Pressure Coefficient Of Frequency Research Articles

The influence of temperature on the pressure sensitivity of surface acoustic wave pressure sensor

This paper illustrates the effect of temperature on AlN-based surface acoustic wave (SAW) pressure sensor. The resonance frequency of the SAW pressure sensor at different temperatures and pressures have been simulated and extracted in the COMSOL Multiphysics software, and the pressure coefficient of frequency (PCF) was obtained as 157.31 ppm/MPa through the linear fitting. The PCF at room temperature was experimentally measured to be 101.46 ppm/MPa in the pressure range of 0 MPa to 2 MPa. In addition, the effect of temperature on PCF has been investigated by simulation analysis and it was found that PCF increases with temperature due to thermal mismatch between different films rather than the effect of temperature on the Young's modulus. The experimental findings have proved the increase of PCF with temperature and the obtained data are found in good agreement with simulation results.

Surface acoustic wave pressure sensor on ScAlN/3C-SiC/Si layer structure incorporating biomimetic microcantilever: modelling and performance enhancement

This paper presents a bio-inspired cantilever-type SAW pressure sensor based on Scandium-doped AlN (ScAlN)/3CSiC/Si layer structure. The proposed biomimetic microcantilever is configured with stress concentration region (SCR) comprising of a series of narrow slits. For a given depth, by properly setting the number and the width of those slits for a given depth, homogeneous stress/strain distribution in vicinity of SCR are achieved. Furthermore, multi-physics finite element modeling for evaluating the pressure coefficient of frequency (PCF) of a one-port SAW resonant sensor is performed and validated. Then the PCF for the proposed SAW pressure sensor with the optimized biomimetic microcantilever is analyzed. The dependence of ScAlN thin film thickness h ScAlN and scandium-doped concentration r of Sc r Al1-r N thin film on PCF for different SAW modes including Rayleigh mode and Sezawa mode are calculated. The investigation results show that the maximum PCF of −111 ppm bar−1 can be achieved for Rayleigh mode, which is 2.4 times larger than that of the previously reported ZnO/Si structure. In addition, its PCF has weak dependence on h ScAlN, which are quite favorable for manufacturing pressure sensors with good reproducibility. The conceived bio-inspired cantilever-type SAW devices based on ScAlN/3 CSiC/Si structure will open the door to develop pressure sensors with a stable and reliable performance and enhanced sensitivity.

GaN Membrane Supported SAW Pressure Sensors With Embedded Temperature Sensing Capability

This paper presents the fabrication and characterization of a GHz operating surface acoustic wave (SAW)-based pressure sensor on a 1.2- $\mu \text{m}$ -thin GaN membrane. Two types of interdigitated transducers are manufactured using electron beam nanolithography to obtain finger and interdigit spacing widths, one with 170 nm and the other 200-nm-half pitch. Micromachining techniques are used to obtain the 1.2- $\mu \text{m}$ -thin membrane. The resonance frequency shift of the SAW, the pressure sensitivity, $s_{p}$ , as well as the pressure coefficient of frequency (PCF), were experimentally determined and analyzed, both for the Rayleigh as well as for the symmetrical Lamb propagation mode, in the 1 to 7 Bar pressure range. Record values for $s_{p}$ (up to 6 MHz/Bar) and PCF (up to 537 ppm/Bar) have been obtained, especially for the symmetrical Lamb propagation mode also due to the very high frequency operation (5–11.5 GHz). The effect of different orientations of the SAW device (in the $\textrm {[1}\bar {\textrm {1}} \textrm {00]}$ and $\textrm {[11}\bar {\textrm {2}} \textrm {0]}$ directions) on the frequency response and sensitivity is also analyzed. The possibility to determine simultaneously the pressure and the temperature with the same SAW structure operating as a dual sensor has been demonstrated.

Diaphragm shape effect on the sensitivity of surface acoustic wave based pressure sensor for harsh environment

Aluminum Nitride (AlN) based surface acoustic wave (SAW) pressure sensors for harsh environment applications are of great interest in recent years. Such sensor employs a thick diaphragm (∼50 μm) to endure the high pressure, but this seriously limits the sensitivity of these devices. Understanding of the working mechanism and the effect of geometrical parameters will yield the design principles to achieve improved sensitivity. In this letter, the effect of diaphragm on the performance of SAW pressure sensors is studied. AlN based SAW resonators on (100) wafer with different diaphragm shapes are fabricated, packaged, and characterized. Pressure coefficient of frequency (PCF) of pressure sensors with circular diaphragm, rectangular diaphragm (small aspect ratio) and rectangular diaphragm (large aspect ratio) is found to be 0.071 ppm/psi, 0.038 ppm/psi, and −0.171 ppm/psi, respectively. The longitudinal and lateral strains along the SAW propagation direction (〈100〉 direction) have the opposite effects on the frequency change, i.e., longitudinal strain increases the resonant frequency while lateral strain decreases the resonant frequency. Hence, the measured PCF is a combined effect of the two strains, whereby increase in lateral strain results in lower PCF. The ratio of longitudinal/lateral strain is determined by the diaphragm shape. The rectangular diaphragm (large aspect ratio) with only lateral strain thus shows negative PCF. Additionally, by changing the wafer plane, SAW propagation direction and ratio of longitudinal/lateral strains may help to enhance the primary strain effect and minimize the reverse strain effect. This approach could further improve the sensitivity of pressure sensor without sacrificing its high pressure sensing range for harsh environment applications.

A Single FBAR-Based Temperature and Pressure Sensors

A novel temperature and pressure sensor based on a single film bulk acoustic resonator (FBAR) is designed. This FBAR support two resonant modes, which response opposite to the change of temperature. By sealed the back cavity of a back-trench membrane type FBAR with silicon wafer, an on-chip single FBAR sensor suitable for measuring temperature and pressure simultaneously is proposed. For unsealed device, the experimental results show that the first resonant mode has a temperature coefficient of frequency (TCF) of 69.5ppm/K, and the TCF of the second mode is -8.1ppm/K. After sealed the back trench, it can be used as a pressure sensor, the pressure coefficient of frequency (PCF) for the two resonant mode is -17.4ppm/kPa and -6.1 ppm/kPa respectively, both of them being more sensitive than other existing pressure sensors.