## 1 Introduction  
The piezoresistive effect of a semiconductor was first discovered in the 1950s, which is the theoretical basis of most pressure sensors [1, 2, 3]. In addition to piezoresistive sensors, several different transduction mechanisms have been applied to convert pressures or strains to signals, such as inductance, capacitance, piezoelectricity, and resonance, which can be detected on circuitry [4, 5]. Among these designs, piezoresistive sensors are generally accepted due to their simple construction and low energy consumption [6]. The micro pressure sensors have been greatly developed and played a pivotal role in the automobile industry, aerospace industry, and medical equipment with the promotion of MEMS technology [7, 8, 9, 10, 11]. In marine engineering, pressure sensors are commonly used in applications involving high pressure up to several megapascal (MPa), high temperature up to several hundred degrees Celsius, and moist external conditions. However, some intrinsic pitfalls of the silicon piezoresistive pressure sensor, such as inadequate performance in harsh environment, e.g., high pressure or high temperature, and output drift due to temperature variation, have limited its application in marine settings. In order to improve the performance of the micro piezoresistive pressure sensor, numerous studies have focused on optimization of structure, fabrication, and encapsulation. [PERSON] et al. [12] introduced a monolithic composite MEMS pressure sensor with an effective range of 450 kPa. [PERSON] et al. [13] modified the structure by integrating rod beams in a silicon diaphragm. A pressure range of 0-689.5 kPa was achieved. [PERSON] et al. [14] fabricated two micro pressure sensors based on polysilicon on insulator (PolySOI) and amorphous silicon on insulator (a-SOI). These two sensors provided a pressure range of 0-1 MPa. [PERSON] et al. [15] presented the fabrication and electromechanical characterization of silicon-based 3D force micro sensors with piezoresistive gauges. The high sensitivity, the high linearity, and the low hysteresis of the sensors submitted to a normal force are obtained. [PERSON] et al. [16] incorporated FEM (finite element method) to give suggestions on the selection of parameters for the piezoresistors, such as shape and the position on the sensitive diaphragm. To prevent micro sensors from being damaged by external environment, most pressure sensors are encapsulated by silicone rubber. However, a large deformation of silicone rubber under a high pressure could lead to a fracture of bonding wires. Previous published work [17; 18] has presented an anticorrosive PDMS (polydimethylsiloxane) coating to prevent the conductive layer of a strain sensor from being damaged by corrosive external environment. In addition, [PERSON] et al. [19] spun polyimide film onto the electrode of the sensor to protect it from the humid environment. However, hardly any previous research has focused on the performance and protection of the micro sensors under a harsh environment, such as high pressure, high temperature, or moist corrosive electrolyte environment, which will lead to a shortening of the micro sensor life. Therefore, our work aims at resolving the contradiction between the output performance and stability with a miniature size in harsh environment. Previous research has established two approaches to treat nonlinearity temperature drift. The first approach is to use an analog compensation circuit, such as the external thermistor. [PERSON] et al. [20] presented a passive technique for temperature compensation of a silicon pressure sensor based on extra polysilicon resistors with negative temperature coefficient of resistivity. The second approach is to use a digital compensation system with the combination of electronic circuits and specific software. However, the first approach has intrinsic pitfalls such as poor reliability, low accuracy, and high design difficulty [21]. Concerning the second approach, neural network has recently been applied. [PERSON] et al.