Gas Sensor, Gas Measuring System Using the Gas Sensor, and Gas Detection Module for the Gas Sensor

Abstract

A gas sensor, which is extremely compact to be arranged for separated gas piping in semiconductor device manufacturing equipment, a gas measuring system using such gas sensor, and a gas detection module for the gas measuring system. The gas sensor has a gas detection device containing a dielectric semiconductor, the electric conductivity of the gas detection device varying in response to the degree of adsorption of gases to the gas detection device, a capacitive element connected in series to the gas detection device, and a pair of electrodes which are connected to electric terminals of an electric element comprising the gas detection device and the capacitive element, wherein the gas sensor is capable of detecting the degree of adsorption of gases to the gas detection device from an electrical response to a voltage which is applied to the electrodes and which periodically varies and reverses in polarity.

1 . A gas sensor comprising:
 a gas detection device containing a dielectric semiconductor, the electric conductivity of the gas detection device varying in response to the degree of adsorption of gases to the gas detection device;   a capacitive element connected in senes to the gas detection device, the capacitance of the capacitive element being larger than the capacitance of the gas detection device; and   a pair of electrodes which are connected to electric terminals of an electric element comprising the gas detection device and the capacitive element,   wherein the gas sensor is capable of detecting the degree of adsorption of gases to the gas detection device from an electrical response changing in response to a voltage which is applied to the pair of electrodes and which periodically varies and reverses in polarity.   
     
     
         2 . The gas sensor according to  claim 1 , wherein the capacitive element is integrated with the gas detection device. 
     
     
         3 . The gas sensor according to  claim 1 , further comprising a metal layer formed directly on the surface of an electric terminal of the gas detection device, the metal layer has a modified dielectric layer obtained by modifying a metal of the metal layer at the interface facing the gas detection device, and the modified dielectric layer is at least a part of the capacitive element. 
     
     
         4 . The gas sensor according to  claim 3 , wherein the modified dielectric layer is an oxide film formed by the oxidation of a metal of the metal layer by oxygen passing through the gas detection device. 
     
     
         5 . The gas sensor according to  claim 1 , further comprising a dielectric material layer formed directly on the surface of an electric terminal of the gas detection device, and the dielectric material layer is at least a part of the capacitive element and prevents charge injection to the gas detection device. 
     
     
         6 . The gas sensor according to  claim 1 , further comprising a pair of inert metal layers each formed directly on the surface of one of the electric terminals of the gas detection device, and a gas detection module which consists of the gas detection device and the pair of inert metal layers sandwiching the gas detection device and does not substantially contain an electric element which has dielectric characteristics other than the gas detection device. 
     
     
         7 . The gas sensor according to  claim 1 , wherein the dielectric semiconductor comprises a fullerene material having electric conductivity which is decreased by the adsorption of a gas. 
     
     
         8 . The gas sensor according to  claim 1 , wherein the dielectric semiconductor comprises an organic semiconductor. 
     
     
         9 . The gas sensor according to  claim 1 , wherein the frequency of the reverse in polarity of the voltage applied to the pair of electrodes varies while in use of the gas sensor. 
     
     
         10 . A gas measuring system comprising: a gas sensor according to  claim 1 , an electric power supply capable of applying a voltage to the electric terminals of the gas sensor, wherein the applied voltage periodically varies and reverses in polarity, and a measuring means for measuring an electric response of the gas sensor to the voltage applied by the electric power supply. 
     
     
         11 . The gas measuring system according to  claim 10 , further comprising a gas desorbing means for desorbing a gas adsorbed by the dielectric semiconductor contained in the gas sensor. 
     
     
         12 . The gas measuring system according to  claim 10  further comprising a temperature measuring means for measuring the temperature of the gas sensor,
 wherein the structure of the temperature measuring means is the same as that of the gas sensor except that the temperature measuring means is sealed so that no gas is adsorbed by a gas detection device of the temperature measuring means. 
 
     
     
         13 . The gas measuring system according to  claim 10 , wherein the electric power supply is capable of varying the frequency of the reverse in polarity. 
     
     
         14 . A method of measuring gases using a gas measuring system, the method comprising:
 a gas sensor according to  claim 1 ;   applying a voltage from an electric power supply to electric terminals of the gas sensor, the applied voltage periodically varying and reversing in polarity; and   measuring an electric response of the gas sensor to the voltage applied by the electric power supply;   wherein the dependence of the real part of the complex capacitance of the gas sensor on the frequency of the applied voltage has a profile which consists of a first zone at a higher frequency, a second zone at a lower frequency, and a third zone between the first zone and the second zone, a value of the first zone being defined mainly by the capacitance of the gas detection device of the gas sensor, and a value of the second zone being defined mainly by the capacitance of the gas detection device; and   the degree of adsorption of gases to the gas sensor is detected by measuring at least one of the value of the second zone and a value of the third zone of the profile.