RF MEMS Capacitors Research Articles

Tuneable RF MEMS capacitors based on electrostatically induced torsion

Tuneable RF MEMS capacitors based on electrostatically induced torsion

Design and characterization of compact digital RF MEMS capacitors and phase shifters in CMOS 0.35 µm technology

This work reports on the design, fabrication and characterization of compact digital RF MEMS capacitors and phase shifters that are built in the back end of line (BEOL) of CMOS 0.35 µm technology. The devices are micromachined using a maskless post-processing sequence with cryogenic cooling on to control the out-of-plane warping of the metal-oxide structural layers. The implemented vertical electrostatic actuation in the developed post process allows the realization of highly compact designs of both devices, and an operating voltage of the devices is stay below 70 V. The 4-bit capacitors provide a measured tuning ratio close to 10:1 which corresponds to 0.15 pF to 1.2 pF over the frequency range 3–10 GHz. The overall footprint of the digital capacitor is 0.6 mm × 0.9 mm. The measured quality factor after de-embedding the losses due to the RF probing pads is up to 120. The measurement of the 4-bit phase shifters reveals low insertion loss <3 dB at 20 GHz along with low variation of the insertion loss <1 dB up to the same frequency. The measured phase shift is 150 at 20 GHz. The overall footprint of the 4-bit phase shifter is around 1 mm × 1 mm.

Design and fabrication of a continuously tuned capacitor by microfluidic actuation

This paper presents the design and fabrication of a continuously tunable RF MEMS capacitor using micro fluidics as a tuning parameter. The impedance variation principle is based on the modification of the capacitor gap permittivity produced by the presence of deionized (DI) water and its displacement in a channel inserted between electrodes. In addition, the electric field distribution changes in an equiponderant way according to the DI water positions in the channel. This change modifies the capacitive coupling, the stored energy and, consequently, the self-resonant frequency. The fabrication process is based on two parts: metallic paths having a spiral form, and obtained by electroplating a 7 µm thick gold layer to constitute electrodes; and fluidic channels, realized by super imposing two SU-8 films. The measurements show a nonlinear variation of the capacitor value according to the water positions. The tuning range is very large, reaching to 4650% for capacitance, and 335% for resonant frequency. However, the quality factor reaches Qmax = 79 at 550 MHz if the capacitor is empty and decreases with the fluid displacement to Qmin = 3.13.

A New Linearly Tunable RF MEMS Varactor with Latching Mechanism for Low Voltage and Low Power Reconfigurable Networks

A new electro-thermally driven high Q tunable RF MEMS capacitor is proposed in this paper. The tuning mechanism of the varactor is chosen to obtain tuning; hence the capacitor has linear tuning range. In order to satisfy the low voltage operation of the varactor electro-thermal actuators were chosen as the drive and latching mechanism. However, those actuators consume lots of power, accordingly, in order to suppress that shortcoming a true mechanically latching mechanism is proposed which considerably decreases the total power consumption of the varactor. In order to investigate important operational aspects of the proposed varactor, different FEM simulations are carried out. The results are as follow; the Q-factor is 43.39 at 1 GHz for a 0.46 pF capacitance value. The tuning ratio is 1.17:1 and self-resonant frequency is 16.61 GHz. The propose varactor works by applying an actuation voltage of 3.1 V and consumes a power of 180 mW for about 2.7 ms for each tuning steps. The proposed varavtor of this paper can be a promising choice for low lass and low power RF tunable networks.

Adjustable Resonance Frequency of RF-MEMS Capacitor by Using Comb- Drive Actuators: A Design Approaches

The needs of smaller size RF varactor is a must today, and MEMS comes to be the potential one. In this paper we proposed an adjustable resonance RF-MEMS varactor by using comb-drive actuators placing in each side of the square movable plate. In our preliminary simulation, we found that the device can work properly but some constraints comes such as the dominancies of harmonic resonance frequencies that influences into the nominal capacitances. Therefore for the next step of development we have to find out the window of the structural dimension for a certain spans and a certain operating frequencies.

Adjustable Resonance Frequency of RF-MEMS Capacitor by Using Comb- Drive Actuators: A Design Approaches

Adjustable Resonance Frequency of RF-MEMS Capacitor by Using Comb- Drive Actuators: A Design Approaches

Handling RF Power: The Latest Advances in RF-MEMS Tunable Filters

RF-MEMS technology permits practical implementations of high-Q (Q from 300 to over 1,000) tunable microwave filters with power handling in the >;1-10 W range, with significant tuning range (>;50% to 100%), and ultra-low power consumption. Continuously frequency-tunable filters with mechanical actuation in the opposite direction of RF-inducted pressure can reach powers up to several watts, using a variable compensation bias. Very high Q, and large tuning range can be achieved with this technology, both in planar and cavity tunable filters. Using several devices in parallel, RF-MEMS capacitor arrays can handle RF-powers better than 1 watt, without the need for any compensation tuning.

Differential RF MEMS interwoven capacitor immune to residual stress warping

A RF MEMS capacitor with an interwoven structure is designed, fabricated in the PolyMUMPS process and tested in an effort to address fabrication challenges usually faced in MEMS processes. The interwoven structure was found to offer several advantages over the typical MEMS parallel-plate design including eliminating the warping caused by residual stress, eliminating the need for etching holes, suppressing stiction, reducing parasitics and providing differential capability. The quality factor of the proposed capacitor was higher than five throughout a 2-10 GHz range and the resonant frequency was in excess of 20 GHz.

A new design for rotational, tunable wideband RF MEMS capacitors

Wide range tunable components are a key point for high frequency performances. We have developed a novel RF MEMS rotational capacitor based on surface variation and high displacement. This paper will present multiple designs with physical parameter variations for comparative test with fabricated device measurements. The goal of this work is to prove the proper operation of the devices according to fulfill target performances. The main parameters will be tunability, capacitance value, resonance frequency and finally maximal actuation voltage allowed.

2.0–2.7 GHz programmable bandpass filter with RF-MEMS capacitance matrices

A programmable bandpass filter for 2.0–2.7 GHz centre frequencies and 450–500 MHz 3 dB bandwidth is presented. The filter is based on packaged RF-MEMS capacitor matrices as the tunable elements. The coupled-resonator filter topology was chosen with added transfer zeros. The results show excellent match between simulation and measurements. The measured insertion loss is 4.5–5.5 dB over the tuning range, and the linearity measurements show an OIP3 of 55–64 dBm.

Performance and operation of stressed dual gap RF MEMS varactors

The design, fabrication and measurement of a continuously tunable RF MEMS capacitor is described. The capacitor’s dual gap height architecture allows for electrostatic tuning with low resistive loss and a large tuning range. A new dual tuning scheme is introduced for use with two voltage sources. This dual tuning, coupled with a stress-induced bridge, is used to reach further device tuning. Measurements indicate a continuously tunable capacitance range of 6.2:1 with a quality factor over 50 at 30 GHz for 310 fF.

High tuning range AlSi RF MEMS capacitors fabricated with sacrificial amorphous silicon surface micromachining

This paper reports the fabrication and electrical characterization of high tuning range AlSi RF MEMS capacitors. We present experimental results obtained by a surface micromachining process that uses dry etching of sacrificial amorphous silicon to release Al–1%Si membranes and has a low thermal budget (<450 °C) being compatible with CMOS post-processing. The proposed silicon sacrificial layer dry etching (SSLDE) process is able to provide very high Si etch rates (3–15 μm/min, depending on process parameters) with high Si: SiO 2 selectivity (>10,000:1). Single- and double-air-gap MEMS capacitors, as well as some dedicated test structures needed to calibrate the electro-mechanical parameters and explore the reliability of the proposed technology, have been fabricated with the new process. S -parameter measurements from 100 MHz up to 2 GHz have shown a capacitance tuning range higher than 100% with the double-air-gap architecture. The tuning range can be enlarged with a proper DC electrical bias of the capacitor electrodes. Finally, the reported results make the proposed MEMS tuneable capacitor a good candidate for above-IC integration in communications applications.

High tuning range AlSi RF MEMS capacitors fabricated with sacrificial amorphous silicon surface micromachining

This paper reports the fabrication and electrical characterization of high tuning range AlSi RF MEMS capacitors. We present experimental results obtained by a surface micromachining process that uses dry etching of sacrificial amorphous silicon to release Al–1%Si membranes and has a low thermal budget (<450 °C) being compatible with CMOS post-processing. The proposed silicon sacrificial layer dry etching (SSLDE) process is able to provide very high Si etch rates (3–15 μm/min, depending on process parameters) with high Si: SiO 2 selectivity (>10,000:1). Single- and double-air-gap MEMS capacitors, as well as some dedicated test structures needed to calibrate the electro-mechanical parameters and explore the reliability of the proposed technology, have been fabricated with the new process. S-parameter measurements from 100 MHz up to 2 GHz have shown a capacitance tuning range higher than 100% with the double-air-gap architecture. The tuning range can be enlarged with a proper DC electrical bias of the capacitor electrodes. Finally, the reported results make the proposed MEMS tuneable capacitor a good candidate for above-IC integration in communications applications.

Dry Etching Techniques of Amorphous Silicon for Suspended Metal Membrane RF MEMS Capacitors

AbstractA novel dry etching technique of amorphous silicon is proposed to suspend the metal membrane of RF MEMS tunable capacitors. The proposed fabrication process is simple and excludes all the drawbacks related to a wet process. Moreover, it has the advantage of being fully compatible with CMOS post-processing. Experimental results demonstrate that the capacitor suspension beams design with meanders can reduce the tuning voltage to less than 5 to 10 V.