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1、An Alpha Alumina Moisture Sensor for Relative and Absolute Humidity Measurement Zhi Chen and Mao Chang Jin Center for Materials Analysis Department of Materials Science and Engineering University of Electronic Science and Technology of China Chengch 6 10 05 4 P R China Abstract A novel humidity sens
2、or using an a alumina porous film has been developed for moisture analysis as well as relative humidity measurement The humidity sensing dielectric used for the sensor mainly consists of a cylindricalpore like a alumina film formed by anodic spark deposition with a dense amorphous alumina thin barri
3、er layer at the pore base formed by reanodization The performance characteristics of the sensor e g hu midity sensitivity humidity hysteresis temperature de pendence response time reproducibility and long term calibration stability were studied in detail It has been revealed that the sensor can be u
4、sed for absolute humidity or moisture detection in the range from 80 C to 10 C frost point as well as relative humidity measurement from 10 to 100 RH with very stable performance INTRODUCTION In recent years humidity sensors were extensively used in the field of industry and various humidity sen sor
5、s appeared l 7 However many humidity sen sors suffered from serious drawbacks e g long term in stability large humidity hysteresis and slow response etc Few were found to be effective for practical applica tion According to the measurement range and the re sponded physical variable humidity sensors
6、are divided into two types relative humidity RH sensors and abso lute humidity moisture sensors Relative humidity sen sors are used to measure the ratio of water vapor pressure to the saturated water vapor pressure at a fixed tempera ture in the range from 10 to 100 RH referred to as high humidity A
7、bsolute humidity sensors are used to detect the water vapor concentration in a flow of gas or in a sealed package ranging from 80 C to 2O C dew frost point Absolute humidity covers a wide range of hu midity compared with relative humidity i e 80 C to 10 C frost point corresponding to 0 5 to 2300 ppm
8、 at 1 atm is referred to as trace moisture and 1O C to 20 dew frost point corresponding to 10 to 100 RH at 20 C overlaps the relative humidity at 2O C Most sensors were found application in the RH range 1 6 Only alumina thin film sensor was used as an absolute humidity sensor 71 81 lo which is espec
9、ial ly useful in the trace mosture range The ability of the a lumina sensor to detect extremely low water vapor levels lppm was ascribed to the very high humidity sensi tivity of the porous alumina film formed by anodization of aluminum in HzS04 solution and leads to its application in in line test
10、of sealed micro electronic circuit packages TI Unfortunately alumina humidity sensors have a serious flaw i e long term calibration drift 91 121 Many researchers tried to improve the alumina sensors by aging the alumina films in boiling water or macerating the films in some ion solutions 111 l2 141
11、However the drift can not be completely elimi This work was finacially supported by the Ministry of Mechanical I b C controlling of humidity charac terisqics and aging Prm 3rd Sensur Symp Tokyo of Japan 1983 pp251 256 1211 Emmer Z Hajek and P Repa Surface adsorption of wa ter vapor on hydrated layer
12、s of A1203 Surf A vol 162 pp303 309 1985 13 System I hygrometer and options Opatmg and Servlcc Mm ual Panametrics Ltd Shannon Ireland 1982 pp ii 1412 Chen M C Jin and C Zhen Humidity sensors with re actively evaporated A I 2 0 3 films as porous dielectrics Scns 15 Z Chen M C Jin C Zhen and G H Chen
13、Properties of modified anodic spark deposited alumina porous ceramic films as humidity sensors J Am Cmm Soc vol 74 no 6 ppl325 1330 June 1991 A C U S B vol 2 pp167 171 1990 l6 M C Jin Z Chen and G H Chen Alumina ceramic thin film humidity sensors Tech Rep U of Elec Sci Tech of China Dec 1990 unpubli
14、shed 17 M C Jin and Z Chen An a alumina absolute humidity sensor for moisture measurement C l t w P a t e n t applwtwn No 91107172 5 April 1991 181R S Alwitt Some physical and dielectric properties of hy drious alumina films J Electroclscm Soc vol 118 1730 1733 1971 19 M S Hunter and P Fowle Determi
15、nation of barrier layer thickness of anodic oxide coatings J Electroclm Soc vol 101 pp 481 485 1954 201R F Luo Mechanism of long term calibration drift of hu midity sensors using metal oxides Roc 2nd Vat Symp on Hunud iy and Modure Humidity Moisture Soc of Chi nese Inst of Instruments Wuhan Hubei China Nov 1988 9 3 2 3 6 1675
