Dzung Viet Dao

The Piezoresistive Effect of SiC for MEMS Sensors at High Temperatures: A Review

Silicon carbide (SiC) is one of the most promising materials for applications in harsh environments thanks to its excellent electrical, mechanical, and chemical properties. The piezoresistive effect of SiC has recently attracted a great deal of interest for sensing devices in hostile conditions. This paper reviews the piezoresistive effect of SiC for mechanical sensors used at elevated temperatures. We present experimental results of the gauge factors obtained for various poly-types of SiC films and SiC nanowires, the related theoretical analysis, and an overview on the development of SiC piezoresistive transducers. The review also discusses the current issues and the potential applications of the piezoresistive effect in SiC.

Development of a dual-axis thermal convective gas gyroscope

This paper presents the development of a dual-axis gas gyroscope, whose working principle is based on the convective heat transfer and thermoresistive effect of lightly doped silicon. The working principle and the cross-sensitivity of the gas gyroscope are also analyzed. Experiments were performed to confirm the simulation results and good agreement has been achieved. The measured sensitivities for the X-axis and Y-axis were 0.107 mV deg−1 s−1 and 0.102 mV deg−1 s−1, respectively. Compared with a gyroscope of the same configuration but using tungsten as a sensing element, this gyroscope has 42 times greater sensitivity and one quarter the power consumption. These advantageous characteristics are inherited from the high TCR and high resistance of lightly doped p-type silicon. Nonlinearity and cross-sensitivity were measured to be smaller than 0.07% FS and 0.5% FS, respectively. The effect of acceleration on the sensitivity is 0.02 (deg s−1)/g and the measurement resolution based on sensitivity and noise analyses is 0.05 deg s−1. The relations between sensor performance, power consumption and ambient temperature were also realized.

Development and Analysis of a Sliding Tactile Soft Fingertip Embedded With a Microforce/Moment Sensor

We describe the development of a tactile hemispherical soft fingertip (FT) of a size similar to that of a human thumb. The sensory core consists of a microscaled force/torque sensor that can output one component of force and two components of moment simultaneously, which was developed beforehand. This sensor is embedded in a polyurethane rubber hemispherical dome to form a complete soft, compliant, and perceptible robotic FT. This system is designed for easy fabrication, high reliability in outputting signals, and stable operation. Static and dynamic mathematical analyses were utilized to investigate the responses of the sensor during the typical sliding motion of an FT. This was followed by experiments to show its potential in tactile and texture recognition. Especially, incipient-slip detection, which is critical in grasping manipulations, can be assessed properly and in a timely way. The development of this tactile FT is considered significant in the field of dexterous manipulation.

Micro/nano-mechanical sensors and actuators based on SOI-MEMS technology

MEMS (micro-electro-mechanical systems) technology has undergone almost 40 years of development, with significant technology advancement and successful commercialization of single-functional MEMS devices, such as pressure sensors, accelerometers, gyroscopes, microphones, micro-mirrors, etc. In this context of MEMS technology, this paper introduces our studies and developments of novel micro/nano-mechanical sensors and actuators based on silicon- on-insulator (SOI)-MEMS technology, as well as fundamental research on piezoresistive effects in single-crystal silicon nanowires (SiNWs). In the first area, novel mechanical sensors, such as 6-DOF micro-force moment sensors, multi-axis inertial sensors and micro-electrostatic actuators developed with SOI-MEMS technology will be presented. In the second area, we have combined atomic-level simulation and experimental evaluation methods to explain the giant piezoresistive effect in single crystalline SiNWs along different crystallographic orientations. This discovery is significant for developing more highly sensitive and miniaturized mechanical sensors in the near future.

Investigation of strain sensing effect in modified single-defect photonic crystal nanocavity

This paper reports the theoretical and experimental investigations on the strain sensing effect of a two dimensions (2D) photonic crystal (PhC) nanocavity resonator. By using the finite element method (FEM) and finite difference time domain (FDTD) simulations, the strain sensitivity of a high quality factor PhC nanocavity was calculated. Linear relationships between the applied strain and the shift in the resonant wavelength of the cavity were obtained. A single-defect silicon (Si) PhC cavity was fabricated, and measurements of the strain sensitivity were performed. Good agreement between the experimental and simulation results was observed.

Thickness dependence of the piezoresistive effect in p-type single crystalline 3C-SiC nanothin films

This paper reports, for the first time, the piezoresistive effect of p-type single crystalline 3C-SiC nanothin films grown by LPCVD at low temperature. Compared to thick SiC films, the gauge factors of the 80 nm and 130 nm films decreased remarkably. This result indicates that the crystal defect at the SiC/Si interface has a significant influence on the piezoresistive effect of ultra-thin film p-type 3C-SiC.

Fundamental piezoresistive coefficients of p-type single crystalline 3C-SiC

The orientation dependence of the piezoresistive effect of p-type single crystalline 3C-SiC thin film grown on a (100)Si wafer was characterized. The longitudinal, transverse gauge factors in [100] orientation, and longitudinal gauge factor in [110] orientation were found to be 5.8, −5.2, and 30.3, respectively. The fundamental piezoresistive coefficients π11, π12, and π44 of p-type 3C-SiC were obtained to be 1.5 × 10−11 Pa−1, −1.4 × 10−11 Pa−1, and 18.1 × 10−11 Pa−1, respectively. From these coefficients, the piezoresistive effect in any crystallographic orientation in p-type single crystalline 3C-SiC can be estimated, which is very valuable in designing micro-mechanical sensors.

Graphite on paper as material for sensitive thermoresistive sensors

This paper reports on the thermoresistive properties of graphite on paper (GOP). A negative temperature coefficient of resistance (TCR) from −2900 to −4400 ppm K−1 was observed for the GOP. This negative and large TCR is attributed to an increase in the thermionic emission current over a low potential barrier with increasing temperature. The potential barrier was found to be 33 meV between the graphite grains. The paper also demonstrates the use of the GOP in a highly sensitive (0.83 mV (m s−1)−0.8 mW−1) GOP-based anemometer, indicating strong feasibility of using this material for low-cost and sensitive thermal sensing applications.

Charge transport and activation energy of amorphous silicon carbide thin film on quartz at elevated temperature

We report on the temperature dependence of the charge transport and activation energy of amorphous silicon carbide (a-SiC) thin films grown on quartz by low-pressure chemical vapor deposition. The electrical conductivity as characterized by the Arrhenius rule was found to vary distinctly under two activation energy thresholds of 150 and 205 meV, corresponding to temperature ranges of 300 to 450 K and 450 to 580 K, respectively. The a-SiC/quartz system displayed a high temperature coefficient of resistance ranging from −4,000 to −16,000 ppm/K, demonstrating a strong feasibility of using this material for highly sensitive thermal sensing applications.

Piezoresistive Effect of p-Type Single Crystalline 3C-SiC Thin Film

This letter presents for the first time the piezoresistive effect of p-type single crystalline 3C-SiC thin film. The 3C-SiC thin film was epitaxially grown on (100) p-type Si substrate using the low-pressure chemical vapor deposition process. The grown 3C-SiC was doped in situ with aluminum to form p-type semiconductor with carrier concentration of 5×1018 cm-3 and sheet resistance of about 40 kΩ/□. Longitudinal and transverse gauge factors (GFs) of the 3C-SiC in [110] orientation at room temperature (23°C) were 30.3 and -25.1, respectively. These results indicated that the p-type single crystalline 3C-SiC possessed a higher GF than the previously reported results in p-type polycrystalline 3C-SiC.