MEMS Filters Research Articles

A novel narrowband MEMS filter with extensional mode resonators

This work proposes a novel electrostatic mechanically coupled narrowband filter based on width extensional mode (WEM) resonators. Rectangle plate WEM resonators have the potential for high quality factor (Q) and low motional resistance. The rectangle plate was slotted to reduce thermoelastic loss and optimize mode shape coefficient of WEMs. The Q values of coupled WEM resonators exceed 80,000, enabling a narrow bandwidth filter. A 3λ/4-length coupling beam filter (CBF) was demonstrated. The 3λ/4 coupling beam filter has a center frequency of 79.79 MHz and a bandwidth of 0.024 %. The CBF exhibits an impressive 26.39 dB stopband rejection and 6.97 dB insertion loss with 5.13 dB passband ripple. The MEMS filters presented in this work hold significant potential for applications in wireless communication systems.

Modeling of surface roughness in deeply etched photonic MEMS mirrors and filters

We study the impact of the surface roughness on the response of deeply etched silicon Bragg mirrors and resonators. The transfer matrix method is extended to account for the roughness in multilayered systems. The model is first verified numerically using the finite difference time domain (FDTD) method for surface roughness values up to 80 nm at a wavelength of 1550 nm. The response of the mirrors and filters having an RMS roughness of 30 nm is calculated by the developed model and compared with the numerical results of the FDTD results, and it shows a good agreement. Then the model results are compared with the experimental data of a Bragg mirror and filter, fabricated by the deep reactive ion etching Bosch process of silicon on an insulator wafer; they show a very good agreement in the insertion loss and 3-dB bandwidth due to the roughness model. Finally, the transmission, 3-dB bandwidth and quality factor of the optical filters based on single, double, and triple silicon layer mirrors are examined using the model and accounting for Gaussian beam excitation. The presented model can be used to guide the requirements on the fabrication quality of optical surfaces and the choice of the optimum number of layers.

RF MEMS filter based on dual liquid variations

This paper discusses the behavior of RF MEMS tunable microwave filter. We have modeled the distribution of magnetic field and electric current density in order to reveal the comportment of each device and to evaluate the relation between the frequency response and the microwave performances. From several modelling and simulations, we catch the resonance phenomenon for magnetic and electric fields at different conditions. Hence, in order to develop a reconfigurable MEMS ensuring a function of tunable band-pass filters, we have identified conditions allowing to vary the resonance frequency from Fres = 0.42 GHz to Fres = 1.85 GHz ensuring a large total variation of Tr = 340.5%. The structure is fabricated using SU-8 resin for circulating microchannels and sealing layers. The extracted parameters from measurements results and retro-simulation reveal a diminution of the total tuning range.

Self-similar reconfigurable low-pass MEMS filters using coplanar waveguide based on silicon

This paper presents a low-pass filter based on microelectromechanical system using periodic self-similar coplanar waveguide. The device is fabricated on 525-μm high-resistivity silicon substrate using surface micromachining process which partial compatible process with IC. The tunable resonant frequency is achieved using micro-electromechanical contact capacitive switches. The total area of the filter is about 6 mm2 including bias lines and pads. The parameters of the filter has been analyzed byapplying the Ansoft-HFSS. When switch is on original state, the measured results of the filter show that the 3-dB cutoff frequency is 16.15 GHz with the average insertion loss of 0.95 dB. The 3 dB cut-off frequency of the reconfigurable filters is 22.85 GHz with the average insertion loss of 2.33 dB. A relativelylowerdriven voltage is around 26 V.

Towards a high bias voltage MEMS filter using electrostatic levitation

Traditional MEMS filters use a comb drive structure that suffers from the pull-in instability, which places a significant limitation on the achievable signal-to-noise ratio of the sensor. Because the output signal from a capacitive sensor is linearly related to the applied voltage, it is desirable to use a capacitive sensor that can withstand large voltages upwards of 100 V. However, the pull-in instability causes high voltages to destroy the device and a trade-off between performance and reliability must be made. Electrostatic levitation, which works by pulling electrodes apart instead of together, eliminates the pull-in instability and allows for very high voltages to be applied without damaging or destroying the sensor/actuator. This study theoretically and experimentally demonstrates that a filter based on electrostatic levitation eliminates the voltage limitation of the capacitive sensor, which has historically hampered the performance of the filter. A model of the filter is derived and validated with experimental data. Voltages up to 100 V are applied without damaging the filter.

Application of plasma cleaning process in MEMS filter micro-assembly

To solve the problems of low efficiency and high void rate in the process of the MEMS filter (die) attach and increase the strength of wire bonding between the die and microwave circuit board, plasma cleaning process was introduced in the micro-assembly process of the MEMS filter switch module. The spreading area of the solder melted on the copper was analyzed before and after the plasma cleaning process. Process parameters including plasma flow, radio frequency time and radio frequency power were optimized by the orthogonal test. It is demonstrated that the plasma cleaning process is effective to decrease the void rates in die attach and enhance the wire bonding strength, thus improve the reliability of the MEMS filter module micro-assembly.

A Highly Reconfigurable Bit-Level Duty-Cycled TRF Receiver Achieving −106-dBm Sensitivity and 33-nW Average Power Consumption

This letter presents a reconfigurable wake-up receiver, which obtains −106-dBm sensitivity with power consumption as low as 33 nW. Bit-level duty cycling provides 68-dB RF gain at sub- $\mu \text{W}$ average power consumption, improving sensitivity over other sub- $\mu \text{W}$ receivers. The receiver rejects interference using a compact RF MEMS filter and a fully automatic gain and offset control loop. Digital tuning of dc power, latency, and sensitivity provides high levels of flexibility to enable a wide variety of applications, spanning latency from 240 ms to 5 s, dc power consumption from 288 nW to 33 nW, and sensitivity from −106 dBm to −103 dBm. Three example modes are presented to highlight the range of this tuning.

Spectroscopic Gas Sensing Based on a MEMS-SOA Swept Fiber Laser Source

In this work, we report on real-time gas sensing using a swept fiber laser source (SFLS) based on a micro-electro-mechanical-system (MEMS) tunable filter, a semiconductor optical amplifier (SOA) gain medium and a fiber ring. The MEMS filter is implemented using deeply-etched silicon-on-insulator (SOI) silicon/air Bragg mirrors attached to a micro-actuator enabling a relatively high-speed tunability and compatibility with single-mode fibers. A theoretical analysis is presented relating the required laser output power and spectral linewidth to the gas detection limits taking into account the signal-to-noise ratio (SNR). The minimum detectable concentrations of nitrous oxide, carbon dioxide, carbon monoxide and acetylene gases were determined. The dependence of the gas spectrum in terms of its absorption line strength, spectral width and spacing on the laser source was emphasized in the analysis, revealing the limits of distinguishing between different gases. The fiber-laser source is then characterized under static and dynamic conditions. An experimental parametric study was carried out varying the fiber cavity length from 20 m to 2 km, the sweep rate up to 2 kHz and the pumping current up to 6 times the threshold current. Finally, the SFLS is exploited to measure the transmission spectrum of carbon dioxide gas – as an example – at various pressures. The effects of the pumping current, the sweeping speed, and the sweeping direction on the measured spectrum were studied in order to determine the optimal conditions. The measured spectrum is compared with the theoretical one taking into consideration the FWHM of the laser source. The comparison shows a good match.

Merging parallel-plate and levitation actuators to enable linearity and tunability in electrostatic MEMS

In this study, a linear electrostatic MEMS actuator is introduced. The system consists of a MEMS cantilever beam with combined parallel-plate and electrostatic levitation forces. By using these two forcing methods simultaneously, the static response and natural frequency can be made to vary linearly with the voltage. The static response shows a linear increase of 90 nm/V and is maintained for more than 12μm of the tip displacement. The natural frequency shows a linear increase of 16 Hz/V and is maintained throughout a 2.9 kHz shift in the natural frequency. This wide range of linear displacement and frequency tunability is extremely useful for MEMS sensors and actuators, which suffer from the inherent nonlinearity of electrostatic forces. A theoretical model of the system is derived and validated with experimental data. Static response, natural frequency, and frequency response calculations are performed. Merging these two mechanisms enables high oscillation branches for a wide range of frequencies with potential applications in MEMS filters, oscillators, and sensors.

Magnet-Less Circulator Using AlN MEMS Filters and CMOS RF Switches

A circulator with three ports allows unidirectional (or non-reciprocal) power transmission and facilitates the development of in-band full duplexers for simultaneous transmit and receive radio frequency (RF) applications. The use of ferromagnetic materials is the dominant approach for the implementation of circulators despite they are bulky and non-integrable with semiconductor electronics. Here, we present a novel magnetic-free electrical circulator using CMOS-integrable filters based on AlN MEMS resonators and CMOS RF switches. This paper describes a compact approach for a circulator that could be used in handheld devices. To break reciprocity, the AlN MEMS filter network is parametrically modulated via a switching matrix. The modulation frequency and duty cycle of the switching matrix were optimized experimentally so that the circulator can provide up to 15dB of isolation over the entire filter bandwidth. This prototype is a very compact solution for the implementation of magnetic-free circulators, which also intrinsically offer sharp pass-band filtering, thus eliminating the need for additional filters. The discussion highlights how possible paths to reduce the circulator insertion loss would make this approach more appealing for a broad range of applications.

Nonlinear spectrum broadening and its impact on performance of Rayleigh-scattering-based distributed strain/temperature fiber optic sensors

A Rayleigh-scattering-based distributed strain/temperature fiber optic sensor using low-coherence light is experimentally investigated at probe pulse powers well above the nonlinear effect threshold. OTDR technology is used for special channel interrogation. It is established that for an SMF-28e+ fiber this threshold is about 100 mW. Exceeding this power leads to the degradation of sensor performance and is explained by nonlinear spectrum broadening. The evolution of the probe pulse spectrum is investigated using a tunable MEMS filter. A novel version of the arrangement for the sensor is proposed, which partially overcomes the limitations associated with said effect. As low as 2.2 µε, the RMS noise level for strain is demonstrated at a distance of 25 km. The spatial resolution is estimated as 1.5 m, the data collection time is 20 min, and the average power in the fiber is about 0.2 mW, which allows the sensor to be used for infrastructure monitoring under explosive conditions.

Design and Characterization Methodology for Efficient Wide Range Tunable MEMS Filters

Design and Characterization Methodology for Efficient Wide Range Tunable MEMS Filters

What is driving the 3D TSV technologies business: Market update and technical trends

Through-silicon vias (TSVs) have now become the preferred interconnect choice for high-end memory. They are also an enabling technology for heterogeneous integration of logic circuits with CIS, MEMS, sensors, and RF filters. In the near future they will also enable photonics and LED function integration. The market for 3D TSV and 2.5D interconnect is expected to reach around 2.1 million wafers in 2021, expanding at an 18% CAGR. The growth is driven by increased adoption of 3D memory devices in high-end graphics, high-performance computing, networking and data centers, and penetration into new areas, including fingerprint and ambient light sensors, RF filters and LEDs. CIS still commanded more than 80% share of TSV market wafer volume in 2015, although this will decrease to around 56% by 2021. This is primarily due to the growth of the other TSV applications, led by 3D memories, RF filters and fingerprint sensors. However, hybrid stacked technology, which uses direct copper-copper bonding, not TSVs, will penetrate around 38% of CIS production by 2021. The presentation will explain the market's dynamics and give an overview of all segments and key markets of the TSV based 3D/2.5D IC packaging.

The implementation of low-power and wide tuning range MEMS filters for communication applications

Theory and optimization were studied in detail to find optimum dimensions of fixed-fixed beam for the sake of low-power and wide-range frequency tuning applications. This optimization also provides a method to avoid device failure due to high thermal stress. The good agreement between theory, simulation, and measurement is achieved and can serve as a guidance for future works. Two resonators, consisting of multiple metal, dielectric, and polysilicon layers, were designed; the first resonator at 303.4 kHz and the second at 2053 kHz achieve the frequency tuning ranges of 35.7%–42.6%, respectively. A power consumption of 900 μW/beam is achieved for the first design of 152 µm length beam while providing a frequency tuning of 35.7%. Further increase in the tuning capability was achieved by the increase in the applied DC bias voltage between adjacent beams.

Tunable low-pass Ka-band MEMS filter based on Electromagnetic-Bandgap Structure

A low-pass Ka-band MEMS tunable filter based on the high-resistivity silicon substrate with Electromagnetic-Bandgap Structure (EBG) is presented. The tunable filter consists of multiple MEMS switches fabricated by a CMOS-compatible surface micromachining process. The equivalent circuit model of the tunable EBG bandstop filter was derived based on the circuit analysis theory. The dispersion characteristics obtained are useful for describing and understanding the propagation characteristics of the EBG and the MEMS bridges. The performance of the single MEMS bridges is discussed. The measurement results of the tunable MEMS filter showsa 3-dB cutoff frequency tunable from 34.25GHz to 26.60GHz, while the average insertion loss varies from 0.25dB to 0.22dB. The whole chip size is 3.6mm×1.6mm. This work demonstrates a high-performance miniaturized tunable low-pass filters at mm-waves frequency bands using Electromagnetic-Bandgap Structure.

RF MEMS and CSRRs-based tunable filter designed for Ku and K bands application

AbstractThis paper presents the design and simulation of a reconfigurable stop-band filter on a silicon substrate based on the combination of RF microelectromechanical system and metamaterial-based technologies. The device is implemented on coplanar waveguide structure by embedding complementary split-ring resonators on the central line and an RF MEMS varactor bridge supporting the neighboring ground planes. The response characteristics of this metamaterial-based filter can be dynamically tuned, thus enhancing its usefulness. The device operates within a frequency range of 16.5–19.5 GHz, giving a tuning range of 15%, and can be tuned from Ku-frequency band to K-frequency band. It works with a comparative low pull-in voltage of 17.42 V and a faster switching time of 0.138 µs. A thorough electromechanical analysis has been done by varying various structural and material parameters. Moreover, a comparative electrical performance of silicon and glass has been shown to overcome the cons of silicon by high-resi...

Erratum to: MEMS filter’s design and modeling based on width-extensional mode plate resonator for wireless applications

Erratum to: MEMS filter’s design and modeling based on width-extensional mode plate resonator for wireless applications

MEMS filter’s design and modeling based on width-extensional mode plate resonator for wireless applications

This paper proposes a new filter's design process and modeling that can be employed in RF wireless communication systems. The filter is constructed by two similar rectangular piezoelectric plates vibrating in the width-extensional mode. Each plate is formed by a piezoelectric film and is sandwiched between two metallic electrodes. The vibrating plates are mechanically coupled by a beam linkage. The resonance frequencies of the vibrating structure are defined by the plate's lateral dimension which allows the integration of the multi-frequency filter banks on the same chip. The coupled resonators exhibit two mechanical resonance modes: in-phase and out-of-phase vibrating modes. These modes define the filter bandwidth. In the first part of this paper, we proposed a theoretical model allowing to define the desired filter bandwidth varying the coupling beams location. In the second part, we used the microwave circuit theory to calculate the generalized ABCD matrix and consequently the filter transmitted coefficient (S21). The filter bandwidth values extracted from the transmitted coefficient (S21) show a consistent agreement with the desired filter bandwidths determined by the theoretical model developed in the first part. As application, a filter with a center frequency of 217 MHz is able to operate with fractional bandwidth varying from very low value (close to 0 %) to 5.5 %. This modeling approach is very important for filter bandwidth control.

Design of MEMS-based micro-filter integrating grating and tunable Fabry-Perot cavity

This paper presents basic designs and operation concepts of a novel micro-electro-mechanical-systems (MEMS) filter integrating a tunable Fabry-Perot (FP) cavity and a grating. It is based on the filtering effect of the tunable FP cavity and the spatial separation function of the grating for the different wavelengths. The combination of two devices could widen the spectral range of the traditional FP filter without affecting its spectral linewidth. A MEMS filter configuration based on the silicon-glass bonded structure has been designed. The FP cavity length depends on the thickness of the silicon wafer itself to realise the long cavity length. The T-S cantilevers could decrease the micromirror deformation, and reduce the driving voltage appropriately. Calculational results indicate that narrow linewidth and wide spectral range could be obtained simultaneously at the long cavity length.

Porous Silicon MEMS Infrared Filters for Micromechanical Photothermal Spectroscopy

Introduction Spectroscopy of gases is of great importance for the defense and security industries [1]. Optical spectroscopy has the following advantages over other methods: high resolution, high sensitivity, and ability to detect gas mixtures [2]. We propose a system for high-resolution photothermal spectroscopy of gases based on a MEMS spectrometer and a MEMS tunable filter, as shown in Fig. 1. This presentation details the progress on development of the two main components of the system. Photothermal Spectrometer We have developed and demonstrated a MEMS-based photothermal spectroscopy system based on optical probing of mechanical bridge deformation [3]. Briefly, when the wavelength of a tunable infrared source corresponds to a rotational or vibrational resonance of an analyte molecule in the sorbent material, the radiation is absorbed, which induces heating and bending of the microstructure. High sensitivity sorbent materials and interferometric readout techniques result in ppb detection levels throughout the 2.5 μm to 14 μm wavelength range. MEMS Tunable Filter In the demonstration of photothermal spectrometer, the source of illumination was a widely-tunable MIRAN source. Integration into a portable system would require a miniaturized source of light in the 3-12 μm range. Many wide-band sources are available, such as a glow bar or a wide-spectrum LED. We report progress towards realization of a MEMS filter based on porous silicon components that provides narrow-band tunability for such sources. The ability to create complicated optical structures with thin films of almost arbitrary index of refraction [4], combined with low dispersion across the entire 3-12 μm wavelength range, makes porous silicon an attractive material for realization of optical filters in the mid-wave and long-wave infrared. A proof-of-principle Fabry-Perot etalon with 95 nm FWHM passband at 8 μm is shown in Figure 3. Porosity and index of refraction gradients in multiple layer optical systems based on porous silicon are discussed, with relevance to optical component design. Three main components of the tunable filter are realized with porous silicon: highly reflective distributed Bragg reflectors, anti-reflective layers, and thermal bimorphs. Progress in fabrication of the tunable filter and its integration with a source and a photothermal spectrometer into a complete system for gas sensing is reported.