Francesc Torres

A CMOS–MEMS RF-Tunable Bandpass Filter Based on Two High-

This letter presents the design, fabrication, and demonstration of a CMOS-MEMS filter based on two high-Q submicrometer-scale clamped-clamped beam resonators with resonance frequency around 22 MHz. The MEMS resonators are fabricated with a 0.35-mum CMOS process and monolithically integrated with an on-chip differential amplifier. The CMOS-MEMS resonator shows high-quality factors of 227 in air conditions and 4400 in a vacuum for a bias voltage of 5 V. In air conditions, the CMOS-MEMS parallel filter presents a programmable bandwidth from 100 to 200 kHz with a <1-dB ripple. In a vacuum, the filter presents a stop-band attenuation of 37 dB and a shape factor as low as 2.5 for a CMOS-compatible bias voltage of 5 V, demonstrating competitive performance compared with the state of the art of not fully integrated MEMS filters.

Q

A micro-electro-mechanical system based vibration energy harvester is studied exploring the benefits of bistable non linear dynamics in terms of energy conversion. An electrostatic based approach to achieve bistability, which consists in the repulsive interaction between two electrets locally charged in both tip free ends of an atomic force microscope cantilever and a counter electrode, is experimentally demonstrated. A simple model allows the prediction of the measured dynamics of the system, which shows an optimal distance between the cantilever and the counter electrode in terms of the root mean square vibration response to a colored Gaussian excitation noise.

22-MHz Polysilicon Clamped-Clamped Beam Resonators

The present work describes the design, fabrication and experimental results of a 3-terminal laterally actuated tungsten nanoelectromechanical (NEM) relay which is monolithically integrated in a 0.35 μm commercial standard CMOS technology. The movable structure is released by means of a simple one-step maskless wet etching. The switch shows an abrupt switching with less than 5 mV/decade and a good on-off current ratio of - 104 although it exhibits an on-state contact resistance RON around 500 MΩ. Also, the relay is cycled up to 1500 times in ambient conditions showing great endurance but variability in its contact.

Inducing bistability with local electret technology in a microcantilever based non-linear vibration energy harvester

This paper describes the frequency mixing operation of a micro electro mechanical system device designed and fabricated in a CMOS commercial technology (AMS 0.35mum). The theory of the MEMS is summarized and a CMOS fully integrated MEMS is characterized as a mixer. The designed MEMS is a polysilicon clamped-clamped beam that presents a resonance frequency in the VHF range. CMOS-MEMS based mixer limitations are treated and a technique based on differential amplification to improve performance is given.

3-terminal tungsten CMOS-NEM relay

A stepped cantilever composed of a bottom-up silicon nanowire coupled to a top-down silicon microcantilever electrostatically actuated and with capacitive or optical readout is fabricated and analyzed, both theoretically and experimentally, for mass sensing applications. The mass sensitivity at the nanowire free end and the frequency resolution considering thermomechanical noise are computed for different nanowire dimensions. The results obtained show that the coupled structure presents a very good mass sensitivity thanks to the nanowire, where the mass depositions take place, while also presenting a very good frequency resolution due to the microcantilever, where the transduction is carried out. A two-fold improvement in mass sensitivity with respect to that of the microcantilever standalone is experimentally demonstrated, and at least an order-of-magnitude improvement is theoretically predicted, only changing the nanowire length. Very close frequency resolutions are experimentally measured and theoretically predicted for a standalone microcantilever and for a microcantilever-nanowire coupled system. Thus, an improvement in mass sensing resolution of the microcantilever-nanowire stepped cantilever is demonstrated with respect to that of the microcantilever standalone.

Mixing in a 220MHz CMOS-MEMS

The influence of the parasitic feedthrough current on the nonlinear electrical response of capacitively sensed cantilever resonators is analyzed theoretically and experimentally. We show that the parasitic current strongly affects the shape of the nonlinear electrical frequency response of such devices. Specifically, we demonstrate that in the electrical measurement, the directions of the jumps from the different transitions between branches of stable solutions depend on the parasitic current and are independent of the jumps directions in the mechanical domain. As a consequence, the nonlinear electrical frequency response of cantilevers with capacitive readout presents three different hysteretic cycle topologies: counterclockwise, bow tie, and clockwise. This is in contrast with the only one topology (counterclockwise) that appears in the nonlinear mechanical frequency response.

Top-down silicon microcantilever with coupled bottom-up silicon nanowire for enhanced mass resolution

In this paper, we present the electrical characterization of the nonlinear tapping mode of the nanorelays capacitively transduced. Such a characterization is carried out utilizing three-terminal tungsten CMOS-NEM relays. Exciting electrostatically the switching devices near its resonance and detecting its movement by means of capacitive detection, we reveal double-side frequency dynamic-contact characteristics when the displacement is large and the tapping occur in the nonlinear regime. In this way, we take advantage of this periodic contact to evaluate the switching characteristics of the device. We report that the switch stands more than 10 billion of tapping cycles (in a cold switching scenario) without showing any failure. Moreover, we measure current-voltage (I-V) curves before and after the cycling test in order to evaluate the changes produced in the ON-state contact resistance and in the pull-in and pull-out voltages. This test reveals that the characterized switch has a consistent and repetitive pull-in voltage without changing its elastic properties. In addition, we observe that the pull-out voltage decreases slightly and the contact resistance diminishes (from an initial value of 2 GΩ to a minimum value of 735 MΩ. We eventually attribute this result to the fact that the superficial oxide is broken down due to the continuous tapping of the cantilever tip on the contact electrode.

The influence of the parasitic current on the nonlinear electrical response of capacitively sensed cantilever resonators

A CMOS-NEM tungsten relay based on a 3-T configuration for logic applications is presented. The relay is integrated monolithically in the BEOL of a standard CMOS technology (AMS 0.35 μm) using the tungsten VIA3 layer. The relay is designed and fabricated during the CMOS process and released by a one-step mask-less wet etching. The measured devices show an essentially zero leakage current and a subthreshold slope less than 5 mV/decade with a 104 ratio between on-off current, although they exhibit a high contact resistance (~ 108 Ω). A cycling test was carried out up to 1800 cycles in ambient conditions. Throughout this test, the switch shows great endurance. Finally, the frequency response was also measured.

Dynamic Properties of Three-Terminal Tungsten CMOS-NEM Relays Under Nonlinear Tapping Mode

In this paper, the phase noise of a 24-MHz complimentary metal–oxide–semiconductor microelectromechanical systems (CMOS-MEMS) oscillator with zero-level vacuum package is studied. We characterize and analyze the nonlinear regime of each one of the modules that compose the oscillator (CMOS sustaining-amplifier and MEMS resonator). As we show, the presented resonator exhibits a high nonlinear behavior. Such a fact is exploited as a mechanism to stabilize the oscillation amplitude, allowing us to maintain the sustaining-amplifier working in the linear regime. Consequently, the nonlinear resonator becomes the main close-to-carrier phase noise source. The sustaining amplifier, which functions as a phase shifter, was developed such that MEMS operation point optimization could be achieved without an increase in circuitry modules. Therefore, the system saves on area and power, and is able to improve the phase noise 26 dBc/Hz (at 1-kHz carrier frequency offset).

CMOS-NEM relay based on tungsten VIA layer

In this paper we will discuss the CMOS circuit design strategies and main results for an all-CMOS MEMS based oscillator in order to reduce the oscillator far-to-carrier noise (which is limited by the circuit noise) and the close-to-carrier noise (which is limited by both the amplifier phase noise and the MEMS quality factor). The feasibility of using the Via layer of a commercial CMOS technology to design a monolithical integrated CMOS-MEMS oscillator will be demonstrated.