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This paper presents a single antenna platform steered by an external magnetic field where a monolithic microwave integrated circuit (MMIC) and capacitors are vertically integrated. Unique process skills are successfully optimized to implement a newly proposed microelectromechanical systems antenna. A silicon grid is patterned on the processing wafer to prevent the destruction of the antenna by benzocyclobutene delamination due to the stress applied to the wafers. Moreover, the stress barrier patterns are designed to increase the fabrication yield by protecting the structure failure during the back-side silicon release step. All the electrical elements, such as the MMIC, capacitors, patch antenna, and signal lines, are integrated on a single silicon chip; thus, the fabricated antenna system has smaller size and higher productivity than the conventional ones. The vertically integrated MMIC particularly results in a uniform gain at entire steering angles and reduced signal losses. The fabricated antenna is driven by a magnetic field externally applied with copper coils, and the antenna beam patterns are obtained with various tilting angles. The scanning angles are -14°, 0°, and +18° in the H-plane and -18°, -12°, 0°, +12°, and +16° in the E-plane, and the center frequency of the fabricated antenna is 59.8 GHz which is close to the designed resonance frequency of 60 GHz.

This article reports on a low temperature cofired ceramic (LTCC)-based RF MEMS packaging and its electrical modeling using lumped elements and microstrip lines. An LTCC cap with vertical vias was flip-chip bonded with a glass substrate, where a coplanar waveguide (CPW) formed to measure the RF characteristics of packaging structure. We measured return loss (S11) and insertion loss (S21) of the fabricated packaging structure in a frequency range of 1 to 30 GHz. The parameters of two different equivalent circuits using lumped elements and physical microstrip lines were extracted from the measured results. The mean absolute errors (MAEs) were calculated to show the agreement between measured properties and electrical equivalent circuits. The calculated MAEs were 0.591 dB (S11) and 0.146 dB (S21) for lumped elements, and 0.926 dB (S11) and 0.179 dB (S21) for microstrip lines, respectively. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 252–257, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24895

In this paper, we describe a self-aligned fabrication method for a nano-patterned bottom electrode using flood exposure from the backside. Misalignments between layers could cause the final devices to fail after the fabrication of the nano-scale bottom electrodes. A self-alignment was exploited to embed the bottom electrode inside the glass substrate. Aluminum patterns act as a dry etching mask to fabricate glass trenches as well as a self-aligned photomask during the flood exposure from the backside. The patterned photoresist (PR) has a negative sidewall slope using the flood exposure. The sidewall slopes of the glass trench and the patterned PR were 54.00° and 63.47°, respectively. The negative sidewall enables an embedment of a gold layer inside 0.7㎛ wide glass trenches. Gold residues on the trench edges were removed by the additional flood exposure with wet etching. The sidewall slopes of the patterned PR are related to the slopes of the glass trenches. Nano-scale bottom electrodes inside the glass trenches will be used in beam resonators operating at high resonant frequencies.

In this article, we proposed the novel monolithic microwave integrated circuit (MMIC) protection technique in plasma etching process for MMIC mounted mechanically movable RF MEMS antenna. We could eliminate the distortion of radiation pattern caused by RF feed line on antenna frame and torsional hinge as using MMIC direct mounting on antenna plate instead of using external RF power source. Silicon-based mechanically movable RF MEMS antenna was released using DRIE process, which was performed on the backside of silicon substrate after MMIC mounting on RF MEMS antenna plate. An aluminum layer on the front side of RF MEMS antenna plays a role of etch stop layer for DRIE process. We measured the radiation pattern as rotating the moving plate along the vertical- and horizontal-direction hinge mechanically. We could obtain the radiation pattern without gain reduction and distortion of radiation pattern. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3089–3093, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23870

In this paper, we proposed a planar type micromachined probe with low uncertainty and showed its feasibility in practical biomedical applications through the in vivo measurements of cancerous tissue xenografted on nude mice. We have succeeded in increasing the fringe capacitance at low frequencies by locating an aperture on the top side of probe. Furthermore, we showed experimental proof of low uncertainty at low frequencies through measurements of known liquid samples below 1 GHz. Measured results using the proposed probe showed superior agreement with the reference values of the Cole-Cole equation in comparison to measurements made using an open-ended coaxial probe. Muscle and tumor tissue samples of mice, as well as 0.9% saline as a liquid sample, were measured using the proposed probe from 1 GHz to 20 GHz, thus demonstrating the feasibility of this method as a practical biomedical application.

Surface plasmon resonance (SPR) based sensors are usually designed using the Kretschmann prism coupling configuration in which an input beam couples with a surface plasmon through a thin metal film. This is generally preferred by sensor developers for building planar devices instead of the Otto prism coupling configuration, which, for efficient coupling, requires the metal surface to be maintained at a distance on the order of the wavelength from the input prism surface. In this paper, we report on the microfabrication and characterization of an Otto chip device, which is suitable for applications of the SPR effect in gas sensing and biosensing.

This paper discusses key issues related to the design of large processing volume chip architectures and high speed system interconnects. Design methodologies and techniques are discussed, where recent trends and considerations are highlighted.

This paper presents a building block approach for the design of frequency identification receivers. The devices are based on a Reconfigurable Discriminator (RD) for frequency measurement, operating from 1 to 4 GHz. The RD is a two-port device used to identify the frequency of an unknown signal. The devices use RF switches, which are implemented with PIN diodes to select different bits used for frequency identification.

We report a strongly amplified photoacoustic (PA) performance of the new functional hybrid material composed of reduced graphene oxide and gold nanorods. Due to the excellent NIR light absorption properties of the reduced graphene oxide coated gold nanorods (r-GO-AuNRs) and highly efficient heat transfer process through the reduced graphene oxide layer, r-GO-AuNRs exhibit excellent photothermal stability and significantly higher photoacoustic amplitudes than those of bare-AuNRs, nonreduced graphene oxide coated AuNRs (GO-AuNRs), or silica-coated AuNR, as demonstrated in both in vitro and in vivo systems. The linear response of PA amplitude from reduced state controlled GO on AuNR indicates the critical role of GO for a strong photothermal effect of r-GO-AuNRs. Theoretical studies with finite-element-method lab-based simulation reveal that a 4 times higher magnitude of the enhanced electromagnetic field around r-GO-AuNRs can be generated compared with bare AuNRs or GO-AuNRs. Furthermore, the r-GO-AuNRs are expected to be a promising deep-tissue imaging probe because of extraordinarily high PA amplitudes in the 4-11 MHz operating frequency of an ultrasound transducer. Therefore, the r-GO-AuNRs can be a useful imaging probe for highly sensitive photoacoustic images and NIR sensitive therapeutics based on a strong photothermal effect.

This paper describes two types of novel compact low-loss millimeter-wave filters using an overlay coplanar waveguide (OCPW) line for lowpass filters and an inverted overlay coplanar waveguide (IOCPW) line for bandpass filters with periodic defected ground structures (DGSs). The OCPW and IOCPW lines are utilized to reduce the conductor and the substrate dielectric loss of the transmission lines. Also, these lines can provide a wide impedance range by controlling the overlapped area. The DGSs implemented on the transmission line have the role of size reduction and harmonic suppression of the filters. The combination of transmission lines having suspended structures and DGSs can provide great potential in terms of compact size, band rejection property and low-loss characteristics. The proposed filters are fabricated by using a micromachining technology and their RF performances are measured and analyzed. One of the proposed filters is a lowpass filter with a five-section stepped impedance topology having a periodic high?low impedance section. In this filter, the low impedance section is composed of the OCPW line with dumbbell-shaped DGSs and its length can be reduced by 52.7% compared to the OCPW line without DGSs. The measured insertion loss of this filter is lower than 0.2 dB up to 9 GHz, and significant spurious bands are not observed up to 40 GHz, resulting in a wide stop band. The other work that is presented here deals with a pi-shaped bandpass filter. This filter consists of three high impedance sections and two low impedance sections, and the line length of the high impedance section can be reduced by using the IOCPW line with spiral-shaped DGSs. The measured center frequency of the fabricated filter is 19 GHz, and the passband loss is 2.3 dB at the measured center frequency. The use of DGSs on the transmission line also enables us to suppress effectively the third-order harmonic component at 57 GHz.

This paper reports two types of compact dual-band bandpass filters for wireless local area network (WLAN) applications operating at two frequency bands of 2.4 and 5.2 GHz. The two types of filters (contact-type and capacitive-type) are focused on their digital mode operations in order to alternatively select the operational frequency band of the WLAN. Different types of micromachined frequency-tuning elements having only two states are implemented on each filter to control the center frequencies of the filters. Two digitally operated WLAN filters are fabricated using a surface micromachining technology, which enables us to make simple planar structures of the filters, resulting in easy integration with other planar circuits. Besides, external switching devices for frequency selection are not required, since they are already implemented on the filter's own structures. One of the proposed filters is a contact-type filter using switched inductors with direct-contact MEMS switches. In this filter, a precise and stable frequency-tuning ratio can be obtained because the center frequency is changed by total inductance change due to ON/OFF actuations of the switch. The measured center frequencies of the filter were 2.5 and 5.1 GHz (49% tuning ratio), and the passband insertion loss and return loss were 4.7 dB and 21.5 dB at 2.5 GHz, and 5.2 dB and 21 dB at 5.1 GHz, respectively. The other is a low-loss capacitive-type filter using micromachined variable capacitors. The frequency tunability of this filter is controlled by discrete change of a capacitance according to simultaneous actuations of a total of 12 variable capacitors. This filter shows lower loss compared to the contact-type filter, since loss due to contact resistance of the switch is not included in this filter configuration. The initial center frequency was measured to be 5.4 GHz and it was shifted to 2.6 GHz (48% tuning ratio) with the applied voltage. The total insertion loss and return loss were 2.8 dB and 24.4 dB at 5.4 GHz and 3.3 dB and 20.1 dB at 2.6 GHz, respectively.

In this paper, a packaging method utilizing an LTCC (low temperature co-fired ceramic) substrate and a BCB (benzocyclobutene) adhesive layer has been developed for RF MEMS devices, and the RF performance and characteristic parameters of the package have been evaluated. LTCC substrates have good RF characteristics in high-frequency applications, and via feedthroughs can be easily incorporated during the manufacturing process. In this paper, an LTCC substrate is used as a capping wafer to reduce the complex processes for vertical interconnections. A layer of BCB, in the form of sealing rims, is used as an adhesive to bond the MEMS substrate with the LTCC cap due to the excellent properties of BCB as a packaging material. A CPW (coplanar waveguide) line has been fabricated on a quartz substrate and packaged to demonstrate the performance of the proposed packaging method. After forming the CPW lines, a 28 µm thick BCB layer is patterned by double-coating photolithography for an adhesive bonding. On the backside of the LTCC cap, a 150 µm deep cavity is formed to improve the RF characteristics. The CPW and the contact pad are connected electrically through the silver via-post in the LTCC substrate by screen-printed silver epoxy. The RF characteristics of the CPW line have been measured before and after packaging. The insertion loss of a bare CPW is 0.047 dB at 2 GHz and 0.092 dB at 20 GHz. After packaging, the insertion loss of the packaged CPW is 0.091 dB at 2 GHz and 0.312 dB at 20 GHz. A leak test has been performed using both IPA (isopropyl alcohol) soaking and the He leak tester. Most of the samples show no leakage for the IPA test, and a measured leak rate of 10−8 atm cc s−1 for the He leak test. In addition, the shear strength of the package was measured to be 25–35 MPa. From the experimental results, we showed the feasibility of a low-loss RF MEMS package from dc to 20 GHz with acceptable package performances.

This paper describes a single-aperture MEMS probe and a MEMS probe array for the measurement of biological properties. We designed and fabricated the single-aperture MEMS probe using surface micromachining and verified it by measuring the permittivity of a standard liquid before introducing the MEMS probe array. The actual aperture size of the single-aperture MEMS probe is only 390 µm × 80 µm, which is very small in comparison with the conventional laser-machined coaxial probe. In order to show the feasibility of the proposed single-aperture MEMS probe for permittivity measurements, we performed in vitro measurements of 0.9% saline. Once the single-aperture probe was verified, we proposed the concept of a probe array for biological measurements and experimentally showed the suitability of the MEMS probe array for biological applications through experiments using pork. The MEMS probe array consists of five microstrip feed lines, each of which is followed by open-ended strip lines, and the permittivity measurement of each port is separately performed through the use of a conventional multiport coaxial switch (Agilent, HP 87106 C), followed by a network analyzer (HP 8510 C). Through broadband measurements of 0.9% saline and pork using the MEMS probe array, we were able to discriminate the muscle and fat of pork through just one contact by placing the MEMS probe array on the boundary of muscle and fat. This newly proposed MEMS probe array has great potential in terms of disposability, low cost, integration with planar circuits and a short detection time for biological measurements.

We developed a small-sized micromachined probe for the measurement of biological properties using microelectromechanical systems (MEMS) technology. We also experimentally showed the suitability of the micromachined probe for biological applications through in vivo, as well as in vitro measurements of various types of tissue. We measured the permittivities of 0.9% saline and the muscle and fat of pork using the micromachined probe after liquid calibration. The measured permittivities of 0.9% saline and pork agreed well with both the expected values of the Cole-Cole equation along with the measured values obtained through the use of a 1-mm-diameter open-ended coaxial probe. We also performed in vivo measurements of breast cancer tissue implanted in an athymic nude mouse to show the suitability of the small-sized micromachined probe for practical biological applications. Through the obtained data, the capability of the micromachined probe of distinguishing different tissue types from one another was shown. The actual aperture size of the micromachined probe is only 240 /spl mu/m /spl times/ 70 /spl mu/m and, therefore, we can extract the biological information from very small biological tissues and drastically decrease the invasiveness of this method through the implementation of the small probe created through the use of MEMS technology.

We developed a silicon MEMS probe for permittivity measurements using an adhesive bonding process. Only two photolithographic masks are required to fabricate the probe, which can be implemented through simple bonding processes using silicon substrates and a benzo cyclo butene (BCB) adhesive layer. Undoped silicon substrates with thicknesses of 300 ?m are used as the dielectric layers of the proposed probe. BCB layers, which have good electrical properties at high frequencies as well as adhesive properties for the bonding process, play the role of bonding materials between the two silicon substrates. The length of the probe is 30 mm, and the aperture located at the tip of the probe is 1.1 mm ? 0.62 mm. The permittivity of 0.5% saline was measured, and the results agreed with the values obtained through the Cole?Cole equation. To validate the feasibility of this probe for practical biological applications, we also performed in vivo measurements of the muscle, skin and blood of mice. Due to the simple fabrication process, the cost of the probe can be reduced in comparison with the previous micromachined probe (Kim et al 2005 J. Micromech. Microeng. 15 543?50) as well as the conventional laser machined probe. Low cost leads to disposability, which is an important factor for practical biomedical applications; and thus, coupled with the probe's capabilities of MMIC integration and CMOS compatibility, this probe has excellent potential in the field of microwave permittivity measurements.

This paper reports the first demonstration of a single crystalline silicon(SCS)-based vertical gap-tuning MEMS variable capacitor with high mechanical reliability using the SiOG (silicon-on-glass) process. The proposed variable capacitor was fabricated by silicon-based micromachining technology, and its mechanical and electrical performances were tested. By adopting SCS, which has nearly zero stresses and superior thermal characteristics as a structural material, we can improve the manufacturability, reproducibility and mechanical reliability of the fabricated devices compared with a conventional metallic variable capacitor. The variable capacitor described in this paper is fabricated on a coplanar waveguide (CPW) transmission line and the top electrode in the driving part is incorporated with a SCS actuating membrane, resulting in a highly rigid structure without structural deformations. The designed SCS variable capacitor is actuated by an electrostatic force, and the total chip size is 1.05 mm × 0.72 mm. The measured pull-in voltage was 37 V, and the RF characteristics of the fabricated SCS variable capacitor from dc to 40 GHz were measured. With and without an applied dc bias voltage, the measured S11 and S21 were changed from −15.6 to −5.1 dB, and from −0.49 to −2.3 dB at 30 GHz, respectively. The measured capacitance at the up and the down states was 30 and 140 fF, respectively, which corresponds to the capacitance ratio of 4.67. The mechanical lifetime of the fabricated variable capacitor was also measured. RF performance degradation and stiction problems were not observed, even after 108 cycles of repeated actuations.

In this paper, fully monolithic reconfigurable millimeter-wave filters are proposed using the CPW-based periodic structures with novel multiple-contact MEMS switches. Millimeter-wave low-pass and band-pass filters were designed, fabricated, and tested. Three cascaded CPW-based periodic structures, with low-pass and band-pass intrinsic filtering characteristics, are reconfigured into a self-similar single unit cell by the operation of the novel multiple-contact MEMS switches with single actuation. By using the multiple-contact MEMS switches, the insertion loss can be reduced and the operating frequency ranges are extended to millimeter-waves with little increase of loss. Additionally, the number of the switching elements has been reduced and the bias-decoupling circuits are not required, resulting in a very small chip size. The measured results of the reconfigurable low-pass filter show the 3-dB cutoff frequency change from 67 to 28 GHz with very small change in the insertion loss from 0.32 to 0.27 dB. The center frequency of the reconfigurable band-pass filter is tuned from 55 to 20 GHz, and the measured 3-dB cutoff bandwidth changed from 32 to 12 GHz, while the average insertion loss changed from 1.27 to 1.61 dB. The chip size of the low-pass and band-pass filter including dc bias line is 1.2 mm /spl times/ 1.5 mm and 1.2 mm /spl times/ 4.5 mm, respectively.

We implemented a micromachined probe for the measurement of biological properties using MEMS technology, and experimentally showed the suitability of the micromachined probe in biological applications. The micromachined probe was fabricated on a silicon substrate, and to remove wave transmission through the silicon substrate, we etched the silicon substrate from beneath a lower ground and made the etched silicon surface conducting by using thermal evaporation of Cr/Au and a coating of conductive epoxy. The micromachined probe consists of a CPW and strip line between benzo cyclo butene (BCB) layers, which is known to be a material with high resistivity, low loss tangent, and low permittivity at high frequency. We measured the permittivity of a number of well-known liquids—0.5%, 0.9% and 1.3% saline, acetone, ethanol, and muscle and fat of pork—as biological samples using the micromachined probe after liquid calibration. The measured permittivity of 0.9% saline agreed well with the expected value of the Cole–Cole equation. In this paper, we first demonstrate that the micromachined probe can provide broadband measurement of measurable solid materials, such as biological samples, and also of well-known liquids at microwave frequencies. The size of the micromachined probe is 2000 µm (width) × 580 µm (thickness) × 30 000 µm (length), and the aperture size of the micromachined probe is only 650 µm × 70 µm. Therefore, we can extract the biological information from very small biological tissues and reduce radiation effects. Thus we show the feasibility of low-cost, small and portable permittivity measurement systems using a micromachined open-ended coaxial RF MEMS probe.

Broad-band analog and digital reflection-type phase shifters (RTPSs), showing constant phase shift over 1:3 bandwidth, have been developed using microelectromechanical systems (MEMS) technology. Two-unit RTPSs centered at two different frequencies have been cascaded to achieve flat phase responses over a wide frequency band. Each phase shifter uses air-gap overlay coplanar-waveguide couplers for low-loss 3-dB coupling and bridge-type MEMS capacitors for reflective terminations. The fabricated analog phase shifter shows the average insertion loss of 3.5 dB, and maximum phase error of /spl plusmn/4.9/spl deg/ from 15 to 45 GHz. The 2-bit digital RTPS shows reduced maximum phase error of /spl plusmn/2.8/spl deg/ together with a comparable insertion loss of 3.1 dB from 5 to 15 GHz. The details of the circuit design, analysis, and fabrication procedures are presented together with the measurement results. Compared with the similar constant phase shifters using semiconductor diodes and transistors, the micromachined RTPS of this study shows superior performance in terms of phase errors, insertion losses, and bandwidth.

An SU8-quartz composite photoresist has been fabricated and characterized from 1.2 to 1.4 THz; the material contains quartz particles from 0 to 50 wt%. The composite can reduce the inherent losses of SU8 photoresist at terahertz frequencies. Calculated and measured data is presented and compared with SU8 without quartz inclusions. The results show a reduction in losses and an increase in permittivity in the composite material as the density of quartz particles increases. This initial experiment proves the possibility of modifying the electrical parameters of SU8; increasing the quartz density of the composite will modify these parameters further at THz frequencies. (c) 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2329-2330, 2016

This paper presents a new type of antenna fabricated by micromachining technology for mechanical beam steering with two degrees of freedom of motion. A V-band two-dimensional mechanical beam-steering antenna was designed and fabricated on a single high-resistivity silicon substrate using microelectromechanical systems technologies. A fabricated antenna is driven by magnetic force to overcome the limit of electrostatic actuation, and a polymer-based hinge structure is used to increase the maximum scanning angle to as much as 40/spl deg/. Simulation result for validating the mechanical beam-steering concept is presented. In addition, mechanical properties such as static actuation angles are investigated together with microwave properties such as the return loss and radiation pattern at the V-band.

Low-loss digital distributed phase shifters have been developed using micromachined capacitive shunt switches for V-band applications. Instead or conventional metal-insulator-metal capacitors, high-Q metal-air-metal capacitors were used in series with the microelectromechanical system (MEMS) shunt capacitive switches to minimize the dielectric loss. The operation voltage for the phase shifters was also reduced by applying the bias directly to the MEMS shunt switches through choke spiral inductors. Fabricated 2-b (270/spl deg/) and 4-b (337.5/spl deg/) distributed phase shifters showed low average insertion losses of 2.2 dB at 60 GHz and 2.8 dB at 65 GHz, respectively. The average phase errors for 2-b and 4-b phase shifters were 6.5% and 1.3%, respectively. The return losses are better than 10 dB over a wide frequency range from 40 to 70 GHz. Most of the circuits operated at 15-35-V bias voltages. These phase shifters present promising solution to low-loss integrated phase shifting devices at the V-band and above.

We have experimented with using continuous self-assembled monolayer (SAM) coatings on different surfaces, such as gold and silicon nitride, as anti-stiction coatings for radio-frequency microelectromechanical systems (RF MEMS). SAMs are coated on gold and silicon nitride surfaces in order to fabricate stiction-free gold structures after the wet release process. SAM coatings on gold and silicon nitride surfaces change the contact angle of a water droplet from 70.6° to 112.6° and from 36.7° to 115.8°, respectively. From atomic force microscopy, we can see that there is little change in the roughness of the gold and silicon nitride before and after the SAM coating. Using the electroplating technique and the wet release process, we have fabricated 4 μm thick gold cantilevers and bridges on a gold surface with a 6.5 μm gap from the substrate. Cantilevers and bridges are fabricated with different lengths in the range of 100–1000 μm with separations of 100 μm. It is observed that cantilevers and bridges with a length of 1000 μm on a gold substrate are released and standing free. A 1000 μm long gold cantilever has only 16.5 μm tip end deflection after the wet release process and SAM coating, much smaller compared with the 120 μm tip end deflection with the dry release process. Gold cantilevers, 100–500 μm long, on silicon nitride are released free and gold bridges on silicon nitride are released with a length of 1000 μm with continuous SAMs. The SAMs are coated on gold and silicon nitride surface in order. This method enables the gold cantilever and bridge on the gold or silicon nitride surface to be released with low deflection.

This paper presents a novel 4-bit reconfigurable discriminator for frequency measurement, operating from 1 to 4 GHz. The discriminator is a two-port device used to identify the frequency of an unknown signal by switching between its 4 states. The device is formed by a fixed reference line and a switchable delay line. The device is implemented using microstrip lines and PIN diodes. Simulated and measured results are presented for the four states of the reconfigurable discriminator.

In this paper, a new type of reconfigurable inductor is proposed for mm-waves based on the reconfiguration of slow-wave coplanar waveguide (CPW) lines using multiple-contact switches. It is then employed together with micro-electro-mechanical systems (MEMS) capacitive shunt switches to realize a reconfigurable low-pass filter, where the values of both inductors and capacitors are changed independently to achieve optimum filter characteristics. The measured 3-dB cut-off frequency of the reconfigurable low-pass filter changes from 53 GHz to 20 GHz while maintaining Tchebycheff low-pass prototype characteristics. The out-of-band rejection characteristics are also improved in this way. To our knowledge, this is among the first demonstrations that both types of MEMS contact switches and capacitive switches are used simultaneously to construct a monolithic tunable filter with independent L/C controlling capability.

A high-performance reconfigurable low-pass filter based on the quasifractal self-similar structures has been developed at millimeter-waves using multiple-contact MEMS switches. Three-cell cascaded low-pass structure was reconfigured to one-cell low-pass counterpart by activating the micromachined switches to achieve 3:1 frequency scaling. Two types of special multiple-contact MEMS switches were developed to reduce the number of switching elements as well as to reduce the insertion loss and, thus, extend the operating frequencies to mm-waves. In addition, bias-decoupling circuits were eliminated, resulting in a small chip size of 1.2 mm /spl times/ 1.5 mm. The measured 3-dB cut-off frequency of the reconfigurable low-pass filter changed from 67 GHz to 28 GHz with minor change in the insertion loss from 0.32 dB to 0.27 dB. This work demonstrates the possibility of high-performance compact-size reconfigurable filters at mm-waves using multiple-contact micromachined switches.

This work presents a novel fabrication method for {111} dual mirror and optical bench using double-sided anisotropic wet etching of oriented silicon wafer. The roughness of the wet etched {111} plane is 8 nm.

This paper suggests a complete solution for thermal isolation which hinders a stable fabrication of silicon micro-structures with a large proof mass and long springs when the device is released using silicon deep etching process. Comprehensive analysis on a thermal equivalent circuit and the implementation of thin metal layers have successfully reduced a temperature rise down to 6.16 °C whereas conventional fabrication method shows 217 °C temperature rise in simulation. The reduction of the temperature rise leads to an improved spring width of 34.2 μm (20 μm without the metal layer) in case of the designed width of 40 μm. As a result, the resonant frequency of a proposed model is improved to 678 Hz while a reference model shows 439 Hz, where the simulated frequency of design is 754 Hz.

This paper describes design guidance for a compensation method of spring width loss during silicon deep RIE (reactive ion etch) process. We found that a compensation factor (CF), defined by circumference (C) of unit etch hole divided by its area (A), is directly related to the variation of resonant frequencies of silicon MEMS resonators. We proposed 5 models with different etch hole shapes and investigated the effect of etch holes on resonant frequencies. The model with proposed etch holes showed three fold smaller variation of resonant frequencies than other models with conventional etch holes.

We firstly propose the concept of a frequency agile electromagnetic decoupling MEMS-based device. We experimentally show the feasibility of such an apparatus, and further work consists in cascading more than one decoupling device to achieve stronger electromagnetic decoupling values. The structure consists of a freestanding half-wavelength resonator mounted on a movable shuttle connected with large displacement comb actuators. The lateral movement of the shuttle over the main transmission line produces different electromagnetic decoupling values with a variable center frequency. The freestanding resonator plays the role of a loading capacitor as well as the decoupling mechanism in the proposed structure. The device is able to produce diverse decoupling and center frequency effects depending on the overlapping region between the main line and the movable shuttle.

This paper reports on a micromachined planar type probe based on a novel hybrid shielded stripline. The proposed structure is for a broadband transverse electromagnetic (TEM) single-mode propagation using substrate integrated waveguide (SIW) and conventional shielded stripline. We suggested a novel probe structure that composed of half-SIW and half-shielded stripline, which combined through a benzocyclobutene (BCB) bonding layer. The structural concept and simple fabrication method has been introduced, and the S11 in air was measured from 0.5 GHz to 30 GHz. The permittivity measurement of 0.9 % saline has been performed to validate the proposed structure at frequencies from 0.5 GHz to 20 GHz.

This paper presents the new concept of RF MEMS silicon contact switch and its verification for high isolation at 50–110 GHz. A high isolation is achieved by locating the floating top contact electrode 30 µm apart from the bottom coplanar waveguide (CPW) signal line in lateral direction at initial off-state. The switch contact is realized by the dual axis movement, namely a lateral movement by comb electrodes and a following vertical movement by a bottom electrode. The actuation voltages are measured for dual axis movement. The isolation of the switch was measured at 50–110 GHz to prove the concept of isolation improvement using dual axis movement.

This paper presents a single antenna platform mechanically steered by magnetic force in which MMIC (Monolithic Microwave Integrated Circuit) and capacitors are fully integrated. The RF source, MMIC is vertically connected to the antenna plate, not on the BCB spring, so the antenna responses are not distorted with various tilting angles. A single MMIC is flip-chip bonded to increase productivity and reduce process time. The maximum deflection angles are 18.3 ° (H-plane) and 17.7 ° (E-plane) respectively and the tilting angles are proportional to the applied magnetic fields. RF beam patterns are obtained with various scanning angles. The scanning angle are − 14 °, 0 °, + 18 ° (H-plane), − 18 °, − 12 °, 0 °, + 12 °, + 16 ° (E-plane).

This paper presents the design, fabrication and measurements on a new metal-contact RF MEMS switch with low sensitivity to stress gradients and temperature variations. The switch is based on a circular geometry with arc type springs, and results in high contact force, fast switching time, and has excellent microwave performance to ≫ 40 GHz.

There is a great scientific and commercial interest in car radars for anti-crash and pre-crash systems, for which beamformer networks with antenna arrays are becoming the norm. In this paper a novel Butler matrix at 24 GHz using a new type of micromachined suspended transmission-line couplers presented. This configuration arranges all the couplers in the center so that no line crossovers are needed. This circuit has been micromachined on a glass-quartz substrate and BCB layers have been used to suspend the transmission lines of the coupler. In this paper the fabrication method will be fully described, simulated and preliminary experimental results are presented.

This paper reports on an RF MEMS package based on LTCC technology and gold-tin eutectic bonding, and also evaluates physical and RF characteristics of the proposed structure. The package consists of an LTCC lid substrate and a bottom substrate, and assembled by gold-tin layer (80 wt. % gold 20 wt. % tin) for hermetic sealing and low temperature bonding. The helium leak rate of 17 packages were 1.38 X 10-8 atm-cc/sec, and the shear strength of the bonded surface showed in the range of 36 - 50 MPa. The RF characteristics were measured up to 10 GHz, and the packaging loss was calculated to be 0.1349 dB at 2 GHz.

The monolithic RF MEMS probe array system for the application of permittivity measurement was firstly proposed and implemented. The proposed system consists of RF MEMS probe array and RF MEMS SP3T(single-pole triple-throw) switches. We succeeded to show the feasibility of the system for the permittivity measurement experimentally through the permittivity measurement of liquid as operating RF MEMS switches in turn.

Directional couplers have extensive applications in microwave circuits such as beamforming networks. Recently there has been growing scientific and commercial interest in microwave components for anti-crash and pre-crash systems in cars centered at 24 GHz. In this paper a novel suspended transmission-line 3 dB coupler at 24 GHz is presented. This circuit has been micromachined on a glass-quartz substrate and BCB layers have been used to suspend the transmission lines of the coupler. In this paper simulated and experimental results are presented and the fabrication method described.

The performance of micro-electro-mechanical system (MEMS) metal switches were investigated at wide temperature range. Measurements were carried out using cryogenic probe station and S-parameters were taken using a network analyser for frequencies up to 20 GHz. A total of 28 switches were evaluated. The investigation shows a 50% increase in the actuation voltage and a decrease in the percentage of operational switches as the temperature was reduced to 10 K. At room temperature the best isolation (when open) was 30 dB at 10 GHz with an insertion loss of 0.14 dB (when closed). Measurement accuracy was reduced at low temperature, however, isolations and insertion losses were similar to room temperature values.

In this work, we demonstrate a novel compact mechanical beam steering transmitter based on a direct vertical integration of a 2-D MEMS-based mechanical beam steering antenna with a VCO on a single silicon platform. By eliminating the long feed lines and waveguide metal blocks, the radiation pattern has been improved vastly, resulting in an almost ideal pattern at every scan angle. The losses incurred by the feed lines and phase shifters are also eliminated, which allows the transmitter to be implemented using only a single VCO. The system complexity has been greatly reduced with a total module size of only 1.5cm times 1.5cm times 0.4cm. Also, presented in this paper is a planar electrical beam steering transmitter that integrates the MEMS-based phase shifters with VCO, PA, power divider and microstrip antennas. This work demonstrates that RF MEMS can be a key enabling technology for high-level integration

In this paper, we reported a packaging method utilizing LTCC (low temperature co-fired ceramic) substrates and BCB (benzocyclobutane) sealing rim for RF MEMS devices. The LTCC substrate is used as a capping substrate and Ag via holes implanted in LTCC substrates are used as RF feedthrough vertical interconnection. BCB layers play a role in bonding of the MEMS device and LTCC capping substrate. We also measured the RF characteristic of the packaged CPW line, and compared with the RF performance before and after packaging. The Measured value of the only CPW line without a packaging has an insertion loss of 0.047 dB at 2 GHz, and 0.092 dB at 20 GHz, respectively. After packaging, the insertion loss of the packaged CPW is 0.091 dB at 2 GHz and 0.312 dB at 20 GHz, respectively. A leak test has been performed using both IPA soaking and He-based leak tester. Most of the samples show no leakage in IPA test, and the measured He-based leak rate is 10/sup -6/ Pa/spl middot/L/s. The shear strength of the package was measured to be 25/spl sim/35 MPa. The proposed packaging shows less than 0.22 dB in insertion loss over DC-20 GHz, and, it also shows an acceptable value in hermitic test and mechanical shear strength.

In this paper, we firstly proposed a mechanically reliable parallel-plate type variable capacitor with a single crystalline silicon (SCS) supporting structure. The demonstrated variable capacitor was fabricated using an SiOG (silicon-on-glass) process, and both mechanical and electrical characteristics were measured. Total chip size was 1.05 mm/spl times/0.72 mm, and the pull-in voltage was measured to be 37 V. With and without the applied DC bias, the measured S/sub 11/ and S/sub 21/ were changed from -15.6 dB to -5.1 dB, and from -0.49 dB to -2.3 dB at 30 GHz, respectively. The measured capacitance at the up and the down state was 30 fF and 140 fF, respectively. Therefore, the capacitance ratio is calculated to be 4.67.

In this paper, a low loss K-band tunable bandpass filter with micromachined variable capacitors has been designed and fabricated, and its electrical performance has been measured. All elements of the tunable filter were fabricated using a surface micromachining technology and subsequent releasing process. The fabricated chip size was 2.75 mm/spl times/1 mm. The measured initial center frequency was 20.7 GHz with a low insertion loss of 2.2 dB. In the analog operating region of the capacitor, the center frequency could be tuned from 20.7 to 18 GHz, which means a tuning-ratio of 13%. The maximum analog-mode capacitance ratio is 1.31 with an actuation voltage of 35 V. With a bias voltage of 60 V, the membrane collapsed to the bottom electrode and the center frequency was changed to 15.5 GHz, thus the tuning ratio is 25%. In this case, the capacitance ratio was calculated to be 1.9.

We implemented a micromachined probe for the measurement of biological properties using MEMS technology. We experimentally showed the suitability of the micromachined probe in biological applications through liquids and solid experiments. The micromachined probe consists of a CPW and strip line between benzo cyclo butene (BCB) layers because it has excellent properties such as high resistivity, low loss tangent and low permittivity at higher frequencies. The aperture size of the micromachined probe is only 650 /spl mu/m /spl times/ 70 /spl mu/m. We measured the permittivity of a number of well- known liquids - 0.5, 0.9 and 1.3 % saline, acetone, and muscle and fat of pork - as biological samples using the micromachined probe after liquid calibration. In this paper, we first demonstrate that the micromachined probe can provide broadband measurement of measurable solid materials, such as biological samples, and also of well-known liquids at microwave frequencies.

Probes fabricated using multi-layer process are proposed for complex permittivity measurements in microwave frequency range. For multi-layer processing, we have considered LTCC (low temperature co-fired ceramic) and MEMS (micro-electro-mechanical systems) process to make the probe smaller and thus to be applicable to small biological tissues. We expect the probe size can be reduced to 0.1mm by 0.2mm if necessary. We also investigate the shielding effect of vias that is normally used to support TEM wave inside the planar transmission line structure. The complex permittivity of 0.9% saline in microwave frequency range (100MHz-40GHz) was measured using MEMS and LTCC probe to verify the usefulness of the propose probes.

In this paper, a micromachined low-loss and ultra wideband reflection-type phase shifter (RTPS) is proposed. The phase shifter shows a constant phase shift from 5 to 17 GHz and consists of two cascaded reflection-type phase shifter. Low-loss reflection termination consists of digital capacitive switches, and air-gap overlay CPW couplers are used in order to employ the low-loss 3 dB coupling. The fabricated phase shifter showed the 5 discrete states, 0/spl deg/, 22.5/spl deg/, 45/spl deg/, 67.5/spl deg/, 90/spl deg/ respectively, the average insertion loss of 3.48 dB, and maximum rms phase error of /spl plusmn/ 1.80/spl deg/ for the relative phase sift from 0/spl deg/ to 90/spl deg/ over 5-17GHz.

In this work, a new V-band CPS analog distributed MEMS phase shifter has been developed. Since this phase shifter is based on the balanced CPS lines, no extra mode transition structure is required for integration with the balanced circuits using CPS or slot line as well as for packaging in the waveguides. MEMS bridges over the coplanar strip lines are used to control the mutual capacitance between two CPS strip lines, consequently the phase response of the capacitively loaded CPS line. The fabricated phase shifter showed 55/spl deg//dB at 40 GHz and 74/spl deg//dB at 60 GHz. The return loss is better than 8 dB over a wide frequency range from 1 to 70 GHz. For measurement with CPW-based on-wafer system, a new ultra wideband CPW-to-CPS transition has also been developed, and showed a low insertion loss less than 1.9 dB from DC to 110 GHz.

A low-loss broadband reflection-type phase shifter (RTPS), showing constant phase shift from 15 to 45 GHz, was developed using MEMS technology. The analog phase shifter consists of two cascaded reflection-type phase shifters for 1:3 bandwidth. Air-gap overlay CPW couplers were employed for low-loss 3 dB coupling, and bridge-type MEMS variable capacitors were used for low-loss reflective terminations. The fabricated phase shifter shows the average insertion loss of 3.63 dB, and rms phase error of 3.7/spl deg/ from 15 to 45 GHz. Compared with the similar RTPS using GaAs PHEMT varactor diodes, much lower loss is observed together with improved bandwidth.

In this letter a novel λ/4 micromachined directional coupler is presented with a 10 μm benzocyclobutene (BCB) layer used to suspend one transmission line over another one in order to achieve a 3-dB coupling. The coupler is centered at a frequency of 24 GHz. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1813–1814, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22574