DocumentCode :
2873625
Title :
A thermal conductivity based humidity sensor in a standard CMOS process
Author :
Okcan, Burak ; Akin, Tayfun
Author_Institution :
Dept. of Electr. & Electron. Eng., Middle East Tech. Univ., Ankara, Turkey
fYear :
2004
fDate :
2004
Firstpage :
552
Lastpage :
555
Abstract :
This paper presents a low-cost, thermal conductivity based humidity sensor implemented using a 0.6 μm CMOS process where suspended p-n junction diodes are used as the humidity sensitive elements. In this method, the difference between the thermal conductivities of air and water vapor at high temperatures is used. Humidity sensing idea is to compare the output voltages of two heated and thermally isolated diodes one of which is exposed to the environment and has a humidity dependent thermal conductance while the other is sealed and has a fixed thermal conductance. Thermal isolation is obtained by a simple front-end bulk silicon etching process in a TMAH solution, while the diodes are protected by electrochemical etch-stop technique. Electrical connections to the suspended diodes are obtained with polysilicon interconnect layers in order to increase the thermal resistance so that the diodes are heated to the desired temperature levels with less power. Due to the high electrical resistance of the polysilicon, temperature sensitivities of the diodes reduced to -1.3 mV/K at 100 μA bias level. The diodes are connected to the readout circuit monolithically using the standard CMOS fabrication. Characterization results show that the humidity sensitivity of the sensor is 14.3 mV/%RH, 26 mV/%RH, and 46.9 mV/%RH for 20°C, 30°C, and 40°C, respectively, with a nonlinearity less than 0.3%. Hysteresis of the sensor is less than 1%. The chip operates from a 5 V supply and dissipates only 1.38 mW power.
Keywords :
CMOS integrated circuits; electrical resistivity; elemental semiconductors; etching; humidity sensors; p-n junctions; silicon; temperature sensors; thermal conductivity; thermal resistance; 0.6 micron; 1.38 mW; 20 C; 30 C; 40 C; 5 V; Si; air; electrical connections; electrical resistance; electrochemical etch; humidity sensor; hysteresis; p-n junction diodes; polysilicon; silicon etching process; standard CMOS process; temperature sensitivity; thermal conductance; thermal conductivity; thermal isolation; thermal resistance; thermally isolated diodes; water vapor; CMOS process; Diodes; Electric resistance; Etching; Humidity; Sensor phenomena and characterization; Temperature sensors; Thermal conductivity; Thermal resistance; Thermal sensors;
fLanguage :
English
Publisher :
ieee
Conference_Titel :
Micro Electro Mechanical Systems, 2004. 17th IEEE International Conference on. (MEMS)
Print_ISBN :
0-7803-8265-X
Type :
conf
DOI :
10.1109/MEMS.2004.1290644
Filename :
1290644
Link To Document :
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