Lateral Strain Profile Research Articles

Piezoelectric Elliptical Plate Micromechanical Resonator With Low Motional Resistance for Resonant Sensing in Liquid

Key to realizing practical resonators for liquid-phase sensing applications is efficient electromechanical transduction and reasonable Q in liquid, which determine the motional resistance (Rm). Both lower Rm and high liquid phase Q are important for realizing a more stable close-loop oscillator to allow a lower detection limit. But Rm usually increases when scaling down resonator size, leading to weak output signals in liquid. This article describes a piezoelectrically transduced micromechanical elliptical plate resonator (EPR) targeting liquid-phase sensing applications. The proposed EPR delivers lower Rm relative to other disk-based modes and has a reasonable Q in water. These two features are critical for eventually realizing a closed-loop system to enable real-time frequency tracking for sensing applications. The low Rm arises from enhanced transduction efficiency associated with the modal lateral strain profile. The EPR's moderate liquid phase Q stems from transducing a stiff lateral bulk mode that increases energy storage. The proposed EPR can be scaled down more efficiently compared to other disk-based modes in the limit of mode shape distortion by anchors when scaling down the resonator below a threshold. Experimental results in water are demonstrated for a 500 μm by 400 μm EPR, which delivers an Rm of only 2.68 kQ in water without feedthrough cancellation. Scaling down the device to 300 μm by 200 μm, we demonstrate an Rm of just 5.5 kQ and Q of 245 in water. The proposed EPR topology boasts the lowest Rm among resonators immersed in liquid after normalizing over the device area.

Effect of geogrid on deformation response and resilient modulus of railroad ballast under cyclic loading

Laboratory investigations were carried out using process simulation test (PST) apparatus to assess the role of geogrid on the deformation response and resilient modulus of railroad ballast at different loading frequencies (f) varying from 10 to 40 Hz. The materials used for testing involved fresh granite ballast and subballast having mean particle sizes (D50) of 42 mm and 3.5 mm, and geogrids with different aperture shapes and sizes. The results from the laboratory investigations reveal that the degradation and deformation behavior of ballast is influenced by the loading frequency (f). The use of geogrids is shown to reduce the extent of deformations in ballast (both lateral and vertical) and its degradation (Bg: ballast breakage), but the effect of geogrid diminishes with the increase in frequency (f). The assessment of the lateral strain profiles along the ballast depth indicates that the geogrid influence zone (GIZ) is dependent on both the type of geogrid used and the loading frequency (f). The GIZ is found to vary from 38 mm (0.90 D50) to 237 mm (5.64 D50), with it being the lowest at f = 40 Hz and for geogrid having relatively larger apertures. Further, the geogrids are found to significantly enhance the resilient modulus (Mr) of ballast. In addition, the Mr is established to increase with f and Bg. The inclusion of geogrids also reduced the extent of vertical stress (σv) including the dynamic amplification factor (DAF).

Fully Differential Piezoelectric Button-Like Mode Disk Resonator for Liquid Phase Sensing.

We present a unique lateral shear resonance mode excited in a microelectromechanical (MEM) disk resonator. We refer to this proposed mode as the button-like (BL) mode. The BL mode has a characteristic lateral strain profile (based on the sum of orthogonal strain components in the plane of fabrication) which resembles a shirt button, hence our choice of name for this mode. The strain profile of the BL mode is highly suited for piezoelectric transduction. Like the more widely reported wine-glass (WG) or elliptical mode, the BL mode offers feedthrough cancellation through fully differential transduction. However, compared to the WG mode, the BL mode possesses a higher coupling coefficient ( [Formula: see text]) and a higher quality ( Q ) factor for the same disk radius. These advantages make the BL mode highly attractive for realizing electrically addressed MEM resonators for liquid-phase sensing. This paper examines various design aspects pertaining to the BL mode: tether geometry, characterization setup, size of disk, and even the effect of the gap around the disk on the Q factor. The highest Q factor measured in water is 410 based on a disk with a radius of [Formula: see text]. The lowest motional resistance in water is 1.36 [Formula: see text] based on a disk with a radius of [Formula: see text].

Application of Optical-Fiber Bragg Grating Sensors in Monitoring the Rail Track Deformations

The lateral flow of ballast during the passage of trains can reduce the stability of rail tracks. Therefore, it is important to monitor and restrain the movement of ballast accordingly in order to prevent track misalignment. This current study explored the use of optical-Fiber Bragg Grating (FBG) sensors to measure the lateral displacement of unreinforced and geogrid-reinforced ballast. The tests were conducted on fresh latite basalt at a loading frequency of 20 Hz and up to 250 000 load cycles. The test results showed that the FBG sensing system is fully capable of measuring the lateral displacement of ballast under high-frequency cyclic loading. A comparison of strains obtained from FBGs installed at different depths along the ballast depth is made and the lateral strain profiles are measured. Moreover, an empirical model to convert the FBG strains to an equivalent lateral displacement of ballast is proposed to effectively use this technology in real-time monitoring of track deformations.

The lateral displacement response of geogrid-reinforced ballast under cyclic loading

Ballast being an unbounded granular medium spreads laterally when subjected to high-frequency cyclic loading. To reduce lateral movement of ballast and to optimize track performance, rail tracks can be reinforced with geogrid. In this study, a novel large-scale process simulation test (PST) apparatus that can capture the lateral strain variation upon loading is described. Laboratory tests were conducted to explore the deformation and degradation response of both unreinforced and reinforced ballast under high-frequency cyclic loading. Fresh Latite basalt having an average particle size (D50) of 35 mm, and geogrids with different aperture sizes were tested. The laboratory experimental results reveal that the ballast deformation (both lateral and vertical) and the breakage during cyclic loading are influenced by the geogrid type and its placement location. Moreover, the lateral strain profiles along the ballast depth have been measured and the geogrid influence zone (GIZ), defined as the distance to which the effect of geogrid in arresting the lateral displacement of ballast exists, has been determined. The GIZ is found to vary from 160 mm (4.60D50) to 225 mm (6.45D50) depending on the location of the geogrid. In addition, the optimum geogrid position in the track has been identified to be 65 mm above the subballast. The test results also exemplify the ability of geogrid to arrest lateral displacement of ballast, reduce settlement and minimize particle degradation under high-frequency cyclic loading.

Asymmetrically strained all-silicon multi-gate n-Tunnel FETs

This paper reports all-silicon asymmetrically strained Tunnel FET architectures that feature improved subthreshold swing and I on / I off characteristics. We demonstrate that a lateral strain profile corresponding to at least 0.2 eV band-gap shrinkage at the BTB source junction could act as an optimized performance Tunnel FET enabling the cancellation of the drain threshold voltage. To implement a real device, we demonstrate using GAA Si NW with asymmetric strain profile using two local stressor technologies to have >4–5 GPa peak of lateral uniaxial tensile stress in the Si NW.

Lateral Strain Profile as Key Technology Booster for All-Silicon Tunnel FETs

In this letter, we propose a lateral asymmetric strain profile in a silicon nanowire or ultrathin silicon film as a key technology booster for the performance of all-silicon tunnel FETs. We demonstrate by simulation that a Gaussian tensile-strain profile with a maximum placed at the source side of a nanowire tunnel FET with a 50-nm channel length provides an optimized solution for a low-standby-power switch. This leads to the following: (1) ultralow I off (more than three decades lower than in the case of a device on uniformly strained silicon); (2) boosting of I on (more than one decade higher compared to a silicon reference); and (3) an average subthreshold swing S avg of 48 mV/dec at room temperature. Furthermore, the inherent finite drain threshold voltage of the tunnel FET, which could be a disadvantage for logic design with tunnel FETs, is exponentially reduced with the strain-induced bandgap shrinkage at the source side.

Nanoscale strain characterisation for ultimate CMOS and beyond

Strain engineering is used to maintain Moore's Law in scaled CMOS devices and as a technology booster for More-than-Moore devices in the nanoelectronics era. Strain is crucial because of its ability to increase electron and hole mobilities in Si. However, accurate correlations between electrical performance and strain measurements are needed to enable the necessary feedback between materials, processing and devices to achieve best possible solutions. In this work, we outline new methods for sensitive 3D profiling of strain on a nanoscale. High-resolution vertical and lateral strain profiles applicable to both global (biaxial) and process-induced (uniaxial) strained Si devices are demonstrated. Raman spectroscopy is pushed to its present limit for precise analysis of strain in small geometry devices, including the use of tip-enhanced Raman spectroscopy (TERS) to improve the spatial resolution further. TERS maps are compared with atomic force microscopy data collected simultaneously and show that variations in surface morphology correlate directly with strain in the epitaxial layers. Sub-nm strain profiling is applied to strained Si and SiGe MOSFET channels. Strain is profiled across patterned uniaxial strained-Si-on-insulator structures and analysed in bended nanowire transistors. Finally strain is investigated across the channel regions of electrically measured SiGe p-MOSFETs. Good agreement between nanoscale strain measurements and finite element modelling is demonstrated. Sample preparation is included in the analysis and genuine effects of processing are investigated.

X-ray study of lateral strain and composition modulation in an AlGaAs overlayer induced by a GaAs lateral surface grating

A lateral surface grating has been prepared by holographic photolithography followed by wet chemical etching on a slightly misaligned GaAs [001] substrate. The structural parameters were investigated before and after thermal annealing by triple-axis high resolution x-ray diffraction (HRXRD) and scanning electron microscopy (SEM). In particular HRXRD was used to collect reciprocal space maps providing periodicity and shape of the grating. After overgrowth of the free standing nanostructure with AlxGa1−xAs the HRXRD technique fails. Only first order grating truncation rods remain in the (004) HRXRD map. They disappear completely running asymmetric reflections. On the other hand SEM at the cleavage plane reveals the perfection of the overgrowth process and the smoothness of the sample surface. Thus nondestructive analysis of the buried lateral nanostructure was performed by triple-axis x-ray grazing incidence diffraction using synchrotron radiation. This method is exclusively sensitive to the lateral strain profile and provides the possibility of depth resolution. Using two complementary in-plane reflections we found lateral strain modulation within the GaAlAs overlayer accompanied by a compositional modulation with the same period as the grating itself. This periodicity still appears close below the sample surface.