We report radio frequency ͑rf͒ electrical readout of graphene mechanical resonators. The mechanical motion is actuated and detected directly by using a vector network analyzer, employing a local gate to minimize parasitic capacitance. A resist-free doubly clamped sample with resonant frequency ϳ34 MHz, quality factor ϳ10 000 at 77 K, and signal-to-background ratio of over 20 dB is demonstrated. In addition to being over two orders of magnitude faster than the electrical rf mixing method, this technique paves the way for use of graphene in rf devices such as filters and oscillators.
Quality factor (Q) is an important property of micro- and nano-electromechanical (MEM/NEM) resonators that underlie timing references, frequency sources, atomic force microscopes, gyroscopes, and mass sensors. Various methods have been utilized to tune the effective quality factor of MEM/NEM resonators, including external proportional feedback control, optical pumping, mechanical pumping, thermal-piezoresistive pumping, and parametric pumping. This work reviews these mechanisms and compares the effective Q tuning using a position-proportional and a velocity-proportional force expression. We further clarify the relationship between the mechanical Q, the effective Q, and the thermomechanical noise of a resonator. We finally show that parametric pumping and thermal-piezoresistive pumping enhance the effective Q of a micromechanical resonator by experimentally studying the thermomechanical noise spectrum of a device subjected to both techniques.
The chicken embryo has two functioning ductus arteriosi (DA) during development. These blood vessels connect the pulmonary arteries to the descending aorta providing a right-to-left shunt of blood away from the nonrespiring lungs and to the systemic circuit and chorioallanotic membrane. The DA consists of two distinct tissue types along its length, a muscular proximal portion and an elastic distal portion. During hatching, the DA must close for proper separation of systemic and pulmonary circulation. We examined the morphological changes of the chicken DA before, during, and after hatching. Occlusion of the proximal DA began during external pipping and was complete at hatching. Anatomical remodeling began as early as external pipping with fragmentation of the internal elastic lamina and smooth muscle actin appearing in the neointimal zone. By day 2 posthatch, the proximal DA lumen was fully occluded by endothelial cells and smooth muscle actin positive cells. In contrast, the distal DA was not fully occluded by day 2 posthatch. Increases in Po 2 of the blood serves as the main stimulus for closure of the mammalian DA. The responsiveness of the chicken proximal DA to oxygen increased during hatching, peaking during external pipping. This peak correlated with an increase in blood gas Po 2 and the initial occlusion of the vessel. The distal portion remained unresponsive to oxygen throughout hatching. In conclusion, the chicken DA begins to close during external pipping when arterial Po 2 increases and vessel tone is most sensitive to oxygen.
This paper presents the use of our approach to comprehensive measurements of the quality factor ( Q) of 1-MHz microelectromechanical system (MEMS) tuning fork resonators. We examined the most important mechanisms that are believed to limit the quality factor in MEMS tuning fork resonators (i.e., gas damping, thermoelastic dissipation (TED), anchor damping, and Akhiezer damping), and we were able to quantitatively account for each mechanism and to eliminate several from consideration. We take advantage of the elimination of TED at ∼120 K, where the linear coefficient of thermal expansion (CTE) becomes 0. These observations enabled the first direct examination of the strength of anchor damping in megahertz tuning fork resonators, allowing the study of the effect of anchor design and other factors. In this megahertz frequency range, the wavelength of elastic waves far exceeds the dimensions of the die, so commonly used models cannot make predictions of anchor damping. Our results show that elastic energy can escape from the resonator through the anchor(s) and still be retained within the die. We find that anchor damping in these megahertz resonators is impacted more by die attach structures at the boundaries of the die than by the resonator anchor designs within the die.[2018-0038] Index Terms-Quality factor, cryogenic experiments, thermoelastic dissipation, coefficient of thermal expansion, anchor damping.
The ability to deposit thin and conformal films has become of great importance because of downscaling of devices. However, because of nucleation difficulty, depositing an electrically stable and thin conformal platinum film on an oxide nucleation layer has proven challenging. By using plasma-enhanced atomic layer deposition (PEALD) and TiO 2 as a nucleation layer, we achieved electrically continuous PEALD platinum films down to a thickness of 3.7 nm. Results show that for films as thin as 5.7 nm, the Mayadas–Shatzkes (MS) model for electrical conductivity and the Tellier–Tosser model for temperature coefficient of resistance hold. Although the experimental values start to deviate from the MS model below 5.7 nm because of incomplete Pt coverage, the films still show root mean square electrical stability better than 50 ppm over time, indicating that these films are not only electrically continuous but also sufficiently reliable for use in many practical applications.
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