A Laterally Vibrating Lithium Niobate MEMS Resonator Array Operating at 500{\deg}C in Air

This paper is the first report of the high-temperature characteristics of a laterally vibrating piezoelectric lithium niobate (LiNbO$_{3}$) MEMS resonator array up to 500{\deg}C in air. After a high-temperature burn-in treatment, device quality factor (Q) is enhanced to 508 and the resonance shifts to a lower frequency and remains stable up to 500{\deg}C. During subsequent in situ high-temperature testing, the resonant frequencies of two coupled shear horizontal (SH0) modes in the array are 87.36 MHz and 87.21 MHz at 25{\deg}C and 84.56 MHz and 84.39 MHz at 500{\deg}C, correspondingly, representing a -3% shift in frequency over the temperature range. Upon cooling to room temperature, the resonant frequency returns to 87.36 MHz, demonstrating recoverability of device performance. The first- and second-order temperature coefficient of frequency (TCF) are found to be -95.27 ppm/{\deg}C and 57.5 ppb/{\deg}C$^{2}$ for resonant mode A, and -95.43 ppm/{\deg}C and 55.8 ppb/{\deg}C$^{2}$ for resonant mode B, respectively. The temperature-dependent quality factor (Q) and electromechanical coupling coefficient ($k_{t}^{2}$) are extracted and reported. Device Q decreases to 334 after high-temperature exposure, while $k_{t}^{2}$ increases to 12.40%. This work supports the use of piezoelectric LiNbO$_{3}$ as a material platform for harsh environment radio-frequency (RF) resonant sensors (e.g. temperature and infrared)

Self organising maps for visualising and modelling

The paper describes the motivation of SOMs (Self Organising Maps) and how they are generally more accessible due to the wider available modern, more powerful, cost-effective computers. Their advantages compared to Principal Components Analysis and Partial Least Squares are discussed. These allow application to non-linear data, are not so dependent on least squares solutions, normality of errors and less influenced by outliers. In addition there are a wide variety of intuitive methods for visualisation that allow full use of the map space. Modern problems in analytical chemistry include applications to cultural heritage studies, environmental, metabolomic and biological problems result in complex datasets. Methods for visualising maps are described including best matching units, hit histograms, unified distance matrices and component planes. Supervised SOMs for classification including multifactor data and variable selection are discussed as is their use in Quality Control. The paper is illustrated using four case studies, namely the Near Infrared of food, the thermal analysis of polymers, metabolomic analysis of saliva using NMR, and on-line HPLC for pharmaceutical process monitoring

Characterization of the piezoresistance in highly doped p-type 3C-SiC at cryogenic temperatures

This paper reports on the piezoresistive effect in p-type 3C-SiC thin film mechanical sensing at cryogenic conditions. Nanothin 3C-SiC films with a carrier concentration of 2 × 1019 cm-3 were epitaxially grown on a Si substrate using the LPCVD process, followed by photolithography and UV laser engraving processes to form SiC-on-Si pressure sensors. The magnitude of the piezoresistive effect was measured by monitoring the change of the SiC conductance subjected to pressurizing/depressurizing cycles at different temperatures. Experimental results showed a relatively stable piezoresistive effect in the highly doped 3C-SiC film with the gauge factor slightly increased by 20% at 150 K with respect to that at room temperature. The data was also in good agreement with theoretical analysis obtained based on the charge transfer phenomenon. This finding demonstrates the potential of 3C-SiC for MEMS sensors used in a large range of temperatures from cryogenic to high temperatures

Lithography and etching-free microfabrication of silicon carbide on insulator using direct UV laser ablation

Silicon carbide (SiC)‐based microsystems are promising alternatives for silicon‐based counterparts in a wide range of applications aiming at conditions of high temperature, high corrosion, and extreme vibration/shock. However, its high resistance to chemical substances makes the fabrication of SiC particularly challenging and less cost‐effective. To date, most SiC micromachining processes require time‐consuming and high‐cost SiC dry‐etching steps followed by metal wet etching, which slows down the prototyping and characterization process of SiC devices. This work presents a lithography and etching‐free microfabrication for 3C‐SiC on insulator‐based microelectromechanical systems (MEMS) devices. In particular, a direct laser ablation technique to replace the conventional lithography and etching processes to form functional SiC devices from 3C‐SiC‐on‐glass wafers is used. Utilizing a single line‐cutting mode, both metal contact shapes and SiC microstructures can be patterned simultaneously with a remarkably fast speed of over 20 cm s−1. As a proof of concept, several SiC microdevices, including temperature sensors, strain sensors, and microheaters, are demonstrated, showing the potential of the proposed technique for rapid and reliable prototyping of SiC‐based MEMS