基于CMOS工艺的复合真空传感器系统研究

High vacuum hot ionization sensor must be used with the low vacuum Pirani sensor, which improves the test system cost and complexity by two individual vacuum sensors mentioned above. This project first proposes the implementation of Pirani vacuum sensor, hot ionization vacuum sensor and the signal processing circuit in the same wafer with the CMOS process. A composite solid vacuum sensor system is formed to measure the vacuum from 1.E+5Pa to 1.E-6Pa covering the measurement range of Pirani sensor and hot ionization sensor. The key devices consist of the tungsten microhotplate for Pirani sensor, the tungsten electron emitter for hot ionization sensor and the circuit for signal sample and amplify. In the sensor fabrication process,the 0.5μm CMOS technology is adopted and the Post-CMOS process including the sacrificial layer etching and tungsten electron emitter exposure for the hot ionization sensor are the key fabrication processes for the sensor. In theory, the micro-scale gas thermal conduction for Pirani sensor and the analysis method for thermal-electric and electromagnetic of hot ionization sensor are deeply improved. The sensor has the small volume size, light weight and the seamless combination of Pirani sensor and hot ionization sensor. Besides the application in the conventional vacuum measurement, the sensor system can also be applied to the small volume vacuum measurement represented by microelectronic packaging and to the field strictly demanding the weight of the vacuum gauge represented by the deep space exploration.

测量高真空的热电离传感器必须搭配测量低真空的皮拉尼传感器，这需要两款分立的真空传感器，因此增加了测试系统的成本和复杂度。本项目首次提出将皮拉尼传感器和热电离传感器以及信号处理电路利用CMOS工艺在同一个硅片上实现，构成一个覆盖热电离传感器和皮拉尼传感器全范围的全固态复合真空传感器系统，量程为1.E+5Pa~1.E-6Pa。核心器件包括皮拉尼传感器的钨微热板，热电离传感器的钨电子发射极和采样、放大等电路。工艺方面，拟采用0.5微米CMOS工艺，重点研究Post-CMOS工艺，掌握牺牲层腐蚀、钨电子发射极的暴露等关键工艺。理论方面，深化皮拉尼传感器中的微小尺度气体导热理论和热电离传感器的电热场及电磁场的分析方法。该传感器系统具有体积小、重量轻、实现两款传感器的无缝衔接等优点，除常规真空测量外，还可用到以微电子封装为代表的微小体积的真空测量和以深空探测为代表的对真空传感器重量要求苛刻的领域。

为了使微型真空传感器能够覆盖粗真空和高真空的测量，本项目提出利用标准CMOS工艺在同一个硅片上加工皮拉尼真空传感器和热电离真空传感器。在理论方面，发展了气体导热的微尺度效应，利用分子动力学方法计算了气体热导率与导热尺度的关系，气体热导率随导热尺寸减小而减小。这与其他理论和实验结果是一致的，能够应用到皮拉尼传感器的设计之中。利用COMSOL多物理场耦合软件仿真了皮拉尼传感器和热电离传感器的电热耦合过程以及电子运行轨迹，指导器件的设计。经过多次0.5微米标准CMOS工艺的流片，已成功将皮拉尼真空传感器与热电离真空传感器在同一个芯片上完成，突破了工艺上的限制。皮拉尼真空传感器采用较成熟的微热板结构，热电离真空传感器的结构从钨加热丝发展到钨的弹簧结构，逐步提高了结构的稳定性及成品率。除了以钨加热电阻作为热电离真空传感器的发射极，也探索了利用CMOS工艺加工场发射电离真空传感器的可能性。采用以运算放大器为核心的恒电流电路分别为皮拉尼真空传感器和热电离真空传感器提供电流。初步测试结果显示，皮拉尼真空传感器能够满足10E-1~10E5 Pa的测量，热电离真空传感器响应区间为0.05~0.5 Pa，进一步的测试正在进行中。