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This paper presents a technique for suppressing specific resonance modes of micromechanical resonators by mechanical means. In particular, attaching multiple miniaturized beam structures with properly designed dimensions acting as anti-resonating tuned mass dampers (TMD’s) to a micromechanical clamped-clamped beam (CC-beam) resonator based on a CMOS-MEMS process platform successfully attenuate the dynamic frequency response of the fundamental mode while retaining the $2^{\mathrm {nd}}$ harmonic mode of the CC-beam. The measured results show that the frequency transmission response of the TMD-embedded CC beam drops as much as $\sim 12$ dB compared to that of a reference resonator. An analytical model is used to study the effects of the parameter variations of the TMD structures. This technique provides an alternative approach to mechanically suppressing vibration modes for the micromechanical resonators that cannot employ the conventional quarter-wavelength support technique. [2020-0289]

A CMOS-MEMS based vibro-impacting resonator with double sided stopper structures has been demonstrated that exhibits a wider tapping bandwidth up to 2.3× compared to the conventional single sided counterpart. In particular, a folded-beam capacitive-comb transduced resonator fabricated using a $0.35-\mu \mathrm{m}$ CMOS process is driven impacts the stopper structure on either side of the shuttle with an air gap of $0.6\ \mu \mathrm{m}$ and results in a flat region in the frequency transmission response, where the tapping occurs, around the resonance frequency of 125 kHz. The effective stiffness of the system and therefore the resonance frequency abruptly increase during tapping, leading to duffed transmission response curves towards higher frequency. Conceptually, the addition stopper in the doubled-sided impacting resonator effects additional stiffness hardening that in turn pushes the impact induced resonance frequency even further. A numerical model established here arrives the same trend about tapping bandwidth widening in the structure with double-sided stoppers.

Frequency stability of micromechanical resonators operating in the nonlinear tapping mode was investigated. In particular, a CC-beam oxide-rich resonator based on a CMOS-MEMS process platform exhibits higher frequency stability at the bifurcation points in the nonlinear tapping frequency transmissions, yielding a ∼2× improvement of short-term Allen deviation compared to that at the midpoint of the tapping regime and that operating under the regular nonlinear spring softening (not entering the tapping mode yet). Differing from the previous studies on stability of MEMS resonators in either nonlinear softening or hardening condition [1] [2], this work explores the frequency stability deeper into the tapping mode of MEMS resonators—essentially behaving as resoswitches with no electrical current flowing through the contact—where the devices are subject to highly nonlinear repulsive forces due to impact. The results would help facilitate not only the understanding of the nonlinear dynamics of resoswitches but also the determination of optimum operating points of the devices.

This paper demonstrates a 125-kHz micromechanical resoswitch-embedded zero quiescent power OOK/FSK communication receiver based on a CMOS-MEMS fabrication platform for low-frequency (LF) active RFID standby receiver applications. In particular, differing from the previously demonstrated receiver using a CMOS-incompatible Au fabrication process [1], this work utilizes a standard $0.35-\mu \mathrm{m}$ CMOS process to achieve a folded-beam comb-driven resoswitch with a digital decoder. Enabled by the key component of the resoswitch, the receiver realizes on-chip signal filtering, power amplification, and demodulation, all together consuming an averaged $10.46\ \mu\mathrm{W}$ when processing “1” and zero power for “0” and at standby. This demonstration verifies the efficacy of using low-cost, high-fidelity CMOS processes towards all-mechanical resoswitch-based RF applications.

A MEMS resoswitch-enabled surface coating condition-monitoring device is demonstrated as a proof of concept that successfully detects the existence of molecule coated on the structure surface. In particular, a CMOS-MEMS clamped-clamped beam (CC-beam) resoswitch exhibits a distinguishable change in the tapping bandwidth of the frequency response against different surface conditions while operating in the nonlinear cold switching mode. By salinizing the surface with (1H, 1H, 2H, 2H)-per-fluorodecyltrichlorosilane (CF 3 (CF 2 )7(CH 2 ) 2 SiCl 3 , FDTS), the resoswitch presents a tapping bandwidth extended from 17.37 kHz to 29.75 kHz due to lowered adhesion forces. The resoswitch-based surface condition could be employed to enable in situ monitoring of, for example, the anti-stiction coating often used in MEMS motion sensors.

A micromechanical CC-beam resonant switch, a.k.a. resoswitch, based on a 0.35-μm 2-poly-4-metal (2P4M) CMOS-MEMS process platform has been demonstrated. In particular, a 2.1-MHz resoswitch that employs (a) the mode-shape derived displacement difference along its CC-beam structure and (b) generic VIA layers available in the CMOS process to achieve displacement gain and metal tungsten-to-tungsten contact yields an average power gain of 23.46 dB when embedded in a simple switched-mode amplifier. Differing from previously reported resoswitches ([1]-[4]), this work demonstrates for the first time resoswitches developed on a standard CMOS process followed by a maskless release step identical to that in [5]. The widely available, low-cost CMOS processes would help expedite the development of resoswitches, which present as enabling components towards zero quiescent power mechanical receivers [2] [3].

This paper presents a micromechanical clamped–clamped beam (CC-beam) displacement amplifier based on a CMOS-MEMS fabrication process platform. In particular, a 2.0 MHz resonant displacement amplifier composed of two identical CC-beams coupled by a mechanical beam at locations where the two beams have mismatched velocities exhibits a larger displacement, up to 9.96×, on one beam than that of the other. The displacement amplification prevents unwanted input impacting—the structure switches only to the output but not the input—required by resonant switch-based mechanical circuits (Kim et al 2009 22nd IEEE Int. Conf. on Micro Electro Mechanical Systems; Lin et al 2009 15th Int. Conf. on Solid-State Sensors, Actuators, & Microsystems (TRANSDUCERS'09); Li et al 2013 17th Int. Conf. on Solid-State Sensors, Actuators, & Microsystems (TRANSDUCERS'13)). Compared to a single CC-beam displacement amplifier, theory predicts that the displacement amplifying CC-beam array yields a larger overall output displacement for displacement gain beyond 1.13 thanks to the preserved input driving force. A complete analytical model predicts the resultant stiffness and displacement gain of the coupled CC-beam displacement amplifier that match well with finite element analysis (FEA) prediction and measured results.

This letter characterizes the effect of surface conditions on the nonlinear responses of micromechanical resonant switches (aka “resoswitches”). In particular, a CMOS-MEMS clamped–clamped beam (CC-beam) resoswitch used as a testing vehicle exhibits variations in the magnitude of the frequency tapping bandwidth upon modification of the surface stiction force by salinization with (1H, 1H, 2H, 2H)-perfluorodecyltrichlorosilane (FDTS) and by altering the operating temperature of the resoswitch. The tapping bandwidth of the CC-beam resoswitch increases from 17.37 to 29.75 kHz after salinization and reduces from 36.75 to 26.06 kHz as the device temperature rises from 35 °C to 80 °C. The experiment of salinization, together with the theory prediction, verifies that FDTS coating would result in a lower surface energy and thus a lower attractive force between the contact surfaces. As a result, the resoswitch would exhibit a larger tapping bandwidth due to the reduction of the attractive force. In contrast, raising the temperature would induce an increase in the surface energy and in the contact asperity radius of curvature due to material softening, both of which cause the attractive force to increase. Understanding the surface condition dependence of the nonlinear tapping frequency response could pave the way toward applications not achieved by the existing technologies, such as in situ monitoring of the anti-stiction coating quality in MEMS motion sensors.