Very High Frequency Silicon Nanowire Electromechanical Resonators

Abstract

We demonstrate very high frequency (VHF) nanomechanical resonators based upon single-crystal silicon nanowires (SiNWs), which are prepared by the bottom-up chemical synthesis. Metallized SiNW resonators operating near 200 MHz are realized with quality factor Q ≈ 2000−2500. Pristine SiNWs, with fundamental resonances as high as 215 MHz, are measured using a VHF readout technique that is optimized for these high resistance devices. The pristine resonators provide the highest Q's, as high as Q ≈ 13 100 for an 80 MHz device. SiNWs excel at mass sensing; characterization of their mass responsivity and frequency stability demonstrates sensitivities approaching 10 zeptograms. These SiNW resonators offer significant potential for applications in resonant sensing, quantum electromechanical systems, and high frequency signal processing.Nanoelectromechanical systems (NEMS), particularly nanomechanical resonators vibrating at high frequencies, 1 are being actively explored for applications including resonant sensors for ultrahigh-resolution mass sensing, 2 force detection, 3 quantum electromechanics, 4 electromechanical signal generation and processing, 5 and high-speed logic and computation. 6 These NEMS resonators are usually made by topdown lithographic techniques and surface nanomachining, which together enable realization of nanomechanical devices with considerable complexity and functionality. By contrast, chemical-synthesis-based bottom-up approaches now provide nanowires with high crystalline quality, perfectly terminated surfaces, and sizes down to the molecular scale. These represent a new class of building blocks for NEMS resonators that offer unique attributes. Si nanowires (SiNWs) are, perhaps, among the most intriguing given silicon's preeminent role in micro-and nanoelectronics and as a structural material for micro-and nanoelectromechanical systems. Development of SiNW-NEMS, however, has been impeded by difficulties in suspending SiNWs to give them mechanical freedom and in subsequent device integration. Recently, a hybrid process has been developed to fabricate SiNWs suspended over microtrenches by employing vapor-liquidsolid (VLS) epitaxial growth.8 This device geometry facilitates the direct probing of mechanical properties of SiNWs via static deflection. 9,10 In this Letter, we describe the first demonstration of resonant mechanical devices operating at very high frequencies (VHF) that are based on such suspended SiNWs. We demonstrate robust SiNW resonators vibrating at frequencies greater than 200 MHz. Furthermore, comprehensive measurements of the resonance characteristics, quality factors, and resonator frequency stability show that these bottom-up SiNWs provide excellent performance. These devices expand and advance prospects for NEMS resonator technologies and enable new possibilities for applications. Parts a and b of Figure 1 show the typical suspended SiNWs in microtrenches. The detailed synthetic procedure via VLS epitaxial growth has been described in ref 8. Briefly, the SiNW begins cry...

Phase Noise and Frequency Stability of Very-High Frequency Silicon Nanowire Nanomechanical Resonators

“…VHF resonators have been demonstrated using both metalized SiNWs better matched to 50Q (with -30nm/5nm Al/Ti metallization), and bare pristine SiNWs with 1100kQ resistances (doping dependent), as described in [4]. Here we highlight the robust VHF operations of SiNW resonators in both linear and nonlinear regimes, as shown in Figure 2 (a) with the measured response from a 188MHz metalized SiNW (SiNW-M188) and in Figure 2 (b) the data from an 80MHz pristine SiNW (SiNW-80).…”

“…SiNW transistors for nanoelectronics [1] and SiNW sensors for biotechnology [2] have received 4 considerable attention. With Si being a classical MEMS material, SiNWs are expected to possess excellent mechanical properties for NEMS applications.…”

“…However, progress has been hindered by the difficulty of making free-standing SiNWs, until the recent development of growth processes for suspended SiNW nanomechanical devices [3]. We have recently demonstrated VHF NEMS resonators based upon such SiNWs [4] and they have exhibited very attractive properties.…”

Effect of geometry in frequency response modeling of nanomechanical resonators

“…These applications have resulted in the specific tendency in one-dimensional nanomechanical resonators made of nanowires (NWs) in the direction of ever smaller and stiffer systems. Such nanoelectromechanical systems (NEMS) with nanomechanical resonators usually operate as transducers, where their mechanical behavior necessitates a sound modeling approach [4]. Recently, it has been shown that due to the dominance of the free surface in nanoscale structures, mechanical properties exhibit a pronounced size dependence [5].…”

Spatial mapping of multimode Brownian motions in high-frequency silicon carbide microdisk resonators

“…Intertwined with miniaturizing sizes, shape engineering and materials innovations in the underlying device structures further add great versatility to these advances. Resonant MEMS/NEMS have already taken a variety of shapes including singly-and doubly-clamped beams 13,14 , free-free beams 15,16 , nanowires and nanotubes 17,18 , stretched nanostrings 19 , square membranes 20,21 and circular disks 22,23 . These make a fascinating toolbox for exploring various resonance modes and degrees of freedom to enable new functions.…”