Microsens Semiconductor Gas Sensor MSGS-3001 Carbon Monoxide Gas Sensor mechanisms to properly occur. These mechanisms modifies the sensitive layer resistance (R S ) by reversible electron charge transfer from surface states to the conduction band. General description Operating principle The measurement of specific oxidizing or reducing gases is based on reversible conductivity change of the sensing element. The operating temperature is controlled by VH applied 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. Sensor description MSGS-3001 Integrated semiconductor carbon monoxide (CO) gas sensors are manufactured using standard microelectronic technology and silicon micromachining techniques. The batch fabrication process of MSGS-3001 miniaturized gas sensors presents the advantages of low cost, reproducibility, small size and low power consumption. RS + (-) VS 2 Figure 2: Sensor equivalent circuit (Top View) 1 2 3 4 Sensor Contact SiO2 Heater Membrane Si Figure 1: Schematic drawing RH +VH 1 -VH 3 The MSGS-3001 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 Doped-SnO2 Features - (+) VS 4 PIN NUMBER Heater Power Sensor Pin Heater Ground Sensor Pin * Sensitivity range: 5 to over 1000 ppm CO * Low humidity dependence in recommended operation mode * Stable long-term operation * Active charcoal filter for enhanced selectivity * Low power consumption * Small size * Durable nylon exterior shell with steel mesh Sensor Pin Application examples * Security * Residential CO Detectors * Industrial Stationary and Portable CO Detectors and Probes * Combustion control * Environment * Indoor air quality * Industrial process control MSGS-3001 CO Sensor specifications 1-2 Table 1: Absolute Maximum Ratings Device specifications 1 Rating * Chip Dimensions: 1.4mm x 1.4mm x 0.38 mm * Sensor Dimensions mounted on a TO-39 package with a filter: O = 10.3 mm; h = 24.0 mm * Typical thermal loss coefficient: = 0.12 mW/C = AEP/AET; = P/(T-Ta) - P = heating power (mW) - Ta = ambient temperature (C) - T = gas sensor temperature (C) Symbol Value Unit Maximum Heater Supply Voltage (pins 1 & 3) VH 2 V Maximum Heater Supply Current (pins 1 & 3) IH 32 mA Maximum Sensor Circuit Voltage (pins 2 & 4) VS 5 V Maximum Heater Power Dissipation PH 65 mW Maximum Sensor Power Dissipation PS 1 mW Maximum Heating Voltage Ramp tHR 0.2 V/ms Operating Ambient Temperature Tao 0 to + 50 C Storage Temperature Range Tsto -40 to + 70 C Symbol Typical value Unit Heating Voltage - Low - 10 seconds (pins 1 & 3) VH 0.8 V Heating Voltage - High - 5 seconds (pins 1 & 3) VH 1.8 V Heater current - Low - 10 seconds (pins 1 & 3) IH 24 mA Heater current - High - 5 seconds (pins 1 & 3) IH 31 mA Heater Power Dissipation - Low - 10 seconds PH 20 mW Heater Power Dissipation - High - 5 seconds PH 56 mW Average Power Consumption PH 32 mW RH(Ta) 23 W Table 2. Recommended Electrical Operating Conditions Characteristics Heater Resistance (VH = 0 volt) Heater Resistance (VH = 1.8 volt) Load Resistance RH(THigh) 57 W RL Variable (PS<1mW) W Symbol Typical value Unit Table 3. Sensitivity Characteristics3 Characteristics Notes: Sensor Resistance (in Synthetic air) RS(air) 36 MW 1. The following specifications apply to the Sensor Resistance (in 100 ppm CO) RS(100) 4 MW Sensor Ratio R(air)/RS(100) S(air/100) 9 --- Sensor Ratio R(air)/RS(60) S(air/60) 6 --- and limited as described in Table 1. Permanent Sensor Ratio R(air)/RS(15) S(air/15) 2 --- damage may occur if the maximum power is Sensor Ratio R(15)/RS(100) S(15/100) 4 --- MSGS-3001 CO sensor are subject to change to accommodate continuous improvement. 2. The heating conditions limits must be observed exceeded. 3. Based on recommended operation: VH(High temperature) = 1.8 volt (5 sec.); VH(Low temperature) = 0.8 volt (10 sec.) Standard test conditions: RH = 50 2%; Ta = 23 1C. The measurement is performed at the end of the "Low" temperature phase. VVHH VVHH Measurement test circuits GAS SENSOR 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 V C on the sensitive layer. A constant-current test circuit can also be used for the gas sensors, considering the recommendation of Table 1 (maximum power sensor dissipation of 1 mW). GAS SENSOR (R(RSS)) VSC RLL) (R V RS = ( VSC Rs Vout 1 * Vout VVSC*R(RF F) (2) Without CO With CO Gs Low 10 sec High 5 sec Time Point of measurement GS = Conductance of the Gas Sensor Figure 5: Principle of the operating mode 10.0 9.0 8.0 RS(gas)/RS(100) 7.0 6.0 RH=50% Ta=23C 5.0 4.0 3.0 2.0 1.0 0.0 0 20 40 60 80 100 CO Concentration [ppm] Figure 6: CO Sensitivity Ratio RS(gas)/RS(100 ppm CO; 50%RH) * Avoid to overheat the sensor (see Table 1) * ESD protection is required when handling these devices GSS = Figure 4: Basic electric circuit for gas sensor Humidity Influence Sensors precautions Vout (1) Principle Figure 7 presents results obtained in different relative humidity. These results confirm the efficiency of the operating mode proposed to decrease the moisture influence. (GS)) (G S VSC Vout RLL) 1 ) * (R Mode of operation An operating mode based on a sequence of two heater temperatures is used for the CO detection. This operating mode increases the CO sensitivity while the influence of humidity is minimized. During the "High" temperature period (5 seconds), water and contaminants are removed from the surface of the sensitive layer, while the thermal energy of the adsorbed oxygen species is increased which causes a drastically higher catalytic conversion from CO to CO2. The CO measurement is carried out at the end of the "Low" temperature phase (10 seconds). (R RFF) - + 12.0 10.0 0 ppm CO 8.0 15 ppm CO 6.0 60 ppm CO 4.0 100 ppm CO 2.0 0.0 0 20 40 60 80 100 Relative Humidity [%] Figure 7: Humidity Influence (Ta=23C) Packaging characteristics The standard packaging used a TO-39 support. A charcoal filter placed in a nylon casing reduces the effects of interfering gases. MSGS-3001-B MSGS-3001-D MSGS-3001-E TO-39 PACKAGE TO-18 PACKAGE PLASTIC PACKAGE 5.3 mm O 9.1 mm O 7.6 mm 4 4.2 mm O 9.1 mm 1 5 mm 2.54 mm 3 3 pins O 1.5 mm 3 pins O 0.4 mm 4 4 3 5 mm 2 1 45 2 0.8 mm 0.8 mm 0.8 mm Die size from 3 x 3 mm down to 1 x 1 mm 0.8 mm 7 mm max 2 1 3 Sensor Die Gold wire TO 39 Package Four pin 2.4 mm 0.5 mm O 0.43 mm longueur = 8 mm Plastic Mesh Nylon Mesh O 0.35 mm longueur = 8.5 Nylon Cap Nylon Mesh Filter Nylon Cap Filter Plastic Cap Filter 16 mm Metal Mesh Metal Cap 16 mm Metal Cap Metal Mesh Sensor Die Sensor Die 8 mm 10.2 mm MICROSENS SA Rue Jaquet-Droz 1, CH-2007 Neuchatel/Switzerland Tel.: ++41-32-720 51 51, Fax: ++41-32-720 57 12 e-mail: microsens@centredoc.ch Metal Mesh Sensor Die