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The Research Of The Integrated Pirani Vacuum Sensor System

Posted on:2011-12-12Degree:DoctorType:Dissertation
Country:ChinaCandidate:J Q WangFull Text:PDF
GTID:1118360305455642Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
The vacuum sensor is a very important device in the vacuum science research and the vacuum measurement technology. An integrated CMOS-compatible Pirani vacuum sensor system has been investigated and developed in this work, combining the traditional Pirani gauge with the MEMS technology.The developed sensor system can be used to measure the gas pressure with a tiny amount of the external components. The sensor signals are then digitized, real-time displayed and interfaced with the external process unit. The design, fabrication and test of the sensory component based on the micro-hotplate, the bias circuit for the sensor, the real-time display of the gas pressure and the interface of the sensor system have been studied in detail. Moreover, the sensing mechanism of the Pirani sensor and the micro-scale thermal conduction of the gas in the silicon-based Pirani sensor have also been investigated in this work.The operational principle of the silicon-based Pirani sensor is based on the fact that the gas thermal conduction is dependent on the gas pressure. Thus, the micro mechanism of the gas thermal conduction is introduced, which is also the mechanism of the Pirani sensor. The micro-scale thermal conduction of the gas is analyzed and introduced to the polysilicon micro-hot-bridge which is the most commonly used sensory component in the silicon-based Pirani sensor, modifying its classical electro-thermal-elastic coupled model. The analytical solutions for the temperature field of the micro-hot-bridge modified model are more approximate to the experimental data than those calculated from the classical model when the micro-hot-bridge is buckled largely. This indicated that such modification could expand the application scope of the classical model.Although it is difficult to get the analytical solutions for the temperature field of the micro-hotplate, it has some specifications comparing to the micro-hot-bridge, such as large effective area and high sensitivity. To further improve the sensitivity of the sensor, the tungsten micro-hotplate fabricated by the surface sacrificial layer etching process is designed with the tungsten plug in the standard CMOS process as the serpentine heating resistor, which is adopted as the sensory component of the Pirani sensor. Comparing to the polysilicon and aluminium heating resistor of the micro-hotplate, the tungsten heating resistor has the higher melting point (3417 C) and it has no electromigration effect. It has been found that the tungsten resistor is more suitable for the micro-hotplate which is used as the sensory component for the integrated Pirani sensor system.The constant current circuit based on the operational amplifier is employed as the bias circuit for the Pirani sensor. Comparing to the constant temperature and constant voltage bias circuit, the micro-hotplate has a higher temperature in the low gas pressure under constant current circuit and the Pirani sensor is more sensitive to the low gas pressure. The micro-hotplate array consisting of four micro-hotplates in series is adopted to increase the effective area of the sensor without the complex manufacturing process, improving the sensitivity more.The Pirani sensor system including the sensor, the analog circuit and the digital circuit is subsequently implemented monolithically in the O.5μm CMOS process with the help of the different design methods and softwares. The testing results show that all the circuit modules reach the requiements of the sensor system and the sensor has a response to the gas pressure ranging from 10-1Pa-105Pa. The integrated Pirani vacuum sensor system in this work can be applied for the gas pressure detector in the medium and rough vacuum measurement.
Keywords/Search Tags:Pirani Gauge, Vacuum Sensor, CMOS-Compatible, MEMS, Tungsten Micro-hotplate
PDF Full Text Request
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