Samsung prepara un micro-obturador para cámaras de celular

La compañía coreana Samsung se encuentra desarrollando una pequeña pieza para las cámaras digitales integradas en teléfonos que puede revolucionar al mercado. Se trata de un obturador de tan sólo 2.2 mm de diámetro basado en tecnología MEMS (sistemas microelectromecánicos).

Básicamente el obturador es la parte que permite la entrada de luz a la cámara y que se encuentra incorporado tras del lente. El obturador se abre cuando se fotografía en lugares oscuros y se cierra a plena luz, dejando un orificio mínimo.

La ventaja de de este micro-obturador -con el tamaño ideal para dispositivos móviles como los celulares- es que mejorará notablemente las imágenes tomadas con cámaras de alta resolución, como la cámara del Sony Ericsson Idou de 12 MP o la de 8 MP del Nokia N86.

Avances tecnológicos como éste son excelentes noticias para los fans de las cámaras con teléfono, ya que dan cuenta que los fabricantes no sólo están preocupados de meter más megapíxeles en los equipos (que en realidad no aporta nada salvo imágenes más grandes), sino que también en mejorar la calidad de las fotos que se pueden obtener con un celular.

Por el momento se desconoce cuánto costará el obturador y cuándo estará totalmente desarrollado. Supuestamente será más barato que los obturadores tradicionales y lo más posible es que falte bastante tiempo para verlo integrado en equipos, pero los resultados valdrán la espera.

 

Montan un lente de cámara dSLR en un iPhone

No es ningún misterio que uno de los puntos en contra del iPhone es su cámara mediocre, pero ponerle un lente de una cámara dSLR parece demasiado loco, aunque justamente es lo que hoy les mostramos. Un hack que permite utilizar un querido lente Canon 18-55 IS, también conocido como pISapapeles junto a tu iPhone.

Con esta modificación casera se gana en zoom óptico y en efectos de enfoque selectivo, pero las aberraciones cromáticas y el viñeteo hacen de las suyas. Sin duda sólo una muestra curiosa de lo que se puede hacer con tiempo y dedicación que puedes replicar siguiendo esta guía.

 
 
Nombre: Lenny D. Ramirez C.
Asignatura: CRF
Dirección: http://www.wayerless.com/up/2009/05/samsung-mems-shutter_01.jp
Ver blogg: http://lennyramirez-crf.blogspot.com/

Structured Design Methodology for MEMS

One important trend in microelectromechanical systems (MEMS) is toward monolithic systems where micromechanical devices are integrated with digital I/O, self-test, auto-calibration, digital compensation, and other signal processing functions. There is a growing demand in the MEMS community for rapid micromechanical design and analysis of complex systems involving multiple physical domains, including mechanical, electrostatic, magnetic, thermal, fluidic, and optical domains.

An important question generated in this workshop is: Can structured design methods for MEMS be developed by making an analogy to the VLSI design methodology? CAD for VLSI spans many levels of abstraction from materials, device, circuit, logic, register, to system level. At each of these levels, a design can be viewed in physical, structural (schematic), or behavioral form. A similar esign hierarchy for MEMS is feasible and sorely needed. Analogous hierarchical levels up to he VLSI ‘circuit’ level are easily made; higher levels of abstraction may evolve for MEMS that are ifferent from the VLSI paradigm. A first task in development of structured MEMS design tools is he formation of standard data representations and standard cell libraries. An enormous effort is necessary o identify and to model reusable MEMS processes, elements, devices, and architectures.

MEMS CAD tools must be integrated, with appropriate links available to the designer to switch between different lateral views and hierarchical levels.

An initial wish-list in the MEMS CAD toolset includes:

• standard MEMS data representations and interchange formats

• standard MEMS cell libraries supporting behavioral, schematic, and physical views at all levels of abstraction (e.g. materials database, layout cells, schematic element library, and a system macro-model library)

• standard MEMS process-module libraries and standard process flows

• process simulation and visualization

• process synthesis and technology file extraction

• 3D rendering and animation

• 3D generation from layout and technology files

• layout of arbitrarily shaped objects with design rule checking

• layout synthesis and verification

• fast modeling and verification tools; coupled multi-domain, numerical analysis (e.g. finiteelement method, boundary-element method)

• parasitic extraction to schematic and behavioral views

• macro-model parameter extraction from physical and schematic views

• multi-domain schematic capture (i.e. schematic view showing connectivity between mechanical, electromechanical, thermal, and circuit lumped-parameter elements)

• mixed-signal multi-level multi-domain simulation

 

Current MEMS CAD Tools

Several groups have existing research programs to address the deficiency in MEMS design tools. Examples from the U.S.A. include MEMCAD (M.I.T.)[1] and CAEMEMS (Univ. of Michigan) [2]; examples from Europe include CAPSIM (Catholic Univ. of Leuven, Belgium)[3], SENSOR (Fraunhofer Institute, Germany)[4], and SESES (ETH, Zürich)[5]. These tools involve general numerical analysis of layout and generation of macro-models for simulation. MEMCAD has evolved into a MEMS modeling framework with rapid self-consistent electromechanical 3D numerical simulation. Recent advances have been made in simplifying the input and visualization of 3D models of micromechanical structures from layout using the MEMBUILDER tool[6]. CAEMEMS is a framework in which the users chooses among modules that address specific design

domains. CAEMEMS automatically generates a set of parameterized response surfaces by launching multiple finite-element analyses. IntelliCAD[7] available from IntelliSense Corp. is a commercial MEMS CAD tool with automated 3D modeling from layout and process integrated with numerical analysis. Other commercial tools by Tanner Research[8] cater to the MEMS community by allowing layout of non-manhattan geometry and supplying MEMS technology files with design rule checking. These tools are definite improvements over use of Magic or KIC for layout and stand-alone numerical analysis tools (e.g. ABAQUS, ANSYS, Maxwell). More effort must be poured into fast multi-domain numerical analysis tools specifically tailored for MEMS design. MEMS process simulation and synthesis tools are needed and are being developed[9], but a discussion is outside the scope of this summary.

Current MEMS Design Practices

Current MEMS design practices focus on physical device and process development. A simplified design methodology is shown in Figure 1. Design concepts are implemented in a manual layout.

The performance is then analyzed using numerical analysis tools, usually resulting in iterations on both the layout and the underlying process. The present state-of-the-art in MEMS CAD relies on device-level extraction of macro-models in a limited set of energy domains for behavioral simulation. Current commercial design tools cannot deal with the complex multi-domain architectures that will be necessary to create the next-generation of commercial MEMS. Much future work should focus on creating very fast multi-domain numerical simulation tools to ease both process development and device macro-modeling. However, these numerical tools by themselves may not be practical for rapid iterative design since the physical layout (and perhaps the process) must be changed for each iteration without necessarily knowing what to change to best to improve the device performance.

Currently, a self-consistent electromechanical analysis of a simple device requires many man-hours to create the 3-D geometry and perform a numerical analysis. The manual design cycle in MEMS has not decreased significantly over the past few years since knowledge from previous development efforts cannot be easily reused by future developers.

MEMS Process Services

MEMS covers a broad, evolving spectrum of fabrication processes. This fact makes it very difficult to foresee the ultimate MEMS CAD framework. Our initial efforts at Carnegie Mellon have focussed on design tools for surface-micromachined MEMS, such as polysilicon MEMS built in MCNC’s MUMPs process[10], and laminated oxide/aluminum MEMS built using MOSIS followed by an in-house dry-etch release step[11]. There are a several important benefits of making microstructures with stable foundry services such as MUMPs and MOSIS:

• sensor fabrication is fast and reliable, all, or most, fabrication steps are done externally, so research resources can be invested in design, not standard processing,

• the process is repeatable, so circuit and microstructure designs can be re-used,

• devices improve as the process technology improves (e.g. scaling), and

• prototypes can be reproduced at any time.

Because of their planar ‘2 1/2-D’ topology, surface micromechanics is a MEMS technology which lends itself to abstraction in conventional schematic capture tools. Once a working structured design methodology is established for surface-micromachined MEMS, the techniques may be extended to other processes, such as bulk-machined Si or a dissolved-wafer process. The long-term goal is to enable rapid, intuitive exploration and analysis of the design space for complex MEMS.

Nombre: Lenny D. Ramirez C.

Asignatura: CRF

Dirección: http://design.caltech.edu/NSF_MEMS_Workshop/fedder.pdf

Ver blogg: http://lennyramirez-crf.blogspot.com/

Giroscopios MEMS de uno y dos ejes

Giroscopios MEMS de uno y dos ejes Ofrece mejoras en interfaces de usuario, juegos, navegación GPS y estabilización de imagen de cámara.

STMicroelectronics, uno de los mayores fabricantes de soluciones MEMS para aplicaciones de consumo y portátiles, ha introducido una nueva familia de giroscopios MEMS (Micro-Electro-Mechanical Systems) de uno y dos ejes.

Beneficiándose de la tecnología ‘micromachining’ de la compañía, que utiliza las propiedades mecánicas exclusivas del silicio al crear estructuras en el chip semiconductor para medir el movimiento, los giroscopios ST desarrollan mejoras en rendimiento y fiabilidad para la detección de movimiento angular en aplicaciones de interface hombre-máquina (HMI), sistemas de navegación y estabilización de imagen en cámaras digitales.

La familia de giroscopios MEMS de uno (viraje) y dos (‘pich-and-roll’ y ‘pich-and-yaw’) ejes ofrecen el rango ‘full-escale’ más amplio de la industria que va de 30 a 6.000 dps (grados por segundo). Sus novedosos sensores pueden dotar de dos salidas separadas para cada eje al mismo tiempo: un valor de salida no amplificada para detección general de movimiento angular y una amplificación 4x para mediciones de alta resolución que aumenta la flexibilidad de diseño y la experiencia del usuario.

Estos modelos de ST se distinguen por una excelente estabilidad sobre un extenso rango de temperatura, con una variación típica inferior a 0.05 dps / °C para nivel ‘zero-rate’, eliminando así la necesidad de compensación de temperatura adicional en la aplicación. La precisión de medición queda garantizada con un nivel mínimo de ruido que apenas afecta la señal de salida (0.014 dps / sqrt (Hz) a 30 dps ‘full-scale’).

Los giroscopios MEMS de elevado rendimiento son resistentes al estrés mecánico como consecuencia del proceso exitosamente aplicado en millones de acelerómetros ST vendidos en el mercado y pueden operar con cualquier tensión de alimentación en el rango de 2.7 a 3.6 V.

El encapsulado LGA de 5 x 5 mm, junto con un diseño innovador, garantiza un alto nivel de integración en aplicaciones con restricciones de espacio, así como un mayor rendimiento y estabilidad de soldadura, superando las prestaciones de alternativas cerámicas.

Entre los primeros giroscopios disponibles se encuentran los modelos LPR503AL ‘pitch-and-roll’ de dos ejes con un rango de 30 a 120 dps, y el LPY550AL ‘pitch-and-yaw’ de dos ejes con un rango de 500 a 2.000 dps.

Nombre: Lenny D. Ramirez C.

Asignatura: CRF
Dirección: http://noticiasit.tincan.es/giroscopios-mems-de-uno-y-dos-ejes/
Ver blogg: http://lennyramirez-crf.blogspot.com/

Aluminum Nitride RF MEMS Resonators

Aluminum Nitride RF MEMS Resonators

Sandia has developed an aluminum nitride (AlN) process for fabricating RF MEMS micro resonators at frequencies ranging from 1 MHz to 3 GHz. This process uses the same equipment and materials that were developed to fabricate FBARS (film bulk acoustic resonators), which are widely used to implement cellular phone duplexers and filters at 1.9 GHz. Like FBARS, the piezoelectric transduction mechanism of these resonators allows the realization of low insertion loss filters. Unlike FBARS, Sandia's AlN process allows resonators at any frequency between 1 MHz and 3 GHz to be fabricated on the same wafer because the resonant frequency is determined lithographically. The AlN resonator process also includes Sandia's unique molded tungsten (W) capabilities. Incorporation of W into the AlN process eliminates the need for resonators that are suspended above the substrate by quarter-wave beams. It is this technology that allows the scaling of AlN resonators into the GHz range without introducing spurious modes, reductions in quality factor (Q), and with acceptable power handling for both the transmit and receive paths in full-duplex radios. This technology is most suited for realizing resonators from 1 MHz to 3 GHz, with Q's approaching 5000, and impedances less than 300 Ohms.

Narrow-gap Polysilicon RF MEMS Resonators

A polysilicon MEMS resonator process has been developed at Sandia for the fabrication of high-Q oscillator references and intermediate frequency (IF) filters. This process can achieve electrode-to-resonator gaps less than 100 nm, which is needed to reduce the impedance of capacitively transduced devices. While high frequency resonators can be implemented in this process, it is best suited for fabricating resonators below 200 MHz because the impedance levels are significantly lower at these frequencies. Advantages of these polysilicon resonators when compared to microfabricated piezoelectric resonators include much higher Q (> 60,000), low drift, tunability, and low vibration sensitivity. These properties make polysilicon µresonators ideal for implementing miniature oscillators and IF filter banks for RF MEMS applications.

RF MEMS Reliability

Through measurement, characterization and analysis, we provide customer feedback to improve operation, performance and reliability of MEMS components, specifically RF switches. We have testing capabilities at the DARPA standard for MEMS switches (RFMIP) of 10 GHz. We have conducted environmentally controlled studies of switch performance and lifetimes at temperatures ranging from -15C to 75C, including cycling. Through failure analysis, we have worked with our customers to enhance understanding of operation, mechanically and electrically. We have performed tests to understand contamination issues that have caused early failures. We are investigating functionality and performance of RF sensor applications to monitor corrosion and to predict critical component failures. By utilizing knowledge of MEMS and by providing unique measurement and characterization capabilities, we can be an integral part of any MEMS project.

Nombre: Lenny D. Ramirez C.
Asignatura: CRF
Direccion: http://www.mems.sandia.gov/about/rf-mems.html
Ver blogg: http://lennyramirez-crf.blogspot.com/

Reliability Enhancements

Reliability Enhancements

Despite the demonstrated performance advantages of RF MEMS switches, the technology to manufacture reliable, environmentally robust devices is still maturing. The dominant reliability issue with capacitive RF MEMS switches is charging of the switch dielectric. Switching voltages across a thin dielectric layer causes electrical charges to tunnel into the dielectric and become trapped within the insulator. As yet, the underlying physics of the charge tunneling and trapping is not well understood. Most of the present knowledge of this phenomenon has come from empirical measurement of the switches.

One novel method of circumventing the charging phenomena is by trading off switch performance for lifetime. Proximity switches, being developed by MEMtronics, enable low loss, effective operation at microwave and millimeter wavelengths without the detrimental effects of charging on switch lifetime. These switches have the potential for operating for > 100 billion cycles and handling hot switching at multi-watt power levels. At microwave and millimeter-wave frequencies, the reduced capacitance ratio of these switches (Con/Coff ~20-40) is still sufficient for constructing high-performance phase shifters and tunable filters.

The key to proximity switches is separating the mechanical support structure from that of the electrical coupling mechanism. This allows the switch to operate with little or no dielectric charging, the dominant mechanism that limits the lifetime of MEMS capacitive switches. Dielectric supports made of silicon nitride or silicon dioxide keep the upper electrode supported a short distance above the lower electrode. The electrical coupling of RF energy from the upper plate to the lower plate is accomplished capacitively through the air gap between the two plates. As most circuit designs can be made quite robust with respect to switch on-capacitance, capacitance ratio can be exchanged for improved switch lifetime.

The proximity switch has several distinct advantages compared to prior designs of capacitive RF MEMS switch:

Absolutely no charging of the gas occurs between the plates. The only charging that may occur is through the mechanical (dielectric) supports maintaining the spacing between the two plates, a very small proportion of the total switch area. This enables the switches to operate with extremely long lifetimes.

Maintaining an air gap between the plates reduces the sensitivity of switch performance to particle contamination. This increases the environmental robustness of the switch.

Lack of dielectric charging also makes these switches ideal candidates for space-based applications, where the impact of radiation on the switch would normally be a reliability issue.

These features make the proximity switch an excellent candidate as a next generation MEMS switch. It is expected that this switch embodiment will have greater than 10x improvement in switch lifetime due to the lack of dielectric charging.

Nombre: Lenny D. Ramirez C.
Asignatura: CRF
Direccion: http://www.memtronics.com/page.aspx?page_id=15
Ver blogg: http://lennyramirez-crf.blogspot.com/

RF MEMS phase shifters

RF MEMS phase shifters

We recently spoke with Dr. Koen Van Caekenberghe, author of several articles on RF MEMS technology for radar sensors, about RF MEMS phase shifters. Koen shares his thoughts on the small but growing RF MEMS phase shifter market including applications, market developments, pricing and vendors of RF MEMS phase shifters as well as alternative technologies.

The radar sensor market has a global turnover of about $6.25 billion annually according to Defense Industry Daily. In Koen's opinion, approximately 50% of the budget is spent on airborne, ground-based, and naval AESA radar sensors, and approximately 25% of the budget is spent on mechanically scanned radar sensors -- and during the next decade, 20% of the mechanically scanned radar sensors might be replaced by PESA radar sensors based on RF MEMS shifters, resulting in a potential global market of $300 million annual

MEMS Investor Journal: Please provide a general description of RF MEMS phase shifters.

Koen: RF MEMS phase shifters alter the phase of an RF signal by means of RF MEMS switches, switched capacitors, and varactors [1, 2]. Phase shifters are used in radars based on electronically scanned arrays.

MEMS Investor Journal: How do radars work?

Koen: Radars sense angle, range and velocity of (moving) scatterers in the environment. Radar figures of merit include field of view in terms of solid angle and maximum unambiguous range and velocity, as well as angular, range and velocity resolution. The angle of a target is detected by scanning the field of view with a directive beam. Scanning is done electronically, by scanning the beam of an array, or mechanically, by rotating an antenna. The range and radial velocity of a target are detected through frequency modulation (FM) ranging and range differentiation (frequency modulated continuous wave radar), or through pulse delay ranging and the Doppler effect (pulse-Doppler radar). The angular resolution is inversely related to the half power beamwidth of the antenna or the array, whereas the range resolution is inversely related to the signal bandwidth.

MEMS Investor Journal: As you mentioned, RF MEMS phase shifters are used in radars based on electronically scanned arrays. What are the main advantages of using them?

Koen: Electronically scanned arrays, or phased arrays, offer several advantages over mechanically scanned antennas such as multiple agile beams and interleaved radar modes. Figures of merit of an electronically scanned array, as shown in Fig. 1, are the bandwidth, the effective isotropically radiated power (EIRP) times the Gr/T product, the field of view, the half-power beamwidth, the pointing error, the polarization purity and the sidelobe level. EIRP is the product of the transmit gain, Gt, and the transmit power, Pt. Gr/T is the quotient of the receive gain and the antenna noise temperature. Gr and Gt are linearly related to the aperture area, whereas the half power beamwidth is inversely related to the largest aperture dimension. The field of view is limited by the antenna element spacing, d, and the pointing error is inversely related to the phase shift resolution (number of effective bits of the phase shifter).

Figure 1: Figures of merit of an electronically scanned array set the radar sensor’s ability to search and track targets.

MEMS Investor Journal: What is the history of RF MEMS phase shifters and where were they first developed?

Koen: RF MEMS phase shifters were pioneered by HRL, Malibu, CA [3], Raytheon, Dallas, TX [4], Rockwell Science, Thousand Oaks, CA [5], and the University of Michigan, Ann Arbor, MI [6], during the nineties. Since then loaded-line, reflection, switched LC network and switched-line phase shifter designs have been implemented using RF MEMS switches, switched capacitors and varactors, as shown in Fig. 2. The switched LC network phase shifter is the most common phase shifter. RF MEMS distributed loaded-line and switched-line true-time-delay phase shifters will enable ultra wideband (UWB) radar sensors, whereas RF MEMS reflection phase shifters will find application in reflect arrays; a reflect array is a particular embodiment of a PESA.

Figure 2: Loaded-line, reflection, switched LC network, and switched-line phase shifter designs have been implemented using RF MEMS switches, switched capacitors and varactors.

MEMS Investor Journal: Are RF MEMS phase shifters an extension of or an improvement on an existing technology? If so, can you describe for our readers the features and benefits as compared with existing systems?

Koen: While most RF MEMS switches, switched capacitors and varactors are biased electrostatically instead of magnetostatically, RF MEMS technology can be thought of being a microscopic extension of electromechanical relay and switch technology, which dates back to the 19th century [7]. The application of electromechanical relay technology is limited to the VHF band (30-300 MHz), which confines its application to tunable filters for multi-band VHF communication equipment such as used in public safety 2-way radio networks. RF MEMS technology enables the use of a broader RF spectrum, ranging from the VHF band to the W-band (75-110 GHz), with a corresponding increase in communication and sensing applications.

RF MEMS phase shifters offer lower insertion loss, and higher linearity and power handling than semiconductor phase shifters, enabling passive electronically scanned arrays (PESAs) with higher EIRP x Gr/T product and longer range detection. They do not consume prime power, but require a high control voltage and wafer-level packaging.

MEMS Investor Journal: How are RF MEMS phase shifters used today and what are the various markets in which they find application?

Koen: RF MEMS phase shifters will find application in airborne and space-borne PESA radar sensors, which require low prime power consumption but do not require long-range search and track capability. The low-altitude unmanned aerial vehicles (UAV) radar sensor market, for example, offers potential for RF MEMS phase shifters.

In general, the choice between an active electronically scanned array (AESA) and a PESA is determined by the range requirement. An AESA has distributed power amplification because every antenna is connected to a T/R module. An AESA therefore has a higher EIRP x Gr/T product (dynamic range) and better search and track capabilities than a PESA. A PESA has centralized power amplification, but offers cost, prime power consumption, size and weight savings, as shown in Fig. 3.

Some airborne platforms, such as fighter jets, have a dual need. For example they have a high-performance nose-cone AESA radar sensor to search and track agile targets, and a low-power pod-mounted PESA radar sensor underneath to measure the height, to follow (avoid) terrain, or to map the ground during a low fly over. The use depends on the range of the envisioned target.

Figure 3: AESA (left) versus PESA (right).

 

Nombre: Lenny D. Ramirez C.

Asignatura: CRF

Direccion http://www.memsinvestorjournal.com/2009/04/rf-mems-phase-shifters-.html

Ver blogg: http://lennyramirez-crf.blogspot.com/

Simulation of an RF MEMS Varactor

Simulation of an RF MEMS Varactor

An RF MEMS variable capacitor, consisting of two MEMS bridges, was simulated with CST MICROWAVE STUDIO® (CST MWS) and the results then compared with actual measurements. Figure 1 shows the structure as constructed in CST MWS. The width of the central conductor of the coplanar waveguide was 100 um, which is also equal to the distance between it and the ground planes. The bridges connecting the ground planes functioned as varactors between the RF signal and the ground. The 500 um thick silicon was used as a substrate, 1000nm thick Molybdenium as a metal of the transmission line, and MEMS bridges were constructed of 1000 nm Aluminium.

Figure 1: Geometry of the RF MEMS-varactor.

The capacitance of the varactor can be changed between 120 fF (up-state) and 360 fF (down-state). As the MEMS bridge represents a parallel plate capacitor, the height of the bridge could be easily calculated. The height of the bridges of the up-state was 1.1 um, and of the down-state 0.2 um. The simulation results of the S11- and S21-parameters of the varactor in the up-state are plotted in Figure 2 and Figure 3 respectively.

From figures 2 and 3 it can be seen that the curves are very close to the measured ones [1]. The measured results have slightly higher losses but the measured loss also contains loss arising from the contact resistance between the probe tip and the aluminium contact pads [1]. In the down-state the reflection becomes higher and the resonance frequency shifts from 44GHz to 34GHz as can be seen from the figure 4.

Figure 4 shows the simulated S11-parameter of the varactor in the down-state and also shows good correlation with measurement results [1

Nombre: Lenny D. Ramirez C.

Asignatura: CRF
Direccion http://www.cst.com/Content/Applications/Article/232
Ver blogg: http://lennyramirez-crf.blogspot.com/

RF MEMS

The RF MEMS acronym stands for radio frequency microelectromechanical system, and refers to components of which moving sub-millimeter-sized parts provide RF functionality. RF functionality can be implemented using a variety of RF technologies. Besides RF MEMS technology, ferrite, ferroelectric, GaAs, GaN, InP, RF CMOS, SiC, and SiGe technology are available to the RF designer. Each of the RF technologies offers a distinct trade-off between cost, frequency, gain, large scale integration, lifetime, linearity, noise figure, packaging, power consumption, power handling, reliability, repeatability, ruggedness, size, supply voltage, switching time and weight

There are various types of RF MEMS components, such as RF MEMS resonators and self-sustained oscillators with low phase noise , RF MEMS tunable inductors, and RF MEMS switches, switched capacitors and varactors.

Switches, switched capacitors and varactors
RF MEMS switches, switched capacitors and varactors, which can replace field effect transistor (FET) switches and PIN diodes, are classified by actuation method (electrostatic, electrothermal, magnetic, piezoelectric), by axis of deflection (laterally, vertically), by circuit configuration (series, shunt), by clamp configuration (cantilever, fixed-fixed beam), or by contact interface (capacitive, ohmic) . Electrostatically-actuated RF MEMS components offer low insertion loss and high isolation, high linearity, high power handling and high Q factor, do not consume power, but require a high supply voltage and hermetic wafer level packaging (WLP) (anodic or glas frit wafer bonding) or single chip packaging (SCP) (thin film capping, liquid crystal polymer (LCP) or low temperature co-fired ceramic (LTCC) packaging).

RF MEMS switches were pioneered by Hughes Research Laboratories, Malibu, CA , Raytheon, Dallas, TX , and Rockwell Science, Thousand Oaks, CA , during the nineties. The component shown in Fig. 1, is a center-pulled capacitive fixed-fixed beam RF MEMS switch, developed and patented by Raytheon in 1994. A capacitive fixed-fixed beam RF MEMS switch is in essence a micro-machined capacitor with a moving top electrode - i.e. the beam

From an electromechanical perspective, the components behave like a mass-spring system, actuated by an electrostatic force. The spring constant is a function of the dimensions of the beam, of the Young's modulus, of the residual stress and of the Poisson ratio of its material. The electrostatic force is a function of the capacitance and the bias voltage. Knowledge of spring constant and mass allows for calculation of the pull-in voltage, which is the bias voltage necessary to pull-in the beam, and of the switching time.

From an RF perspective, the components behave like a series RLC circuit with negligible resistance and inductance. The up- and down-state capacitance are in the order of 50 fF and 1.2 pF, which are functional values for millimeter-wave circuit design. Switches typically have a capacitance ratio of 30 or higher, while switched capacitors and varactors have a capacitance ratio of about 1.2 to 10. The loaded Q factor is between 20 and 50 in the X-, Ku- and Ka-band.

RF MEMS switched capacitors are capacitive fixed-fixed beam switches with a low capacitance ratio. RF MEMS varactors are capacitive fixed-fixed beam switches which are biased below pull-in voltage. Other examples of RF MEMS switches are ohmic cantilever switches, and capacitive single pole N throw (SPNT) switches based on the axial gap wobble motor .

Microfabrication

An RF MEMS fabrication process allows for integration of SiCr or TaN thin film resistors (TFR), metal-air-metal (MAM) capacitors, metal-insulator-metal (MIM) capacitors, and RF MEMS components. An RF MEMS fabrication process can be realized on a variety of wafers: fused silica (quartz), borosilicate glass, LCP, sapphire, and passivated silicon and III-V compound semiconducting wafers. As shown in Fig. 2, RF MEMS components can be fabricated in class 100 clean rooms using 6 to 8 optical lithography steps with a 5 μm contact alignment error, whereas state-of-the-art monolithic microwave integrated circuit (MMIC) and radio frequency integrated circuit (RFIC) fabrication processes require 13 to 25 lithography steps. The essential microfabrication steps are

•Deposition of the bias lines (Fig. 2, step 3)
•Deposition of the electrode layer (Fig. 2, step 4)
•Deposition of the dielectric layer (Fig. 2, step 5)
•Deposition of the sacrificial spacer (Fig. 2, step 6)
•Deposition of seed layer and subsequent electroplating (Fig. 2, step 7)
•Beam definition, release and critical point drying (Fig. 2, step 8)

RF MEMS fabrication processes, unlike barium strontium titanate (BST) or lead zirconate titanate (PZT) ferroelectric and MMIC fabrication processes, do not require electron beam lithography, molecular beam epitaxy (MBE), or metal organic chemical vapor deposition (MOCVD). With the exception of the removal of the sacrificial spacer, the fabrication steps are compatible with a CMOS fabrication process.

Applications

Applications of RF MEMS resonators and switches include oscillators and routing networks. RF MEMS components are also applied in radar sensors (passive electronically scanned (sub)arrays and T/R modules) and software-defined radio (reconfigurable antennas, tunable band-pass filters).

Antennas

Polarization and radiation pattern reconfigurability, and frequency tunability, are usually achieved by incorporation of lumped components based on III-V semiconductor technology, such as single pole single throw (SPST) switches or varactor diodes. However, these components can be readily replaced by RF MEMS switches and varactors in order to take advantage of the low insertion loss and high Q factor offered by RF MEMS technology. In addition, RF MEMS components can be integrated monolithically on low-loss dielectric substrates, such as borosilicate glass, fused silica or LCP, whereas III-V semiconducting substrates are generally lossy and have a high dielectric constant. A low loss tangent and low dielectric constant are of importance for the efficiency and the bandwidth of the antenna.

The prior art includes an RF MEMS frequency tunable fractal antenna for the 0.1–6 GHz frequency range , and the actual integration of RF-MEMS on a self-similar Sierpinski gasket antenna to increase its number of resonant frequencies, extending its range to 5GHz, 14GHz and 30GHz , , an RF MEMS radiation pattern reconfigurable spiral antenna for 6 and 10 GHz , an RF MEMS radiation pattern reconfigurable spiral antenna for the 6–7 GHz frequency band based on packaged Radant MEMS SPST-RMSW100 switches , an RF MEMS multiband Sierpinski fractal antenna, again with integrated RF MEMS switches, functioning at different bands from 2.4 to 18 GHz , and a 2-bit Ka-band RF MEMS frequency tunable slot antenna .

Filters

RF bandpass filters are used to increase out-of-band rejection, if the antenna fails to provide sufficient selectivity. Out-of-band rejection eases the dynamic range requirement of low noise amplifier LNA and mixer in the light of interference. Off-chip RF bandpass filters based on lumped bulk acoustic wave (BAW), ceramic, surface acoustic wave (SAW), quartz crystal, and thin film bulk acoustic resonator (FBAR) resonators have superseded distributed RF bandpass filters based on transmission line resonators, printed on substrates with low loss tangent, or based on waveguide cavities. RF MEMS resonators offer the potential of on-chip integration of high-Q resonators and low-loss bandpass filters. The Q factor of RF MEMS resonators is in the order of 1000-1000 .

Tunable RF bandpass filters offer a significant size reduction over switched RF bandpass filter banks. They can be implemented using III-V semiconducting varactors, BST or PZT ferroelectric and RF MEMS switches, switched capacitors and varactors, and yttrium iron garnet (YIG) ferrites. RF MEMS technology offers the tunable filter designer a compelling trade-off between insertion loss, linearity, power consumption, power handling, size, and switching time .

Phase shifters

RF MEMS phase shifters have enabled wide-angle passive electronically scanned arrays, such as lenses, reflect arrays, subarrays and switched beamforming networks, with high effective isotropically radiated power (EIRP), also referred to as the power-aperture product, and high Gr/T. EIRP is the product of the transmit gain, Gt, and the transmit power, Pt. Gr/T is the quotient of the receive gain and the antenna noise temperature. A high EIRP and Gr/T are a prerequisite for long-range detection. The EIRP and Gr/T are a function of the number of antenna elements per subarray and of the maximum scanning angle. The number of antenna elements per subarray should be chosen to optimize the EIRP or the EIRP x Gr/T product.

Nombre: Lenny D. Ramirez C.

Asignatura: CRF
Direccion: http://reference.findtarget.com/search/RF%20MEMS/
Ver blogg: http://lennyramirez-crf.blogspot.com/

RF MEMS and Reconfigurable Systems

RF MEMS switches enable wireless device manufacturers to dramatically reduce system level power consumption. Under development are low-loss and extremely-linear switches for diversity antenna, transmit-receive, load-match, and frequency-band select.

MicroAssembly’s RF MEMS process incorporates RF switches, high-Q passives and other RF components via a proprietary interconnect technology enabling MEMS/CMOS integration. This process also leverages our proprietary wafer-scale hermetic packaging capability for low-cost. 

An advanced actuator design enables high contact forces to provide reliable operation.

 
 

MEMS Packaging

MicroAssembly has wafer-scale and die-scale MEMS packaging capability, with the flexibility to rapid-turn for prototyping and also meet volume requirements with low-cost. Why MicroAssembly's micropackage is different:
Low temperature processing -- compatible with a wide variety of MEMS devices -- from room temperature to 300 C
Wafer scale: large volumes at low cost
Die scale: quick turnaround prototyping
Very thin, non-contaminating, metal-to-metal seals – no organics
Near 100% yield -- reliability data with demonstrated hermeticity and very strong bond strength
Harsh environments including cryogenic temperatures and high-g shock

Nombre: Lenny D. Ramirez C.

Asignatura: CRF
Direccion:http://www.microassembly.com/rfmems.html
Ver blogg: http://lennyramirez-crf.blogspot.com/

MEMS Packaging

MEMS Packaging, In the past decades, many advances have been made in the fabrication of miniaturized mechanical structures called MEMS. Yet the application of this technology is hampered by the lack of production-worthy, MEMS-compatible packages. MEMS packages must not only protect the often-fragile mechanical structures and provide the interface to the next level in the packaging hierarchy, but they must also be fabricated in a cost effective manner to allow for affordable mass-produced circuits. Since several thousand RF switches are simultaneously fabricated on a single substrate, a cost effective packaging process should perform most of the packaging steps at a wafer level, before separation into discrete circuits.

There are several wafer-level packaging (WLP) techniques widely used with silicon micromachining; these include fusion bonding, anodic bonding, eutectic bonding, thermal compression bonding, and glass-frit bonding. While some of these packaging techniques have been demonstrated with non-RF MEMS circuits, their use for RF MEMS is limited. An ideal bonding technique should yield a hermetic seal that has a dielectric constant equal to the substrate, can be processed at low temperatures, and can tolerate a large degree of non-planarity/roughness.

One drawback of most wafer-level packaging techniques is the requirement for a seal ring. The inclusion of a seal ring and the appropriate bonding pads outside the ring significantly increases the area of an RF MEMS circuit. In such a circuit, there are four areas that need to be considered: 1) the RF MEMS circuit, 2) the seal ring, 3) the interconnect area, and 4) the saw kerf. The regions required for the seal ring, interconnect area, and the saw kerf increase the final size of the RF circuit, thereby reducing the available number of circuits per wafer. The glass-frit WLP technique typically requires a seal ring and interconnects area of 0.3-0.7 mm per side. The difference in realized circuits per wafer is substantial. For example, assuming a 1 x 2 mm RF MEMS phase shifter and a 150 mm wafer (with a 5 mm exclusion zone and 150 µm saw kerf), there are 2152 potential phase shifter die per wafer for glass-frit WLP. The same circuit without a 0.5 mm seal ring/interconnect area all around the die yields 6000 potential circuits per wafer. This produces 2.8x more phase shifters for the same wafer area! Eliminating the seal ring area greatly increases the number of available circuits per wafer, which significantly reduces the cost per circuit.

Advantages – An innovative approach to packaging currently being developed at MEMtronics is called wafer-level microencapsulation (WLµE). Microencapsulation is designed to be completely compatible with RF MEMS switch fabrication This wafer-level packaging scheme eliminates the seal ring to give the potential payoff of much smaller, lower cost circuits. Instead of bonding a separate glass wafer to the RF MEMS wafer, individual micropackages are constructed on top of each RF switch using the same MEMS processes used to construct the switch. This microencapsulation process yields a protective, low-loss, package with RF friendly interconnects. These packaging processes require only moderate process temperatures (200oC – 250oC) and tolerate both non-planarity and roughness. Utilizing standard semiconductor and MEMS fabrication processes for microencapsulation creates a cost-efficient and effective packaging alternative. MEMtronics’ innovative micro-encapsulation process accounts for only 28% of total packaged switch cost compared to many conventional strategies that account for 70-80% of total cost.

Some of the advantages of this unique microencapsulation technique are:

No seal ring

Extremely small volume cavity

No requirement for a package lid
No double-wafer alignment required

Requires only standard MEMS processing

Substantial increase in the number of circuits per wafer

Extremely low insertion loss

No added parasitics
Packaged circuits are thinner/lighter than any other packaging technique

Microencapsulation Construction – After the switches are constructed, the process steps to produce a wafer-level micro-encapsulation of RF MEMS switches are as follows:

Use a sacrificial layer to form a temporary encapsulation above and around the unreleased membrane.

Deposit an insulator to form a structural shell.

Pattern and etch the insulator to form a cage-like structure on top of the sacrificial layer.

Plasma ash the photoresist to create a microcavity structure and also release the membrane. Once the sacrificial layer is removed, there is in place a cage-like structure, separated by a gap, over the released membrane.

Apply a liquid encapsulant, such as benzocylcobutene (BCB), to the entire wafer. The surface tension of the encapsulant ensures the cage structure is covered without wicking through the holes to encroach onto the switch.

Cure the encapsulant to create a closed seal over the microcavity. This step can go up to 250°C since all sacrificial layers have been removed.

Apply optional sealant overcoats (such as parylene) for additional protection.

Results – MEMtronics has developed the new technique called wafer-level micro-encapsulation to effectively package RF MEMS switches. This technology was designed to be completely compatible with high-performance RF MEMS capacitive switch fabrication. The packages exhibit extremely low package-added insertion loss of 0.04 dB at 35 GHz, and < .10 dB for frequencies up to 110 GHz. Substantial lifetime characterization of these packages is an on-going activity, but initial results are promising. Preliminary accelerated lifetime data show using BCB spin-on encapsulation indicates an RF MEMS lifetime of ~55 years at room conditions. Additional sealant layers have shown very good promise by increasing the lifetime by an order of magnitude (>600 years). The compatibility of the package with MEMS switch processing, the extremely low loss and RF parasitics, and the potential for near-hermetic encapsulation makes this technology a promising solution for packaging and protecting RF MEMS switches. MEMtronics’ innovative approach to packaging ensures protection for RF MEMS devices under harsh conditions, while providing a reliable, cost effective product.

Nombre: Lenny D. Ramirez C.
Asignatura: CRF
Direccion: http://www.memtronics.com/page.aspx?page_id=36
Ver blogg: http://lennyramirez-crf.blogspot.com/