This paper focuses on the design and fabrication of a high-temperature piezoresistive pressure sensor with an integrated signal-conditioning circuit, which consists of an encapsulated pressure-sensitive chip, a temperature compensation circuit and a signal-conditioning circuit. A silicon on insulation (SOI) material and a standard MEMS process are used in the pressure-sensitive chip fabrication, and high-temperature electronic components are adopted in the temperature-compensation and signal-conditioning circuits. The entire pressure sensor achieves a hermetic seal and can be operated long-term in the range of −50 °C to 220 °C. Unlike traditional pressure sensor output voltage ranges (in the dozens to hundreds of millivolts), the output voltage of this sensor is from 0 V to 5 V, which can significantly improve the signal-to-noise ratio and measurement accuracy in practical applications of long-term transmission based on experimental verification. Furthermore, because this flexible sensor’s output voltage is adjustable, general follow-up pressure transmitter devices for voltage converters need not be used, which greatly reduces the cost of the test system. Thus, the proposed high-temperature piezoresistive pressure sensor with an integrated signal-conditioning circuit is expected to be highly applicable to pressure measurements in harsh environments.

The main limitation of high-temperature piezoresistive pressure sensors is the variation of output voltage with operating temperature, which seriously reduces their measurement accuracy. This paper presents a passive resistor temperature compensation technique whose parameters are calculated using differential equations. Unlike traditional experiential arithmetic, the differential equations are independent of the parameter deviation among the piezoresistors of the microelectromechanical pressure sensor and the residual stress caused by the fabrication process or a mismatch in the thermal expansion coefficients. The differential equations are solved using calibration data from uncompensated high-temperature piezoresistive pressure sensors. Tests conducted on the calibrated equipment at various temperatures and pressures show that the passive resistor temperature compensation produces a remarkable effect. Additionally, a high-temperature signal-conditioning circuit is used to improve the output sensitivity of the sensor, which can be reduced by the temperature compensation. Compared to traditional experiential arithmetic, the proposed passive resistor temperature compensation technique exhibits less temperature drift and is expected to be highly applicable for pressure measurements in harsh environments with large temperature variations.

In this letter, we present a sapphire direct bonding method using plasma surface activation, hydrophilic pre-bonding, and high temperature annealing. Through the combination of sapphire inductively coupled plasma etching and the direct bonding process, a vacuum-sealed cavity employable for high temperature applications is achieved. Cross-sectional scanning electron microscopy (SEM) research of the bonding interface indicates that the two sapphire pieces are well bonded and the cavity structure stays intact. Moreover, the tensile testing shows that the bonding strength of the bonding interface is in excess of 7.2 MPa. The advantage of sapphire direct bonding is that it is free from the various problems caused by the mismatch in the coefficients of thermal expansion between different materials. Therefore, the bonded vacuum-sealed cavity can be potentially further developed into an all-sapphire pressure sensor for high temperature applications.

The proposed method for measuring the liquid level focuses on the ultrasonic impedance and echo energy inside a metal wall, to which the sensor is attached directly, not on ultrasonic waves that penetrate the gas–liquid medium of a container. Firstly, by analyzing the sound field distribution characteristics of the sensor in a metal wall, this paper proposes the concept of an "energy circle" and discusses how to calculate echo energy under three different states in detail. Meanwhile, an ultrasonic transmitting and receiving circuit is designed to convert the echo energy inside the energy circle into its equivalent electric power. Secondly, in order to find the two critical states of the energy circle in the process of liquid level detection, a program is designed to help with calculating two critical positions automatically. Finally, the proposed method is evaluated through a series of experiments, and the experimental results indicate that the proposed method is effective and accurate in calibration of the liquid level outside a sealed metal container.

This study presents a novel method for determining the liquid level from the outside of a sealed container, which is based on the balance of echo energy received by two receiving sensors. The proposed method uses one transmitting transducer and two receiving sensors that are encapsulated in a coupling plane and arranged by certain rules. The calculation and comparison of echo energy are grounded on the difference ultrasonic impedance between gas and liquid media. First, by analyzing the propagation and attenuation characteristics of ultrasonic waves in a solid, an acoustic model for calculating the echo energy is established and simulated in MATLAB. Second, the proposed method is evaluated through a series of experiments. The difference and ratio of echo energy received by two receiving sensors are calculated and compared under two different coupling conditions. Two kinds of the sensors that are arranged by different rules are selected for measuring the liquid level, and the measurement are analyzed and discussed in detail. Finally, the experimental results indicate that the proposed method can meet the proposed accuracy requirements and can effectively solve the problems caused by some poor coupling conditions.

Deep Reactive Ion Etching (DRIE), as a key process in silicon micromachining, remains constrained in high-precision applications by sidewall angle deviation and aspect ratio limitations. This study systematically investigates the mapping relationship between process parameters and etching morphology, focusing on the following aspects: the influence mechanism of C₄F₈ passivation time and bottom RF power on sidewall perpendicularity; and the effect patterns of etch cycle count, single-step time, and bottom RF power on aspect ratio and top–bottom line width (CD) difference. The findings reveal that dynamic adjustment of bottom RF power significantly influences sidewall angle: incremental adjustment tends to cause sharp angles (decreased angular precision), while decremental adjustment tends to form obtuse angles. Simply increasing the cycle count leads to a bottleneck in etch depth growth. Combining incremental bottom RF power adjustment can overcome depth limitations but induces axial variation in aperture dimensions. Optimizing the passivation-to-etch time ratio effectively controls etch morphology characteristics. This study achieved an etch depth of 112.2 μm for a 5 μm wide trench with an overall aperture size difference of 0.279 μm, providing a theoretical basis and practical guidance for parameter optimization in DRIE processes for high-precision silicon structure fabrication.