Microsens Semiconductor Gas Sensor MSGS-3002 Methane Gas Sensor mechanisms to properly occur. These mechanisms modifies the sensitive layer resistance (RS) 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-3002 Integrated semiconductor methane (CH4) gas sensors are manufactured using standard microelectronic technology and silicon micromachining techniques. Features - (+) VS 4 The batch fabrication process of MSGS-3002 miniaturized gas sensors presents the advantages of low cost, reproducibility, small size and low power consumption. * Sensitivity range: 100 to over 10000 ppm CH4 RS RH +VH 1 -VH 3 * Low humidity dependence in recommended operation mode * Stable long-term operation + (-) VS 2 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 Figure 2: Sensor equivalent circuit (Top View) 1 2 3 4 PIN NUMBER Heater Power Sensor Pin Heater Ground Sensor Pin * Active charcoal filter for enhanced selectivity * Small size * Low power consumption * Durable nylon exterior shell with steel mesh Application examples * Security Doped-SnO2 Heater Sensor Contact - Residential CH4 Detectors SiO2 - Industrial Stationary and Portable CH4 Detectors and measurement systems Membrane Si Figure 1: Schematic drawing * Industrial process control MSGS-3002 CH4 Sensor specification 1-2 Table 1: Absolute Maximum Ratings Rating Symbol Value Unit Device specifications1 Maximum Heater Supply Voltage (pins 1 & 3) VH 2 V Maximum Heater Supply Current (pins 1 & 3) IH 32 mA * Chip Dimensions: 1.4mm x 1.4mm x 0.38 mm Maximum Sensor Circuit Voltage (pins 2 & 4) VS 5 V Maximum Heater Power Dissipation PH 65 mW * Sensor Dimensions mounted on a TO-39 package with a filter: O = 10.3 mm; h = 24.0 mm Maximum Sensor Power Dissipation PS 1 mW Maximum Heating Voltage Ramp tHR 0.2 V/ms Operating Ambient Temperature Tao 0 to +50 C * Typical thermal loss coefficient: = 0.12 mW/C = AEP/AET; = P/(T-Ta) Storage Temperature Range Tsto -40 to +70 C Symbol Typical value Unit Heating Voltage - Low - 10 seconds (pins 1 & 3) VH 1.2 V Heating Voltage - High - 5 seconds (pins 1 & 3) VH 1.8 V Heater current - Low - 10 seconds (pins 1 & 3) IH 27 mA Heater current - High - 5 seconds (pins 1 & 3) IH 31 mA Heater Power Dissipation - Low - 10 seconds PH 32 mW Heater Power Dissipation - High - 5 seconds PH 56 mW Average Power Consumption PH 40 mW RH(Ta) 23 W - P = heating power (mW) - Ta = ambient temperature (C) - T = gas sensor temperature (C) 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 RS(air) 1000 KW RS(5000) 330 KW Table 3. Sensitivity Characteristics3 Characteristics Notes: Sensor Resistance (in Synthetic air) 1. The following specifications apply to the Sensor Resistance (in 5000 ppm CH4) MSGS-3002 CH4 sensor are subject to change Sensor Ratio R(air)/RS(10000) S(air/10000) 4 --- Sensor Ratio R(air)/RS(5000) S(air/5000) 3 --- and limited as described in Table 1. Permanent Sensor Ratio R(air)/RS(2000) S(air/2000) 2 --- damage may occur if the maximum power is Sensor Ratio R(2000)/RS(10000) S(2000/10000) 2 --- 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) = 1.2 volt (10 sec.) Standard test conditions: RH = 50 2%; Ta = 23 1C. The measurement is performed at the end of the "High" temperature phase. VVHH VVHH GAS SENSOR Measurement test circuits RLL) (R V RS = ( VSC Rs Vout 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 (R RFF) - + (GS)) (G S VSC Vout RLL) 1 ) * (R Vout GSS = (1) 1 * Vout VVSC*R(RF F) (2) Figure 4: Basic electric circuit for gas sensor Without CH4 Gs With CH4 Low 10 sec High 5 sec Time Point of measurement GS = Conductance of the Gas Sensor Mode of operation Figure 5: Principle of the operating mode Principle 4.0 An operating mode based on a sequence of two heater temperatures is used for the CH4 detection. This operating mode minimizes the influence of humidity. During the "High" temperature period (5 seconds), water and contaminants are removed from the surface of the sensitive layer, while the high temperature allows the CH 4 dissociation/reaction with the adsorbed oxygen species. The CH4 measurement is carried out at the end of the "High" temperature phase (5 seconds). 3.5 Rs(gas)/RS(10000 ppm) 3.0 RH = 50% Ta = 23C 2.5 2.0 1.5 1.0 0.5 0 Humidity Influence Sensors precautions * Avoid to overheat the sensor (see Table 1) * ESD protection is required when handling these devices CH4 Concentration [ppm] Figure 6: CO Sensitivity Ratio RS(gas)/RS(10000 ppm CH4; 50% RH) Figure 7 presents results obtained in different relative humidity. These results confirm the efficiency of the operating mode proposed to decrease the moisture influence. 2000 4000 6000 8000 10000 12000 4 3.5 3 0 ppm CH4 2000 ppm CH4 5000 ppm CH4 10000 ppm CH4 2.5 2 1.5 1 0.5 0 20 40 60 80 100 Relative Humidity [%] Figure 7: Humidity Influence (Ta=23C) 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 MSGS-3002-D MSGS-3002-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