S. Widodo
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o g
R R
S =
or
o o
g
R R
R S
− =
, 2
where S is sensitivity, R
o
is sensor resistance at normal air no gas, and R
g
is the
resistance of the sensor when there is a gas.
As for the p-type material sensor, sensitivity above definition be changed Cirera, 2000 for the CO sensor range 9 ppm.
b. Selectivity
The existence of two or more of the gas mixture should be discriminated against by the sensor system developed without any interference from each other.
c. Power consumption
Option fabrication technology used must consider the power consumption of sensor devices produced. For power consumption used in gas sensors are: Thick Film
Technology ranged from 200 mW–1 W.
d. Originality
Choice of materials, modifications, and methods used must pay attention to the process of novelty, so it can produce devices that have high commercial potential.
This study aims to apply a thick film technology in the manufacture of gas sensor CO of tin-dioxide SnO2 materials. In this study will be the design, fabrication and characterization
system based metal oxide gas sensor, gas sensor device which includes a single-use technology thick films with sensitive materials such as SnO2. Various additives such as Pt, Pd,
and Ag will be used as a dopant and a catalyst to increase the sensitivity and selectivity of the sensor, but it also will be made of a digital display system hardware to display the
measurement results of the gas in the environment.
Sensitive layer
Sensitive layer or layers of the sensor material is the part that is directly related to gas, where the electrochemical reaction occurs at the surface of this layer. This layer is made of
SnO2, the metal oxide n-type which has a relatively wide energy gap 3.6 eV. The dimensions of this layer which represents the concentration of SnO
2
will determine the measurement range of the sensor. The theory of the determination of the
dimensions of the sensor layer is as follows. The first thing is to determine the maximum measurement range of the sensor in units of ppm. Because this process is happening is the
reaction gas, ppm converted into molL. Assuming the gas is a gas under ideal conditions, the equation used is as follows.
L mol
ppm L
mol 15
, 24
1 x
= ,
3 with reference to the equation equilibrium reaction between carbon dioxide and SnO2,
namely XO2 + 2X + ↔ 2YO 2YO2 + 2e, it is known molarity ratio between SnO2 gas and reducing gas. With reference to Eq. 3, the mole SnO
2
will be obtained. Furthermore, the mass of SnO2 obtained by
M m
n =
, 4
with n is molality mol, m is mass g, and M is molarity gmol. Furthermore, by looking at the density ρ of the material data obtained dimensions volume of the sensor layer, using
the following equation:
Fabrication process of CO gas sensor devices based tin oxide SnO
2
by Thick Film Technology
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V m
= ρ
, 5
in which ρ is density gvolume, m is mass of material grams, and V is dimensionsvolume unit volume. By determining the layer thickness, the width of the sensor layer will be
obtained.
Shape sensor response
Basically, the gas sensor response thick film technology is the change in the value of konduktans sensor to change the gas concentration. Generally expressed as:
G G
S =
, 6
with S is sensitivity, G is conductance sensor when a reducing gas, G is conductance sensor
when no reducing gas. The above equation is identical to the equation proposed by Cirera sensitivity. Maxwell-Boltzmann statistics appropriate, conductivity G is formulated by
[ ]
kT eVs
e env
R G
. 1
= =
, 7
with v is the bulk mobility and n is the electron concentration. Medium voltage V
s
is the Schottky barrier, is defined as:
2
1
Π
+ =
ρ ρ
V V
s
. 8
V is the barrier height in the absence of a reducing gas, is defined as:
D s
N N
V
. .
e .
2
2
ε =
, 9
while the parameters of the gas conditions in concentration, pressure and temperature. By N
s
is the sensing surface density m
-2
, N
D
is the donor concentration oxygen vacancies m
- 3
, e is the electron charge eV, ε is the dielectric constant of the semiconductor material, ρ
is the density of the gas kgm
-3
, p is the partial pressure of the gas Nm
-2
, and П being defined as:
kT h
mkT
2 3
2
2
=
Π
π
, 10
where m is time reducing gas in this case CO, h is planck constant 4,134.10-5 eV, and T = absolute temperature
o
K. Using the above equation, and by defining G0 as a conductivity sensor in free air, then
kT eV
vne e
G =
. 11
From the above equations, the equation for the relationship obtained sensor sensitivity GG0 as follows:
Π +
− =
p kT
eV G
G ρ
1 1
1 exp
12
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At the moment there is no gas p = 0, the equation of sensitivity being worth 1 GG0 = 1. At high gas concentrations high pressure, ie when ρ p П 1, then the sensitivity
reached saturation point:
kT eV
sat
e G
G .
=
. 13
From Eqs. 9 and 10, we obtain:
− −
=
c sat
G G
G G
β 1
1 1
, 14
where c is the concentration of the gas in ppm, GG sat and β are parameters obtained
by combining equations with experimental data Barsan, 2008. Broadly speaking, the gas sensor technology thick film is composed of a pair of
electrodes, heater and sensitive layer sensitive to stimuli gas, all of which are printed on the substrate strip of material alumina Al2O3 96.
Our expectations are 1. Modification of metal oxide material to improve the sensitivity of the sensor.
2. The use of an array of sensors to increase the selectivity of the sensor. 3. The use of thick films technology and Sputtering techniques to produce devices with low
power consumption. 4. Selection of materials and methods that process has not been much explored its use in
the design of the gas sensor will give originality aspect.
2. Methodology
