M. Riverola

3-terminal tungsten CMOS-NEM relay

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.

A monolithically integrated torsional CMOS-MEMS relay

We report experimental demonstrations of a torsional microelectromechanical (MEM) relay fabricated using the CMOS-MEMS approach (or intra-CMOS) which exploits the full foundry inherent characteristics enabling drastic reduction of the fabrication costs and batch production. In particular, the relay is monolithically integrated in the back end of line of a commercial standard CMOS technology (AMS 0.35 μm) and released by means of a simple one-step mask-less wet etching. The fabricated torsional relay exhibits an extremely steep switching behaviour symmetrical about both contact sides with an on-state contact resistance in the k-range throughout the on-off cycling test.

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

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.

CMOS-NEM relay based on tungsten VIA layer

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.

Torwards a fully-integrated CMOS microcalorimeter with on-chip quasi-digital output signal

We analyze and characterize the static and dynamic thermal response of two sub-micrometer scale metal beam resonators to evaluate its potential as resonant thermal sensors. The fabricated resonators are a cantilever and a CC-beam which resonant frequency, around 6.5 MHz and 15 MHz respectively, changes due to the heat received from a probe pad, acting as a sample stage, through a metal track. Unlike other works, where off-chip piezoelectric excitation and optical readout are used, the mechanical resonator constitutes the frequency-determining element of an oscillator circuit that is fully-integrated in a 0.35-μm CMOS chip. For this first prototypes a heat conduction efficiency of 5.5% has been obtained for the metal CC-beam and a temperature resolution at the sample stage as low as 3.5 mK. In addition, some sensor layout considerations are detailed to further increase the sensor performance in future designs.

Intrinsic feedthrough current cancellation in a seesaw CMOS-MEMS resonator for integrated oscillators

The parasitic feedthrough capacitance that inherently appears in capacitive transduced MEMS resonators presents two main drawbacks: it partially, or even totally, masks the magnitude of the resonance peak; and also, it reduces the π-phase transition produced by the resonance peak. This reduction in the phase transition not only complicates to meet the Barkhausens phase condition in oscillator systems, but also it reduces the quality factor, deteriorating in this way the phase noise performance of oscillator systems. In this paper, we report on the initial experimental demonstration of a dual-mode seesaw CMOS-MEMS resonator that intrinsically mitigates the effect of the parasitic current on the magnitude and phase of the resonance frequency. Finally, a dual-clock application with the presented dual-mode resonator is proposed and experimentally demonstrated.

Optimization of the Close-to-Carrier Phase Noise in a CMOS–MEMS Oscillator Using a Phase Tunable Sustaining-Amplifier

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).

Noise effects on resonator bias polarization in CMOS-MEMS oscillators

In this paper, the effects of noise components in the DC bias voltage of the MEMS-NEMS resonators, electrostatically driven and capacitively sensed over the total system behavior are studied. The effect of first, white noise and second, a pure tone, in power spectrum, phase noise and time jitter of the output signal of a CMOS MEMS-NEMS oscillator system are analyzed.

Ultra compact CMOS-MEMS oscillator based on a reliable metal-via MEMS resonators with noise-matched high-gain transimpedance CMOS amplifier

In this paper we present a high-transimpedance, low-noise and noise-matched pre-amplifier for integrated CMOS-MEMS sensing devices. The thermomechanical noise of a MEMS resonator has been characterized under atmospheric conditions in order to prove the low input noise of the designed transimpedance pre-amplifier. Results of the CMOS-MEMS system in a Pierce oscillator configuration demonstrates the lowest floor noise reported until now in a capacitively coupled CMOS-MEMS oscillator.

Passive temperature compensation method in nonlinear NEMS resonators based on the nonlinear duffing effect

This paper reports on the experimental study of the frequency thermal dependence of a DETF NEMS resonator operated in the nonlinear regime. We show that the linear dependence of the DETF resonator (251 ppm/°C) is compensated just by operating the resonator in the nonlinear regime, improving the thermal stability of the resonance frequency from 10100 ppm to 1600 ppm, over a temperature range from -40°C to 0°C. As a result, a new technique to passively compensate the thermal dependence of the resonance frequency in M/NEMS resonators is proposed.