Tunable mechanical coupling between driven microelectromechanical resonators

Abstract

We present a microelectromechanical system, in which a silicon beam is attached to a comb-drive actuator, that is used to tune the tension in the silicon beam, and thus its resonance frequency. By measuring the resonance frequencies of the system, we show that the comb-drive actuator and the silicon beam behave as two strongly coupled resonators. Interestingly, the effective coupling rate (∼ 1.5 MHz) is tunable with the comb-drive actuator (+10%) as well as with a side-gate (−10%) placed close to the silicon beam. In contrast, the effective spring constant of the system is insensitive to either of them and changes only by ±0.5%. Finally, we show that the comb-drive actuator can be used to switch between different coupling rates with a frequency of at least 10 kHz.Micro-and nanoelectromechanical resonators have attracted much attention thanks to their potential application as sensors [1][2][3][4][5][6][7][8], filters [9][10][11], amplifiers [12,13], and logic gates [14], with frequencies varying from the kHz to the GHz range [15][16][17]. By applying tension, the resonance frequencies can be tuned in-situ [18][19][20]. This is usually done by applying a DC voltage to a nearby gate to induce a deformation of the resonator via the electrostatic potential [21][22][23]. However, one does not only induce tension by applying an electrostatic potential, but one also changes the number of charge carriers [24][25][26], which both affect the properties of the resonator [27,28]. An ideal candidate to circumvent this problem is the comb-drive actuator, which is nowadays widely used to detect accelerations and rotations as well as to manipulate, stretch, or move objects [29][30][31][32][33]. By mechanically fixing a resonator to a comb-drive, one can purely mechanically induce strain in the resonator. Depending on the type of comb-drive actuator, this induced strain can be either tensile or compressive. The former allows the disentanglement of strain and charge carrier density effects in mechanical resonators, whereas the latter is particularly relevant to gain control over buckling modes in mechanical resonators [34,35].Coupled micro-and nanomechanical resonators are known to show sensitive sympathetic oscillation dynamics that show better performance in potential applications than a single resonator [36][37][38][39][40]. One major challenge for this type of resonators is an in-situ control over the coupling [41]. From a fundamental point of view, a tunable mechanical coupling is interesting because of the feasibility to coherently manipulate phonon populations in coupled resonators [42,43] and to create intrinsically localized modes [44]. From an applied point of view, researchers are able to build novel mass sensors, bandpass filters, and single-electron detectors [45][46][47]. Fast in-situ control over the coupling between mechanical resonators is an important step towards mechanical logic gates [48]. Comb drives are suspended microelectromechanical sys- The scale bars indicate 20 µm, 2 µm and 10 µm, from left to right. T...

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