MSGS-3002-D - Microsens SA

Features

• Sensitivity range:

100 to over 10000 ppm CH4

• Low humidity dependence in

recommended operation mode

• Stable long-term operation

• Active charcoal filter for

enhanced selectivity

• Small size

• Low power consumption

• Durable nylon exterior shell with

steel mesh

Application examples

• Security

- Residential CH4Detectors

- Industrial Stationary and

Portable CH4Detectors and

measurement systems

• Industrial process control

Microsens Semiconductor Gas Sensor

MSGS-3002 Methane Gas Sensor

General description

Operating principle

The measurement of specific oxidizing

or reducing gases is based on reversible

conductivity change of the sensing ele-

ment.

Sensor description

MSGS-3002 Integrated semi-

conductor methane (CH4) gas sensors

are manufactured using standard

microelectronic technology and silicon

micromachining techniques.

The batch fabrication process of

MSGS-3002 miniaturized gas sensors

presents the advantages of low cost,

reproducibility, small size and low

power consumption.

The MSGS-3002 structure consists

of a doped tin-oxide (SnO2) thin-film

layer over an embedded thin film heater

(figure 1). This integrated heater

resistance (RH) is used to control the

sensitive layer temperature which is

necessary for Chemisorption Reaction

mechanisms to properly occur. These

mechanisms modifies the sensitive

layer resistance (RS) by reversible elec-

tron charge transfer from surface states

to the conduction band.

The operating temperature is

controlled by VHapplied on the heater

resistor (RH). A polarization voltage (VS)

is applied to the sensitive layer which

resistance can be mesured using an

electric circuit shown in figure 4. The

4-pins package is indicated on figure 2.

Figure 1: Schematic drawing

Sensor Contact

SiO2

Membrane

Doped-SnO2

Heater

RS+VH

-VH

- (+) VS 4

+ (-) VS 2

PIN NUMBER

1 Heater Power

2 Sensor Pin

3 Heater Ground

4 Sensor Pin

Figure 2: Sensor equivalent circuit

(Top View)

Table 1: Absolute Maximum Ratings

Rating Symbol Value Unit

Maximum Heater Supply Voltage (pins 1 & 3) VH2V

Maximum Heater Supply Current (pins 1 & 3) IH32 mA

Maximum Sensor Circuit Voltage (pins 2 & 4) VS5V

Maximum Heater Power Dissipation PH65 mW

Maximum Sensor Power Dissipation PS1mW

Maximum Heating Voltage Ramp tHR0.2 V/ms

Operating Ambient Temperature Tao 0 to +50 °C

Storage Temperature Range Tsto -40 to +70 °C

Table 2. Recommended Electrical Operating Conditions

Characteristics Symbol Typical value Unit

Heating Voltage - Low - 10 seconds (pins 1 & 3) VH1.2 V

Heating Voltage - High - 5 seconds (pins 1 & 3) VH1.8 V

Heater current - Low - 10 seconds (pins 1 & 3) IH27 mA

Heater current - High - 5 seconds (pins 1 & 3) IH31 mA

Heater Power Dissipation - Low - 10 seconds PH32 mW

Heater Power Dissipation - High - 5 seconds PH56 mW

Average Power Consumption PH40 mW

Heater Resistance (VH= 0 volt) RH(Ta) 23 W

Heater Resistance (VH= 1.8 volt) RH(THigh) 57 W

Load Resistance RL

Variable (PS<1mW)

Table 3. Sensitivity Characteristics3

Characteristics Symbol Typical value Unit

Sensor Resistance (in Synthetic air) RS(air) 1000 KW

Sensor Resistance (in 5000 ppm CH4)R

S(5000) 330 KW

Sensor Ratio R(air)/RS(10000) S(air/10000) 4 ---

Sensor Ratio R(air)/RS(5000) S(air/5000) 3 ---

Sensor Ratio R(air)/RS(2000) S(air/2000) 2 ---

Sensor Ratio R(2000)/RS(10000) S(2000/10000) 2 ---

MSGS-3002 CH4Sensor specification 1-2

Standard test conditions: RH= 50 ± 2%; Ta = 23 ± 1°C. The measurement is

performed at the end of the "High" temperature phase.

Device specifications1

• Chip Dimensions:

1.4mm x 1.4mm x 0.38 mm

• Sensor Dimensions mounted on a

TO-39 package with a filter:

Ø = 10.3 mm; h = 24.0 mm

• Typical thermal loss coefficient:

ß = 0.12 mW/°C

ß= ÆP/ÆT; ß = P/(T-Ta)

- P = heating power (mW)

- Ta = ambient temperature (°C)

- T = gas sensor temperature (°C)

Notes:

1. The following specifications apply to the

MSGS-3002 CH4sensor are subject to change

to accommodate continuous improvement.

2. The heating conditions limits must be observed

and limited as described in Table 1. Permanent

damage may occur if the maximum power is

exceeded.

3. Based on recommended operation:

VH(High temperature) = 1.8 volt (5 sec.);

VH(Low temperature) = 1.2 volt (10 sec.)

Measurement

test circuits

Two different basic electric circuits

which can be used with the gas sensors

are presented on the figure 4. The

amplifier system (2) presents however

the advantage of maintaining a

constant voltage VCon the sensitive

layer. A constant-current test circuit can

also be used for the gas sensors, consi-

dering the recommendation of Table 1

(maximum power sensor dissipation of

1 mW).

Mode of operation

Principle

An operating mode based on a

sequence of two heater temperatures is

used for the CH4detection. This opera-

ting mode minimizes the influence of

humidity. During the "High" temperature

period (5 seconds), water and contami-

nants are removed from the surface of

the sensitive layer, while the high tem-

perature allows the CH4disso-

ciation/reaction with the adsorbed oxy-

gen species. The CH4measurement is

carried out at the end of the "High" tem-

perature phase (5 seconds).

Humidity Influence

Figure 7 presents results obtained

in different relative humidity. These

results confirm the efficiency of the

operating mode proposed to decrease

the moisture influence.

Sensors precautions

• Avoid to overheat the sensor

(see Table 1)

• ESD protection is required when

handling these devices

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 2000 4000 6000 8000 10000 12000

CH4 Concentration [ppm]

Rs(gas)/RS(10000 ppm)

RH = 50%

Ta = 23°C

0.5

1.5

2.5

3.5

020406080100

Relative Humidity [%]

Ratio RS(gas)/RS(10000 ppm CH4; 50% RH)

0 ppm CH4

2000 ppm CH4

5000 ppm CH4

10000 ppm CH4

VCRLVout VCVout

GAS SENSOR

(GS)

GAS SENSOR

(RS)

GS=• VoutRs = • RL

(1 )

Vout

VC•RF

–

(1) (2)

)(R

)

Time

With CH4

Without CH4

High

5 sec

Low

10 sec

Point of measurement

GS = Conductance of the Gas Sensor

Figure 5: Principle of the operating mode

Figure 4: Basic electric circuit for gas sensor

Figure 6: CO Sensitivity

Figure 7: Humidity Influence (Ta=23°C)

Packaging characteristics

The standard packaging used a TO-39 support (cf. description in the previous Data Sheet). A charcoal filter placed in a

nylon casing reduces the effects of interfering gases.

MSGS-3002-B

TO-39 PACKAGE

MSGS-3002-D

TO-18 PACKAGE

MSGS-3002-E

PLASTIC PACKAGE

MICROSENS SA

Rue Jaquet-Droz 1, CH-2007 Neuchâtel/Switzerland

Tél.: ++41-32-720 51 51, Fax: ++41-32-720 57 12

e-mail: microsens@centredoc.ch

Nylon Cap

Nylon Mesh

Filter

Metal Mesh

Sensor Die

Metal Cap

Plastic Mesh

Filter

Metal Mesh

Sensor Die

Plastic Cap

16 mm

Nylon Cap

Nylon Mesh

Filter

Metal Mesh

Sensor Die

Metal Cap

16 mm

8 mm

10.2 mm

2.4 mm 0.5 mm

5.3 mm

5 mm

7 mm max

3 pins Ø 0.4 mm

3 pins Ø 1.5 mm

Ø 9.1 mm

Ø 7.6 mm

Gold wire TO 39 Package

Four pin

Sensor Die

Die size

from 3 x 3 mm

down to 1 x 1 mm

0.8 mm

45°

4.2 mm

2.54 mm

0.8 mm

Ø 0.35 mm

longueur = 8.5

Ø 0.43 mm

longueur = 8 mm