Temperature and pressure sensors are the most widely used microelectromechanical system (MEMS) devices in the market due to their small size, simple integration and direct signal transduction mechanism, etc (Dang et al. 2024). Multi-channel temperature and pressure combination sensor is a device that integrates temperature and pressure sensitive elements at the component level, which can achieve synchronous measurement of temperature and pressure in the same structure (Yuan et al. 2024). Due to its small size and light weight, it has a wide range of application prospects in the field of aviation (Wang et al. 2022). To improve its reliability, temperature and pressure sensor has to be designed as a multi-channel device with three or four channels to get synchronous measurement of multiple temperatures and pressures, real-time monitoring and flight parameter recording information (Zhang et al. 2024).

In the field of aircraft measurement and control, it is necessary to test multiple parameters to comprehensively judge the equipment status, and so a single sensor parameter can no longer meet the requirements (Li et al. 2020). Considering future development of miniaturization and combination of the sensors, multi-channel temperature pressure sensors possess obvious advantages in same position acquisition, synchronous testing, weight reduction, data fusion, fault prediction, etc (Zhu et al. 2024) It is also significant for the standardization and modularization of the sensors. Temperature and pressure are usually designed as four channels (two channels temperature, two channels pressure), which can realize comprehensive evaluation of medium parameter measurement through the dual channel output comparison, improving the accuracy of medium parameter monitoring (Liu et al. 2022, Gao et al. 2024).

Temperature and pressure sensors are mainly used in various systems such as environmental control system, fuel system, oxygen system, rescue system and landing system, etc. They are applied to monitor the temperature and pressure parameters of gases and liquids in different pipelines, pumps, and other locations (Hong et al. 2024). In aviation engines, they are mainly used to monitor the temperature and pressure of various engine sections, fuel and oil, hydraulic systems, and other environments (Song et al. 2023, Fiorillo et al. 2018). By monitoring the temperature and pressure parameters of each major component and their changes, signals are transmitted to the computer to get the control, health assessment, fault prediction, and diagnosis of the aircraft (Wang et al. 2023).

At present, with the continuous development of the aviation technology, the new aircrafts have characteristics such as high thrust and strong maneuverability. Thus, the system has put forward the new requirements for temperature and pressure sensors (Xu et al. 2023, Xia et al. 2024). Meanwhile, with the increasing number of the sensors in the electromechanical and engine systems, the volume and weight of the sensors are requested be smaller and lighter (Zhou et al. 2023). It is no longer sufficient to meet weight reduction only by simply optimizing the mechanical structure of sensors (He et al. 2023, Xin et al. 2023). Therefore, this paper utilized dual chip packaging (DCP) and system in package (SIP) technologies to miniaturize the pressure core and signal processing section of the sensor, satisfying the size and weight requirements of the four-channel temperature and pressure sensor.

In this paper, the pressure core of the sensor was designed as a dual redundancy structure by the dual chip package, which contained two pressure chips in one core, replacing the traditional dual redundancy structure of two cores. The dual chip package structure used gold wire bonding technology to extract electrical signals. Finally, the ceramic was filled in the core cavity to reduce the amount of oil, which can reduce the temperature drift of the output. The metal corrugated sheet and core shell were connected by welding process, and finally the oil filling and ball sealing process were chosen. The structure of the dual chip package is shown in Fig. 1. The dual redundant core is composed by 1-corrugated sheet, 2-gold wire, 3-chip a, 4-chip b, 5-silicone oil, 6-ceramic base, 7-lead, and 8-shell. Chip a and chip b are identical, achieving dual redundant design.

The traditional dual redundant pressure sensors generally chose two pressure cores fixing in the pipe joint through welding process, as shown in Fig. 2 (a). Considering the requirement of the sealing, electron beam welding was chosen. A high amount of heat was usually generated during the welding. Meanwhile, the first welded core would be affected when the second welded core was implemented, which easily caused the zero-point change of the first core, increasing the risk of output drift for the sensor. In severe cases, it could cause the damage of the first core and reduced the assembly qualification rate. On the other hand, using two pressure cores increased the volume and weight of the sensor, which was not beneficial for weight reduction of the aircraft system. This paper achieved a dual redundant pressure device by encapsulating two chips inside a core, as shown in Fig. 2 (b). By comparing the traditional sensor structure, the size and weight of the sensor were reduced obviously when the proposed pressure core was chosen. At the same time, the proposed sensor only had one welding seam, and then the sealed connection was completed. Thus, the thermal impact of soldering was weakened and the stability and yield of the sensor were improved. The physical pressure core based on dual chip package is shown in Fig. 2(c).

The conventional four-channel temperature and pressure sensor circuit included two temperature regulation circuits, two pressure regulation circuits and one electromagnetic protection circuit, as shown in Fig. 3(a). In order to reduce the size and weight of the sensor, this study utilized HTCC and thick-film hybrid integration technology to package the temperature regulation circuit, pressure regulation circuit, and electromagnetic protection circuit separately into different SIP modules, namely, SIP temperature module, SIP pressure module, and SIP electromagnetic protection module. Then, these SIP modules were mounted on the PCB by surface-mount technology (SMT) as shown in Fig. 3(b), replacing the multilayer PCB interconnection approach.

For the SIP temperature and pressure modules used in the sensor, the HTCC unit module supplemented by different peripheral resistors and capacitors was implemented. This design greatly improved the standardization and modularization level of sensors. In terms of structural design, Al₂O₃ thick film substrates and Al₂O₃ HTCC shells were chosen as component carriers. The bare chip utilized a micro-assembly process and ceramic shell sealing process for packaging. Thick film resistors were printed on the thick film substrates, and surface mount capacitors were assembled on the ceramic shells. Finally, parallel seam welding was applied for sealing to form an airtight package. The SIP electromagnetic protection module adopted an LCC packaging form, and a thick film ceramic substrate was embedded in the middle of the tube shell. The electrical signals on the thick film substrate were led out to the HTCC shell through wire bonding. The three-dimensional SIP modules with the proposed design are shown in Fig. 4(a) and Fig. 4(b). The original components and substrate inside the SIP packaging module unit cavity were bonded, which solved the problems of insufficient space, improved the assembly density and reduced product size. The parallel soldering was used, and the bottom cavity was sealed with Au80Sn20 solder. The physical pictures are shown in Fig. 4(c) and Fig. 4(d).

The four-channel temperature pressure sensor in this paper physically combined two temperature and two pressure sensors together. Through the structural design, it realized the requirement of simultaneously measuring two channels of temperature and two channels of pressure within a single mechanical installation interface. The sensor was mainly composed by 1-temperature sensing element, 2-mounting seat, 3-pressure core with dual chip package, 4-circuit board with SIP module, 5-mounting bracket, 6-metal shell, 7-aviation plug, as shown in Fig. 5(a).

The temperature sensing element adopted PT1000 thin film platinum resistors. Two identical PT1000 resistors were encapsulated into the sensor probe through encapsulation technology. The PT1000 thin film platinum resistors were connected to the mounting base by continuous laser welding technology, and a pressure test was conducted after welding to verify sealing performance. Four-point positioning laser was used between the pressure core and the mounting seat at the beginning. After that, the continuous laser welding was used at the same position. After welding, the sealing also need to be checked. To improve the temperature resistance of the pressure core, an aging process was required for stress release after welding. The different SIP modules were installed on the PCB board through SMT, and the PCB board was fixed inside the sensor. There were 12 leads in the sensor, which were connected to the aviation plug pins through soldering technology. The aviation plug and the shell were connected by continuous laser welding for one cycle. The physical picture of the proposed sensor is shown in Fig. 5(b).

To verify the comprehensive accuracy of the proposed sensor, different temperature points from − 55 ℃ to 150 ℃ were selected to measure the pressure output characteristics of the sensor at different pressures. Based on the pressure sensor calibration procedures, the pressure signals increased from low to high until 1MPa, and then decreased from 1 MPa to 0. For each pressure point, the output data would not be read until the pressure was stable. For each temperature point, three measurements were carried out in order to get a precise value. Figure 6(a) illustrates the relationship between the output of the sensor and the standard pressure under different temperatures. The performance of the pressure test is shown in Table 1. The results indicate that both of channel 1 and channel 2 show high performance index. The linearity and repeatability are better than 0.08%FS, the hysteresis is higher than 0.05%FS. Thus, the accuracy of the two channels is better than 0.17% FS across the entire temperature range, exhibiting a high precision.

In order to test the temperature performance of the sensor, the output of the sensor under different temperatures was tested. The results indicate that the output possesses a linear transformation with increasing temperature, as shown in Fig. 6(b). The accuracy from − 55 ℃ to 150 ℃ displays a high level, which is higher than 0.21%FS across the entire temperature range, as shown in Table 2.

The core of the high accuracy of the sensor is because of the high accuracy conversion circuit. Due to the mV signal output by the presence of temperature drift and nonlinearity, it is necessary to amplify and compensate for the sensor signal (Kato et al. 2020). The main function of the signal source circuit is to amplify and compensate the mV signal of the sensor into a V-level signal (Zhao et al. 2023). This integrated circuit is a CMOS integrated circuit for high-precision bridge sensor signal processing. This core conversion chip has amplification, calibration, and temperature compensation functions, and its comprehensive working characteristics can approximate the inherent repeatability of the sensor (Yao et al. 2016). Its fully analog signal channel does not introduce quantization noise in the output signal and utilizes an integrated 16-bit analog-to-digital converter (DAC) for digital correction. The integrated circuit includes one programmable sensor driver, one programmable gain amplifier (PGA), one internal EEPROM, four 16-bit ADCs, one general-purpose amplifier, and one embedded temperature sensor. By the reasonable algorithms, a span compensation of 1.5 ℃ can be achieved. This circuit can be applied to high-precision applications with a maximum compensation accuracy of 0.1%FS. The schematic diagram of the signal source circuit is shown in Fig. 7(a).

Due to the fact that the signal source circuit outputs a voltage signal of 0.8V∼4.0V DC, and thus an additional signal output circuit is required. Considering the limited internal space of the sensor, an integrated device is used for the 4mA∼20mA signal output circuit, which is paired with a small package of MOS and NPN transistors. This device can directly convert the 0.8V∼4.0V DC voltage signal output into a 4mA∼20mA current signal. This circuit can be operated in an environment of -55°C to 150°C, with extremely high temperature characteristics, an output accuracy of up to 0.01%, and a response frequency greater than 100KHz. The schematic diagram of the signal output circuit is shown in Fig. 7(b).

The conversion chip in the signal source circuit is the core for the high accuracy, which consists five parts, namely the analog front-end module, built-in MCU and digital control logic, analog output module, power and driver module, and serial interface circuit. The analog front-end module includes a main signal channel composed of instrument PGA and 24-bit ADC, an auxiliary temperature measurement channel composed of built-in temperature sensor and 24-bit ADC, and a digital filter, providing high-precision sensor signals and temperature acquisition.

The auxiliary temperature measurement channel is used to measure the working temperature of the sensor and compensate for the temperature of the sensor signal results. This channel works in parallel with the sensor signal measurement channel. The core conversion chip supports two modes: internal temperature sensor and external temperature sensor. When the medium temperature is the same as the operating temperature or the error is within an acceptable range, a low-cost internal temperature sensor can be selected. If the working conditions is special, such as wide temperature range, rapid temperature change, and large difference between the measured medium temperature and the ambient temperature, an external temperature sensor temperature measurement mode is adopted. The external temperature sensor uses a pressure chip Wheatstone bridge resistor to detect the medium temperature and transmit it to the temperature pin of the conversion chip.

During the calibration process of the sensor, a total of 4 pressure compensation points was set up to compensate the sensor in sequence at -55 ℃, 25 ℃, 100℃ and 150 ℃. Started heating from − 55 ℃ until the temperature in the test chamber reached the set temperature point in sequence. When the temperature in the chamber reached the set temperature point, waited for 30 minutes and followed the calibration flowchart. The sensor in this article required a 4mA∼20mA output, therefore it was set to 4T4P mode, external temperature sensor calibration, and on-board ammeter calibration. The temperature signal of the external temperature sensor was from the bridge arm resistance. According to the principle that the bridge arm resistance changed with temperature, the temperature parameters of the measured medium were accurately recorded in the conditioning chip. Four pressure points, including zero-point output, two intermediate points, and full range output, were collected at -55 ℃, 25 ℃, 100℃ and 150 ℃. Finally, the output of 4mA∼20mA for the proposed sensor was realized by the linear variation corresponding to the medium environment.

The four-channel temperature and pressure sensor based on DCP and SIP packaging developed in this paper was compared with the conventional four-channel temperature and pressure sensor in the previous stage, as shown in Table 3. Based on DCP and SIP package, the four channel-temperature and pressure sensor achieved the almost identical performance indicators to conventional four-channel temperature and pressure sensor, while a maximum outer diameter reduction of 27% and a weight reduction of 40%. The miniaturization and lightweighting effects were significant. At the same time, based on the research results of this article, multiple modules could be combined freely according to the actual demand, such as single degree temperature and pressure, double degree temperature sensors, et al, improving the standardization and modularization design level of sensors.

In this paper, a four-channel temperature and pressure sensor based on DCP and SIP package technology was developed, which achieved a miniaturization and lightweight effect. Compared with traditional four-channel temperature pressure sensor, the proposed sensor got a maximum outer diameter reduction of 27% and a weight reduction of 40%. Through selecting a high accuracy conversion chip and external compensation mode, the proposed sensor possessed a high performance. Meanwhile, the SIP modules could be combined freely according to the actual demand, which was beneficial to improve the standardization and modularization design level of the sensors.