkimus osoitti että MEMS laitteiden tutkimukseen ja kehitykseen liittyy monia potentiaalisia painopistealueita tulevaisuudessa. Käyttömahdollisuuksien parantamiseksi monet jo vakiintuneet laitteet kaipaavat vielä parannuksia. Toisaalta, jo olemassa olevia laitteita voidaan hyödyntää uusissa sovelluksissa. Lisäksi monet uusista ja kehitteillä olevista MEMS laitteista vaativat vielä kehitystyötä.MEMS technology has long been applied to the fabrication of various devices from which some have already been in use for several years, whereas others are still under development. In order to find future focus areas in research and development activities in the industry, it is important to know where the development is going. This thesis was conducted as a part of National MEMS technology roadmap, and it aimed for determining the evolution of MEMS devices. The work was conducted as an extensive literature review. In addition, experts from the Finnish MEMS industry were interviewed in order obtain a broader insight to the results. In this thesis various existing and emerging MEMS devices were reviewed and analyzed from technological and commercial perspectives. The study showed that the MEMS market has long been composed of established devices, such as inkjet print-heads, pressure sensors, accelerometers and RF filters. Also gyroscopes, microphones and optical MEMS devices have already been on the market for a long time. Lately, many new devices have started to find their place in the markets. The most recently introduced commercial devices include microfluidic devices, micro bolometers, and combo sensors. There are also a few devices including magnetometers, MEMS oscillators, and auto-focus devices that are currently crossing the gap from R&D to commercialization. In addition to the already available devices, many new MEMS devices are under development, and might offer significant opportunities in the future. These emerging devices include various bioMEMS devices, atomic clocks, micro-coolers, micro speakers, power MEMS devices, and RFID devices. All of the emerging devices might not find commercial success, but the constant stream shows, that there are numerous applications, where MEMS devices could be applied in. From a market point of view, the greatest potential in the future lies in consumer electronics market. Other highly potential markets include medical and industrial markets. The results of the thesis indicate that there are many potential focus areas in the future related to MEMS devices, including improvements of the existing devices in order to gain better utilization, application of the existing devices in new areas, and development work among the emerging devices

A MEMS Light Modulator Based on Diffractive Nanohole Gratings

We present the design, fabrication, and testing of a microelectromechanical systems (MEMS) light modulator based on pixels patterned with periodic nanohole arrays. Flexure-suspended silicon pixels are patterned with a two dimensional array of 150 nm diameter nanoholes using nanoimprint lithography. A top glass plate assembled above the pixel array is used to provide a counter electrode for electrostatic actuation. The nanohole pattern is designed so that normally-incident light is coupled into an in-plane grating resonance, resulting in an optical stop-band at a desired wavelength. When the pixel is switched into contact with the top plate, the pixel becomes highly reflective. A 3:1 contrast ratio at the resonant wavelength is demonstrated for gratings patterned on bulk Si substrates. The switching time is 0.08 ms and the switching voltage is less than 15V

Low Power Autonomous Microsystem for Oil Well Logging Applications

Downhole environmental monitoring can provide significant benefits to the petroleum industry. The rapid development of semiconductor technology enables autonomous sensing microsystems to operate at extreme environments. By injecting these microsystems into the boreholes and retrieving them after deployment, the geophysical conditions in the area of interest can be obtained. Challenges include high temperature, high pressure, miniaturized system size and packaging. This dissertation describes three generations of the environmental logging microsystem (ELM) for downhole geophysical logging applications. The first generation of the microsystem, ELM1.0, is designed for temperature logging in downhole environments. Each system consists of a power management circuit, a microcontroller with an integrated temperature sensor, and optical indicators. The system electronics are integrated on a flexible printed circuit board and packaged in a steel shell. The ELM1.0 has a packaged size of 8.9×8.9×6.85 mm3. It was tested at up to 125°C, 50 MPa in high salinity condition. The second generation (ELM2.0 & ELM2.1) is upgraded from ELM1.0 by adding a micromachined capacitive pressure sensor for pressure sensing up to 50 MPa. The ELM2.0 & ELM2.1 systems are packaged in steel shells filled with transparent polymer for pressure transfer. The packaged systems have a dimension of 9.5×9.5×6.5 mm3. The third generation (ELM3.0) is upgraded from ELM2.0 with a power switch and a low-cost polyimide pressure sensor for coarse pressure measurement up to 50 MPa. Both ELM2.0 and ELM3.0 systems were successfully tested at up to 125°C, 50 MPa in corrosive environments using laboratory instruments, and in a brine well at a depth up to 1235 m. A progressive polynomial calibration method was used for interpretation of the pressure sensor data from these tests. In addition, a high power micromachined RF switch for radio transceiver applications was designed, fabricated and tested. The RF switch can potentially be used to establish antenna networks for RF communication in the ELM. The switch consists of a bridge structure for electrostatic actuation and capacitive contact. The switch was fabricated with a 7-mask process. The fabricated device showed limited RF performance because of challenges related to the control of residual stress in suspended elements.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138647/1/sui_1.pd

Reconfigurable Antennas Using Liquid Crystalline Elastomers

This dissertation demonstrates the design of reversibly self-morphing novel liquid crystalline elastomer (LCE) antennas that can dynamically change electromagnetic performance in response to temperature. This change in performance can be achieved by programming the shape change of stimuli-responsive (i.e., temperature-responsive) LCEs, and using these materials as substrates for reconfigurable antennas. Existing reconfigurable antennas rely on external circuitry such as Micro-Electro-Mechanical-Systems (MEMS) switches, pin diodes, and shape memory alloys (SMAs) to reconfigure their performance. Antennas using MEMS or diodes exhibit low efficiency due to the losses from these components. Also, antennas based on SMAs can change their performance only once as SMAs response to the stimuli and is not reversible. Flexible electronics are capable of morphing from one shape to another using various techniques, such as liquid metals, hydrogels, and shape memory polymers. LCE antennas can reconfigure their electromagnetic performance, (e.g., frequency of operation, polarization, and radiation pattern) and enable passive (i.e., battery-less) temperature sensing and monitoring applications, such as passive radio frequency identification device (RFID) sensing tags. Limited previous work has been performed on shape-changing antenna structures based on LCEs. To date, self-morphing flexible electronics, including antennas, which rely on stimuli-responsive LCEs that reversibly change shape in response to temperature changes, have not been previously explored. Here, LCE antennas will be studied and developed. Also, the metallization of LCEs with different metal conductors and their fabrication process, by either electron beam (E-Beam) evaporation or optical gluing of the metal film will be observed. The LCE material can have a significant impact on sensing applications due to its reversible actuation that can enable a sensor to work repeatedly. This interdisciplinary research (material polymer science and electrical engineering) is expected to contribute to the development of morphing electronics, including sensors, passive antennas, arrays, and frequency selective surfaces (FSS)