CN1955729A - Acetone steam gas sensitive sensing element - Google Patents

Abstract

An air sensitive transducer used for determining concentration of acetone steam is prepared as winding electrodes led out by Pt wire at two ends of a ceramic tube, arranging electric heating wire in ceramic tube for heating ceramic tube up, sputtering a layer of ZnO film on external surface of ceramic tube, connecting electric heating wire and electrodes led out by Pt wire and set on ZnO film separately to heating circuit and electrode leading out loop then connecting them to test circuit.

Description

Acetone steam gas sensitive sensing element

Technical field:

The invention belongs to a kind of gas sensor element, particularly a kind of acetone steam gas sensitive sensing element of ZnO film type high selectivity.

Technical background:

Gas sensor is the core component of gas sensor, and the height of its quality level has determined the quality of gas sensor.The all responsive broad spectrum type gas sensor element of pair organic gas is arranged in the market, but only do not have gas sensor the acetone sensitivity.The TGS822 type gas sensor element produced of Tianjin Figaro Electronics Co., Ltd. for example.Consult the technical information announced in its website on October, last 2005 as can be known, this gas sensor prepares with the chemical membrane method, it is SnO2 base film type gas sensor, organic solvent to alcohol and other is all very responsive. the existence that therefore can not in numerous organic vapors, detect acetone whether with and concentration. the present invention adopts physical film deposition method (sputtering method) preparation gas sensor, and different preparation methods with it are more advanced.

The prepared gas sensor that goes out of the present invention only has sensitivity characteristic to the acetone steam, for other common organic vapors (as ethanol, toluene, formaldehyde, gasoline etc.) insensitive substantially, can be in numerous mixing organic vapors, whether and concentration the existence that detects the acetone steam.

Summary of the invention:

Utilize d.c. sputtering or radio frequency sputtering method, select suitable technological parameter (as sputtering voltage, sputtering current, vacuum tightness, the oxygen argon compares etc.) on commercially available ceramic pipe or quartz ampoule outside surface, to prepare ZnO film.Ceramic pipe is built-in with electric furnace heating wire, in order to the heating ceramic pipe.With the platinum wire extraction electrode on electric furnace heating wire and the ZnO film respectively with draw the loop and be connected with test circuit, the resistance that utilizes ZnO film changed with the concentration and the time of the acetone steam of introducing, and just can measure the concentration of acetone steam.Element has shown a high selectivity gas-sensitive property to the acetone vapor sensitive.

The gas-sensitive property of gas sensor characterizes with sensitivity usually.Sensitivity be defined as the resistance value Rs of element in air atmosphere and the resistance value Rg of element in certain density tested gas atmosphere with it than:

$s=\frac{\mathrm{Rs}}{\mathrm{Rg}}$

The method of testing of sensitivity: give the power supply of the resistance wire in the element, resistance wire heats up and generates heat, with indirect mode heating ceramic pipe (or quartz ampoule).Pull-up resistor R and component resistance Rz are in series, and test voltage Vc is supplied with at its two ends.Measure voltage Vout at output terminal.The resistance of element: $\mathrm{Rz}=\frac{\mathrm{Vc}}{\mathrm{Vout}}(1-R).$ Rz=Rs under air atmosphere, under the acetone vapor atmosphere, Rz=Rg.

The present invention compared with prior art has following advantage:

(1) on commercially available pottery or quartz ampoule, prepare ZnO film with sputtering method of the present invention, quality of forming film is better.

When (2) adopting sputtering technology to prepare film, select suitable technological parameter, can make gas sensor that acetone is had very high selectivity, can resist the interference of other organic steam.

Main application: detect acetone steam.In the organic steam of numerous mixing, optionally detect the existence and the concentration thereof of acetone steam.

Description of drawings:

Figure 1 shows that the structure of element:

1. be ceramic pipe or quartz ampoule; 2. be around the platinum wire at pipe two ends or the tinsel of other resistance to oxidation and high temperature; 3. be of the present invention, 4. for being placed in the heater strip in ceramic pipe or the quartz ampoule at the ZnO film of ceramic pipe outside surface with the sputtering method preparation.

Figure 2 shows that test circuit:

Rz is a sensitive element resistance, and R is a pull-up resistor, and R selects according to the Rz size.Vc is the test loop service voltage; Vout is the test voltage of output.Vh is the service voltage of heating circuit, selects according to the heating-up temperature that needs.

Figure 3 shows that gas sensor test typical consequence figure, show acetone gas sensor involved in the present invention response (recovery) characteristic acetone steam and other organic steam (as gasoline, toluene, ethanol etc.).

Embodiment:

Example 1.

The dc magnetron reactive sputtering legal system is equipped with ZnO film

The method is to adopt direct current reaction magnetron sputtering deposit ZnO film on the ceramic pipe outside surface.Before the experiment, ceramic pipe is cleaned with alcohol.Then they are placed on the instrumented substrate.The target of magnetron sputtering is that purity is 99.99% zinc, and the distance between target and the substrate is 70mm.In the reactive deposition process, argon gas (Ar) is sputter gas, oxygen (O ₂) be reacting gas.Sputter ZnO film and test process are as follows on direct current reaction magnetron sputtering equipment:

1. will be before the sputter with system's vacuum pumping, process is as follows: earlier with power supply opening, the gas in extracting vacuum chamber and the molecular pump is in turn observed both air pressure simultaneously.When both air pressure when equating, open the valve between vacuum chamber and molecular pump, until the air pressure of system near 10 ^-3Pa.More than one hour time of this process need.

2. after system's vacuum pumping, next step begins sputter: earlier the gas valve of argon bottle is opened aerating oxygen (the easy build-up of luminance of zinc target like this) again after system feeds argon gas, waits sputter a period of time, its Ar/O ₂=40: 120.The voltage that is added between Zn target and substrate is 370V, and electric current is 0.2A.(put a block plate between target and substrate, this is because the surface of zinc target is not too pure before the sputter, can introduce impurity to want pre-sputter 10 minutes during sputter just.Again block plate is withdrawn after 10 minutes), sputter procedure picks up counting, and stops later on up to 0.5 hour.During this period, the experimenter will observe voltage table and reometer always.When electric current raises suddenly, in time reset (voltage be zero), and then voltage gone up.When system stability, the frequency of molecular pump is 350Hz.After sputter finishes, stop sputter, take out sample.

3. the result who uses HW-30A type air-sensitive tester to measure

When gas sensor working temperature of the present invention is 300 ℃ (instrument is displays temperature automatically), its air-sensitive test result is as follows: the acetone gas sensor of this invention is only to the acetone steam sensitivity, and its response time is 4 seconds, and be 2 seconds release time.Insensitive to other interference gases such as gasoline.

Example 2.

The radio-frequency sputtering ZnO film

The method adopts rf magnetron sputtering deposit ZnO film on the ceramic pipe outside surface.Before the experiment, ceramic pipe is cleaned with alcohol.The target of rf magnetron sputtering is ZnO, and the distance between target and the substrate is approximately 40mm.In the reactive deposition process, argon gas (Ar) is sputter gas, oxygen (O ₂) be reacting gas.

ZnO film prepares on JGP500D1 type ultra-high vacuum multifunctional rf magnetron sputtering equipment.The ZnO film and the test process that prepare on rf magnetron sputtering equipment are as follows:

1. cleaned ceramic pipe is contained on the instrument slide glass, sends slide glass to Sample Room.By the control of computer equipment, slide glass is delivered to sputtering chamber by Sample Room.

2. with the power supply opening of system, extract the gas in sputtering chamber and the Sample Room simultaneously.This process approximately takes 40 minutes, and the pressure in the system has reached 3 * 10 ^-3Pa.

3. after exhausting vacuum, open the gas circuit valve of oxygen and argon gas, in system, feed these two kinds of gases, its Ar/O ₂=50: 50.

4. after feeding gas, give the heating of ceramic pipe slide glass, temperature reaches 250 ℃.

5. begin sputter at last: voltage is 300V between ZnO target and slide glass.Just begun to want pre-sputter about 10 minutes, and then the timing sputter.Sputter procedure continues 20 minutes.

6. sputter can not be taken out sample after finishing at once, allow the temperature of system reduce, and then gives system deflation, and sample is taken out.Each sample is packed in the small plastic bag, and writes zero-time, termination time and the oxygen argon ratio of sample name, sputtering voltage, electric current, sputter on label.

7. measure its gas-sensitive property with HW-30A type air-sensitive tester, working temperature is chosen to be 350 ℃.The result is: to acetone with isoconcentration, and ethanol, gasoline, toluene, the sensitivity of formaldehyde is respectively: S=52.3,4.5,2.8,2.1,1.7.When measuring acetone, the response time of gas sensor of the present invention is 4 seconds, and be 2 seconds release time.This shows that gas sensor of the present invention has very strong selectivity to acetone, can get rid of the interference of measuring other common organic steams in the atmosphere.

Claims (3)

1. the invention belongs to a kind of gas sensor element, be particularly related to a kind of invention of acetone gas-sensitive sensing element of ZnO film type high selectivity, the outside surface sputter layer of ZnO film that it is characterized in that alumina ceramic tube (or quartz glass tube). the method for sputter both can be a direct current magnetron sputtering process, it also can be radio-frequency sputtering, and suitable technological parameter (sputtering voltage, sputtering current be set, vacuum tightness, oxygen argon compare etc.).When the present invention requires to detect the acetone steam ZnO sputtering layer is heated.Resistance variations according to the ZnO layer detects the acetone steam.

2. outside surface sputter as claimed in claim 1 have the ceramic pipe of ZnO layer or quartz ampoule should be anti-temperature more than 1200 ℃, it is characterized in that ZnO should be the thin layer that utilizes the sputtering method preparation.

3. the ceramic pipe or the quartz ampoule of outside surface sputter layer of ZnO as claimed in claim 1, under certain working temperature (250-350 ℃), only to the sense of acetone air-sensitive, and insensitive to toluene, ethanol, CO, formaldehyde, gasoline etc.

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