Microelectromechanical Systems Switches Research Articles

Sacrificial layer optimization for RF MEMS switches

This paper introduces the characterization of AZ-P4620 photoresist as a sacrificial layer for Radio Frequency MEMS (Micro-Electro-Mechanical System) switches. The surface micromachining process is opted for the fabrication of RF MEMS switches, which includes a suspended structure. Initially, a thick photoresist is coated and patterned, to be utilized as a sacrificial layer and then the structural layer is deposited on it. For proper connectivity of the structural layer, edge coverage is required. This photoresist is optimized at different post-baking temperatures. We investigated that slope angles decrease with an increase in post bake temperature. Using the optimized recipe, the RF MEMS switch is fabricated and characterized successfully. The measured isolation, pull-in voltage, and insertion loss, are − 30 dB, 23 V, and − 0.2 dB, respectively at 18 GHz frequency.

A Hybrid RF MEMS Switch Actuated by the Combination of Bidirectional Thermal Actuations and Electrostatic Holding

Radio frequency microelectro-mechanical system (RF MEMS) switches have received attention due to their higher performances at high frequencies compared with semiconductor-based switches. However, most of the previous MEMS switches used electrostatic actuation, which requires a high actuation voltage and has a low actuation force. Herein, we propose a new hybrid RF MEMS switch for low-voltage and low-power operation that is actuated by the combination of bidirectional thermal actuation and electrostatic holding. The proposed hybrid RF MEMS switch is actuated by the combination of two actuation mechanisms, i.e.: 1) bidirectional thermal actuation of the large force with low actuation voltage and 2) electrostatic holding for low-power consumption. The large actuation force enables high signal isolation at the “OFF” state of the switch because of the high initial gap between the signal line and the contact metal. Also, the bidirectional thermal actuator that enables upward actuation prevents any stiction of the membrane, which enhances both the power handling capability and the reliability of the actuator. In this work, we successfully fabricated the proposed RF MEMS switch and measured both its mechanical characteristics and RF characteristics. The required actuation voltage for the switch is less than 0.3 V for thermal actuation, and the required voltage for electrostatic holding is 15.4 V. The power consumption was measured as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.24~\mu \text{J}$ </tex-math></inline-formula> per switching. Also, we measured the RF characteristics, and the insertion loss of signals was 0.23 dB at 2.4 GHz, and the isolation of signals was 38.80 dB at 2.4 GHz.

Ni–P electroless on nonconductive substrates as metal deposition process for MEMS fabrication

During past decades Micro Electro Mechanical Systems (MEMS) have been developed and presented in the market. It is important to find new processes and methods to facilitate MEMS production regarding to growing demand of MEMS devices in IoT, smart and intelligent systems, consumer electronics and medical applications. In this paper, Ni–P layer deposition on insulator substrates is presented. The layer is deposited based on chemical reactions in electroless process. There is a similar method, electroplating, for metal deposition but the substrate must be conductor to transfer electrons and provide essential conditions for electroplating. Electroplating process is not applicable for insulator substrates, while the proposed electroless process can be useful. Different steps, materials, conditions and experimental results for Ni–P electroless are presented. A fabrication process for DC contact RF MEMS switch based on Ni–P electroless is introduced, too. As one advantage of this process, Ni and Ni–P are ferromagnetic material and any suspended structure can be actuated by magnetic fields. It will be beneficial when applying other actuation mechanisms like electrostatic, thermal or piezoelectric are difficult or impossible to be applied.

Physics-aware macromodels for MEMS switches

Purpose The purpose of this paper is to propose a physics-aware algorithm to obtain radio frequency (RF)-reduced models of micro-electromechanical systems (MEMS) switches and show how, together with multiphysics macromodels, they can be realized as circuits that include both lumped and distributed parameters. Design/methodology/approach The macromodels are extracted with a robust procedure from the solution of Maxwell’s equations with electromagnetic circuit element (ECE) boundary conditions. The reduced model is extracted from the simulations of three electromagnetic field problems, in full-wave regime, that correspond to three configurations: signal lines alone, switch in the up and down positions. Findings The technique is exemplified for shunt switches, but it can be extended for lateral switches. Moreover, the algorithm is able take frequency dependence into account both for the signal lines and for the switch model. For the later, the order of the model is increased until a specified accuracy is achieved. Originality/value The use of ECE as boundary conditions for the RF simulation of MEMS switches has the advantage that the definition of ports is unambiguous and robust as the ports are clearly defined. The extraction approach has the advantage that the simplified model keeps the basic phenomena, i.e. the propagation of the signal along the lines. As the macromodel is realized with a netlist that uses transmission lines models, the lines’ extension is natural. The frequency dependence can be included in the model, if needed.

Design and fabrication of a 4-bit RF MEMS attenuator with a high attenuation accuracy

This paper presents a 4-bit micro-electromechanical system (MEMS) digital attenuator with improved attenuation accuracy by surface micromachining. The attenuator is consisted of monoblack type radio frequency MEMS switches and TaN film resistors fabricated on a glass substrate to control the reconfigurable power within DC ~ 18 GHz. The simulation results revealed that the device had favorable terminal matches ranging from 0 to 70 dB with a 10 dB step. The attenuation accuracy was better than 1.2 dB, the insertion loss was less than 1.32 dB, and the voltage standing wave rations were better than 1.56 under these eight attenuation steps. Additionally, the package size of this device was designed as 8.28 mm × 2.37 mm × 0.85 mm, such that it could be applied to miniaturized microwave instruments.

Linearity and RF Power Handling on Capacitive RF MEMS Switches

Linearity characteristics of capacitive tuners under large radio frequency (RF) power have become an important issue for today’s cellphone industry. The use of these devices as antenna tuners has become critically important due to the RF spectrum opening in the low-frequency range. Capacitive tuners connected directly to the antenna to change the RF voltage/current pattern and tune lower frequencies are subjected to suffer large voltage swings, especially in the isolation state or minimum capacitance. In this article, we analyze the effects of the large RF power or equivalent rms voltage to capacitive micro-electromechanical systems (MEMS) switches. The theoretical analysis combined with Coventor MEMS+ simulations will allow us to study the capacitance change and MEMS mechanical frequency response. This article evaluates two types of measurement setups to investigate the RF power effects on nominal capacitance and mechanical frequency response. Measurements up to 6 W were completed with two capacitive MEMS tuner products, confirming the modeling predictions and demonstrating the robustness of this technology under large RF power or voltage swings.

Contact resistance and lifecycle of an ohmic MEMS switch with single and multiple contact bumps

Microelectromechanical systems (MEMS) switches potentially have a wide range of applications due to their promising characteristics, but relatively low reliability limits implementation of these devices. Contact region degrades during operation that increases the resistance and lowers the lifecycle. In this paper we demonstrate how these parameters can be enhanced by changing the design of the switch. The devices of four types having different number of contact bumps and beams are fabricated by surface micromachining and tested in a cold switching DC regime. The switch with two bumps has about 25% lower contact resistance and almost two times longer lifecycle than the one-bump device. Using four beams instead of one gives threefold increase of the lifecycle, but does not reduce the resistance significantly.

Design of a novel structure capacitive RF MEMS switch to improve performance parameters

This study reports the design and analysis of novel step structure RF micro-electromechanical system (MEMS) switch for low pull-in voltage, low insertion loss and high isolation by using uniform single meander. The central beam of the membrane is designed with 0.5 µm lower than the side beams to form a step-down structure which reduces the pull-in voltage. Stress analysis, electromechancial, switching time, quality factor and RF analysis have done to understand the behavioural characteristics of the proposed step-down switch. The analysis has been carried out for different beam and dielectric materials among them switch with gold material exhibits low pull-in voltage of 4.7 V, low insertion loss <1 dB and high isolation of −38.3 dB at 28.2 GHz for silicon nitride. The switch also shows good quality factor of 0.95 for gold material along with high capacitance ratio of 132. The upstate capacitance of 56.8 pF contributes low return loss and made the switch to transmit the signal up to 26.2 GHz and provides 7.2 pF of downstate capacitance to produce high isolation at 26.2 GHz which is efficiently used for K-band satellite applications.

Pairing electrostatic levitation with triboelectric transduction for high-performance self-powered MEMS sensors and actuators

We demonstrate that an electrostatic levitation microelectromechanical systems (MEMS) switch can be operated by applying mechanical pressure to a triboelectric generator. The toggling mechanism of the switch draws no current but requires a high actuating voltage, while the generator can supply a high voltage but only produces microwatts of power. The synergistic combination results in an entirely self-powered sensor and switch; the normally closed MEMS switch can be toggled open by applying a threshold force to the generator without the need for any outside power or supplementary circuitry. A model of the MEMS switch and electrostatic force is validated with experimental data. An output voltage vs input force relationship for the generator is experimentally extracted.

Novel capacitance evaluation model for microelectromechanical switch considering fringe and effect of holes in pull-up and pull-down conditions

This paper reports a model and investigates into capacitive studies of microelectromechanical system switch through considerations of material’s behavior on various parameters like dielectric thickness, thickness and width of bridge structure and also with distance between two electrodes including fringe field effect on pull up and down capacitance. The pull up capacitance and pull-down capacitances are investigated considering effect of fringe field and holes independently as well as combined together. In pull up state, the total capacitance is found to be 6.9945 fF in which three components of the capacitance $$ C_{1,u} $$, $$ C_{2,u} $$ and $$ C_{3,u} $$ contribute 1.1624 fF (16.61%), 2.1924 fF (31.34%) and 3.6397 fF (52.03%) respectively. In pull down state, the total capacitance is found as 2.1439 pF and capacitance sharing of each component ($$ C_{1,d} $$), ($$ C_{2,d} $$) and ($$ C_{3,d} $$) is 0.6503 pF (30.33%), 1.1164 pF (52.07%) and 0.3772 pF (17.59%) respectively. The pull-down capacitance ($$ C_{t,d} $$) and pull up capacitance ($$ C_{t,u} $$) ratio is also calculated and $$ \left( {\frac{{C_{t,d} }}{{C_{t,u} }}} \right)_{max} $$ using model is found as 521.64. The capacitance ratio range is also calculated and range is 48.41–521.64. This model can be used to measure the capacitances in symmetric and asymmetric microelectromechanical switch with error range 2–5%.

Reliability of platinum contacts in a cold operated MEMS switch

Lifetime testing results of an electrostatically actuated microelectromechanical systems (MEMS) switch with Pt-Pt contact are presented. Moveable electrode of the switch is an aluminium beam with platinum contact bumps, which comes in contact with platinum thin-film electrodes. The switch operates in a cold DC mode. Testing is performed at several levels of the input current. Dependence of the switch resistance in the “on” state on the number of actuation cycles is measured. Lifetime of the device is limited by the sharp increase of the on-resistance up to 100 MΩ and depends on the switch design and the input current. Morphology and chemical composition of the contacting surfaces are investigated and mechanisms of the contact degradation are determined.

The strong effect on MEMS switch reliability of film deposition conditions and electrode geometry

Microelectromechanical systems (MEMS) or nanoelectromechanical systems (NEMS) switches are of interest for applications ranging from radio frequency (RF) communication circuitry to power surge protection to low power computing. Reliable operation of the switch contacts is critical. Many researchers have investigated the effect of different materials on reliability, but little work has been reported on the effects of process conditions. In this study, the effects of the angle of deposition incidence, the microstructure, the interface adhesion, the base pressure, and the process transferability have been evaluated in Pt-coated MEMS switches. Among them, base pressure attained prior to deposition was most important, while an interaction between electrode geometry and film microstructure was also identified to play a role. A lower base pressure (2•10−6 Torr) improved cycle count significantly while a higher base pressure (8•10−6 Torr) resulted in low cycle counts (106 or less). Failure analysis indicated surface wear due to damage at a corner junction, where films deposited at different angles of deposition incidence meet. Mass spectroscopy analysis detected higher carbon content in Pt films with high base pressure. This suggests that grain boundaries weakened by impurity segregation exacerbated the geometric effect. Switches tested in a follow-up experiment, in which the base pressure was 5•10−7 Torr, again resulted in high cycle counts (330•106), reinforcing the importance of achieving low base pressure in improving the mechanical reliability of the corner junction.

Design and Simulation of RF MEMS Switch for X-band Applications

This article presents the design and simulation of RF microelectromechanical systems (MEMS) switch which works at X-band frequency(8-12 GHz). The design consists of a thin micromechanical bridge suspended over a silicon nitride which is used as the dielectric material with 0.1 µm thickness and air gap of switch is 0.9 µm. The design, modelling and simulation are done using the COMSOL Multiphysics 5.1. The designed switch has low actuation voltage, low pull-in voltage, optimum capacitance ratio, low switching time which makes it a perfect switch to work at X-band frequency. The switch has actuation voltage of 5 V, pull-in voltage of 1.58 V, capacitance ratio 66 and switching timing of 35 µs.

Low voltage, high speed and small area in-plane MEMS switch

Electrostatic in-plane microelectromechanical systems (MEMS) relays/switches are widely applied for their low power consumption and simple process. However, compared to the out-of-plane designs, in-plane designs usually suffer from high pull-in voltage, since the feature size of the bulk-silicon process limits the gap between the driving electrodes. Area cost and speed usually have to be sacrificed to enhance the driving force and decrease the pull-in voltage.Balancing the pull-in voltage, speed and area cost is difficult for MEMS relays/switches but is essential in many practical applications. Comb structure is promising to relieve this contradiction. In this paper, we integrated the comb structure with the cantilever structure. As a result, the pull-in voltage decreased with the decreasing of the mass and area cost. A novel electrostatic lateral MEMS switch was introduced. The experiments have shown that 12 V pull-in voltage, 120 s switching time with a 28 V driving voltage at atmospheric pressure, and small area were fabricated using a conventional bulk-silicon process.

Double-Tuned Surface 1H–23Na Radio Frequency Coils at 7 T: Comparison of Three Decoupling Methods

Magnetic Resonance Imaging (MRI) and Spectroscopy (MRS) with nuclei other than protons (X-nuclei) often require the acquisition of proton signal for shimming and co-registration procedures. Double-Tuned Radio Frequency (DT-RF) coils improve these procedures, avoiding the need for movement and repositioning of the subject during the examination. The drawback of DT-RF coils is basically the coupling between the two resonant structures, which increases signal losses leading to a degradation of the final MR image. To improve MR signal quality acquired via DT-RF coils, a suitable decoupling strategy should be implemented. For this purpose, three DT-RF coil prototypes, which differed only in the decoupling method, were built and their performances were compared through workbench measurements. Each prototype consisted of two concentric loops. The inner and outer loops were tuned at sodium (≈ 79 MHz) and proton (≈ 300 MHz) Larmor frequency at 7 Tesla, respectively. Active and passive decoupling designs were compared measuring the Q factor and the S21 parameter for each prototype. Active decoupling was tested as an alternative to the standard passive decoupling with a trap circuit, in which a non-negligible amount of current flows at resonance, perturbing the magnetic field responsible for producing the MR image. Workbench measurements showed satisfactory Q factors and S21 for both active and passive decoupling cases. Thus, active decoupling could be a promising alternative to achieve better MR signal quality. Furthermore, for active decoupling, two circuit elements were examined: PIN diodes and micro-electromechanical system (MEMS) switches.

Novel Test Fixture for Characterizing MEMS Switch Microcontact Reliability and Performance.

In microelectromechanical systems (MEMS) switches, the microcontact is crucial in determining reliability and performance. In the past, actual MEMS devices and atomic force microscopes (AFM)/scanning probe microscopes (SPM)/nanoindentation-based test fixtures have been used to collect relevant microcontact data. In this work, we designed a unique microcontact support structure for improved post-mortem analysis. The effects of contact closure timing on various switching conditions (e.g., cold-switching and hot-switching) was investigated with respect to the test signal. Mechanical contact closing time was found to be approximately 1 μs for the contact force ranging from 10–900 μN. On the other hand, for the 1 V and 10 mA circuit condition, electrical contact closing time was about 0.2 ms. The test fixture will be used to characterize contact resistance and force performance and reliability associated with wide range of contact materials and geometries that will facilitate reliable, robust microswitch designs for future direct current (DC) and radio frequency (RF) applications.

SR‐Crossbar topology for large‐scale RF MEMS switch matrices

With the development of multifunctional satellites, the integration and multiplexing of satellite resources become increasingly important. Large-scale radio-frequency microelectromechanical system (RF MEMS) switch matrix technology is one of the key technologies to design a multifunctional satellite. This study proposed a novel sequential rotation crossbar (SRCrossbar) topology for large-scale RF MEMS switch matrices. A specifically designed novel configuration scheme or arraying method for SR-Crossbar topology is also proposed. The number of switch elements in the SR-Crossbar RF MEMS switch matrix is significantly reduced; hence, the reliability and performance of the matrix can be improved simultaneously. For an N × N RF MEMS switch matrix, in a fully configured scenario, the maximum number of switch elements in all the paths are N(N + 1)/2. When N ≥ 4, the proposed SR-Crossbar RF MEMS switch matrix topology is better than the planar Benes topology, which is already an optimised planar switch matrix topology with the minimum number of nodes.

Uncertainty Considerations for Nonlinear Dynamics of a Class of MEMS Switches Undergoing Tip Contact Bouncing

Batch fabrication processes used to produce micro-electro-mechanical systems (MEMS) are prone to uncertainties in the system geometrical and contact parameters as well as material properties. However, since the common design method for these systems is typically based on precise deterministic assumptions, it is necessary to get more insight into their variations. To this end, understanding the influences of uncertainties accompanied by these processes on the system performance and reliability is warranted. The present paper focuses on predictions of uncertainty measures for MEMS switches based on the transient dynamic response, in particular, the bouncing behavior. To understand and quantify the influence of pertinent parameters on the bouncing effects, suitable mathematical model that captures the bouncing dynamics as well as the forces that are dominant at this micron scale are employed. Measure of performance in terms of second-order statistics is performed, particularly for the beam as well as beam tip parameters since excessive tip bounce is known to degrade switch performance. Thus, the present study focusses on the influence of uncertainties in the beam tip geometry parameters such as beam tip length/width as well as contact asperity variables such as the area asperity density and the radius of asperities. In addition to beam tip parameters, this study quantifies the effects of uncertainties in Young's modulus, beam thickness as well as actuation voltage. These influences on significant switch performance parameters such as initial contact time and maximum bounce height have been quantified in the presence of interactive system nonlinearities.

New Analytical Capacitance Modeling of the Perforated Switch Considering the Fringing Effect

Movable suspended microstructures are common features of sensors and devices in the field of micro electro mechanical systems (MEMS). This paper addresses the study of approach to model the capacitance for the crab-type meander-based RF MEMS shunt switch with etching holes on the beam. The presented paper evaluates the parallel-plate capacitance and fringing-field capacitance caused by the etching holes on the beam and introduces empirical formulae. From the literature study, an accurate empirical formula is presented. The capacitance involves a parallel plate and a fringing field. The parallel-plate capacitance term is proposed by the authors of this work; the fringing-field capacitance term is adopted from previous work. The proposed accurate empirical capacitance formulae are derived by curve fitting the simulated values through the commercially available FEM solver. The two existing benchmark models of fringing-field capacitance are used to modify the perforated MEMS switch to obtain the proposed formula. With the existing models and presented formula, the capacitances are computed for a wide range of dimensions; the simulated results of the presented formula are validated with the calculated results. The deviation of the presented formula has an error estimation of ±0.1%. The variation of the capacitance with different deictic thicknesses and errors is estimated and analyzed for the presented formula. The Mejis model is found to be satisfactory for a lower air gap and a 1-μm-thick beam. The Yang's model is sufficient for a higher air gap and a large number of etching holes. The proposed formulae are good for the ligament efficiency μ ≤ 0.5, with thickness >1 μm, and the deviation of error estimation is within ±5%.

Lifetime testing of a MEMS switch with Pt-Pt contact

This paper presents the lifetime testing results of an electrostatically actuated microelectromechanical systems (MEMS) switch with the resistive contact and the active contact breaking mechanism. Moveable electrode of the switch is an aluminium beam with platinum contact bumps located on its bottom surface, which comes in contact with platinum thin-film electrodes. The switch operates in a cold DC mode in a standard laboratory environment. Testing is performed at three levels of the input current: 0.05, 0.5 and 5 mA. The dependence of the resistance in the “on” state on the number of actuation cycles is measured. Resistance of the “fresh” samples is in the range from 150 to 350 Ω. Instability of the resistance is observed during cycling, that is probably related to contamination of the contacts. Lifetime of the switch is limited by the sharp increase of the on-resistance up to 100 MΩ and varies from 2×103 to 5×104 cycles depending on the switch design and the input current.